Seismic ocean thermometry based on CTBTO hydrophone data

Abstract:

As the major buffer of Earth’s energy imbalance, the ocean absorbs almost all the excess heat due to increasingly abundant anthropogenic greenhouse gases and regulates global climate and temperature changes. However, accurate estimation of global ocean heat content change remains a challenging sampling problem. To complement existing point measurements, we develop a novel and low-cost method of using travel time changes of seismic waves from repeating natural earthquakes to infer basin-scale average ocean temperature changes. We have implemented this method using the GSN seismic station DGAR in the central Indian ocean and demonstrated its capability to resolve signals missing in previous oceanographic datasets within a high accuracy of 0.0060 K. In this study, we extend the method to CTBTO hydrophones H08 near the DGAR station, which record clearer T waves than DGAR and therefore permit the usage of more small repeating earthquakes. We use the template-matching method to scan through continuous seismic data in search for more a complete set of repeating earthquakes in 2005–2016 around the Nias Island off Sumatra. The ocean temperature change inferred from H08 data is generally consistent with DGAR results and has, as expected, an even higher spatial resolution, resulting from using earthquakes missing in the ISC catalog. These results suggest that the global hydrophone network offers new opportunities for monitoring ocean warming.