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

  • Author(s): Chen-Tung Arthur Chen
  • DOI: 10.3319/TAO.1992.3.1.59(O)
  • Keywords:
  • Citation: Chen, C.-T. A., 1992: Comparisions of Summer-Winter Carbonate and Nutrient Data in the Southwest Indian Ocean. Terr. Atmos. Ocean. Sci., 3, 59-80, doi: 10.3319/TAO.1992.3.1.59(O)

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.

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