Research Document - 2014/049

Chemical and Biological Oceanographic Conditions in the Estuary and Gulf of St. Lawrence during 2011 and 2012

By S. Plourde, M. Starr, L. Devine, J.-F. St-Pierre, L. St-Amand, P. Joly, and P. S. Galbraith

Abstract

This document reports on the chemical and biological conditions in the Gulf of St. Lawrence (GSL) for 2011 and 2012 in the context of a strong warming event that began in 2008. Data from these two years are compared to time-series observations starting in 1999. Zooplankton indices and the spatial scales considered were modified from previous reports to match more closely those of other regions involved in the Atlantic Zone Monitoring Program (AZMP). All phytoplankton and zooplankton abundance indices and nutrient inventories were relatively coherent through the time series (1999–2012) among fixed stations, sections, and large subregions. Winter, spring, and fall surface nitrate inventories have been below the normal since 2010 in many regions of the Gulf. A shift to earlier timing of the spring bloom has also been observed since 2010 across many of the Gulf subregions. In addition, chlorophyll levels during late spring, summer, and fall have tended to be predominately below normal since 2010. There is evidence of ontogenetic and phenological changes in Calanus species that appear to be the direct effects of the warmer environmental conditions experienced by the region over the last few years. High abundances of large-bodied arctic and subarctic species occurring simultaneously with the near-record high surface temperature in 2012 suggest that these species avoid or adapt their life cycle strategy to minimize potential negative effects of warm conditions in the surface layer. At the same time, an increased abundance of warm-water species was observed. High abundances of cold/arctic species concomitant with those of warm-water species likely reflect the complex hydrography of the GSL system and highlight the Gulf’s position as a transitional zone between the “upstream” Labrador/Newfoundland shelf and the “downstream” Scotian Shelf.

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