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

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

2. The problem: multiple times scales of variability years Humans century decades centuries

3. 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

4. Generation times Tuna Sardine Anchovy Salmon Krill Copepods Jellyfish Phytoplankton Bacteria 1 year 1 day 1 hour 1 week 10 years 15 years 1 month 5 years 20 years • Life Spans • # Reproductive years • Body size • Swimming speed • Energy reserves Time scales

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

6. Main effects of climate oscillations on pelagic species • Changes in temperature/nutrients affect primary production and food web • Higher trophic levels affected by changes in food availability • Changes in temperature affect rates of growth/survival • Fish/nekton with limited temperature range can move to water of preferred temperature, leading to range shifts

8. 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

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

11. ENSO warm event (El Niño): weaker upwelling, deeper thermocline, upwelled water is warmer and has lower nutrient concentration ENSO cold event (La Niña): stronger upwelling, shallower thermocline, upwelled water is cooler and has more nutrients

12. Fish and other nekton can vertically migrate to water of a preferred temperature. They can also migrate horizontally.

13. Jan. 1998 El Niño July 1998 La Niña

14. 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

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

16. Major El Niños (warm) Major La Niñas (cool) Biomass of Zooplankton >500 m California Current -El Niño reduces upwelling -Lower nutrients/deeper mixed layer reduce primary production -Low primary production leads to low zooplankton biomass Lavaniegos and Ohman 2003

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

18. Normal year El Niño year 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

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

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

21. Major El Niño Sardine: lifespan 12-25 years, eat zooplankton, prefer warm water

22. -ENSO effects are evident in sardine & anchovy landings from Peru. -ENSO effects are small relative to long-term variability. Major El Niños Major El Niños Chavez et al. 2003

23. 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

24. 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: 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

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

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

28. - PDO (cool) + PDO (warm) Major El Niños (warm) Major La Niñas (cool) Biomass of Zooplankton >500 m California Current -Zooplankton biomass is low when warm -Effects of warm PDO and warm El Niño events are additive Lavaniegos and Ohman 2003

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

30. Salmon catch also tracks PDO, but species-specific warmcool warm Selected Pacific salmon catch records with PDO signatures. For sockeye, black bars denote values that are greater than the long-term median. The shading convention is reversed for WOC coho and Columbia River spring chinook catch. Dotted vertical lines are drawn in each panel to mark the PDO polarity reversal times in 1925, 1947, and 1977. The top panel is the PDO index. Mantua et al. 1997

31. -PDO (cool) +PDO (warm)

32. +PDO (warm) is sardine regime -PDO (cool) is anchovy regime Catch (Percent of maximum) -PDO (cool) +PDO (warm) -PDO (cool) Bakun & Broad 2003

33. 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

34. Atlantic has a different decadal-scale oscillation, the North Atlantic Oscillation, that we will cover on Monday • On top of these cycles there is a secular warming trend (Theme 5, November).