Virginia Institute of Marine Science
Photosynthetic CO(2) uptake by oceanic phytoplankton and subsequent export of particulate organic carbon (POC) to the ocean interior comprises a globally significant biological carbon pump, controlled in part by the composition of the planktonic community. The strength and efficiency of this pump depends upon the balance of particle production in the euphotic zone and remineralization of those particles in the mesopelagic (defined here as depths between 150 and 300 m), but how these processes respond to climate-driven changes in the physical environment is not completely understood. In the Sargasso Sea, from similar to 1996-2007, we have observed a decade-long > 50% increase in euphotic zone integrated autotrophic biomass (estimated from chlorophyll TChl-alpha), prokaryotic phytoplankton, primary production and shallow (150 m) POC export coinciding with a shift in the mean phase of the winter North Atlantic Oscillation (NAO) from consistently positive to neutral but variable. During this same period mesopelagic POC flux attenuation has doubled such that carbon sequestration below 300 m, the maximum winter/spring ventilation depth, has not changed. The increased mesopelagic POC attenuation appears mediated by changes in plankton community composition and metabolic activity in both the euphotic and mesopelagic zones. These changes are counter to extant hypotheses regarding inter-relationships between phytoplankton community composition, productivity and carbon export, and have significant impacts on how the Sargasso Sea ecosystem, at least, is modeled. Moreover, these time-series observations suggest that processes in the euphotic zone and mesopelagic are tightly coupled and should be considered together in future research.
ATLANTIC TIME-SERIES; PHYTOPLANKTON COMMUNITY STRUCTURE; VERTICALLY MIGRATING ZOOPLANKTON; LONG-TERM CHANGES; NORTH-ATLANTIC; SUBTROPICAL GYRE; ORGANIC-CARBON; INCREASED TEMPERATURE; OLIGOTROPHIC WATERS; ACTIVE-TRANSPORT
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The authors thank the captains and crews of the R/Vs Weatherbird II and Atlantic Explorer as well as the BATS technicians and scientists, past and present, whose diligence and dedication has resulted in the generation of the dataset presented in this manuscript. Specifically we thank Debra Lomas who assisted with the data analysis. We thank the National Science Foundation Chemical and Biological Oceanography Programs for continued support of the BATS program through the following awards: OCE 88-01089, OCE 93-01950, OCE 9617795, OCE 0326885, and OCE 0752366. This is BIOS contribution No. 1720.
Lomas, M. W., Steinberg, D. K., Dickey, T., Carlson, C. A., Nelson, N. B., Condon, R. H., and Bates, N. R.: Increased ocean carbon export in the Sargasso Sea linked to climate variability is countered by its enhanced mesopelagic attenuation, Biogeosciences, 7, 57-70, https://doi.org/10.5194/bg-7-57-2010, 2010.