Nitrate Utilization in Surface Waters of the Iceland Basin during Spring and Summer of 1989

Oceanographic sampling at 59.5-degrees-N, 21-degrees-W over the spring and summer months of 1989 provided the basis to quantify the amount of new (nitrate) production and to evaluate the effect of selected environmental factors on new production. Surface water nitrate decreased linearly from 14 muM in early April to approximately 2.5 muM in August, and suggested that new production averaged 5.4 mmol NO3 m-2 day-1, almost double the rate suggested by a similar analysis at Ocean Weather Sta. P. Equivalent carbon export in the northern Iceland Basin would be 63 g C m-2 over this period. During a week in early July, it appeared that regenerated production compensated for a sharp decrease in new production to maintain carbon productivity at a fairly consistent level despite a decrease in F-ratio from 0.46 to 0.20. New production was predominantly associated with particles over 5 mum, although a subsurface (35m) peak in (NO3)-N-15 uptake may have been due to bacterial uptake. We suggest that light was the single-most dominant factor regulating nitrate uptake during this time. However the relationship between new production and light was non-linear in that the light efficiency of nitrate uptake varied significantly between stations in addition to variations in available light.