Inter-annual variability of shelf water volume on the northeastern Canadian and United States continental shelf, 1973–2013

Abstract

Understanding the variability of waters confined to the northeastern United States and Canadian continental shelf is essential in determining factors that influence hydrographic patterns and structure, changes in fisheries stocks and planktonic assemblages, and the impact of Arctic warming. Shelf waters (SHW) located between Newfoundland and Cape Hatteras are characterized by lower salinity (<34 PSU) and lower temperatures than the generally warmer and more saline slope waters located farther offshore. Significant inter-annual variability of SHW volume has been noted from previous studies within the more limited Mid Atlantic Bight sub-region. Multiple factors may impact the volume of SHW, including local and remote river runoff and precipitation, release and equator-ward transport of fresh water from the Arctic and sub-polar gyre, ice melt from Greenland, cross-shelf removal, and both vertical and horizontal mixing processes. Here, we estimate inter-annual variability of SHW volume over the large shelf domain located between Newfoundland and Cape Hatteras from 1973 through 2013. Objectively-analyzed (OA) annual mean SHW thickness and error (as a percent of data variance) is computed for each of eleven sub-regions spanning our study domain for the 41-year period. Results show significant decreasing trends in SHW volume within 5 of the 11 sub-regions (The Grand Banks through the Eastern Scotian Shelf sub-regions) in agreement with previous work which has shown a decreasing trend of northern Labrador Current transport. OA annual mean SHW volume anomalies were cross-correlated with annual mean shelf slope front (SSF) position anomalies for corresponding sub-regions, displaying a highly significant relationship for the Georges Bank, the Mid Atlantic Bight, and the DelMarVa Hatteras shelf, with higher volumes corresponding to more offshore SSF positions. Annual mean near-surface salinity anomalies, when cross-correlated with OA annual mean SHW volume anomalies, displayed significant positive correlations from the Gulf of St. Lawrence northeast to the Newfoundland shelf and displayed primarily negative correlations from the Gulf of Maine to the DelMarVa Hatteras sub-region. The North Atlantic Oscillation annual indices displayed significant cross-correlations with annual mean OA SHW volume anomalies only for the Tail of the Grand Banks and Georges Bank., There were no significant cross correlations computed between the OA annual mean SHW volume anomalies and the NAO winter index for corresponding years.