2010-10-06 15:25:48Has anyone seen these yet?
Daniel Bailey
Daniel Bailey
yooper49855@hotmail...
130.36.62.140
Some interesting recent developments on the methane clathrate/PETM front.

1. From GEOLOGY (Abstract only available):
"Changes in ocean circulation have been proposed as a trigger mechanism for the large coupled climate and carbon cycle perturbations at the Paleocene-Eocene Thermal Maximum (PETM, ca. 55 Ma). An abrupt warming of oceanic intermediate waters could have initiated the thermal destabilization of sediment-hosted methane gas hydrates and potentially triggered sediment slumps and slides. In an ensemble of fully coupled atmosphere-ocean general circulation model (AOGCM) simulations of the late Paleocene and early Eocene, we identify such a circulation-driven enhanced intermediate-water warming. Critically, we find an approximate twofold amplification of Atlantic intermediate-water warming when CO2 levels are doubled from 2× to 4× preindustrial CO2  compared to when they are doubled from 1× to 2×. This warming is largely focused on the equatorial and South Atlantic and is driven by a significant reduction in deep-water formation from the Southern Ocean. This scenario is consistent with altered PETM circulation patterns inferred from benthic carbon isotope data and the intensity of deep-sea carbonate dissolution in the South Atlantic. The linkage between intermediate-water warming and gas hydrate destabilization could provide an important feedback in the establishment of peak PETM warmth."
Source:
CO2-driven ocean circulation changes as an amplifier of Paleocene-Eocene thermal maximum hydrate destabilization


2. From Philosophical Transactions Of The Royal Society A (Abstract only available):
"The plausible range of carbon mass input, approximately 4000–7000 PgC, strongly suggests a major alternative source of carbon in addition to any contribution from methane hydrates. We find that the potential range of PETM atmospheric pCO2 increase, combined with proxy estimates of the PETM temperature anomaly, does not necessarily imply climate sensitivities beyond the range of state-of-the-art climate models."
Source:
A Palaeogene perspective on climate sensitivity and methane hydrate instability


3. From a poster presentation at the EGU, 2010
"Hyperthermal climate events are geologically brief (~10-100kyrs) transient periods of marked global warming associated with prominent negative carbon isotope excursions and deep-sea carbonate dissolution. They are most likely the result of massive injections of isotopically light carbon into the ocean-atmosphere system. One plausible source of isotopically light carbon is a widespread dissociation of continental slope, sediment-hosted methane gas hydrates. Proposed triggers for the dissociation of such deep-water hydrates include a pronounced (~4ºC) warming of intermediate to deep waters driven by changes in global overturning circulation (Dickens et al., 1995).

The most prominent hyperthermal event of the Ceonzoic is the Paleocene Eocene thermal maximum (~55Ma; PETM)."

"CONCLUSIONS
We show modelling results which support the hypothesis that Eocene hyperthermals could be paced by orbital variations. The mechanism for this forcing is orbitally induced switches in ocean circulation, which lead to non-linear intermediate ocean warming, with the possibility of resulting destabilization of methane gas hydrates. The switches in circulation are associated with high eccentricity and obliquity and maximum seasonality in the Northern Hemisphere."
Poster Source:
Is There An Orbital Control On Eocene Hyperthermals?

Apologies for no links to the full articles (both paywalled).  I've requested the articles through my employer library; will offer up a deeper dish when I get them.

The Yooper