Nitrogen uptake rates and f-ratios in the Equatorial and Southern Indian Ocean

摘要

We report data on nitrate, ammonium and urea uptake rates from the Equatorial and Southern Indian Oceans. Productivity (0.81-2.23 mmol N m(-2) d(-1)) over the Equatorial Indian Ocean was low, but the f-ratio (0.13-0.45) was relatively high. In the Southern Indian Ocean total N-uptake rate varied from 1.7 to 12.3 mmol Nm(-2) d(-1); it was higher in the Antarctic coast (69 degrees S) and lower over most of the Southern Ocean, the lowest being at 58 degrees S. The f-ratio also showed significant spatial variation, but was higher compared to values at the Equatorial Indian Ocean. The mean f-ratio in the Southern Indian Ocean was 0.50. The nitrate-specific uptake rates and f-ratios appear to have increased significantly in the recent past relative to earlier estimates. While productivity in the Southern Ocean is comparable to that in the Equatorial Indian Ocean, higher f-ratios in the former underscore its importance in the uptake of CO2.