Stephen C. Riser: Research Interests
Research Interests

Stephen C. Riser: Research Interests

My primary interests are in deducing the general circulation of the ocean through direct observations of the ocean circulation, and using these results to assess the ocean's role in climate. In recent years I have also been thinking about the interactions between physical aspects of the ocean circulation and biogeochemical properties of the ocean. I am very interested in the development of novel instrumentation techniques that can be used to measure and understand the ocean circulation in new ways. I have several ongoing, funded research projects that are examining these issues. Most of my work involves the use of observations made from floats deployed in the Argo program. I am the PI of the UW float group, which is part of the US Argo Consortium; as such, we are funded through the NOAA Climate Program Office to build and deploy approximately 120 Argo floats per year. We purchase the components of APEX floats from Teledyne/Webb Corporation and carry out the construction, testing, and calibration of the floats in our lab at UW. Since 2001 we have built and deployed over 2500 such floats throughout the world ocean. Most of the UW floats deployed in the past decade have been deployed in the Pacific (mainly South Pacific) and Indian Oceans, largely because there were not many other Argo groups in the world deploying floats in these regions. Working in these remote regions has required new approaches to deploying floats: in the South Pacific, the UW group and the float group at Scripps Institution of Oceanography have worked together with our colleagues in New Zealand to charter the vessel Kaharoa, based at the NIWA Laboratory in Wellington, New Zealand. This workhorse vessel has deployed UW and Scripps floats throughout the South Pacific and the Indian Ocean. The Argo project has resulted in over 4000 publications from scientists around the world. A summary of the history of this project and some of its more important results can be found in the paper by Riser et al. (2016).

The data from these floats have been used in a number of funded UW projects to examine ocean/atmosphere interaction in the layer of the ocean above 2000 m, from the tropics to high latitudes. One of these is the Southern Ocean Climate and Circulation Observations and Modeling (SOCCOM) project, a large, multi-institutional program funded by the US National Science Foundation. The goal of this program is to deploy and maintain an array of 200 biogeochemical (BGC) profiling floats in the Southern Ocean and the seasonal ice zone around the Antarctic continent by 2021, and to use the data from the floats to assess the ocean-atmosphere flux of CO2. In addition to measuring temperature and salinity, the floats carry BGC sensors for dissolved oxygen, nitrate, pH, chlorophyll fluorescence, and particulate backscatter. The floats are able to operate under the ice in winter, collecting unprecedented observations of these physical and BGC variables. The data and associated improvement in models for the region have been used in a number of high-profile scientific papers.

In the fall of 2020, the US National Science Foundation announced the award of $53 Million to a consortium of US research laboratories in order to produce and deploy the GO-BGC Array of biogeochemical (BGC) profiling floats. This array will eventually consist of 500 floats carrying CTD, oxygen, nitrate, pH, chlorophyll, and particulate backscatter sensors, to be deployed over a 5-year period. Many of the floats will also carry radiometers. The University of Washington is one of the members of this group and will supply over 300 of these BGC floats. The first deployments took place in the North Atlantic in the spring of 2021. As of this writing, 96 floats have been deployed throughout the world ocean.