Climate variability and vertical advection of nitrates in the Gulf of St. Lawrence, Canada

Abstract

Using a modeling approach, we constructed a time series to examine interannual vari- ability in the spring nitrate concentrations in the surface layer of the Gulf of St. Lawrence (GSL) for the period 1947 to 2000. This 2-step modeling approach used the lower boundary of the cold inter- mediate layer (CIL), a persistent summer characteristic of the temperature profiles in the GSL, to infer interannual variations in the depth of the winter mixed layer. Using a linear model describing the dis- tribution of nitrates at intermediate depths, we estimated a time series of spring nitrate concentration in the surface waters of the GSL for the period 1947 to 2000. This early spring time series showed interannual fluctuations in nitrate concentrations of about 1 order of magnitude, attributable to vari- ability in winter convection. Such variability in the spring nitrate availability should have a significant impact on the ecosystem. Some elements that should be taken into account in any future attempt to validate this estimated nitrate time series are discussed.