On the role of climate modes in modulating the air–sea CO<sub>2</sub> fluxes in eastern boundary upwelling systems
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Published:2019-01-24
Issue:2
Volume:16
Page:329-346
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ISSN:1726-4189
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Container-title:Biogeosciences
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language:en
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Short-container-title:Biogeosciences
Author:
Brady Riley X.ORCID, Lovenduski Nicole S.ORCID, Alexander Michael A.ORCID, Jacox Michael, Gruber NicolasORCID
Abstract
Abstract. The air–sea CO2 fluxes in eastern boundary upwelling systems (EBUSs)
vary strongly in time and space, with some of the highest flux densities
globally. The processes controlling this variability have not yet been
investigated consistently across all four major EBUSs, i.e., the California
(CalCS), Humboldt (HumCS), Canary (CanCS), and Benguela (BenCS) Current
systems. In this study, we diagnose the climatic modes of the air–sea
CO2 flux variability in these regions between 1920 and 2015, using
simulation results from the Community Earth System Model Large Ensemble
(CESM-LENS), a global coupled climate model ensemble that is forced by
historical and RCP8.5 radiative forcing. Differences between simulations can
be attributed entirely to internal (unforced) climate variability, whose
contribution can be diagnosed by subtracting the ensemble mean from each
simulation. We find that in the CalCS and CanCS, the resulting anomalous
CO2 fluxes are strongly affected by large-scale extratropical modes
of variability, i.e., the North Pacific Gyre Oscillation (NPGO) and the North
Atlantic Oscillation (NAO), respectively. The CalCS has anomalous uptake of
CO2 during the positive phase of the NPGO, while the CanCS has
anomalous outgassing of CO2 during the positive phase of the NAO. In
contrast, the HumCS is mainly affected by El Niño–Southern Oscillation
(ENSO), with anomalous uptake of CO2 during an El Niño event.
Variations in dissolved inorganic carbon (DIC) and sea surface temperature
(SST) are the major contributors to these anomalous CO2 fluxes and
are generally driven by changes to large-scale gyre circulation, upwelling,
the mixed layer depth, and biological processes. A better understanding of
the sensitivity of EBUS CO2 fluxes to modes of climate variability is
key in improving our ability to predict the future evolution of the
atmospheric CO2 source and sink characteristics of the four EBUSs.
Funder
Krell Institute Division of Ocean Sciences Schweizerischer Nationalfonds zur Förderung der Wissenschaftlichen Forschung
Publisher
Copernicus GmbH
Subject
Earth-Surface Processes,Ecology, Evolution, Behavior and Systematics
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