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Research Document - 2008/044

Optical, chemical and biological oceanographic conditions in the Maritimes region in 2007

By G. Harrison, C. Johnson, E. Head, J. Spry, K. Pauley, H. Maass, M. Kennedy, C. Porter and V. Soukhovtsev

Abstract

Optical, chemical, and biological oceanographic conditions in the Maritimes region (Georges Bank, eastern Gulf of Maine, Bay of Fundy and the Scotian Shelf) during 2007 are reviewed and related to conditions during the preceding year and over the longer-term, where applicable. In addition to descriptions of AZMP core data collections (fixed stations, seasonal sections, ecosystem trawl (or groundfish) surveys, CPR, remote-sensing), some data from outside the region are discussed also to provide the larger, zonal perspective.

Optical properties at the Maritimes fixed stations in 2007 differed by site but were, for the most part, comparable to conditions observed in previous years. The most notable features in physical structure of the water column in 2007 were the slightly stronger stratification and shallower summer mixed layers at Halifax-2 and the record shallow summer-fall mixed layers at Prince-5.

Wintertime maximum nitrate concentrations in surface waters at Halifax-2 were at normal levels in 2007 while they were above normal at P-5. Deep (50-150 m) nutrient inventories in spring were lower than normal, shelf-wide. Summer levels and the depth of nitrate depletion were among the lowest (deepest) observed since systematic measurements began in 1999. Concentrations in deep waters were near normal at both stations.

The most prominent feature of phytoplankton in the Maritimes region in 2007 was the record high and shelf-wide spring bloom in April, with concentrations >8 mg m-2 penetrating to depths of 100 m and inventories approaching 1,000 mg m-2. Phytoplankton community structure at the two fixed stations in 2007 was similar to that seen in previous years with diatoms dominating during the spring bloom (~90%) and flagellates dominating (~50-80%) in summer-fall at Halifax-2 and diatoms dominating (~95%) the community at Prince-5 year-round. CPR data continue to show that contemporary (1990s/2000s) phytoplankton levels are at or above the long-term average and that the seasonal growth cycle starts earlier in the year than observed during the decade of the 1960s/1970s when observations began.

In 2007, zooplankton biomass and abundance were highly variable in space and time, as in past years. Zooplankton biomass and abundance, overall, were low in 2007, although near-record peaks in zooplankton biomass and C. finmarchicus abundance were observed at Halifax-2. Low zooplankton biomass was observed during the February, March, and July trawl surveys, at Halifax-2 during non-peak periods, and at Prince-5 throughout the year. Zooplankton seasonal zooplankton peak timing tended to be later than normal in 2007. Warm-water zooplankton taxa that are usually abundant during summer and fall were less abundant than normal on the Scotian Shelf, and some warmwater and off-shelf species were nearly absent. Arctic species were more abundant than normal on the eastern Scotian Shelf. At Prince-5, there was a major shift in community composition in the summer and fall, with low abundances of most of the normally dominant species, and a high abundance of two cladoceran species. The 2006 CPR data generally continued the trends of 2005. The abundance of C. finmarchicus early copepodid stages was close to normal on the Scotian Shelf and in the northwest Atlantic region. The abundance of C. finmarchicus late stages and euphausiids were higher than normal, and Para- and Pseudocalanus abundance was lower than normal on the Scotian Shelf, while the opposite was true in the northwest Atlantic region.

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