Modeling the fate of methane hydrates under global warming

Abstract

Large amounts of methane hydrate locked up within marine sediments are vulnerable to climate change. Changes in bottom water temperatures may lead to their destabilization and the release of methane into the water column or even the atmosphere. In a multimodel approach, the possible impact of destabilizing methane hydrates onto global climate within the next century is evaluated. The focus is set on changing bottom water temperatures to infer the response of the global methane hydrate inventory to future climate change. Present and future bottom water temperatures are evaluated by the combined use of hindcast high‐resolution ocean circulation simulations and climate modeling for the next century. The changing global hydrate inventory is computed using the parameterized transfer function recently proposed by Wallmann et al. (2012). We find that the present‐day world's total marine methane hydrate inventory is estimated to be 1146 Gt of methane carbon. Within the next 100 years this global inventory may be reduced by ∼0.03% (releasing ∼473 Mt methane from the seafloor). Compared to the present‐day annual emissions of anthropogenic methane, the amount of methane released from melting hydrates by 2100 is small and will not have a major impact on the global climate. On a regional scale, ocean bottom warming over the next 100 years will result in a relatively large decrease in the methane hydrate deposits, with the Arctic and Blake Ridge region, offshore South Carolina, being most affected.

The challenges of quantifying the carbon stored in Arctic marine gas hydrate

“…A 2°C increase over 100 yr is enough to start dissociating the base of the GHSZ at those shallow water depths, and so most of the carbon stored in GH is liberated. Our estimated reduction of the GH inventory using the M C _1 model is similar to that from Kretschmer et al (2015) of 0.14±0.01Gt…”

“…This result suggests that the marine GH inventory in the Arctic is probably larger than that recently estimated of 116 Gt of carbon (Kretschmer et al, 2015).…”

“…Based on Wallmann's et al (2012) transfer equation for steady-state compaction and a slight modification of Burwicz et al (2013) to consider Quaternary accumulation rates, Kretschmer et al (2015) estimated a present day volume of the GHSZ of 3.80x10 15 m 3 containing 116 Gt of carbon. Our lower value of GH inventory using the same transfer function as Kretschmer et al (2015) is likely because they estimated a larger volume of the GHSZ and assumed higher sedimentation rates at continental slopes (between 200-500 m water depth).…”

The global methane budget 2000–2012

“…No experimental data or estimation procedures have been explicitly described along the chain of references since then (Lelieveld et al, 1998;Denman et al, 2007;Kirschke et al, 2013;IPCC, 2001). It was recently estimated that ∼ 473 Tg CH 4 was released in the water column over 100 years (Kretschmer et al, 2015). Those few Tg per year become negligible once consumption in the water column has been accounted for.…”

Submarine vortices derived from natural gas hydrate conversion: a mechanism for ocean mixing

“…Due to its low latitude, relatively small size, and isolation from the Atlantic cold deep water, the Mediterranean Sea is a natural laboratory for observing the effects of temperature variation from glacial to interglacial conditions on the GHSZ. Like the Arctic Ocean, due to its particular geography and location, the effects of ocean temperature changes since the last glacial period (e.g., Bindoff et al, 2007) have a greater impact than elsewhere (Biastoch et al, 2011) and allow further analysis of the effects of climate forcing of NGH (e.g., Archer, 2007;Kretschmer et al, 2015). Temperature changes typically induce heterogeneous changes in the Mediterranean Sea, but in recent years ecological responses have been at the basin-scale (Rivetti et al, 2014) indicating an increase in the rate of change and making the Mediterranean Sea a possible model for the GHSZ in open ocean conditions under the high-end IPCC representative concentration pathway scenarios (Pachauri & Reisinger, 2007;Pachauri et al, 2014).…”