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Recent studies have reported up to 1.9 × 1029 bacterial endospores in the upper kilometre of deep subseafloor marine sediments, however, little is understood about their origin and dispersal. In cold ocean environments, the presence of thermospores (endospores produced by thermophilic bacteria) suggests that distribution is governed by passive migration from warm anoxic sources possibly facilitated by geofluid flow, such as advective hydrocarbon seepage sourced from petroleum deposits deeper in the subsurface. This study assesses this hypothesis by measuring endospore abundance and distribution across 60 sites in Eastern Gulf of Mexico (EGM) sediments using a combination of the endospore biomarker 2,6‐pyridine dicarboxylic acid or 'dipicolinic acid' (DPA), sequencing 16S rRNA genes of thermospores germinated in 50°C sediment incubations, petroleum geochemistry in the sediments and acoustic seabed data from sub‐bottom profiling. High endospore abundance is associated with geologically active conduit features (mud volcanoes, pockmarks, escarpments and fault systems), consistent with subsurface fluid flow dispersing endospores from deep warm sources up into the cold ocean. Thermospores identified at conduit sites were most closely related to bacteria associated with the deep biosphere habitats including hydrocarbon systems. The high endospore abundance at geological seep features demonstrated here suggests that recalcitrant endospores and their chemical components (such as DPA) can be used in concert with geochemical and geophysical analyses to locate discharging seafloor features. This multiproxy approach can be used to better understand patterns of advective fluid flow in regions with complex geology like the EGM basin. [ABSTRACT FROM AUTHOR]

The thin layers in the ocean are temporally-coherent aggregations of phytoplankton with high concentrations at small vertical scales, presenting important hotspots of ecological activity. Lidar could identify thin phytoplankton layers at a large spatial scale due to its capabilities of profile detection with a high efficiency. However, studies that linked thin layers to environmental factors are few, which limits our understanding of the layer formation mechanism. This paper investigates the characteristics and formation conditions of thin phytoplankton layers in the northern Gulf of Mexico using airborne lidar. The results depict that the chlorophyll concentration determines the formation probability of the phytoplankton layer. The layer is mainly formed at concentrations less than 6 mg m−3 and mostly distributed at 2 mg m−3. In addition, layer thicknesses were within 5 m and layer depths were mainly in the range of 10–15 m. Layer depths in the nearshore region were shallower than those in the offshore region. We conclude that the characteristics and formation conditions of the thin phytoplankton layers depend on the nutrients and light that are related to the seabed topography, turbidity, eddies and upwelling. The findings of this paper will enhance the understanding of layer formation mechanisms. [ABSTRACT FROM AUTHOR]

Offshore infrastructure often interacts cyclically with the seabed over the operational life of a project. Previous research on the evolution of soil's undrained strength under long-term, large-amplitude cyclic loading has focused on contractile clays and demonstrated that this cyclic interaction can lead to the initial generation and later dissipation of positive excess pore pressure in the soil. This process generally leads to an initial strength reduction, with subsequent densification and soil strength gains that can have consequences on the performance of seabed infrastructure during its design life. In this paper, new experimental data from T-bar penetrometer testing in kaolin and reconstituted Gulf of Mexico clays is presented. The data illustrate how the stress history, quantified via the overconsolidation ratio, affects soil strength changes during large-amplitude cyclic loading. The experiments explore both long-term continuous loading cycles and episodic loading with packets of undrained cycles followed by quiescent consolidation periods. A critical state-based framework is used to interpret the experimental data and provide predictions of the long-term steady-state strength of both soils as a function of the initial in situ state of the soil. [ABSTRACT FROM AUTHOR]

This paper discusses the flotation of cables and pipelines that have been trenched using jet trenching during reconsolidation of the seabed soil. Utilising previously published data on the variation of clay strength with liquidity index, it is demonstrated for the first time that, while current industry guidance is appropriate for the low-plasticity clays for which much previous research has been carried out, it may be overly conservative for high-plasticity clays such as those found in the Gulf of Guinea or the Gulf of Mexico, owing to the differing strength and density characteristics of these soils. [ABSTRACT FROM AUTHOR]

Instruments are often deployed at depth for weeks to years for a variety of marine applications. In many cases, divers can be deployed to retrieve instruments, but divers are constrained by depth limitations and safety concerns. Acoustic release technology can also be employed but can add considerable expense and acoustic releases will at times fail. Here, we report a simple method that utilizes a commercially available mooring hook integrated with a mini remotely operated vehicle to attach lines to instruments deployed on the sea floor, which can then be winched to the surface. The mooring hook apparatus was tested in a pool setting and then used to retrieve acoustic telemetry receiver bases (50 kg) or fish traps (30–50 kg) from the northern Gulf of Mexico continental shelf at depths between 28 and 80 m. During 2013–2019, 539 retrievals (100% success rate) were made of receiver bases (n = 239) and traps (n = 300) on 30 sea days using this approach. This method could easily be applied to other types of instruments, or recovery and salvage of objects that are too deep for standard diving operations. [ABSTRACT FROM AUTHOR]

Marine cold seeps transmit fluids between the subseafloor and seafloor biospheres through upward migration of hydrocarbons that originate in deep sediment layers. It remains unclear how geofluids influence the composition of the seabed microbiome and if they transport deep subsurface life up to the surface. Here we analyzed 172 marine surficial sediments from the deep-water Eastern Gulf of Mexico to assess whether hydrocarbon fluid migration is a mechanism for upward microbial dispersal. While 132 of these sediments contained migrated liquid hydrocarbons, evidence of continuous advective transport of thermogenic alkane gases was observed in 11 sediments. Gas seeps harbored distinct microbial communities featuring bacteria and archaea that are well-known inhabitants of deep biosphere sediments. Specifically, 25 distinct sequence variants within the uncultivated bacterial phylaAtribac-teria and Aminicenantes and the archaeal order Thermoprofundales occurred in significantly greater relative sequence abundance along with well-known seep-colonizing members of the bacterial genus Sul-furovum, in the gas-positive sediments. Metabolic predictions guided by metagenome-assembled genomes suggested these organisms areanaerobic heterotrophs capable of nonrespiratory breakdown of organic matter, likely enabling them to inhabit energy-limited deep sub-seafloor ecosystems. These results point to petroleum geofluids as avector for the advection-assisted upward dispersal of deep biospheremicrobes from subsurface to surface environments, shaping the micro-biome of cold seep sediments and providing a general mechanism for the maintenance of microbial diversity in the deep sea. [ABSTRACT FROM AUTHOR]

Although many studies have been performed in the northern Gulf of Mexico, there have been a paucity of high-resolution sediment data collected from seabed. New multicores were collected repeatedly at 4 fixed stations in the inner Louisiana shelf on March 12, 2021, July 7, 2021, November 20, 2021, and March 5, 2022, respectively, to study detailed spatial and temporal variations of surficial sediment. Being a very high sediment accumulation zone, Raccoon Island dredge pit and its nearby shelf were selected as our study area and additional six vibracores were collected inside and outside the pit for comparison. This study area is about 140 km west of the modern Mississippi Delta and 70 km southeast of the Atchafalaya Delta. A total of 624 samples from both vibracores and multicores were analyzed for this study. Spatially, our results show that sediment near Ship Shoal was the coarsest and sediment deposited in the pit was the finest. The organic matter was highest inside the pit and lowest near Ship Shoal. The carbonate content was the lowest near Ship Shoal. Temporally, surficial sediments were generally coarser in July and November of 2021 and finer in March of 2021 and March of 2022. Although the Mississippi and Atchafalaya Rivers supply a large amount of sediment during spring season, it takes time for the river-derived sediment to be delivered into the study area. Hurricanes Delta, Zeta and Ida passed this area and greatly impacted sediment transport in the years 2021 and 2022. The comparatively coarser sediment in July and November of 2021 were likely related to the resuspension of some coarse sediment by these hurricane events. Besides the river supply, Ship Shoal and barrier islands are nearby localized sandy sources and inner Louisiana shelf is a widespread mud source. This spatial heterogeneity of surficial sediment interplays with the timing of Mississippi and Atchafalaya River flood season and hurricanes and together dictates the sediment texture. This research on a filled-up dredge pit can benefit future evaluation of the safety of existing oil infrastructure and the feasibility of building new pipelines and platforms after dredging activities. Our results also shed light on the study of river- and hurricane-impacted sediment transport in muddy and mixed-texture passive continental margins around the world. • Pit sediment hasn't reached an equilibrium with ambient environment yet. • Surficial sediments were coarser in July and November and finer in March. • Sediment grain size spatial variations were categorized into four groups. • This research will benefit future coastal restoration and sediment management. [ABSTRACT FROM AUTHOR]

The article talks about the deep sea drilling and offshore platforms, the seabed sediments, marine activities of human that includes test mining of hydrate, damage to the stability of seabed sediments and occurrence of natural disasters. It talks about the study of the sediments of the Gulf of Mexico with the use of diameter core, shear strength, volume density and the shallow surface that is composed of clay and powder grains.

Biological indices such as AZTI’s Marine Biotic Index (AMBI) and multivariate AMBI (M-AMBI) have been used in monitoring programs worldwide to assess the benthic ecological status (ES) of transitional and coastal waters. However, their reliability is reduced under faunal impoverishment and defaunation, low abundance/number of taxa, and/or high percentage of taxa not assigned or mis-assigned to ecological group, which imply removing these data from the analysis. In order to avoid loss of robustness when these situations are met, here we propose an approach based on decision criteria that utilize these indices together with environmental and contaminants data. Our area of study is the southern Gulf of Mexico seafloor, where a survey was carried out during the rainy season across a sampling grid of 75 sites. To achieve this, we first distinguished homogeneous groups of sites and then defined states (‘good’, ‘fair’, and ‘bad’) from three sediment quality elements: benthic indices, environmental data by quartile values, and contaminant concentrations in the context of sediment quality guidelines. Overall, 69% of sampling sites showed low abundance and defaunation, mainly at sites located on the continental shelf, where most of them ranged from ‘moderate’ to ‘poor’ ES, principally by ‘fair’ environmental data and secondly, oil-related disturbance. Conversely, sites located near the mouths of rivers and coastal lagoons recorded the highest abundance and showed diverse sensitivity levels, ranging from ‘high’ to ‘bad’ ES. In conclusion, the use of this states-based approach allowed us to support and interpret the results of AMBI and M-AMBI, since their values were related to environmental and contaminants data. This approach may be useful in many contexts to avoid the loss of data when assessing the ES of the seafloor under defaunation or low abundance conditions. [ABSTRACT FROM AUTHOR]

Several studies have examined the horizontal or two-dimensional (2-D) movements of red snapper, Lutjanus campechanus , but none have described the long-term depth preferences of this economically important fish species. Red snapper were tagged with depth transmitters and movements were tracked (n = 7; VR2W Positioning System, Vemco Ltd., Nova Scotia) on an artificial reef site 28 km south of Dauphin Island, Alabama in the northern Gulf of Mexico for two years. More than 3.5 million accurate positions (∼1 m) were obtained and used to assess red snapper depth patterns over monthly and hourly time periods. In addition, three-dimensional (3-D) patterns of red snapper volume use (m 3 ) were estimated based on depth and location (latitude, longitude) from >700,000 3-D positions. Red snapper depth preferences and volume use varied over time periods. Red snapper tended to stay at deeper depths during the colder months (<3 m from seafloor), and move up in the water column more frequently in the late spring and summer months ( F 23,127 = 45.5, P < 0.0001). Similarly, volume use patterns varied significantly by month (core, F 23,127 = 13.14, P < 0.0001; home range, F 23,127 = 27.6, P < 0.0001) with the smallest movements in February and largest in August (2013) or October (2014) depending on year. Diel home range volume showed that red snapper made fewer movements during night (1900–0400 h) compared to day (0600–1700 h; F 23,3585 = 13.2, P < 0.0001). The present habitat use patterns were surprising, because for the most part red snapper were previously considered a benthic oriented reef species. However, in the present study depth and volume shape patterns showed use of the entire water column during the spring and summer. These higher water column use patterns were likely related to spawning patterns and prey availability over both diel and monthly time periods, but further studies are needed to help confirm such correlations. [ABSTRACT FROM AUTHOR]

Aim To test the hypothesis that low productivity drives the nestedness component of β-diversity in polychaetes at the deep-sea floor. Location Western Gulf of Mexico. Methods We used A. Baselga's (2010, Global Ecology and Biogeography, 19, 134-143) metrics of species replacement and nestedness to assess their overall significance with differences in depth and particulate organic carbon ( POC) flux to the seafloor. We used M. A. Rodríguez-Gironés & L. Santamaría's (2006, Journal of Biogeography, 33, 924-935) BINMATNEST to calculate the significance and direction of nestedness with depth and POC flux. Results Nestedness was the most significant part of β-diversity with depth and POC flux. The rank order of nestedness increased significantly with increasing depth, and decreased significantly with increasing POC flux. There was little endemism below 2000 m. Main conclusion The polychaete fauna in the deepest western Gulf of Mexico is largely a nested subset of the shallower upper to mid-bathyal fauna. While the causes of β-diversity in the deep sea are undoubtedly multivariate, the relative importance of turnover and nestedness appears to be modulated by productivity in the form of POC flux to the seafloor. Under circumstances of extremely low POC flux and animal density in the deepest reaches of the Gulf, nestedness may be caused by some populations being maintained by immigration from larger populations upslope, or by biogeographic filtering for tolerance to abyssal conditions. Resources at great depths in regions of exceptionally low productivity may be too limited to permit adaptation resulting in endemism and continued downslope turnover. If productivity helps to explain the nestedness part of β-diversity, this may lead to a more unified theory of deep-sea biodiversity. [ABSTRACT FROM AUTHOR]

Polychaete worms (Annelida), the dominant macrofaunal taxon in most fine-grained marine sediments, were sampled in 1983–85 and then again in 2000–02 at nine locations at depths of 324–1454 m. on the upper continental slope of the northern Gulf of Mexico (GoM). The assemblages exhibited relative stability in abundance and diversity, but fell into six separate groups of species (>35% similarity) that were related to time-of-sampling, location, depth. This depth gradient experiences an increase in oxygen from 2.5 to 4.5 ml/L, a six degree decrease in temperature (10–12° down to 4 °C) and a decline of 30–37 mg C m −2 day −1 down to 7 mg C m −2 day −1 in estimates of the particulate organic carbon (POC) input to the sea floor, but these steep gradients had secondary effects on species turnover or depth-related zonation (Beta diversity). The species composition of four of the six groups was separated on the basis of sampling between 1983–85 and 2000–02 as opposed to depth or location. The species composition of the two groups on the eastern transect was different from the western sites and the two eastern groups differed in species composition from each other between 1983–85 and 2000–02. The two groups of species at the three deeper sites to the west (864–1410 m) were also separated on the basis of time-of-sampling but the group of species located at the three shallow locations (324–625 m) was not; it was a mixture of the two sampling periods. Significantly higher densities (p<0.05) in April 1984, on the eastern transect, suggest that seasonal recruitment may have occurred but the higher densities were attributed to only two species. [ABSTRACT FROM AUTHOR]

The article focuses on the BP Deepwater Horizon Explosion and Oil Spill in the Gulf of Mexico in 2010 and discusses what happened to all of the oil in the spill. Topics include various physical, chemical, and biological processes stated to have affected the fate and distribution of the spilled petrocarbon, some of the spilled oil directly removed by mitigating measures, some was rapidly biodegraded and some was deposited on the seafloor.

This study quantified the coastal gradients of salinity, temperature, nutrients, chlorophyll and oxygen along a transect from 5 to 18 m depth in the northeastern Gulf of Mexico (NEGOM) through measurements of water column profiles over 4.5-years and recordings of probes mounted at 0.5 m above the seafloor over 2-years. The main goal was to determine the influences of the coastal gradients on water column oxygen concentration distributions. Apalachicola River discharge affected the study region as reflected in low-salinity surface layers. Decreasing rates of oxygen production and consumption from the shallowest station to the deepest station were attributed to measured coastal gradients of nutrients and the decreasing influence of seafloor processes with increasing distance from shore. Water column photosynthetic oxygen production at a realistic irradiance of 200 μE m −2 s −1 ranged from 0.5 to 4.5 mmol O 2 m −3 h −1 , and dark consumption rates from 0.2 to 2.6 mmol O 2 m −3 h −1 . Based on July irradiance profiles and associated production and consumption rates, the water column in July 2009 produced 0.9 (1SD=0.2) g C m −2 d −1 with rates remaining relatively constant over the length of this coastal transect. Benthic boundary layer production reaching 26–43% of the surface layer production underlines the role of the benthic boundary layer for production in the inner shelf. Oxygen in the benthic boundary layer never decreased below 73% air saturation, and hypoxic zones, as reported from shelf areas west of the study region, did not occur. Oxygen production exceeded consumption suggesting a net autotrophic system. [ABSTRACT FROM AUTHOR]

The ephemeral nature of marine oil and gas seepages and their complex trajectories in the water column make seep sampling difficult and costly. Here we report on how active natural seepage can be detected and located in the water column and at the sea bed in real time through the integration of marine X-band radar, synthetic aperture radar, field observations, high resolution single beam acoustic methods, and meta-ocean data from the marine environment with a simple bubble rise model. The extent of predictions made using a bubble rise model narrow down the likely seafloor origin point of an observed surface feature to within a radius of 630 m within which clusters of acoustic contacts were detected. Use of averaged deep current velocities and directions narrows the radius to 130 m, and use of a smaller established range of bubble rise speeds from the Gulf of Mexico can narrow the predicted seafloor origin radius further to 16.5 m. These results are useful for focussing detailed sea bed search patterns for natural seepage and are also suggestive of a seep system with complex water column trajectories associated with Biloxi Dome in the Gulf of Mexico. [ABSTRACT FROM AUTHOR]

Authigenic carbonate rocks recovered from the Gulf of Mexico Gas Hydrate Seafloor Observatory in Mississippi Canyon block 118 (MC118) at approximately 900 m water depth were studied using mineralogical, bulk geochemical, and lipid biomarker analyses. Carbonate rocks occurred as fractured blocks and nodular masses incorporated in carbonate breccias. The carbonates were comprised mainly of high-Mg-calcite and aragonite. The stable carbon isotope composition (δ 13 C) of authigenic carbonate varied from − 29.8‰ to − 18.1‰ vs. V-PDB, suggesting a complex mixture of various carbon sources, including dissolved marine inorganic carbon (DIC), oil, as well as methane. Oxygen isotopes (δ 18 O) varied from + 3.4‰ to + 5.8‰. The observed 18 O-enrichment in relation to calculated equilibrium values in the carbonates probably reflects decomposition of gas hydrates. The most abundant lipid biomarkers in the carbonates were isoprenoidal glycerol dibiphytanyl glycerol tetraethers (GDGTs), predominated by GDGT-2 and GDGT-3, which are typically indicators of anaerobic methane oxidizing archaea (ANMEs). Mono- and bicyclic biphytanes (derived after ether cleavage of GDGT-2 and GDGT-3) showed strong 13 C-depletion, which is characteristic for ANMEs. Interestingly, large differences between the δ 13 C values of the archaeal diether archaeol and acyclic biphytane on the one hand and monocyclic biphytane on the other hand suggest the presence of archaea other than ANMEs. Archaeol and GDGT-0 (containing two acyclic biphytane moieties) are commonly assigned to various methanogenic archaea. Where methane seepage activity is intermediate or low within acoustic wipeout zones at the MC118 gas hydrate site nowadays, microbial communities must have coped with changing conditions as well as longer-term fluctuations in oil and gas seepage or the temporary cessation of hydrocarbon flux in the past. The change from methane seepage to oil seepage or vice versa in addition to flux variability apparently favors the establishment of complex prokaryotic communities dominated by archaea. In addition to anaerobic oxidation of methane, local production of methane is apparently prominent at the study site based on the occurrence of biomarkers of methanogens in the authigenic carbonate. This finding adds to the ongoing multidisciplinary effort to better constrain the environment at the MC118 observatory site and to determine the locally dominant biogeochemical processes. [ABSTRACT FROM AUTHOR]

Abstract: High salinities and high temperatures at the seafloor record the upward flow of water and hydrocarbons from depth at natural vents in the deepwater Gulf of Mexico. We present a multiphase heat- and solute-transport model, in which water supplied from depth transports heat and salt, and hydrocarbon transports heat. We show that there is a unique water and hydrocarbon flux that simulates the observed salinity and temperature. We estimate the hydrocarbon flux to be and from two vents at lease blocks MC852/853 and GB425. These fluxes are 1–4 orders of magnitude greater than previous estimates from individual deepwater vents. If these results are extrapolated to the entire Gulf of Mexico, then we estimate the regional hydrocarbon flux to be at least 100× greater than previous estimates and 14–120% of the hydrocarbon flux from the Macondo oil spill. Large natural seepage may inoculate marine basins such as the Gulf of Mexico from oil spills like the 2010 Deepwater Horizon blowout by sustaining populations of hydrocarbon-degrading bacteria. [Copyright &y& Elsevier]

Abstract: Woolsey Mound, a carbonate/hydrate complex of cold seeps, vents, and seafloor pockmarks in Mississippi Canyon Block 118, is the site of the Gulf of Mexico Hydrates Research Consortium’s (GOMHRC) multi-sensor, multi-disciplinary, permanent seafloor observatory. In preparation for installing the observatory, the site has been studied through geophysical, biological, geological, and geochemical surveys. By integrating high-resolution, swath bathymetry, acoustic imagery, seafloor video, and shallow geological samples in a morpho-bio-geological model, we have identified a complex mound structure consisting of three main crater complexes: southeast, northwest, and southwest. Each crater complex is associated with a distinct fault. The crater complexes exhibit differences in morphology, bathymetric relief, exposed hydrates, fluid venting, sediment accumulation rates, sediment diagenesis, and biological community patterns. Spatial distribution of these attributes suggests that the complexes represent three different fluid flux regimes: the southeast complex seems to be an extinct or quiescent vent; the northwest complex exhibits young, vigorous activity; and the southwest complex is a mature, fully open vent. Geochemical evidence from pore-water gradients corroborates this model suggesting that upward fluid flux waxes and wanes over time and that microbial activity is sensitive to such change. Sulfate and methane concentrations show that microbial activity is patchy in distribution and is typically higher within the northwest and southwest complexes, but is diminished significantly over the southeast complex. Biological community composition corroborates the presence of distinct conditions at the three crater complexes. The fact that three different fluid flux regimes coexist within a single mound complex confirms the dynamic nature of the plumbing system that discharges gases into bottom water. Furthermore, the spatial distribution of bio-geological processes appears to be a valid indicator of multiple fluid flux regimes that coexist at the mound. [Copyright &y& Elsevier]

Abstract: Significant horizontal stress anisotropy was encountered in three blocks in the Gulf of Mexico drilled by the Gulf of Mexico gas hydrates Joint Industry Project, namely, Atwater Valley 13, Atwater Valley 14, and Walker Ridge 313. The geological factors responsible for this state of stress and the implications for wellbore stability and drilling operations are explored. In Atwater Valley 13 and 14, stresses at the well sites were perturbed by the underlying salt. In Walker Ridge 313, a combination of thrusting by adjacent salt and material anisotropy associated with the regional minibasin structure caused the maximum horizontal stress to rotate with depth. Horizontal stress anisotropy combined with a lack of heavy mud caused breakouts to form in the well Walker Ridge 313-G (WR313-G). A simple formula to predict the depth at which wells drilled with seawater are prone to breakouts is derived. Evidence is presented that the breakouts in WR313-G produced heavy cavings which were mainly responsible for the tight hole conditions encountered while drilling this well. However, it is shown that bottom hole assembly (BHA) design and drilling practices such as backreaming may have exacerbated these problems. Modifications to drilling practices based on the experience gained from drilling WR313-G helped to improve the quality of the neighboring borehole WR313-H. [Copyright &y& Elsevier]

Abstract: Through the use of 3-D seismic amplitude mapping, several gas hydrate prospects were identified in the Alaminos Canyon (AC) area of the Gulf of Mexico. Two locations were drilled as part of the Gulf of Mexico Gas Hydrate Joint Industry Project Leg II (JIP Leg II) in May of 2009 and a comprehensive set of logging-while-drilling (LWD) logs were acquired at each well site. LWD logs indicated that resistivity in the range of ∼2 ohm-m and P-wave velocity in the range of ∼1.9 km/s were measured in the target sand interval between 515 and 645 feet below sea floor. These values were slightly elevated relative to those measured in the sediment above and below the target sand. However, the initial well log analysis was inconclusive regarding the presence of gas hydrate in the logged sand interval, mainly because large washouts caused by drilling in the target interval degraded confidence in the well log measurements. To assess gas hydrate saturations in the sedimentary section drilled in the Alaminos Canyon 21 B (AC21-B) well, a method of compensating for the effect of washouts on the resistivity and acoustic velocities was developed. The proposed method models the washed-out portion of the borehole as a vertical layer filled with sea water (drilling fluid) and the apparent anisotropic resistivity and velocities caused by a vertical layer are used to correct the measured log values. By incorporating the conventional marine seismic data into the well log analysis, the average gas hydrate saturation in the target sand section in the AC21-B well can be constrained to the range of 8–28%, with 20% being our best estimate. [Copyright &y& Elsevier]

Abstract: High-quality logging-while-drilling (LWD) downhole logs were acquired in seven wells drilled during the Gulf of Mexico Gas Hydrate Joint Industry Project Leg II in the spring of 2009. Well logs obtained in one of the wells, the Green Canyon Block 955 H well (GC955-H), indicate that a 27.4-m thick zone at the depth of 428 m below sea floor (mbsf; 1404 feet below sea floor (fbsf)) contains gas hydrate within sand with average gas hydrate saturations estimated at 60% from the compressional-wave (P-wave) velocity and 65% (locally more than 80%) from resistivity logs if the gas hydrate is assumed to be uniformly distributed in this mostly sand-rich section. Similar analysis, however, of log data from a shallow clay-rich interval between 183 and 366 mbsf (600 and 1200 fbsf) yielded average gas hydrate saturations of about 20% from the resistivity log (locally 50−60%) and negligible amounts of gas hydrate from the P-wave velocity logs. Differences in saturations estimated between resistivity and P-wave velocities within the upper clay-rich interval are caused by the nature of the gas hydrate occurrences. In the case of the shallow clay-rich interval, gas hydrate fills vertical (or high angle) fractures in rather than filling pore space in sands. In this study, isotropic and anisotropic resistivity and velocity models are used to analyze the occurrence of gas hydrate within both the clay-rich and sand dominated gas-hydrate-bearing reservoirs in the GC955-H well. [Copyright &y& Elsevier]

Abstract: Subsurface interpretation, utilizing a database of more than 450,000 km2 (175,000 mi2) of three-dimensional (3-D) seismic in the northern Gulf of Mexico (GoM), reveals 145 discrete areas, totaling 4450 km2 (1.1 million acres) where the base of gas hydrate stability (BGHS) can be confidently inferred from seismic data. Unlike many other areas of the world, the majority of these features are not Bottom Simulating Reflectors (BSRs) in the “classic” sense, meaning continuous coherent events that cross-cut primary stratigraphy. Those typical, or continuous BSRs, are noted in only 24% of the features identified within this study. In contrast, the most common seismic manifestation of the BGHS in the GoM (59%) is the discontinuous “BSR”, delineated by widely separated anomalous seismic events that align in general conformance with seafloor bathymetry. A third type of seismic feature, pluming “BSRs”, are continuous events that are not bottom-simulating, but are bowed toward the seafloor and represent areas where large, but areally-limited increases in heat flow (linked to strong vertical fluid flux), perturb the BGHS. The limited nature of continuous BSRs and the relative abundance of discontinuous and pluming forms are attributed to the strong lithologic and structural heterogeneity of the northern GoM basin. This lithologic and structural complexity has served to disrupt and localize regionally pervasive and homogeneous gas flux that is consistent with the formation of large, continuous BSRs noted across other less complex continental margins. The various BSR forms identified in this study are shown to be closely associated (125 of 145) with the occurrence of seafloor amplitude anomalies, which are in turn usually associated with the flanks and crests of salt-cored ridges. These associations are interpreted to reflect the co-dependence of BSRs and seafloor reflectivity along the migration pathways that typify this geologic setting. [Copyright &y& Elsevier]

Oil flow rates and cumulative discharge from the BP Macondo Prospect well in the Gulf of Mexico are calculated using a physically based model along with wellhead pressures measured at the blowout preventer (BOP) over the 86-day period following the Deepwater Horizon accident. Parameters appearing in the model are determined empirically from pressures measured during well shut-in and from pressures and flow rates measured the preceding day. This methodology rigorously accounts for ill-characterized evolution of the marine riser, installation and removal of collection caps, and any erosion at the wellhead. The calculated initial flow rate is 67?100 stock-tank barrels per day (stbd), which decays to 54?400 stbd just prior to installation of the capping stack and subsequent shut-in. The calculated cumulative discharge is 5.4 million stock-tank barrels, of which 4.6 million barrels entered the Gulf. Quantifiable uncertainties in these values are -9.3% and +7.5%, yielding a likely total discharge in the range from 4.9 to 5.8 million barrels. Minimum and maximum credible values of this discharge are 4.6 and 6.2 million barrels. Alternative calculations using the reservoir and sea-floor pressures indicate that any erosion within the BOP had little affect on cumulative discharge. [ABSTRACT FROM AUTHOR]

Oil and gas production in the Gulf of Mexico is an important aspect of our domestic energy strategy and to successfully obtain oil from deep beneath the ocean floor, ha thousands of feet of water, an impressive array of technology is utilized by the oil and gas industry. One of the many lessons learned, however, from the Deepwater Horizon disaster is that this technology can present significant risks to human life and the environment if it fails. This Article presents an overview of the technology used to conduct deepwater oil and gas drilling operations, and then examines how the failure to adequately regulate this risky technology played a major role ha the Deepwater Horizon catastrophe. This Article also summarizes the actions taken by regulators in response, and questions whether the actions taken are sufficient to prevent another deepwater disaster. The Article concludes by suggesting a number of other actions for consideration by policymakers to reduce the risks associated with producing oil from tens of thousands of feet beneath the ocean's floor. [ABSTRACT FROM AUTHOR]

Abstract: In mudstones of the Ursa Basin, Gulf of Mexico, the volume of voids to solids, or void ratio, ranges from 4 (porosity=80%) at the seafloor to 0.6 (porosity=37%) at 600m below seafloor. This seven-fold change in void ratio can only be described by a compaction model that includes greater sediment stiffening with stress than has commonly been used in geotechnical or geological approaches. Through uniaxial consolidation experiments, we show that specific volume (v=1+void ratio) declines as an exponential function of effective stress. We use this relationship to successfully predict in-situ overpressures at Integrated Ocean Drilling Program (IODP) Sites U1322 and U1324. This technique can be used around the world to describe sediment compaction and predict pore pressure in the first 1000m below seafloor. Rapid sediment consolidation near the seafloor provides the fluid source that generates overpressure despite the fact that these sediments have high permeability. Ultimately sediment consolidation is a first order control on when and at what depth overpressure will be generated in the subsurface. This in turn will impact whether submarine landslides are expected and the regional gradient of continental margins. [Copyright &y& Elsevier]

Abstract: A chronostratigraphic framework is constructed from sediments surrounding an active gas-hydrate and cold-seep field, situated on the northern Gulf of Mexico slope within federal offshore lease block Mississippi Canyon 118 (MC118). Accelerator mass spectrometer (AMS) radiocarbon dating, foraminiferal biostratigraphy and nannofossil biostratigraphy are used to constrain the age of sediments from 10 gravity cores collected around the field. X-ray fluorescence (XRF) core scanning is employed to develop continuous down-core elemental profiles, which are used to evaluate biogenic calcium and siliciclastic titanium sediment inputs, and provide a means to correlate sediments across the study area and infer changes in sedimentation through time. Spatial reconstruction of sedimentation surrounding the field indicates the following: (1) a consistent pattern of stratigraphic thinning in close proximity to the field over the past 14,000yrs and (2), temporal changes in sedimentation that primarily reflect deglacial sea-level rise as well as regional factors such as Mississippi delta lobe switching. These results highlight the variability of sedimentation along a continental slope setting where marine cold seeps and gas hydrate persist, yet do not suggest slope failure or destabilization of the seafloor at this site, at least during the past 14,000yrs. The evaluation of sedimentation at this location provides an important context for ongoing biogeochemical and geophysical monitoring of the MC118 site, which has been designated the first National Gas Hydrate Seafloor Observatory by the Gulf of Mexico Hydrate Research Consortium. [ABSTRACT FROM AUTHOR]

Abstract: In underwater hydrocarbon seepage environments, gas hydrates are considered to play a significant role as shallow gas reservoirs and buffers for light hydrocarbon expulsion. Here we report on mixed hydrate structures from the Chapopote Knoll in the southern Gulf of Mexico and discuss several options on how a mixture of structure I (sI) and structure II (sII) gas hydrate may occur in nature. Locally resolving microscopic methods are needed to characterize the coexistence of different hydrate structures at geological hydrate deposits; we used Raman spectroscopy, X-ray diffraction, and gas chromatography for our investigations. Gas hydrates were found within the matrix and pores of the asphalts extruded at the seafloor. Two of the three hydrate pieces investigated comprised only sI, formed mostly from methane. In contrast, one piece comprised an intimate mixture of both sI and sII with sII representing ca. 25wt.% and sI ca. 75wt.% of the hydrate present. The two structures were closely associated within individual grain agglomerates. The crystallites of sII were significantly larger than of sI, suggesting differences in the nucleation density or different crystallite ages. The structural coexistence may be a result of one or more processes: i) de-mixing into two hydrate structures during the growth from the gas phase, which provides an additional degree of freedom for lowering the free energy in the system; ii) fractionated crystallization with a subsequently changing molecular composition; iii) crystallization from separated gas bubbles with different hydrocarbon compositions and water; and iv) partial transformation from sII to sI after hydrate nucleation, ceasing when a thermodynamically stable state was reached. The presented work will affect future assessments of natural hydrate deposits at thermogenic hydrocarbon systems, as it shows that both hydrate types I and II can be present at a certain geological site, and may provide a lingering strength to the system if conditions fall below the sI stability limit. This suggests that present worldwide hydrate occurrences are likely to be underestimated. [Copyright &y& Elsevier]

The microbial community structures of gas hydrate-bearing (Core 9) and non-hydrate-bearing (Core 1) marine sediments were investigated at Mississippi Canyon (MC) 118 in the Gulf of Mexico. Quantification by quantitative competitive (QC)-PCR showed that bacterial abundance was 2-3 orders of magnitude higher than archaeal abundance in these cores. Sulfate-reducing bacteria (SRB) were present at 103-104 dsrAB gene copies/g in both cores; methanogens or anaerobic methanotrophs were only present in Core 9 (102-105 mcrA gene copies/g). Denaturing gradient gel electrophoresis (DGGE) showed distinct patterns of bacterial community structure between Core 9 and Core 1 with ε-Proteobacteria predominating in the former and γ-Proteobacteria in the latter. Clone libraries were successfully constructed for both Archaea and Bacteria using functional genes (mcrA and dsrAB, respectively). The mcrA gene was present in Core 9, suggesting enhanced abundance or activity of methanogens or methane-oxidizing archaea in the hydrate-impacted sediment. The mcrA gene sequences were dominated by group c-d and group e. The majority (80%) of the dsrAB gene sequences fell into Syntrophobacteraceae-related group. This study indicates that microbial community structures are considerably different between the hydrate-bearing and non-hydrate-bearing sediment at MC 118. Our study is among the initial steps toward a comprehensive and long-term monitoring of microbial dynamics associated with gas hydrates in the Gulf of Mexico. [ABSTRACT FROM AUTHOR]

Abstract: The Campeche Knolls in the Bay of Campeche, southern Gulf of Mexico, were investigated through detailed seafloor mapping, ROV surveys, and sediment and pore water sampling. The knolls are elongated, submarine hills created by salt tectonics with a positive relief of up to 800m above the surrounding seafloor. Several of the knolls are associated with sea-surface oil slicks identified from satellite data, indicating the presence of hydrocarbon seeps on the seafloor. One of the knolls, named “Chapopote”, was studied in detail during two international research expeditions (SO174/2 and M67/2) and is characterized by extensive hydrocarbon seepage including large asphalt flows, oil and gas seeps, and seafloor gas hydrate deposits. Chemosymbiotic biological communities and authigenic carbonate deposits are associated with the seeps and are the result of both biogeochemical turnover and the interaction between downward-diffusing seawater and hydrocarbon-rich pore fluids at shallow sediment depth. Authigenic carbonates are characterized by aragonite, exhibit a porous texture, and are cemented by a matrix of microsparitic to sparitic aragonite. Macropores of the carbonates were completely filled with liquid oil. Carbonate microfabrics include peloidal or clotted fabrics that may indicate the existence of microenvironments resulting from microbial metabolism. Banded/botryoidal aragonite cements line the intra- and bioclasts and incompletely fill the pore spaces. The stable carbon isotopic composition of authigenic aragonite varies between −28.6‰ and −17.9‰ (PDB), identifying oil oxidation as the primary source of carbon to the DIC pool, while lipid biomarker data demonstrate the concurrent existence of microbial communities responsible for anaerobic oxidation of methane (AOM). These observations indicate the presence of additional, AOM-independent reactions responsible for carbon sequestration at hydrocarbon seeps and demonstrate the complexity of biogeochemical processes at seep sites in the Gulf of Mexico basin. Oxygen isotope data of authigenic aragonite vary from +2.5‰ to +3.8‰ (PDB), indicating carbonate precipitation in slight disequilibrium with the surrounding pore fluids. [Copyright &y& Elsevier]

Abstract: Observations of topographic Rossby waves (TRW), using moored current meters, bottom pressure gauges, and Lagrangian RAFOS floats, are investigated for the deep basin of the Gulf of Mexico. Recent extensive measurement programs in many parts of the deep gulf, which were inspired by oil and gas industry explorations into ever deeper water, allow more comprehensive analyses of the propagation and dissipation of these deep planetary waves. The Gulf of Mexico circulation can be divided into two layers with the ∼800–1200m upper layer being dominated by the Loop Current (LC) pulsations and shedding of large (diameters ∼300–400km) anticyclonic eddies in the east, and the translation of these LC eddies across the basin to the west. These processes spawn smaller eddies of both signs through instabilities, and interactions with topography and other eddies to produce energetic surface layer flows that have a rich spectrum of orbit periods and diameters. In contrast, current variability below 1000m often has the characteristics of TRWs, with periods ranging from ∼10–100days and wavelengths of ∼50–200km, showing almost depth-independent or slightly bottom intensified currents through the weakly stratified lower water column. These fluctuations are largely uncorrelated with simultaneous upper-layer eddy flows. TRWs must be generated through energy transfer from the upper-layer eddies to the lower layer by potential vorticity adjustments to changing depths of the bottom and the interface between the layers. Therefore, the LC and LC eddies are prime candidates as has been suggested by some model studies. Model simulations have also indicated that deep lower-layer eddies may be generated by the LC and LC eddy shedding processes. In the eastern gulf, the highest observed lower-layer kinetic energy was north of the Campeche Bank under the LC in a region that models have identified as having strong baroclinic instabilities. Part of the 60-day TRW signal propagates towards the Sigsbee Escarpment (a steep slope at the base of the northern continental slope), and the rest into the southern part of the eastern basin. Higher energy is observed along the escarpment between 89°W and 92°W than either under the northern part of the LC or further south in the deep basin, because of radiating TRWs from the western side of the LC. In the northern part of the LC, evidence was found in the observations that 20–30-day TRWs were connected with the upper layer through coherent signals of relative vorticity. The ∼90° phase lead of the lower over the upper-layer relative vorticity was consistent with baroclinic instability. Along the Sigsbee Escarpment, the TRWs are refracted and reflected so that little energy reaches the lower continental slope and a substantial mean flow is generated above the steepest part of the escarpment. RAFOS float tracks show that this mean flow continues along the escarpment to the west and into Mexican waters. This seems to be a principal pathway for deepwater parcels to be transported westward. Away from the slope RAFOS floats tend to oscillate in the same general area as if primarily responding to the deep wave field. Little evidence of westward translating lower-layer eddies was found in both the float tracks and the moored currents. In the western gulf, the highest deep energy levels are much less than in the central gulf, and are found seaward of the base of the slope. Otherwise, the situation is similar with TRWs propagating towards the slope, probably generated by the local upper-layer complex eddy field, being reflected and forcing a southward mean flow along the base of the Mexican slope. Amplitudes of the lower-layer fluctuations decay from the northwest corner towards the south. [Copyright &y& Elsevier]

Abstract: Gas hydrates accumulate on the Gulf of Mexico seafloor around hydrocarbon seeps in waters sufficiently deep to provide adequate pressure/temperature combinations. High microbial activities occur around the hydrate accumulations. To understand apparent catalytic effects of bioproducts on hydrate formation, the mechanism of sII hydrate nucleation in unconsolidated porous media was investigated in our laboratory. Because smectite clays interacting with biopolymers had been shown to promote laboratory hydrates by decreasing induction times, increasing formation rates and altering morphology, these materials commonly found in near-surface sediments were selected for study as possible nucleating agents. Dynamic light scattering (DLS) with a helium–neon laser was used to measure particle diameters down to about 2 nm. Scanning electron microscopy (SEM) was utilized to verify particle sizes and to give additional information on biopolymer–clay associations. This paper presents evidence that nanometer-sized particles of mineral–bioproduct associations of about 80 nm–450 nm diameter may act as nucleation sites for hydrate crystal initiations in sediments and then remain dispersed throughout the accumulated hydrate mass. Emulsan biopolymer was shown by SEM to apparently unfold and associate with the smectite (nontronite) in a backbone arrangement and to give multiple hydrate nucleation sites along a linear network. SEM and DLS measurements were in agreement on particle sizes and shapes. X-ray diffraction suggested that biopolymer intercalates the smectite interlayer, probably driven by clay associations with biopolymer hydrophilic groups. It is hypothesized that hydrocarbon gases attach to biopolymer hydrophobic fatty-acid branches protruding from clay interlayers and subsequently facilitate hydrate structure formation by interacting with nearby water associated with the hydrophilic segments of the biopolymer. [Copyright &y& Elsevier]

Abstract: The circulation and distribution of water properties in the water column of the Gulf of Mexico influence the flux of carbon to the benthic environment. The eddy field of the upper 1000m creates environmental conditions that are favorable for biological productivity in an otherwise oligotrophic subtropical ocean. This eddy field results in the transport of nutrients and organic matter into the photic zone through cross-margin flow of shelf waters, upwelling in cyclones, and uplift from the interaction of anticyclones with bathymetry. These conditions then allow the productivity that becomes a possible source of carbon to the benthos. Data from four cruises during summers of 2000–2002 are used to describe the currents and water property distributions in the deepwater Gulf of Mexico, which consists of water depths greater than 400m. Comparisons are made to historical data sets to provide an understanding of the persistence of the characteristics of the Gulf and the processes that occur there. The currents in the Gulf are surface intensified, have minimum in 800–1000m depths, and also exhibit bottom intensification, especially near sloping topography. Historical time series records show current speeds near-bottom reach 50–100cms−1. At basin scales, these currents tend to flow cyclonically (counter-clockwise) along the bathymetry. These near-bottom, episodic, high-speed currents provide a mechanism for the transport of organic material, in both large and small particle sizes, from one benthic area to another. The distributions of temperature, salinity, nutrients, and dissolved oxygen during the study appear to be unchanged from historical findings. The source waters for the deep Gulf are the water masses brought into the Gulf by the Loop Current system. The properties in the upper 100–200m are the most variable of the water column, consistent with their proximity to wind mixing, river discharge mixing, and atmospheric influences. Below 1500m, there are no major horizontal variations in these water properties. [Copyright &y& Elsevier]

Abstract: The Deep Gulf of Mexico Benthos Program (DGoMB) investigated the structure and function of sea-floor biota on the continental slope and abyssal plain of the Gulf of Mexico. Supported by the Minerals Management Service of the US Department of the Interior, DGoMB''s purpose was to gain better understanding of how oil and gas exploration and production might affect the ecosystem and its natural inhabitants. The goal of assessing both community structure (abundance, biomass and species composition) and biogeochemical processes (community function) was unique, because traditionally such studies have been investigated independently. The field work aboard R/V Gyre was conducted in two phases over a 3-year period (2000–02). The first phase, a broad geographic survey stretching from the western GoM near Mexico to the upper Florida slope, was designed to provide a database from which large detailed maps could be created to explore potential controls on community structure. Physiographic features (depth, the base of steep escarpments, the axes of canyons, methane seep sites, mesoscale “salt” basins, etc.) were sampled in replicate locations to assess the relationships between topography and spatial distribution patterns. During the second phase (2001–02), a limited number (7) of locations were investigated with measurements designed to estimate rates of processes related to the cycling of organic matter. The strategy was successful in defining the quantitative relationships between carbon cycling (trophic conditions) and community structure (zonation and diversity), for those groups for which “species” lists were generated (harpacticoid copepods in the meiofauna, macrofauna, megafauna and fishes). In retrospect, additional “process” locations in the western GoM would have improved the second phase of the study by more rigorously describing the relationships between broader geographic patterns in community structure and trophic conditions. [Copyright &y& Elsevier]

The possibility of naval mines buried in the seafloor poses difficulties for navies concerned with port and seaway operations. To devise countermeasures, predictions of degrees of impact burial over wide areas of seabed must be made. Under ideal conditions, this is done with a knowledge of local seabed shear strengths, but in practice, such data are rarely available. We describe an alternative prediction method. Probabilistic predictions of mine impact burial are made across areas of variable seafloor by combining data on sedimentary character directly with experimental impact burial results. The most useful seafloor characteristics are mud content and consolidation. The predictions are relatively accurate (SD 1-22%), and are computable in detail over wide geographic areas. They are of a form immediately useful for naval operations (including calculations of risk) and are easily displayed in geographic information systems (GIS). An example is shown for the northern Gulf of Mexico. [ABSTRACT FROM AUTHOR]

Gas hydrates were discovered in a mud mound in the lease block Mississippi Canyon 798, Gulf of Mexico, through piston coring. Subsequently, a seismic experiment was carried out to investigate the dynamics behind the hydrate formation. During the experiment, high-resolution multichannel seismic reflection data using a 24-channel, 240 m long streamer and wide-aperture data using six ocean bottom seismometers were collected along five lines. High-reflectivity zones (HRZs) are present in the reflection data along all lines. To better constrain the interpretation of the reflection data, the traveltimes from the multichannel and wide-aperture data sets were jointly inverted to estimate a 2-D P-wave layered velocity model for each line. A minimum-parameter/minimum-structure modelling approach yielded simple models and a comparison of the models at their intersection points shows they are consistent to within ±10 m s−1 in velocity and ±20 m in depth. In the final P-wave velocity models, the HRZs are associated with a lowering of velocity. In the reflection data, the top of the HRZs show a polarity reversal with respect to the seafloor. Presence of free gas in the HRZs best explains the velocity lowering and polarity reversal. It is speculated that the gas has deeper sources and migrates upwards through conduits formed by salt movement in the vicinity. The upward migrating gas accumulates in the axis of a channel complex and manifests itself as HRZs in the reflection data. The fluids circulating along the conduits push the base of the hydrate stability zone close to the seafloor. From the channel axis, the free gas migrates further upwards and close to the seafloor, and as it comes within the gas hydrate stability zone, it forms hydrates. [ABSTRACT FROM AUTHOR]

Gas hydrates are common within near-seafloor sediments immediately surrounding fluid and gas venting sites on the continental slope of the northern Gulf of Mexico. However, the distribution of gas hydrates within sediments away from the vents is poorly documented, yet critical for gas hydrate assessments. Porewater chloride and sulfate concentrations, hydrocarbon gas compositions, and geothermal gradients obtained during a porewater geochemical survey of the northern Gulf of Mexico suggest that the lack of bottom simulating reflectors in gas-rich areas of the gulf may be the consequence of elevated porewater salinity, geothermal gradients, and microbial gas compositions in sediments away from fault conduits. [ABSTRACT FROM AUTHOR]

A passive acoustic method is presented for tracking sperm whale dive profiles, using two or three hydrophones deployed as either a vertical or large-aperture towed array. The relative arrival times between the direct and surface-reflected acoustic paths are used to obtain the ranges and depths of animals with respect to the array, provided that the hydrophone depths are independently measured. Besides reducing the number of hydrophones required, exploiting surface reflections simplifies automation of the data processing. Experimental results are shown from 2002 and 2003 cruises in the Gulf of Mexico for two different towed array deployments. The 2002 deployment consisted of two short-aperture towed arrays separated by 170 m, while the 2003 deployment placed an autonomous acoustic recorder in tandem with a short-aperture towed array, and used ship noise to time-align the acoustic data. The resulting dive profiles were independently checked using single-hydrophone localizations, whenever multipath reflections from the ocean bottom could be exploited to effectively create a large-aperture vertical array. This technique may have applications for basic research and for real-time mitigation for seismic airgun surveys. [ABSTRACT FROM AUTHOR]

This paper reports the results derived from radium isotopes of a submarine groundwater discharge (SGD) intercomparison in the northeast Gulf of Mexico. Radium isotope samples were collected from seepage meters, piezometers, and surface and deep ocean waters. Samples collected within the near-shore SGD experimental area were highly enriched in all four radium isotopes; offshore samples were selectively enriched. Samples collected from seepage meters were about a factor of 2–3 higher in radium activity compared to the overlying waters. Samples from piezometers, which sampled 1–4 meters below the sea bed were 1–2 orders of magnitude higher in radium isotopes than surface waters. The two long-lived Ra isotopes, 228Ra and 226Ra, provide convincing evidence that there are two sources of SGD to the study area: shallow seepage from the surficial aquifer and input from a deeper aquifer. A three end-member mixing model can describe the Ra distribution in these samples. The short-lived radium isotopes, 223Ra and 224Ra, were used to establish mixing rates for the near-shore study area. Mixing was retarded within 3 km of shore due to a strong salinity gradient. The product of the mixing rate and the offshore 226Ra gradient established the 226Ra flux. This flux must be balanced by Ra input from SGD. The flux of SGD within 200 m of shore based on the 226Ra budget was 1.5 m3 min-1. This flux agreed well with other estimates based on seepage meters and 222Rn. [ABSTRACT FROM AUTHOR]

Part of an experiment to test a measurement package in a shallow water region in the Gulf of Mexico was designed to gather broadband acoustic data suitable for inversion to estimate seabed geoacoustic parameters. Continuous wave tow acoustic signals at multiple frequencies and broadband impulsive source signals were recorded on a horizontal line array in a high-noise environment. Simulated annealing with a normal mode forward propagation model is utilized to invert for a geoacoustic representation of the seabed. Several inversions are made from different data samples of two light bulb implosions, the measured sound speed profiles at the HLA and at the positions of the light bulb deployments, and for two different cost functions. The different cost functions, measured sound speed profiles, and measured time series result in different inverted geoacoustic profiles from which transmission loss is generated for comparison with measurements. On the basis of physical consistency and from the comparison of the transmission loss and time series, a best estimate geoacoustic profile is selected and compared to those obtained from previously reported inversions. Uncertainties in the sound speed profile are shown to affect the uncertainties of the estimated seabed parameters. [ABSTRACT FROM AUTHOR]

This paper details the development and application of a new serial sampler capable of acquiring multiple deep-sea gas-tight fluid samples. It consists of a custom-made multiport sampling valve with six sampling cylinders distributed around it in a circle. The serial sampler can operate on the seabed to depths of 7000 m. Each cylinder has a sampling volume of about 160 ml and can maintain the sample at near in-situ pressure. It can be deployed by HOV or ROV to collect gas-tight fluid samples via remote or automatic operation. The new serial sampler was successfully field-tested at cold seep sites in the Gulf of Mexico and the South China Sea and also at hydrothermal vent sites on the Juan de Fuca Ridge and in the Indian Ocean. • The sampler could be deployed at seafloor to automatically collect time series gas-tight fluid samples. • A unique multiport sampling valve allows fluid to enter any one of the six titanium bottles of the sampler. • A flushing pump is integrated into the sampler to reduce the influence of the dead zone volume. [ABSTRACT FROM AUTHOR]

Reports that the Terra Siesmic Services in Oslo, Norway, had become the first customer for the VectorSeis Ocean redeployable seabed system. Deployment of the system in the Gulf of Mexico to acquire data for use by major integrated oil and gas company; Revenues from the sale; Proprietary features of the seabed system.

The article reports on the six vessel contracts won by SeaBird Exploration Ltd. It says that the contracts have increased the company's backlog value for its two dimensional/three dimensional segments from approximately 20 million dollars to 32 million dollars. It mentions the time charter contract as source vessel in the Gulf of Mexico, and the seismic contract in West Africa. Moreover, the company has also completed the ocean bottom node (OBN) survey based in the Gulf of Mexico.