Decadal-scale hydrographic and circulation variability in the Scotia–Maine regionSUM

Historical data, geostrophic computations and numerical circulation models are used to examine decadal-scale hydrographic “regime shifts” and associated circulation changes in the Scotian Shelf and Gulf of Maine region. Ocean temperature and salinity data indicate multi-year periods with cooler (by a few °C) and fresher (by a few 0.1 psu) conditions over the shelf and slope around 1940 and 1960, apparently associated with increased Labrador Current transport as suggested previously. Three-dimensional seasonal hydrographic fields for the cold 1960s period show the detailed structure of the hydrographic anomalies, including largest magnitudes in winter at depth along the shelf edge and extending into shelf basins, and at the surface over the continental slope. Model estimates of the associated circulation changes in winter and spring, obtained through prognostic model refinement of diagnostic fields, suggest that the predominant circulation feature of southwestward shelf-edge flow was increased by 1–2 Sv during the cold 1960s compared to the warm 1970s — an amount comparable to its climatological mean value. In contrast, the model solutions indicate limited decadal-scale variability in the major shelf circulation features away from the shelf edge. The relation of the Scotia–Maine decadal-scale variability to larger-scale variability in the northwestern Atlantic and its potential implications for ecosystems are discussed.