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

2. The problem: multiple time 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 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: years
Time scales

5. 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: years
Time scales

6. 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: years
Time scales

7. 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: years
Time scales

8. 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

10. 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

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

12. 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

13. The most notable El Niño events
#1:
#3:
#2:
‘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, was the strongest El Nino on record, followed by , , , , ….
Note the scale is reversed relative to Southern Oscilation Index,
so El Niño is on top, La Niña on bottom

14. Jan El Niño
July 1998 La Niña

15. 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

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

17. -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

18. (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

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

20. 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

21. 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

22. (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

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

24. 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

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

26. Three most intense El Niños occurred during a warm PDO phase

27. -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

28. 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

29. +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)

30. 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

31. 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.).