interannual time scales: enso decadal time scales: basin wide variability (e.g. pacific decadal...

Interannual Time Scales:

ENSO

Decadal Time Scales:

Basin Wide Variability (e.g. Pacific Decadal Oscillation, North Atlantic Oscillation)

Longer Time Scales:

Warming trend

Marine Ecosystems and

Climate Variability

Negative Phase

Positive Phase

Mean Sea Level Pressure

Anomaly PDO Negative PhaseMean Sea Level Pressure

Anomaly PDO Positive Phase

Anomaly PDO Negative Phase

Anomaly PDO Positive Phase

SST Anomalies

SST Anomalies

From anchovies to sardines and back: Multidecadal change in the Pacific Ocean

Chavez FP, Ryan J, Lluch-Cota SE, et al.SCIENCE 299 (5604): 217-221 JAN 10 2003

Posted on website (only 7 pages)

Material on the Pacific Decadal Oscillation connectionsto the marine ecosystem is found in:

Interannual Time Scales:

ENSO

Decadal Time Scales:

Basin Wide Variability (e.g. Pacific Decadal Oscillation, North Atlantic Oscillation)

Longer Time Scales:

Warming trend

Marine Ecosystems and

Climate Variability

Mean Sea Level Pressure North AtlanticIceland Low

Azores High

NAO Index = SLP(Azores High) – SLP(Iceland Low)

North Atlantic OscillationIceland Low

Azores High

measured November through March



The North Atlantic Oscillation Index

The North Atlantic Oscillation Index

The NAO index shows large variations from year to year. This interannual signal was especially strong during the end of the 19th century.

Sometimes the NAO index stays in one phase for several years in a row. This decadal variability was quite strong at the beginning and end of the 20th century.

One might also interpret the recent 30 years as a trend in the NAO index possibly linked to "global warming".


North Atlantic OscillationIceland Low

Azores High


The positive NAO index phase The positive NAO index phase

shows a stronger than usual subtropical high pressure center and a deeper than normal Icelandic low.

The increased pressure difference results in more and stronger winter storms crossing the Atlantic Ocean on a more northerly track.

This results in warm and wet winters in Northern Europe and in cold and dry winters in Mediterranean region.

The eastern US experiences mild and wet winter conditions.

Martin Visbeck 19 April 2023

Wet

Dry

The negative NAO index phase

The negative NAO index phase shows a weak subtropical high and weak Icelandic low.

The reduced pressure gradient results in fewer and weaker winter storms crossing on a more west-east pathway.

They bring moist air into the Mediterranean and cold weather to northern Europe.

The US east cost experiences more cold air outbreaks and hence snowy winter conditions.


Dry

Wet

more storms

fewer storms

SST Anomalies [C]Positive NAO

Dry

Wet

Dry

WetStronger Currents

Negative NAO

Weaker Currents

Impacts of the NAO

Martin Visbeck

19 April 2023

Us East Coast Impacts of the NAO

The US East coast experiences milder winter conditions during a positive NAO index phase.

The amount of snow cover is reduced.

Warmer than usual ocean temperatures cause more frequent occurrence of "red tides" in the summer.

Colder than usual tropical ocean temperatures reduce the number of hurricanes in the following summer.

Cold ocean temperatures in the spawning grounds over the Grand Banks cause less cod reproduction.


Impacts of the NAO in Europe

Northern Europe experiences mild and wet winter during the positive NAO index phase.

This has dramatic consequences for hydro-electric power generation and heating oil consumption.

South-Eastern Europe receives less rain and hence causes significant problems with drinking water supply and reduced stream flow volume in the Middle East.

Harvest yield of grapes and olives have been shown to depend significantly on the NAO.


NAO and significant wave heights

Martin Visbeck19 April 2023

NAO and fish catch in the North AtlanticTopliss, BIO, Canada

Ecological effects of the North Atlantic Oscillation

Geir Ottersen, Benjamin Planque, Andrea Belgrano, Eric Post, Philip C. Reid, Nils C. Stenseth

Posted on class website (12 pages)

…more than 100 documented correlation between NAO and marine ecosystems.

How to make sense?

more storms

fewer storms

SST Anomalies [C]Positive NAO

Dry

Wet

Dry

Wet

Stronger Currents

Negative NAO

Weaker Currents

The response to NAO is classififed into 3 type:

DIRECT - A direct ecological response to one of the environmental parameters synchronised with the NAO.

INDIRECT - The indirect effects of the NAO are non-trivial mechanisms that either involve several physical or biological intermediary steps between the NAO and the ecological trait and/or have no direct impact on the biology of the population.

INTEGRATED - The integrated effects of the NAO involve simple ecological responses that can occur during and after the year of an NAO extreme. This is the case when a population has to be repeatedly affected by a particular environmental situation before the ecological change can be perceived (biological inertia). or when the environmental parameter affecting the population is itself modulated over a number of years (physical inertia)

Direct EffectsTemperature Mediated ResponseLength of active growing season, Individual growth (size), growth rate, eggs variability, timing of reproduction, spawning, time of food availability, larval growth and mortality,

Indirect Effects

Physically induced by changes in oceanic transportChanges in spatial distribution of phytoplankton and larvae, alteration in competition between different levels of the trophic chain alteration in food web

Effects on Predator-PreyThrough changes/alteration in the food

Flowering

Flo

weri

ng

Fecu

nd

ity (

1 y

ear

late

r)

Ab

bu

nd

an

ce (

2 y

ear

late

r)

NAO Index NAO Index

Phenology to herbivore dynamics (red deer)

Integrated Effects

Cartoon of Red Deer correlation with NAO

Difficult to identify causes of observed relationships

NAO and Copepods (Calanus Finmarchicus)

1) Changes in food availability

2) Alteration of competition balance

3) Variations in transport of individuals from North Atlantic

Calanus Finmarchicus distribution

Calanus Helgolandicus distribution

NAO and global warming

Some scientist argue that changes in the stratospheric circulation can influence the phase of the NAO.

Ozone depletion and increase of CO2 both result in a strong polar night vortex which might cause the NAO to prefer a positive state.

Will "global warming" cause a persistent positive NAO phases?


Some facts The North Atlantic Oscillation is the largest mode of climate

variability in the Atlantic Sector and possibly of the northern hemisphere.

The dynamics of the NAO are not fully understood and in partiuclar its sensitivity to ocean, land or changes in the sea-ice conditions need more study.

Its impacts reach from the upper atmosphere to the bottom of the ocean and reach from N. America over to Europe and far into Asia.

The Ecological Impacts of NAO can be direct, indirect and integrated.

Some scientist argue that the NAO is strongly coupled to the stratosphere and will be significantly influenced by "global warming".

Other scientist see evidence for coupling with the North Atlantic Ocean.

It has also been suggested that tropical ocean temperatures can influence the phase of the NAO.


Additional Slides

Atlantic Ocean SSTs and the NAO

Some scientist have suggested that the storage and propagation of temperature anomalies by the ocean gives an important feed back to the atmosphere and is responsible for the decadal signal.

If correct one could make use of the "slow ocean dynamics" to predict aspects of the NAO.


NAO and Energy in Norway Norway experience cold

winters during a negative NAO phase.

Heating Oil consumption in Norway varies by 30% in good (anti) correlation with the NAO.

Correlation with precipitation results in variability in hydropower generation.

Martin Visbeck

19 April 2023

NAO and Water Resources in Turkey and the Middle East

Precipitation in Turkey is well correlated with the

NAO.

As a result spring stream flow in the

Euphrates River varies by about 50% with the

NAO.

An upward trend in the NAO will lead to

drought conditions in the Middle East.

Martin Visbeck19 April 2023

NAO and stream flow in the US

Martin Visbeck

19 April 2023

Corre

latio

n

North Atlantic SST connectionNAO related tripole

in sea surface temperatures

Source: Rowan Sutton and D.B. Stephenson

Jacob Aaal Bonnevie Bjerknes 1897-1975

NAO impact on Atlantic Ocean SSTs

Ocean surface temperatures (SST) changes with the phase of the NAO.

During a positive year the ocean warms just east of the US east coast and cools in the subpolar gyre between England, Newfoundland and Iceland.

The Gulf stream transports those temperature anomalies downstream towards Europe. Martin Visbeck 19 April 2023

NAO movie

Animation of sea level pressure and surface winds during an idealized NAO cycle of 12 year duration.

The lower panel shows the land temperature response and the propagation of SST anomalies in the ocean.

The ocean is simulated by the Lamont Ocean model (LOAM)

All other data are regressions from the NCEP/NCAR reanalysis.


NAO forced by Atlantic SST's ?

Some scientist argue that changes in the Atlantic Oceans SST can influence the phase of the NAO.

Others argue that changes in the tropical Atlantic influence the extratropical climate.

A (small) number argue that the ocean plays no role at all.

CLIVAR has decided to make those issues of high programatic priority.


NAO Prediction

No robust predictability has been demonstrated.

Different methods are used:SST based => 2001 positiveSSA based => negative soonglobal warming based => stay positive next decades


Hamilton, University College London

interannual time scales: enso decadal time scales: basin wide variability (e.g. pacific decadal...

Documents

enso decadal time scales

marchnao index

decadal variability

atlantic ocean

basin wide variability

wet winter conditions

snowy winter conditions

stronger winter storms