We compare sediment vertical methane flux off the Mahia Peninsula, on the Hikurangi Margin, east ... more We compare sediment vertical methane flux off the Mahia Peninsula, on the Hikurangi Margin, east of New Zealand’s North Island, with a combination of geochemical, multichannel seismic and sub-bottom profiler data. Stable carbon isotope data provided an overview of methane contributions to shallow sediment carbon pools. Methane varied considerably in concentration and vertical flux across stations in close proximities. At two Mahia transects, methane profiles correlated well with integrated seismic and TOPAS data for predicting vertical methane migration rates from deep to shallow sediment. However, at our “control site”, where no seismic blanking or indications of vertical gas migration were observed, geochemical data were similar to the two Mahia transect lines. This apparent mismatch between seismic and geochemistry data suggests a potential to underestimate gas hydrate volumes based on standard seismic data interpretations. To accurately assess global gas hydrate deposits, multip...
2D numerical modeling algorithms of multi-component, multi-phase filtration processes of mass tra... more 2D numerical modeling algorithms of multi-component, multi-phase filtration processes of mass transfer in frost-susceptible rocks using nonlinear partial differential equations are a valuable tool for problems of subsurface hydrodynamics considering the presence of free gas, free water, gas hydrates, ice formation and phase transitions. In this work, a previously developed one-dimensional numerical modeling approach is modified and 2D algorithms are formulated through means of the support-operators method (SOM) and presented for the entire area of the process extension. The SOM is used to generalize the method of finite difference for spatially irregular grids case. The approach is useful for objects where a lithological heterogeneity of rocks has a big influence on formation and accumulation of gas hydrates and therefore it allows to achieve a sufficiently good spatial approximation for numerical modeling of objects related to gas hydrates dissociation in porous media. The modeling...
: This report provides a preliminary summary of geochemical contribution to methane hydrate resea... more : This report provides a preliminary summary of geochemical contribution to methane hydrate research and exploration on the Hikurangi Margin, off the northeastern coast of New Zealand from June 20 to July 3, 2006. Geochemical porewater profiles taken from shallow piston cores and vertical fluid migration measured with heatflow probing were compared with seismic summaries of potential deep sediment hydrates deposits. Research goals for this expedition include: (1) Refine geophysical, geochemical, and microbiological technologies for prospecting hydrate distribution and content; (2) Contribute to establishing high-priority geographical regions of prospective interest, in terms of methane volume estimates; (3) Prediction of environmental effects and geologic risks at the continental margin associated to the natural resource occurrence and resource exploitation; and (4) Expand understanding of the biogeochemical parameters and associated microbial community diversity in shallow sediment...
: The Naval Research Laboratory (NRL), supported through ONRG-Chile, DOE/NETL, and ONR, participa... more : The Naval Research Laboratory (NRL), supported through ONRG-Chile, DOE/NETL, and ONR, participated in a research cruise along the mid-Chilean coast. Specific research topics addressed by NRL in this program include survey and prediction of geotechnical and geoacoustical anomalies, estimation of coastal hydrate distribution, refining protocol for hydrate exploration, and understanding the variation in microbial community diversity in hydrate-rich regions. The Chile-FONDEF goal in this program is to locate hydrates along the Chilean coast in terms of distribution and methane content for understanding the available energy and geological hazards. This effort integrates future energy exploration with ocean and climate research topics. The examination of sediments in this region was conducted in a collaborative effort between NRL, Milbar Hydrotest, Inc., Virginia Institute of Marine Science, Pontificia Universidad Catolica de Valparaiso, University of Concepcion, and Rice University. Pi...
: Marine Desalination Systems (MDS) is currently developing new technology in gas hydrate formati... more : Marine Desalination Systems (MDS) is currently developing new technology in gas hydrate formation to supply potable water. To scale this technology to support different country needs there is a requirement to assess the environmental impact of desalination. The NRL MDS collaboration on biological influence of marine desalination focuses on water quality of processed water and environmental impact of the marine desalination application. With this segment of the project accomplished, the subsequent evaluation will focus on the impact of large scale marine desalination on environmental quality. To assess the environmental impact of the marine desalinization system there is a need to understand resulting changes to key bacterial and elemental cycles. Seawater vertical transport, alteration of water flow, and filtration have potential to change the microbial community diversity, substrate availability, electron acceptors and key element speciation. Microorganisms surveyed in this analy...
: From May 14-20, 2004, piston core and heat flow measurements were collected across two mound st... more : From May 14-20, 2004, piston core and heat flow measurements were collected across two mound structures, mound D and mound F, in an area designated as Atwater Valley, a shallow trough on the continental slope south of the Mississippi Delta. Atwater Valley lies at 1,200 to 1,500 m water depth. Several small mound structures occur in the valley, rising less than 50 m above the surrounding seafloor. The UNOLS vessel RV Gyre was contracted to support this work. The work took place in about 1,300-m water depth through a 4-km transect at lat. 27.9356 degrees N, Ion. 89.2794 degrees W (lease block Atwater Valley 14). Previous USGS seismic lines AV65, AV97 and AV82 and a 3.5 kHz echosounder profile collected during the cruise were used to guide operations. Total sampling included mounds D and F and a transect between the mounds. During 4 days on site, we acquired 15 piston cores and 23 thermal profiles on a transect from mound F to mound D. Extensive piston coring and heatflow was conduct...
The depth of bottom simulating reflections (BSRs) is routinely used to constrain heatflow on cont... more The depth of bottom simulating reflections (BSRs) is routinely used to constrain heatflow on continental margins, including the Hikurangi Margin, New Zealand. Comparison between BSR-derived heatflow and results from either seafloor thermometry or measurements in boreholes in most regions are in reasonable agreement, with a few notable exceptions. In 2006, we measured the thermal gradient with seafloor heat probes at several locations on the southern Hikurangi Margin as ~0.05 K/m. This contrasts with a thermal gradient of ~0.025 K/m obtained from up to ~700-m deep BSRs. We here revisit these analyses. The observed discrepancy cannot be readily explained by an increase of thermal conductivity with depth for commonly used seismic velocity-porosity-thermal conductivity relations. Likewise, for as long as a Structure-I hydrate is formed, gas and pore-fluid composition do not shift temperatures at the BSR sufficiently upwards to be compatible with seafloor measurements. BSRs at the base of Structure-II hydrates would provide an explanation (the stability range of Structure-II hydrate is quite large depending on the amount of e.g., propane added to the gas mix) but we dismiss this scenario as unlikely since coring did not show any evidence for higher-order hydrocarbons and, also, we are not aware of any wide-spread BSRs beneath Structure-II hydrates anywhere else. We therefore investigate two basic scenarios; 1) unusual rock thermal properties and 2) transient processes. Thermal conductivity deeper in the margin may be higher than velocity-porosity relations would suggest, if the margin consists of highly consolidated but fractured mudstones. This could reconcile both datasets. On the other hand, transient processes that could cause the observed discrepancies include a margin-wide ancient sedimentation pulse. Perhaps the most intriguing explanation would be fluid pulses originating at the subduction interface after subduction earthquakes (or slow slip) leading to transient advective heatflow as proposed for a similar discrepancy between BSR and seafloor thermometry off Chile (Grevemeyer et al., 2006, Geophys. J. Int., 166, 461-468). We have not reached any conclusions as to which mechanism is most likely to cause the discrepancies in thermal gradients. However, the suggested processes could have profound implications. If rock properties were responsible, heatflow on this margin would have been underestimated so far, affecting e.g., the predicted limits of the seismogenic zone. Transient processes on the other hand may provide a mechanism for gas hydrate formation. For example, cooling after a fluid pulse would lead to ``freezing'' of gas to hydrate because of a downward moving base of gas hydrate stability.
In June 2007 sediment cores were collected in Alaminos Canyon, Gulf of Mexico across a series of ... more In June 2007 sediment cores were collected in Alaminos Canyon, Gulf of Mexico across a series of seismic data profiles indicating rapid transitions between the presence of methane hydrates and vertical gas flux. Vertical profiles of dissolved sulfate, chloride, calcium, magnesium, and dissolved inorganic carbon (DIC) concentrations in porewaters, headspace methane, and solid phase carbonate concentrations were measured at each core location to investigate the cycling of methane-derived carbon in shallow sediments overlying the hydrate bearing strata. When integrated with stable carbon isotope ratios of DIC, geochemical results suggest a significant fraction of the methane flux at this site is cycled into the inorganic carbon pool. The incorporation of methane-derived carbon into dissolved and solid inorganic carbon phases represents a significant sink in local carbon cycling and plays a role in regulating the flux of methane to the overlying water column at Alaminos Canyon. Targeted...
Coastal methane hydrate deposits are globally abundant. There is a need to understand the deep se... more Coastal methane hydrate deposits are globally abundant. There is a need to understand the deep sediment sourced methane energy contribution to shallow sediment carbon relative to terrestrial sources and phytoplankton. Shallow sediment and porewater samples were collected from Atwater Valley, Texas-Louisiana Shelf, Gulf of Mexico near a seafloor mound feature identified in geophysical surveys as an elevated bottom seismic reflection. Geochemical data revealed off-mound methane diffusion and active fluid advection on-mound. Gas composition (average methane/ethane ratio ~11,000) and isotope ratios of methane on the mound (average δ 13 C CH4(g) = −71.2‰; D 14 C CH4(g) = −961‰) indicate a deep sediment, microbial source. Depleted sediment organic carbon values on mound (δ 13 C SOC = −25.8‰; D 14 C SOC = −930‰) relative to off-mound (δ 13 C SOC = −22.5‰; D 14 C SOC = −629‰) suggest deep sourced ancient carbon is incorporated into shallow sediment organic matter. Porewater and sediment dat...
Methane hydrate has become one promising energy resource for humankind. In this study, recent wor... more Methane hydrate has become one promising energy resource for humankind. In this study, recent worldwide onshore/offshore drilling and production activities are analysed. The most recent reports fro...
<p>... more <p>For over 100 years scientists have puzzled over the mechanisms responsible for the repeated climate changes known as Ice Ages. A breakthrough was achieved when ice cores and marine archives revealed that the Ice Ages were paced at 100kyr intervals in alignment with Earth’s eccentricity cycle for the past million years. A second breakthrough was achieved when ice core records revealed that the Ice Ages were accompanied by ~80-90ppm variations in atmospheric pCO<sub>2</sub>. But after decades of research the mechanisms responsible for those atmospheric pCO<sub>2</sub> variations remains an open and unresolved puzzle.</p><p>Here we present new findings that challenge the long-standing paradigm that geologic processes that regulate carbon exchange between the Earth’s interior and exterior act too slowly to have influenced the ocean and atmosphere carbon budgets on glacial time scales. The evidence includes large Δ<sup>14</sup>C excursions found in biogenic sediments in each of the Ocean basins at the last glacial termination. These excursions point to a sustained release of <sup>14</sup>C-dead carbon spanning several thousand years.  In the Atlantic, Pacific and Indian Ocean the excursions are found near seafloor deformation features, including pockmarks that are indicative of gas-rich fluid release from sub-surface reservoirs. In the eastern equatorial Pacific, the Δ<sup>14</sup>C excursions are associated with enhanced hydrothermal metal concentrations including Fe, and Z that point to a hydrothermal source. Our ongoing research seeks to identify the storage and release mechanisms that operate on these carbon reservoirs on glacial time scales and to put constraints on the amount of carbon released at the last glacial termination. While the amount of carbon released from these geologic sources remains an open question for now, it is clear that geologic processes have affected changes in the global carbon budget on glacial time scales.</p>
We compare sediment vertical methane flux off the Mahia Peninsula, on the Hikurangi Margin, east ... more We compare sediment vertical methane flux off the Mahia Peninsula, on the Hikurangi Margin, east of New Zealand’s North Island, with a combination of geochemical, multichannel seismic and sub-bottom profiler data. Stable carbon isotope data provided an overview of methane contributions to shallow sediment carbon pools. Methane varied considerably in concentration and vertical flux across stations in close proximities. At two Mahia transects, methane profiles correlated well with integrated seismic and TOPAS data for predicting vertical methane migration rates from deep to shallow sediment. However, at our “control site”, where no seismic blanking or indications of vertical gas migration were observed, geochemical data were similar to the two Mahia transect lines. This apparent mismatch between seismic and geochemistry data suggests a potential to underestimate gas hydrate volumes based on standard seismic data interpretations. To accurately assess global gas hydrate deposits, multip...
2D numerical modeling algorithms of multi-component, multi-phase filtration processes of mass tra... more 2D numerical modeling algorithms of multi-component, multi-phase filtration processes of mass transfer in frost-susceptible rocks using nonlinear partial differential equations are a valuable tool for problems of subsurface hydrodynamics considering the presence of free gas, free water, gas hydrates, ice formation and phase transitions. In this work, a previously developed one-dimensional numerical modeling approach is modified and 2D algorithms are formulated through means of the support-operators method (SOM) and presented for the entire area of the process extension. The SOM is used to generalize the method of finite difference for spatially irregular grids case. The approach is useful for objects where a lithological heterogeneity of rocks has a big influence on formation and accumulation of gas hydrates and therefore it allows to achieve a sufficiently good spatial approximation for numerical modeling of objects related to gas hydrates dissociation in porous media. The modeling...
: This report provides a preliminary summary of geochemical contribution to methane hydrate resea... more : This report provides a preliminary summary of geochemical contribution to methane hydrate research and exploration on the Hikurangi Margin, off the northeastern coast of New Zealand from June 20 to July 3, 2006. Geochemical porewater profiles taken from shallow piston cores and vertical fluid migration measured with heatflow probing were compared with seismic summaries of potential deep sediment hydrates deposits. Research goals for this expedition include: (1) Refine geophysical, geochemical, and microbiological technologies for prospecting hydrate distribution and content; (2) Contribute to establishing high-priority geographical regions of prospective interest, in terms of methane volume estimates; (3) Prediction of environmental effects and geologic risks at the continental margin associated to the natural resource occurrence and resource exploitation; and (4) Expand understanding of the biogeochemical parameters and associated microbial community diversity in shallow sediment...
: The Naval Research Laboratory (NRL), supported through ONRG-Chile, DOE/NETL, and ONR, participa... more : The Naval Research Laboratory (NRL), supported through ONRG-Chile, DOE/NETL, and ONR, participated in a research cruise along the mid-Chilean coast. Specific research topics addressed by NRL in this program include survey and prediction of geotechnical and geoacoustical anomalies, estimation of coastal hydrate distribution, refining protocol for hydrate exploration, and understanding the variation in microbial community diversity in hydrate-rich regions. The Chile-FONDEF goal in this program is to locate hydrates along the Chilean coast in terms of distribution and methane content for understanding the available energy and geological hazards. This effort integrates future energy exploration with ocean and climate research topics. The examination of sediments in this region was conducted in a collaborative effort between NRL, Milbar Hydrotest, Inc., Virginia Institute of Marine Science, Pontificia Universidad Catolica de Valparaiso, University of Concepcion, and Rice University. Pi...
: Marine Desalination Systems (MDS) is currently developing new technology in gas hydrate formati... more : Marine Desalination Systems (MDS) is currently developing new technology in gas hydrate formation to supply potable water. To scale this technology to support different country needs there is a requirement to assess the environmental impact of desalination. The NRL MDS collaboration on biological influence of marine desalination focuses on water quality of processed water and environmental impact of the marine desalination application. With this segment of the project accomplished, the subsequent evaluation will focus on the impact of large scale marine desalination on environmental quality. To assess the environmental impact of the marine desalinization system there is a need to understand resulting changes to key bacterial and elemental cycles. Seawater vertical transport, alteration of water flow, and filtration have potential to change the microbial community diversity, substrate availability, electron acceptors and key element speciation. Microorganisms surveyed in this analy...
: From May 14-20, 2004, piston core and heat flow measurements were collected across two mound st... more : From May 14-20, 2004, piston core and heat flow measurements were collected across two mound structures, mound D and mound F, in an area designated as Atwater Valley, a shallow trough on the continental slope south of the Mississippi Delta. Atwater Valley lies at 1,200 to 1,500 m water depth. Several small mound structures occur in the valley, rising less than 50 m above the surrounding seafloor. The UNOLS vessel RV Gyre was contracted to support this work. The work took place in about 1,300-m water depth through a 4-km transect at lat. 27.9356 degrees N, Ion. 89.2794 degrees W (lease block Atwater Valley 14). Previous USGS seismic lines AV65, AV97 and AV82 and a 3.5 kHz echosounder profile collected during the cruise were used to guide operations. Total sampling included mounds D and F and a transect between the mounds. During 4 days on site, we acquired 15 piston cores and 23 thermal profiles on a transect from mound F to mound D. Extensive piston coring and heatflow was conduct...
The depth of bottom simulating reflections (BSRs) is routinely used to constrain heatflow on cont... more The depth of bottom simulating reflections (BSRs) is routinely used to constrain heatflow on continental margins, including the Hikurangi Margin, New Zealand. Comparison between BSR-derived heatflow and results from either seafloor thermometry or measurements in boreholes in most regions are in reasonable agreement, with a few notable exceptions. In 2006, we measured the thermal gradient with seafloor heat probes at several locations on the southern Hikurangi Margin as ~0.05 K/m. This contrasts with a thermal gradient of ~0.025 K/m obtained from up to ~700-m deep BSRs. We here revisit these analyses. The observed discrepancy cannot be readily explained by an increase of thermal conductivity with depth for commonly used seismic velocity-porosity-thermal conductivity relations. Likewise, for as long as a Structure-I hydrate is formed, gas and pore-fluid composition do not shift temperatures at the BSR sufficiently upwards to be compatible with seafloor measurements. BSRs at the base of Structure-II hydrates would provide an explanation (the stability range of Structure-II hydrate is quite large depending on the amount of e.g., propane added to the gas mix) but we dismiss this scenario as unlikely since coring did not show any evidence for higher-order hydrocarbons and, also, we are not aware of any wide-spread BSRs beneath Structure-II hydrates anywhere else. We therefore investigate two basic scenarios; 1) unusual rock thermal properties and 2) transient processes. Thermal conductivity deeper in the margin may be higher than velocity-porosity relations would suggest, if the margin consists of highly consolidated but fractured mudstones. This could reconcile both datasets. On the other hand, transient processes that could cause the observed discrepancies include a margin-wide ancient sedimentation pulse. Perhaps the most intriguing explanation would be fluid pulses originating at the subduction interface after subduction earthquakes (or slow slip) leading to transient advective heatflow as proposed for a similar discrepancy between BSR and seafloor thermometry off Chile (Grevemeyer et al., 2006, Geophys. J. Int., 166, 461-468). We have not reached any conclusions as to which mechanism is most likely to cause the discrepancies in thermal gradients. However, the suggested processes could have profound implications. If rock properties were responsible, heatflow on this margin would have been underestimated so far, affecting e.g., the predicted limits of the seismogenic zone. Transient processes on the other hand may provide a mechanism for gas hydrate formation. For example, cooling after a fluid pulse would lead to ``freezing'' of gas to hydrate because of a downward moving base of gas hydrate stability.
In June 2007 sediment cores were collected in Alaminos Canyon, Gulf of Mexico across a series of ... more In June 2007 sediment cores were collected in Alaminos Canyon, Gulf of Mexico across a series of seismic data profiles indicating rapid transitions between the presence of methane hydrates and vertical gas flux. Vertical profiles of dissolved sulfate, chloride, calcium, magnesium, and dissolved inorganic carbon (DIC) concentrations in porewaters, headspace methane, and solid phase carbonate concentrations were measured at each core location to investigate the cycling of methane-derived carbon in shallow sediments overlying the hydrate bearing strata. When integrated with stable carbon isotope ratios of DIC, geochemical results suggest a significant fraction of the methane flux at this site is cycled into the inorganic carbon pool. The incorporation of methane-derived carbon into dissolved and solid inorganic carbon phases represents a significant sink in local carbon cycling and plays a role in regulating the flux of methane to the overlying water column at Alaminos Canyon. Targeted...
Coastal methane hydrate deposits are globally abundant. There is a need to understand the deep se... more Coastal methane hydrate deposits are globally abundant. There is a need to understand the deep sediment sourced methane energy contribution to shallow sediment carbon relative to terrestrial sources and phytoplankton. Shallow sediment and porewater samples were collected from Atwater Valley, Texas-Louisiana Shelf, Gulf of Mexico near a seafloor mound feature identified in geophysical surveys as an elevated bottom seismic reflection. Geochemical data revealed off-mound methane diffusion and active fluid advection on-mound. Gas composition (average methane/ethane ratio ~11,000) and isotope ratios of methane on the mound (average δ 13 C CH4(g) = −71.2‰; D 14 C CH4(g) = −961‰) indicate a deep sediment, microbial source. Depleted sediment organic carbon values on mound (δ 13 C SOC = −25.8‰; D 14 C SOC = −930‰) relative to off-mound (δ 13 C SOC = −22.5‰; D 14 C SOC = −629‰) suggest deep sourced ancient carbon is incorporated into shallow sediment organic matter. Porewater and sediment dat...
Methane hydrate has become one promising energy resource for humankind. In this study, recent wor... more Methane hydrate has become one promising energy resource for humankind. In this study, recent worldwide onshore/offshore drilling and production activities are analysed. The most recent reports fro...
<p>... more <p>For over 100 years scientists have puzzled over the mechanisms responsible for the repeated climate changes known as Ice Ages. A breakthrough was achieved when ice cores and marine archives revealed that the Ice Ages were paced at 100kyr intervals in alignment with Earth’s eccentricity cycle for the past million years. A second breakthrough was achieved when ice core records revealed that the Ice Ages were accompanied by ~80-90ppm variations in atmospheric pCO<sub>2</sub>. But after decades of research the mechanisms responsible for those atmospheric pCO<sub>2</sub> variations remains an open and unresolved puzzle.</p><p>Here we present new findings that challenge the long-standing paradigm that geologic processes that regulate carbon exchange between the Earth’s interior and exterior act too slowly to have influenced the ocean and atmosphere carbon budgets on glacial time scales. The evidence includes large Δ<sup>14</sup>C excursions found in biogenic sediments in each of the Ocean basins at the last glacial termination. These excursions point to a sustained release of <sup>14</sup>C-dead carbon spanning several thousand years.  In the Atlantic, Pacific and Indian Ocean the excursions are found near seafloor deformation features, including pockmarks that are indicative of gas-rich fluid release from sub-surface reservoirs. In the eastern equatorial Pacific, the Δ<sup>14</sup>C excursions are associated with enhanced hydrothermal metal concentrations including Fe, and Z that point to a hydrothermal source. Our ongoing research seeks to identify the storage and release mechanisms that operate on these carbon reservoirs on glacial time scales and to put constraints on the amount of carbon released at the last glacial termination. While the amount of carbon released from these geologic sources remains an open question for now, it is clear that geologic processes have affected changes in the global carbon budget on glacial time scales.</p>
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