|Interrelation of Global Climate and the Response of Oceanic Hydrate Accumulations
||Last Reviewed 8/21/2013
Field Work Proposals: ESD07-014 (LBNL) and 08FE-003 (LANL)
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.
Example of an envelope of CH4-hydrate stability in ocean sediments
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 climate modeling team completed a report entitled: “Global Scale Simulations of the Interaction Between Hydrate Dissociation and Global Climate” (listed under "Additional Information" below). The report describes modelers’ efforts to simulate the release of methane from oceanic deposits on a global scale, using temperature change data taken directly from the Community Earth System Model, a fully-coupled, global climate model that provides state-of-the-art computer simulations of past, present, and future climate states; these were the first such simulations performed. The results show that the methane release is likely to be confined to a narrow region of high dissociation susceptibility, defined mainly by depth and temperature, and that any release will be relatively uniform and controlled, rather than explosive. In addition, simulations indicate that the bulk of the climate-sensitive hydrates exist in the high northern latitudes, and that shallow hydrates (in water depths of 300–600m) make up the bulk of hydrates sensitive to warming scenarios.
- Researchers completed a technical report entitled "Testing of the Clathrate Gun Hypothesis" (listed under "Additional Information" below).
- The hydrate-climate modeling team published a paper discussing the results of the project. The paper, “Contribution of Oceanic Gas Hydrate Dissociation to the Formation of Arctic Ocean Methane Plumes,” was published in the September 2011 Journal of Geophysical Research. In the study researchers conducted 2-D simulations of hydrate dissociation at conditions representing the Arctic Ocean margin to determine if hydrates contribute to observed gas release. Results indicated that shallow, low saturation hydrates subjected to predicted warming trends at the seafloor can release methane in quantities similar to recently published observations.
- The entire Arctic Ocean basin bathymetry was mapped and 1-D simulations were performed. As seen in the smaller-scale models, the region of potential hydrate dissociation and significant methane flux is confined to a narrow zone of sensitivity—mainly deposits in water depths of 320 m to about 450 m. Deeper hydrates are not likely to release large amounts of methane unless temperature changes continue for centuries, penetrating deep into the water column. Preliminary results of mapping and 1-D simulations of the entire Arctic Ocean basin bathymetry research were presented at the International Conference on Gas Hydrates in Edinburgh, Scotland in July 2011.
- A paper entitled “Marine Methane Cycle Simulations for the Period of Early Global Warming," was published in the January 2011 edition of the Journal of Geophysical Research-Biogeosciences. The research represents an attempt to assess the fate of hydrate-derived methane as it is affected and controlled by marine geochemistry during its transit through the seafloor sediments into the sea.
- Simulations of temperature-driven hydrate dissociation as a function of depth and location, using initial conditions representing the Sea of Okhotsk and the Beaufort Sea continental shelf were performed. Results indicate that the most sensitive hydrate deposits under ocean warming scenarios are located in a narrow zone along continental margins. This narrow zone is also likely to be the only source of large-scale gaseous fluxes of methane, and thus may be the only region where it can escape oxidation and enter the water column. The results of this research were presented at the 2010 AGU Fall Meeting and at the 2011 SPE Arctic Technology Conference.
- LBNL & LANL completed the 1-D studies of hydrate dissociation under various conditions of depth, temperature, rate of warming, sediment permeability, and sea level change. The simulation work has been expanded to a large-scale 2-D simulation, which is being applied to hydrate systems at various locations, depths, temperatures, and slope angles. Combined with the map of likely destabilization zones, this forms a basis and set of tools for the assessment of hydrate stability and release over large scales.
- The reduction of TOUGH+HYDRATE to a modular subroutine accessible to the POP ocean code was completed, and the new structure underwent testing at LBNL for final incorporation into the POP model. The coupled use of TOUGH+HYDRATE and C.CANDI determined that the ability of sediment biogeochemical processes to mitigate methane release is highly limited, and that large-scale oxidation-reduction of methane to stable carbonates can only occur under a limited set of conditions.
- Researchers completed the reactive transport enhancements including the development of marine methane cycle simulation capabilities and the introduction of arctic patch clathrate destabilizations. Runs were conducted in an inert tracer mode in order to bracket atmospheric release from surface waters of the Arctic Ocean.
- Global warming scenarios were assessed and quantified using outputs from the Community Climate System Model (CCSM) in order to generate realistic scenarios of temperature evolution over time assuming current trends of global warming. Initial estimates were extracted from existing simulations used for the most recent Intergovernmental Panel on Climate Change assessment (IPCC 1996). These estimates defined an envelope of possible temperature increase scenarios in response to various scenarios of future atmospheric CO2 levels and releases. Comparisons with ongoing eddy-resolving POP ocean-only simulations were used to quantify known biases in coarse resolution CCSM simulations and evaluate potential impacts on the CCSM predictions. This study involved global-scale simulations to yield temperature time-series at desired locations. The temperature changes determined in this task were used as inputs in the small-scale studies of greenhouse gas releases at the ocean floor on limited spatial scales.
- The results generated through this project have resulted in the publication of four papers in the peer-reviewed literature by LBNL and LANL researchers. (For more information, see the methane hydrate bibliography document.)
- The first paper, published in the Journal of Geophysical Research (Vol. 13, C12023, 2008) assessed the stability of three types of hydrate deposits and the dynamic behavior of these deposits under the influence of moderate ocean temperature increases. The results indicated that deep-ocean hydrates are stable under the influence of moderate increases in ocean temperature; however, shallow deposits can be very unstable and release significant quantities of methane under the influence of as little as 1° C of seafloor temperature increase.
- A second paper, published in Geophysical Research Letters (Vol. 36, L23612, 2009) presented the first results of the 2-D slope-scale modeling, demonstrating that shallow hydrates in sloping systems may, alone, generate significant methane and lead to the formation of gas plumes at the seafloor. The results were consistent with the observation of methane venting along the upper limit of a receding GHSZ off Spitsbergen.
- The third paper, published in Geophysical Research Letters (Vol. 37, L12607, 2010) and the fourth paper, published in the Journal of Geophysical Research, present the first results of forward-coupled methane release, water column chemistry, and transport via ocean currents using a 1° C version of the POP code. These establish a new paradigm for understanding the response of the oceans to methane release on a large scale. In particular, the work highlights the importance of resource limitations. Large, concentrated methane plumes may deplete the surrounding water of oxygen and other trace nutrients, reducing the ability of methanotrophs to consume the methane and increasing the chance of release into the atmosphere. This is in sharp contrast to previous assumptions of “99% consumption” of methane for all release scenarios.
- Researchers have made 12 presentations at conferences, including invited presentations at the DOE LERDWG (Laboratory Energy R&D Working Group) meeting and at the European Geosciences Union Annual Meeting (for more information, see the methane hydrate bibliography document), submitted two conference papers, and contributed an article to Fire in the Ice.
- This research was highlighted in feature articles in Nature Reports Climate Change (February 2009, April 2009).
- Dr. George Moridis of Lawrence Berkeley National Laboratory and Principal Investigator of research for this project, gave a keynote presentation at the 2009 Goldschmidt Conference in Davos, Switzerland, in June 2009.
- Dr. Matthew Reagan of Lawrence Berkeley National Laboratory was interviewed for feature articles inEnvironmental Science and Technology, E&E News Climate Wire, and on the air for NPR’s Living on Earth.
Current Status (August 2013):
The project has been completed. The final report is available below under "Additional Information".
Project Start: June 1, 2008
Project End: April 30, 2013
Project Cost Information:
|All DOE Contribution: $1,244,900
NETL – Skip Pratt (firstname.lastname@example.org or 304-285-4396)
LBNL – Matthew Reagan (email@example.com or 510-486-6517)
LANL – Philip Jones (firstname.lastname@example.org or 505-667-6387)
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]
Progress Report January - September 2010 [PDF-208KB]
2009 Annual Report [PDF-225KB]
Interrelation of Global Climate and the Response of Oceanic Hydrate Accumulations [PDF-1.09MB]
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]