Time scales of physics vs. biology ENSO effects on biology Pacific Decadal Oscillation (PDO)

years decades centuries The problem: multiple time scales of variability Humans century

Generation time: Doubling time for unicellular organisms, or time to first reproduction for animals Dominant environmental forcing: Typically the physical process responsible for the greatest amount of variability in a biological response

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 Time scales Life Spans # Reproductive years Body size Swimming speed Energy reserves Generation times

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 Seasonal Cycles Time scales Life Spans # Reproductive years Body size Swimming speed Energy reserves

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

Main effects of climate oscillations on pelagic species Temperature/nutrients affect primary production Food availability affects higher trophic levels Temperature affects rates of growth or survival (all trophic levels) Larger/faster species move to find preferred temperature, causing range shifts

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

Major episodes occur every 3-7 years and last 9-18 months Temperature anomaly

El NiñoLa Niña Equatorial upwelling Much weakerMuch stronger California Current upwelling WeakerStronger California Current temperature WarmerCooler California Current thermocline DeeperShallower West Pacific warm pool Spreads east across equator Compressed in western Pacific

The most notable El Niño events Note the scale is reversed relative to Southern Oscilation Index, so El Niño is on top, La Niña on bottom #1: #2: #3: ????

Jan El Niño July 1998 La Niña

El Niño year looks more like this La Niña year looks more like this Weak upwelling Strong upwelling In El Niño conditions, upwelling is weaker, and the coastal jet (warm water) reconnects with the coast farther north near CA. In La Niña conditions, upwelling is stronger, and the coastal jet (warm water) reconnects with the coast farther south near Baja.

Normal year El Niño year SST distribution in California Current Shaded area = 16 to 17 o C

Lavaniegos and Ohman 2003 California Current -El Niño reduces upwelling -Lower nutrients  reduced primary production -Low primary production  low zooplankton biomass etc. Biomass of Zooplankton >500 μm Major El Niños (warm) Major La Niñas (cool)

Comparisons of distribution patterns of an eastern tropical Pacific species of krill, Euphausia eximia, between 1962, a typical year, and 1958, an El Niño year. Brinton 1967 El Niño year Normal year Some tropical krill follow warm water (population moves in/out of CalCOFI grid)

California Current krill community - response to SST is species-specific Brinton & Townsend 2003 Euphausia pacifica (cool water, widespread) Jaime Gomez Nyctiphanes simplex (subtropical) ocean.stanford.edu/blsaenz Abundance anomalies Life span <1 year Life span ~2 years El Niños (warm) La Niñas (cool)

Skipjack tuna tolerate 15 to 30 o C Recruitment in Pacific El Niño (average distribution October March 1983) and La Niña (average distribution October March 1989) skipjack recruitment. Biomass distribution of first skipjack age class (0-3 months) in tonnes per degree square. Lehodey et al El Niño La Niña

Squid: average lifespan ~1 year, juveniles eat zooplankton Adults vertically migrate to surface at night, eat small fish Major El Niño

Mackerel: average lifespan 6-8 years, eat large zooplankton & fish, tropical or sub-tropical Major El Niño

Sardine: lifespan years, eat small zooplankton, prefer warm water Major El Niño

Chavez et al Major El Niños -ENSO weakly affects sardine & anchovy landings in Peru. -Compared to sardines, anchovy have shorter life span and are more negatively affected by El Niños. -ENSO effects are small relative to long-term variability.

Pacific Decadal Oscillation (PDO) ~15 to 30 year cycle Positive PDO pattern Negative PDO pattern +- The PDO Index is a spatial average of monthly sea surface temperature (SST) anomaly of the Pacific Ocean north of 20°N. The global average anomaly is subtracted to account for global warming (Mantua, 2000). Highly correlated with temperature in California Current

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

El Niño, +PDO PatternLa Niña, -PDO Pattern Sea Surface Temperature Anomalies -ENSO and PDO index both change continuously. -Their patterns are additive.

Positive PDONegative PDO Equatorial upwelling WeakerStronger California Current upwelling Much weakerMuch stronger California Current temperature WarmerCooler Calif. Current thermocline DeeperShallower West Pacific warm pool Spreads east across equator Compressed in western Pacific

warm cool warm Long positive (warm) and negative (cool) phases of PDO

Biomass of Zooplankton >500 μm - PDO (cool)+ PDO (warm) Major El Niños (warm) Major La Niñas (cool) Lavaniegos and Ohman 2003 California Current -Zooplankton biomass is low during warm phases with weak upwelling -Effects of warm PDO and warm El Niño events are additive

Some krill track PDO better than ENSO Brinton & Townsend 2003 Euphausia pacifica (widespread) Jaime Gomez Nyctiphanes simplex (subtropical) ocean.stanford.edu/blsaenz El Niños (warm) La Niñas (cool) - PDO (cool)+ PDO (warm) Abundance anomalies Life span <1 year Life span ~2 years

-PDO (cool) +PDO (warm) +PDO (warm) is sardine regime -PDO (cool) is anchovy regime (anchovies are also affected by ENSO cycle)

ENSO vs. PDO effects on biology El Niño/La Niña and Pacific Decadal Oscillation have similar “fingerprints” but different time scales Short-lived species more responsive to ENSO, longer-lived species more responsive to PDO BUT effects on abundance and distribution of zooplankton and fish are species- specific Tropical species less likely to be negatively impacted by El Niño or +PDO

On top of these cycles there is a global warming trend (Theme 4, up next).