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Research Document - 2005/054

Optical, chemical, and biological oceanographic conditions in the Maritime/Gulf regions in 2004

By Harrison, G., D. Sameoto, J. Spry, K. Pauley, H. Maass, M. Kennedy, V. Soukhovtsev

Abstract

Optical, chemical, and biological oceanographic conditions in the Maritimes/Gulf regions (Georges Bank, eastern Gulf of Maine, Bay of Fundy, Scotian Shelf and Southern Gulf of St. Lawrence) during 2004 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, groundfish surveys, CPR, remote-sensing), some data from outside the Maritimes/Gulf regions are discussed also to provide the larger, zonal perspective.

Optical properties at the Maritimes/Gulf fixed stations in 2004 differed by site but were, for the most part, comparable to conditions observed in previous years. Mixed-layer depths at the Halifax-2 station in 2004 were deeper in early spring and late fall than observed previously. In addition, onset of stratification was later in spring and break-up earlier in fall than typically observed at this station.

Nitrate concentrations in surface waters in 2004 were higher in winter at the Halifax-2 and Prince-5 fixed stations and lower in summer at Halifax-2 than seen in previous years. Below surface (>50 m) nitrate concentrations were lower than observed in previous years at all fixed stations in 2004 and considerably lower than the climatological mean. Nitrate concentrations were also lower than observed previously in bottom waters of the Scotian Shelf in summer 2004 while concentrations were higher in bottom waters of the Southern Gulf in fall. The springtime reduction in surface nitrate concentrations at the Prince-5 fixed station occurred almost 2 month earlier in 2004 than in previous years.

The most prominent feature of the phytoplankton in the Maritimes/Gulf regions in 2004 was the widespread and strong spring bloom; peak chlorophyll concentratioins were close to the record high levels observed in 2003. High spring chlorophyll concentrations were most evident at the Halifax-2 fixed station, along the spring section survey on the eastern and western Scotian Shelf and in the Southern Gulf and on Georges Bank from satellite ocean colour data. At the Prince-5 fixed station, the bloom, although not as strong as in 2003, occurred almost two months earlier than in previous years. Surface chlorophyll levels were lower on the Scotian Shelf in summer and higher in the Southern Gulf in fall in 2004 than in the previous year. CPR data continue to show that contemporary 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.

Zooplankton biomass and C. finmarchicus abundance were lower in 2004 than in the previous year at the Shediac Valley fixed station and on the central and western Scotian Shelf (in spring). Biomass and C. finmarchicus abundance were higher in 2004 than in 2003 on Georges Bank in winter and on the central and eastern Scotian Shelf and in the Southern Gulf in fall. In 2004, the timing of C. finmarchicus reproduction at Halifax-2 appeared to be earlier than in the previous years. At all fixed stations, but most prominent at Prince-5, the contribution of Calanus to the copepod community has steadily increased over the past several years. CPR data continue to show that contemporary zooplankton levels are at or well below numbers observed during the decade of the 1960s/1970s when observations began.

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