Climate-driven Trends in Contemporary Ocean Productivity

Michael BehrenfeldOregon State University

Robert O’Malley Jorge Sarmiento Wayne EsaiasDon Shea Gene Feldman Robert FrouinDave Siegel Allen Milligan Compton TuckerEmmanuel Boss Ricardo Letelier Dorota KolberToby Westberry James Randerson Nathan PollackChuck McClain Christopher Field Stephane MaritorenaPaul Falkowski Sietse Los

or

“The World According to SeaWiFS”

• Biospheric NPP increased 6 Pg from 1997 El Nino to 1999 La Nina, with clearest response in oceans

• In most central ocean gyres, chlorophyll concentrations decreased between 1997 and 2003

• Declines in mid-ocean gyres chlorophyll associated with increases in sea surface temperature

7 December 2006 Vol. 444 Nature

Tidbits

• Based on Vertically Generalized Production Model (VGPM)

• Initial increase = 1,930 TgC/yr

• Subsequent decrease = 190 TgC/yr

• Global trends dominated by changes in permanently stratified ocean regions (ann. ave. SST < 15oC)

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• Six different coupled climate models• Ocean biological responses to climate warming from industrial revolution to 2050• Marginal sea-ice biome area decreases 42% (N) and 17% (S)• Expansion of low production permanently stratified ocean by 4% (N) to 9.4% (S)• Subpolar gyre biome expands 16% (N) and 7% (S)• Stratification decreases nutrient supply and thus productivity in permanently stratified oceans• Stratification, extended growing season, and sea ice retreat enhance production at high latitudes• Significant shifts in community composition

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…are there alternative explanations?L

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• Nutrient-driven changes in NPP

So, what do we really know?....• Satellites measure neither NPP or chlorophyll, they tell us about optics• SeaWiFS has recorded changes in ocean optical properties over vast regions• These changes are clearly linked to effects of climate variability on upper ocean temperature and stratification - not instrument or atmospheric artifacts

• Photo-oxidation of cDOM

• Light-driven changes in photoacclimation

Spectral matching algorithms are a path to a solution…• Do not rely on the ‘bio-optic’ assumption – now known to be wrong• Would allow changes in cDOM photo-oxidation to be detected• Would allow changes in photoacclimation to be detected from Chl:C• Are not optimized with heritage ‘ocean color’ wavebands

Difference in chlorophyll estimates for standard wavelength-ratio and

spectral matching algorithms

cDOM from spectral matching algorithm

•Uncertainty in remote sensing products reflects inadequacy of heritage wavebands for separating different absorbing and scattering components.

Measurement Maturity Index

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* NOTE: MODIS Aqua climate-quality ocean biology data have only been achieved because SeaWiFS data were available for comparison

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Contemporary Changes in Ocean Chlorophyll during the SeaWiFS Era

El Nino – La Nina changes

Chlsat vs Chleuphotic

Other NPP models

Chlorophyll and MEI

NPP and MEI update

Zonal temperature changes

Surface chlorophyll updates

The 2006 minimum

Credit really belongs to the Ocean Color Group at NASA Goddard Space Flight Center and Ocean Biology and Biogeochemistry Program at NASA Headquarters

• Biospheric NPP increased 6 Pg from 1997 El Nio to 1999 La Nia, with clearest response in oceans

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Tidbits

• Three models: VGPM – polynomial VGPM – Eppley CbPM – Chl:C-based growth

• All show 2 primary trends

• Biggest differences is in slope of initial El Nino – La Nina period

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Quality and Maturity DefinitionsQuality and Maturity Definitions

Measurement Maturity Index1 = No known operational use for measurement2 = Parameter identified as having potential for operational significance 3 = Operational significance demonstrated through simulations4 = Pathfinder mission launched. Need for long term record widely accepted 5 = Pilot decision support tool (DST) use of space-based measurements6 = Space ops over sustained period. Adds value to DSTs.7 = Ready for transfer to operational use 8 = Measured operationally. Used operationally in existing DSTs.

Measurement Quality Index1 = Measurement identified as potentially providing significant science return2 = Initial measurements produced and calibrated3 = Geophysical, biological, or chemical properties inferred or estimated from

calibrated measurements4 = Geophysical, biological, or chemical properties inferred or estimated from

calibrated measurements and validated5 = Significant improvement in calibration, spatial resolution, spectral resolution,

temporal revisit, and/or spatial coverage over initial measurements6 = Second significant improvement in calibration resolution, temporal revisit,

and/or spatial coverage over initial measurements7 = Further significant improvement in calibration resolution, temporal revisit,

and/or spatial coverage over initial measurements8 = Measurement approaches theoretical or practical limits on performance