Date of Award

12-2009

Level of Access

Open-Access Dissertation

Degree Name

Doctor of Philosophy (PhD)

Department

Oceanography

Advisor

Neal Pettigrew

Second Committee Member

Huijie Xue

Third Committee Member

Kate Beard

Abstract

The salinity and vertical density structure (stratification) of the Gulf of Maine strongly influence the physical and biological character of the region including: circulation and transport, vertical mixing, and primary productivity. Variability in salinity and stratification also provides insights into the character and timing of the oceanic waters entering the region, a key to predicting regional climate change. This thesis addresses outstanding questions related to variability in salinity and the relative role of salinity and temperature in creating stratification. Hourly observations from Ocean Observing System buoys throughout the Gulf provide the primary data source for this investigation. Analysis of estimated annual cycles, cross-correlations, and short-term (10-30 day) events indicate that Scotian Shelf Water (SSW) moves cyclonically around the Gulf, typically traveling from the southwest Scotian Shelf to Jordan Basin over one to two months and to the western Maine shelf over three to four months. SSW contributes to both freshening and salting, depending on season and location. River waters contribute to localized freshening of the Maine coastal shelf, especially during spring and autumn, and shelf waters contribute to near-surface (1m) freshening in Jordan Basin during the summer. The SSW, river inflows, and Slope Water contribute to seasonally and spatially variable stratification. Surface layer stratification is strongest in late July or early August, except on the western Maine shelf where peak stratification occurs in April, May, or June during years with large river inflows. Salinity is the primary determinant of stratification throughout the region. Salinity dominates surface layer stratification during winter, spring, and fall, and contributes 35-45% of the stratification during summer. Below 50m depth in Jordan Basin and the Northeast Channel mean temperature gradients are inverted and salinity completely supports stratification. A negative salinity anomaly of 0.6-0.8 in the surface, intermediate, and deep waters during 2004 and early 2005 occurred because of cold fresh Shelf Water inflows in February-April 2004 and September-November 2004, along with either less Slope Water or fresher Slope Water than average. St. Lawrence River discharge during 2003, unusual northerly winds, and unusually cold intermediate water on the Scotian Shelf may have contributed to these conditions.

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