Date of Award

5-2011

Level of Access

Campus-Only Dissertation

Degree Name

Doctor of Philosophy (PhD)

Department

Oceanography

Advisor

David W. Townsend

Second Committee Member

Neal R. Pettigrew

Third Committee Member

Andrew C. Thomas

Abstract

While the Gulf of Maine has been historically well sampled relative to remote offshore regions, descriptions of the nutrient distributions and dynamics have provided only brief glimpses of restricted areas in space and time. The primary objectives of this study are to compile and evaluate the historical nutrient data within the region to determine the spatial and temporal variability of nutrient distributions, identify the environmental influences responsible for these patterns, and quantify the variability that exists within nutrient fluxes throughout the Gulf of Maine. Within five distinct regions in the Gulf of Maine, average seasonal cycles of dissolved inorganic nitrogen are similar, although there is regionally variable timing and magnitude of both nitrate and satellite measured chlorophyll biomass. A seasonal cycle of nitrate exists at all depths, however the variability is greater interannually than seasonally at depths greater than 50m. Seasonal surface anomalies can be explained by the timing of the spring phytoplankton bloom, correlated with salinity anomalies, and even related to zooplankton populations. All localized regions and depths within the Gulf of Maine are positively correlated, suggesting the entire Gulf typically varies as a cohesive unit. An objective analysis kriging interpolation generates a spatially explicit monthly climatology and identifies major features of the average nitrate concentrations in the water. This analysis also provides an objective measure of the historical sampling effort and indentifies locations and seasons lacking descriptive observations. A coupled nitrate-silicate box model for the Gulf of Maine shows that while nitrate is influenced heavily by offshore inputs, silicate has a dominant continental source. The historical data suggest biologically available nutrient fluxes can vary by as much as 50% annually and are highly dependent on outflows of Maine Intermediate Water. While the variability in nutrient concentrations is not the only factor determining biological productivity, these results show the possible influence of nutrient variability from a bottom-up trophic perspective within the Gulf of Maine.

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