A sink for atmospheric carbon dioxide in the northeast Indian Ocean (original) (raw)

Abstract

Intensive observations in the northeast Indian Ocean (Bay of Bengal) during the presouthwest and northeast monsoon seasons of 1991 reveal that freshwater discharge from rivers of the Indian subcontinent exerts the dominant control over total carbon dioxide (TCO2) and pCO 2 distributions in surface waters. Low pCO 2 levels occur within the low-salinity zones, with a large area in the northxvestem bay acting as a sink for atmosl:heric CO 2. Only a part of the observed pCO 2 variation can be accounted for by the effect of salinity, and biological production suppoaed by external nutrient inputs in conjunction with strong thermohaline stratification may be more important in lowering surface water pCO 2 by > 100 patm relative to that in the atmosphere. The pCO 2 distribution is seasonally variable and appears to be controlled by the spreading of fresher waters by the prevailing surface circulation.

Figures (4)

Figure 1. Distribution of salinity (in practical salinity units) at sea surface in the Bay of Bengal during (a) pre- southwest monsoon and (b) northeast monsoon.

Figure 1. Distribution of salinity (in practical salinity units) at sea surface in the Bay of Bengal during (a) pre- southwest monsoon and (b) northeast monsoon.

Figure 2. As in Figure | for total carbon dioxide (TCO,) in micromolars.

Figure 2. As in Figure | for total carbon dioxide (TCO,) in micromolars.

Figure 4. Relation between salinity and pCO, (in microatmos- pheres) in the upper 30 m of the Bay of Bengal during the northeast monsoon. Solid line indicates the pCO, expected from conservative mixing between riverwater and seawater. The most interesting feature of Figure 3 is that a large area of the Bay of Bengal is characterized by pCO, levels far below those in the atmosphere (~350 patm), particularly during the northeast monsoon when the air-sea pCO, gradient sometimes exceeds 100 jzatm. The relationship between pCO, and salinity, exemplified by the northeast monsoon data that showed large salinity variations (Figure 4), together with Figures 1 and 3, suggests that thi. deficiency is closely related to river runoff and the subsequent spreading of fresher waters by the prevailing

Figure 4. Relation between salinity and pCO, (in microatmos- pheres) in the upper 30 m of the Bay of Bengal during the northeast monsoon. Solid line indicates the pCO, expected from conservative mixing between riverwater and seawater. The most interesting feature of Figure 3 is that a large area of the Bay of Bengal is characterized by pCO, levels far below those in the atmosphere (~350 patm), particularly during the northeast monsoon when the air-sea pCO, gradient sometimes exceeds 100 jzatm. The relationship between pCO, and salinity, exemplified by the northeast monsoon data that showed large salinity variations (Figure 4), together with Figures 1 and 3, suggests that thi. deficiency is closely related to river runoff and the subsequent spreading of fresher waters by the prevailing

Figure 3. As in Figure 1 for pCO, (in microatmospheres).

Figure 3. As in Figure 1 for pCO, (in microatmospheres).

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