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

Tuna Sardine Anchovy Salmon Krill Copepods Jellyfish Phytoplankton Bacteria 1 hour 1 day 1 week 1 month 1 year 5 years 10 years 15 years 20 years ENSO Duration PDO +/- Duration Seasonal Cycles ENSO Frequency Time scales Life Spans # Reproductive years Body size Swimming speed Energy reserves

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 duration 2-8 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: 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 Index Normalized NAO Index (winter) Year Long periods of + /- NAO phases started mid-20 th century Beginning 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 Barcelona, March 2010

Recent NAO Index - how will the winter be? Mild & rainy? Cold & snowy?

The maps at left show the relationships between a strong positive NAO and precipitation and temperature. (Images courtesy Lamont-Doherty Earth Observatory) 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 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 : mostly negative NAO : 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 Normalized NAO Index (winter) Year Cool (-)Warm (+)

Cool (-NAO) Warm (+NAO) 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

NAO Index 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 form in deep water, late winter to spring Planktonic eggs drift in currents Larvae hatch, develop, eat progressively larger plankton Reach maturity at 2-8 years Grow to 6 feet long

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

Several major cod stocks in North Atlantic Georges Bank North Sea Barents Sea

Red symbols indicate strength and sign of effect of NAO on cod recruitment + Barents Sea - Georges Bank

Otterson et al NAO positively related to cod recruitment in Barents Sea NAO index temperatureLength 1/2 year old cod (mm) Length 1/2 year old cod Log(abundance age s) temperature Log(abundance age s) Start here, read clockwise

Georges Bank NAO - 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)