Seafloor Echoes Used to Map Gulf Methane Ice Don't Line up With Theory

A survey of the northern Gulf of Mexico has found that 70 bottom simulating reflections (the seismic echo geologists use to trace how deep methane hydrate reaches beneath the seafloor) do not coincide with the calculated base of methane hydrate stability, according to a study published on Aug. 31, 2026, in Communications Earth & Environment.

Methane hydrate is methane locked into an ice-like solid in seafloor sediment. A bottom simulating reflection, or BSR, is a bright reflection in seismic data that runs roughly parallel to the seafloor and has long been read as the bottom of the zone where hydrate is stable.

The researchers found that the depths of the 70 BSRs vary over hundreds of meters, failing to coincide with the calculated thermodynamic base of methane hydrate stability. Furthermore, BSR depth does not correlate strongly with water depth, running counter to the expected pattern where BSRs usually parallel the seafloor and deepen as water depths increase.

"Hydrate stability is well defined in laboratory measurements, but we argue that fundamental constraints on hydrate stability are not understood in natural systems," the authors write.

The 70 reflections were measured in publicly archived marine seismic surveys held by the U.S. Geological Survey, which the study credits. The work is by Aditya Kumar and Ann E. Cook of the School of Earth Sciences at Ohio State University, with co-authors at IACT-CSIC in Granada, the University of Texas at Austin and Fugro in Perth.

Subsurface salt "appears to control broad trends in BSR depths in the Gulf of Mexico," the researchers note, adding that unaccounted processes still influence the stability of these systems. At several deepwater locations, BSRs approach the seafloor, suggesting that hydrate there "could be at risk of dissociation."

The study's opening line puts global natural gas hydrate at "hundreds to thousands of gigatons of metastable carbon." It is open access, was received Feb. 16, 2026, and accepted on Aug. 20, 2026. The journal is publishing this accepted manuscript ahead of the final version of record.