Vertical‐Slice Ocean Tomography With Seismic Waves. Issue 8 (15th April 2023)

• Record Type: Journal Article
• Authors: Callies, Jörn; Wu, Wenbo; Peng, Shirui; Zhan, Zhongwen
• Is Part Of: Geophysical research letters. Volume 50:Issue 8(2023)
• Page Start: n/a
• Page End: n/a
• Publication Date: 2023-04-15
• Subjects: ocean heat uptake -- ocean acoustic tomography -- T waves; Geophysics -- Periodicals; Planets -- Periodicals; Lunar geology -- Periodicals; 550
• DOI: 10.1029/2023GL102881
• Languages: English
• ISSNs: 0094-8276

Abstract

Abstract: Seismically generated sound waves that propagate through the ocean are used to infer temperature anomalies and their vertical structure in the deep East Indian Ocean. These T waves are generated by earthquakes off Sumatra and received by hydrophone stations off Diego Garcia and Cape Leeuwin. Between repeating earthquakes, a T wave's travel time changes in response to temperature anomalies along the wave's path. What part of the water column the travel time is sensitive to depends on the frequency of the wave, so measuring travel time changes at a few low frequencies constrains the vertical structure of the inferred temperature anomalies. These measurements reveal anomalies due to equatorial waves, mesoscale eddies, and decadal warming trends. By providing direct constraints on basin‐scale averages with dense sampling in time, these data complement previous point measurements that alias local and transient temperature anomalies. Plain Language Summary: Taking up almost all of the excess heat trapped on Earth by anthropogenic greenhouse gases, the ocean exerts a key control on our warming climate. Despite progress, tracking that heat remains an observational challenge. This study presents new measurements of ocean warming by making use of sound waves that are generated by earthquakes and propagate long distances through the ocean. These sound waves propagate faster in warmer seawater, so they arrive slightly earlier if warming has occurred. In this study, we measure such changes in arrival time at different frequencies—or pitches—that are sensitive to different parts of the water column, so warming in the upper ocean can be distinguished from warming in the deep ocean. Key Points: Seismic T waves at different frequencies sample different parts of the water column Frequency‐dependent travel time changes between repeating earthquakes constrain the depth‐dependent temperature change between the events These data reveal the vertical structure of temperature anomalies produces by equatorial waves, mesoscale eddies, and decadal warming