Impact of Arctic Oscillation on cloud radiative forcing and September sea ice retreat

The Arctic Oscillation(AO)has important effects on the sea ice change in terms of the dynamic and thermodynamic processes.However,while the dynamic processes of AO have been widely explored,the thermodynamic processes of AO need to be further discussed.In this paper,we use the fifth state-of-the-art reanalysis at European Centre for Medium-Range Weather Forecasts(ERA5)from 1979 to 2020 to investigate the relationship between AO and the surface springtime longwave(LW)cloud radiative forcing(CRF),summertime shortwave(SW)CRF in the Arctic region(65°-90°N).In addition,the contribution of CRF induced by AO to the sea ice change is also discussed.Results indicate that the positive(negative)anomalies of springtime LW CRF and summertime SW CRF are generally detected over the Arctic Ocean during the enhanced positive(negative)AO phase in spring and summer,respectively.Meanwhile,while the LW(SW)CRF generally has a positive correlation with AO index(AOI)in spring(summer)over the entire Arctic Ocean,this correlation is statistically significant over 70°-85°N and 120°W-90°E(i.e.,region of interest(ROI))in both seasons.Moreover,the response of CRF to the atmospheric conditions varies in spring and summer.We also find that the positive springtime(summertime)AOI tends to decrease(increase)the sea ice in September,and this phenomenon is especially prominent over the ROI.The sensitivity study among sea ice extent,CRF and AOI further reveals that decreases(increases)in September sea ice over the ROI are partly attributed to the springtime LW(summertime SW)CRF during the positive AOI.The present study provides a new pattern of AO affecting sea ice change via cloud radiative effects,which might benefit the sea ice forecast improvement.

Response of phytoplankton community to different water types in the western Arctic Ocean surface water based on pigment analysis in summer 2008

Nutrients and photosynthesis pigments were investigated in the western Arctic Ocean during the 3rd Chinese Arctic Research Expedition Cruise in summer 2008. The study area was divided into five provinces using the K- means clustering method based on the physical and chemical characteristics of the sea water, and to discuss the distribution of the phytoplankton community structure in these provinces. CHEMTAX software was performed using HPLC pigments to estimate the contributions of eight algal classes to the total chlorophyll a （TChl a）. The results showed that on the Chukchi Shelf, the Pacific Ocean inflow mainly controlled the Chl a biomass and phytoplankton communities by nutrient concentrations. The high nutrient Anadyr Water and Bering Shelf Water （AnW and BSW） controlled region have high Chl a levels and the diatom dominated community structure. In contrast, in the region occupied by low-nutrient like Alaska Coastal Water （ACW）, the Chl a biomass was low, with pico- and nano-phytoplankton as dominated species, such as prasinophytes, chrysophytes and cryptophytes. However, over the off-shelf, the ice cover condition which would affect the physical and nutrient concentrations of the water masses, in consequence had a greater impact on the phytoplankton community structure. Diatom dominated in ice cover region and its contribution to Chl a biomass was up to 75%. In the region dose to the Mendeleev Abyssal Plain （MAP）, controlled by sea-ice melt water with relatively high salinity （MW-HS）, higher nutrient and Chl a concentrations were found and the phytoplankton was dominated by pico- and nano-algae, while the diatom abundance reduced to 33%. In the southern Canada Basin, an ice-free basin （IfB） with the lowest nutrient concentrations and most freshened surface water, low Chl a biomass was a consequence of low nutrients. The ice retreating and a prolonged period of open ocean may not be beneficial to the carbon export efficiency due to reducing the Chl a biomass or intriguing smaller size algae growth.

THE ENVIRONMENTAL EVENTS ON KING GEORGE ISLAND SINCE THE LAST GLACIATION

The extension of ice sheet on King George Island during the last glaciation was an environment event since the last glaciation. At that time South Shedlands Islands were a large unified island and the ice mass on King George Island might come from the Antarctic Peninsula. The model of ice retreat and ice advance events in the Holocene show that the ice sheet was separated into three small ice caps and then dispeared gradually. At present the retreating velocity of glacier is about 1. 3m each year. After the retreat of ice sheet the isostatic compensation appeared in the crust there, and then 5-6 steps of the uplifted marine terraces have been developed along the coast. The uplift rate of the crust may be 6-10mm/a.

Changes of marine productivity and sedimentary environment recorded by biogenic components in the Antarctica Ross Sea since the last deglaciation

Changes in the marine productivity and sedimentary environment since the last deglaciation in the Ross Sea are presented in this paper.Opal has replaced calcium carbonate as the major biogenic component and has a significantly positive correlation with total organic carbon(TOC),which indicates that siliceous phytoplankton controlled the absorption and release of carbon by the biological pump and was the main producer of marine organic matter.Using the AMS 14C age framework,foraminiferal fossils and redox sensitive elements(RSEs),we found that both the sedimentary environment and marine productivity changed clearly in^11 cal ka BP,which is more likely related with the melting and retreat of the Ross Ice Shelf.In addition,the increase of marine productivity promoted the sinking of more organic-matter to the seabed.A large proportion of oxygen in the bottom water body was consumed and more carbon dioxide was produced during the decomposition of organic matter,making the bottom water body more soluble to calcium carbonate.

Possible Links between Arctic Sea Ice Loss Events and Cold Eurasian Anomalies in Winter

Recently,there have been two competing perspectives on the links of rapid sea ice retreat over the Barents–Kara Seas(BKS)and in midlatitude severe cold winters over Eurasia.By using the daily ECMWF reanalysis(ERA)-Interim dataset during 1979–2016,we reconcile two contrasting viewpoints,namely,if an upward turbulent heat flux appears and maintains several days after the rapid sea ice loss over the BKS in winter,a dipole structure which consists of a primary positive center of action around the Barents Sea with the other opposite-sign center of action over Eurasian continent is easily amplified,and consequently a cold anomaly over Eurasia will occur,but not vice versa.Our work casts light on the links between the Arctic sea ice loss and Eurasian cold winter anomalies by revealing the different responses of the surface turbulent heat flux(STHF)after rapid sea ice retreat on a daily basis.