The Seasonal Evolution Of Co₂ Source/ Sink Between Autumn And Winter In Jiaozhou Bay

Continental shelf as a transition zone between the land and the ocean, is easily impacted by anthropogenic activities because of its adjacent to the land and special geography structure, in addition to primary production, mineralization, upwelling and runoff which make it complicated to evaluate its CO2 sink/source mechanism, and also the hot spot for all the researchers around the world. As the most intensify interact area between the land and ocean ecosystem, estuary and bay has become the highlight researching area in land-ocean interaction and global carbon cycle. But there's not enough discussion on the carbon cycle and sink/source mechanism of China continental shelf, estuary and bay. Distribution seasonal variation and influencing factors of temperature, organic degradation and phytoplankton activity were discussed based on the data obtained through continuous underway measurements of surface water pCO2 and associated parameters in Jiaozhou Bay in November,2007 and February,2008.The highest value of pCO2 appears at the Licun river estuary, and decrease from the Licun river estuary to the southwest of the bay in autumn. The pCO2 range from 315 to 720μatm and the average is 423μatm,△pCO2 range from-82 to 235μatm and the average is 32μatm. The whole Jiaozhou bay acts as a source in autumn. Temperature don't play the main role on the distribution of pCO2. Urbanization has greatly affected the Jiaozhou Bay in autumn and the extent of organic pollution in the near shore area is apparently higher than the middle and the mouth of the bay. The experiment of organic degradation shows that the respiration level of Jiaozhou Bay is on a quite high level,pCO2 and DOC is always correspond with the level of respiration, and the distribution of pCO2 is greatly affected by organic degradation. In the mean time, because of affluent nutrient brought in case of runoff and seaculture, apart from the mouth of the bay and the seaculture area in the northeast bay, phytoplankton activity also has affected the distribution of the bay, especially the western coastal area where Chl a and DO saturation value is high. The distribution of pCO2 in autumn is mainly affected by organic degradation and phytoplankton activity. There's an obvious stepwise distribution of pCO2 in Jiaozhou Bay Winter which increasing from the northern part to the mouth of the bay.The pCO2 value range from 145 to 361μatm with the average 236 uatm,△pCO2 value between-235 to -70μatm with the average-135μatm. The whole Jiaozhou bay acts as a strong sink in winter. In case of the freezing of the land, except the east near shore area which is greatly affected by the urbanization, other part of the bay is hardly influenced by the land. Temperature's influence on the distribution of the pCO2 can be neglected since the variation range of the temperature is about 1℃. Organic degradation has weak influence on the pCO2 whereas the pollution level, temperature and the amount of the heterotrophy bacteria is low.In this paper, three gas exchange coefficients calculated from the Liss & Merlivat(1986), Wanninkhof(1992), McGillis et al.(2004) and the average wind speed are used to estimate the monthly and seasonally flux of the Jiaozhou Bay. The carbon flux is 2.76 mmol m-2 d-1 in November and-14.54 mmol m-2 d-1 in February. In autumn, the whole bay acts as a source and can release 0.90*103tC to the atmosphere. In winter, the whole bay acts as a strong sink and can absorb about 4.76*103tC from the atmosphere. It can be found that seasonal variation of CO2 source/sink in Jiaozhou Bay is significant. The absorbing flux in winter is about five times of autumn's releasing. The results show that temperature, organic degradation and phytoplankton activity play important roles in seasonal variation of pCO2 and CO2 flux from autumn to winter. The results calibrated and calculated from Takahashi(1993) and Takahashi et al.(2002) calculations also showed that the role of temperature and biological activities in seasonal variation of pCO2 are about the same, and they control the seasonal variation of pCO2 together.