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Research Document - 2003/072

Optical chemical and biological oceanographic conditions in the Maritimes/Gulf Regions in 2002

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


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 2002 are reviewed and related to conditions during the preceding year and over the longerterm 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 2002 were, for the most part, comparable to conditions observed in previous years. Light attenuance, however, was higher (and euphotic depths shallower) at Shediac Valley, due in large measure to the higher than normal chlorophyll levels observed there throughout the year. Indices of stratification at the fixed stations followed patterns seen previously, however summer-time mixed-layer depths were shallower at Shediac Valley and deeper at Prince-5 in 2002 than in 2001. Winter-time mixed-layer depths in 2002 were also shallower at Halifax-2 than seen previously.

Surface nitrate levels at the Halifax-2 and Prince-5 fixed stations, along the seasonal sections and during groundfish surveys were generally comparable in 2002 to levels seen in 2001; levels were moderately elevated at the Shediac Valley station. Summer-time minimum nitrate levels at Prince- 5 were elevated and winter-time maximum levels at Halifax-2 were low in 2002 compared with the previous year; nitrate levels at Halifax-2 overall were lower than the climatological mean. Deepwater (>50 m) nitrate levels at the fixed stations were higher in 2002 than in 2001 but below the climatological mean. A similar pattern was seen in the nitrate levels of the deep central basins of the Scotian Shelf. Oxygen levels (% saturation) in bottom waters were lower in 2002 than in 2001.

A prominent feature of the phytoplankton in the Maritimes/Gulf Regions in 2002 was the persistent and widespread high concentrations of chlorophyll in the Southern Gulf of St. Lawrence, particularly evident in the September groundfish survey data. A greater proportion of the phytoplankton community was represented by diatoms at Shediac Valley in 2002 than in previous years. Notable also were the early onset of the spring bloom at Halifax-2 and delayed start at Prince-5 in 2002 compared with the previous year. Satellite-based chlorophyll data suggest also that the magnitude of the spring boom has progressively decreased on the eastern Scotian Shelf over the past 5 years. CPR data continue to show that contemporary phytoplankton levels are well above the longterm mean and that the timing of the spring bloom is earlier than observed in the 30-40 years ago.

Zooplankton levels, in general, declined at the Maritimes/Gulf fixed stations in 2002. This was most evident at Halifax-2 where abundance of total zooplankton, total copepods and the dominant copepod species, C. finmarchicus have shown a continuous decline since AZMP observations began in 1999. Zooplankton biomass observed during the groundfish surveys, however, indicated levels were about the same in 2002 as in 2001. 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 than 30-40 years ago, similar to the seasonal shift observed in phytoplankton abundance.

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