Biology and the Carbon Cycle
Transfer of Shelf-Derived Carbon to the
Interior of the Arctic Ocean
Raymond Sambrotto
The upper water column fluxes of carbon in the Arctic Ocean have been
characterized as dominated by the lateral movement of total dissolved inorganic
carbon (ΣCO2) regenerated from productive shelves to deep water regions. At
least some of this movement is associated with the production and sinking of
brine during sea ice formation on the shelves. This suggests a simple carbon
system in which the abundant organic matter produced on the Arctic shelves
provides the source for the elevated ΣCO2 found in the upper halocline of
most of the stations thus far examined. At the same time, however, the domi-
nance of such a horizontal flux of carbon would make the Arctic dramatically
different from the carbon systems in lower-latitude basins, which are thought
to be dominated by the vertical flux of organic matter.
Determining the amount of carbon that enters the Arctic is important to
efforts to understand the role of the ocean as a whole as a sink for atmospheric
carbon dioxide and other greenhouse gases that have increased in recent years
due to human activities. The major goal of my research during AOS-94, there-
fore, was to evaluate the carbon flux in the interior of the Arctic Ocean quan-
titatively, particularly in the Canada Basin, which has been sparsely sampled.
A total of 164 bottle samples were collected from the surface 400 m of 15
stations along the AOS-94 cruise track of the Polar Sea and were analyzed for
ΣCO2 using a coulometric technique. Most samples were analyzed onboard,
except samples from the last few stations, which were analyzed upon return to
the laboratory.
The ΣCO2 values measured during the Polar Sea cruise were positively
correlated with salinity, and the maximum values were associated with salini-
ties characteristic of the upper halocline (approximately 33.1 psu). Also, ΣCO2
concentrations were correlated with those of silicate, which suggests that both
signals share a common source on the surrounding shelves, which are sites of
prodigious diatom production during the summer months. The organic material
that is the source of the remineralized ΣCO2, therefore, may be in large part
attributable to diatoms, whose frustules provide much of the silicate as they
dissolve.
Raymond Sambrotto is with the LamontDoherty Earth Observatory in Palisades, New York, U.S.A.
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