A group of scientists from EAS led by Martial Taillefert, his graduate students (Eryn Eitel, Shannon Owings), and two EAS undergraduates (Ben Fields and Tony Boever) returned from a 26 days journey in the Gulf of Mexico on the RV Savannah (Skidaway Institute of Oceanography).
Along with two science groups from France and a group from the Mote Marine Laboratory (Florida), they investigated the geochemical composition of the sediment and the flux of dissolved species from the seafloor. This study took place on the continental shelf in the hypoxic zone west of the Mississippi delta and the continental slope across from the Mississippi delta. This research cruise had two main objectives:
First, to determine whether dissolved iron is released from the sediment exposed to large influx of inorganic material from the Mississippi River. Iron is an essential nutrient for phytoplankton growth that is limited in surface waters, and the biogeochemical processes and the intensity of the iron flux from the sediment have been poorly characterized.
This NSF-funded three-year project has focused on determining whether continental slope sediments provide a significant source of iron to the overlying waters. The first two years, Taillefert’s group investigated the carbon depocenter off Cape Fear in North Carolina, but this last year, the focus shifted to the Gulf of Mexico where sulfate reduction may affect negatively the flux of iron from the sediment.
Second, to determine whether the intense biogeochemical processes taking place in the sediments surrounding the Mississippi delta provided a source of alkalinity (a reserve of bases) to the overlying waters as a buffer to the acidification of the oceans resulting from the increase in CO2 in the atmosphere.
The French groups have been investigating the role of large rivers on the buffering of the water column by these processes, first in the Rhone River delta in the Mediterranean Sea, then in the Mississippi delta. Both science teams and the Savannah crew worked relentlessly for two long weeks to deploy and recover three benthic landers as well as a multi-coring device at water depths as deep as 1000 m and as shallow as 15 m.
The cruise went extremely well, despite the intense navigation around the thousands of oil platforms in this region of the Gulf. So far, the science results revealed a small iron flux persisting from the continental slope but no flux from the continental shelf. In addition, the alkalinity flux was not as high as expected for reasons that need to be explored.
The science crew recovered a variety of sediment samples, overlying waters, and pore waters extracted from these sediments that need to be analyzed in the last few months of this project. For more details on these projects, contact Martial Taillefert (firstname.lastname@example.org).