Distribution of dissolved organic carbon in and near the Prydz Bay, Antarctica

Marine carbon cycling is a hotspot in international marine research due to its close link to global change. Dissolved or ganic carbon(DOC),the most important carbon pool in the ocean,play an important role in marine carbon cycling.One particular interest pertaining to the Southern Ocean relates to its important role as a region for CO₂ sequestration through biological processes of carbon uptake,which can counteract greenhouse gasaccumulation in the atmosphere.During the 16th Chinese National Antarctic Research Expedition(CHIN ARE) (from November 1999 to A pril 2000),seawater samples were collected for DOC determination in the Prydz Bay and its nearby sea areas. All of samples were filtered through the pre-combusted GF/F membranes and drained into the pre-combusted brown glass bottles.After acidification with high grade phosphoric acid,samples were stored in a freezer till DOC determination in laboratory.DOC concentration was determined by high temperature catalytic oxidation(HTCO) method (TOC-5000A,Shimadzu Corp.).The results show that the average DOC concentration in the upper water column(0~100 m) ranges from 23.3 to 110.3 μmol/dm³,with averag ing 52.5 μmol/dm³ (n=55).These values are slightly higher than those reported for the Ross Sea,the Pacific Ocean and others.Profiles of the DOC concentration in the study areas show a decreasing concentration with increasing depth in the upper 100 m,which is related to biological activities in the water column.The DOC concentrations below 200 m are relatively constant with a mean of 40.4 μmol/dm³.These DOC are unactive for physical and biological activities and are called refractory DOC.The concentration of the refractory DOC in the study area is consistent with previous reported values for the Southern Ocean,which are about 41 mol/dm³.Based on the difference between the DOC concentration and refractory concentration,the excess DOC concentration in the upper column can be calculated at every station.The excess DOC shows a spatial change with a higher excess in the north of 64°and little excess in the south of 64°.In conclu-sion,the DOC concentrations in the Prydz Bay and its nearby sea areas are consistent with previous reported values in the Souther n Ocean.All of them show a low DOC concentration with respect to the other ocean.The distribution of surface DOC concentrations in the study areas shows an increase from the south-western to the north-eastern, which is ascribe to the northern spread of continental shelf water from the Prydz Bay in summer.The concentration and distribution of DOC in the Prydz Bay and its nearby sea areas are mainly contr olled by physical and biological