Distribution And Influencing Factors Of The Surface PCO₂in Jiaozhou And Sungo Bay During Spring

Coastal oceans play a disproportionally important role in oceanic carbon cycles,and have become a hotspot for present global carbon researches. In comparison withcontinental shelves, the offshore areas are affected more severely by humandisturbances and biological processes here are suffering more from human inputs.Within this condition, natural sink and/or source of CO2in the offshore areas aretotally changed or intensified. Studies on pCO2and air-sea CO2flux in the offshoreareas, which are affected seriously by human activities, contribute to clarifying thedominant mechanisms in the coastal carbon cycles. Both the Jiaozhou Bay, influencedby the urbanization and the Sungo Bay, mainly affected by farming activities ofshellfish are typically influenced by human activities. Based on field investigations inspring and the previous data, spatial distribution of pCO2in these two bays wereanalyzed and their air-sea CO2fluxes were estimated. In addition, controlling factorsof pCO2such as temperature and biological processes were discussed.The main conclusions are as follows:(1)Water in the Jiaozhou Bay mixed very well vertically during April, resultingin the fact that carbonate system of the sea surface was badly affected. The surfacepCO2ranged from392to597μatm, with an average of459μatm. As a result, thewhole Jiaozhou Bay acted as a source of atmospheric CO2, and the strong respirationwas responsible for this. Based on results from three classic models, the air-sea CO2flux of the Jiaozhou Bay was13.11mmol·m-2·d-1.(2)Annually, pH had obvious temporal and spatial distribution characteristics,with a range from7.28to8.73. Furthermore, monthly mean pH of the whole JiaozhouBay exhibited a two-peak pattern throughout the whole year. The variation range ofthe monthly mean pH in the eastern coastal area was larger than that of the otherregion. Temperature and biological processes were dominant in the annual distributionof pCO2and pH in the Jiaozhou bay. The Jiaozhou Bay acted as the atmospheric CO2sink in January, February and March, due to low temperature and strong primaryproduction. In addition, pH in these three months was at a higher level compared withother months. For April and May, high pCO2and low pH in the Jiaozhou bay was affected mainly by respiration. Temperature was responsible for the fact that theJiaozhou Bay acted as the source of atmospheric CO2even during phytoplanktongrowth peak in August; In September pCO2and pH were mainly controlled bytemperature and strong respiration process while respiration was the main reason forhigh pCO2and low pH during October. Temperature, together with biologicalprocesses affected the pCO2and pH, and the difference of them determined whetherthe Jiaozhou bay acted as a CO2source or sink.(3)Different from the Jiaozhou bay, surface pCO2in the Sungo Bay ranged from225to344μatm during the2012May, and it acted as an atmospheric CO2sink.Overall spatia1distribution of pCO2was distributed as follows: shellfishmono-culture zone<shellfish and seaweed polyculture zone<seaweed mono-culturezone<non-culture zone. Distribution of the surface pCO2, DO%, DIC and TA in theSungo Bay was controlled mainly by primary production. The air-sea CO2flux of theSungo Bay was-5.21mmol·m-2·d-1. Undoubtedly, this investigation was not enoughto conform that the Sungo Bay was the atmospheric CO2sink, and more observationsare still needed on large temporal-spatial scales. In addition, questions like how muchthe resuspension and degradation of the deposited particulate organic mattercontributes to the pCO2in the water-air interface, and how much the particulateorganic matter is actually buried are urgent to be solved.