博士 / 國立中山大學 / 海洋地質及化學研究所 / 92 / With regard to the concerns on the role of oceanic uptake of the increasing atmospheric CO2 concentration, a total of eight ocean time-series programs, have been established worldwide since the JGOFS era (i.e. late 1980s). Among these, the Southeast Asia Time-series Study (SEATS) site is the only one located in a “subtropical marginal sea”, namely the South China Sea (SCS). TA, TCO2, ��13CTCO2 and other pertinent chemical parameters were measured for seawater samples collected at the SEATS site from eight separate cruises between March 2002 and August 2003. Based on these measurements, the characteristics of the seasonal variability of CO2 species in the mixed-layer, the processes controlling the vertical distributions of NTA, NTCO2 and ��13CTCO2, and the magnitude of anthropogenic CO2 influence throughout the water column are thoroughly investigated to better understand the carbon cycles in such a subtropical marginal sea.
Results show that the decline of NTCO2 in spring-summer mainly results from in situ biological utilization in the mixed-layer, while the resurgence of NTCO2 in fall-winter is due to entrainment of the CO2-rich subsurface waters from below. Based on the drawdown of NTCO2 from winter to summer, the primary production is estimated to be 177�b34 ~ 363�b69 mgC m-2 day-1 in the mixed-layer. fCO2 increases progressively from spring to summer, then decreases from fall to winter. The seasonal variability of fCO2 is in phase with temperature changes, suggesting that the fCO2 seasonality is primarily controlled by temperature effect, though other factors have compensated partially to yield the observed low amplitude of its variability. The SEATS site is an atmospheric CO2 “source” in summer and early fall, but a “sink” in winter. The largest CO2 flux occurs in winter due to the high wind speed during winter monsoon. The annual sea-to-air CO2 flux at the SEATS site is estimated to be around -1.28�b0.94 to -2.73�b2.20 gC m-2 year-1.
A close examination on processes controlling the vertical variations of NTA, NTCO2 and ��13CTCO2 reveals that the increasing trend of NTA is resulted mainly from higher preformed-NTA and carbonate dissolution at deep, while organic oxidation and greater preformed-NTCO2 are responsible for the observed increasing trend in NTCO2. The decrease in ��13CTCO2 with depths, however, is principally owing to the decomposition of organic matter. Furthermore, carbonate dissolution accounts for approximately 30% of TCO2 production in the SCS deep waters, and it may have taken place at depths well above aragonite and calcite saturation depths at 600 m and 2500 m, respectively, in the SCS. Moreover, the penetration depth of anthropogenic CO2 at the SEATS site is estimated to be about 1200 m, based on both carbonate and ��13CTCO2 data. The ratio of the decrease of ��13CTCO2 to TCO2 increase, i.e. ����13CTCO2/�幅CO2, due to the uptake of anthropogenic CO2 is about -0.024‰ (�慆ol kg-1)-1.
| Identifer | oai:union.ndltd.org:TW/092NSYS5271004 |
| Date | January 2004 |
| Creators | Wen-Chen Chou, 周文臣 |
| Contributors | Chen-Tung Arthur Chen, David Der-Duen Sheu, 陳鎮東, 許德惇 |
| Source Sets | National Digital Library of Theses and Dissertations in Taiwan |
| Language | zh-TW |
| Detected Language | English |
| Type | 學位論文 ; thesis |
| Format | 211 |
Page generated in 0.0015 seconds