Variation of Antarctic marginal ice zone extent (1989-2019)

The Antarctic marginal ice zone(MIZ)is the transition region between open water and consolidated pack ice,which is defined as an area with 15%-80%sea ice concentration.The MIZ represents the outer circle of Antarctic sea ice and the biological activity circle of Antarctic organisms,which provides a direct indication of the extent of Antarctic sea ice.In this study,the joint total variation and nonnegative constrained least square algorithm are applied to retrieve the Antarctic MIZ extent based on passive microwave data sets from 1989 to 2019.The spatial and temporal variations of the Antarctic MIZ extent and five regions are analyzed.The results show that the Antarctic MIZ extent follows a strong monthly variation pattern,decreasing from November to February and increasing from March to October.The annual MIZ extent is largest in the Weddell Sea and smallest in the Western Pacific Ocean.The edge of the sea ice begins to form a closed ring in May,which eventually closes near the Antarctic Peninsula.The ring width variation is large in summer,but generally stabilizes between 350 and 370 km in winter.The average latitude of the Antarctic MIZ is relatively stable in summer,but changes substantially in winter with a difference of approximately 3°.In October,the lowest mean latitude of the MIZ can reach 64.35°S.The sea surface pressure,2-m temperature,and 10-m wind speed are negatively correlated with the MIZ extent variation,among which the second-order partial correlation coefficient of the sea surface pressure and MIZ extent is−0.8773 in the Western Pacific Ocean.

Horizontal distribution of tintinnids(Ciliophora)in surface waters of the Ross Sea and polynya in the Amundsen Sea(Antarctica)during summer 2019/2020

Information on tintinnid horizontal distribution in the Antarctic Continental Zone is scarce.During the summer of 2019/2020,tintinnid diversity and horizontal distribution in surface waters were investigated in the Ross Sea and Amundsen Sea polynya.Eight tintinnid species were found and the dominant species showed obvious horizontal distribution characteristics.In the Ross Sea,three tintinnid community groups were identified.Cymatocylis cristallina and Laackmanniella prolongata(group I)were dominant species and were mainly distributed in stations closer to the coast than were species in the other two groups.Codonellopsis gaussi(group II)and Cy.convallaria(group III)were mainly distributed in nearshore and offshore stations,respectively.In the Amundsen Sea polynya,the dominant species Cy.cristallina,L.prolongata and Salpingella faurei(group I)were mainly distributed in stations closer to the coast than were species in the other two groups.Cy.convallaria(group III)was mainly distributed in offshore stations.The distribution area where C.gaussi and C.cristallina were found in high abundance and abundance proportion of loricae with protoplasts was divided by the approximate boundary of the Antarctic Slope Front Current and Coastal Current in the Ross Sea.The highest abundance proportion in the Ross Sea was the 32-36μm lorica oral diameter(LOD)size class(75.7%),and the 36-40μm LOD size class(56.0%)was found in the Amundsen Sea polynya.Temperature-salinity-plankton diagrams of the two seas revealed that temperature may be the main reason for species distribution.Our results contribute to a better understanding of horizontal distribution of the microbial food web,and serve as a baseline for future studies of pelagic community change in the Antarctic Continental Zone.