The significance of the Mississippi River drainage for biological conditions in the Northern Gulf of Mexico.
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Plankton collections and bottom hauls made during the 1935 expedition of the Atlantis to the Gulf of Mexico suggested that there is a zone of high productivity in the shallow water area near the mouth of the Mississippi, and since the effect of river outflow on ocean life is a phase of marine biology which has not yet received adequate attention, further investigation seemed desirable. The present work was therefore undertaken during the 1937 cruise of the Atlantis, jointly sponsored by the Woods Hole Oceanographic Institute and Yale University (Bingham Oceanographic Laboratory), in an attempt to determine whether or not the incoming nutrients from the Mississippi have an observable quantitative effect on plant growth and nutrient matter present in the Gulf of Mexico. The Mississippi River carries large quantities of nutrient salts into the Gulf of Mexico. The quantity of phosphate per unit volume is approximately four times as much as the amount found in the sea water of the surrounding region. In the Gulf there is a superficial zone of high phosphorus content around the mouth of the Mississippi, extending from Mobile Bay westward to Longitude 91 . Evidence is presented to show that this phosphorus is largely derived from the Mississippi and that the soluble phosphate of the river is more important in this respect than that in organic combination. There is a zone of high phytoplankton content near the river which roughly coincides with the area of high phosphorus. A causal connection between the two is indicated. It is suggested on purely theoretical grounds that some other nutrient which is discharged from the Mississippi in the same manner as phosphate is a limiting factor in this region. A few notes are presented on the distribution of copper in the Gulf. It was present in all samples analyzed in both soluble and combined form. In deep water there appears to be a slight accumulation of soluble copper in the hypothalassa.