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

Abstract

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 (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 from in situ fluorescence measurements and satellite remote sensing data, showed the subsurface chl-a maximum of up to 1.52mgm−3 at ~25–70m depths and the surface monthly average values (August 2015) up to 0.55 to 0.71mgm−3, which fall in the range of ~0.5–2.0mgm−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.