Nutrient Dynamics on the NE Continental Shelf: Sample Analyses

David W. Townsend, University of Maine


The accelerated melting of the Greenland ice sheet and the Arctic ice cap in recent decades are well documented climate change-related phenomena that are cause for a broad range of environmental concerns.  One aspect of these phenomena that appears to be influencing marine ecosystems far removed from the Arctic is an apparent associated change in the circulation of the Labrador Sea and the Northwest Atlantic continental shelf and slope waters, which in turn appears to have resulted in an increased baroclinic transport of low salinity shelf waters to regions farther south.  Consequently, those changes are altering the water properties and nutrient regime in the Gulf of Maine over the past several decades.  Our retrospective analyses of available hydrographic data back to the 1960s have revealed that deep water layers in the Gulf (>100m) have become fresher and cooler, with lower nitrate but higher and more variable silicate concentrations over a period coincident with recent, rapid melting in the Arctic (Townsend et al. 2010).  Those changes in the nutrient regime may also be forcing changes in the structure of the planktonic ecosystem.
It is imperative that we seize all opportunities to collect and analyze hydrographic and nutrient data on the Northeast US Continental Shelf in order to continue to monitor what appears to be an ecosystem in the process of undergoing dramatic change.  In addition to individual, ongoing research programs like the NOAA-sponsored GOMTOX Program to study Alexandrium blooms in the Gulf of Maine and Georges Bank, which the PI is part of, we (Townsend’s laboratory at the University of Maine) have begun to analyze samples collected as part of the NOAA Northeast Fishery Science Center’s Ecosystem Monitoring Program in collaboration with Dr. Jon Hare.  They execute survey cruises approximately four times each year in the Gulf of Maine – Georges Bank – New England shelf region (Stations shown in Figure here).  At each station they make a CTD cast and collect plankton, but in support of our proposed work they have begun to collect water samples for nutrient analyses as part of their standard sampling and as of this date we have processed samples from two of their cruises.
We provide the NOAA cruise personnel sample vials and filters with which to collect water samples to be frozen at sea and analyzed on shore at UMaine for nitrate plus nitrite, silicate, phosphate and ammonium using standard autoanalyzer techniques.  Those data are delivered to NOAA following each cruise.
We propose here to continue this collaborative arrangement with the NEFSC and to continue to analyze nutrient samples they collect.  We are requesting here a modest $12,000 in Year 1 (five year total 65,314, which includes annual salary adjustments) to help defray a portion of our costs at the University of Maine.