Comparisons of Summer-Winter Carbonate and Nutrient Data in the Southwest Indian Ocean

西南印度洋二氧化碳及營養鹽之冬夏對比

陳鎮東(Chen-Tung Arthur Chen)

《Terrestrial, Atmospheric and Oceanic Sciences》 3卷1期 (1992/03) Pp. 59-80

摘要

1984年南半球冬季（七月）及1985年南半球夏季（二、三月）時，作者利用法國研究船Marion Dufresne號於西南印度洋取得了若干化學數據。取得之冬季數據代表南極中層水於其一個重要形成地區之起始値。有了起始値之後，方能研判南極中層水於印度洋流動時所產生之化學變化。
取得之數據可作冬夏對比，並且可與1978年Geosecs航次取得之數據比較。初步結果顯示：表水之pH，及鹽度標準化後之硝酸鹽(NNO3)，鹼度(NTA)及總二氧化碳(NTCO2)與水温間之變化呈直線關係；偏離直線之部份與次南極鋒面、亞熱帶鋒面、及赤道湧昇流有關；同一地點之硝酸鹽濃度及pH顯示相當大的季節性變化。於相同水温處相比，則變化較小；但NTA及NTCO2即使於相同水溫時相比，似乎亦顯現出季節性變化；南極水流至印度洋中部時所減少之NTA及NTCO2，可能能夠以消耗NNO3及水溫上昇解釋；殘餘之北大西洋深層水之鹽度信號甚小，不易辨別，但可輕易地由pH及總二氧化碳信號分辨出；營養鹽及溶氧亦有助於追蹤北大西洋深層水。

並列摘要

Chemical data were obtained in the southwestern Indian Ocean in the austral Winter (July) of 1984 and in the austral summer (Feb.-March)of 1985 aboard the French research vessel, MARION DUFRESNE. The winter data represent initial chemical concentrations in an important source region of the Antarctic Intermediate Water at the time of its formation. For the first time, one can evaluate variations in the chemical cycles in the Antarctic Intermediate Water of the Indian Ocean with reference to the source water in winter. These winter data were compared with our summer data and with the summer data obtained in 1978 during the GEOSECS Expedition. Preliminary results indicate the following: the surface pH and normalized nitrate, alkalinity and total CO2 values are found to correlate linearly with temperature; small deviations from the linearity are related to the Subantarctic and Subtropical Fronts and to the equatorial upwelling; large variations in nitrate and pH are found in surface waters collected at the same location but in different seasons; however, there is less variation between pH or normalized nitrate concentrations when compared at the same temperature; a seasonal difference in alkalinity and total CO2 may exist, even when compared at the same salinity and temperature; the decrease in alkalinity and total CO2 between the Antarctic Waters and the Indian Central Water found north of the Subtropical Front can perhaps be attributed to the decrease in nitrate and the increase in temperature; the remnant North Atlantic Deep Water(NADW), which has a very weak salinity signal, is identified clearly by pH and total CO2 data; and nutrient and oxygen data also help in tracing NADW.