Stable Carbon And Nitrogen Isotopic Composition In Particulate Organic Matter In The Prydz Bay And The Antarctic Peninsula

To better constrain the spatial distribution of POC,PN,?13CPOC,?15NPN and their controlling factors in the Prydz Bay and the Antarctic Peninsula,carbon and nitrogen isotopic composition in suspended particulate organic matter(SPOM)from surface to bottom were measured during the 29th and the 30th Chinese Antarctic Research Expedition.Furthermore,the carbon and nitrogen isotopes fractionation factors during phytoplankton assimilating dissolved inorganic carbon and nitrate in the mixed layer,as well as nitrogen isotope fractionation factor during POM remineralization below the mixed layer were estimated using Rayleigh model and steady state model respectively.The main conclusions had been obtained as follows.The POC and PN concentrations were higher in the shelf than those in the slope and basin,and decreased with the increasing depth,indicating that particulate organic matter were mainly produced by phytoplankton in the Prydz Bay and its adjacent areas.?13CPOC and ?15NPN in the mixed layer in the Prydz Bay and its adjacent areas increased from the inner bay to the outer ocean,ascribing to the effect of isotope fractionation during phytoplankton assimilating aqueous CO2 and nitrate.The carbon isotope fractionation factor during phytoplankton assimilating aqueous CO2 in the mixed layer was estimated as 23.4� based on the relationship between ?13CPOC and 1/[CO2(aq)].The nitrogen isotope fractionation factor during phytoplankton assimilating nitrate was estimated as 10.0� by state state model,which was more reasonable than that calculated by Rayleigh model.Profiles of ?13CPOC and ?15NPN showed an increase with the increasing depth due to isotopic fractionation during POM remineralization.Nitrogen isotope fractionation factor during PN remineralization below the mixed layer were estimated as 6.9� and 5.6� by Rayleigh model and steady state model,respectively.Interestingly,nitrogen isotope fractionation factor during PN remineralization showed an increase from shelf to slope and basin in the Prydz Bay and its adjacent areas.The POC and PN concentrations were higher in the shelf than slope,and decreased with the increasing depth,implying the particulate organic matter in the Antarctic Peninsula and its adjacent areas were biogenic.?13CPOC were negatively correlated to[CO2(aq)]in the Antarctic Peninsula and its adjacent areas,indicating ?13CPOC variations were controlled by carbon isotopic fractionation during phytoplankton assimilating aqueous CO2.The carbon isotope fractionation factor during phytoplankton assimilating aqueous CO2 in the mixed layer was estimated as 25.6� based on the relationship between ?13CPOC and 1/[CO2(aq)].However,?15NPN had no correlation with[NO3-]in the Antarctic Peninsula and its adjacent areas,probably caused by simultaneous uptake of nitrate and ammonium by phytoplankton.Profiles of ?13CPOC and ?15NPN showed an increase with the increasing depth due to isotopic fractionation during POM remineralization.Nitrogen isotope fractionation factor during PN remineralization below the mixed layer were estimated as 2.6�using steady state model.They also showed an increase from shelf to slope in the Antarctic Peninsula and its adjacent areas.