Gas Hydrate Destabilization Research Articles

A 6600 year earthquake history in the region of the 2004 Sumatra-Andaman subduction zone earthquake

In order to investigate the possibility of a long-term paleoseismic history from offshore sedimentary records in Sumatra, we collected 144 deep-sea sediment cores in the trench and in lower slope piggyback basins of the Sumatra accretionary prism. We used multibeam bathymetry and seismic reflection data to develop an understanding of catchment basins, turbidity current pathways, and depositional styles, as well as to precisely locate our gravity cores, piston cores, Kasten cores, and multicores. We use detailed physical property data, including computed tomographic X-ray, gamma density, magnetic susceptibility, grain-size analysis, faunal analysis, and smear slides, to evaluate the turbidite stratigraphy and sedimentology at each site. We use radiocarbon age control for piggyback basin sites above the carbonate compensation depth, and use 210 Pb and 137 Cs to evaluate the timing of the most recent sedimentary deposits. Using well-log correlation methods and radiometric age control, we test for potential correlations between isolated sites in piggyback basins and the trench. We find evidence for very young surface turbidites along the northern Sumatra margin, most likely emplaced within the past few decades at the seafloor in both the 2004 and 2005 earthquake rupture zones, with no overlying hemipelagic sediment. Based on the young soupy deposits, lack of oxidation, and 210 Pb and 14 C age determinations, we interpret the uppermost turbidite in 21 cores within the 2004 rupture area to have been deposited within a few years of collection in 2007, and most likely as a result of the 2004 moment magnitude (M w ) ∼9.2 earthquake. The likely 2004 turbidite has a distinctive stacked structure of three major fining-upward sequences observed at several basin and trench sites, similar to the pattern of moment release in the 2004 earthquake. We observe rapid die out of the 2004 and 2005 deposits with distance from the slip zones, from local sources of sediment supply, and in the segment boundary between the slip zones. Many individual turbidites show strong similarities between isolated sites, as well as having similar emplacement times. Based upon radiocarbon age control and lithostratigraphic correlations between isolated basin and trench core sites, we interpret that 43 turbidites can be linked spatially over a distance of ∼230 km within the southern portion of the 2004 rupture zone. Sampling at deep-water sites isolated from terrestrial and shallow-water sediment sources, as well as potential storm or tsunami wave triggers, limits potential mechanisms for initiating turbidity currents to plate boundary, crustal, or slab earthquakes. Other potential triggers, such as tectonic oversteepening, random self-failures, gas hydrate destabilization, are unlikely to be correlative between any two isolated sites. The most probable explanation for the similarity of timing, turbidite sequences, and individual turbidite structure in isolated basin and trench stratigraphic sequences is a seismogenic origin. The mean emplacement time for turbidites (likely triggered by Great earthquakes, magnitude > ∼8) in the 2004 rupture region for the past 6.6 ± 0.14 k.y. is 160 yr for 43 turbidites. The ages of 8 of the 10 uppermost turbidite deposits, spanning the past ∼1500 yr, are largely consistent with the terrestrial paleoseismic and/or tsunami records in Thailand, Sumatra, India, and the Andaman Islands, suggesting either coincidence or a common origin. The mean interseismic time from the turbidite record for this same period is 170 yr, comparable to the ∼210 yr recurrence for regional tsunami. The turbidite record, at 180 yr (6 events), compares reasonably well to the average for all events on northern Simeulue of 220 yr, and is identical to the tsunami interval of 180 yr for the same time period (6 events). Of the 43 correlated turbidites in the 2004 earthquake region, 13 are well correlated in our cores along strike lengths of 150 km or greater, and satisfy criteria for robustness; 24 turbidites correlated along a shorter strike distance may represent other plate boundary earthquakes of shorter spatial extent and may include turbidite beds sourced from crustal and slab earthquakes.

Gas hydrate dissociation prolongs acidification of the Anthropocene oceans

AbstractAnthropogenic warming of the oceans can release methane (CH4) currently stored in sediments as gas hydrates. This CH4 will be oxidized to CO2, thus increasing the acidification of the oceans. We employ a biogeochemical model of the multimillennial carbon cycle to determine the evolution of the oceanic dissolved carbonate system over the next 13 kyr in response to CO2 from gas hydrates, combined with a reasonable scenario for long‐term anthropogenic CO2 emissions. Hydrate‐derived CO2 will appreciably delay the neutralization of ocean acidity and the return to preindustrial‐like conditions. This finding is the same with CH4 release and oxidation in either the deep ocean or the atmosphere. A change in CaCO3 export, coupled to CH4 release, would intensify the transient rise of the carbonate compensation depth, without producing any changes to the long‐term evolution of the carbonate system. Overall, gas hydrate destabilization implies a moderate additional perturbation to the carbonate system of the Anthropocene oceans.

Sluggish and steady focussed flows through fine-grained sediments: The methane-derived cylindrical concretions of the Tertiary Piedmont Basin (NW Italy)

In the Cenozoic succession of the Tertiary Piedmont Basin (NW Italy) a wide array of methane-derived carbonate rocks including both seafloor and sub-seafloor products have been reported in the last decades. The most intriguing features are cylindrical concretions, more than 1 m long and around 10 cm across, that were found within fine-grained sediments of Messinian age in their original stratigraphic position, crossing the bedding planes at high angles. These concretions result from cementation of the host muddy sediments by intergranular dolomite microcrystals, and lack any evidence of exposure at the sea floor. Their C and O stable isotope signature suggests that dolomite precipitation was induced by anaerobic oxidation of methane, possibly sourced by gas hydrate destabilization. Such cylindrical morphologies are interpreted as the result of carbonate precipitation and cementation of the sediments around fluid conduits and record a relatively long period of steady, sluggish flux of methane-rich fluids that opened their way rising up through fine-grained unconsolidated sediments. They formed immediately below the sea floor, in a narrow horizon bracketed between the sulphate–methane interface and the oxic/anoxic interface. Cylindrical concretions represent only the highest part of pipes through which methane-rich fluids flowed up. The deeper part of the conduits, conversely, left no trace in the stratigraphic record because of the lack of chemical/microbiological conditions favourable for carbonate precipitation.

Gas hydrate destabilization and methane release events in the Krishna–Godavari Basin, Bay of Bengal

Methane release events have been linked to global warming, alteration of the carbon cycle and influence on biota. However, unequivocal evidence of paleomethane release events are limited. We report several negative carbon stable isotope excursions in planktic and benthic foraminifera in a core (MD161-8) from the Krishna-Godavari (K–G) Basin, Bay of Bengal. The most negative δ13C spikes are recorded during the marine isotope stages MIS-4 and at the transition of MIS-5 to 4. Occurrence of highly 13C depleted (average δ13C = −48 ± 2.4‰ VPDB) authigenic high magnesian calcite are also reported within this time window from the core MD161-8. In the present work an unequivocal explanation for the observed 13C depletion in the marine planktic and benthic foraminifera is difficult to achieve solely from the optical/electron microscopy or C–O stable isotope ratio analyses due to possible influence of diagenetic alteration. We attribute the observed episodic methane expulsion events, as inferred from the negative δ13C excursions and earlier reports on the occurrence chemosynthetic bivalves and Mo concentration anomaly to the destabilization of the base of gas hydrate stability zone (BGHSZ). Sea level drop and shale tectonics induced focused fluid flow are the two possible causes of hydrate destabilization discussed here. Shale tectonics were possibly responsible for creating fault systems which acted as the conduit for gas flow through the sediment column and subsequent seepage. Shale and salt tectonics in the passive continental margins being a globally observed phenomenon, its role as an important driving force for enhanced methane emission needs detailed investigation to understand the climatic perturbations through geologic time. Additional evidence of methane emission from site MD161-15 further supports the link between shale tectonics and methane emission.

Fluid escape structures in the north Sicily continental margin

High resolution and multichannel seismic profiles coupled with multibeam echosounder (seafloor relief) data, acquired along the northern Sicily continental margin (southern Tyrrhenian Sea), document the occurrence of mound and pockmark features, revealing fluid escape processes. Along this margin, morphology of the high-gradient continental slope is irregular due to the presence of structural highs, slope failures and canyons, and is interrupted by flat areas at a mean depth of 1500 m.Seismostratigraphic analysis tools and methods were used to identify fluid escape structures and to work out a classification on the basis of their morpho-acoustic characteristics. The detailed 3D bathymetric chart was used to define the top view morphologic features and their areal distribution. With the aim to evaluate the geochemical content of fluids, we collected a 2.3 m long sediment core in correspondence of a pockmark at a depth of 414 m. Pore waters were sampled every 10 cm and analysed in relation to their conductivity (EC) and composition (δ18O, δD, Li, Na, K, Mg, F, Cl, Br, NO3, SO4).The new data show the occurrence of different types of structures with highly contrasting seismic and morphologic signatures, both dome-type and concave-upward structures. The latter have a characteristic circular shape and are known as pockmarks. Morphobathymetric, stratigraphic and structural data suggest that these structures occur along fault planes, mainly associated with diagenetic carbonates and fluid venting activity. Pockmarks could be the result of both fault and landslide structures, as they appear aligned along a straight direction and occur in proximity of the slope, and are associated with slope instabilities. The structural features are possibly associated with the recent tectonics mapped on-land as well as the widespread seismicity of the margin.Geochemical features reveal that pore water is slightly enriched in heavy isotopes with respect to Mediterranean seawater, while the distribution profiles of EC, ion concentration (Cl, SO4, Na, K, Mg, Ca), ion/Chloride ratios (Na/Cl, K/Cl, Ca/Cl, Mg/Cl and Alk/Cl) seem to indicate the existence of an external source of fluids and the occurrence of sediment-fluids interaction processes. A possible mechanism causing pore water freshening could be the destabilisation of gas hydrates.

Methane Gas Hydrate Stability Models on Continental Shelves in Response to Glacio-Eustatic Sea Level Variations: Examples from Canadian Oceanic Margins

We model numerically regions of the Canadian continental shelves during successive glacio-eustatic cycles to illustrate past, current and future marine gas hydrate (GH) stability and instability. These models indicated that the marine GH resource has dynamic features and the formation age and resource volumes depend on the dynamics of the ocean-atmosphere system as it responds to both natural (glacial-interglacial) and anthropogenic (climate change) forcing. Our models focus on the interval beginning three million years ago (i.e., Late Pliocene-Holocene). They continue through the current interglacial and they are projected to its anticipated natural end. During the current interglacial the gas hydrate stability zone (GHSZ) thickness in each region responded uniquely as a function of changes in water depth and sea bottom temperature influenced by ocean currents. In general, the GHSZ in the deeper parts of the Pacific and Atlantic margins (≥1316 m) thinned primarily due to increased water bottom temperatures. The GHSZ is highly variable in the shallower settings on the same margins (~400–500 m). On the Pacific Margin shallow GH dissociated completely prior to nine thousand years ago but the effects of subsequent sea level rise reestablished a persistent, thin GHSZ. On the Atlantic Margin Scotian Shelf the warm Gulf Stream caused GHSZ to disappear completely, whereas in shallow water depths offshore Labrador the combination of the cool Labrador Current and sea level rise increased the GHSZ. If future ocean bottom temperatures remain constant, these general characteristics will persist until the current interglacial ends. If the sea bottom warms, possibly in response to global climate change, there could be a significant reduction to complete loss of GH stability, especially on the shallow parts of the continental shelf. The interglacial GH thinning rates constrain rates at which carbon can be transferred between the GH reservoir and the atmosphere-ocean system. Marine GH can destabilize much more quickly than sub-permafrost terrestrial GHs and this combined with the immense marine GH reservoir suggests that GH have the potential to affect the climate-ocean system. Our models show that GH stability reacts quickly to water column pressure effects but slowly to sea bottom temperature changes. Therefore it is likely that marine GH destabilization was rapid and progressive in response to the pressure effects of glacial eustatic sea level fall. This suggests against a catastrophic GH auto-cyclic control on glacial-interglacial climate intervals. It is computationally possible but, unfortunately in no way verifiably, to analyze the interactions and impacts that marine GHs had prior to the current interglacial because of uncertainties in temperature and pressure history constraints. Thus we have the capability, but no confidence that we can contribute currently to questions regarding the relationships among climate, glacio-eustatic sea level fluctuations and marine GH stability without improved local temperature and water column histories. We infer that the possibility for a GH control on climate or oceanic cycles is speculative, but qualitatively contrary to our model results.

Recent changes to the Gulf Stream causing widespread gas hydrate destabilization

The Gulf Stream is an ocean current that modulates climate in the Northern Hemisphere by transporting warm waters from the Gulf of Mexico into the North Atlantic and Arctic oceans. A changing Gulf Stream has the potential to thaw and convert hundreds of gigatonnes of frozen methane hydrate trapped below the sea floor into methane gas, increasing the risk of slope failure and methane release. How the Gulf Stream changes with time and what effect these changes have on methane hydrate stability is unclear. Here, using seismic data combined with thermal models, we show that recent changes in intermediate-depth ocean temperature associated with the Gulf Stream are rapidly destabilizing methane hydrate along a broad swathe of the North American margin. The area of active hydrate destabilization covers at least 10,000 square kilometres of the United States eastern margin, and occurs in a region prone to kilometre-scale slope failures. Previous hypothetical studies postulated that an increase of five degrees Celsius in intermediate-depth ocean temperatures could release enough methane to explain extreme global warming events like the Palaeocene-Eocene thermal maximum (PETM) and trigger widespread ocean acidification. Our analysis suggests that changes in Gulf Stream flow or temperature within the past 5,000 years or so are warming the western North Atlantic margin by up to eight degrees Celsius and are now triggering the destabilization of 2.5 gigatonnes of methane hydrate (about 0.2 per cent of that required to cause the PETM). This destabilization extends along hundreds of kilometres of the margin and may continue for centuries. It is unlikely that the western North Atlantic margin is the only area experiencing changing ocean currents; our estimate of 2.5 gigatonnes of destabilizing methane hydrate may therefore represent only a fraction of the methane hydrate currently destabilizing globally. The transport from ocean to atmosphere of any methane released--and thus its impact on climate--remains uncertain.

Messinian carbonate-rich beds of the Tertiary Piedmont Basin (NW Italy): Microbially-mediated products straddling the onset of the salinity crisis

The seven Messinian microbial carbonate-rich layers cropping out in the Pollenzo section (Tertiary Piedmont Basin, NW Italy) are interbedded with a precession-related cyclic succession composed of euxinic shale/marl couplets and straddle the onset of the Messinian salinity crisis (MSC). A sharp change of sedimentological, compositional and geochemical characteristics was observed from the onset of the MSC onward, suggesting strong differences in the mechanisms responsible for carbonate precipitation. Pre-MSC beds are mainly composed of dolomite and are interpreted as the product of early diagenesis, formed by bacterial sulphate reduction in the shallow subsurface along the sulphate–methane interface. Dolomite precipitation was temporarily enhanced by an upward flux of methane-rich fluids, possibly sourced by gas hydrate destabilisation. Conversely, from the onset of the MSC onward, carbonate beds are thinly laminated and show abundant filaments interpreted as Beggiatoa-like bacteria, while calcite (and aragonite) are the dominant authigenic phases. These beds are interpreted as microbialites, resulting from the lithification of chemotrophic bacterial mats dominated by sulphide-oxidizing bacteria. The carbonate necessary for their preservation was provided by bacterial sulphate reduction. These microbialites, that appear as the deeper water counterpart of bottom-grown selenite layers deposited in the marginal part of the basin, formed on an anoxic sea bottom under a density stratified water column. The high sulphate concentration in the pore waters, related to the presence of concentrated brines and to the regeneration of sulphate by sulphide-oxidizing bacteria, is considered as the driving factor controlling the mineralogical change from dolomite to calcite and aragonite. Finally, the sharp shift towards negative δ18O values of carbonates, observed from the onset of the MSC onward, was probably related to fractionation processes operated by sulphate-reducing bacterial communities in the pore waters. This suggests that care must be taken, when dealing with microbial carbonates, in the interpretation of the oxygen isotope values in terms of fluctuating salinity condition of the water mass. In conclusion, this study suggests that the onset of the MSC had a strong impact on microbial populations governing carbonate precipitation, in a sector of the basin dominated by depositional conditions not suitable for gypsum precipitation.

Quaternary mass wasting on the western Black Sea margin, offshore of Amasra

In recent years, the western Black Sea margin has become well-studied due to its potential for petroleum plays in relatively deeper waters. In 2010, multi‐channel seismic, multibeam bathymetry and Chirp high resolution seismic data were collected in order to define the existing geohazards along the margin, to identify the seabed morphology and to determine mass movement types and their run‐out distances.Seismic data indicate that the western Black Sea margin is an unstable region with sediment erosion. Particularly, an unstable area offshore of Amasra in the NW consisting of four slides and four buried debris lobes is named the Amasra mass failure zone. Different types of sliding with varying sizes and different mechanisms are observed. These include sliding in the steep slope zones where block‐type sliding occurs, smaller‐scale slides on the canyon walls, and relatively larger slides in the Amasra mass failure zone. Block‐type sliding is observed on the upper continental slope to the south as well as on the canyon walls. They are formed along the rotational faults and occur due to the gravitational loading on the steep slope zones possibly triggered by local seismic activity. In addition, seven large debris lobes identified in the northern toe of the slope buried in the Quaternary sediments triggered by excess pore pressures due to high sediment input and submarine fluid flow.We suggest that earthquake activity may be an important agent for all kind of mass movements in the area. In addition, we propose that the slides in the Amasra mass failure zone are triggered by excess pore pressures in shallow sediments due to the submarine fluid flow possibly produced from gas hydrate dissociation. Warmer Mediterranean seawater input during the rapid transgression period after the Last Glacial Maximum in the Black Sea together with the rapid sedimentation resulted in destabilization of gas hydrates, which caused excess pore pressures in shallow sediments leading to massive sediment failures. Small‐scale normal faults around the scarps may be a secondary factor promoting the failures providing the suitable pathways for the fluid flow as well as the suitable weak surfaces for the sliding.

Inferred gas hydrate and permafrost stability history models linked to climate change in the Beaufort-Mackenzie Basin, Arctic Canada

Abstract. Atmospheric methane from episodic gas hydrate (GH) destabilization, the "clathrate gun" hypothesis, is proposed to affect past climates, possibly since the Phanerozoic began or earlier. In the terrestrial Beaufort-Mackenzie Basin (BMB), GHs occur commonly below thick ice-bearing permafrost (IBP), but they are rare within it. Two end-member GH models, where gas is either trapped conventionally (Case 1) or where it is trapped dynamically by GH formation (Case 2), were simulated using profile (1-D) models and a 14 Myr ground surface temperature (GST) history based on marine isotopic data, adjusted to the study setting, constrained by deep heat flow, sedimentary succession conductivity, and observed IBP and Type I GH contacts in Mallik wells. Models consider latent heat effects throughout the IBP and GH intervals. Case 1 GHs formed at ~0.9 km depth only ~1 Myr ago by in situ transformation of conventionally trapped natural gas. Case 2 GHs begin to form at ~290–300 m ~6 Myr ago in the absence of lithological migration barriers. During glacial intervals Case 2 GH layers expand both downward and upward as the permafrost grows downward through and intercalated with GHs. The distinctive model results suggest that most BMB GHs resemble Case 1 models, based on the observed distinct and separate occurrences of GHs and IBP and the lack of observed GH intercalations in IBP. Case 2 GHs formed >255 m, below a persistent ice-filled permafrost layer that is as effective a seal to upward methane migration as are Case 1 lithological seals. All models respond to GST variations, but in a delayed and muted manner such that GH layers continue to grow even as the GST begins to increase. The models show that the GH stability zone history is buffered strongly by IBP during the interglacials. Thick IBP and GHs could have persisted since ~1.0 Myr ago and ~4.0 Myr ago for Cases 1 and 2, respectively. Offshore BMB IBP and GHs formed terrestrially during Pleistocene sea level low stands. Where IBP is sufficiently thick, both IBP and GHs persist even where inundated by a Holocene sea level rise and both are also expected to persist into the next glacial even if atmospheric CO2 doubles. We do not address the "clathrate gun" hypothesis directly, but our models show that sub-IBP GHs respond to, rather than cause GST changes, due to both how GST changes propagates with depth and latent heat effects. Models show that many thick GH accumulations are prevented from contributing methane to the atmosphere, because they are almost certainly trapped below either ice-filled IBP or lithological barriers. Where permafrost is sufficiently thick, combinations of geological structure, thermal processes and material properties make sub-IBP GHs unlikely sources for significant atmospheric methane fluxes. Our sub-IBP GH model histories suggest that similar models applied to other GH settings could improve the understanding of GHs and their potential to affect climate.

Dynamics of a stepped carbon-isotope excursion: Ultra high-resolution study of Early Toarcian environmental change

In the Toarcian (Early Jurassic; ~183Myr ago), the ocean–atmosphere system was subject to one of the largest perturbations of the carbon cycle in the last 250Myr known as the Toarcian Oceanic Anoxic Event (T-OAE). This event was accompanied by a −6‰ negative carbon-isotope excursion (CIE) caused by massive injection of isotopically light carbon into the ocean–atmosphere system, possibly from destabilisation of gas hydrates. This study reveals the pacing and sequence of events leading up to the CIE and to widespread deposition of organic-rich sediments. The very high-resolution isotopic record from exceptionally well-preserved carbonate and organic matter from the Paris Basin enables recognition of increased CO2 levels ~130kyr in advance of the major negative CIE. An accelerated increase in the pCO2 is registered ~25kyr before the onset of this negative excursion and was so rapid and so intense that it led to a water column undersaturated with respect to calcium carbonate in the Paris Basin. Undersaturation is expressed as a dramatic drop in the accumulation of the biogenic calcite produced by the surface-dwelling calcifiers. These environmental perturbations, representing precursor phases of CO2 injection, predate the first step towards relatively light carbon isotopes in carbonate and organic matter and are tentatively attributed to Karoo–Ferrar magmatism. This negative shift was registered slightly earlier in terrestrial carbon than marine carbonate. Subsequent global warming is credited with liberating isotopically light carbon, and ultimately fostered anoxia in the Paris Basin: the response of these cumulative inputs of carbon to the Earth system. Isotopic and sedimentological evidence indicates continuously elevated phytoplanktonic productivity throughout the first step of the negative CIE, suggesting that the biological pump accelerated the drawdown of excess carbon leading to temporary recovery of carbonate sedimentation, ~45kyr after the first step of the CIE. This re-establishment of the saturation state of the water column was only fleeting before the later stepwise release of isotopically light carbon.

Methane Index: A tetraether archaeal lipid biomarker indicator for detecting the instability of marine gas hydrates

Gas hydrates represent one of the largest pools of readily exchangeable carbon on Earth's surface. Releases of the greenhouse gas methane from hydrates are proposed to be responsible for climate change at numerous events in geological history. Many of these inferred events, however, were based on carbonate carbon isotopes which are susceptible to diagenetic alterations. Here we propose a molecular fossil proxy, i.e., the “Methane Index (MI)”, to detect and document the destabilization and dissociation of marine gas hydrates. MI consists of the relative distribution of glycerol dibiphytanyl glycerol tetraethers (GDGTs), the core membrane lipids of archaea. The rational behind MI is that in hydrate-impacted environments, the pool of archaeal tetraether lipids is dominated by GDGT-1, -2 and -3 due to the large contribution of signals from the methanotrophic archaeal community. Our study in the Gulf of Mexico cold-seep sediments demonstrates a correlation between MI and the compound-specific carbon isotope of GDGTs, which is strong evidence supporting the MI-methane consumption relationship. Preliminary applications of MI in a number of hydrate-impacted and/or methane-rich environments show diagnostic MI values, corroborating the idea that MI may serve as a robust indicator for hydrate dissociation that is useful for studies of global carbon cycling and paleoclimate change.

CO2-driven ocean circulation changes as an amplifier of Paleocene-Eocene thermal maximum hydrate destabilization

Research Article| October 01, 2010 CO2-driven ocean circulation changes as an amplifier of Paleocene-Eocene thermal maximum hydrate destabilization Daniel J. Lunt; Daniel J. Lunt * 1School of Geographical Science, University of Bristol, Bristol BS8 1SS, UK2British Antarctic Survey, Cambridge CB3 0ET, UK *E-mail: d.j.lunt@bristol.ac.uk. Search for other works by this author on: GSW Google Scholar Paul J. Valdes; Paul J. Valdes 1School of Geographical Science, University of Bristol, Bristol BS8 1SS, UK Search for other works by this author on: GSW Google Scholar Tom Dunkley Jones; Tom Dunkley Jones † 3Department of Geography, University College London, London WC1E 6BT, UK †Current address: Department of Earth Science and Engineering, Imperial College, London SW7 2AZ, UK. Search for other works by this author on: GSW Google Scholar Andy Ridgwell; Andy Ridgwell 1School of Geographical Science, University of Bristol, Bristol BS8 1SS, UK Search for other works by this author on: GSW Google Scholar Alan M. Haywood; Alan M. Haywood 4School of Earth and Environment, University of Leeds, Leeds LS2 9JT, UK Search for other works by this author on: GSW Google Scholar Daniela N. Schmidt; Daniela N. Schmidt 5Department of Earth Sciences, University of Bristol, Bristol BS8 1RJ, UK Search for other works by this author on: GSW Google Scholar Robert Marsh; Robert Marsh 6School of Ocean and Earth Science, University of Southampton, National Oceanography Centre, Southampton SO14 3ZH, UK Search for other works by this author on: GSW Google Scholar Mark Maslin Mark Maslin 3Department of Geography, University College London, London WC1E 6BT, UK Search for other works by this author on: GSW Google Scholar Author and Article Information Daniel J. Lunt * 1School of Geographical Science, University of Bristol, Bristol BS8 1SS, UK2British Antarctic Survey, Cambridge CB3 0ET, UK Paul J. Valdes 1School of Geographical Science, University of Bristol, Bristol BS8 1SS, UK Tom Dunkley Jones † 3Department of Geography, University College London, London WC1E 6BT, UK Andy Ridgwell 1School of Geographical Science, University of Bristol, Bristol BS8 1SS, UK Alan M. Haywood 4School of Earth and Environment, University of Leeds, Leeds LS2 9JT, UK Daniela N. Schmidt 5Department of Earth Sciences, University of Bristol, Bristol BS8 1RJ, UK Robert Marsh 6School of Ocean and Earth Science, University of Southampton, National Oceanography Centre, Southampton SO14 3ZH, UK Mark Maslin 3Department of Geography, University College London, London WC1E 6BT, UK *E-mail: d.j.lunt@bristol.ac.uk. †Current address: Department of Earth Science and Engineering, Imperial College, London SW7 2AZ, UK. Publisher: Geological Society of America Received: 04 Mar 2010 Revision Received: 06 May 2010 Accepted: 07 May 2010 First Online: 09 Mar 2017 Online ISSN: 1943-2682 Print ISSN: 0091-7613 © 2010 Geological Society of America Geology (2010) 38 (10): 875–878. https://doi.org/10.1130/G31184.1 Article history Received: 04 Mar 2010 Revision Received: 06 May 2010 Accepted: 07 May 2010 First Online: 09 Mar 2017 Cite View This Citation Add to Citation Manager Share Icon Share Facebook Twitter LinkedIn MailTo Tools Icon Tools Get Permissions Search Site Citation Daniel J. Lunt, Paul J. Valdes, Tom Dunkley Jones, Andy Ridgwell, Alan M. Haywood, Daniela N. Schmidt, Robert Marsh, Mark Maslin; CO2-driven ocean circulation changes as an amplifier of Paleocene-Eocene thermal maximum hydrate destabilization. Geology 2010;; 38 (10): 875–878. doi: https://doi.org/10.1130/G31184.1 Download citation file: Ris (Zotero) Refmanager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex toolbar search Search Dropdown Menu toolbar search search input Search input auto suggest filter your search All ContentBy SocietyGeology Search Advanced Search Abstract 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. You do not have access to this content, please speak to your institutional administrator if you feel you should have access.

Climate forcing of geological and geomorphological hazards

The 12 research papers and two summaries of conference discussion sessions contained in this Theme Issue build upon presentations and dialogue at the Third Johnston–Lavis Colloquium held at University College London in September 2009. The meeting brought together delegates from the UK, Europe and

Gas hydrates: past and future geohazard?

Gas hydrates are ice-like deposits containing a mixture of water and gas; the most common gas is methane. Gas hydrates are stable under high pressures and relatively low temperatures and are found underneath the oceans and in permafrost regions. Estimates range from 500 to 10,000 giga tonnes of carbon (best current estimate 1600-2000 GtC) stored in ocean sediments and 400 GtC in Arctic permafrost. Gas hydrates may pose a serious geohazard in the near future owing to the adverse effects of global warming on the stability of gas hydrate deposits both in ocean sediments and in permafrost. It is still unknown whether future ocean warming could lead to significant methane release, as thermal penetration of marine sediments to the clathrate-gas interface could be slow enough to allow a new equilibrium to occur without any gas escaping. Even if methane gas does escape, it is still unclear how much of this could be oxidized in the overlying ocean. Models of the global inventory of hydrates and trapped methane bubbles suggest that a global 3( degrees )C warming could release between 35 and 940 GtC, which could add up to an additional 0.5( degrees )C to global warming. The destabilization of gas hydrate reserves in permafrost areas is more certain as climate models predict that high-latitude regions will be disproportionately affected by global warming with temperature increases of over 12( degrees )C predicted for much of North America and Northern Asia. Our current estimates of gas hydrate storage in the Arctic region are, however, extremely poor and non-existent for Antarctica. The shrinking of both the Greenland and Antarctic ice sheets in response to regional warming may also lead to destabilization of gas hydrates. As ice sheets shrink, the weight removed allows the coastal region and adjacent continental slope to rise through isostacy. This removal of hydrostatic pressure could destabilize gas hydrates, leading to massive slope failure, and may increase the risk of tsunamis.

Potential for a hazardous geospheric response to projected future climate changes

Periods of exceptional climate change in Earth history are associated with a dynamic response from the geosphere, involving enhanced levels of potentially hazardous geological and geomorphological activity. The response is expressed through the adjustment, modulation or triggering of a broad range of surface and crustal phenomena, including volcanic and seismic activity, submarine and subaerial landslides, tsunamis and landslide 'splash' waves, glacial outburst and rock-dam failure floods, debris flows and gas-hydrate destabilization. In relation to anthropogenic climate change, modelling studies and projection of current trends point towards increased risk in relation to a spectrum of geological and geomorphological hazards in a warmer world, while observations suggest that the ongoing rise in global average temperatures may already be eliciting a hazardous response from the geosphere. Here, the potential influences of anthropogenic warming are reviewed in relation to an array of geological and geomorphological hazards across a range of environmental settings. A programme of focused research is advocated in order to: (i) understand better those mechanisms by which contemporary climate change may drive hazardous geological and geomorphological activity; (ii) delineate those parts of the world that are most susceptible; and (iii) provide a more robust appreciation of potential impacts for society and infrastructure.

The mid-Capitanian (Middle Permian) mass extinction and carbon isotope record of South China

Conodont, C isotope and fossil and facies data are presented for the Capitanian (Middle Permian) mass extinction record seen in platform carbonates (Maokou and Wuchiaping formations) of South China, where limestones interdigitate with the volcanic succession of the Emeishan large igneous province. The Maokou Formation provides an extinction record marked by the loss of keriothecal-walled fusulinaceans and a turnover in calcareous algae. In sections within the Emeishan province this crisis occurs at the base of the oldest record of volcanism from the Jinogondolella altudaensis conodont zone (of mid-Capitanian age). Around the periphery of the Emeishan province this extinction level lies within the upper part of the Maokou Formation at a level where platform carbonate deposition was frequently interrupted by thick volcanic ash depositional events. The assemblages of the uppermost Maokou Formation are characterised by typical “Late Permian” taxa although these levels still lie within the Middle Permian (Guadalupian Series). “Disaster” taxa, such as Earlandia and Diplosphaerina are locally prolifically abundant in the aftermath of the mass extinction. The crisis is particularly noteworthy amongst photosynthetic taxa such as calcareous algae and fusulinaceans that probably harboured photosymbionts. Therefore, a kill mechanism involving cooling from explosive volcanism and potentially acid rain from sulphate aerosols appears appropriate. A composite δ 13C carb curve, calibrated against a high-resolution conodont biostratigraphy reveals a major intra-Capitanian negative excursion (of > 5‰) superimposed on typically heavy (4–5‰) Middle Permian values. This curve can also be recognised in Panthalassan seamount carbonates of Japan although this requires reassignment of apparently Upper Permian limestones to the Middle Permian. In both China and Japan the Capitanian mass extinction occurs during the early stage of this major, intra-Capitanian negative excursion. Assuming typical platform carbonate accumulation rates, the records of the Maokou Formation suggest δ 13C carb values fell at ∼ 0.01‰/kyr suggesting a catastrophic origin (such as gas hydrate destabilisation) is unlikely, although a volcanic source is possible.

Authigenic carbonates in Upper Miocene sediments of the Tertiary Piedmont Basin (NW Italy): Vestiges of an ancient gas hydrate stability zone?

Research Article| July 01, 2010 Authigenic carbonates in Upper Miocene sediments of the Tertiary Piedmont Basin (NW Italy): Vestiges of an ancient gas hydrate stability zone? Francesco Dela Pierre; Francesco Dela Pierre † 1Dipartimento di Scienze della Terra, Università di Torino, Via Valperga Caluso, 35–10125 Torino, Italy2Consiglio Nazionale delle Ricerche Istituto di Geoscienze e Georisorse, Via Valperga Caluso, 35–10125 Torino, Italy †E-mail: francesco.delapierre@unito.it Search for other works by this author on: GSW Google Scholar Luca Martire; Luca Martire 1Dipartimento di Scienze della Terra, Università di Torino, Via Valperga Caluso, 35–10125 Torino, Italy Search for other works by this author on: GSW Google Scholar Marcello Natalicchio; Marcello Natalicchio 1Dipartimento di Scienze della Terra, Università di Torino, Via Valperga Caluso, 35–10125 Torino, Italy Search for other works by this author on: GSW Google Scholar Pierangelo Clari; Pierangelo Clari 1Dipartimento di Scienze della Terra, Università di Torino, Via Valperga Caluso, 35–10125 Torino, Italy Search for other works by this author on: GSW Google Scholar Catalin Petrea Catalin Petrea 1Dipartimento di Scienze della Terra, Università di Torino, Via Valperga Caluso, 35–10125 Torino, Italy3Institul de Speologic Emil Racovita, Calea 13 Septembrie 13, 50711 Bucuresti, Romania Search for other works by this author on: GSW Google Scholar GSA Bulletin (2010) 122 (7-8): 994–1010. https://doi.org/10.1130/B30026.1 Article history received: 09 Feb 2009 rev-recd: 29 Jun 2009 accepted: 10 Jul 2009 first online: 08 Mar 2017 Cite View This Citation Add to Citation Manager Share Icon Share Facebook Twitter LinkedIn MailTo Tools Icon Tools Get Permissions Search Site Citation Francesco Dela Pierre, Luca Martire, Marcello Natalicchio, Pierangelo Clari, Catalin Petrea; Authigenic carbonates in Upper Miocene sediments of the Tertiary Piedmont Basin (NW Italy): Vestiges of an ancient gas hydrate stability zone?. GSA Bulletin 2010;; 122 (7-8): 994–1010. doi: https://doi.org/10.1130/B30026.1 Download citation file: Ris (Zotero) Refmanager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex toolbar search Search Dropdown Menu toolbar search search input Search input auto suggest filter your search All ContentBy SocietyGSA Bulletin Search Advanced Search Abstract A wide array of carbonate-rich rocks has been recognized in the Tertiary Piedmont Basin (NW Italy), hosted in lower Messinian slope deposits. Carbonate cements show negative δ13C values and positive δ18O values, suggesting that carbonate precipitation was induced by microbial degradation of methane produced from gas hydrate destabilization. Two groups of rocks have been distinguished: (1) Lucina-bearing mud breccias, representing the seafloor product of an ancient seepage site; and (2) Lucina-free concretions, originating below the sediment-water interface. Within this group, two subtypes have been further distinguished: stratiform concretions and cylindrical concretions. Stratiform concretions result from precipitation of dolomite in the pores of muddy sediments. Some of them display a brecciated structure; others show a network of septarian-like cracks that are empty, filled with sediments, or zoned carbonate cements. Their internal features are related to the formation of gas hydrates within the sediments and to their destabilization. Thus, these rocks mark a portion of the sedimentary column located within a (paleo) gas hydrate stability zone. Cylindrical concretions represent ancient fluid conduits related to the upward migration of CH4-rich fluids subsequent to gas hydrate destabilization.The carbonate-rich rocks of the Tertiary Piedmont Basin stand as one of the first examples of methane-derived rocks that record successive episodes of dissociation and re-formation of gas hydrates, and they provide precious elements to model the general evolution of a portion of the sedimentary column located within the hydrate stability zone. You do not have access to this content, please speak to your institutional administrator if you feel you should have access.

Patterns of carbonate authigenesis at the Kouilou pockmarks on the Congo deep-sea fan

Different types of seep carbonates were recovered from the ‘Kouilou pockmarks’ on the Congo deep-sea fan in approximately 3100 m water depth. The carbonate aggregates are represented by pyritiferous nodules, crusts and slabs, tubes, and filled molds. The latter are interpreted to represent casts of former burrows of bivalves and holothurians. The nodules consisting of high-Mg-calcite apparently formed deeper within the sediments than the predominantly aragonitic crusts and slabs. Nodule formation was caused by anaerobic oxidation of methane dominantly involving archaea of the phylogenetic ANME-1 group, whereas aragonitic crusts resulted from the activity of archaea of the ANME-2 cluster. Evidence for this correlation is based on the distribution of specific biomarkers in the two types of carbonate aggregates, showing higher hydroxyarchaeol to archaeol ratios in the crusts as opposed to nodules. Formation of crusts closer to the seafloor than nodules is indicated by higher carbonate contents of crusts, probably reflecting higher porosities of the host sediment during carbonate formation. This finding is supported by lower δ 18O values of crusts, agreeing with precipitation from pore waters similar in composition to seawater. The aragonitic mineralogy of the crusts is also in accord with precipitation from sulfate-rich pore waters similar to seawater. Moreover, the interpretation regarding the relative depth of formation of crusts and nodules agrees with the commonly observed pattern that ANME-1 archaea tend to occur deeper in the sediment than members of the ANME-2 group. Methane represents the predominant carbon source of all carbonates ( δ 13C values as low as − 58.9‰ V-PDB) and the encrusted archaeal biomarkers ( δ 13C values as low as − 140‰ V-PDB). Oxygen isotope values of some nodular carbonates, ranging from + 3.9 to + 5.1‰ V-PDB, are too high for precipitation in equilibrium with seawater, probably reflecting the destabilization of gas hydrates, which are particularly abundant at the Kouilou pockmarks.

Authigenic carbonates from methane seeps of the northern Congo fan: Microbial formation mechanism

Authigenic carbonates were collected from methane seeps at Hydrate Hole at 3113 m water depth and Diapir Field at 2417 m water depth on the northern Congo deep-sea fan during RV Meteor cruise M56. The carbonate samples analyzed here are nodules, mainly composed of aragonite and high-Mg calcite. Abundant putative microbial carbonate rods and associated pyrite framboids were recognized within the carbonate matrix. The δ 13C values of the Hydrate Hole carbonates range from −62.5‰ to −46.3‰ PDB, while the δ 13C values of the Diapir Field carbonate are somewhat higher, ranging from −40.7‰ to −30.7‰ PDB, indicating that methane is the predominant carbon source at both locations. Relative enrichment of 18O ( δ 18O values as high as 5.2‰ PDB) are probably related to localized destabilization of gas hydrate. The total content of rare earth elements (REE) of 5% HNO 3-treated solutions derived from carbonate samples varies from 1.6 ppm to 42.5 ppm. The shale-normalized REE patterns all display positive Ce anomalies (Ce/Ce* > 1.3), revealing that the carbonates precipitated under anoxic conditions. A sample from Hydrate Hole shows a concentric lamination, corresponding to fluctuations in δ 13C values as well as trace elements contents. These fluctuations are presumed to reflect changes of seepage flux.