Destabilization of equatorial permafrost methane clathrate during Marinoan Ice Age: Affects of Methane Clathrate on global climate systems.

The Edicaran period was one of the most severe climate change events in Earth history. Termed the Marinoan ice age, Marinoan glacial marine deposits occurred at equatorial palaeolatitudes. Given their sharp overlain thin intervals of carbonate, it preserved marine carbon and sulphur isotopic excursions at -5 and +15 parts per thousand, as these deposits are thought to have recorded oceanic carbonate precipitation during postglacial sea level rises.

Accounted by the abruptness of deglaciation and the induction of ice albedo feedback, deep ocean-out gassing during the post glacial oceanic overturn and methane hydrate destabilization brought a range of oxygen isotope values to be measured to be -25% to +12% in marine sediments within Marinoan deglacial sediments underlying carbonated caps. The mixing between ice-sheets derived from meteoric waters and clathrates derived fluids during flushing and destabilization of clathrate fields by glacial meltwater being the likely cause of these values.

Findings suggest that methane released from low latitude permafrost clathrates acted as catalysts creating strong positive feedback for deglaciation and warming. Methane hydrate destabilization has increasingly brought positive feedback to climate change, coinciding with critical boundaries in the geological record, possibly representing an important active climate force mechanism.

Methane coldseep origin diagnostics are indicative to vertical fluid and gas migration, overpressure, seafloor working and complex seafloor paragensis. This morphology contrasts the extensive regional laminated dolomicrite of overlying Nuccaleena Formation and the sparry calcite that fills cross-cutting fractures aligned with regional folding, accounting concurrent methanotrophy and mixing between isotopically heavy methanogenic CO2 and marine bicarbonate.

The value of thermal equilibration is inconsistent with (1) microcrystalline morphology of cement, (2) the isotopic heterogeneity of millimeter scales, and (3) the relatively heavy δ ¹⁸ organic carbon (O) values of the Nuccaleena carbonate cap and late-stage (tectonic) cross-cutting spar fill fractures. The isotopic signature of most depleted cementes (-25%) requires porewater values as low as -28 to -30%, unique to meltwater released from glacial ice in modern hydrological cycles. In the geological record, these low values found in thermal altered carbonate pars are formed from glacial meltwater in ancient carbonates.

Seep shallow environments in which meotric fluid is derived from ice sheets mixed with δ ¹⁸O enriched clathrate derived fluids are enriched with depleted δ ¹⁸O end members due to sub centimeter spatial association and synsedimentary timing relationship between stable isotopic endmembers. Shelf settings occurs when the hydraulic drive of melting ice sheets charge water tables, flushing and destabilizing clathrate fields. Water could not be enough to stabilize clathrates due to the fact that marine clathrates require both sea water at additional pressures of more then 250m of water and deepening succession midway between preceding glacial sealevel lowstand would not be deep enough to create clathrate stabilization. Therefore stabilization must be created from pressure of shelfeborne ice sheets from permafrost conditions or frost wedging. Permafrost clathrates can then accumulate beneath broad exposed shelves in the Arctic during the Pleistocene destabilization resulting in post glacial flooding and global warming. Similarly, the retreat of Marinoan ice sheets would destabilize methane clathrates by reducing hydrostatic pressure, warming permafrost shelves by flooding sea water and flushing clathrate fields with meteoric water derived from meltwater discharge.

 The role of methane in climate systems is important in the extension of volatile permafrost clathrate pools to equatorial paleaolatitudes. The Marinoan shelf is particularly low in latitude where it is sensitive to subtle external forces brought by warming or simply inherent icesheets of instability, enough to trigger local methane destabilization through meteoric flushing of permafrost clathrate fields in the Marinoan shelf. Destabilitization in higher latitudes eventually forms methane clathrates initiating positive feedback through positive greenhouse warming then amplified by methane and CO2. The total present day shelf area, including lower latitudes could increase to the potential 3,000 Gt extending to the Holoscene permafrost reservoir occurring over the Arctic shelves.

 

Balancing feedbacks and progressive glacial interglacial cycles of the Cenozoic deglaciation is an important phenomena to analyze as the violent opening of the highly volatile shelf-permafrost methane clathrate pool could have acted as a trigger to a catastrophic climate and biogeochemical reorganization of the Earth systems, bringing the icy Cryogenian period to a close and setting the stage for the appearance of a metazoans and dominance of the new Earth System. This event both identifies the range of function of the hydrate clathrate systems and demonstrates the strength of climate forces projected for the future effects of extreme atmospheric green house gases.