The Formation of High Nutrient–Low Salinity Water in the Gulf of Maine: a Nutrient Trap?

Waters with low salinity and high nitrate were identified in the south-western Gulf of Maine by Townsend and Christensen (1992). Their extreme characteristics were attributed to local remineralization processes, and the operation of a nutrient trap. This paper uses a newly compiled data set, and an algorithm relating nitrate to hydrographic properties to examine the occurrence and characteristics of this type of water. Observations of low salinity–high nitrate water are not uncommon, and represent approximately 20% of the database. Based on the occurrence of the most extreme waters of this type identified by the algorithm, it is concluded that two related mechanisms cause its formation. The mixing of low salinity Maine Surface Water with remnant Maine Intermediate Water in the fall starts this process. The interaction of newly formed Maine Intermediate Water with the spring freshet of Maine rivers completes it. These mechanisms can explain the formation of low salinity–high nitrate water, including ‘ nutrient trap ’ water, in general.