The primary objectives of this project are to: 1) investigate the effect of rising water temperatures on the stability of oceanic hydrate accumulations, 2) estimate the global quantity of hydrate-originating carbon that could reach the upper atmosphere as CH4 or CO2 thus affecting global climate, 3) quantify the interrelationship between global climate and the amount of hydrate-derived carbon reaching the upper atmosphere focusing on the potential link between hydrate dissociation and cascading global warming and 4) test the discharge phase of the Clathrate Gun Hypothesis which stipulates large-scale hydrate dissociation and gas release and rapid warming over very short geological periods.
Lawrence Berkeley National Laboratory, Berkeley, CA 94720
Los Alamos National Laboratory, Albuquerque, NM 87545
Gas hydrates are solid crystalline compounds in which gas molecules are lodged within the lattices of ice crystals. Natural gas hydrate deposits occur in two distinctly different geologic settings where the low temperatures and relatively high pressures necessary for their formation and stability exist: in or beneath arctic permafrost and in deep ocean sediments. A review of the literature on the subject indicates that (a) estimates of in situ methane hydrate reserves are enormous, ranging from 1015 m3 (Milkov, 2004) to as high as 7.6x1018 m3(Dobrynin, 1981), and (b) the oceanic reserves are about 2 orders of magnitude larger than the permafrost deposits.
In oceanic deposits, the sediment/water depth range over which hydrates remain stable depends on the pressure (as imposed by the water depth) and temperature (see figure). A pressure decrease due to a lowering of the sea level, or an increase in the temperature of the ocean water in contact with the seabed, could induce hydrate dissociation, leading to methane (CH4) release. The released CH4 would be transferred to the exchangeable carbon reservoir by ebullition and diffusion into the water column, advection by the water current, chemical and biochemical oxidation reactions in the water column and, finally, by ebullition into the atmosphere if the rate of CH4 release exceeds the rate of oxidation (Kennett et al., 2000). The latter would be significantly enhanced in cases of sediment slope failure, sliding or collapse (Dickens et al., 1995).
Because CH4 is a powerful greenhouse gas (about 26 times more effective than CO2), there is considerable concern that a rise in the temperature of sea water at the ocean floor will induce dissociation of oceanic hydrate accumulations, potentially releasing very large amounts of CH4 into the atmosphere. Such a release could have dramatic climatic consequences because it could lead to further atmospheric and oceanic warming, further amplifying the problem by accelerating dissociation of the remaining hydrates.
Such hydrate dissociation has been proposed as the main culprit for a repeated, remarkably rapid sequence of global warming events that occurred in less than one human life span during the late Quaternary (Kennett et al., 2000, 2002; Behl et al., 2003). The Clathrate Gun Hypothesis (Kennett et al., 2002) proposes that the marine hydrate accumulations undergo repeated cycles of reloading and discharge, with hydrates accumulating during cold glacial intervals and dissociating when triggered by pulses of warmer water impinging on the continental slopes. This mechanism (the validity of which is not assured) could have greatly amplified and accelerated global warming episodes, and its potential impact in the current global warming trend cannot be ignored.
The objectives of this study are to be accomplished by means of numerical simulation that will involve the coupling of codes already developed by Lawrence Berkeley National Laboratory (LBNL) and Los Alamos National Laboratory (LANL). These codes include TOUGH+/HYDRATE, which models non-isothermal gas release from hydrates, phase behavior and flow of fluids and heat in complex geologic media; POP/CCSM, where POP (Parallel Ocean Program) is the active ocean-model component of the CCSM (Community Climate System Model) for modeling ocean/climate interactions; TOUGHREACT, a geochemical code for simulating chemically reactive non-isothermal flows of multiphase fluids in porous and fractured media; and C.CANDI, a code used to describe benthic biogeochemistry.
More specifically, TOUGH+/HYDRATE and a biogeochemical code will provide a source term to POP/CCSM, while POP/CCSM will provide ocean floor temperature and water elevation data to the TOUGH+HYDRATE and biogeochemical codes. C.CANDI is the code used to describe benthic biogeochemistry in the preliminary LBNL studies on the environmental/climatic impact of hydrate dissociation. However, it is possible that, in the course of this effort, the TOUGHREACT code (a geochemical code developed by LBNL, and easily accessible by TOUGH+/HYDRATE – Xu et al., 2004; 2006) may also be employed to augment the biogeochemical capabilities of the coupled codes. Using appropriate estimates of the global spatial distribution of hydrates in the oceanic subsurface, the resulting integrated/coupled model will be able to track the net influxes of CH4 (originating from hydrate dissociation) and of CO2 (resulting from CH4 oxidation) into the atmosphere using a 3D global grid (encompassing the oceans, the land masses and the atmosphere), and will be capable of estimating the climatic effect of these releases.
The development of a complete thermo-hydrological-chemical model for benthic methane hydrates may help to finally answer pressing questions about the significance of gas hydrates in the global carbon budget, and consequently, on global climate. The dynamic treatment of gas hydrate decomposition, including transport of fluids, heat transfer, and hydrate phase behavior, will bridge the gap between estimates of hydrate abundance and hypothesized climate impacts of the hydrate-related carbon. Distinguishing between catastrophic, chronic, and minor releases and quantifying the amount and time scales involved will help to confirm or deny the possibility of clathrate-enhanced climate cycles.
This effort will develop, for the first time, a tool for the systematic quantification of the potential impact of dissociating marine hydrates on the global climate. The results of this study will be important in testing the validity of the Clathrate Gun hypothesis, and the corollary hypothesis that rapid hydrate dissociation can have a cascading effect resulting in enhanced hydrate dissociation and accelerating global warming, with potentially catastrophic physical and economic consequences.
The project has been completed. The final report is available below under "Additional Information".
All DOE Contribution: $1,244,900
FY08 $158,000 $92,000
FY09 $174,000 $140,000
FY10 $165,000 $165,000
FY12 $175,000 $175,000
In addition to the information provided here, a full listing of project related publications and presentations as well as a listing of funded students can be found in the Methane Hydrate Program Bibliography [PDF].
Additional LBNL hydrate-related publications can also be found on the LBNL Gas Hydrate Publications webpage.
Final Project Report [PDF-271KB] - July, 2013
Technical Report [PDF-1.46MB] - Testing of the Clathrate Gun Hypothesis
Technical Report [PDF-813KB] - Global Scale Simulations of the Interrelation Between Hydrate Dissociation and Global Climate
Tecnical Report [PDF-504KB] - Regional Assessments of Methane Release from Submarine Hydrates in the Arctic due to Ocean Warming
2010 Annual Report [PDF-226KB]
2009 Annual Report [PDF-225KB]
2008 Hydrate Peer Review [PDF-2.47MB]
2008 ICGH Paper - Modeling of Oceanic Gas Hydrate Instability and Methane Release in Response to Climate Change [PDF]