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

Abstract

The seawater samples fromthe Chukchi and East Siberian Seaswere collected along a shelf-slope-basin gradient and analyzed for chromophoric and fluorescent DOM(i.e., CDOMand FDOM, respectively). Unexpected high protein- like FDOM (0.35 ± 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-a data, estimated fromin situ fluorescence measurements and satellite remote sensing data, showed the subsurface chl-a maximum of up to 1.52 mg m？3 at ~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 ~0.5？2.0 mg m？3 during fall phytoplankton blooms in this area. Meanwhile, the depth profile ofDOMparameters revealed subsurfacemaximaof 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 ecosystemappear to make progress in response to changing climate in the Arctic Ocean.