Developing an autonomous biogeochemical profiling float to monitor biological productivity, ocean-atmosphere CO2 fluxes, and hypoxia in the Tropical Pacific Ocean

PIs: Sarah Purkey, Todd Martz, Lynne Talley, Dean Roemmich, Matthew Mazloff, Daniel Rudnick, Ariane Verdy (SIO-UCSD); Neil Bogue (MRV Systems LLC); Ken Johnson (MBARI)


The Tropical Pacific is the largest natural oceanic source of CO2 to the climate system and houses one of the world’s most productive ecosystems. However, the drivers and consequences of the interannual-to-decadal variability associated with ENSO on biogeochemical processes in the region still have high uncertainty. This award is to advance US’s technical and commercial readiness to support the new TPOS and the larger global BGC Argo array. The award is to design, test, and commercialize a new model of float that can measure temperature, salinity, oxygen, pH, nitrate, chlorophyll-a, backscatter, and downwelling irradiance. This award will support the design and building of 5 BGC floats to be deployed in the Tropical Pacific as part of the TPOS in 2022. In addition, this award supports the development of a biogeochemical ocean model of the Tropical Pacific. The model developed through this award uses physical dynamics constrained by ocean and atmospheric data between 2010-2019 to produce a high-resolution reconstruction of the interior ocean’s biogeochemistry over the time period. This product is a powerful tool for observing system design and for advancing our understanding of the chemistry and biology of the Tropical Pacific.

Expected Outcome

The major outcomes of this project will be: (1) A new model of biogeochemical (BGC) Argo profiling float based on SIO’s SOLO-II core Argo model. The new model will utilize the reliable, robust SOLOII body and add 6 BGC sensors and be Commercialize through MRV systems. A total of 5 test floats (4 built by SIO and 1 by MRV systems) will be built, tested and then deployed along the equator of the Tropical Pacific, capable of monitoring the biogeochemical variability in the upper 2000m as part of the TPOS 2020. (2) The development of a coupled BGC model to the Tropical Pacific Ocean State Estimate (TPOSE) to assess temporal and spatial length scales of the climate variability. The model will be used to better plan an optimize the monitoring system of the biogeochemistry of the Tropical Pacific in line with TPOS 2020’s requirements, and to provide a major BGC analysis tool.

Relevance to TPOS Strategy: The profiling BGC Argo floats will contributes to the requirements of TPOS by (1) accurately measuring subsurface chlorophyll concentration, particulate backscatter, oxygen, nitrate and pH to monitor the seasonal to interannual variability in the biogeochemistry in order to assess the rates of ocean productivity and ecosystem health, including subsurface oxygen budgets and the expansion of oxygen minimum zones, (2) add a new platform to the current proposed pCO2 monitoring system to quantify seasonal-to-interannual variability in ocean-atmosphere carbon exchange, and (3) provide in-situ chlorophyll estimates for calibration of the broad scale surface ocean color satellite observations. The floats will also support many of the TPOS 2020 key backbone functions, which require doubling the Argo float concentration between 10°S and 10°N to enhance coverage of subsurface temperature and salinity profiles.

In addition, analysis of TPOSE will inform the future Tropical Pacific BGC observing system as a whole by evaluating the magnitude and relative spatial scales of the large seasonal to interannual variability in tropical BGC properties and fluxes. These results will provide a concrete assessment of the value of the BGC Argo array to TPOS 2020 and provide guidance on the needed future size and distribution of the array.