During the fourth Chinese National Arctic Research Expedition cruise in summer 2010, a time-series observation was carried out to examine the response of nutrients and phytoplankton community in the ice-water interface to the ice melting ice in the central Arctic Ocean. Phosphate and silicate in the ice-water interface were rich relative to dissolved inorganic nitrogen （DIN）, based on the Redfield ratio （16N：1P：16Si）, suggesting that DIN was the potential limiting nutrient. DIN concentrations in the sea ice were about 3-4 times that in the surface seawater, indicating that melting ice delivered DIN to the surface water. Pigment analysis showed that fucoxanthin and chlorophyll a contribute to carotenoids and chlorophylls in particles. The mean concentrations of chlorophyll c, diatoxanthin, diadinoxanthin and fucoxanthin from 15 August to 18 August were 6 ug.m-3, 22 ug.m-a, 73 ug.m-3 and 922 ug.m-3, respectively, suggesting that diatoms dominated in the phytoplankton community composition. Furthermore, a notable enhancement in fucoxanthin and chlorophyll a during a large-scale ice melting was likely attributed to senescent diatoms released from the bottom sea-ice as well as phytoplankton diatoms growth in the water column due to the input of nutrients （i.e., DIN） and reducing light limitation from melting ice. Temporal distribution patterns of prasinoxanthin and lutein differed from fucoxanthin, indicating that the response of green algae and diatoms to ice melting were different.
ZHUANG YanpeiJIN HaiyanCHEN JianfangWANG BinLI HongliangCHEN FajinLU YongXU Jie
Diatoms from surface sediment samples in the Bering and Chukchi seas were analyzed to reveal the distribution patterns and their relationship with the ocean environment. A low abundance was found to the north of the Arctic Sea ice Minimum （ASIMin）, indicating that diatom growth is strongly inhibited by perennial sea ice. Between the ASIMin and the Arctic Sea Ice Maximum （ASIMax） which experiences seasonal sea ice, the sea ice related diatoms （mainly Fragilariopsis oceanica and Fragi- lariopsis cylindrus） were dominant, thereby confirming that sea ice is an important influencing factor. The Chaetoceros resting spores were more abundant in the Chukchi Sea, which corresponds well with the active phytoplankton distribution in the water column, and is possibly attributed to the stronger hydrodynamic conditions present in the Bering Sea. The abundances of Chaeto- ceros resting spores were the lowest on the northeast Bering Shelf, possibly because of lower water depth, stronger coastal cur- rents, river influx, coarser particle sizes and stronger winds and bottom currents. The Arctic Diatom Group （dominated by Bac- terosira bathyomphala, Thalassiosira antarctica v. borealis and Thalassiosira antarctica resting spores） was more abundant in the Bering Basin and the areas central of and to the north of Chukchi Plateau, while the Coastal Benthic Diatoms （including Paralia sulcata and Delphineis surirella） were mainly found on the northeast Bering Shelf and nearby Cape Lisburne in the Chukchi Sea. Thalassiosira nordenskioeldii was found to be the most abundant around the Bering Strait, while Neodenticula seminae was only found in the Bering Sea and mainly distributed in the Bering Basin, indicating its close correlation with the Pacific waters
RAN LihuaCHEN JianfangJIN HaiyanLI HongliangLU YongWANG Kui
