Regional disparities of phytoplankton in relation to environmental factors in the western Arctic Ocean during summer of 2010

Global warming has caused Arctic sea ice to rapidly retreat,which is affecting phytoplankton,the primary producers at the base of the food chain,as well as the entire ecosystem.However,few studies with large spatial scales related to the Arctic Basin at high latitude have been conducted.This study aimed to investigate the relationship between changes in phytoplankton community structure and ice conditions.Fifty surface and 41 vertically stratified water samples from the western Arctic Ocean（67.0°–88°26′N,152°–178°54′W） were collected by the Chinese icebreaker R/V Xuelong from July 20 to August 30,2010 during China＇s fourth Arctic expedition.Using these samples,the species composition,spatial distribution,and regional disparities of phytoplankton during different stages of ice melt were assessed.A total of 157 phytoplankton taxa（〉5 μm） belonging to 69 genera were identified in the study area.The most abundant species were Navicula pelagica and Thalassiosira nordenskioeldii,accounting for 31.23% and 14.12% of the total phytoplankton abundance,respectively.The average abundance during the departure trip and the return trip were 797.07×10~2 cells/L and 84.94×10~2 cells/L,respectively.The highest abundance was observed at Sta.R09 in the north of Herald Shoal,where Navicula pelagica was the dominant species accounting for 59.42% of the abundance.The vertical distribution of phytoplankton abundance displayed regional differences,and the maximum abundances were confined to the lower layers of the euphotic zone near the layers of the halocline,thermocline,and nutricline.The species abundance of phytoplankton decreased from the low-latitude shelf to the high-latitude basin on both the departure and return trips.The phytoplankton community structure in the shallow continental shelf changed markedly during different stages of ice melt,and there was shift in dominant species from centric to pennate diatoms.Results of canonical correspondence analysis（CCA） showed that there were two distinct communities of phytoplankton in the western Arctic Ocean,and water temperature,ice coverage and silicate concentration were the most important environmental factors affecting phytoplankton distribution in the surveyed sea.These findings will help predict the responses of phytoplankton to the rapid melting of Arctic sea ice.

Regional disparities of phytoplankton in relation to different water masses in the Northwest Pacific Ocean during the spring and summer of 2017

The West Pacific Ocean is considered as the provenance center of global marine life and has the highest species diversity of numerous marine taxa.The phytoplankton,as the primary producer at the base of the food chain,effects on climate change,fish resources as well as the entire ecosystem.However,there are few large-scale surveys covering several currents with different hydrographic characteristics.This study aimed to explore the relationships between the spatio-temporal variation in phytoplankton community structure and different water masses.A total of 630 water samples and 90 net samples of phytoplankton were collected at 45 stations in the Northwest Pacific Ocean(21.0°–42.0°N,118.0°–156.0°E)during spring and summer 2017.A total of 281 phytoplankton taxa(>5μm)belonging to 61 genera were identified in the study area.The distribution pattern of the phytoplankton community differed significantly both spatially and temporally.The average abundances of phytoplankton in spring and summer were 797.07×10~2 cells/L and 84.94×10~2 cells/L,respectively.Whether in spring or summer,the maximum abundance always appeared in the northern transition region affected by the Oyashio Current,where nutrients were abundant and diatoms dominated the phytoplankton community;whereas the phytoplankton abundance was very low in the oligotrophic Kuroshio region,and the proportion of dinoflagellates in total abundance increased significantly.The horizontal distribution of phytoplankton abundance increased from low to high latitudes,which was consistent with the trend of nutrient distributions,but contrary to that of water temperature and salinity.In the northern area affected by the Oyashio Current,the phytoplankton abundance was mainly concentrated in the upper 30 m of water column,while the maximum abundance often occurred at depths of 50–75 m in the south-central area affected by the Kuroshio Current.Pearson correlation and redundancy analysis(RDA)showed that phytoplankton abundance was significant negatively correlated with temperature and salinity,but positively correlated with nutrient concentration.The phytoplankton community structure was mainly determined by nutrient availability,especially the N:P ratio.