Sammendrag
Under-ice blooms of phytoplankton in the Chukchi Sea have been observed, with strong implications for our understanding
of the production regimes in the Arctic Ocean. Using a combination of satellite remote sensing of phytoplankton biomass,
in situ observations under sea ice from an autonomous underwater vehicle (AUV), and in vivo photophysiology, we
examined the composition, magnitude and origin of a bloom detected beneath the sea ice Northwest of Svalbard (Southern
Yermak Plateau) in May 2010. In situ concentration of up to 20 mg chlorophyll a [Chl a] m−
3, were dominated by the northern
planktonic spring species of diatoms, Thalassiosira nordenskioeldii, T. antarctica var. borealis, Chaetoceros socialis
species complex and Fragilariopsis oceanica. These species were also found south of the marginal ice zone (MIZ). Cells in
the water column under the sea ice were typically high-light acclimated, with a mean light saturation index (Ek) of 138 μmol
photons m−
2 s−1 and a ratio between photoprotective carotenoids (PPC) and Chl a (w:w) of 0.2. Remotely sensed data of
[Chl a] showed a 32,000 km2 bloom developing south of the MIZ. In effect, our data suggest that the observed under-ice
bloom was in fact a bloom developed in open waters south of the ice edge, and that a combination of northward-flowing
water masses and southward drifting sea ice effectively positioned the bloom under the sea ice. This have implications for
our general understanding of under-ice blooms,
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