Research Document 2017/009

Optical, chemical, and biological oceanographic conditions on the Newfoundland and Labrador Shelf during 2014-2015

By Pepin, P., Maillet, G., Fraser, S., Doyle, G., Robar, A., Shears, T., and G. Redmond

Abstract

The cold winters of 2014 and 2015 resulted in colder conditions than had been observed since 2010 which had consequences to the biogeochemical state of the Newfoundland and Labrador (NL) Shelves. Integrated (50 m – bottom) silicate and nitrate inventories recovered somewhat in 2015 relative to the long-term decline that had been observed since at least 2008, although the increase was modest, with the exception of deep nitrate inventories on the Labrador Shelf. Cooler than normal conditions in 2014-15 resulted in a delayed onset of the spring phytoplankton bloom of lower magnitude and reduced integrated chlorophyll concentration, relative to the average, throughout much of the region. The abundances of Oithona similis, Pseudocalanus sp. Temora longicornis and Triconia sp. are at or near record levels of abundance from the Bonavista Bay to the southern Grand Banks sections. In contrast, the abundance of the dominant large copepods (Calanus finmarchicus, Calanus hyperboreus, and Calanus glacialis) has been declining for the last 3–5 years throughout much of the region, although there are local exceptions that have seen an increase for which the cause remains unclear. The overall pattern of variation among the three trophic levels surveyed in this report (nutrients, phytoplankton biomass, and zooplankton abundance) does not reveal any clear association among trophic levels but some consistency in some trends may be starting to provide new insights into trophic relationships. More comprehensive analyses and modelling are required to understand the drivers of change in productivity on the NL Shelves.

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