1. Marine Ecosystems Climate Variability
and
Climate Variability
Interannual Time Scales:
ENSO
Decadal Time Scales:
Basin Wide Variability (e.g. Pacific Decadal Oscillation, North Atlantic Oscillation)
Longer Time Scales:
Warming trend

2. Marine Ecosystems Climate Variability
and
Climate Variability
Interannual Time Scales:
ENSO
Decadal Time Scales:
Basin Wide Variability (e.g. Pacific Decadal Oscillation, North Atlantic Oscillation)
Longer Time Scales:
Warming trend

3. Mean Sea Level Pressure
Negative Phase
Positive Phase

4. Mean Sea Level Pressure
Anomaly PDO Negative Phase
Anomaly PDO Positive Phase

5. SST Anomalies
Anomaly PDO Negative Phase
SST Anomalies
Anomaly PDO Positive Phase

6. Material on the Pacific Decadal Oscillation connections
to the marine ecosystem is found in:
From anchovies to sardines and back: Multidecadal change in the Pacific Ocean 
Chavez FP, Ryan J, Lluch-Cota SE, et al.
SCIENCE 299 (5604): JAN
Posted on website (only 7 pages)

7. Marine Ecosystems Climate Variability
and
Climate Variability
Interannual Time Scales:
ENSO
Decadal Time Scales:
Basin Wide Variability (e.g. Pacific Decadal Oscillation, North Atlantic Oscillation)
Longer Time Scales:
Warming trend

8. Mean Sea Level Pressure North Atlantic
Iceland Low
Azores High

9. NAO Index = SLP(Azores High) – SLP(Iceland Low)
North Atlantic Oscillation
Iceland Low
Azores High
NAO Index = SLP(Azores High) – SLP(Iceland Low)
measured November through March

10. The North Atlantic Oscillation Index
NAO Index = SLP(Azores High) – SLP(Iceland Low)
measured November through March

11. 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".

12. NAO Index = SLP(Azores High) – SLP(Iceland Low)
North Atlantic Oscillation
Iceland Low
Azores High
NAO Index = SLP(Azores High) – SLP(Iceland Low)
measured November through March

13. 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.
Wet
Dry
Martin Visbeck
3 May, 2019

14. 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
Martin Visbeck
3 May, 2019

15. SST Anomalies [C] Positive NAO Negative NAO Wet Dry Dry Wet
Stronger Currents
more storms
Dry
Dry
fewer storms
Wet
Weaker Currents
Negative NAO

16. Impacts of the NAO
Martin Visbeck
3 May, 2019

17. 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.
Martin Visbeck
3 May, 2019

18. 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.
Martin Visbeck
3 May, 2019

19. NAO and significant wave heights
Martin Visbeck
3 May, 2019

20. NAO and fish catch in the North Atlantic
Topliss, BIO, Canada

21. 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?

22. SST Anomalies [C] Positive NAO Negative NAO Wet Dry Dry Wet
Stronger Currents
more storms
Dry
Dry
fewer storms
Wet
Weaker Currents
Negative NAO

23. 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)

24. Direct Effects Indirect Effects Temperature Mediated Response
Length 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 transport
Changes in spatial distribution of phytoplankton and larvae, alteration in competition between different levels of the trophic chain  alteration in food web
Effects on Predator-Prey
Through changes/alteration in the food

25. Integrated Effects Flowering Fecundity (1 year later)
Abbundance (2 year later)
NAO Index
Flowering
NAO Index
Phenology to herbivore dynamics (red deer)

26. Cartoon of Red Deer correlation with NAO

27. NAO and Copepods (Calanus Finmarchicus)
Difficult to identify causes of observed relationships
Calanus Finmarchicus distribution
1) Changes in food availability
2) Alteration of competition balance
3) Variations in transport of individuals from North Atlantic
Calanus Helgolandicus distribution

28. 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?
Martin Visbeck
3 May, 2019

29. 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.
Martin Visbeck
3 May, 2019

30. Additional Slides

31. 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.
Martin Visbeck
3 May, 2019

32. 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
3 May, 2019

33. 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 Visbeck
3 May, 2019

34. NAO and stream flow in the US
Correlation
Martin Visbeck
3 May, 2019

35. North Atlantic SST connection
Jacob Aaal Bonnevie Bjerknes
NAO related tripole
in sea surface temperatures
Source: Rowan Sutton and D.B. Stephenson

36. 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
3 May, 2019

37. The ocean is simulated by the Lamont Ocean model (LOAM)
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 movie
Martin Visbeck
3 May, 2019

38. 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.
Martin Visbeck
3 May, 2019

39. NAO Prediction No robust predictability has been demonstrated.
Hamilton, University College London
No robust predictability has been demonstrated.
Different methods are used: SST based => 2001 positive SSA based => negative soon global warming based => stay positive next decades
Martin Visbeck
3 May, 2019