Project: Coupling of carbonate cycling and redox reactions in the bioturbated zone of marine sediments

NSF Award Abstract:
The top meter of sediment, called the bioturbation zone, is impacted by the variety of biological activities that occur on the seafloor. Marine animals such as worms or plant-like creatures often burrow in and out of, or grow roots into sediment, respectively. Because of this, the bioturbation zone is an area of constant sediment exchange between deep water and surface sediment. Every centimeter of sediment on the ocean floor can have unique chemical properties from the centimeter of sediment above and below it, but in the bioturbation zone, the activity of marine animals mixes these layers. Usually, oceanographers hoping to study what the past chemistry of the ocean was use the chemistry of sediment because, if one knows how fast it takes a centimeter of sediment to settle on part of the seafloor, then a piece of sediment at a defined depth corresponds to a time in the past; however, in the bioturbation zone this is impossible because very old (deep) sediment may have been transferred by a marine animal upward to be mixed in with newly settled (shallow) sediment. Because of this, the bioturbation zone is less studied and generally disregarded in studies of past ocean chemistry, which means there is little, if any, information on ocean processes from the last few decades. The researchers of this project plan to change that by making field measurements, performing laboratory experiments, and developing new sensor technology to advance our understanding of bioturbation zone effects on sediment chemistry. This will be a significant advancement for chemical oceanographers and geologists who hope to understand the ocean chemistry of approximately the last 50 years. Also, the sensors developed by these investigators will be a fantastic new tool for oceanographers, and these researchers are also dedicated to supporting broadening participation in ocean sciences by mentoring students from a wide variety of diverse backgrounds.

Scientists from the State University of New York, Stony Brook propose to advance oceanographers' technical capabilities and abilities to model redox and acid-base reactions within the bioturbation zone. They plan to determine the impact of bioturbation on the dissolution, precipitation, and burial of carbonate minerals, as well as determine net alkalinity fluxes at the sediment-water interface. In past research, this team has developed optical sensors to get qualitative, 2-D images of surface sediment properties. With the progression of their work, the investigators plan to develop sensors that build on their past work to create 3-D images. By developing this 3-D image capability and making extensive field measurements and conducting laboratory experiments, they will be able to use their data to analyze the images created by the sensors quantitatively. This will advance oceanographers' ability to model the effects of bioturbation on carbon cycling in surface sediment, which will, in turn, significantly constrain a missing component of the oceanic flux of inorganic carbon.