global and regional sea level variability and change palma ... · modelling historical and future...

Global and Regional Sea Level Variability and Change Palma de Mallorca, June 10-12, 2015


Contents Keynotes speakers ................................................................................................................................... 9

Sea-level changes during past centuries reconstructed from salt-marsh sediments. Prof. Roland Gehrels, University of York, UK ............................................................................................................ 9

Considering vertical land motion in understanding sea level change. Prof. Guy Woppelmann, University of La Rochelle, France ......................................................................................................... 9

The time-mean ocean dynamic topography: How well can we measure, model, and understand it?. Prof. Chris W. Hughes, National Oceanography Centre, UK .............................................................. 10

What are the challenges facing quantifying impacts and adapting to global sea-level rise?. Dr. Sally Brown, University of Southampton, UK ............................................................................................. 10

Semi-empirical modelling of sea-level change. Prof. Stefan Rahmstorf, Postdam University, Germany ........................................................................................................................................................... 11

Tide gauge reconstructions and the separation of regional and global mean sea level signals. Prof. Mark Merrifield, University of Hawaii, USA ....................................................................................... 11

Sea level variability: from surface gravity waves to mean sea level. Prof. Charitha Pattiaratchi, University of Western Australia, Australia ......................................................................................... 12

Modelling historical and future mean sea level change. Prof. Jonathan Gregory, University of Reading, UK ........................................................................................................................................ 12

Status and challenges on sea level monitoring and forecasting in the Mediterranean Dr. Begoña Pérez Gómez, Puertos del Estado, Spain ............................................................................................ 13

Paleo Sea Level....................................................................................................................................... 14

Oral Presentations ............................................................................................................................. 14

Holocene relative sea level changes in the Baltic Sea basin: syntheses of geological and archaeological data. Alar Rosentau .............................................................................................. 14

Sea-level changes in the western Mediterranean during the last 12,000 years: a tool to better constrain the future projection of sea-level rise. Matteo Vacchi, Nick Marriner, Christophe Morhange, Giorgio Spada, Alessandro Fontana, Alessio Rovere ................................................... 14

Late Holocene sea-level change in the Falkland Islands: testing the Greenland melt hypothesis. Newton, T. L., Gehrels, W. R., Daley, T.J., Blake, W. ...................................................................... 15

Posters ............................................................................................................................................... 15

Decoding sea level changes during the MIS 5 by means of Phreatic Overgrowths on Speleothems (POS) research in coastal caves of Mallorca (western Mediterranean). Joan J. Fornós, Àngel Ginés, Joaquín Ginés, Francesc Gràcia, Yemane Asmeron, Bogdan P. Onac, Victor Polyak, Paola Tuccimei ....................................................................................................................................................... 15

Sea-level highstands in Mallorca during the last interglacial. Thomas Lorscheid, Paolo Stocchi, Alessio Rovere, Lluís Gómez-Pujol, Bas de Boer, Thomas Mann, Hildegard Westphal, Joan J. Fornós ....................................................................................................................................................... 16

Vertical Land Movements ...................................................................................................................... 16



Combination Results of the Tide Gauge Benchmark Monitoring (TIGA) Analysis Centre Re-processing Products. Addisu Hunegnaw, Norman Teferle ............................................................. 16

Models of land uplift in northern Europe. Holger Steffen ............................................................. 17

Relative sea level history during the Holocene and models of the glacial isostatic adjustment process: constraints from the regions of forebulge collapse. Keven Roy, W.R. Peltier ................. 17

Posters ............................................................................................................................................... 18

Updated GPS vertical velocity field at tide gauges: application to global and regional sea level change. Médéric Gravelle, Alvaro Santamaria-Gomez, Marta Marcos, Phil Thompson, Guy Wöppelmann .................................................................................................................................. 18

Using InSAR to monitor vertical ground motions in coastal cities. G. Le Cozannet, D. Raucoules, G. Wöppelmann .................................................................................................................................. 18

Vertical land movements from the combined use of satellite altimetry and tide gauges. Marta Marcos, Guy Wöppelmann ............................................................................................................ 19

GNSS reflectometry for tide gauge levelling. Alvaro Santamaría-Gómez, Christopher Watson, Médéric Gravelle, Matt King, Guy Wöppelmann ........................................................................... 19

Leveling for the altimetric control of tide gauge sensors and GNSS permanent stations in Barcelona’s and Ibiza’s ports. Tapia Gómez, A; López Bravo, R; Gili Ripoll JA; Martínez Benjamín, JJ; Pros LLavador, F; Palau Teixidò, V ............................................................................................. 19

A New Datum-Controlled Tide Gauge Record for Sea Level Studies in the South Atlantic Ocean: King Edward Point, South Georgia Island. Norman Teferle, Addisu Hunegnaw, Philip Woodworth, Peter Foden, Simon Williams, Jeffrey Pugh, Angela Hibbert .......................................................... 20

Mean Sea Level Observations and Processes ........................................................................................ 21


The GOCE geoid in support to sea level analysis. Thomas Gruber ................................................ 21

On the decadal trend of global mean sea level and its implication on ocean heat content change. Lee-Lueng Fu .................................................................................................................................. 21

Deep-ocean contribution to sea level and energy budget not detectable over the past decade. W. Llovel, J. K.Willis, F.W. Landerer, I. Fukumori ................................................................................. 22

Synchronization of sea level to oceanic and atmospheric forcing. Francisco M. Calafat.............. 22

Annual sea level variability of the coastal ocean: the Baltic Sea-North Sea transition zone. Marcello Passaro, Paolo Cipollini, Jerome Benveniste .................................................................................. 22

A probabilistic reassessment of 20th century global mean sea level. Carling Hay, Eric Morrow, Robert E. Kopp, Jerry X. Mitrovica .................................................................................................. 23

Considerations for Estimating the 20th Century Trend in Global Mean Sea Level. Philip R. Thompson, Benjamin D. Hamlington ............................................................................................. 23

Detecting sea level seasonality in the northwestern Pacific. Xiangbo Feng, M. N. Tsimplis, M. Marcos and F. M. Calafat ............................................................................................................... 24

Detection and attribution of global mean thermosteric sea level change. Aimée B. A. Slangen, John A. Church, Xuebin Zhang, Didier Monselesan ................................................................................ 24


Detecting anthropogenic footprints in sea level rise. Sönke Dangendorf, Marta Marcos, Alfred Müller, Eduardo Zorita, Jürgen Jensen ........................................................................................... 25

Posters ............................................................................................................................................... 25

Regional Sea Level change in the North Sea since 1900. Frauke Albrecht, Saskia Esselborn, Ralf Weisse ............................................................................................................................................ 25

Sea level trends and long-term variability in the South China Sea. A.M. Amiruddin, I.D. Haigh, M.N. Tsimplis, F.M. Calafat and S. Dangendorf ...................................................................................... 26

Altimetric sea level variation and reconstruction in the Arctic. Ole B. Andersen, P. Limkilde Svendsen, A. Aasbjerg and P. Knudsen .......................................................................................... 26

On the causes of the differential mean sea level variations between the northern and southern hemispheres of the Earth. Yuri Barkin, José M. Ferrándiz, Isabel Vigo, David García .................. 27

Sea level reconstruction from satellite altimetry and tide gauges using advanced signal decomposition techniques. Sandra-Esther Brunnabend, Jürgen Kusche, Roelof Rietbroek, and Ehsan Forootan .............................................................................................................................. 27

Quality control and validation of the new IOP and GOP ocean products from CryoSat-2. Francisco M. Calafat, Paolo Cipollini, Helen Snaith, Jérôme Bouffard, Pierre Féménias, Tommaso Parrinello ....................................................................................................................................................... 28

Coastal sea level measurements and trends from improved satellite altimetry. Paolo Cipollini, Francisco M. Calafat, David Cotton, Marcello Passaro, Helen Snaith ........................................... 28

Impact of large-scale climate patterns on sea-level variability in the Gulf of Guinea with focus on Ghana. Evadzi, P., Hünicke, B., Zorita, E. ........................................................................................ 29

Variation of sea level and net water flux in the Mediterranean Sea. Luciana Fenoglio-Marc ...... 29

Time-varying trends in regional sea level from tide gauge data. Thomas Frederikse, Riccardo Riva, Cornelis Slobbe, Taco Broerse, Martin Verlaan .............................................................................. 30

Scientific roadmap towards height system unification with GOCE. Th. Gruber, R. Rummel, M. Sideris, E. Rangelova, P. Woodworth, C. Hughes, J. Ihde, G. Liebsch, A. Rülke, Ch. Gerlach, R. Haagmans ...................................................................................................................................... 30

The Various of Wet Tropospheric Corrections effect on the Regional Sea Level Variability in the Indonesia Seas. Eko Yuli Handoko, Maria Joana Fernandes, Clara Lazaro .................................... 31

Ocean Bottom Pressure Records at the Permanent Service for Mean Sea Level. Angela Hibbert, Andrew Matthews, Chris W. Hughes, Mark E. Tamisiea ............................................................... 31

The Semiannual Oscillation of Southern Ocean Sea Level. Angela Hibbert, Harry Leach, Phil Woodworth .................................................................................................................................... 31

Celebrating 30 Years of the South Atlantic Tide Gauge Network. Angela Hibbert, Pete Foden, Jeff Pugh, Geoff Hargreaves, Steve Mack, Phil Woodworth................................................................. 32

Observed changes and variability of mean sea-level in the Baltic Sea region during the last 200 years –a review. Birgit Hünicke,l Eduardo Zorita ........................................................................... 32

Variability of decadal sea-level trends in the Baltic Sea. Sitar Karabil, Eduardo Zorita, Birgit Huenicke ......................................................................................................................................... 33


Forcing of Global Mean Sea Level Interannual variability for the period 1950-2010. Gabriel Jordà, Francisco Mir Calafat, Mikis Tsimplis ............................................................................................. 33

Nordic Sea Level – Analysis of PSMSL RLR Tide Gauge data. Per Knudsen, Ole Andersen, Carlo Sørensen ......................................................................................................................................... 34

Variability of the ocean bottom pressure along the Gulf of Cadiz and its effect on the sea level spatial distribution. Irene Laiz, Marta Marcos, Jesús Gómez-Enri, Evan Mason, Begoña Tejedor, Alazne Aboitiz, Pilar Villares ........................................................................................................... 34

Satellite altimetry Calibration/Validation at the Australian Bass Strait site in the context of the new missions Jason-3 and Sentinel-3. Legresy B., C. Watson, J. Church, N. White, J. Beardsley, J. Andrewartha .................................................................................................................................. 34

Sensitivity of sea-level rise reconstruction from 1900 to present. Legresy B. , J. Church , N. White, D. Monselesan and A. Slangen ....................................................................................................... 35

Relative sea-level change along the Italian coast during the late Holocene and projections for 2100: Coastal plain impacts based on high-resolution DTMs and geodetic data. Valeria Lo Presti., Fabrizio Antonioli , Alessandro Amorosi , Marco Anzidei , Gianni De Falco , Alessandro Fontana , Giuseppe Fontolan , Giuseppe Mastronuzzi , Enrico Serpelloni , Antonio Vecchio ........................ 35

Sea Level Oscillations in The Baltic Sea: From Minutes to Centuries. Igor P. Medvedev, Alexander B. Rabinovich, Evgueni A. Kulikov .................................................................................................. 36

Tides in the Baltic, Black and Caspian Seas. Igor P. Medvedev, Alexander B. Rabinovich, Evgueni A. Kulikov ............................................................................................................................................ 36

Comparing coastal and open ocean sea level variability and trend from altimetric data. A. Melet, M. Nonti, B. Chide, B. Meyssignac, F. Birol .................................................................................... 36

Global and Regional Sea Level Change Over the 20th Century: How Can it Inform Us About the 21st Century?. R. S. Nerem, B. D. Hamlington, F. Landerer, R. Leben, and J. Willis ....................... 37

Global Sea Level rise from an Empirical Mode Decomposition perspective. Marco Olivieri, Giorgio Spada, Gaia Galassi ........................................................................................................................ 37

The Annual Global-Mean Thermosteric Height Budget. Christopher G. Piecuch, Rui M. Ponte .... 38

Deriving sea level from tide gauges. Jens Schröter, Manfred Wenzel, Klaus Grosfeld, Roelof Rietbroek ........................................................................................................................................ 38

The South Atlantic sea level variability. Raisa de Siqueira Alves, Angela Hibbert and Harry Leach ....................................................................................................................................................... 38

Closing the gap between regional and global sea level in the Bay of Bengal. Bernd Uebbing, Roelof Rietbroek, Sandra-Esther Brunnabend, Jürgen Kusche .................................................................. 39

How long does it take to measure a trend in ocean bottom pressure?. Joanne Williams, Chris Hughes, Mark Tamisiea ................................................................................................................. 39

Modelling Sea Level Changes ................................................................................................................. 40


Long-Term Internal Variability Effects on Centennial Dynamic Sea Level Projections. Mohammad H. Bordbar Thomas Martin, Mojib Latif, Wonsun Park.................................................................. 40


Interannual Predictability of North Atlantic Sea Level Dynamics. Robert Fraser, Laure Zanna, Chris Wilson ............................................................................................................................................ 40

Seasonal coastal sea-level prediction using a dynamical model. John A. Church, Peter C. McIntosh, Elaine R. Miles, Ken Ridgway, Claire M. Spillman .......................................................................... 41

Regional Budgets of Sea Level in the ECCO-Production Release 1 Ocean State Estimate. Christopher G. Piecuch, Rui M. Ponte, Gael Forget, Ichiro Fukumori ............................................. 41

Imprints of oceanic intrinsic variability on altimetric measurements: an OGCM study. Guillaume Sérazin, Thierry Penduff, Laurent Terray, Bernard Barnier, Jean-Marc Molines ........................... 42

A near-uniform fluctuation dominating sea level and ocean bottom pressure variations across the Arctic Ocean and the Nordic Seas. Ichiro Fukumori, Ou Wang, William Llovel, Ian Fenty, Gael Forget ............................................................................................................................................. 42

Pacific sea level trends: internally or externally forced? Felix Landerer ....................................... 42

Spatial scales and the detection of externally forced signals in regional sea surface height in CMIP5 models. Kristin Richter, Ben Marzeion ........................................................................................... 43

Worst-case scenarios for sea level rise from ice sheet melt. Carmen Boening, Nicole Schlegel, Michael Schodlok, Daniel Limonadi, Eric Larour, Michael M. Watkins .......................................... 43

Asymmetry in regional sea level rise projections due to skewed ice sheet contributions. Renske de Winter, Thomas Reerink and Roderik van de Wal ......................................................................... 44

Posters ............................................................................................................................................... 44

Analysis of the regional pattern of sea level change due to ocean dynamics and density change for 1993–2099 in observations and CMIP5 AOGCMs. Roberto A. F. Bilbao, Jonathan M. Gregory, Nathaelle Bouttes .......................................................................................................................... 44

Global reconstructed daily storm surge levels from the 20th century reanalysis (1871-2010). Alba Cid, Paula Camus, Sonia Castanedo, Fernando Méndez, Raúl Medina ......................................... 45

Nonlinear model of the long-term sea-level fluctuations in the Caspian Sea. Anatoly V. Frolov . 45

Sea Level Complexity in Observations And Models. M. Karpytchev, M. Becker, M. Marcos, S. Jevrejeva, S. Lennartz-Sassinek ...................................................................................................... 46

Explaining the spread of CMIP5 climate models in global-mean thermosteric sea level rise over the 20th and 21st centuries. B. Meyssignac, A. Melet .................................................................. 46

Multi-annual predictability of regional sea level in a global climate model. C. D. Roberts, N. Dunstone. L. Hermanson, M. Palmer, D. Smith .............................................................................. 47

Statistical modeling of Sea Level for regional semi-enclosed basins. Luca Scarascia and Piero Lionello ........................................................................................................................................... 47

Projections of 21st Century Sea Level Changes for Norway. Matthew J. R. Simpson, J. Even Ø. Nilsen, Oda Ravndal, Kristian Breili, Halfdan P. Kierulf, Holger Steffen, Eystein Jansen, Hilde Sande, Mark Carson ................................................................................................................................... 48

Sea surface height variability in the North East Atlantic from satellite altimetry. Paul Sterlini, Hylke de Vries and Caroline Katsman ...................................................................................................... 48


What is the most robust time series analysis tool to isolate mean sea level from tide gauge records?. Phil Watson .................................................................................................................... 49

Regional evaluation of surface mass balance forcing of an ice flow model for the Greenland Ice Sheet using GRACE mascon solutions. D. N. Wiese, N.-J. Schlegel, M. M. Watkins, E. Y. Larour, J. E. Box, X. Fettweis, M. R. van den Broeke .......................................................................................... 49

Sea Level Extremes ................................................................................................................................ 50


Nineteenth Century Sea-level and Extremes on the US East and West Coast. Stefan Talke, David Jay, Patrick Lau, Conrad Hilley, Lumas Helaire, Drew Mahedy, Ramin Familkhalili ...................... 50

Storm surge clustering and spatial footprints: How extreme was the 2013-2014 UK storm surge season? Ivan D. Haigh, Matthew P. Wadey, Shari L. Gallop, Robert J. Nicholls ............................ 50

Regional climate variability in extreme sea levels from satellite altimetry observations over two decades. Melisa Menendez, Philip L. Woodworth ......................................................................... 51

Time varying trends in sea level extremes. Marta Marcos, Francisco M. Calafat, Angel Berihuete, Sönke Dangendorf .......................................................................................................................... 51

Cyclone Xaver seen by Geodetic Observations. Leonor Mendoza, Luciana Fenoglio-Marc, Remko Scharroo, Alessandro Annunziato, Matthias Becker, John Lillibridge ............................................ 52

Future storm surge levels - the example of Denmark. Kristine S. Madsen, Torben Schmith, Tian Tian ................................................................................................................................................ 52

Meteorological Tsunamis In The World Oceans: An Overview. Alexander Rabinovich ................. 53

The impact of sea level rise on storm surge water levels and wind waves. Arne Arns, Jürgen Jensen ....................................................................................................................................................... 53

Atmospheric Circulation Changes and their Impact on Extreme Sea Levels and Coastal Currents in Australia. Kathleen L. McInnes, Frank Colberg, Julian O’Grady ..................................................... 54

Global Secular Changes in different Tidal High Water, Low Water and Range levels. Robert J. Mawdsley, Ivan D. Haigh,N.C. Wells ............................................................................................. 54

Posters ............................................................................................................................................... 55

How to interpret expert judgment assessments of 21st century sea-level rise? Hylke de Vries, Roderik S.W. van de Wal ................................................................................................................ 55

Long-term changes in sea level extremes and tides on the Chinese coasts. Xiangbo Feng, M. N. Tsimplis and P.L. Woodworth......................................................................................................... 55

Expected Vertical Load in coastal GPS due to a Tsunami like the 1775 Lisbon Tsunami: GPS Tsunami Early-Warning capabilities. Leonor Mendoza ................................................................................ 55

Analysis of recent high-frequency sea level events in the European Atlantic coast: impact on the design of automatic algorithms for tsunami detection. Begoña Pérez Gómez, Marta Gómez Lahoz, Enrique Álvarez Fanjul, Carlos González, François Schindele ......................................................... 56

Estimation extreme sea levels from the combination of tides and storm surges for the coasts of the Sea of Okhotsk. Georgy Shevchenko ....................................................................................... 56


Spatial variation in extreme water levels in the Baltic Sea – North Sea transition from tide gauge records. Carlo Sørensen, Ole B. Andersen, Per Knudsen ................................................................ 57

The Impact of an Eroding Barrier Island on Extreme Water Levels in the Tampa Bay Area. Marius Ulm, Arne Arns, Jürgen Jensen ....................................................................................................... 57

Coastal Impacts of Sea Level Changes ................................................................................................... 58


Evaluating uncertainties in future coastal flooding occurrence as sea-level rises. Gonéri Le Cozannet, Jeremy Rohmer, Anny Cazenave, Déborah Idiera, Roderik Van de Wal, Renske de Winter, Rodrigo Pedreros, Yann Balouin, Charlotte Vinchon, Carlos Oliveros ............................................ 58

Effects of scale and input data on assessing the future impacts of coastal flooding. An application of DIVA for the Emilia-Romagna coast. Claudia Wolff, Athanasios T. Vafeidis, Daniel Lincke, Christian Marasmi, Jochen Hinkel .................................................................................................. 58

An assessment of extreme sea levels, waves and coastal flooding in the Maldives. Matthew Wadey, Ivan Haigh, Sally Brown, Robert Nicholls .......................................................................... 59

Land subsidence and sea level rise at Lipari island (Italy): implications for flooding scenario. Anzidei Marco, Bosman Alessandro, Carluccio Roberto, Carmisciano Cosmo, Casalbore Daniele, Chiappini Massimo, Chiocci Francesco Latino, D’Ajello Caracciolo Francesca, Esposito Alessandra, Fabris Massimo, Muccini Filippo, Nicolosi Iacopo, Pietrantonio Grazia, Sepe Vincenzo, Vecchio Antonio ....................................................................................................................................................... 60

Posters ............................................................................................................................................... 60

Simulating overtopping and coastal flooding in urban areas: Perspectives to quantify sea level rise effects. Sylvestre Le Roy, Rodrigo Pedreros, Camille André, François Paris, Sophie Lecacheux, Fabien Marche, Charlotte Vinchon ................................................................................................ 60

Tidal influence on high frequency harbor oscillations in a narrow entrance bay. S. Monserrat, I. Fine, A. Amores, M. Marcos ........................................................................................................... 61

A probability-based method to estimate sea level rise and future flooding risks on the Finnish coast. Hilkka Pellikka, Milla M. Johansson, Ulpu Leijala, Katri Leinonen, Kimmo K. Kahma ......... 61

Combining sea state and land subsidence rates in an assessment of flooding hazards at the Danish North Sea coast. Carlo Sørensen, Niels Broge, Per Knudsen, Ole B. Andersen .............................. 62

Special session on Mediterranean sea level .......................................................................................... 62


To what extent can Mediterranean sea level evolve differently from global sea level rise?. Gabriel Jordà, Damià Gomis, Marta Marcos .............................................................................................. 62

On the connection between the sea level variability in the Mediterranean and in the Black Seas. Denis Volkov, Felix Landerer .......................................................................................................... 63

Meteotsunamis in the Mediterranean Sea: rare but destructive extreme sea level events occurring under specific synoptic conditions. Ivica Vilibic, Jadranka Sepic ................................................... 63


Τsunami impact in the European-Mediterranean region from the antiquity up to the present. Gerassimos A. Papadopoulos, Georgia Diakogianni, Anna Fokaefs, Antonia Papageorgiou, Ioanna Triantafyllou ................................................................................................................................... 64

Evolution of sea level and other variables on the XXI century: a picture derived from Vanimedat II and ESCENARIOS projects. Enrique Álvarez Fanjul, Damià Gomis, E. Rodríguez-Camino, Marta Marcos, Gabriel Jordà, R. Aznar, J. C. Sánchez-Perrino, A. Martínez Asensio, J. Llasses, Elena Padorno, Begoña Pérez, M. N. Tsimplis, F.M. Calafat, Samuel Somot, F. Sevault, F. Adloff, J. M. Rodríguez ....................................................................................................................................... 64

Future evolution of sea level extremes along the Mediterranean coastline as produced by the superposition of storminess and sea level rise. Piero Lionello, Dario Conte, Luigi Marzo, Luca Scarascia ........................................................................................................................................ 65

Posters ............................................................................................................................................... 65

Sea level at 2ka BP in the Balearic Islands from Roman age coastal quarries. Fabrizio Antonioli, Marcus Heinrich Hermanns, Marco Anzidei ................................................................................... 65

Sensitivity of the Mediterranean sea level to atmospheric pressure and free surface elevation numerical formulation in NEMO. Antonio Bonaduce, Paolo Oddo, Nadia Pinardi, Antonio Guarnieri ....................................................................................................................................................... 66

Rescuing historic Maltese tide gauge data. Elizabeth Bradshaw .................................................. 66

Long-wave analysis of coastal sea-level records and implications for hazard monitoring and assessment: an application to the Siracusa, Italy, tide-gauge station. Lidia Bressan, Stefano Tinti ....................................................................................................................................................... 67

Mesoscale eddies in the Western Mediterranean Sea. Romain Escudier, Ananda Pascual, Pierre Brasseur, Lionel Renault ................................................................................................................. 67

Improved satellite altimeter mapped sea level anomalies in the Mediterranean Sea. Marta Marcos, Ananda Pascual, Isabelle Pujol ......................................................................................... 68

Determination of Mean Dynamic Topography over the Mediterranean Sea from Jason-2 Altimetry Measurements and EGM2008 Data. Ali Rami, Sofiane Khelifa ..................................................... 68

Interannual variability of the Surface Geostrophic Circulation of the Mediterranean Sea. M. Sempere, S. Esselborn, I.Vigo ......................................................................................................... 69

Seasonal Cycle of Surface Geostrophic Circulation of the Mediterranean Sea. M.Sempere, I. Vigo, M. Trottini, S. Esselborn ................................................................................................................. 69

High-frequency sea-level oscillations in the Mediterranean Sea: analysis and synoptic preconditioning. Jadranka Sepic, Ivica Vilibic, Amaury Lafon, Loic Macheboeuf, Zvonko Ivanovic ....................................................................................................................................................... 70

Mean sea level secular trends from PSMSL RLR data: A case study for the Mediterranean basin. Hebib Taibi , Mahdi Haddad .......................................................................................................... 70

Relative sea level trend and long term variability in the Northern Mediterranean from tide gauge data: implications for future projections. Antonio Vecchio, Marco Anzidei .................................. 70


Keynotes speakers

Sea-level changes during past centuries reconstructed from salt-marsh sediments. Prof. Roland Gehrels, University of York, UK

In recent years a number of sea-level records have been published that use salt-marsh sediments, and the fossils contained within, as indicators of sea-level change. High-quality sea-level reconstructions from salt-marsh sediments have now been established for coastal sites in eastern North America (Nova Scotia, Maine, Connecticut, New Jersey, North Carolina, Florida), Europe (Iceland, Scotland, England, northern Spain), New Zealand and Tasmania. These proxy records are particularly useful because they can provide high-resolution sea-level data beyond the period that is covered by tide gauges, including the centuries immediately preceding the observational era. The overlap with tide-gauge records provides a check on the validity of the proxy reconstructions. The chronology of proxy records is provided by a range of radiometric dating techniques (AMS14C, 210Pb, 137Cs, 241Am) and by specific stratigraphic markers (e.g., pollen, tephra, Pb concentrations, Pb isotopic ratios, paleomagnetism). High-precision Accelerator Mass Spectrometry (AMS) 14C dating, in combination with bomb-spike AMS14C analyses, is used to circumvent limitations associated with radiocarbon dating. The resolution of proxy records depends on the sedimentation rates in the marshes and is usually on the order of one or two data points per decade.

Many salt-marsh based proxy sea-level records show a marked positive inflexion in the late 1800s or the early 1900s. Combined with long tide-gauge records they demonstrate that in the first half of the 20th century the rate of sea-level rise started to exceed the late Holocene background value. The magnitude of the 19th/20th inflexion is large in southern hemisphere sites compared to the North Atlantic which could point at northern hemisphere land-based ice as an important melt source for a global sea-level acceleration in the early 20th century. Along the North American east coast there is some evidence for a period of accelerated sea-level rise in the late 18th century, when rates approached those that have been observed in the 20th century. In Iceland the highest rates of sea-level rise occurred during positive shifts of the reconstructed North Atlantic Oscillation (NOA) index. A 19th/20th century sea-level acceleration is muted in the eastern Atlantic. Accelerations of sea-level rise in the North Atlantic are confined to the regional scale and are possibly driven, at least in part, by re-distribution of water masses due to changes in long-term wind patterns. Without exception all salt-marsh proxy sea-level records show that the highest rates of sea-level rise of the last 2000 years were achieved during the 20th century.

Considering vertical land motion in understanding sea level change. Prof. Guy Woppelmann, University of La Rochelle, France

Vertical land motion plays an important role in understanding sea level change over multi-decadal to century timescales. On the one hand, they need to be corrected in sea level trends recorded by tide gauges to derive the climatic contributions to sea level. On the other hand, they need to be considered to understand and anticipate the magnitude of future sea levels along specific coastlines. Indeed,


vertical land motion can substantially amplify or attenuate sea level rise from the sole climatic contributions. In any case, whether global or local, an accurate estimate of vertical land motion appears mandatory. In this presentation, we will review how vertical land motion has been considered in past estimates of global sea level change, how it can be determined and what are the current limits in its accurate observation for understanding relative sea level changes at the coast.

The time-mean ocean dynamic topography: How well can we measure, model, and understand it?. Prof. Chris W. Hughes, National Oceanography Centre, UK The combination of altimetry with GOCE and GRACE gravimetry means we now have an accurate global picture of the mean ocean dynamic topography. Addition of tide gauges, GNSS positioning, and regional gravity measurements extends this knowledge to points precisely at the coast. With a global range of about three metres, it is clearly important that we understand how this dynamic component of sea level is maintained, if we are to have confidence in model predictions of how it might change. In this talk, I will address the question of how well current ocean models can reproduce the observed mean dynamic topography, and how well we understand the reasons for those observations. While the models do a generally good job, I will argue that our understanding remains rather patchy for the open ocean, and is still quite rudimentary for coastal sea level.

What are the challenges facing quantifying impacts and adapting to global sea-level rise?. Dr. Sally Brown, University of Southampton, UK

Sea-level rise and extreme events pose on-going and long-term threats to coastlines, particularly where hazards coincide with human population. Globally, up to 5% of the population could be affected annually by sea-level rise by 2100 if protection standards are not raised. Such a situation in unlikely as often humans and natural environments are responsive to change, whether due to a sudden event, or resulting from slow incremental changes. This represents challenges: Firstly, with much uncertainty in the projections of sea-level rise and other drivers, what levels will humans or the natural environment be adapting to? Secondly, given a response to reduce impacts, what will be affected and where will impacts occur? Thirdly, how will that adaptation take place?

To answer these questions, this presentation explores how past sea-levels, vertical land movements, present observations, plus extreme events influence future projections of impacts and adaptive responses. Sea-level rise projections and impacts today will be analysed from global to local scales, including areas that are particularly at risk world-wide. Adaptation to reduce impacts will also be considered, from successful past adaptation where transitions to safer coasts have been made, to potential future responses.

Increasingly the assessment of impacts requires a systems approach, understanding multiple drivers of coastal changes. Recognition into multiple drivers of change, their interactions and relative importance is increasingly, such as how population and economic growth can influence or induce impacts. Gathering accurate data on coastal change and impacts is sometimes challenging today, not alone for the future. The adaptation challenge remains in enabling long-term climate change


adaptation today, without compromising short-term needs, development and livelihoods. Thus, whilst sea-level rise is an important driver of change, it is increasingly recognised that other drivers can be more responsible for adverse impacts of change: Sea-level rise remains a societal challenge, depending on good governance to identify, monitor and reduce impacts.

Semi-empirical modelling of sea-level change. Prof. Stefan Rahmstorf, Postdam University, Germany The talk will discuss the semi-empirical approach to modelling sea level, its robustness and validation issues, and the role that paleo-climatic data can play in constraining the parameters for future sea-level rise.

References:

Rahmstorf, S. (2007), A semi-empirical approach to projecting future sea-level rise, Science, 315(5810), 368-370, doi:10.1126/science.1135456.

Vermeer, M., and S. Rahmstorf (2009), Global sea level linked to global temperature, Proceedings of the National Academy of Sciences of the United States of America, 106(51), 21527-21532, doi:10.1073/pnas.0907765106.

Kemp, A. C., B. P. Horton, J. P. Donnelly, M. E. Mann, M. Vermeer, and S. Rahmstorf (2011), Climate related sea-level variations over the past two millennia, Proceedings of the National Academy of Sciences of the United States of America, 108(27), 11017-11022, doi:10.1073/pnas.1015619108.

Rahmstorf, S., M. Perrette, and M. Vermeer (2012), Testing the robustness of semi-empirical sea level projections, Clim. Dyn., 39(3-4), 861-875, doi:10.1007/s00382-011-1226-7.

Schaeffer, M., W. Hare, S. Rahmstorf, and M. Vermeer (2012), Long-term sea-level rise implied by 1.5 degrees C and 2 degrees C warming levels, Nature Clim. Change, 2(12), 867-870, doi:10.1038/nclimate1584.

Bittermann, K., S. Rahmstorf, M. Perrette, and M. Vermeer (2013), Predictability of twentieth century sea-level rise from past data, Environmental Research Letters, 8(1), doi:10.1088/1748-9326/8/1/014013.

Tide gauge reconstructions and the separation of regional and global mean sea level signals. Prof. Mark Merrifield, University of Hawaii, USA Reconstructions of global mean sea level (MSL) based on tide gauge datasets include decadal time scale fluctuations that have drawn considerable attention. These low frequency MSL fluctuations have been attributed to various physical phenomena, including volcanic activity, enhanced land ice melt, and changes in ocean circulation and heat uptake. Alternatively, the limited spatial sampling afforded by the tide gauge network may lead to the misrepresentation of regional sea level variability into the global mean. To gain further perspective on this issue, we review various ways that changing surface


winds result in regional sea level patterns, and consider how effective the tide gauge array is at distinguishing these patterns from MSL change. We use the tide gauge data to highlight that regional variations detected during the satellite altimeter period are not necessarily stationary over the past century, and that the sparse array prior to the mid 1950s is poorly suited for the separation of regional and global patterns. Lastly, we consider prominent MSL decadal variations in various tide gauge reconstructions and examine the potential for contamination of regional sea level signals into the mean.

Sea level variability: from surface gravity waves to mean sea level. Prof. Charitha Pattiaratchi, University of Western Australia, Australia Coastal sea level variability occurs over a range timescales ranging from seconds to centuries.

The action of the wind on the sea surface generates surface gravity waves with periods of the order of 10s and plays a major role in defining coastal processes. Infra-gravity waves with periods 30-300 s influence oscillations in semi-enclosed basins such as ports and harbours. Globally, the astronomical forces of the Sun and the Moon result in tidal variability with periods of 12 and 24 hours as well as tidal modulations with periods up to 18.6 years. In many regions, the effects of the tides dominate the water level variability – however, in regions where the tidal effects are small other processes also become important in determining the local water level. In this presentation, sea level data from Fremantle (tidal range ~0.5m), which has one of the longest time series records in the southern hemisphere, and other sea level recoding stations from Western Australia are presented to highlight the different processes ranging from seiches, tsunamis (generated through earthquake and meteorological events), tides, storm surges, continental shelf waves and annual and inter-annual variability. As the contribution from each of these processes is of the same order of magnitude – the study of sea level variability in the region is very interesting and reveals both local and remote forcing.

Modelling historical and future mean sea level change. Prof. Jonathan Gregory, University of Reading, UK The rate of global mean sea level rise (GMSLR) has accelerated during the last two centuries, from the order of magnitude of 0.1 mm yr-1 during the late Holocene, to about 1.5 mm yr-1 for 1901-1990, with ocean thermal expansion and glacier mass loss being probably the dominant contributors. Process-based models suggest that the larger rate of rise since 1990, of about 3 mm yr-1, results from increased radiative forcing of global climate change, and from increased ice-sheet outflow induced by warming of the immediately adjacent oceans. Ocean thermal expansion is the largest contributor to projections of GMSLR during the 21st century. For a given scenario, there is a substantial spread in climate model projections of global ocean heat uptake and thermal expansion, and in the geographical pattern of sea level change due to ocean density and circulation change. Larger uncertainty in projections of GMSLR comes from the land-ice contributions, especially ice-sheet dynamical change. These contributions also influence regional sea-level change, through their effect on gravity and the solid Earth. By 2100 the rate of GMSLR for a scenario of high emissions could approach the average rates that occurred during the last deglaciation, whereas for a strong emissions mitigation scenario it could stabilise at rates


similar to those of the early 21st century. In either case, GMSLR will continue for many subsequent centuries, because of the long timescales of ice-sheet change and deep-ocean warming, and could be partly irreversible.

Status and challenges on sea level monitoring and forecasting in the Mediterranean Dr. Begoña Pérez Gómez, Puertos del Estado, Spain

After a review of the main characteristics of the relevant sea level processes and variability expected in the Mediterranean sea, a detailed analysis of the adequacy of the existing monitoring networks and forecasting systems in the region is presented. The tide gauges spatial distribution and their data sampling and latency will be first considered, in order to determine the capability of the existing in-situ network to fulfill the new requirements not only of climate scientists and oceanographers but also of the sea level related hazards warning systems. The latter include both storm surge and tsunami warning. For years storm surge forecasts have not been a priority in the Mediterranean; however, a new set of forecasting systems are in operation nowadays, what reveals the interest of this variable, reinforced by the expected increase of mean sea level for the next decades. Operational general circulation models are now being designed for including sea level forecasts for this reason. On the other hand, the risk of tsunamis in the Mediterranean is significantly larger than in the rest of Europe: having access to high-frequency sea level data in real time from the entire basin is crucial for an early detection and final early warning to the population: in this aspect the lack of stations from the North of Africa is a great weakness of the regional tsunami warning systems.


Paleo Sea Level

Oral Presentations

Holocene relative sea level changes in the Baltic Sea basin: syntheses of geological and archaeological data. Alar Rosentau In the early phases of cultural development, Mesolithic and Neolithic human populations in the Baltic region experienced periods of significant marine transgressions and regressions owing to the melting of the continental ice sheet and glacial isostatic land uplift. Geological–archaeological studies in the southern Baltic Sea area have revealed a number of Mesolithic and Neolithic traces of human occupation off the Danish and German coasts as a result of Holocene sea-level rise. Prehistoric coastal sites in the northern Baltic Sea areas have, however, been uplifted and are located successively at different altitudes as a result of glacial rebound. In transitional areas, prehistoric man experienced transgressions and regressions of the shifting coastline owing to competition between glacial rebound and eustatic sea level rise. In the current paper case studies form the transitional area will be presented demonstrating the potential of archaeological records for reconstruction of transgressions and regressions during the Litorina Sea. Geological and archaeological data indicate acceleration in sea-level rise rates around 7.8 and 7.6 cal. ka BP when relative sea-level rose c. 6 m within c. 500 years. This caused the flooding of peat and palaeosoil layers, by the submergence of the Mesolithic sites and by the abrupt appearance of brackish water diatoms in different small lake basins. The SPLASHCOS COST Action TD0902 completed in 2013 is producing an Atlas of over 2500 submerged prehistoric sites that may be useful in palaeo-sea level reconstructions.

Sea-level changes in the western Mediterranean during the last 12,000 years: a tool to better constrain the future projection of sea-level rise. Matteo Vacchi, Nick Marriner, Christophe Morhange, Giorgio Spada, Alessandro Fontana, Alessio Rovere Global sea-level rise is the result of an increase in the ocean volume, which evolves from changes in ocean mass due to melting of continental glaciers and ice sheets, and the expansion of ocean water as it warms. The elevation of the ocean surface relative to the ocean floor is defined as a relative sea level (RSL), and any shift in height of either of these two surfaces produces a RSL change. Present-day sea level variations in the Mediterranean depend on various factors, including recent climatic forcing, tectonic activity, anthropogenic effects, and glacio-isostatic adjustment. Our understanding of current rates of sea-level rise from tide gauge and satellite data, requires correction for glacial isostatic adjustment (GIA) effects that are both calibrated to, and independently tested by, observations of former sea levels. With this purpose, we created a database of Holocene (last 12.0 ka) geological and geo-archeological sea-level data across the Western Mediterranean. We reconsidered ~600 published and unpublished sea-level data along the western Mediterranean Sea and we proposed a standardized approach for the production of index and limiting points following the protocol described by the International Geoscience Programme (IGCP) projects 61, 200, 495 and 588. We then reconstructed the RSL histories in 21 regions located in Spain, France, Italy, Malta, Tunisia, Slovenia and Croatia. At the basin scale, RSL rose rapidly from 12.0 to 6.0 ka BP. Younger data showed a significant decrease in the rising rates in the last 7.5 ka. During the late Holocene (last 4.0 ka BP) GIA, sediment compaction and


local neotectonic activity played a major role in controlling sea-level variability between regions. Preliminary comparison with long-term tidal gauge data (>50 years) indicates a significative increase in rates of sea-level rise during the last 100 years.

Results of this study are relevant for understanding how GIA operates in the far field of late-Pleistocene ice sheets and to assess sea level rise hazards, which are particularly magnified in low-lying or subsiding coastal areas.

Late Holocene sea-level change in the Falkland Islands: testing the Greenland melt hypothesis. Newton, T. L., Gehrels, W. R., Daley, T.J., Blake, W. Instrumental and proxy sea-level records indicate that 20th century sea-level rise (SLR) in the North Atlantic Ocean departed significantly from average late Holocene trends reconstructed by geological methods. Southern hemisphere instrumental records are too short to identify any recent acceleration. Recent studies have documented the inflexion in proxy records from New Zealand and Tasmania, giving rise to the hypothesis that the 20th century sea-level acceleration was global in extent. Importantly, the magnitude of change in the rate SLR at the beginning of the 20th century is greater in southern hemisphere sites than in the North Atlantic. Such spatial differences are potentially highly significant as sea-level theory predicts that land-based ice melt produces increased rates of SLR in the far-field locations from which the melt source is located. The greatest rates of SLR as a consequence of Greenland melt are predicted to be in the South Atlantic Ocean, in the seas surrounding the Falkland Islands.

To test this hypothesis we present a new late Holocene relative sea-level (RSL) record for the Falkland Islands, the first for this region. Our reconstruction is based on palaeo-sea level positions derived from diatom, testate amoebae and foraminifera analyses obtained from saltmarsh sediments. The reconstruction shows that RSL in the Falkland Islands for much of the last 7000 years was within 0.7m of present RSL. Our high-resolution reconstruction for the last ~2000 years documents a rising trend in RSL with a recent inflexion toward present sea level for the most recent part of the record. This pattern of sea-level change is consistent with proxy records from Tasmania and New Zealand which suggest that northern hemisphere land-based ice was the most significant melt source for late Holocene global sea-level rise.

Posters

Decoding sea level changes during the MIS 5 by means of Phreatic Overgrowths on Speleothems (POS) research in coastal caves of Mallorca (western Mediterranean). Joan J. Fornós, Àngel Ginés, Joaquín Ginés, Francesc Gràcia, Yemane Asmeron, Bogdan P. Onac, Victor Polyak, Paola Tuccimei The littoral caves of southeastern Mallorca have formed by the mixing of freshwater and seawater in the coastal phreatic zone, and are extensively decorated with speleothems that formed during Quaternary times when the caves become air-filled chambers. Throughout the Middle and Upper Pleistocene the caves were repeatedly flooded by glacio-eustatic sea level oscillations. The water level of each flooding event was recorded by a distinct encrustation (a Phreatic Overgrowth on Speleothems, POS) of calcite or aragonite deposited less than 40 cm below the brackish water/air


interface (water table) at elevations equivalent to sea-level, over existing speleothems and along cave walls. These carbonate precipitates, which appear as horizontal alignments of crystallizations delimiting the tidal fluctuation range of the coastal water-table, are excellent recorders of sea level changes, being readily datable by U-series methods. Thus, stable sea-level stands result in POS that have grown large enough to be used as accurate sea-level markers. Marine isotope stage (MIS) 5 of the last interglacial (LIG) is of great interest because it serves as an analog for the Holocene. Changes in sea-level are, in part, indicative of the global-scale changes in climate. Acknowledgements: This research has been supported by the MINECO projects CGL 2010-18616 and CGL-2013-48441-P to JJF and by a NSF grant AGS 1103108 to BPO and VJP

Sea-level highstands in Mallorca during the last interglacial. Thomas Lorscheid, Paolo Stocchi, Alessio Rovere, Lluís Gómez-Pujol, Bas de Boer, Thomas Mann, Hildegard Westphal, Joan J. Fornós Deposits of the last interglacial, analysed in light of glacio-hydro-isostatic adjustment models, can provide us with information on the sea-level history and the response of polar ice-sheets in slightly warmer climates. Mallorca is one of the key areas in the Western Mediterranean for such deposits. The outcrops representing this period were intensely investigated by several authors since CUERDA 1979. According to their observations, the sedimentological and fossil content is well known and the age was determined by the presence of the Senegalese fauna and, more recently, by dating with U/Th and AAR. Three aspects of Mallorcan deposits were still underinvestigated. i) precise elevation measurements with differential GPS. ii) estimates of reference water level and indicative range of the deposits and landforms at each site. iii) estimates of glacial isostatic adjustment (GIA) effects since MIS 5e. In this study we present the results of two field trips aimed at measuring last interglacial deposits in Mallorca with high-accuracy GPS and establishing, using modern shorelines as analogs, indicative ranges and reference water level values for paleo deposits. We then used an earth-ice coupled GIA-model to investigate isostatic adjustment since MIS 5e in the island, and compared the elevation of our deposits to the expected GIA signal in this region. We discuss our results in terms of tectonics and eustasy.

Vertical Land Movements

Oral Presentations

Combination Results of the Tide Gauge Benchmark Monitoring (TIGA) Analysis Centre Re-processing Products. Addisu Hunegnaw, Norman Teferle In 2013 the International GNSS Service (IGS) Tide Gauge Benchmark Monitoring (TIGA) Working Group (WG) started their re-processing campaign, which proposes to re-analyze all relevant Global Positioning System (GPS) observations from 1994 to 2013. This re-processed data set will provide high-quality estimates of vertical land movements for more than 400 stations, enabling regional and global high-precision geophysical/geodetic studies. Several of the TIGA Analysis Centres (TACs) have completed processing the full history of GPS observations recorded by the IGS global network and


many other GPS stations at or close to tide gauges, which are available from the TIGA data centre at the University of La Rochelle (www.sonel.org). Following the recent improvements in processing models and strategies, this is the first complete re-processing attempt by the TIGA WG to provide homogeneous position time series.

In this study we report on a first multi-year weekly combined solution from the TIGA Combination Centre (TCC) at the University of Luxembourg (UL). Using two independent combination software packages, CATREF and GLOBK, we have computed a first solution of the TAC solutions already available. These combinations allow an evaluation of any effects from the combination software and of the individual TAC parameters and their influences on the combined solution. Some major results of the UL TIGA multi-year combinations in terms of geocentric sea level changes will be presented and discussed.

Models of land uplift in northern Europe. Holger Steffen Glacial isostatic adjustment (GIA) is the dominating process in northern Europe leading to a maximum absolute land uplift of about 1 cm/year near the Swedish city of Umeå. In contrast, the areas of the southern Baltic and North seas are subsiding due to the collapse of the peripheral bulge. Both effects have enormous impact on coastal changes and thus on society and economy, especially in view of current sea-level rise which may increase or decrease uplift or subsidence depending on the location.

The Nordic countries have developed and are frequently updating land uplift models for usage in the national geodetic surveys. We present current models that are used as well as further efforts for the development of high precision and high resolution land uplift and GIA models which could also help in sea level research. This includes most recent results of land uplift/subsidence and sea-level change for the North and Baltic seas.

Relative sea level history during the Holocene and models of the glacial isostatic adjustment process: constraints from the regions of forebulge collapse. Keven Roy, W.R. Peltier Models of the glacial isostatic adjustment (GIA) process enable us to study and understand the regular cycles of glaciation and deglaciation that have characterized the Earth's climate over the past 800,000 years or so, in particular in terms of the large variations in sea level that have accompanied them.

These models, which require as fundamental inputs a history of ice-sheet loading and a representation of the radial variation of mantle viscosity, can be tested and refined by comparing their predictions to a wide range of geophysical and geological observables, among which inferences of past relative sea level based upon appropriate geological indicators are particularly important. These geophysical observables, depending on the region from which they originate, provide constraints on different features of the GIA process. However, while the relaxation process in regions near former centers of glaciation can be parametrized in a simple fashion, its evolution in regions of forebulge collapse, located at the periphery of the former ice sheets, is much more complex.

In this paper, we examine how recently available high-quality geological data sets of relative sea level history for regions of forebulge collapse, such as that of Engelhart et al. (2011, Geology) for the U.S. East coast or Engelhart et al. (2015, QSR) for the U.S. West coast, enable us to gain critical information concerning the response of these regions and provide new complementary constraints on GIA models


and, consequently, on our understanding of relative sea level evolution around the world. In particular, we will focus on how misfits between these new sea level evolution inferences and current state-of-the-art GIA model predictions (ICE-6G_C (VM5a) (Peltier et al., 2015, JGR)) can be eliminated, and then explore the consequences of these changes on our knowledge of the deglaciation history over North America.

Posters

Updated GPS vertical velocity field at tide gauges: application to global and regional sea level change. Médéric Gravelle, Alvaro Santamaria-Gomez, Marta Marcos, Phil Thompson, Guy Wöppelmann The relative importance of the non-climate contribution of vertical land movement to the observed rates of sea level change at the coast is investigated based on the last GPS solution of the ULR consortium taking part to the International GNSS Service (IGS) Repro2 campaign. This solution stems from 20 years of GPS data (1995-2014) reanalyzed using state-of-the-art models and corrections. It includes 749 GPS stations distributed worldwide of which 575 are dedicated to a sea level application. In this study, we correct the tide gauge trends for vertical land movements using the GPS velocity field, and we investigate global and regional mean sea level estimates

Using InSAR to monitor vertical ground motions in coastal cities. G. Le Cozannet, D. Raucoules, G. Wöppelmann Before the altimetry era, tide gauge are a unique source of information to evaluate past sea-level changes. However, they can be affected by vertical ground motions acting at different space scales. We use synthetic aperture radar techniques to assess these ground motions and their consequences for geodetic instruments such as Tide Gauge, GPS, Doris stations. Summarizing results obtained at Alexandria (Egypt; Woppelmann et al., 2013), Manila (Philippines; Raucoules et al., 2013) and Dakar (Senegal; Le Cozannet et al., subm.), we identify different situations in terms of data availability and ground motion context:

- when strong ground motions affect the tide gauge, the technique can easily help rejecting tide gauges records from the database of reliable datasets (case of Manila)

- however, when no ground motions can be observed using InSAR in the vicinity of geodetic instruments (Case of Alexandria and Dakar), it remains challenging to reach the accuracy required to confirm that tide gauge records are indeed suitable for monitoring sea level changes.

To reach the required accuracy of this InSAR application, a large set of SAR data must have been acquired over the area. For future science application of Sentinel 1 in the field of geodesy underpinning sea level science, it will be necessary to define appropriate background missions covering coastal sites where key records have been aquired.


Vertical land movements from the combined use of satellite altimetry and tide gauges. Marta Marcos, Guy Wöppelmann Vertical ground displacements at tide gauge sites were estimated from the differenced time series of monthly satellite altimetry sea level anomalies minus tide gauge. We have used the time series of satellite altimetry that are routinely processed and distributed by four major data providers (three gridded and one along-track products) together with monthly tide gauge records from the datum controlled data set of the Permanent Service for Mean Sea Level (PSMSL). Differenced time series were built using three variants of altimetric time series. Each resulting record was analyzed assuming a combination of white noise and power-law noise of a priori unknown spectral index. The rate uncertainties, computed taking into account the noise content in the differenced time series, will be discussed. In particular, in the context of the departures from the white noise (expected only if both the satellite altimeter and the tide gauge were recording mostly the same sea level signals and their instrumental errors were negligible) and its amplitude. The most suitable altimetric product in terms of correlation and variance reduction at tide gauges, among those investigated, will be identified. Rates of vertical land motion computed with Global Positioning System (GPS) and rates obtained from the combination of altimetry and tide gauge records will be finally compared for those stations where both measurements are available.

GNSS reflectometry for tide gauge levelling. Alvaro Santamaría-Gómez, Christopher Watson, Médéric Gravelle, Matt King, Guy Wöppelmann The GNSS reflectometry (GNSS-R) technique provides valuable information related to the geometry and physical properties of reflecting surfaces surrounding the GNSS antenna (e.g., Global Positioning System, GPS), including the vertical distance to them.

Here, we use sea-surface reflections of GNSS signals, recorded as oscillations in the observed signal-to-noise ratio (SNR), to estimate the GNSS to tide gauge (TG) levelling connection and thus the ellipsoidal height of the TG. This can be done remotely, continuously and at no additional cost.

The same technique can be used to monitor sea-surface height changes, transforming the GNSS station in an alternative TG and thus providing sea-level change in a global height system.

We describe how this technique works, its benefits and limitations, including ongoing work and future improvements. At the time of writing, comparison with traditional in situ levelling reveals promising differences at the centimetre level. These differences include errors from this technique, but also errors related to the traditional in situ levelling (errors in the GNSS antenna calibration) and to the calibration of the TG zero. The latter opens the possibility of using this technique to monitor the stability of the TG zero

Leveling for the altimetric control of tide gauge sensors and GNSS permanent stations in Barcelona’s and Ibiza’s ports. Tapia Gómez, A; López Bravo, R; Gili Ripoll JA; Martínez Benjamín, JJ; Pros LLavador, F; Palau Teixidò, V The main objective of the work performed is to determine altimetrics movements that may affect the data stability, of both tide gauges and global positioning, transmitted by these two types of sensors.


We will present the work effected at the port of Barcelona that started in 2011, the year in which settlements are detected in the area compared to 2008 data, and which have continued until today. The area where the tide gauge of Puertos del Estado and the GNSS permanent station of the Autoritat Portuària de Barcelona, distant about 50 meters, are located, is newly reclaimed land sea. Plus, the GNSS station is located on the roof of the control tower of the port, a building 45 meters high with a unique metal frame.

As well, we will present the work effected at the port of Ibiza, tide gauge of Puertos del Estado and GNSS control station on the roof of a building about 10 meters high and distant about 80 meters.

The need for GNSS stations to have a clear horizon, forces their location to be on buildings which difficult a precise leveling, we will describe leveling geometric designed as ad hoc.

The tasks carried out in the port of Barcelona until September 2014, settlements have been detected up to 39 millimeters, while in the port of Ibiza the settlements are estimated at a value close to 1 mm/year.

The results confirm that altimetrics checks need to be done periodically starting from the moment they are installed and in fixed points. The frequency of checks will be determined by the results that are obtained.

A New Datum-Controlled Tide Gauge Record for Sea Level Studies in the South Atlantic Ocean: King Edward Point, South Georgia Island. Norman Teferle, Addisu Hunegnaw, Philip Woodworth, Peter Foden, Simon Williams, Jeffrey Pugh, Angela Hibbert In 2008 a new pressure tide gauge with Global Sea Level Observing System Number 187 was installed at King Edward Point (KEP), South Georgia Island, South Atlantic Ocean. This installation was carried out as part of the Antarctic Circumpolar Current Levels by Altimetry and Island Measurements (ACCLAIM) programme. In 2013 the KEP Geodetic Observatory was established in support of various scientific applications including the monitoring of vertical land movements at KEP. Currently, the observatory consists of two state-of-the-art Global Navigation Satellite System (GNSS) stations with local benchmark networks. In 2014 a tide board was added to the tide gauge, which, together with the measurements from the KEP Geodetic Observatory, now enables a calibration of the tide gauge. This will make it possible to include the KEP tide gauge in the Permanent Service for Mean Sea Level (PSMSL) database and make it available for future sea level studies.

In this study, we will present the GNSS and levelling observations from the KEP Geodetic Observatory for the period from February 2013 to May 2015 used for the calibration of the tide gauge. While it is still too early to obtain accurate vertical land movement estimates from the GNSS data, the levelling campaigns in 2013 and 2014 indicated 7-9 mm of subsidence near the tide gauge. For the computation of the new height datum, geoid undulations derived from a seamless combination of the latest Gravity Observation Combination (GOCO) and Earth Gravitational Model (EGM) 2008 models were used. The use of this combined gravity model introduced a datum shift of approximately -24 cm compared to the previous datum.


Mean Sea Level Observations and Processes

Oral Presentations

The GOCE geoid in support to sea level analysis. Thomas Gruber The accuracy of the final geoid models derived from GOCE and complementary satellite data is estimated to be about 1.5 cm with 100 km spatial resolution and worldwide consistency. This opens new possibilities for sea level research, where geoid quality and consistency over large distances often plays an important role. One example for this is the problem of connecting tide gauge records across the oceans. In principle there are two ways to perform this connection. First, via the oceans by estimating the dynamic ocean topography at the tide gauges from the GOCE geoid and satelllite altimetry and, second, by unifying the regional or continental height systems to which the tide gauges are connected by estimating their offsets to the global GOCE geoid. Both approaches in principle require the true geoid at the tide gauge locations, which not always is provided by the GOCE geoid because of its limited spatial resolution or in other words due to the omission error, i.e. the part of the signal which cannot be observed with GOCE. The paper provides a summary of the characteristics of the GOCE geoid solutions, some results for connecting tide gauges applying both methods and specifically investigates the impact of the omission error on the results obtained.

On the decadal trend of global mean sea level and its implication on ocean heat content change. Lee-Lueng Fu The variability of the trend of global mean sea level on decadal scales is of great importance to determining its long-term evolution. In this paper we have reexamined the approach to estimating such a trend. Most climate time series such as the altimeter sea level record are characterized by a red noise process. The temporal correlation of the residuals from a linear trend fit has often been neglected in estimating the uncertainly of the fit, leading to underestimate of its errors. We suggest to cast the problem as optimal estimation to minimize the residuals weighted by autocovariance. The approach takes into account the various time scales present in the time series and their effects on estimating a trend. In the case of the altimeter record, the resulting error estimate is a factor of four larger than estimates neglecting the temporal correlation. Although the dominant error in the altimetric sea level trend is derived from comparison to tide gauge observations, which have long-term (tectonic scales) errors from land motions. Such errors essentially cause a bias in the estimate of a trend over decadal scales. Such bias would be canceled for evaluating the change of decadal trends, of which the errors are thus dominated by the uncertainty in the estimation error. The approach was also applied to the sea level change from ocean mass estimated from the GRACE observations of the change of Earth’s gravity. The steric sea level was then estimated from the difference between the sea level from altimetry and its mass component from GRACE. The decadal trend of steric sea level was favorably compared to the Argo observations. The results have shed light on the prospects of estimating decadal change in ocean heat content from space, a variable of great importance to climate change and sea level rise.


Deep-ocean contribution to sea level and energy budget not detectable over the past decade. W. Llovel, J. K.Willis, F.W. Landerer, I. Fukumori As the dominant reservoir of heat uptake in the climate system, the world’s oceans provide a critical measure of global climate change. Here, we infer deep-ocean warming in the context of global sea-level rise and Earth’s energy budget between January 2005 and December 2013. Direct measurements of ocean warming above 2,000m depth explain about 32% of the observed annual rate of global mean sea-level rise. Over the entire water column, independent estimates of ocean warming yield a contribution of 0.77 +/ - 0.28mm/yr in sea-level rise and agree with the upper-ocean estimate to within the estimated uncertainties. Accounting for additional possible systematic uncertainties, the deep ocean (below 2,000 m) contributes -0.13+/ -0.72mm/yr to global sea-level rise and -0.08+/ -0.43W/m^2 to Earth’s energy balance. The net warming of the ocean implies an energy imbalance for the Earth of 0.64 +/ - 0.44W/m^2 from 2005 to 2013.

Synchronization of sea level to oceanic and atmospheric forcing. Francisco M. Calafat Synchronization is a basic phenomenon in physics wherein the phases of two oscillators, either chaotic or periodic, become entrained to a common behaviour through coupling or forcing. Strictly speaking, the ocean-atmosphere system represents an example of bidirectional coupling in which the two subsystems mutually influence each other's dynamics, although in many ocean applications one can assume, without incurring significant error, that the atmosphere is a freely-evolving force acting upon the ocean. Irrespective of the coupling configuration, the interaction between the two subsystems can lead to the appearance of relations between some of their properties that are crucial too understand the evolution of the ocean, especially in a situation of climate change. Here we are concerned with the synchronization, in the sense of phase-locking, between some of the components of sea level and their driving forces. In particular, we investigate changes in the dynamics of the phase of sea level extremes and the seasonal sea level cycle in tide gauge observations in relation to the evolution of their driving mechanisms such as wind forcing, surface heat fluxes, and hurricane seasonality. In order to detect phase shifts or locking we explore instantaneous phases via a non-linear and non-Gaussian state-space model which is learned through a particle Markov chain Monte Carlo filter.

Annual sea level variability of the coastal ocean: the Baltic Sea-North Sea transition zone. Marcello Passaro, Paolo Cipollini, Jerome Benveniste Up to now, the use of satellite altimetry for sea level studies in the coastal regions has been has been limited due to the lack of confidence in the accuracy of the satellite measurements close to land and in shallow areas. This research focuses on validating the coastal capabilities of satellite altimetry to detect the annual cycle of sea level on a regional and sub-regional scale. The study area is the intersection of North Sea and Baltic Sea.

Coastal-dedicated satellite altimetry data (from ALES) are compared with the state-of-the-art standard altimetry products (from the ESA Climate Change Initiative). Estimations of the annual cycle of sea level are also derived from a network of coastal tide gauges. The analysis spans the Envisat years (2002-


2010) and is performed both along each satellite track (or grid point for the mapped dataset) and by dividing the area into sub-basins.

We demonstrate that dedicated processing improves the quality of the altimetry dataset in the area, showing for example that the root mean square difference between the annual cycle sinusoid estimated by the tide gauges and coastal altimetry within only 15 km of the coast is constantly less than 1.5 cm. We provide interpretation of the results by using wind stress data and a local climatology, highlighting small-scale differences, such as a smaller annual variability in the West Arkona due to steric cycle phase opposed to mass component phase and a slope in the amplitude of the annual cycle along the Norwegian coast due to a coastal current.

To our knowledge, this is the first time that the improvements brought by coastal satellite altimetry to the description of the annual variability of the sea level have been evaluated and discussed. The methodology applied in this paper is generally applicable to other coastal areas and the coastal reprocessed ALES dataset will soon be available to the community over the whole coastal ocean.

A probabilistic reassessment of 20th century global mean sea level. Carling Hay, Eric Morrow, Robert E. Kopp, Jerry X. Mitrovica Tide gauge observations of sea level over the 20th century show significant spatial and temporal variability on a continuum of length and time scales. The variability seen in these records is due to processes that include ongoing sea-level changes due to glacial isostatic adjustment (GIA), thermal expansion of the ocean, dynamic effects associated with ocean circulation changes and ocean-atmosphere interactions, and present day melting of land ice. The geographic signatures associated with this latter process are unique for every ice sheet and glacier, and can be used, in principle, to estimate the contribution of each source to global sea-level change. The combination of data sparsity and geographic variability makes it challenging to obtain robust estimates of global mean sea level (GMSL).

We overcome the difficulties associated with the tide gauge records by modeling the underlying physics responsible for the observed geographic variability in the observations. This allows us to infer global information from the incomplete records. Using two probabilistic techniques, we conclude that GMSL rose at 1.2 ± 0.2 mm/yr over the time period 1901-1990, ~30-40% lower than previous estimates. This lower rate agrees with the sum of the estimated individual GMSL contributions recently reported in the Fifth Assessment Report of the IPCC, allowing us to close the 20th century sea-level budget. By contrast, our estimated rate for the period 1993-2010 (3.0 ± 0.7 mm/yr) agrees with previously published results, suggesting that the acceleration of sea-level rise over recent decades has been significantly greater than previously thought.

Considerations for Estimating the 20th Century Trend in Global Mean Sea Level. Philip R. Thompson, Benjamin D. Hamlington Recent reconstruction efforts result in a range of published estimates for the 20th century trend in global mean sea level (GMSL). Discrepancies can be attributed to two factors: 1) differences in analysis and/or reconstruction techniques; and 2) differences in tide gauge selection and quality control of the data. In this paper, we isolate the effect of tide gauge selection on estimates of GMSL by applying a


simple and consistent analysis technique to the sets of tide gauges used in three recent publications: Ray and Douglas (2011), Church and White (2011), and Hay et al. (2015). We describe the differences in selection philosophy employed by each study, and we show how tide gauge selection choices can affect estimates of the long-term global trend derived from each set. In particular, we find that discrepancies between 20th century GMSL trend estimates are related to the decision to include or exclude gauges from a small number of coastal regions. These regions exhibit large-scale coherent variability and/or long-term trends that are inconsistent with changes in GMSL, and we conclude that any reconstruction including gauges from these regions must demonstrate the ability to account for this non-global variability using non-uniform basis functions. Finally, we demonstrate how to treat tide gauge selection as an analytical process and examine the tide gauge residuals from GIA and fitted non-uniform basis functions in a reconstruction. We show which tide gauge records contain reasonable long-term trends and regional variability consistent with spatial basis functions derived from altimetry. We also evaluate which altimetry basis functions are actually useful when accounting for decadal and longer sea level variability in tide gauges. The balance between including more tide gauge data vs. the limitations of the basis functions available to the reconstruction is key to achieving optimal estimates of 20th century GMSL trends.

Detecting sea level seasonality in the northwestern Pacific. Xiangbo Feng, M. N. Tsimplis, M. Marcos and F. M. Calafat Tide gauges and AVISO altimetry data are used to investigate the seasonal sea level cycles in the whole region of the NW Pacific, along with other atmospheric and oceanographic reanalysis. The regression model of seasonal cycles can explain over 60% of sea level variations in vast majority of the region, with higher values in the northern marginal seas. The annual cycle parameters based on three different data sources, i.e. tide gauges, AVISO and Simple Ocean Data Assimilation (SODA), were inter-compared. We found that in relation to tide gauge observations AVISO usually underestimates the annual cycle amplitude at half of stations by overall 3.5cm. Compared with observations, SODA can well capture the seasonal cycles in vast majority of area, except in the shallow water regions, but overestimate the magnitude of inter-annual variability. The forcing of seasonal sea level signals was explored, such as the attributions from atmosphere pressure, steric height, wind regimes and ocean surface current.

Detection and attribution of global mean thermosteric sea level change. Aimée B. A. Slangen, John A. Church, Xuebin Zhang, Didier Monselesan Changes in sea level are driven by a range of natural and anthropogenic forcings. To better understand the response of global mean thermosteric sea level change to these forcings, we compare three observational data sets to experiments of 28 climate models with up to five different forcing scenarios for 1957–2005. We use the preindustrial control runs to determine the internal climate variability. Our analysis shows that anthropogenic greenhouse gas and aerosol forcing are required to explain the magnitude of the observed changes, while natural forcing drives most of the externally forced variability. The experiments that include anthropogenic and natural forcings capture the observed increased trend toward the end of the twentieth century best. The observed changes can be explained by scaling the natural-only experiment by 0.70 +/ - 0.30 and the anthropogenic-only experiment (including opposing forcing from greenhouse gases and aerosols) by 1.08 +/ - 0.13 (+/ -2휎).


Detecting anthropogenic footprints in sea level rise. Sönke Dangendorf, Marta Marcos, Alfred Müller, Eduardo Zorita, Jürgen Jensen While there is scientific consensus that global mean sea level (MSL) is rising since the late 19th century, it remains unclear how much of this rise is due to natural variability or anthropogenic forcing. Uncovering the anthropogenic contribution requires profound knowledge about the persistence of natural MSL variations. This is challenging, since observational time series represent the superposition of various processes with different spectral properties. Here we statistically estimate the upper bounds of naturally forced centennial MSL trends on the basis of two separate components: a slowly varying volumetric (mass and density changes) and a more rapidly changing atmospheric component. Resting on a combination of spectral analyses of tide gauge records, ocean reanalysis data and numerical Monte-Carlo experiments, we find that in records where transient atmospheric processes dominate, the persistence of natural volumetric changes is underestimated. If each component is assessed separately, natural centennial trends are locally up to 0.5 mm/yr larger than in case of an integrated assessment. This implies that external trends in regional MSL rise related to anthropogenic forcing might be generally overestimated. By applying our approach to a spatially homogeneous centennial ocean reanalysis (SODA) in combination with fingerprints of glacial ice melt and hydrology changes, we estimate maximum natural trends in the order of 1 mm/yr for the global average. This value is larger than previous estimates, but consistent with recent paleo evidence from periods in which the anthropogenic contribution was absent. Comparing our estimate to the available reconstructions of 20th century global MSL rise of 1.3-2.0 mm/yr suggests a minimum external contribution of at least 0.3 mm/yr. We conclude that an accurate detection of anthropogenic footprints in global and regional MSL rise requires a more careful assessment of the persistence of intrinsic natural variability.

Posters

Regional Sea Level change in the North Sea since 1900. Frauke Albrecht, Saskia Esselborn, Ralf Weisse The regional mean sea level of the North Sea is investigated. Variability in both time and space are analysed for the period 1900-2012. The sea level is reconstructed using the approach presented in Church et al. (2004)* . That is tide gauge and altimetry data are combined using the advantage of each dataset. The length of the tide gauge data is combined with the spatial distribution of the altimetry data using an EOF-analysis. The analysis considers yearly means of 14 GIA corrected tide gauges, which are equally distributed over the region. For the altimetry data yearly means of Topex, Jason-1 and Jason-2 data are used. The altimetry data covers the area 4°W-9°E, 51°N-60°N with a resolution is 0.5°x 0.5°. No inverse barometer correction has been applied.

The quality of the reconstruction is validated against the altimeter data. The patterns of the spatial variability are well reconstructed. The spatial correlation for the period 1993-2012 is in general very good (0.6) with exceptions in the southwest and northwest, where the values are a bit lower. The linear trend of the time period 1993-2012 shows the general pattern of the altimetry data, but an overestimation especially in the German Bight and along the Danish coast can be seen. The spatial mean of the reconstruction is compared to earlier reconstructions of this area. Its linear trend for the


period 1900-2012 is 1.2mm/yr. This value is a bit lower than reconstructions of the same area only using tide gauge data, which might be due to the relatively few tide gauge data used or the reduced variability of the time series, which is a byproduct of the method.

Additionally hindcast dataset CoastDat is included in the analysis. It contains wind and the inverse barometric effect from 1948-2012. This data has been subtracted from the tide gauge and altimetry data in order to analyse how much the linear trend is influenced by the meteorological signal.

*Church, J.A., White N.J., Coleman R., Lambeck K., and Mitrovica J.X. (2004) Estimates of the regional distribution of sea-level rise over the 1950 to 2000 period, J. Clim., 17, 2609–2625.

Sea level trends and long-term variability in the South China Sea. A.M. Amiruddin, I.D. Haigh, M.N. Tsimplis, F.M. Calafat and S. Dangendorf During the last two decades, sea level rise around the South China Sea (SCS) is nearly three times of the global mean rate. Due to the economic importance and high density population, rising sea levels will severely threaten this region. Here, inter-annual variability and longer-term trends in mean sea level in the SCS have been examined using satellite altimetry data and tide gauge records, along with steric and meteorological data. Relative sea level trends from tide gauge records longer than 40 years range between –0.5 ± 0.2 mm/yr and 5.4 ± 0.4 mm/yr. The contribution of atmospheric pressure changes to sea level trends at the tide gauges is statistically non-significant. For the period 1993-2012, the basin average sea level rise obtained from altimetry data is 4.8 ± 1.2 mm/yr. The trend is larger in the Philippines Sea with maximum values reaching 9.9 ± 2.1 mm/yr. Steric trends (1993-2012) computed down to 1500 m depth, explains a large fraction of the observed trends in most parts of the Philippines Sea with values as large as 7.5 ± 2.2 mm/yr. Using regional indices from the tide gauge records, the first and second Empirical Orthogonal Function (EOF) explains 80% and 12% of the variance, respectively. The first EOF is closely related to the El Niño Southern Oscillation (ENSO) while the second EOF is associated with the Indian Ocean Dipole (IOD). Inter-annual sea level variability, especially in the Philippines Sea and the Malacca Strait, can be partly explained by the influence of ENSO. A considerable part of the variability in the Malacca Strait and off the southern coast of Vietnam is found to be linked with the IOD. The strength of the link between inter-annual sea level variability and these climate indices as measured by correlation varies over time. Further research will assess the decadal variability and their forcing mechanism.

Altimetric sea level variation and reconstruction in the Arctic. Ole B. Andersen, P. Limkilde Svendsen, A. Aasbjerg and P. Knudsen The Arctic is still extremely challenging region for the use of remote sensing for ocean studies and particularly satellite altimetry. One is the fact that despite 20 years of altimetry only very limited sea level observations exists in the interior of the Arctic Ocean. By carefully reprocessing and re-editing conventional altimetry from ERS-1/ERS-2 and Envisat we have been able to derive a multi-decade time series containing far more data in the interior of the Arctic Ocean than ever before, by furthermore adding in 3 years of Cryosat-2 SAR data quantified as either Lead or Ocean data within the Cryosat-2 SAR mask in the Arctic Ocean we can further extend the time series to more than 20 years. Good altimetric data is seen to crucial for sea level studies and profoundly for sea level reconstruction where we present a 60 years sea level reconstruction based on this new data set.


We here present a new multi-decade altimetric dataset and a 60 year reconstruction of sea level based on this together with tide gauge information. We also highlight the importance of careful editing of tide gauges in the Arctic where many tide gauges are more representative of river variations than actual sea level variations.

On the causes of the differential mean sea level variations between the northern and southern hemispheres of the Earth. Yuri Barkin, José M. Ferrándiz, Isabel Vigo, David García In the last decades, satellite altimetry has provided sea level data more densely distributed in space and time, with the consequent improvement of information with respect to the sea level observation series from historical tide gauge records. It is well known that sea level does not rise (or fall) uniformly all over the oceans, but follow complex patterns in space and time. Among the attempts of gathering the observed behaviour in few intuitive parameters, a candidate to consider are the variations restricted to some large chosen oceanic areas. Several studies have shown, e.g. differences in the secular trend of sea level variations between the northern and southern hemispheres of the Earth. In 2011 Barkin pointed an averaged trend of about 2.45 ± 0.32 mm / year sea level rise in the northern hemisphere, in contrast to a much lower average rate of 0.67 ± 0.30 mm / yr in the southern one. That estimation showed a clear difference of 1.78 mm / year between the N/S hemispherical rates of sea level change. It is in good agreement with more recent determinations obtained from the coastal tide gauge observations, like those reported by Woppelman et al. in 2014, which included corrections for the vertical geodetic displacements of the stations.

That observed behaviour has not been fully explained yet. Among the potential causes, we analyze the effects of the changes of the gravitational attraction of the core, which is not invariant but experiences changes of various reported origins. Among them, we consider here the shifting with respect to the centre of mass of the whole Earth, which was suggested by Barkin et al in 2008 and treated later in 2011. In that previous work it was shown that the displacement of the core relative to the mantle would generate a slow tide of inner origin, asymmetric with respect to the equator and thus redistributing the oceanic and atmospheric masses between the southern and the northern hemispheres. This dynamical effect can contribute to driving the observed distinct behaviour of mean sea level rates between the opposite northern and southern hemispheres and even to be a leading mechanism to an extent that must be assessed.

Along with the fundamental core of the tide, we consider other phenomena that can produce secular changes in sea level. Factors as e.g. the role of the asymmetric arrangement of the continents in relation to the northern and southern hemispheres, and the ocean volume and its thermal expansion, have been also invoked in the literature as potential sources of differences in the regional behaviour of sea level variations.

Sea level reconstruction from satellite altimetry and tide gauges using advanced signal decomposition techniques. Sandra-Esther Brunnabend, Jürgen Kusche, Roelof Rietbroek, and Ehsan Forootan Satellite altimetry and tide gauge records are used in many studies for the reconstruction of global mean sea level and regional mean sea level. Most of them used the method of empirical orthogonal functions (EOF) to reduce noise and investigate the different signals in climate time series. However,

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