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Research Document - 2016/003

Optical, chemical, and biological oceanographic conditions on the Scotian Shelf and in the eastern Gulf of Maine in 2014

By C. Johnson, B. Casault, E. Head, and J. Spry


The Atlantic Zon4 Monitoring Program (AZMP) derives its information on the marine environment and ecosystem from data collected at a network of sampling locations (fixed point, high frequency sampling stations, cross-shelf sections, ecosystem trawl surveys) in each Fisheries and Oceans Canada region (DFO; Québec, Gulf, Maritimes, and Newfoundland) sampled at a frequency of twice-monthly to once annually. This report provides an assessment of the distribution and variability of nutrients and plankton on the Scotian Shelf and in the eastern Gulf of Maine, focusing on conditions in 2014. Surface and deep ocean temperatures were warmer than average overall in the DFO Maritimes Region in 2014, especially in the slope waters and western Scotian Shelf in the second half of the year. Stratification was higher than average at an annual scale, but stratification anomalies were variable at sub-annual scales at the fixed stations and deep mixing events were observed at Halifax-2 in late winter and spring. Although annual average anomalies of surface- and deep-layer nitrate were near normal in most areas, there was substantial sub-annual variability in nitrate anomalies, particularly for deep-layer nitrate at Halifax-2. Scotian Shelf spring phytoplankton bloom magnitudes observed by remote sensing were low, while summer-fall blooms were higher than average in several areas. Spring blooms at the fixed stations were unusually deep, and therefore their magnitude would not have been accurately represented in satellite ocean colour observations. Both zooplankton biomass and Calanus finmarchicus abundance were lower than average overall in 2014. The abundance of Arctic Calanusspecies, an indicator of cold water on the Scotian Shelf, was lower than average in 2014, while the abundance of warm offshore species was higher than average on the central and western Scotian Shelf. Higher than average occurrence of thaliaceans (mainly salps) was observed, perhaps related to strong sub-annual variability. Ocean conditions in the DFO Maritimes Region have been characterized by strong sub-annual and mesoscale variability in 2013 and 2014, in addition to warmer temperatures, and interannual variability has been strong during the AZMP period since 1999. It is important to evaluate not only how the ecosystem responds to changes in mean conditions but also the response to changes in sub-annual to interannual variability. Continuous Plankton Recorder (CPR) sampling showed that in 2013 abundances of Calanus I-IV and C. finmarchicus V-VI returned to normal or relatively high levels from the historically low levels seen in 2012 across the Scotian Shelf. C. glacialis, C. hyperboreus and Oithona spp. were at near normal levels shelf-wide. Anomalies for three indices of phytoplankton abundance were below or close to normal on the Eastern Scotian Shelf (ESS) but above or close to normal on the Western Scotian Shelf (WSS). Many zooplankton taxa also exhibited contrasting patterns for the annual average abundance on the ESS versus the WSS.

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