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

SST Anomalies – Jan 1998

SST Anomalies – Dec 1999

A

B

ºC

Pt. 1

Pt. 2

Pt. 3y

x

ENSO

Warm Phase

ColdPhase

Less upwelling

Less primary production

Less CO2 flux out of the ocean

More upwelling

More primary production

More CO2 flux out of the ocean

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

PACIFIC OCEAN

Marine Ecosystems and

Climate Variability

Decadal scale variations

(source: Checkley et al., 2000)Sardine Eggs

Changes in Fish abundance is driven by the variability of hydrographic conditions

Point Conception

Regional indices of Climate variability

PACIFIC OCEAN

Most of the regional indices reflectlarge-scale climate variations

in the North Pacific they can be summarized

Pacific Decadal Oscillation Index

Currents SST

January Mean Sea Level Pressure

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

Pacific Decadal Oscillation

++ -

Large-scale indices of Climate variability

PACIFIC OCEAN

..and biology

1976 Regime Shift ?

WARM PHASE of PDO

COLD PHASE of PDO

Transitions in the Ecosystem may by nonlinear and sudden.

There could be predictive skill (in terms of climate change) in monitoring closely the ecosystem

Ocean Temperature

ZooplanktonLoge Tot. Vol.

5

7

6

4

Anomalies

199019701950 200019801960

C

-1

1

0

Ocean Temperature

ZooplanktonLoge Tot. Vol.

5

7

6

4

Anomalies

199019701950 200019801960

C

-1

1

0

Observationsalong the California Coast

Zoo-plankton

Phytoplankton

Ab

un

dan

ce

Population Dynamics

A simple Ecosystem model

Phyto

Detritus

NO3

NH4

Zoo

Physical Environment

The seasonal cycle of the simple model

Increasing nutrient supply

Seasonal cycles

A simple Ecosystem model

Phyto

Detritus

NO3

NH4

Zoo

Physical Environment

Fish andHigher Trophic

Levels

HUMANS

Historical Overfishing and the Recent Collapse of Coastal Ecosystems

Jackson et al., Science, Vol 293, Issue 5530, 629-637 , 27 July 2001

KELP FOREST

Historical Overfishing and the Recent Collapse of Coastal Ecosystems

Jackson et al., Science, Vol 293, Issue 5530, 629-637 , 27 July 2001

and more comlpex…

Coral Reefs

A simple Ecosystem model

Phyto

Detritus

NO3

NH4

Zoo

Physical Environment

Fish andHigher Trophic

Levels

HUMANSGLOBAL WARMINGand

Carbon Cycle

End of lecture

Short Climate Variability occurs in all oceans

Aleutian Low

What is the North Atlantic Oscillation ?

A sea saw of atmospheric mass which alternates between the polar and subtropical regions.

Changes in the mass and pressure fields lead to variability in the strength and pathway of storm systems crossing the Atlantic from the US East coast to Europe.

The NAO is most noticeable during the winter season (November - April) with maximum amplitude and persistence in the Atlantic sector. Martin Visbeck 20 April 2023

The North Atlantic Oscillation Index

An Index can be constructed that represents the phase of the NAO. Most commonly the NAO index is based on the surface pressure (SLP) difference between the Subtropical (Azores) high and the Subpolar (Island) low.

Very often the pressure readings from two stations one on Iceland and the other either the Azores, Lisbon or Gibraltar are used to construct the NAO index. The twice daily reading are averaged from November through March and the difference in then the winter NAO index.

Martin Visbeck 20 April 2023

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 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". Martin Visbeck 20 April 2023

The positive NAO index phase The positive NAO index phase shows a stronger than usual subtropical high pressure center and a deep 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 Europe and in cold and dry winters in northern Canada and Greenland.

The eastern US experiences mild and wet winter conditions.

Martin Visbeck 20 April 2023

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.

Greenland, however, will have milder winter temperatures.

Martin Visbeck 20 April 2023

North Altantic Oscillation

Reading/Homework assignment:

What is interesting about the relationship between Climate and Ocean Biology?

Examples:

•Fisheries and food•Global Warming problem •Preservation of species

An example

1) The Pacific Decadal Oscillation and ecosystem responses

2) Understanding the ecosystem response with models

3) The North Atlantic Oscillation and ecosystem responses

Nitrate Concentration

Abundance Reached at equilibrium

Abundance

Days

Oscillation beginOscillation stop

hysteresis

Limit cycles

The ecosystem may become Very unpredictable