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

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

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

Generation times affect vulnerability 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 # Reproductive years Swimming speed Energy reserves Life Spans Body size Longer life and larger size confer some resiliency when faced with poor conditions on a short time scale Species most affected by oscillations on order of their generation time or longer. Anchovy life span: 3-10 years Sardine life span: 12-25 years Time scales

Generation times affect vulnerability Seasonal Cycles 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 # Reproductive years Swimming speed Energy reserves Life Spans Body size Longer life and larger size confer some resiliency when faced with poor conditions on a short time scale Species most affected by oscillations on order of their generation time or longer. Anchovy life span: 3-10 years Sardine life span: 12-25 years Time scales

Generation times affect vulnerability Seasonal Cycles ENSO Duration ENSO Frequency 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 # Reproductive years Swimming speed Energy reserves Life Spans Body size Longer life and larger size confer some resiliency when faced with poor conditions on a short time scale Species most affected by oscillations on order of their generation time or longer. Anchovy life span: 3-10 years Sardine life span: 12-25 years Time scales

Generation times affect vulnerability Seasonal Cycles ENSO Duration ENSO Frequency PDO +/- Duration 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 # Reproductive years Swimming speed Energy reserves Life Spans Body size Longer life and larger size confer some resiliency when faced with poor conditions on a short time scale Species most affected by oscillations on order of their generation time or longer. Anchovy life span: 3-10 years Sardine life span: 12-25 years Time scales

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 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 Normal El Nino Open University, 1998

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

El Niño La Niña Equatorial upwelling Much weaker Much stronger California Current upwelling Weaker Stronger California Current temperature Warmer Cooler California Current thermocline Deeper Shallower West Pacific warm pool Spreads east across equator Compressed in western Pacific

The most notable El Niño events #1: 1997-1998 #3: 1982-1983 #2: 2015-2016 ‘87-’88 ‘72-’73 SOI based on sea level pressure difference (Tahiti vs Darwin). NOI based on SST anomaly. Multivariate ENSO Index (MEI) is based on the six main observed variables over the tropical Pacific. These six variables are: sea-level pressure (P), zonal (U) and meridional (V) components of the surface wind, sea surface temperature (S), surface air temperature (A), and total cloudiness fraction of the sky (C). Before 2015, 1997-98 was the strongest El Nino on record, followed by 1982-83, 1972-73, 1957-58, 1987-88, 2009-2010…. Note the scale is reversed relative to Southern Oscilation Index, so El Niño is on top, La Niña on bottom

Jan. 1998 El Niño July 1998 La Niña

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. El Niño year looks more like this La Niña year looks more like this

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

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

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

Major El Niño Major El Niño Squid: average lifespan ~1 year, juveniles eat zooplankton Adults live in shallow coastal water, eat small fish

Sardine and anchovy landings in Peru Major El Niños -Anchovy are more negatively affected by El Niños. -Compared to sardines, anchovy have shorter life span, prefer cooler water, and eat larger plankton. -ENSO effects are small relative to long-term variability. Chavez et al. 2003

Pacific Decadal Oscillation (PDO) ~15 to 30 year cycle + - The PDO is quantified by the use of an index, referred to as the PDO Index. The PDO Index is calculated by spatially averaging the monthly sea surface temperature (SST) of the Pacific Ocean north of 20°N. The global average anomaly is then subtracted to account for global warming (Mantua, 2000). Normally only October to March values are used in calculating the PDO index because year-to-year fluctuations are most apparent during the winter months (Mantua, 2001). Positive PDO pattern Negative PDO pattern The PDO Index is a spatial average of winter monthly sea surface temperature (SST) anomaly of the Pacific Ocean north of 20o N. The global average anomaly is subtracted to account for global warming (Mantua, 2000). Highly correlated with temperature in California Current

(low-frequency oscillation) El Niño = ENSO warm event La Niña = ENSO cool event 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: 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 Pacific Decadal Oscillation (PDO) Positive/warm PDO phase Negative/cool PDO phase

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

Positive PDO Negative PDO Equatorial upwelling Weaker Stronger California Current upwelling Much weaker Much stronger California Current temperature Warmer Cooler Calif. Current thermocline Deeper Shallower West Pacific warm pool Spreads east across equator Compressed in western Pacific

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

Three most intense El Niños occurred during a warm PDO phase https://www.esr.org/pdo_index.html

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

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

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

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 in Oct On top of these cycles there is a global warming trend (Theme 4 in Oct./Nov.).