Decadal Variability in the Pacific Ocean:

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Decadal Variability in the Pacific
Ocean Physics, Biology and Feedbacks Arthur J.
Miller Scripps Institution of Oceanography Univers
ity of California, San Diego La Jolla, CA
USA AMS 13th Conference on Interactions of
the Sea and Atmosphere Portland, Maine August
10, 2004
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• Decadal Variability in the Pacific Ocean
• Physics, Feedbacks and Ecosystem Impacts
• Outline
• Basic physics that organizes the patterns of
  Pacific ocean decadal variability
• Relations to our current research on regional
  ecosystem response
• Comments on possible biologically induced
  feedbacks
• Recent Collaborators
• Physics Schneider, Di Lorenzo, Pierce, Kim,
  Bograd,
• Alexander, Capotondi, Deser, Lynn, McWilliams,
  Mestas-Nunez
• Biology Moisan, McGowan, Neilson, Chai, Chiba,
  Gabric
• Funding NSF, NASA, NOAA, DOE, ONR

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Schematic of Pacific Oceanic Response to Decadal
Forcing by the Aleutian Low
Canonical SST Pattern
Rossby waves
2 - 5 yrs Lagged KOE SST Pattern
(Miller and Schneider, 2000, Prog. Oceanogr.)
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Canonical Pattern of Decadal SST Response
(Aleutian Low Strengthening)
Schematic
SST
Warming
SST Cooling
Driven by surface atmospheric forcing
Canonical Pattern of Decadal SST Response
Equator
Tropical SST Warming
From Miller, Chai, Chiba, Moisan and Neilson
(2004, J Oceanogr.)
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Lagged Pattern of Decadal SST Response
(Aleutian Low Strengthening)
Schematic
sCooling
SST Cooling
Driven by thermocline changes
via wind-stress curl
Lagged Pattern of Decadal SST Response
Equator
From Miller, Chai, Chiba, Moisan and Neilson
(2004, J Oceanogr.)
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Basin-Scale Pattern of Decadal Thermocline
Response (Aleutian Low
Strengtherning)
Schematic
Thermocline
Deepening
Thermocline Shallowing
Lagged response in west due to
Rossby wave propagation
Basin-Scale Pattern of Decadal Thermocline
Response
Equator
Tropical Thermocline Deepening
From Miller, Chai, Chiba, Moisan and Neilson
(2004, J Oceanogr.)
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Sources of North Pacific Decadal Variability

• Tropical Teleconnections (requires tropical
  decadal mechanism)
• a. Atmospheric (ENSO-like)
• - canonical SST pattern
• - basin-scale thermocline
  response
• b. Oceanic (ENSO-like)
• - eastern boundary thermocline
  response
• Subduction Modes
• Midlatitude Gyre Modes
• Stochastic Forcing
• - oceanic spectral peaks possible
• - predictable components possible
• Deterministic Forcing
• - solar cycles, greenhouse gases

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Summary of Some Regional Ecosystem Impacts
Organized by Pacific Decadal Variability
GOA
Steller Sea Lions Zooplankton Phytoplankton
KOE
Sardines Zooplankton Phytoplankton
CCS
Sardines Zooplankton Phytoplankton
Adapted from Yasuda et al., 1999, Fish. Oceanogr.
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The Warming of the California Current Dynamics
and Ecosystem implications Di Lorenzo, Miller,
Schneider and McWilliams Journal of Physical
Oceanography, in press.
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CalCOFI Observations along the Southern
California Coast
Over 50 yrs 1 deg C warming of SST 70
decline in macro zooplankton
Roemmich and McGowan Science, 1995
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Local Atmospheric and Remote Oceanic Forcings
That Can Affect the Regional Oceanic Heat Budget
Mean Advection
Anomalous Advection
Southern California
Alongshore Wind Stress
Di Lorenzo et al., JPO, in press
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NCEP Winds
Wind Stress Curl
Upwelling Favorable Winds
mode 1 72
mode 1 60
EOF 1
EOF 1
N m-2
(106 N) m-3
Latitude N
Longitude W
Longitude W
PC 1
Di Lorenzo et al., JPO, in press
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Net Surface Heat Fluxes
EXP 2
Timeseries of surface net heat fluxesaveraged
over Southern California
Ocean is Cooling
Ocean is Heating
Di Lorenzo et al., JPO, in press
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An eddy-permitting ocean model hindcast captures
the observed SST and thermocline variations
Interannual and Decadal physical variations
CalCOFI Observed Thermocline
Thermocline depth over the last 50 yrs shows an
overall deepening of 20 m
10
0
m
-10
Model Thermocline
Warming is due to large-scale decadal
surface heat fluxes combined with southward
advection of concomitantly warmed water
Increase in upwelling favorable winds partially
cools water column
Di Lorenzo, Miller, Schneider and McWilliams,
JPO, in press.
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Increased winds only
Chlorophyll response to these physical changes
NPZD-type 7-component model hindcast
Decline in Chl-a linked to thermocline deepening
in the model simulation. This is consistent
with the observed zooplankton decline.
Warming and winds together
Miller, Gabric, Moisan, Chai, Neilson, Pierce and
Di Lorenzo, sub judice, 2004
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Observed changes in the seasonal cycle of
Zooplankton in the CCS
After 76-77
Before 76-77
McGowan, Bograd, Lynn and Mller, DSR, 2003
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The Climate-Ocean Regime Shift Hypothesis of the
Steller Sea Lion Decline Relating temporal
variability in the physical system to ecosystem
changes
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SSL population declines since 1976-77 Climate
ShiftWestern Gulf of Alaska population
droppedEastern Gulf of Alaska population was
stable
NMFS
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(Trites, 2004)
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Observed Changes in Ekman pumping
Pre-shift mean conditions 1960-75 Dec-May
Change after shift (1977-97) -(1960-75)
Capotondi, Alexander, Deser and Miller
(JPO, sub judice)
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Circulation Changes in the Gulf of Alaska
associated with the Decline of the Steller Sea
Lion Population

• Post 1976-77, eddy-resolving model hindcast
  reveals
• Stronger Alaska Stream north of Kodak
  Island
• Reduced eddy variance south of Kodiak
  Island
• Alaska Current mean and eddy fields
  unchanged
• Consistent with sea lion populations being
  reduced 80 in the western Gulf, but remaining
  stable in the eastern Gulf

Miller, Di Lorenzo, Neilson, Alexander,
Capotondi, Bograd, Schwing, Musgrave, and
Hedstrom, Atmosphere-Ocean, sub judice, 2004
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Eddy-Permitting Model Mean Surface Currents
Before 76-77 Shift
After 76-77 Shift
Kodiak Is.
Difference
Large in western gulf Little change in east
Miller et al., Atmosphere-Ocean, sub judice
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Eddy-Permitting Model Eddy Surface Currents
Before 76-77 Shift
After 76-77 Shift
Kodiak Is.
Difference
More eddies north of Kodiak Fewer eddies
southwards
Miller et al., Atmosphere-Ocean, sub judice
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Ecosystem response processes in KOE on long
timescales
Strengthened Aleutian Low
Miller, Chai, Chiba, Moisan and Neilson, J.
Oceanogr., 2004
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Physical-Biological Hindcast of Pacific Ocean
Decadal Variability
First EOF of Combined SST, Phyto-, and
Zooplankton fields
Miller, Chai, Chiba, Moisan, and Neilson, J.
Oceanogr., 2004
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Physical-Biological Hindcast of Pacific Ocean
Decadal Variability
First EOF of Combined Thermocline, Phyto-, and
Zooplankton fields
Miller, Chai, Chiba, Moisan, and Neilson, J.
Oceanogr., 2004
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Schematic of the Gu-Philander class of decadal
mode
Schematic of the Latif-Barnett class of decadal
mode
Miller et al., 2003, Bull. Am. Meteorol. Soc.
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Schematic of the Gu-Philander class of decadal
mode with DMS aerosols and phytoplankton heat
absorbtion effects
Schematic of the Latif-Barnett class of decadal
mode with DMS aerosols and phytoplankton heat
absorbtion effects
Miller et al., 2003, Bull. Am. Meteorol. Soc.
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Directions.
Atmosphere - Details of atmosphere response over
KOE region - Sensitivity to ocean biology DMS
aerosols - Regional downscaling over mountains
and coasts
Ocean - Physical mechanisms of adjustment to
forcing - Lags and predictable compoments -
Changes in eddy statistics - Sensitivity to
ocean biology phytoplankton absorbtion
Biology - Organization of response by ocean
patterns - Lags and predictable components -
Distinguishing forced from intrinsic variations
and Global Change effects on all these.
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Effects of anthropogenic forcing on biological
activity
Biological Model Phytoplankton mmol C/m3
Ratio, Year 2100 / Year 2000
Pierce, Climate Change, 2004
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Thanks !