Fall 2007 Update: Spring Chlorophyll Distribution

A general pattern is evident where chlorophyll concentration is greatest in continental shelf waters, intermediate over the deeper slope water, and lowest in the vicinity of the Gulf Stream and Sargasso Sea (see upper map figure showing concentration of chlorophyll during April 2006 from Cape Hatteras to Nova Scotia). High levels of chlorophyll during spring occur in the tidally mixed central areas of Georges Bank and Nantucket Shoals, and in the Middle Atlantic Bight estuaries and coastal waters enriched by estuarine plumes. The high chlorophyll values (3-8 mg m-3) in the western Gulf of Maine indicate that spring bloom is underway during April. The same geographic range is used to illustrate how chlorophyll conditions during April 2006 compare with the average values for this month, where the average is computed from April data from 1997 through 2006 (see lower map figure showing ratio of chlorophyll concentration). The ratio of April 2006 chlorophyll to the 9-year April mean chlorophyll indicates that levels in the western Gulf of Maine were above normal whereas levels over Nantucket Shoals and the SNE mid-shelf area were below normal values for April. Surface chlorophyll levels are also low just seaward of the Southern New England shelf break (100m isobath), reflecting the influence of the warm Gulf Stream meander on phytoplankton production in this region (see April temperature map above).

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