Sensitivity of Global Ocean Heat Content Estimates to Mapping Methods, XBT Bias Correction, and Climatology Tim Boyer1, Catia Domingues2, Simon Good3, Greg Johnson4, John Lyman5, Masayoshi Ishii6, Viktor Gouretski7, John Antonov8, Nathan Bindoff2, John Church9, Rebecca Cowley9, Josh Willis10, Susan Wijffels 9 1NOAA/United States National Oceanographic Data Center Silver Spring, Maryland, USA 2 Antarctic Climate and Ecosystems Cooperative Research Institute, Hobart, Tasmania, Australia 3United Kingdom Met Office, Exeter, Devon, United Kingdom 4NOAA/Pacific Marine Environmental Laboratory, Seattle, Washington, USA 5Joint Institute for Marine and Atmospheric Research, University of Hawai’i at Manoa, Honolulu, Hawai’i, USA 6Frontier Research Center for Global Change, Japan Agency for Marine-Earth Science and Technology, Showamachi, Kamazawa-ku, Yokahama, Japan 7Klima Campus, University of Hamburg, Hamburg, Germany 8University Corporation for Atmospheric Research, Boulder, Colorado, USA 9Commonwealth Scientific and Industrial Research Organization, Hobart, Tasmania 10Jet Propulsion Laboratory, California Institute of Technology, Pasadena, California, USA

Objectives Quantify the uncertainties in Ocean Heat Content Anomaly (OHCA)due to differences in mapping methods for irregular spatial and temporal data. Quantify the effects of different XBT corrections and baseline climatologies on different mapping methods. Use a uniform quality controlled data set as input to the calculations to eliminate data and quality control choice differences as an uncertainty element.

JM Lyman et al. Nature 465, 334-337 (2010) doi:10.1038/nature09043 Uncertainties in OHCA. JM Lyman et al. Nature 465, 334-337 (2010) doi:10.1038/nature09043

Same temperature datasets and quality control used: 1969 2000 2004 2008 Same temperature datasets and quality control used: Hadley Center EN3v2a 1969 – 2004 [XBT, bottle, CTD only] CSIRO Barker Argo dataset 2000-2008

Mapping Methods in this Experiment DOM -Domingues, C. M., J. A. Church, N. J. White, P. J. Gleckler, S. E. Wijjfels, P. M. Barker, J. R. Dunn (2008) Improved estimates of upper-ocean warming and multi-decadal sea-level rise, Nature, 453, 1090-1093. LEV - Levitus, S., J. I. Antonov, T. P. Boyer, O. K. Baranova, H. E. Garcia, R. A. Locarnini, A.V. Mishonov, J. R. Reagan, D. Seidov, E. S. Yarosh, M. M. Zweng (2012) World Ocean heat content and thermosteric sea level change (0-2000 m) 1955-2010. Geophys. Res. Lett. , 39, L10603, doi:10.1029/2012GL051106. PMEL - Lyman, J. M. and G. C. Johnson (2008) Estimating global upper ocean heat content despite irregular sampling. Journal of Climate, 21, 5629-5641, doi:10.1175/2008JCLI2259.1 [Note appears as LYM in some figures] ISH - Ishii, M. and M. Kimoto (2009) Reevaluation of Historical Ocean Heat Content Variations with an XBT depth bias Correction. J. Oceanogr. 65, 287299, doi:10.1007/s10872-009-0027-7 EN - Ingelby, B. and M. Huddleston (2007) Quality control of ocean temperature and salinity profiles – historical and real-time data, J. Marine Systems, 65, 158-175 [Note appears as UKM in some figures] GOU - Gouretski, V., J. Kennedy, T. Boyer and A. Köhl (2012) Consistent near-surface ocean warming since 1900 in two largerly independent observing networks. Geophys. Res. Lett., doi:10.1029/2012GL052975

XBT Bias Correction Algorithms W08 -Wijffels, S. E., J. Willis, C. M. Domingues, P. Barker, N. J. White, A. Gronell, K. Ridgway, J. A. Church 2008 Changing Expendable Bathythermograph Fall Rates and Their Impact on Estimates of Thermosteric Sea Level Rise. J. Climate, 21, 56575672. doi: http://dx.doi.org/10.1175/2008JCLI2290.1 [Note: Table 1] L09 - Levitus, S., J.I. Antonov, T.P. Boyer, R.A. Locarnini, H.E. Garcia, and A.V. Mishonov (2009) Global Ocean Heat Content 1955-2008 in light of recently revealed instrumentation problems. Geophys. Res. Lett. , 36, L07608, doi:10.1029/2008GL037155. C13 - Cowley, R., S. Wijffels, L. Cheng, T. Boyer, S. Kizu (2013) Biases in Expendable BathyThermograph data: a new view based on historical side-by-side comparisons, Journal of Atmospheric and Oceanic Technology, 30, 1195–1225. doi: http://dx.doi.org/10.1175/JTECH-D-12-00127.1 [Note: Thermal Gradient corr.] G11 - Good, S. A. (2011) Depth Biases in XBT Data Diagnosed Using Bathymetry Data. J. Atmos. Oceanic Technol., 28, 287–300. doi: http://dx.doi.org/10.1175/2010JTECHO773.1 GR12 - Gouretski, V. (2012) Using GEBCO digital bathymetry to infer depth biases in the XBT data, Deep Sea Research-I, 62,40-52 I09 - Ishii, M., M. Kimoto and M. Kachi (2003) Historical ocean subsurface temperature analysis with error estimates, Mon. Wea. Rev., 131, 51–73. NONE – no correction

XBT Bias Correction Types Depth Correction only: W08, I09, G11 Temperature Correction Only: L09 Depth and Temperature Corrections: GR12, C13 Hanawa correction only - NONE

Baseline Climatologies Used 0 – Bottle/ CTD/profiling float only. Linear warming trend removed, all years. Alory, G., Wijffels, S. and Meyers, G. M. (2007) Observed temperature trends in the Indian Ocean over 1960-1999 and associated mechanisms. Geophys. Res. Lett., 34, L02606, 10.1029/2006GL028044. 1 – Same as 0 except XBTs used as well. 2 – All available data only for years 2005-2012. Locarnini, R. A., A. V. Mishonov, J. I. Antonov, T. P. Boyer, H. E. Garcia, O. K. Baranova, M. M. Zweng, C. R. Paver, J. R. Reagan, D. R. Johnson, M. Hamilton, and D. Seidov (2013) World Ocean Atlas 2013, Volume 1: Temperature. S. Levitus, Ed., A. Mishonov Technical Ed.; NOAA Atlas NESDIS 73, 40 pp.

Case 0_W08

Case 0_W08 Case 0_NONE

0_W08 0_C13 0_G11 0_GR12 0_L09 0_I09 Ocean Heat Content Anomaly (OHCA) with different mapping methods

Standard Deviation of OHCA for Mapping Methods By Year Colored Curves – For each XBT correction Colored Straight Lines – Average of all years for each XBT correction

DOM LEV EN PMEL ISH GOU OHCA for year 2008: Case 0_W08

DOM LEV EN PMEL ISH GOU OHCA for year 1980: Case 0_W08

LEV MAPPING L09 CORRECT/WOA09 BASELINE LEV MAPPING CASE 0_WO8 EN3 DATASET/QC: YEAR 1980 LEV MAPPING L09 CORRECT/WOA09 BASELINE WOD DATASET/QC: YEAR 1980

Fractional Geographic Coverage by Year for each method

Ocean Heat Content Anomaly (OHCA) with different XBT corrections 0_DOM 0_LEV 0_PMEL_M 0_PMEL_R 0_EN 0_GOU 0_ISH Ocean Heat Content Anomaly (OHCA) with different XBT corrections

Standard Deviation of OHCA for XBT correction By Year Colored Curves – For each mapping method Colored Straight Lines – Average of all years for each mapping method

0_DOM 0_LEV 0_PMEL_M 0_PMEL_R 0_EN 0_GOU 0_ISH Ocean Heat Content Anomaly (OHCA) with different climatological baselines

Standard Deviation of OHCA for different baseline climatology By Year Colored Curves – For each mapping method Colored Straight Lines – Average of all years for each mapping method

Mapping Method XBT Correction Baseline Cimatology DOM 17.7 ZJ 19.7 ZJ 15.2 ZJ LEV 11.6 ZJ 2.7 ZJ PMEL_M 8.4 ZJ 13.2 ZJ PMEL_R 13.6 ZJ EN 9.0 ZJ 4.7 ZJ ISH 5.5 ZJ GOU 6.6 ZJ UNCERTAINTY DUE TO DIFFERENT FACTORS IN CALCULATION OF OHCA

Linear Trend for Each Mapping Method and Case

Conclusions Uncertainty in calculation of OHCA from irregularly spatial and temporal data distribution is larger than interannual variability in OHCA (consistent with Lyman et al. 2010) Long-term trends are still robust (consistent with Lyman et al. 2010) Robust trend detection needs 10 (LEV, GOU) to 14 (DOM) years. Difference in mapping method contributes the largest uncertainty Differences due to XBT correction and to baseline climatology contribute differently to uncertainty for each mapping method. Come to a consensus on XBT correction and we can reduce the uncertainty in the calculation of OHCA

Come to a consensus on XBT correction and we can reduce the uncertainty in the calculation of OHCA Thank You