1. 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

2. 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.

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

4. 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

5. 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,
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 ( m) Geophys. Res. Lett. , 39, L10603, doi: /2012GL
PMEL - Lyman, J. M. and G. C. Johnson (2008) Estimating global upper ocean heat content despite irregular sampling. Journal of Climate, 21, , doi: /2008JCLI [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, , doi: /s
EN - Ingelby, B. and M. Huddleston (2007) Quality control of ocean temperature and salinity profiles – historical and real-time data, J. Marine Systems, 65, [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: /2012GL052975

6. 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, doi: [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 in light of recently revealed instrumentation problems. Geophys. Res. Lett. , 36, L07608, doi: /2008GL
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: [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:
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

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

8. 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 and associated mechanisms. Geophys. Res. Lett., 34, L02606, /2006GL
1 – Same as 0 except XBTs used as well.
2 – All available data only for years 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.

9. Case 0_W08

10. Case 0_W08
Case 0_NONE

11. 0_W08
0_C13
0_G11
0_GR12
0_L09
0_I09
Ocean Heat Content Anomaly (OHCA) with different mapping methods

12. 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

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

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

15. 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

16. Fractional Geographic Coverage by Year for each method

17. 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

18. 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

19. 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

20. 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

21. 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

22. Linear Trend for Each Mapping Method and Case

23. 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

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