High abundance of protein-like fluorescence in the Amerasian Basin of Arctic Ocean: Potential implication of a fall phytoplankton bloom

The seawater samples from the Chukchi and East Siberian Seas were collected along,a shelf-slope-basin gradient and analyzed for chromophoric and fluorescent DOM (i.e., CDOM and FDOM, respectively). Unexpected high protein -like FDOM (035 +/- 0.40 and 0.24 +/- 0.34 RU for peaks B and T, respectively) levels were identified, which corresponded to 1-2 orders of magnitude higher than those documented by previous reports. This unique phenomenon could be attributed to a fall phytoplankton bloom. The seawater chl-alpha data, estimated from in situ fluorescence measurements and satellite remote sensing data, showed the subsurface chl-a maximum of up to 1.52 mg m(-3) at similar to 25-70 m depths and the surface monthly average values (August 2015) up to 0.55 to 0.71 mg m(-3), which fall in the range of similar to 0.5-2.0 mg m(-3) during fall phytoplankton blooms in this area. Meanwhile, the depth profile of DOM parameters revealed subsurface maxima of protein-like fluorescence peaks along the shelf-slope gradient. The positive correlations between the protein-like peaks and biological index implied the lateral transport of DOM and nutrients from the shelf to the slope and basin. Despite still being a largely ice-covered environment, potential shifts in the ecosystem appear to make progress in response to changing climate in the Arctic Ocean. (C) 2017 Elsevier B.V. All rights reserved.