Volume 15, issue 12 | Copyright
Biogeosciences, 15, 3841-3855, 2018
https://doi.org/10.5194/bg-15-3841-2018
© Author(s) 2018. This work is distributed under
the Creative Commons Attribution 4.0 License.

Research article 25 Jun 2018

Research article | 25 Jun 2018

Utilizing the Drake Passage Time-series to understand variability and change in subpolar Southern Ocean pCO2

Amanda R. Fay1, Nicole S. Lovenduski2, Galen A. McKinley1, David R. Munro2, Colm Sweeney3,4, Alison R. Gray5, Peter Landschützer6, Britton B. Stephens7, Taro Takahashi1, and Nancy Williams8 Amanda R. Fay et al.
  • 1Lamont Doherty Earth Observatory of Columbia University, New York, NY, USA
  • 2Department of Atmospheric and Oceanic Sciences and Institute of Arctic and Alpine Research, University of Colorado, Boulder, CO, USA
  • 3Cooperative Institutes for Research in Environmental Sciences, University of Colorado, Boulder, CO, USA
  • 4NOAA Earth System Research Laboratory, Boulder, CO, USA
  • 5School of Oceanography, University of Washington, Seattle, WA, USA
  • 6Max Planck Institute for Meteorology, Hamburg, Germany
  • 7National Center for Atmospheric Research (NCAR), Boulder, CO, USA
  • 8College of Earth, Ocean, and Atmospheric Sciences, Oregon State University, Corvallis, OR, USA

Abstract. The Southern Ocean is highly under-sampled for the purpose of assessing total carbon uptake and its variability. Since this region dominates the mean global ocean sink for anthropogenic carbon, understanding temporal change is critical. Underway measurements of pCO2 collected as part of the Drake Passage Time-series (DPT) program that began in 2002 inform our understanding of seasonally changing air–sea gradients in pCO2, and by inference the carbon flux in this region. Here, we utilize available pCO2 observations to evaluate how the seasonal cycle, interannual variability, and long-term trends in surface ocean pCO2 in the Drake Passage region compare to that of the broader subpolar Southern Ocean. Our results indicate that the Drake Passage is representative of the broader region in both seasonality and long-term pCO2 trends, as evident through the agreement of timing and amplitude of seasonal cycles as well as trend magnitudes both seasonally and annually. The high temporal density of sampling by the DPT is critical to constraining estimates of the seasonal cycle of surface pCO2 in this region, as winter data remain sparse in areas outside of the Drake Passage. An increase in winter data would aid in reduction of uncertainty levels. On average over the period 2002–2016, data show that carbon uptake has strengthened with annual surface ocean pCO2 trends in the Drake Passage and the broader subpolar Southern Ocean less than the global atmospheric trend. Analysis of spatial correlation shows Drake Passage pCO2 to be representative of pCO2 and its variability up to several hundred kilometers away from the region. We also compare DPT data from 2016 and 2017 to contemporaneous pCO2 estimates from autonomous biogeochemical floats deployed as part of the Southern Ocean Carbon and Climate Observations and Modeling project (SOCCOM) so as to highlight the opportunity for evaluating data collected on autonomous observational platforms. Though SOCCOM floats sparsely sample the Drake Passage region for 2016–2017 compared to the Drake Passage Time-series, their pCO2 estimates fall within the range of underway observations given the uncertainty on the estimates. Going forward, continuation of the Drake Passage Time-series will reduce uncertainties in Southern Ocean carbon uptake seasonality, variability, and trends, and provide an invaluable independent dataset for post-deployment assessment of sensors on autonomous floats. Together, these datasets will vastly increase our ability to monitor change in the ocean carbon sink.

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The Southern Ocean is highly under-sampled and since this region dominates the ocean sink for CO2, understanding change is critical. Here we utilize available observations to evaluate how the seasonal cycle, variability, and trends in surface ocean carbon in the well-sampled Drake Passage region compare to that of the broader subpolar Southern Ocean. Results indicate that the Drake Passage is representative of the broader region; however, additional winter observations would improve comparisons.
The Southern Ocean is highly under-sampled and since this region dominates the ocean sink for...
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