The Gulf of Mexico receives many nutrients from the rivers that empty into it, especially the Mississippi River, causing the Gulf’s northern shelf waters to become overly enriched and more susceptible to algae growth.
However, it remains largely obscure whether a significant portion of those nutrients ever leaves the Gulf to impact the chemistry of the North Atlantic Ocean potentially.
It is essential to track the nutrient input from the Mississippi and Atchafalaya River System to the Gulf as those nutrients contribute to harmful algal blooms on the Northern Gulf Shelf.
In a new study, scientists from Florida State University are shedding light on nutrient levels in the Gulf of Mexico. To conduct the study, the team collected and analyzed water samples taken during four different research cruises to the Gulf and the Florida Straits from 2011 to 2018.
This finding is valuable to know, as these ecosystems must harbor the nutrient burden.
Scientists did not found any evidence that nitrate from the Mississippi-Atchafalaya River System is mixing across the Northern Gulf shelf into the Gulf of Mexico’s open waters. The findings are consistent with recent modeling work by fellow scientists indicating that 90 percent of Mississippi River nutrients are retained in the near-shore ecosystem, which implies that nutrients from the Mississippi River do not leave the Gulf.
This is the first study that offers isotopic composition measurements of nitrate in the Gulf of Mexico and a new isotopic profile from the Florida Straits.
Scientists then compared water column profiles with prior measurements from the North and South Atlantic and with the magnitude of nitrogen inputs to the Gulf.
Associate Professor of Oceanography Angela Knapp said, “The study looked for distinct geochemical signatures of nitrate from the Mississippi River and whether this nitrate made it off the Northern Gulf of Mexico shelf into the deep waters of the Gulf that mix with the Loop Current and left via the Florida Straits to enter the North Atlantic.”
“This work has important implications for understanding the fate of nutrients from the Mississippi Atchafalaya River System and how to manage human inputs to coastal ecosystems.”
- Samantha Howe et al., The Dual Isotopic Composition of Nitrate in the Gulf of Mexico and Florida Straits, Journal of Geophysical Research: Oceans (2020). DOI: 10.1029/2020JC016047