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Projected Climate Impacts on the Pelagic Ecosystem Size Structure and Catches in the North Pacific Over the
21st Century
Jeffrey J. Polovina1 ,Phoebe Woodworth1, Julia L. Blanchard2, and
John Dunne3, 1NOAA Pacific Islands Fisheries Science Center,2University of Sheffield,
3NOAA Geophysical Fluid Dynamics Laboratory
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NOAA GFDL Earth System Model 2.1 (ESM2.1 A2 NPZ)
1°
x 1°
north of 30°N, with latitudinal resolution increasing to 0.33°
at equator
Ocean has 50 levels, with 22 10m spacing levels in the upper 220mWe used monthly values from 1991 -
2100
CM 2.1 (Atmos., Land, Ice)
Coupled Climate BiogeochemicalTracers of Phytoplankton with Allometric Zooplankton (TOPAZ)*
Major nutrients + 4 phytoplankton groups
A2 scenario
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Projected Climate Changes for N Pacific over the 21st
CenturyBasin-wide warming
Tropical easterlies weaken
Westerlies and polar easterliesweaken and shift poleward
Reduced wind-stress curl
Nutrient redistribution
Weakened vertical velocitiesand increased stratification
Rykaczewski and Dunne 2010, Sarmiento et al. 2004, Vecchi et al. 2006, Yin 2005
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Extending climate model results to higher trophic levels –
2 approaches
•
Using climate model output to define dynamic biomes and then examine spatial and temporal changes in model-derived biomes in response to climate change
•
Using climate model output to drive a size-based ecosystem model at specific locations
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20-year Mean Total Phytoplankton Density 2001 –
2020
Polovina et al. (2011)
Total Phytoplankton D
ensity (g C m
-
2)
Temperate Biome
Subtropical Biome
Equatorial Upwelling Biome
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Polovina et al. (2011)
Total Phytoplankton D
ensity (g C m
-
2)
20-year Mean Total Phytoplankton Density 2081 –
2100
Temperate Biome
Subtropical Biome
Equatorial Upwelling Biome
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Impacts of increasing SSTMean SST at the Beginning and End of the 21st
Century
1998 -
20172080 -
2099
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Change Over the 21st Century
∆PP
∆SST∆Lg
∆Sm
Gnanadesikan et al. 2006
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Size-based model
Jennings et al. 2008, Proc. R. Soc. B; Blanchard et al. 2009 J Anim Ecol; Blanchard et al. 2010 Theor. Ecol.
Input: monthly plankton size spectrum and SST
Output: monthly population size spectrum
Assumes size-based predation, and size-
specific growth and mortality are functions of food availability and SST
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Size Spectra
Minimum Size Fished
Barnes et al. 2010, Benoit and Rochet 2004, Blanchard et al. 2009, Jennings et al. 2008, Stock and Dunne 2010
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Areas of Interest
Biome Boundaries
Biome Interiors
California Current
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Areas of Interest
Biome Boundaries
Biome Interiors
California Current
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Areas of Interest
Biome Boundaries
Biome Interiors
California Current
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Projected Catch of Fish > 2 kg, F=0.2
Biome Boundary Regionsdecline 52 –
77%
Biome Interior Regionsdecline 0 –
38%
California Current Regionincrease 43%
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Correlation between Size Composition and Catch
Subtropical Biome
Temperate Biome
EU Biome
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Additional Implications
−
Biome boundary regions
may see earliest and greatest impacts and hence are ideal areas for monitoringphytoplankton size structure
−
Transition Zone for usedforaging and migration
−
Possible eastward redistribution of skipjack andyellowfin, and bigeye tuna
-
Results present come from only one climate model. Need to consider output from several climate models
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Summary
•
Over 21st
century a change in wind field and increased ocean warming will increase oceanic vertical stratification and redistribute nutrients.
•
For much of oceanic North Pacific fish density and catch declines, with greatest declines (50-80%) near the boundary of the expanding subtropical gyre.
•
However, in the California Current, nutrient upwelling increases
resulting in an increase in fish density and catch.
•
Changes in density of large phytoplankton is a dominant biological response to climate change which alters the length of food chains and hence fish yields.
•
Size-based model couples well with climate model to assess high tropic impacts from climate change.