Air-sea CO₂Flux In Jiaozhou Bay And Its Controls

Despite their relatively small area, continental shelves are more subject tocomplex biogeochemical processes. Recently, coastal ocean is considered as the hotspots for scientific researchers for its extremely high air-sea CO2flux anddistinguished pCO2spatial-temporal variation. It is of high importance to realize thesink/source role and trophic state of the continental shelves based on variousbiogeochemical processes including remineralization, biological activity, upwelling,river input, thermal dynamics and anthropogenic effect.Based on nine cruises and a series of measured chemical parameters includingpartial pressure of carbon dioxide (pCO2), dissolved oxygen (DO), dissolvedorganic/inorganic carbon (DOC/DIC), alkalinity (TA), chemical oxygen demand(COD) etc in Jiaozhou Bay, we are aiming to answer the following questions: Whichfactors control the annual distribution of sea surface pCO2in Jiaozhou Bay? Whichelse biogeochemical processes should be considered when the open-water NetCommunity Production (NCP) calculation was applied in Jiaozhou Bay? What’s theannual air-sea CO2flux in Jiaozhou Bay?(1) Annually, pCO2ranged from148to1112μatm with an average of474μatm.Spatial distribution of pCO2in the eastern coastal area was controlled by respirationin most of the year except for winter due to urbanization-induced sewage input allalong the year; primary production and respiration controlled the spatial distributionof pCO2in the other region of Jiaozhou Bay alternatively: praimary productionprevailed in summer and winter in accordance with the bimodal distribution of thephytoplankton, and respiration overwhelmed in spring and autumn.Both temperature and biological activity controlled the seasonal variation ofpCO2in Jiaozhou Bay. On an annual baisis, biological activity showed a dominantcontrol on pCO2variation in the eastern coastal area, which again showed the impactfrom urbanization; temperature effect on the annual variation of pCO2was slightlyhigher than that from biological activity. (2) Jiaozhou Bay acted as a source to the atmospheric CO2for most of the yearexcept from January to March when the whole bay acted as a carbon sink. Februaryhad the highest air-sea CO2influx (-13.87mmol m-2d-1) while October occupied thehighest efflux (21.27mmol m-2d-1). The whole bay acted as a carbon source annuallywith a flux of5.08mmol m-2d-1, which equals a release of6.74×103ton carbon to theatmosphere.(3) Jiaozhou Bay is heterotrophic annually based on three simple models we used.The first two models were open-water DIC/O2methods and the third models paidmore attention to the DIC difference within a cruise during physical mixing. JiaozhouBay is annualy heterotrphic with a net community production between-2.84to-2.55mmol m-2yr-1. There is a large uncertainty from the open water O2method which mayattribute to nitrification, diverse land input and air-sea O2exchange.