Distribution And Sources Of Micronutrients Zinc And Cadmium And Their Role In Tracing Primary Productivity In Prydz Bay,Antarctica

Zinc and cadmium are important micronutrients for marine phytoplankton. They take part in biological process and influence the carbon fixation and burial in the ocean floor through regulating community structure of phytoplankton and marine primary production, especially in the Southern Ocean of High Nutrients Low Chlorophylls (HNLC) regions. Prydz Bay in the Southern Ocean as the research object in the study, the contents of zinc and cadmium in sea water, sediment, settling particulate, phytoplankton assemblage and purified diatom opal from the bay were determined by Atomic Absorption Spectrometer and Inductively Coupled Plasma Mass Spectrometry. The distribution of zinc and cadmium in different environmental medium and organisms were described and the resources of micronutrients were analyzed by using statistical methods. According to the geochemical index of aluminum, the influence of human activities on the accumulation of zinc and cadmium were estimated, and the lithogenic and biogenic inputs of trace elements in the sediments and settling particles were calculated. Based on the relationships among trace elements, phytoplankton biomass, dissolved nutrients, organic carbon and biogenic silica, the role of zinc and cadmium on tracing primary productivity was discussed. The following are the main conclusions in terms of this work:(1) Zinc and cadmium are generally not the limited micronutrients for the phytoplankton in Prydz Bay, however, not sufficient supply of zinc during phytoplankton bloom at the edge of ice shelf in austral summer may lead to the stimulated uptake of cadmium by phytoplankton.(2) The distribution of dissolved zinc and cadmium were influenced by phytoplankton uptake, Prydz Bay Gyre in the upper water and re-mineralization of settling biogenic particulate; the resources and their constitution play the key role on the distribution of zinc and cadmium in the sediments and settling particles.(3)The biogenic input at the edge of ice shelf is relatively low comparing to the continental shelf and deep sea regions, which is mainly caused by a large amount of lithogenic particle inputs from melting ice; however, trace elements on the continental shelf and deep sea region are mainly from biogenic input, which is the result of high biomass on the continental shelf, and relatively low lithogenic input and intensive adsorption of zinc on the iron-and-manganese oxides, respectively. (4)The enrichment factors for zinc and cadmium by phytoplankton on the continental shelf in Prydz Bay are4.6×105and5.0×104, respectively; the uptake of zinc and cadmium by phytoplankton is characterized by the following: appropriate content of zinc leads to simultaneous uptake of both trace elements, extremely low content of zinc leads to stimulated uptake of cadmium, and high content of zinc inhibits the uptake of cadmium in contrast; zinc and cadmium are easily to degrade relatively to silica and they are almost simultaneous during degradation in the water column.(5) According to the perfect linear relationships among trace elements and biomass, nutrients, organic carbon and biogenic silica, and high preservation of zinc and cadmium with an average rate above50%in the sediments, zinc and cadmium could be the good proxies for the export phytoplankton production.The results of this work would provide new understanding to reveal whether zinc and cadmium are the limited micronutrients for the phytoplankton in the Prydz Bay and its adjacent area, and to demonstrate the possibility of zinc and cadmium to be the scientific proxies for the reconstruction of primary production in the upper water.