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Observing multidecadal trends in Southern Ocean CO 2 uptake: What can we learn from an ocean model?
Author(s) -
Lovenduski Nicole S.,
Fay Amanda R.,
McKinley Galen A.
Publication year - 2015
Publication title -
global biogeochemical cycles
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 2.512
H-Index - 187
eISSN - 1944-9224
pISSN - 0886-6236
DOI - 10.1002/2014gb004933
Subject(s) - sink (geography) , hindcast , biome , climatology , predictability , environmental science , biogeochemical cycle , proxy (statistics) , oceanography , atmospheric sciences , geology , geography , ecosystem , chemistry , ecology , machine learning , computer science , environmental chemistry , biology , physics , cartography , quantum mechanics
We use output from a hindcast simulation (1958–2007) of an ocean biogeochemical and ecological model to inform an observational strategy for detection of a weakening Southern Ocean CO 2 sink from surface ocean pCO 2 data. Particular emphasis is placed on resolving disparate conclusions about the Southern Ocean CO 2 sink that have been drawn from surface ocean pCO 2 observation studies in the past. We find that long‐term trends in Δ pCO 2 ( pCO 2 oc − pCO 2 atm ) can be used as a proxy for changes in the strength of the CO 2 sink but must be interpreted with caution, as they are calculated from small differences in the oceanic and atmospheric pCO 2 trends. Large interannual, decadal, and multidecadal variability in ΔpCO 2 persists throughout the simulation, suggesting that one must consider a range of start and end years for trend analysis before drawing conclusions about changes in the CO 2 sink. Winter‐mean CO 2 flux trends are statistically indistinguishable from annual‐mean trends, arguing for inclusion of all availablepCO 2 ocdata in future analyses of the CO 2 sink. The weakening of the CO 2 sink emerges during the observed period of our simulation (1981–2007) in the subpolar seasonally stratified biome (4°C < average climatological temperature < 9°C); the weakening is most evident during periods with positive trends in the Southern Annular Mode. With perfect temporal and spatial coverage, 13 years of pCO2 ocdata would be required to detect a weakening CO 2 sink in this biome. Given available data, it is not yet possible to detect a weakening of the Southern Ocean CO 2 sink with much certainty, due to imperfect data coverage and high variability in Southern Ocean surface pCO 2 .