Deuterium Distribution in the Gulf of Mexico

Abstract

The variations of the stable isotopes of hydrogen (protium and deuterium) were determined in the various water masses of the Gulf of Mexico. Surface waters of the central Gulf were found to have an average δD=5.6‰ relative to Standard Mean Ocean Water (SMOW), whereThe subsurface water masses, Subtropical Underwater, Antarctic Intermediate Water, and Gulf Basin Water, were found to be characterized by deuterium contents of 5.0–5.5, −0.5 and 0.9‰, respectively. In addition, a high deuterium feature (δD=5.5–6.3‰) was shown in the water column at about 100 m depth just above Subtropical Underwater. The δD values for the fresh water contribution to the Gulf via the Mississippi and Coatzacoalcos Rivers were found to be −42.3 and −19.3‰, respectively. The value for the net fresh water addition to the Gulf was ∼−33‰. The isotopic composition of near-shore waters is consistent with a simple mixing model of fresh water from runoff with ocean water modified by the mixing of sea waters from distinct sources.