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Research Document - 2006/081

Optical, chemical and biological oceanographic conditions in the Maritimes/Gulf regions in 2005

By Harrison, G., D. Sameoto, J. Spry, K. Pauley, H. Maass, M. Kennedy, C. Porter and 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 2005 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 2005 differed by site but were, for the most part, comparable to conditions observed in previous years. Mixed-layer depths at the Prince-5 station in 2005 were shallower and stratification stronger than observed previously. At the Halifax-2 station, the onset of stratification was later, by ~months, than typically observed at this station.

Nitrate concentrations in surface waters in 2005 were lower in winter at the Halifax-2 and Prince-5 fixed stations and lower in summer at the Shediac station than seen in previous years. The depth of the nitrate depletion zone at Halifax-2 was the deepest observed since systematic measurements began in 1999. In addition, deep (>50 m) nitrate concentrations were the lowest on record at Halifax-2 and considerably lower than the climatological mean.

The most prominent feature of the phytoplankton in the Maritimes/Gulf regions in 2005 was the strong but short-lived spring bloom; peak chlorophyll concentrations at the Halifax-2 station were close to the record high levels observed in 2003 but the bloom’s duration was the shortest on record (half the long term average duration). High springtime chlorophyll concentrations were also evident along the shelf section surveys; record high levels were observed along the Halifax line. At the Prince-5 fixed station, in contrast, chlorophyll concentrations were the lowest since observations began in 1999 and the peak growth season started later than usual. 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.

Zooplankton biomass and C. finmarchicus abundance were geographically and seasonally highly variable in 2005. Record high C. finmarchicus numbers were observed in Cabot Strait in spring but numbers were at record lows in fall. Higher than usual C. finmarchicus numbers were also seen on the central Scotian Shelf in fall. Zooplankton biomass from the spring and summer Scotian Shelf groundfish surveys was the lowest seen since observations began in 1999. 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 below those observed during the decade of the 1960s/1970s, however, some species (e.g. C. finmarchicus) appear to be recovering.

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