METHANE HYDRATE AND QUATERNARY CLIMATE CHANGE: EVIDENCE FROM SEDIMENT RECORDS AND MODERN METHANE SEEPS

Methane hydrates have been implicated as a possible forcing mechanism for rapid climate change during the late Quaternary. Releases from the hydrate reservoir are recorded as carbon isotopic spikes in marine sediment records and may represent a significant perturbation of the global carbon cycle. While the role of methane hydrates in rapid climate change is controversial, aspects of this hypothesis are currently being tested using high-resolution sediment records and studies at modern methane seep environments.

Carbon isotopic (d13C) spikes previously recorded in Santa Barbara Basin (ODP Site 893) have been interpreted as evidence of massive local gas hydrate destabilization. Further studies of stadial/interstadial transitions ODP Site 893 at ultra-high resolution have uncovered additional d13C excursions. These d13C spikes occur immediately following bottom water warming associated with the onset of interstadials. These spikes occur in both benthic and planktonic foraminifera, and are very brief, lasting only decades.

The observed d13C spikes are similar in magnitude to those observed in foraminifera from modern methane seeps (Santa Barbara Basin and Hydrate Ridge, Oregon). Benthic foraminifera living at modern methane seeps record negative d13C values (to –10‰). In addition, certain foraminiferal species are well adapted to the high-organic, low-oxygen methane seep environment. Because these trends are recorded in live foraminifera, concern about authigenic carbonate altering the d13C signature is negated.

Ongoing research is comparing the relative response of surface and intermediate waters during abrupt climatic warming. Intermediate waters are important because they reside at the critical depth of potential instability of the methane hydrate reservoir in the late Quaternary. In Santa Barbara Basin, d18O changes record inferred intermediate water warmings of 2-3°C during stadial to interstadial transitions. These records also indicate that during stadial/interstadial transitions and the deglacial episode, intermediate water warming either preceded or may have been synchronous with surface water warming. This research continues to test and lend supportive evidence to the hypothesis that the methane hydrate reservoir may have played a crucial role in late Quaternary climate change.