Abstract
The seasonal evolution of dissolved inorganic carbon (DIC) and CO2 air-sea fluxes in the Jiaozhou Bay was investigated by means of a data set from four cruises covering a seasonal cycle during 2003 and 2004. The results revealed that DIC had no obvious seasonal variation, with an average concentration of 2035 mu mol kg(-1) C in surface water. However, the sea surface partial pressure of CO2 changed with the season. pCO(2) was 695 mu atm in July and 317 mu atm in February. Using the gas exchange coefficient calculated with Wanninkhof's model, it was concluded that the Jiaozhou Bay was a source of atmospheric CO, in spring, summer, and autumn, whereas it was a sink in winter. The Jiaozhou Bay released 2.60 x 10(11) mmol C to the atmosphere in spring, 6.18 x 10(11) mmol C in summer, and 3.01 x 10(11) mmol C in autumn, whereas it absorbed 5.32 x 10(10) mmol C from the atmosphere in winter. A total of 1.13 x 10(11) mmol C was released to the atmosphere over one year. The behaviour as a carbon source/sink obviously varied in the different regions of the Jiaozhou Bay. In February, the inner bay was a carbon sink, while the bay mouth and the Outer bay were carbon sources. In June and July, the inner and Outer bay were carbon sources, but the strength was different, increasing from the inner to the outer bay. In November, the inner bay was a carbon source, but the bay Mouth was a carbon sink. The outer bay was a weaker CO2 Source. These changes are controlled by many factors, the most important being temperature and phytoplankton. Water temperature in particular was the main factor controlling the carbon dioxide system and the behaviour of the Jiaozhou Bay as a carbon source/sink. The Jiaozhou Bay is a carbon dioxide source when the water temperature is higher than 6.6 degrees C. Otherwise, it is a carbon sink. Phytoplankton is another controlling factor that may play an important role in behaviour as a carbon source or sink in regions where the source or sink nature is weaker.
Highlights
It has been shown that the ocean is a net sink for atmospheric carbon dioxide and can absorb 2 pg C every year (Sabine et al, 2000; Dyrssen, 2001; Miller et al, 2002; Takahashi et al, 2002)
Jiaozhou Bay was a source of Bay released 2.60 × 1011 mmol atmospheric CO2 in C to the atmosphere in spring, 6.18 × 1011 mmol C in summer, and 3.01 × 1011 mmol C in autumn, whereas it absorbed 5.32 × 1010 mmol C from the atmosphere in winter
Phytoplankton is another controlling factor that may play an important role in behaviour as a carbon source or sink in regions where the source or sink nature is weaker
Summary
It has been shown that the ocean is a net sink for atmospheric carbon dioxide and can absorb 2 pg C every year (Sabine et al, 2000; Dyrssen, 2001; Miller et al, 2002; Takahashi et al, 2002). Other studies show that they can absorb about 0.2 to 1 pg C every year (Tsunogai et al, 1999; Liu et al, 2000; Frankignoulle and Borges, 2001; DeGrandpre et al, 2002; Chen, 2004; Thomas et al, 2004) It is currently uncertain whether shelf seas act as a net sink or source of atmospheric CO2 , because shelf seas are strongly affected by both natural and human activities. Anderson and Mackenzie (2004) modelled in detail the change of air-sea fluxes for the coastal ocean since pre-industrial times and suggested that the shallow-water ocean environment has served as a net CO2 source throughout most of the past 300 years, but its role as a source has substantially decreased and the net flux is expected to be reversed at some point in time. Some studies have estimated the air-sea CO2 flux of coastal seas (Borges, 2005), more data are necessary to fully understand the coastal contribution to the marine carbon cycle
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