Biological signature of Scotian Shelf Water crossovers on Georges Bank during spring 1997

Episodic crossovers of cold low salinity Scotian Shelf Water (SSW) onto the Northeast Peak of Georges Bank are a potentially important mechanism transporting plankton species, including the copepod Calanus finmarchicus and its prey and predators, onto the Bank each spring. We provide the first detailed investigation of horizontal and vertical zooplankton distributions in SSW crossovers compared to other onbank locations from three GLOBEC cruises during spring 1997. SSW crossovers are physically and biologically distinct from other Bank locations. In late spring, chlorophyll concentrations and in vivo fluorescence are elevated and light transmission is reduced in SSW, while during early spring, these parameters are more variable. SSW communities do not contain a unique zooplankton assemblage or indicator species but instead show differences in abundance and life history parameters for various taxa compared to other Bank locations. SSW has high abundances of young C. finmarchicus life history stages, almost no diel vertical migration of zooplankton, low abundances of invertebrate predators, and low fish egg abundance. Population development of C. finmarchicus in SSW lags that in adjacent water. The potential biological impact of SSW crossovers on Georges Bank varies seasonally. In April, density inversions and interleaving of SSW and non‐SSW suggest active mixing, resulting in similar community composition of SSW and adjacent non‐SSW. SSW crossovers are probably an important source to Georges Bank of young stages of C. finmarchicus in early spring. In May, after stratification strengthens, the greater differentiation between SSW plankton and elsewhere indicates that mixing between communities is more limited.