Seismic ocean thermometry
More than 90% of the energy trapped on Earth by increasingly abundant greenhouse gases is absorbed by the ocean. Monitoring the resulting ocean warming remains a challenging sampling problem. To complement existing point measurements, we introduce a method that infers basin-scale deep-ocean temperature changes from the travel times of sound waves that are generated by repeating earthquakes. A first implementation of this seismic ocean thermometry constrains temperature anomalies averaged across a 3000-kilometer-long section in the equatorial East Indian Ocean with a standard error of 0.0060 kelvin. Between 2005 and 2016, we find temperature fluctuations on time scales of 12 months, 6 months, and ~10 days, and we infer a decadal warming trend that substantially exceeds previous estimates.
© 2020 American Association for the Advancement of Science. This is an article distributed under the terms of the Science Journals Default License. Received 28 March 2020; accepted 31 July 2020. This work was supported in part by the Caltech Seismological Laboratory Director's Postdoctoral Scholar fellowship awarded to W.W. and by the Resnick Sustainability Institute. S.N. was supported by the National Natural Science Foundation of China (grant 41590854) and the Chinese Academy of Sciences (grant XDB18000000). Author contributions: W.W. conceived the original idea. Z.Z. and J.C. supervised the study. W.W. processed the seismic data and conducted the seismic modeling. S.P. and J.C. processed the oceanographic data, and J.C. performed the data inversion. The paper was written by W.W. and J.C. with input from Z.Z. and S.N. All authors discussed the results and commented on the manuscript. The authors declare no competing interests. Data and materials availability: The seismic data are archived at the Incorporated Research Institutions for Seismology (IRIS) and are accessible through the IRIS Data Management Center (http://ds.iris.edu/). ECCO data are available from NASA's Data Portal (https://data.nas.nasa.gov/). Argo data are collected and made freely available by the International Argo Program and the national programs that contribute to it. The float data are available from the Global Data Assembly Centre (41). The figures were prepared using the Generic Mapping Tools (www.soest.hawaii.edu/gmt/), Obspy (https://github.com/obspy/obspy), Cartopy (https://scitools.org.uk/cartopy/), and Matplotlib (https://matplotlib.org/).
Supplemental Material - abb9519_Wu_SM.pdf