Annual and interannual variability of nutrients and their estimated fluxes in the Scotian Shelf - Gulf of Maine region

Nitrate, silicate, and phosphate observations are used to determine their annual cycles for the Scotian Shelf and the Gulf of Maine. Concentrations increase from fall through winter, decrease rapidly at shallow depths in late winter, and remain at low levels through spring and summer. Deep layers exhibit a weak annual cycle with highest concentrations in summer. Winter nitrate concentrations (depth less than or equal to 50 m) are highest on the eastern Scotian Shelf, decreasing southwestwards into the Gulf of Maine. The Gulf of St. Lawrence is the primary source of nitrate (9300 mol.s(-1)) and silicate (7680 mol.s(-1)) during winter for the Scotian Shelf; in spring and summer, vertical diffusive fluxes, 1500-1000 mol.s(-1) for the central Scotian Shelf, are as large as the horizontal advective ones and can provide the entire nitrate requirement. The 50-m vertical diffusive fluxes of nitrate and silicate vary by a factor of 4 in the Scotian Shelf - Gulf of Maine region. The interannual variability of nitrate and dissolved oxygen on the Scotian Shelf are coupled to water mass changes, with low (high) nitrate and high (low) dissolved oxygen concentrations corresponding to the dominance of Labrador (Warm) Slope water.