Abstract: During the 4th Chinese National Arctic Expedition cruise in summer 2010, in a high Arctic, a time-series observation was carried out in order to examine the response of nutrients and phytoplankton in the ice-ocean interface to the ice melting. Phosphate and silicate in the ice-ocean interface were rich relative to nitrogen, based on Redfield ratio (16N:1P:16Si), suggesting that nitrogen was the potential limiting nutrient. Nitrogen concentration in the sea ice was about 3-4 times that in the surface seawater, indicating that melting water delivered nitrogen to the surface water. Pigments analysis showed that fucoxanthin and chlorophyll a were the main contributor of carotenoids and chlorophylls in particles, respectively. The mean concentrations of chlorophyll c, diatoxanthin, diadinoxanthin and fucoxanthin during 15 to 18 August were 6, 22, 73 and 922 μg/m3, respectively, suggesting that diatoms dominated in the phytoplankton community composition. Furthermore, a notable enhancement in fucoxanthin and chlorophyll a during a large-scale 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. nitrogen) from melting water. Temporal distribution pattern of diagnostic pigments prasinoxanthin and lutein differed from fucoxanthin, indicating that green algae and diatoms responded differently to ice melting.

Key words: ice melting, photosynthetic pigments, Arctic