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Research Document - 2009/054

Optical, chemical, and biological oceanographic conditions in the Maritimes Region in 2008

By G. Harrison, C. Johnson, E. Head, 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 2008 are reviewed and related to conditions during the preceding year and over the longer-term, where applicable. In addition to descriptions of Atlantic Zonal Monitoring Program (AZMP) core data collections (fixed stations, seasonal sections, ecosystem trawl or groundfish surveys, remote-sensing), some data from outside the region are discussed also to provide the larger, zonal perspective.

Optical properties at the Maritimes fixed stations in 2008 differed by site but were, for the most part, comparable to conditions observed in previous years. The most notable features in physical structure of the water column in 2008 were the slightly stronger stratification and shallower summer mixed layers at Halifax-2.

Wintertime nutrient inventories in surface waters at Halifax-2 were above average in 2008, while they were at normal levels at Prince-5. Deep (>50 m) nutrient inventories in spring were higher than normal, shelf-wide. Summer surface and deep nutrient inventories were below average.

The record high and widespread spring bloom seen on the Scotian Shelf in 2007 did not recur in 2008. In fact, spring chlorophyll levels were at or below normal. On the other hand, fall chlorophyll levels were above average on the western shelf in 2008. Phytoplankton community structure at the 2 fixed stations in 2007 was similar to that seen in previous years with diatoms dominating during the spring bloom and flagellates dominating in summer-fall at Halifax-2 and diatoms dominating the community at Prince-5 year-round.

In 2008, zooplankton biomass and Calanus finmarchicus abundance both exhibited late peaks of near-average magnitude at Halifax-2 and both were above average in the summer. High C. finmarchicus abundance persisted in the fall. Two numerically dominant small copepod species, Pseudocalanus spp. and Oithona similis, and the shallow water copepod Temora longicornis, were more abundant than average on the eastern Scotian Shelf. At Halifax-2, cold water Calanus species (C. hyperboreus and C. glacialis) were more abundant than average, while warm water shelf species (Centropages typicus and Paracalanus spp.) were less abundant than normal. However, these trends were reversed on the Scotian Shelf. At Prince-5, zooplankton biomass and copepod abundance exhibited an earlier than average peak, which was dominated by offshore species such as Pseudocalanus spp. and Calanus finmarchicus. The copepod community at Prince-5 was dominated by offshore species in 2008, especially in the summer. The abundance of Limacina spp., a species susceptible to ocean acidification, remained low on the eastern Scotian Shelf and was close to average on the western Scotian Shelf.

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