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Jon Albretsenwith contributions from Jan Aure, Roald Sætre and Didrik Danielssen

Decadal hydrographic variability in the Skagerrak and along the Norwegian coast

Santander, Spain, 10-12 May 2011

ICES/NAFO Symposium on the Variability of the North Atlantic and its Marine Ecosystems during 2000-2009

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Content

Decadal hydrographic variability in the Skagerrak and along the Norwegian coast

Analysis is primarily based on measurements

Focus on the hydrographic properties of the Norwegian Atlantic Drift and implications to the North Sea and Skagerrak and the Norwegian coast from the south to the Barents Sea.

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Norwegian waters

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Data usedThe fixed stations along the Norwegian coast1940’s – 2010 (IMR)

The Skagerrak transect (Torungen – Hirtshals)1952 – 2010 (IMR)

The Shetland polygon1940’s – 2010 (NISE and ICES)

Winter inflow to the North Sea1955 – 2008 (IMR, NORWECOM)

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From real values to normalized values

Data from the winter season (JFM) is applied in our analysis as we believe it better reflects the long-term climatic signals.

Want to compare hydrographic properties at areas with different level of variability – normalize all time series according to the 1961-90 state.

Interpretation: the value normalized value is in terms of the number of standard deviations the value is above or below the mean

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Hydrographic decadal changesHirtshals Torungen Lista

Utsira Eggum Ingøy

Depth 200m, representing Atlantic water masses

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Hydrographic changes in Atlantic water masses for the last decade from south to north

Skagerrak → Nordic Sea → Barents Sea

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Modelled winter inflow to the North Sea between Norway (Utsira) and the Orkneys

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Comparison of decadal changes in temperature with the salinity change

West of Shetland Skagerrak and the Norwegian coast

Normalized values at 200m depth from 1940-2009 (sources: NISE and ICES)

Normalized decadal means at 200m depth from 1940-2009 from 9 stations in Skagerrak and along the Norwegian coast

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Quantifying the temperature increase

South → North

Decadal anomalies for 1990-99 and 2000-09 (JFM)

Hátun et al. (2005)

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Reflecting the global temperature increase

Decadal anomalies at 200m depth from 1940-2009 from 9 stations in Skagerrak and along the Norwegian coast

Red: Before 1990Blue: After 1990

≈ 0.5 oC

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Hydrographic conditions in the Skagerrak bottom water – decadal variability

Sill depth 270m

Max. depth 700m

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600m depth

T

S

D

O2

Hydrographic conditions in the Skagerrak bottom water – time series from the 1960’s

and the last decade1960-69 2000-2010

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Summary

Measurements of the hydrographic properties of the Atlantic water in the Shetland-Faroe Island channel, the Skagerrak and along the Norwegian coast indicate an enhanced warming the last decade.

After increased inflow of Atlantic water masses into the North Sea in the 1990’s, the volume transport has normalized (i.e., been reduced) during the last decade. Despite the lower inflow of Atlantic water during the last decade, the temperature has increased.

The warming is quantified to about 1 oC where half of this is accounted for in the decadal fluctuating strength of the Subpolar Gyre. The remaining increase in temperature (0.5 oC) reflects the monitored NOAA global temperature increase well.

Cold winters in the North Sea area (as in 2010) may induce a cooling of the Skagerrak bottom waters, and this type of physical process may have implications to the marine life, e.g. the shrimp stock.