Reevaluation of historical ocean heat content variations with time-varying XBT and MBT depth bias corrections
Rent the article at a discountRent now
* Final gross prices may vary according to local VAT.Get Access
As reported in former studies, temperature observations obtained by expendable bathythermographs (XBTs) and mechanical bathythermographs (MBTs) appear to have positive biases as much as they affect major climate signals. These biases have not been fully taken into account in previous ocean temperature analyses, which have been widely used to detect global warming signals in the oceans. This report proposes a methodology for directly eliminating the biases from the XBT and MBT observations. In the case of XBT observation, assuming that the positive temperature biases mainly originate from greater depths given by conventional XBT fall-rate equations than the truth, a depth bias equation is constructed by fitting depth differences between XBT data and more accurate oceanographic observations to a linear equation of elapsed time. Such depth bias equations are introduced separately for each year and for each probe type. Uncertainty in the gradient of the linear equation is evaluated using a non-parametric test. The typical depth bias is +10 m at 700 m depth on average, which is probably caused by various indeterminable sources of error in the XBT observations as well as a lack of representativeness in the fall-rate equations adopted so far. Depth biases in MBT are fitted to quadratic equations of depth in a similar manner to the XBT method. Correcting the historical XBT and MBT depth biases by these equations allows a historical ocean temperature analysis to be conducted. In comparison with the previous temperature analysis, large differences are found in the present analysis as follows: the duration of large ocean heat content in the 1970s shortens dramatically, and recent ocean cooling becomes insignificant. The result is also in better agreement with tide gauge observations.
- AchutaRao, K. M., Ishii, M., Santer, B. D., Gleckler, P. J., Taylor, K. E., Barnett, T. P., Pierce, D. W., Stouffer, R. J., Wigley, T. M. L. (2007) Simulated and observed variability in ocean temperature and heat content. Proc. Natl. Acad. Sci. 104: pp. 10768-10773 CrossRef
- Antonov, J. I., Levitus, S., Boyer, T. P. (2004) Climatological annual cycle of ocean heat content. Geophys. Res. Lett. 31: pp. L04304 CrossRef
- Boyer, T. P., J. I. Antonov, H. E. Garcia, D. R. Johnson, R. A. Locarnini, A. Mishonov, M. T. Pitcher, O. K. Baranova and I. V. Smolyar (2006): World Ocean Database 2005. NOAA Atlas NESDIS 60, ed. by S. Levitus (available at http://www.nodc.noaa.gov/OC5/WOD05/docwod05.html).
- Conkright, M. E., Locarnini, R. A., Garcia, H. E., Brien, T. D. O., Boyer, T. P., Stephens, C., Antonov, J. I. (2001) World Ocean Atlas 2001: Objective Analyses, Data Statistics, and Figures. U.S. Government Printing Office, Washington, D.C
- Fahrbach, E. (1989): The use of electronic digital thermometers and pressure meters. WOCE Newsletter No. 8, 12–13.
- Gouretski, V., Koltermann, K. P. (2007) How much is the ocean really warming. Geophys. Res. Lett. 34: pp. L01610 CrossRef
- Hanawa, K., Raul, P., Bailey, R., Sy, A., Szabados, M. (1995) A new depth-time equation for Sippican or TSK T-7, T-6, and T-4 expendable bathythermographs (XBTs). Deep-Sea Res. 42: pp. 1423-1451 CrossRef
- Ishii, M., Kimoto, M., Kachi, M. (2003) Historical ocean subsurface temperature analysis with error estimates. Mon. Wea. Rev. 131: pp. 51-73 CrossRef
- Ishii, M., Kimoto, M., Sakamoto, K., Iwasaki, S.-I. (2006) Steric sea level changes estimated from historical subsurface temperature and salinity analyses. J. Oceanogr. 61: pp. 155-170 CrossRef
- Kizu, S., Hanawa, K. (2002) Recorder-dependent temperature error of expendable bathythermograph. J. Oceanogr. 58: pp. 469-476 CrossRef
- Kizu, S., Yoritaka, H., Hanawa, K. (2005) A new fall-rate equation for T-5 expendable bathythermograph (XBT) by TSK. J. Oceanogr. 61: pp. 115-121 CrossRef
- Levitus, S. and J. Antonov (1997): Limatological and Interannual Variability of Temperature, Heat Storage, and Rate of Heat Storage in the Upper Ocean. NOAA Atlas NESDIS 16, 186 pp.
- Levitus, S., C. Stephens, J. I. Antonov and T. P. Boyer (2000): Yearly and Year-Season Upper Ocean Temperature Anomaly Fields, 1948-1998. NOAA Atlas NESDIS 40 (available from http://www.nodc.noaa.gov/OC5/PDF/ATLAS/ nesdis40.pdf).
- Levitus, S., Antonov, J. I., Boyer, T. P., Garcia, H. E., Locarnini, R. A. (2005) Linear trends of zonally averaged thermosteric, halosteric, and total steric sea level for individual ocean basins and the world ocean, (1955–1959)–(1994–1998). Geophys. Res. Lett. 32: pp. L16601 CrossRef
- Lombard, A., Cazenave, A., Traon, P.-Y., Ishii, M. (2005) Contribution of thermal expansion to present-day sea-level change revisited. Global and Planetary Change 47: pp. 1-16 CrossRef
- Lombard, A., Garcia, D., Ramillien, G., Cazenave, A., Biancale, R., Lemoine, J. M., Flechtner, F., Schmidt, R., Ishii, M. (2007) Estimation of steric sea level variations from combined GRACE and Jason-1 data. Earth Planet. Sci. Lett. 254: pp. 194-202 CrossRef
- Quadfasel, D., N. Verch and J. Langhof (1990): Are mercury deep-sea reversing thermometers out of date? Ocean Dynamics, 145–152.
- Reynolds, R. W., Smith, T. M. (1994) Improved global sea surface temperature analyses using optimum interpolation. J. Climate 7: pp. 929-948 CrossRef
- Sakamoto, T., H. Hasumi, M. Ishii, S. Emori, T. Suzuki, T. Nishimura and A. Sumi (2005): Responses of the Kuroshio and the Kuroshio Extension to global warming in a highresolution climate model. Geophys. Res. Lett., 32, doi:10.1029/2005GL023384.
- Smith, D. M., Murphy, J. M. (2007) An objective ocean temperature and salinity analysis using covariances from a global climate model. J. Geophys. Res. 112: pp. C02022 CrossRef
- Wijffels, S., Willis, J., Domingues, C. M., Baker, P., White, N. J., Cronell, A., Ridgway, K., Church, J. A. (2008) Changing expendable bathythermograph fallrates and their impact on estimates of thermosteric sea level rise. J. Climate 21: pp. 5657-5672 CrossRef
- Willis, J. K., Roemmich, D., Cornuelle, B. (2004) Interannual variability in upper ocean heat content, temperature, and thermosteric expansion on global scales. J. Geophys. Res. 109: pp. C12036 CrossRef
- Willis, J. K., J. M. Lyman, G. C. Johnson and J. Gilson (2008): In situ data biases and recent ocean heat content variability. J. Atmos. Oceanic Tech. (in press).
- Wyatt, B., R. Still, D. Barstow and W. Gilbert (1967): Hydrographic Data from Oregon Waters 1965. Department Oceanography, School of Science, Oregon State Univ. Date Report No. 27.
- Reevaluation of historical ocean heat content variations with time-varying XBT and MBT depth bias corrections
Journal of Oceanography
Volume 65, Issue 3 , pp 287-299
- Cover Date
- Print ISSN
- Online ISSN
- Springer Netherlands
- Additional Links
- Ocean temperature
- XBT fall-rate equation
- oceanographic observation
- ocean heat content
- objective analysis
- Industry Sectors
- Author Affiliations
- 1. Frontier Research Center for Global Change, Japan Agency for Marine-Earth Science and Technology, Showamachi, Kanazawa-ku, Yokohama, 236-0001, Japan
- 2. Center for Climate System Research, The University of Tokyo, Kashiwa, 277-8586, Japan