• Alexander, M. A., , I. Bladé, , M. Newman, , J. R. Lanzante, , N.-C. Lau, , and J. D. Scott, 2002: The atmospheric bridge: The influence of ENSO teleconnections on air–sea interaction over the global oceans. J. Climate, 15, 22052231, doi:10.1175/1520-0442(2002)015<2205:TABTIO>2.0.CO;2.

    • Search Google Scholar
    • Export Citation
  • Alory, G., , S. Wijffels, , and G. Meyers, 2007: Observed temperature trends in the Indian Ocean over 1960–1999 and associated mechanisms. Geophys. Res. Lett., 34, L02606, doi:10.1029/2006GL028044.

    • Search Google Scholar
    • Export Citation
  • Balmaseda, M. A., , A. Vidard, , and D. L. T. Anderson, 2008: The ECMWF Ocean Analysis System: ORA-S3. Mon. Wea. Rev., 136, 30183034, doi:10.1175/2008MWR2433.1.

    • Search Google Scholar
    • Export Citation
  • Balmaseda, M. A., , K. Mogensen, , and A. T. Weaver, 2013: Evaluation of the ECMWF Ocean Reanalysis System ORAS4. Quart. J. Roy. Meteor. Soc., 139, 11321161, doi:10.1002/qj.2063.

    • Search Google Scholar
    • Export Citation
  • Barnett, T. P., , D. W. Pierce, , K. M. AchutaRao, , P. J. Gleckler, , B. D. Santer, , J. M. Gregory, , and W. M. Washington, 2005: Penetration of human-induced warming into the world’s oceans. Science, 309, 284287, doi:10.1126/science.1112418.

    • Search Google Scholar
    • Export Citation
  • Boyer, T. P., and et al. , 2009: Introduction. Vol. 1, World Ocean Database 2009, NOAA Atlas NESDIS 66, 219 pp.

  • Cai, W., , A. Sullivan, , and T. Cowan, 2008: Shoaling of the off-equatorial south Indian Ocean thermocline: Is it driven by anthropogenic forcing? Geophys. Res. Lett., 35, L12711, doi:10.1029/2008GL034174.

    • Search Google Scholar
    • Export Citation
  • Carton, J. A., , and B. S. Giese, 2008: A reanalysis of ocean climate using Simple Ocean Data Assimilation (SODA). Mon. Wea. Rev., 136, 29993017, doi:10.1175/2007MWR1978.1.

    • Search Google Scholar
    • Export Citation
  • Chung, C. E., , and V. Ramanathan, 2006: Weakening of north Indian SST gradients and the monsoon rainfall in India and the Sahel. J. Climate, 19, 20362045, doi:10.1175/JCLI3820.1.

    • Search Google Scholar
    • Export Citation
  • Dee, D. P., and et al. , 2011: The ERA-Interim reanalysis: Configuration and performance of the data assimilation system. Quart. J. Roy. Meteor. Soc., 137, 553597, doi:10.1002/qj.828.

    • Search Google Scholar
    • Export Citation
  • D’Mello, J. R., , and S. P. Kumar, 2015: Why is the Bay of Bengal experiencing a reduced rate of sea surface warming? Int. J. Climatol., 36, 15391548, doi:10.1002/joc.4414.

    • Search Google Scholar
    • Export Citation
  • Dong, L., , and T. J. Zhou, 2014: The Indian Ocean sea surface temperature warming simulated by CMIP5 models during the 20th century: Competing forcing roles of GHGs and anthropogenic aerosols. J. Climate, 27, 33483362, doi:10.1175/JCLI-D-13-00396.1.

    • Search Google Scholar
    • Export Citation
  • Dong, L., , T. J. Zhou, , and B. Wu, 2014: Indian Ocean warming during 1958–2004 simulated by a climate system model and its mechanism. Climate Dyn., 42, 203217, doi:10.1007/s00382-013-1722-z.

    • Search Google Scholar
    • Export Citation
  • Dong, L., , T. J. Zhou, , A. Dai, , F. Song, , B. Wu, , and X. Chen, 2016: The footprint of the inter-decadal Pacific oscillation in Indian Ocean sea surface temperatures. Sci. Rep., 6, 21251, doi:10.1038/srep21251.

    • Search Google Scholar
    • Export Citation
  • Du, Y., , and S.-P. Xie, 2008: Role of atmospheric adjustments in the tropical Indian Ocean warming during the 20th century in climate models. Geophys. Res. Lett., 35, L08712, doi:10.1029/2008GL033631.

    • Search Google Scholar
    • Export Citation
  • Easterling, D. R., , and M. F. Wehner, 2009: Is the climate warming or cooling? Geophys. Res. Lett., 36, L08706, doi:10.1029/2009GL037810.

    • Search Google Scholar
    • Export Citation
  • England, M. H., and et al. , 2014: Recent intensification of wind-driven circulation in the Pacific and the ongoing warming hiatus. Nat. Climate Change, 4, 222227, doi:10.1038/nclimate2106.

    • Search Google Scholar
    • Export Citation
  • Feng, M., , M. J. McPhaden, , and T. Lee, 2010: Decadal variability of the Pacific subtropical cells and their influence on the southeast Indian Ocean. Geophys. Res. Lett., 37, L09606, doi:10.1029/2010GL042796.

    • Search Google Scholar
    • Export Citation
  • Feng, M., , C. Böning, , A. Biastoch, , E. Behrens, , E. Weller, , and Y. Masumoto, 2011: The reversal of the multidecadal trends of the equatorial Pacific easterly winds, and the Indonesian Throughflow and Leeuwin Current transports. Geophys. Res. Lett., 38, L11604, doi:10.1029/2011GL047291.

    • Search Google Scholar
    • Export Citation
  • Giese, B. S., , and S. Ray, 2011: El Niño variability in Simple Ocean Data Assimilation (SODA), 1871–2008. J. Geophys. Res., 116, C02024, doi:10.1029/2010JC006695.

    • Search Google Scholar
    • Export Citation
  • Goes, J. I., , P. G. Thoppil, , H. Gomes, , and J. T. Fasullo, 2005: Warming of the Eurasian landmass is making the Arabian Sea more productive. Science, 308, 545547, doi:10.1126/science.1106610.

    • Search Google Scholar
    • Export Citation
  • Good, S. A., , M. J. Martin, , and N. A. Rayner, 2013: EN4: Quality controlled ocean temperature and salinity profiles and monthly objective analyses with uncertainty estimates. J. Geophys. Res. Oceans, 118, 67046716, doi:10.1002/2013JC009067.

    • Search Google Scholar
    • Export Citation
  • Han, W., and et al. , 2010: Patterns of Indian Ocean sea-level change in a warming climate. Nat. Geosci., 3, 546550, doi:10.1038/ngeo901.

    • Search Google Scholar
    • Export Citation
  • Han, W., , J. Vialard, , M. J. McPhaden, , T. Lee, , Y. Masumoto, , M. Feng, , and W. P. M. de Ruijter, 2014: Indian Ocean decadal variability: A review. Bull. Amer. Meteor. Soc., 95, 16791703, doi:10.1175/BAMS-D-13-00028.1.

    • Search Google Scholar
    • Export Citation
  • Harrison, D. E., , and M. Carson, 2007: Is the World Ocean warming? Upper ocean trends, 1950–2000. J. Phys. Oceanogr., 37, 174187, doi:10.1175/JPO3005.1.

    • Search Google Scholar
    • Export Citation
  • Hirst, A. C., , and J. S. Godfrey, 1993: The role of Indonesian Throughflow in a global ocean GCM. J. Phys. Oceanogr., 23, 10571086, doi:10.1175/1520-0485(1993)023<1057:TROITI>2.0.CO;2.

    • Search Google Scholar
    • Export Citation
  • Hoerling, M., , J. W. Hurrell, , T. Xu, , G. T. Bates, , and A. S. Phillips, 2004: Twentieth century North Atlantic climate change. Part II: Understanding the effect of Indian Ocean warming. Climate Dyn., 23, 391405, doi:10.1007/s00382-004-0433-x.

    • Search Google Scholar
    • Export Citation
  • Ishii, M., , A. Shouji, , S. Sugimoto, , and T. Matsumoto, 2005: Objective analyses of sea-surface temperature and marine meteorological variables for the 20th century using ICOADS and the Kobe Collection. Int. J. Climatol., 25, 865879, doi:10.1002/joc.1169.

    • Search Google Scholar
    • Export Citation
  • Kanamitsu, M., , W. Ebisuzaki, , J. Woollen, , S.-K. Yang, , J. J. Hnilo, , M. Fiorino, , and G. L. Potter, 2002: NCEP–DOE AMIP-II reanalysis (R-2). Bull. Amer. Meteor. Soc., 83, 16311643, doi:10.1175/BAMS-83-11-1631.

    • Search Google Scholar
    • Export Citation
  • Kaplan, A., , M. A. Cane, , Y. Kushnir, , A. C. Clement, , M. B. Blumenthal, , and B. Rajagopalan, 1998: Analyses of global sea surface temperature 1856–1991. J. Geophys. Res., 103, 18 56718 589, doi:10.1029/97JC01736.

    • Search Google Scholar
    • Export Citation
  • Kennedy, J. J., , N. A. Rayner, , R. O. Smith, , D. E. Parker, , and M. Saunby, 2011a: Reassessing biases and other uncertainties in sea surface temperature observations measured in situ since 1850: 1. Measurement and sampling uncertainties. J. Geophys. Res., 116, D14103, doi:10.1029/2010JD015218.

    • Search Google Scholar
    • Export Citation
  • Kennedy, J. J., , N. A. Rayner, , R. O. Smith, , D. E. Parker, , and M. Saunby, 2011b: Reassessing biases and other uncertainties in sea surface temperature observations measured in situ since 1850: 2. Biases and homogenization. J. Geophys. Res., 116, D14104, doi:10.1029/2010JD015220.

    • Search Google Scholar
    • Export Citation
  • Köhl, A., 2015: Evaluation of the GECCO2 ocean synthesis: Transports of volume, heat and freshwater in the Atlantic. Quart. J. Roy. Meteor. Soc., 141, 166181, doi:10.1002/qj.2347.

    • Search Google Scholar
    • Export Citation
  • Kosaka, Y., , and S. P. Xie, 2013: Recent global-warming hiatus tied to equatorial Pacific surface cooling. Nature, 501, 403407, doi:10.1038/nature12534.

    • Search Google Scholar
    • Export Citation
  • Krishnan, R., , K. V. Ramesh, , B. K. Samala, , G. Meyer, , J. M. Slingo, , and M. J. Fennessy, 2006: Indian Ocean–monsoon coupled interactions and impending monsoon droughts. Geophys. Res. Lett., 33, L08711, doi:10.1029/2006GL025811.

    • Search Google Scholar
    • Export Citation
  • Lee, S.-K., , W. Park, , M. O. Baringer, , A. L. Gordon, , B. Huber, , and Y. Liu, 2015: Pacific origin of the abrupt increase in Indian Ocean heat content during the warming hiatus. Nat. Geosci., 8, 445449, doi:10.1038/ngeo2438.

    • Search Google Scholar
    • Export Citation
  • Lee, T., , and M. J. McPhaden, 2008: Decadal phase change in large-scale sea level and winds in the Indo-Pacific region at the end of the 20th century. Geophys. Res. Lett., 35, L01605, doi:10.1029/2007GL032419.

    • Search Google Scholar
    • Export Citation
  • Lee, T., , I. Fukumori, , D. Menemenlis, , Z. Xing, , and L. L. Fu, 2002: Effects of the Indonesian Throughflow on the Pacific and Indian Oceans. J. Phys. Oceanogr., 32, 14041429, doi:10.1175/1520-0485(2002)032<1404:EOTITO>2.0.CO;2.

    • Search Google Scholar
    • Export Citation
  • Lee, T., , I. Fukumori, , and B. Tang, 2004: Temperature advection: Internal versus external processes. J. Phys. Oceanogr., 34, 19361944, doi:10.1175/1520-0485(2004)034<1936:TAIVEP>2.0.CO;2.

    • Search Google Scholar
    • Export Citation
  • Lee, T., and et al. , 2010: Consistency and fidelity of Indonesian-Throughflow total volume transport estimated by 14 ocean data assimilation products. Dyn. Atmos. Oceans, 50, 201223, doi:10.1016/j.dynatmoce.2009.12.004.

    • Search Google Scholar
    • Export Citation
  • Levitus, S., and et al. , 2012: World Ocean heat content and thermosteric sea level change (0–2000 m), 1955–2010. Geophys. Res. Lett., 39, L10603, doi:10.1029/2012GL051106.

    • Search Google Scholar
    • Export Citation
  • Li, Y., , and W. Han, 2015: Decadal sea level variations in the Indian Ocean investigated with HYCOM: Roles of climate modes, ocean internal variability, and stochastic wind forcing. J. Climate, 28, 91439165, doi:10.1175/JCLI-D-15-0252.1.

    • Search Google Scholar
    • Export Citation
  • Liu, Q.-Y., , M. Feng, , D. Wang, , and S. Wijffels, 2015: Interannual variability of the Indonesian Throughflow transport: A revisit based on 30 year expendable bathythermograph data. J. Geophys. Res. Oceans, 120, 82708282, doi:10.1002/2015JC011351.

    • Search Google Scholar
    • Export Citation
  • Luo, J.-J., , W. Sasakia, , and Y. Masumoto, 2012: Indian Ocean warming modulates Pacific climate change. Proc. Natl. Acad. Sci. USA, 109, 18 70118 706, doi:10.1073/pnas.1210239109.

    • Search Google Scholar
    • Export Citation
  • Lyon, B., , and D. G. DeWitt, 2012: A recent and abrupt decline in the East African long rains. Geophys. Res. Lett., 39, L02702, doi:10.1029/2011GL050337.

    • Search Google Scholar
    • Export Citation
  • Meehl, G. A., , J. M. Arblaster, , J. T. Fasullo, , A. Hu, , and K. E. Trenberth, 2011: Model-based evidence of deep-ocean heat uptake during surface-temperature hiatus periods. Nat. Climate Change, 1, 360364, doi:10.1038/nclimate1229.

    • Search Google Scholar
    • Export Citation
  • Meehl, G. A., , A. Hu, , J. M. Arblaster, , J. Fasullo, , and K. E. Trenberth, 2013: Externally forced and internally generated decadal climate variability associated with the interdecadal Pacific oscillation. J. Climate, 26, 72987310, doi:10.1175/JCLI-D-12-00548.1.

    • Search Google Scholar
    • Export Citation
  • Nidheesh, A. G., , M. Lengaigne, , J. Vialard, , A. S. Unnikrishnan, , and H. Dayan, 2013: Decadal and long-term sea level variability in the tropical Indo-Pacific Ocean. Climate Dyn., 41, 381402, doi:10.1007/s00382-012-1463-4.

    • Search Google Scholar
    • Export Citation
  • Nieves, V., , J. K. Willis, , and W. C. Patzert, 2015: Recent hiatus caused by decadal shift in Indo-Pacific heating. Science, 349, 532535, doi:10.1126/science.aaa4521.

    • Search Google Scholar
    • Export Citation
  • Nishida, T., , T. Kitakado, , and H. Matsuura, 2011: Validation of the Global Ocean Data Assimilation System (GODAS) data in the NOAA National Centre for Environmental System (NCEP) by theory, comparative studies, applications and sea truth. Indian Ocean Tuna Commission Rep. IOTC-2011-WPB09-11, 18 pp. [Available online at http://www.iotc.org/documents/validation-global-ocean-data-assimilation-system-godas-data-noaa-national-centre.]

  • Pierce, D. W., , T. P. Barnett, , K. AchutaRao, , P. Gleckler, , J. Gregory, , and W. Washington, 2006: Anthropogenic warming of the oceans: Observations and model results. J. Climate, 19, 18731900, doi:10.1175/JCLI3723.1.

    • Search Google Scholar
    • Export Citation
  • Praveen Kumar, B., , J. Vialard, , M. Lengaigne, , V. S. N. Murty, , and M. J. McPhaden, 2012: TropFlux: Air–sea fluxes for the global tropical oceans—Description and evaluation. Climate Dyn., 38, 15211543, doi:10.1007/s00382-011-1115-0.

    • Search Google Scholar
    • Export Citation
  • Rayner, N. A., , D. E. Parker, , E. B. Horton, , C. K. Folland, , L. V. Alexander, , D. P. Rowell, , E. C. Kent, , and A. Kaplan, 2003: Global analyses of sea surface temperature, sea ice, and night marine air temperature since the late nineteenth century. J. Geophys. Res., 108 (D14), 4407, doi:10.1029/2002JD002670.

    • Search Google Scholar
    • Export Citation
  • Reason, C. J. C., , R. J. Allan, , and J. A. Lindesay, 1996: Evidence for the influence of remote forcing on interdecadal variability in the southern Indian Ocean. J. Geophys. Res., 101 (C5), 11 86711 882, doi:10.1029/96JC00122.

    • Search Google Scholar
    • Export Citation
  • Reynolds, R. W., , N. A. Rayner, , T. M. Smith, , D. C. Stokes, , and W. Wang, 2002: An improved in situ and satellite SST analysis for climate. J. Climate, 15, 16091625, doi:10.1175/1520-0442(2002)015<1609:AIISAS>2.0.CO;2.

    • Search Google Scholar
    • Export Citation
  • Roxy, M. K., , K. Ritika, , P. Terray, , and S. Masson, 2014: The curious case of Indian Ocean warming. J. Climate, 27, 85018509, doi:10.1175/JCLI-D-14-00471.1.

    • Search Google Scholar
    • Export Citation
  • Roxy, M. K., , K. Ritika, , P. Terray, , R. Murtugudde, , K. Ashok, , and B. N. Goswami, 2015: Drying of Indian subcontinent by rapid Indian Ocean warming and a weakening land–sea thermal gradient. Nat. Commun., 6, 7423, doi:10.1038/ncomms8423.

    • Search Google Scholar
    • Export Citation
  • Roxy, M. K., and et al. , 2016: A reduction in marine primary productivity driven by rapid warming over the tropical Indian Ocean. Geophys. Res. Lett., 43, 826833, doi:10.1002/2015GL066979.

    • Search Google Scholar
    • Export Citation
  • Schott, F. A., , S. P. Xie, , and J. P. McCreary, 2009: Indian Ocean circulation and climate variability. Rev. Geophys., 47, RG1002, doi:10.1029/2007RG000245.

    • Search Google Scholar
    • Export Citation
  • Schwarzkopf, F. U., , and C. W. Böning, 2011: Contribution of Pacific wind stress to multi‐decadal variations in upper-ocean heat content and sea level in the tropical south Indian Ocean. Geophys. Res. Lett., 38, L12602, doi:10.1029/2011GL047651.

    • Search Google Scholar
    • Export Citation
  • Smith, T. M., , R. W. Reynolds, , T. C. Peterson, , and J. Lawrimore, 2008: Improvements to NOAA’s historical merged land–ocean surface temperature analysis (1880–2006). J. Climate, 21, 22832296, doi:10.1175/2007JCLI2100.1.

    • Search Google Scholar
    • Export Citation
  • Sohn, B. J., , S. W. Yeh, , J. Schmetz, , and H. J. Song, 2013: Observational evidences of Walker circulation change over the last 30 years contrasting with GCM results. Climate Dyn., 40, 17211732, doi:10.1007/s00382-012-1484-z.

    • Search Google Scholar
    • Export Citation
  • Sprintall, J., , S. E. Wijffels, , R. Molcard, , and I. Jaya, 2009: Direct estimates of the Indonesian Throughflow entering the Indian Ocean: 2004–2006. J. Geophys. Res., 114, C07001, doi:10.1029/2008JC005257.

    • Search Google Scholar
    • Export Citation
  • Terray, P., , S. Masson, , C. Prodhomme, , M. K. Roxy, , and K. P. Sooraj, 2015: Impacts of Indian and Atlantic Oceans on ENSO in a comprehensive modeling framework. Climate Dyn., 46, 25072533, doi:10.1007/s00382-015-2715-x.

    • Search Google Scholar
    • Export Citation
  • Trenary, L., , and W. Han, 2013: Local and remote forcing of decadal sea level and thermocline depth variability in the south Indian Ocean. J. Geophys. Res. Oceans., 118, 381398, doi:10.1029/2012JC008317.

    • Search Google Scholar
    • Export Citation
  • Ueda, H., , Y. Kamae, , M. Hayasaki, , A. Kitoh, , S. Watanabe, , Y. Miki, , and A. Kumai, 2015: Combined effects of recent Pacific cooling and Indian Ocean warming on the Asian monsoon. Nat. Commun., 6, 8854, doi:10.1038/ncomms9854.

    • Search Google Scholar
    • Export Citation
  • Wang, B., , J. Liu, , H. J. Kim, , P. J. Webster, , and S. Y. Yim, 2012: Recent change of the global monsoon precipitation (1979–2008). Climate Dyn., 39, 11231135, doi:10.1007/s00382-011-1266-z.

    • Search Google Scholar
    • Export Citation
  • Watanabe, M., , H. Shiogama, , H. Tatebe, , M. Hayashi, , M. Ishii, , and M. Kimoto, 2014: Contribution of natural decadal variability to global warming acceleration and hiatus. Nat. Climate Change, 4, 893897, doi:10.1038/nclimate2355.

    • Search Google Scholar
    • Export Citation
  • Yu, L., , and M. M. Rienecker, 1999: Mechanisms for the Indian Ocean warming during the 1997–98 El Niño. Geophys. Res. Lett., 26, 735738, doi:10.1029/1999GL900072.

    • Search Google Scholar
    • Export Citation
  • Yu, L., , X. Jin, , and R. A. Weller, 2008: Multidecade global flux datasets from the objectively analyzed air–sea fluxes (OAFlux) project: Latent and sensible heat fluxes, ocean evaporation, and related surface meteorological variables. OAFlux Project Tech. Rep. OA-2008-01, Woods Hole Oceanographic Institution, 64 pp.

  • Zhang, X., , and M. J. McPhaden, 2010: Surface layer heat balance in the eastern equatorial Pacific Ocean on interannual time scales: Influence of local versus remote wind forcing. J. Climate, 23, 43754394, doi:10.1175/2010JCLI3469.1.

    • Search Google Scholar
    • Export Citation
  • Zhou, T. J., and et al. , 2009: Why the western Pacific subtropical high has extended westward since the late 1970s. J. Climate, 22, 21992215, doi:10.1175/2008JCLI2527.1.

    • Search Google Scholar
    • Export Citation
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Interhemispheric SST Gradient Trends in the Indian Ocean prior to and during the Recent Global Warming Hiatus

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  • 1 NOAA/Pacific Marine Environmental Laboratory, Seattle, Washington
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Abstract

Sea surface temperatures (SSTs) have been rising for decades in the Indian Ocean in response to greenhouse gas forcing. However, this study shows that during the recent hiatus in global warming, a striking interhemispheric gradient in Indian Ocean SST trends developed around 2000, with relatively weak or little warming to the north of 10°S and accelerated warming to the south of 10°S. Evidence is presented from a wide variety of data sources showing that this interhemispheric gradient in SST trends is forced primarily by an increase of Indonesian Throughflow (ITF) transport from the Pacific into the Indian Ocean induced by stronger Pacific trade winds. This increased transport led to a depression of the thermocline that facilitated SST warming, presumably through a reduction in the vertical turbulent transport of heat in the southern Indian Ocean. Surface wind changes in the Indian Ocean linked to the enhanced Walker circulation also may have contributed to thermocline depth variations and associated SST changes, with downwelling-favorable wind stress curls between 10° and 20°S and upwelling-favorable wind stress curls between the equator and 10°S. In addition, the anomalous southwesterly wind stresses off the coast of Somalia favored intensified coastal upwelling and offshore advection of upwelled water, which would have led to reduced warming of the northern Indian Ocean. Although highly uncertain, lateral heat advection associated with the ITF and surface heat fluxes may also have played a role in forming the interhemispheric SST gradient change.

Pacific Marine Environmental Laboratory Contribution Number 4431.

Corresponding author address: Lu Dong, NOAA/Pacific Marine Environmental Laboratory, 7600 Sand Point Way NE, Seattle, WA 98115. E-mail: lu.dong@noaa.gov

Abstract

Sea surface temperatures (SSTs) have been rising for decades in the Indian Ocean in response to greenhouse gas forcing. However, this study shows that during the recent hiatus in global warming, a striking interhemispheric gradient in Indian Ocean SST trends developed around 2000, with relatively weak or little warming to the north of 10°S and accelerated warming to the south of 10°S. Evidence is presented from a wide variety of data sources showing that this interhemispheric gradient in SST trends is forced primarily by an increase of Indonesian Throughflow (ITF) transport from the Pacific into the Indian Ocean induced by stronger Pacific trade winds. This increased transport led to a depression of the thermocline that facilitated SST warming, presumably through a reduction in the vertical turbulent transport of heat in the southern Indian Ocean. Surface wind changes in the Indian Ocean linked to the enhanced Walker circulation also may have contributed to thermocline depth variations and associated SST changes, with downwelling-favorable wind stress curls between 10° and 20°S and upwelling-favorable wind stress curls between the equator and 10°S. In addition, the anomalous southwesterly wind stresses off the coast of Somalia favored intensified coastal upwelling and offshore advection of upwelled water, which would have led to reduced warming of the northern Indian Ocean. Although highly uncertain, lateral heat advection associated with the ITF and surface heat fluxes may also have played a role in forming the interhemispheric SST gradient change.

Pacific Marine Environmental Laboratory Contribution Number 4431.

Corresponding author address: Lu Dong, NOAA/Pacific Marine Environmental Laboratory, 7600 Sand Point Way NE, Seattle, WA 98115. E-mail: lu.dong@noaa.gov
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