Review ENSO & PDO North Atlantic Oscillation Continuous Plankton Recorder survey NAO effects on...

•Review ENSO & PDO•North Atlantic Oscillation•Continuous Plankton Recorder survey•NAO effects on plankton, jellyfish, cod

Tuna

Sardine

Anchovy

Salmon

Krill

Copepods

Jellyfish

Phytoplankton

Bacteria1 hour

1 day1 week

1 month

1 year5 years

10 years

15 years

20 years

ENSO Duration

PDO +/- Duration

SeasonalCycles

ENSO Frequency

Time scales

• Life

Sp

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Rep

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Top: normal Bottom: El Niño condition

Open University, 1998

Normal

El Nino

Eastern boundary

•Shallow thermocline•Cold, nutrient-rich water•Mixing depth shallower than critical depth•High NPP

•Deep thermocline •Warm, nutrient-poor water•Mixing depth not as much shallower than critical depth•Lower NPP

El Niño = ENSO warm event La Niña = ENSO cool event

Pacific Decadal Oscillation (PDO)

Positive/warm PDO phase Negative/cool PDO phase

ENSO events: 6-18 month duration2-8 year frequency

ENSO index is based on sea level but has characteristic temperature pattern (Walker circulation affects location and extent of Pacific warm pool)

PDO cycle:15-30 year phase (low-frequency oscillation)

PDO index is based on patterns of temperature anomaly but has sea level patterns like those of ENSO

warm cool warm

SOI

PDO

Some climate oscillations and indices

• El Nino Southern Oscillation (ENSO)

• Pacific Decadal Oscillation (PDO)

• North Atlantic Oscillation (NAO)

• North Pacific Gyre Oscillation (NPGO)

• Arctic Oscillation (AO)

• Atlantic Multidecadal Oscillation (AMO)

• Hale (sunspot) cycle

North Atlantic Oscillation (NAO)

NAO index: winter average anomaly of sea-level air pressure at Reykjavik minus Lisbon. No correction for climate change.

Positive NAO •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 Europe and in cold and dry winters in northern Canada and Greenland•The eastern US experiences mild and wet winter conditions

•Ocean winds are stronger•Winter is warm and rainy in Eastern US & Northern Europe

Negative NAO•Negative NAO index phase shows a weak subtropical high and a weak Icelandic low.•The reduced pressure gradient results in fewer and weaker winter storms crossing on a more west-east pathway.•Storms bring moist air into the Mediterranean and cold air to northern Europe•The US east coast experiences more cold air outbreaks and hence snowy weather conditions.•Greenland, however, will have milder winter temperatures

•Ocean winds are weaker•Winter is colder & snowier in US and N. Europe

North Atlantic Oscillation IndexN

orm

aliz

ed N

AO

Ind

ex (

win

ter)

Year

Long periods of +/- NAO phases started mid-20th centuryBeginning early 1970’s, a >30-year mostly positive phase

In 2009/2010 the winter NAO index reached a 30-year low. That winter was much colder and snowier than normal in Northern Europe.

There were many deaths, power failures, transportation disruptions, and postponed soccer games.

United Kingdom, Jan. 2010

Barcelona, March 2010

Recent NAO Index - how will the winter be?

Mild & rainy?

Cold & snowy?

http://www.cpc.ncep.noaa.gov/products/precip/CWlink/pna/nao.shtml

The maps at left show the relationships between a strong positive NAO and precipitation and temperature.

(Images courtesy Lamont-Doherty Earth Observatory)

+ NAO produces higher temperatures and more precipitation in N. Europe and US East coast

Winter surface temperature anomaly

Visbeck, et al., 2001 Correlation of winter temperature and NAO

Long-term plankton data in Atlantic from Continuous Plankton Recorder (CPR)

McGowan 1990

Operated by Sir Alister Hardy Foundation for Ocean Science (SAHFOS) in United Kingdom

Greenpeace

Containerships

Passenger ferries

Cargo ships

Research vessels

• CPR is towed behind many different ships

• Opportunistic sampling of the North Sea and North Atlantic since 1931

NAO negatively affects plankton biomass

McGowan 1990

-NAO +NAO

Problem: averages are taken over entire sampling region, including some areas where T and NAO are negatively correlated.

-NAO +NAO

CPR data on zooplankton abundance

McGowan 1990

1950-1970: mostly negative NAO

1970-2000: mostly positive NAO

After 1970, zooplankton abundance declines and is seasonally compressed.

Spatial effects of NAO can be seen in copepod distributions. Next slides show data from cool (-)

phase and warm (+) phase N

orm

aliz

ed N

AO

Ind

ex (

win

ter)

Year

Cool (-) Warm (+)

Coo

l (-N

AO

)W

arm

(+

NA

O)

Beaugrand et al. 2002

Geographic pattern of effect of NAO on sea surface temperature

North Sea-strongest positive correlation

Jellyfish in North Sea: NAO-related increase in frequency

NAOIndex

Frequency of Jellyfish in CPR samples Is positively related to NAO index

Attrill et al. 2007

Jellyfish frequency significantly correlated with NAO and Atlantic inflow

Mean annual inflow from Atlantic to North Sea (Sv)

Cod fishery in North Atlantic

Cod life cycle (~13 to 25-year life span)Spawning aggregations formin deep water, late winter to spring

Planktonic eggs drift in currents

Larvae hatch, develop, eat progressively larger plankton

Reach maturity at 2-8 yearsGrow to 6 feet long

North Sea cod in state of collapseSome stocks <1% of numbers in 70’s

Several major cod stocks in North Atlantic

Georges Bank

North Sea

BarentsSea

Red symbols indicate strength and sign of effect of NAO on cod recruitment

+ Barents Sea

- Georges Bank

Otterson et al. 2001

NAO positively related to cod recruitment in Barents Sea

NAO index NAO index

temperatureLength 1/2 year old cod (mm)

Leng

th 1

/2 y

ear

old

cod

Log(

abun

danc

e ag

e 3

1000

s)

tem

pera

ture

Log(

abun

danc

e ag

e 3

1000

s)

Start here, read clockwise

70 75 80 85 90 9510

50

90

Plan

kton

Vo

lume 2

0

-2

-4 NA

Od

t

70 75 80 85 90 95Year

-1.5

-1.0Co

d In

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2

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-2

-4 NA

Od

t

Georges BankNAO - Plankton - Cod

Plankton Volume and Cod Survival negatively correlated with NAO (Fogarty and Haidvogel)

ENSO vs. PDO vs. NAO• Pacific Ocean: temperature anomaly patterns are

similar during El Niño (an ENSO warm event) and during a positive/warm cycle of the Pacific Decadal Oscillation. Patterns are similar during La Niña (an ENSO cool event) and during a negative/cool cycle of the Pacific Decadal Oscillation. ENSO and PDO effects are additive.

• ENSO and PDO differ mainly in time scale. El Niño’s happen every 2 to 8 years and last only 6 to 18 months. The Pacific Decadal Oscillation can remain in one phase (warm or cool) for 15 to 30 years.

• Atlantic Ocean: North Atlantic Oscillation (NAO) dominates. Oscillations have long time scales but are less regular than PDO. Effects on marine biology are not straightforward.

How to interpret all this information?

• Most ecosystem effects can be understood in terms of mixed layer dynamics

• Long term climate cycles affect temperature, nutrients, stratification

• Biological response depends on trophic level and species characteristics

• Oceanographic response to climate oscillations is less well characterized in Atlantic than in Pacific

• Some things become clearer by considering the effects of long-term climate change on marine ecosystems (November-December)