Biology and the Carbon Cycle
concentrations decreased from 10 to
5.0 M. These decreases may reflect
the relative strength of influence of
Pacific and Atlantic water masses, or
they may reflect biological utilization
of nutrients in water moving in the
Transpolar Drift. Nitrate, however,
showed the opposite pattern. Nitrate
concentrations increased from 1.0 to
4.0 M along the transect. Nitrate
concentrations varied more with
depth from 0 to 300 m than did
phosphate and silicate concentra-
tions. The wider range in concentra-
tions combined with differences in
diffusion and other mixing processes may account for the differences in pat-
Pat Wheeler in the
wet lab aboard the
terns of changes in nutrients along the transect.
Polar Sea.
Particulate organic carbon (POC) ranged from 3.5 to 8.0 g/m2 and gener-
ally decreased along the transect. Particulate organic nitrogen (PON) ranged
from 0.4 to 1.3 g/m2 and also generally decreased along the transect. The C/N
ratio of particulate organic material ranged from 8 to 14 and nearly doubled
along the transect. These levels of POC and PON are relatively high; this
material is composed of approximately 40% living material--10% phytoplank-
ton and 30% heterotrophs (bacteria and protists). Zooplankton standing stocks
ranged from 0.2 to 2 gC/m2, making a significant additional contribution to
the total organic carbon and accounting for about 40% of the total particulate
organic carbon in the central Arctic.
The largest pool of organic carbon was dissolved organic carbon (DOC),
which ranged from 60 to 120 M. DOC and zooplankton standing stocks
both increased in the poleward direction, reaching maximum values around
85 to 87N. Earlier investigators attributed the high DOC concentrations to
the refractory nature of DOC from riverine inputs and presumably low rates
of bacterial metabolism due to low temperatures in the central Arctic. Gosse-
lin et al. measured significant rates of DOC excretion by phytoplankton and
ice algae; these results, along with the similar spatial patterns of the distribu-
production of DOC.
Bacterial production ranged from 17 to 53 mg C/m2-day, comparable to
rates measured in Antarctic waters. Since bacteria are the main consumers of
dissolved organic carbon, bacterial production can be used to estimate the
mean turnover time of DOC. Bacterial carbon utilization divided by concen-
trations of DOC indicated that the average turnover time for the total DOC
pool is less than one year in the central Arctic. Since the mean residence time
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