1Lamont-Doherty Earth Observatory of Columbia University, Palisades, NY, USA
2Helmholtz Centre for Ocean Research Kiel, Marine Biogeochemistry, Kiel, Germany
3National Institute of Water and Atmospheric Research, 301 Evans Bay Pde., Hataitai, Wellington, New Zealand
4Climate and Environmental Physics, Physics Institute, University of Bern, Switzerland; and Oeschger Centre for Climate Change Research, University of Bern, Switzerland
5Woods Hole Oceanographic Institution, MA, USA
6Institute of Biogeochemistry and Pollutant Dynamics, ETH Zurich, Switzerland
7Atmospheric and Ocean Sciences, University of Wisconsin – Madison, WI, USA
8Research Institute of Global Change, Japan Agency for Marine-Earth Science and Technology, Yokosuka, Japan
9Instituto de Investigaciones Marinas, IIM-CSIC, C/Eduardo Cabello 6, 36208 Vigo, Spain
10NOAA Pacific Marine Environmental Laboratory, Seattle, WA, USA
Received: 15 Jun 2012 – Discussion started: 23 Jul 2012
Abstract. The global ocean is a significant sink for anthropogenic carbon (Cant), absorbing roughly a third of human CO2 emitted over the industrial period. Robust estimates of the magnitude and variability of the storage and distribution of Cant in the ocean are therefore important for understanding the human impact on climate. In this synthesis we review observational and model-based estimates of the storage and transport of Cant in the ocean. We pay particular attention to the uncertainties and potential biases inherent in different inference schemes. On a global scale, three data-based estimates of the distribution and inventory of Cant are now available. While the inventories are found to agree within their uncertainty, there are considerable differences in the spatial distribution. We also present a review of the progress made in the application of inverse and data assimilation techniques which combine ocean interior estimates of Cant with numerical ocean circulation models. Such methods are especially useful for estimating the air–sea flux and interior transport of Cant, quantities that are otherwise difficult to observe directly. However, the results are found to be highly dependent on modeled circulation, with the spread due to different ocean models at least as large as that from the different observational methods used to estimate Cant. Our review also highlights the importance of repeat measurements of hydrographic and biogeochemical parameters to estimate the storage of Cant on decadal timescales in the presence of the variability in circulation that is neglected by other approaches. Data-based Cant estimates provide important constraints on forward ocean models, which exhibit both broad similarities and regional errors relative to the observational fields. A compilation of inventories of Cant gives us a "best" estimate of the global ocean inventory of anthropogenic carbon in 2010 of 155 ± 31 PgC (±20% uncertainty). This estimate includes a broad range of values, suggesting that a combination of approaches is necessary in order to achieve a robust quantification of the ocean sink of anthropogenic CO2.
Revised: 27 Jan 2013 – Accepted: 25 Feb 2013 – Published: 02 Apr 2013
Khatiwala, S., Tanhua, T., Mikaloff Fletcher, S., Gerber, M., Doney, S. C., Graven, H. D., Gruber, N., McKinley, G. A., Murata, A., Ríos, A. F., and Sabine, C. L.: Global ocean storage of anthropogenic carbon, Biogeosciences, 10, 2169-2191, doi:10.5194/bg-10-2169-2013, 2013.