Marine Science Faculty Publications

Winter-summer Variations of Calcite and Aragonite Saturation in the Northeast Pacific

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New carbonate data obtained on February-March and June-July cruises in the northeast Pacific during 1985 were utilized to describe processes affecting seasonal variations of calcite and aragonite saturation. Large gradients in saturation state occur in the region between the Subtropical and the Subarctic Fronts in the north-south direction. These gradients are a function of largescale mixing and biological processes in the North Pacific. The saturation values in the upper kilometer of the water column were observed to be significantly lower in winter than in summer. These decreases were due to a number of processes including: (i) the seasonal decrease in the temperature of the water column; (ii) the seasonal increase in vertical mixing causing CO2-enriched deep waters to be upwelled; and (iii) the seasonal enhancement of respiration over photosynthesis. Seasonal changes in total CO2 (TCO2) concentrations appeared to have the greatest overall effect on the saturation state. Aragonite dissolution rate experiments were conducted during the June-July cruise to provide an independent verification of the saturation calculations. In all cases, significant increases in aragonite dissolution were observed below the 100% saturation depth. In the northeast Pacific, shallow undersaturation horizons provide for significant dissolution rates at depths below 400 m.

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Marine Chemistry, v. 25, issue 3, p. 227-241