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•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
an
s• #
Rep
rod
uctiv
e y
ear
s• B
ody
siz
e• S
wim
min
g s
pee
d• E
ner
gy
rese
rve
s
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
dex
2
0
-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)