Export of Carbon
(^) Export of organic carbon from the upper layer of the Arctic Ocean has been measured
with both floating and moored sediment traps. Results from traps at 200 m are highly
variable in space and time, ranging from 1.3 to 31 g C m−2 yr−1 in the central Arctic
and from 3.1 to 197 g C m−2 yr−1 over shelves and within polynyas (open water
surrounded by ice) (Wassmann et al. 2004). Sedimentation appears to be episodic and
patchy, making generalizations and comparisons among subregions difficult. Sinking
fluxes are highest in the northern Bering Strait and Chukchi Sea and support an
abundant benthos dominated by clams and amphipods. Fluxes are lower in the Fram
Strait, and its stocks of benthos are dominated by polychaetes. In other arctic shelf
seas, fluxes are moderate and show significant terrestrial inputs.
(^) Significant levels of phytoplankton nutrient (e.g. 3 μM NO 3 −) remain in the surface
water of the central Arctic throughout the growing season (Wheeler et al. 1997; Olli
et al. 2007). Olli et al. argue that in the central Arctic, top-down control of primary
production by heavy copepod grazing pressure limits primary production of larger
phytoplankton and limits the vertical flux of organic carbon by maintaining low
phytoplankton stock. Nutrient levels are lower in the Canadian Basin portion of the
central Arctic, and it is possible that phytoplankton growth there is seasonally nutrient
limited.
Subtropical Gyre Biomes
(^) Longhurst placed the boundaries of his trades zone at about 30°N and 30°S. Those
pass right through the ecologically quite uniform central gyres, although satellite
results do show a modest increase of chlorophyll north of 30°N. John McGowan and
others have chosen ∼28–30°N as the latitude at which to study the fundamentals of
subtropical gyre ecology. The Bermuda Atlantic Time Series, BATS, station is at
32°N. BATS is a study of the subtropical Sargasso Sea. There is a basis in
biogeography for lumping all of the warmer ocean waters: many species ranges
extend from 45 or 40°N to the equivalent southern latitude, stretching right across the
equator. However, the satellite images show that the central gyres have lower surface
chlorophyll (phytoplankton stocks) and are certainly less productive than the zones
∼15°N to 15°S that are affected by equatorial upwelling. Moreover, many species of
plankton live in the central gyres only. So, we will treat subtropical (or central) gyre
and trades (equatorial) biomes as separable. Thanks to the CLIMAX studies in the
1960s–1980s (McGowan & Walker 1985; Venrick 1999) and to the Hawaii Ocean
Time Series (HOT, sampling at Station “ALOHA”, e.g. Siegel et al. 2001), work