Abstract：
The Southern Ocean is a major sink for anthropogenic carbon that is critical to the current and future carbon cycle. Float measurements of pH are now widely used to estimate pCO2, measuring year-round, including during winter months when rough weather makes shipboard observations rare. A recent meta-analysis of float pCO2 accuracy found biases are likely ~6 µatm (float pCO2 high). We find that biases in float oxygen sensors propagate through the pH sensor correction process, accounting for half, or more, of the reported bias in float-derived pCO2.
With an improved understanding of the seasonal carbon cycle in the Southern Ocean, we examine output from 45 models with a focus on the accuracy of the seasonal timing of CO2 fluxes and pCO2. We assess the impact of model biases in dissolved inorganic carbon, sea surface temperature, and total alkalinity timing and magnitude using a simple seasonal model and perturbation experiments to understand individual model biases in pCO2 timing. The large range of pCO2 biases can be explained by comparatively small changes in seasonal dissolved inorganic carbon (DIC) and sea surface temperature (SST) magnitude or timing that impact the rate of change of DIC relative to the rate of change in SST. Biases in SST and DIC can be linked to biases in mixed layer depth and integrated net primary production and indicate that some of the models with the best correlation with observed pCO2 get the right answer for the wrong reasons. We also iteratively adjust a simplified version of each model's seasonal cycle of carbonate system parameters to determine which variables must be corrected to bring models back into phase with observations and whether models get the correct pCO2 seasonal cycle through multiple compensating biases. We find that only 4 models get the correct pCO2 timing for the right mechanistic reasons. Importantly for the potential development of new observational constraints on the future carbon cycle, these models also project a relatively narrow range of cumulative 21st century pCO2 uptake. However, this is a relatively small sample to reach a definitive conclusion about the use of this approach to narrow future Southern Ocean carbon cycle uptake.
Bio：
Chemical oceanographer primarily focused on the global cycles of oxygen and carbon. Current projects study: (1) air-sea gas exchange, (2) how different water masses transport carbon, oxygen, and nutrients from the surface ocean into the interior, (3) the role of biological production in exporting carbon to the deep ocean, and (4) determination/improvement of sensor biases for autonomous vehicles, which are my primary research tool.
Dr. Bushinsky studied biology during undergraduate at Stanford University, receiving BS in 2006, worked at the Monterey Bay Aquarium Research Institute as a technician in the Biological Oceanography Group for two years prior to starting graduate school in Chemical Oceanography at the University of Washington with Prof. Steven Emerson. He earned MS in 2011 and PhD in 2015 before moving to Princeton University as a postdoctoral scholar with Prof. Jorge Sarmiento. In 2019 he began the position as an Assistant Professor in the Department of Oceanography at the University of Hawaiʻi at Mānoa.
