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Research Document - 2007/050

Optical, chemical and biological oceanographic conditions in the Maritimes region in 2006

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 region (Georges Bank, eastern Gulf of Maine, Bay of Fundy and the Scotian Shelf) during 2006 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 to provide the larger, zonal perspective.

Optical properties at the Maritimes fixed stations in 2006 differed by site but were, for the most part, comparable to conditions observed in previous years. Stratification, however, was slightly stronger than usual at both stations during the latter half of the year.

Winter maximum nitrate concentrations in surface waters at Halifax-2 continued to decline in 2006 and in summer, the depth of the summer nitrate depletion zone was among the deepest observed since systematic measurements began in 1999. Nitrate concentrations at Prince-5, in contrast, continued to increase in 2006.

One of the most prominent features of phytoplankton in the Maritimes region in 2006 was the weakened and short-lived spring bloom at Halifax 2 compared with the strong blooms of the previous three years. Over the observation period of AZMP, the spring blooms at this station have been starting later and ending earlier and background chlorophyll levels have been decreasing. At Prince-5, chlorophyll concentrations were higher than usual in 2006 and the summer maximum occurred two months later than normally seen. 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 Calanus finmarchicus abundance were highly variable (geographically and seasonally) in 2006. Zooplankton biomass, overall, was lower in 2006 than seen previously; record low levels were seen during the March groundfish survey. Calanus finmarchicus abundance was also low at the Halifax-2 fixed station, especially the younger developmental stages, and was at record low levels on the central Scotian Shelf during the spring section survey. On the other hand, C. finmarchicus numbers were higher than usual in 2006 at the Prince-5 fixed station and on the western Scotian shelf in spring, central shelf in fall and was at record high levels shelf-wide during the summer groundfish survey. Smaller copepod species (Pseudocalanus sp., Oithona sp.) at Halifax-2 have been decreasing over the past few years in relative abundance and biomass compared with the larger species (C. finmarchicus, Metridia sp.). CPR data continue to show that contemporary zooplankton levels are at or below those observed during the decade of the 1960s/1970s, however, several species (e.g. C. finmarchicus, Paracalanus/Pseudocalanus sp., euphausiids) are recovering, particularly on the Scotian Shelf.

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