Synthetic Biogeochemical Argo Float Capabilities in E3SM
Schematic illustration of (top) synthetic modeled and (bottom) real-world biogeochemical Argo floats. The synthetic floats in E3SMv2 drift at a parking depth of 1000m for a day and then instantaneously sample model tracers and diagnostics throughout the water column in open waters and under sea-ice cover. Real-world biogeochemical Argo floats drift at a parking depth of 1000m for about 9 d, descend to 2000m, and then sample temperature, salinity, oxygen, nitrate, pH, chlorophyll, particulate backscatter, and irradiance in the upper 2000m on their ascent. Real-world float positions are determined via GPS, such that their exact positions are unknown while under sea ice.
Image by Cara Nissen, University of Colorado Boulder
This study presents the new synthetic biogeochemical float capabilities in the ocean component of the Energy Exascale Earth System Model (E3SM). The synthetic floats sample the model fields online during model run time, which facilitates a realistic assessment of what floats truly see when they sample the ocean. The paper describes the implementation of synthetic floats into E3SM and showcases the utility of this tool for a variety of physical, biogeochemical, and biological research questions.
Since their advent over 2 decades ago, autonomous Argo floats have revolutionized the field of oceanography, and the recent addition of biogeochemical and biological sensors to these floats has greatly improved our understanding of carbon, nutrient, and oxygen cycling in the ocean. This paper introduces and describes a novel tool for the DOE E3SM: synthetic floats that drift with simulated ocean currents and sample their physical and biogeochemical properties online at model runtime. This new tool has the potential to transform our approach to oceanographic observational system simulation.
Here, we implement synthetic biogeochemical Argo floats into the Energy Exascale Earth System Model version 2 (E3SMv2), which builds upon the Lagrangian In Situ Global High-Performance Particle Tracking (LIGHT) module in E3SMv2 (E3SMv2-LIGHT-bgcArgo-1.0). Since the synthetic floats sample the model fields at model run time, the end user defines the sampling protocol ahead of any model simulation, including the number and distribution of synthetic floats to be deployed, their sampling frequency, and the prognostic or diagnostic model fields to be sampled. Using a 6-year proof-of-concept simulation, we illustrate the utility of the synthetic floats in different case studies. In particular, we quantify the impact of (i) sampling density on the float-derived detection of deep-ocean change in temperature or oxygen and on float-derived estimates of phytoplankton phenology, (ii) sampling frequency and sea-ice cover on float trajectory lengths and hence float-derived estimates of current velocities, and (iii) short-term variability in ecosystem stressors on estimates of their seasonal variability.