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Research Document - 2004/67

Optical, chemical and biological oceanographic conditions in the Maritimes/Gulf Regions in 2003.

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

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 2003 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 2003 were, for the most part, comparable to conditions observed in previous years. Light attenuance, however, was lower (and euphotic depths deeper) at Shediac Valley than in the previous year, due in large measure to the lower (but more typical) chlorophyll levels observed there compared to the record high levels seen in 2002. Indices of stratification at the fixed stations followed patterns seen previously, however, winter-time mixed-layer depths were somewhat deeper at Halifax than seen in the previous year.

Nitrate levels below surface (>50 m) were somewhat lower at all the fixed stations in 2003 than seen in the previous year and considerably lower than the climatological mean (Halifax-2). Surface nitrate levels in winter, however, were higher at Halifax-2 and Prince-5 than in the previous year; levels at Halifax-2 were the highest seen in the 5-year AZMP data record for that station.

The most prominent feature of the phytoplankton in the Maritimes/Gulf regions in 2003 was the widespread and large spring bloom. Record high chlorophyll concentrations were seen at the Halifax-2 fixed station, during the spring seasonal sections survey and groundfish survey as well as being evident from Georges Bank to the Newfoundland coastal waters from satellite ocean colour data. At the Halifax-2 fixed station and adjacent waters, the bloom was not only of greater magnitude than seen before but also appeared to persist longer than normal. In contrast to most regions, chlorophyll levels were lower in 2003 in the Southern Gulf than seen in the previous year, however, in 2002 chlorophyll was unusually high in the Southern Gulf. The diatom-dominated phytoplankton community seen in the Southern Gulf in 2002 reverted in 2003 back to the more typical mix of diatoms and post-bloom flagellates. CPR data continue to show that contemporary phytoplankton levels are well above the long-term mean and that the seasonal growth cycle started earlier in the year than seen during the first decade of observations in the 1960s and 1970s.

Zooplankton levels, in general, increased at most sites in the Maritimes/Gulf regions in 2003. This was most evident at the Shediac Valley fixed station where the steady yearly increase in biomass and C. finmarchicus abundance reached record high levels in 2003. Higher C. finmarchicus abundance was also seen at Halifax-2, reversing the recent trend of declining numbers. In 2003, the timing of C. finmarchicus reproduction at Halifax-2 appeared to be later than in the previous year. At all fixed stations, but most prominent at Prince-5, the contribution of C. finmarchicus to the copepod community has steadily increase over the past few years; reaching highest fractions on record in 2003. Despite increases at the fixed stations, zooplankton biomass on Georges Bank in winter appears to be on the decline; lowest levels on record were observed in 2003. CPR data continue to show that contemporary zooplankton levels are well below the long-term mean and that the peak seasonal abundance of important species such as C. finmarchicus is occurring earlier in the year now that during the decade of the 1960s and 1970s when observations began.

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