Active Methane Seeps Research Articles

Geological and glaciological controls of 21,700 active methane seeps in the northern Norwegian Barents sea

Geological and glaciological controls of 21,700 active methane seeps in the northern Norwegian Barents sea

New cold seep sites on the continental slope southwest to Svalbard

We discovered seafloor features such as bacterial mats and carbonate crusts typical for active methane seeps on the continental slope southwest of Svalbard. These features are associated with two main northwest-southeast trending morphological structures that are oriented parallel to the regional continental slope. Both structures occur at c. 800 m water depth, at the boundary between the Storfjorden trough mouth fan to the south and the Hornsund trough mouth fan to the north, which suggests a loading related fluid seepage. The main structure displays depressions and ridges forming a crater in its center. Other occurring features include small sediment mounds, domes often covered by bacterial mats, and hummocky seafloor colonized by siboglinid tubeworms. Free gas bubbles were spotted close to the centre and plumes along the rims of the structure. Thick carbonate crusts indicate a long seepage history in the center of the structure and on top of the ridges. The sources of the seeps are likely to be Miocene old organic-rich deposits, or Paleocene hydrocarbon reservoirs.

A carbonate corrosion experiment at a marine methane seep: The role of aerobic methanotrophic bacteria.

Methane seeps are typified by the formation of authigenic carbonates, many of which exhibit corrosion surfaces and secondary porosity believed to be caused by microbial carbonate dissolution. Aerobic methane oxidation and sulfur oxidation are two processes capable of inducing carbonate corrosion at methane seeps. Although the potential of aerobic methanotrophy to dissolve carbonate was confirmed in laboratory experiments, this process has not been studied in the environment to date. Here, we report on a carbonate corrosion experiment carried out in the REGAB Pockmark, Gabon-Congo-Angola passive margin, in which marble cubes were deployed for 2.5 years at two sites (CAB-B and CAB-C) with apparent active methane seepage and one site (CAB-D) without methane seepage. Marble cubes exposed to active seepage (experiment CAB-C) were found to be affected by a new type of microbioerosion. Based on 16S rRNA gene analysis, the biofilms adhering to the bioeroded marble mostly consisted of aerobic methanotrophic bacteria, predominantly belonging to the uncultured Hyd24-01 clade. The presence of abundant 13 C-depleted lipid biomarkers including fatty acids (n-C16:1ω8c , n-C18:1ω8c , n-C16:1ω5t ), various 4-mono- and 4,4-dimethyl sterols, and diplopterol agrees with the dominance of aerobic methanotrophs in the CAB-C biofilms. Among the lipids of aerobic methanotrophs, the uncommon 4α-methylcholest-8(14)-en-3β,25-diol is interpreted to be a specific biomarker for the Hyd24-01 clade. The combination of textural, genetic, and organic geochemical evidence suggests that aerobic methanotrophs are the main drivers of carbonate dissolution observed in the CAB-C experiment at the REGAB pockmark.

CAGE20-7 Cruise Report: Sediment and water column analyses around flares at Norskebanken, Hinlopen and offshore Prins Karls Forland

During the cruise CAGE 20-7 (November 2nd to 16th 2020), we observed and investigated a large active methane seepage area south from the Yermak plateau (Northern Svalbard), in particular to characterize the water column and the sediment near known flares in Norskebanken (Geissler et al., 2016). Some flares were targeted for gas composition, DNA and bubble size distribution. The combination of the R/V Kronprins Haakon and the ROV ÆGIR 6000 from the Norwegian Marine Robotics Laboratory at the University of Bergen allowed this investigation to happen in this rough environment, while collecting invaluable data from the ROV. The cruise may be known as: CAGE20_7

Sexual dimorphism in the methane seep-dwelling Costa Rican yeti crab Kiwa puravida (Decapoda: Anomura: Kiwaidae)

Deep-sea chemosynthesis-based ecosystems support unique biological communities, but human impacts are an increasing threat. Understanding the life-history traits of species from deep-sea chemosynthesis-based ecosystems can help to develop adequate management strategies, as these can have impacts on ecological responses to changes in the environment. Here we examined the occurrence of sexual dimorphism in the yeti crab Kiwa puravida, an endemic species from the Costa Rican Pacific margin that aggregates at active methane seeps and depends on chemosynthetic bacteria for nutrition. The two morphological features examined included the claws, suspected to be under sexual selection and used for defense, and the carpus of the second pereopod not suspected to be under sexual selection. A total of 258 specimens, 161 males, 81 females, 16 juveniles, were collected from Mound 12 at 1,000-1,040 m depth in 2017 and 2018 and analyzed. We found that males have larger and wider claws than females, while there were no differences in carpus length. These results suggest that claw weaponry is under sexual selection in K. puravida, which is probably related to the mating system of this deep-sea species. This is the first attempt to study the reproductive biology of K. puravida, and additional observations will be necessary to shed more light on this matter.

Does substrate matter in the deep sea? A comparison of bone, wood, and carbonate rock colonizers.

Continental margins host methane seeps, animal falls and wood falls, with chemosynthetic communities that may share or exchange species. The goal of this study was to examine the existence and nature of linkages among chemosynthesis-based ecosystems by deploying organic fall mimics (bone and wood) alongside defaunated carbonate rocks within high and lesser levels of seepage activity for 7.4 years. We compared community composition, density, and trophic structure of invertebrates on these hard substrates at active methane seepage and transition (less seepage) sites at Mound 12 at ~1,000 m depth, a methane seep off the Pacific coast of Costa Rica. At transition sites, the community composition on wood and bone was characteristic of natural wood- and whale-fall community composition, which rely on decay of the organic substrates. However, at active sites, seepage activity modified the relationship between fauna and substrate, seepage activity had a stronger effect in defining and homogenizing these communities and they depend less on organic decay. In contrast to community structure, macrofaunal trophic niche overlap between substrates, based on standard ellipse areas, was greater at transition sites than at active sites, except between rock and wood. Our observations suggest that whale- and wood-fall substrates can function as stepping stones for seep fauna even at later successional stages, providing hard substrate for attachment and chemosynthetic food.

Two New Species of Cyphocaris (Amphipoda, Amphilochidea, Cyphocarididae) From Water Columns Above a Methane Seep in the South China Sea

The Formosa Ridge methane seep is one of three known active methane seepage areas discovered on the northern slope of the South China Sea. Cyphocaris is a genus of pelagic amphipods. Two new species of Cyphocaris collected from water columns above the Formosa Ridge methane seep are reported in the present study. Cyphocaris lubrica sp. nov. collected at a depth of 1,118 m is characterized by pereonite 1 dorsal projection not extending beyond head, and the pereopod 5 having a spur beyond pereonite 7. Cyphocaris formosa sp. nov. collected at a depth of 500–800 m is characterized by well-developed pereonite 1 dorsal projection extending beyond head and pereopod 5 without spur. The present work describes these two new species and compares them with closely related species, and provides a modified key of world Cyphocarididae species.

Magnesium Isotopes in Pore Water of Active Methane Seeps of the South China Sea

The magnesium (Mg) isotopic composition of marine authigenic carbonates is considered as promising archive of ancient seawater geochemistry and paleoenvironments. Previous experimental and theoretical work has shown that Mg isotope fractionation during carbonate mineral formation is a function of mineralogy and precipitation rate. However, information on Mg isotope fractionation is limited for well-defined precipitation rates in natural settings. Here, we investigate pore waters from sediments of an area of active methane seepage in the South China Sea. Low δ13C values (< −48.3‰ VPDB) of dissolved inorganic carbon (DIC) near the sulfate-methane transition zone (SMTZ) indicate that sulfate-driven anaerobic oxidation of methane (SD-AOM) is the predominant biogeochemical process. Pore water composition of dissolved Mg, calcium (Ca), and strontium (Sr) agrees with aragonite as the dominant carbonate mineral at the site ROV1, and high Mg-calcite at sites ROV2 and ROV4. Calculated carbonate precipitation rates are 0.92 μmol cm−2 yr−1 for site ROV2 and 1.24 μmol cm−2 yr−1 for site ROV4; these estimates are similar to previous calculations for seeps from other areas. The pore water δ26Mg values (−0.88‰ to −0.71‰) obtained for the three study sites are similar to those of seawater, in accord with a minor effect of Rayleigh fractionation due to abundant supply of Mg from seawater and insignificant consumption of Mg during carbonate precipitation. The modeled Mg isotope fractionation (ϵ = −2.0‰ to −1.0‰ for core ROV2; ϵ = −1.3‰ to −0.3‰ for core ROV4) can be explained by kinetic isotope fractionation during carbonate precipitation. The calculated carbonate precipitation rates and the degree of fractionation of Mg isotopes support the notion that fractionation is small at high precipitation rates. However, the carbonate precipitation rates calculated for the studied seep environments are much smaller than those in laboratory experiments, documenting a discrepancy of isotopic fractionation between carbonate authigenesis in laboratory experiments and natural environments. These results, including the modeled precipitation rates, provide new constraints for Mg isotope fractionation in natural settings.

Episodic massive release of methane during the mid-Cretaceous greenhouse

Abstract Methane-derived carbonates (MDCs) are common along modern and ancient continental margins, and the majority of such formations are associated with seafloor cold seeps. Here, we document petrographic, rare earth element + yttrium (REE + Y), carbonate clumped isotope temperature (TΔ47), and carbon-isotopic evidence from a shale succession in southern Tibet spanning a ~28 m.y. interval (ca. 113–85 Ma) that coincided with the mid-Cretaceous greenhouse event. At least nine limestone nodule-bearing horizons exhibit seep-associated sedimentary structures, including carbonate fabrics (e.g., micritic crusts, crystal fans, and botryoidal textures) and 13C-depleted isotopic compositions (δ13Ccarb < –32.3‰), which are indicative of methane-derived carbon sources. Along with sedimentary evidence, the patterns of TΔ47–δ13Ccarb–δ18Ocarb support precipitation of these MDCs over a large temperature range. The REE + Y compositions and europium (Eu) anomalies indicate that the release of methane was associated with hydrothermal fluids. Methane may have been derived from both thermogenic and biogenic sources based on the inorganic carbon isotopic signatures of the carbonate. These nodular carbonate horizons document multiple episodes of seafloor methane release during the mid-Cretaceous and represent exceptionally long-lived, active methane seepage. Massive methane release events may have played a role in generating the greenhouse climate of the mid-Cretaceous.

Analysis of non-derivatized bacteriohopanepolyols using UHPLC-HRMS reveals great structural diversity in environmental lipid assemblages

Bacteriohopanepolyols (BHPs) are lipids with great chemotaxonomic potential for microbial populations and biogeochemical processes in the environment. The most commonly used methods for BHP analysis are chemical degradation followed by gas chromatography-mass spectrometry (MS) or derivatization followed by high performance liquid chromatography (HPLC)-atmospheric pressure chemical ionization/MS. Here we report on significant advances in the analysis of non-derivatized BHPs using U(ltra)HPLC-electrospray ionization-high resolution MS2. Fragmentation mass spectra provided information on the BHP core, functionalized side chain, as well as the conjugated moiety of composite BHPs. We successfully identified the common bacteriohopanepolyols and their (di)methylated and (di)unsaturated homologues, aminoBHPs, and composite BHPs (e.g., cyclitol ethers and methylcarbamate-aminoBHPs) in biomass of several known BHP-producing bacteria. To show how the method can be exploited to reveal the diversity of BHPs in the environment, we investigated a soil from an active methane seep, in which we detected ca. 130 individual BHPs, including a complex distribution of adenosylhopanes. We identified the nucleoside base moiety of both adenosylhopane type-2 and type-3. Adenosyl hopane type-3 contains a methylated adenine as its nucleobase, while type-2 appears to contain a deaminated and methylated adenine, or N1-methylinosine. In addition, we detected novel adenosylhopanes. Furthermore, we identified a series of novel composite BHPs comprising of bacteriohopanepolyols conjugated to an ethenolamine moiety. The novel ethenolamineBHPs as well as aminoBHPs were also detected acylated to fatty acids. The analytical approach described allows for simultaneous analysis of the full suite of IPLs, now including BHPs, and represents a further step towards environmental lipidomics.

Перенос свободного метана струйными газовыделениями из анаэробных в аэробные воды Чёрного моря

«Дыхание недр» в форме метановых струйных газовыделений из морского дна (метановые сипы, или пузырьковые эманации) — явление планетарного масштаба, на которое обратили внимание лишь в конце XX столетия. Изучение этого явления как важного звена процессов взаимодействия литосферы, гидросферы, атмосферы и биосферы не потеряло своей актуальности до настоящего времени. В данной работе определены потоки метана в известном районе интенсивных метанопроявлений биогенной природы, географически привязанных к палеоруслу р. Днепр в северо-западной части Чёрного моря. Впервые оценено, что поток струйного (свободного) метана из анаэробных в аэробные воды на участке активных метановых газовыделений в районе палеорусла р. Днепр в диапазоне глубин 140–725 м составляет (в среднем по участку) 1,2·10³ м³·км−2·год−1 (STP), или 2,8 % от выделившегося из дна струйного метана. Величина исследованного потока — 4,2 % от удельного потока струйного метана в водный столб на шельфовом участке (глуби́ны менее 140 м) в этом же районе. Полученная в работе оценка потока метана — значимый экологический фактор в условиях стратификации вод Чёрного моря, где перенос метана струйными газовыделениями является основным механизмом внесения глубоководного метана в биогеохимические циклы и процессы трансформации углерода аэробной зоны Чёрного моря.

Geological controls of giant crater development on the Arctic seafloor

Active methane seepage occurs congruent with a high density of up to 1 km-wide and 35 m deep seafloor craters (>100 craters within 700 km2 area) within lithified sedimentary rocks in the northern Barents Sea. The crater origin has been hypothesized to be related to rapid gas hydrate dissociation and methane release around 15–12 ka BP, but the geological setting that enabled and possibly controlled the formation of craters has not yet been addressed. To investigate the geological setting beneath the craters in detail, we acquired high-resolution 3D seismic data. The data reveals that craters occur within ~250–230 Myr old fault zones. Fault intersections and fault planes typically define the crater perimeters. Mapping the seismic stratigraphy and fault displacements beneath the craters we suggest that the craters are fault-bounded collapse structures. The fault pattern controlled the craters occurrences, size and geometry. We propose that this Triassic fault system acted as a suite of methane migration conduits and was the prerequisite step for further seafloor deformations triggered by rapid gas hydrate dissociation some 15–12 ka BP. Similar processes leading to methane releases and fault bounded subsidence (crater-formation) may take place in areas where contemporary ice masses are retreating across faulted bedrocks with underlying shallow carbon reservoirs.

Geochemical evidence of methane seepage in the sediments of the Qiongdongnan Basin, South China Sea

In this paper, the QS-1 sediments (3.64 m long; at 1500 m water depth) collected from the Qiongdongnan Basin were used to analyze the relationship between sedimentary geochemical anomalies and methane seepage. Mo-U covariation, Ce anomaly, and Mg/Ca-Sr/Ca end-member model were analyzed to identify the variations of redox environment and authigenic carbonate precipitation, finally constructing the methane release events in this study area. These observations suggest that: 1) Significant Mo/U enrichments and Ba front indicate the presence of high-flux active methane seepage with SMI of 260 cmbsf in this study area. The depositional environment evolved as oxic-anoxic-reducing-sulfide environment from bottom to top, as evidenced by Mo-U covariation and Ce anomaly; 2) Based on Sr/Ca and Mg/Ca end-member model proposed by Bayon et al. (2007), the high-Mg calcite was the dominant authigenic carbonate currently which usually precipitated behind the methane seep events; and 3) The active cold seep can be divided into three methane release events (MREs): MRE I, the most intense methane seepage occurred at 22.1 ka BP; MRE II, three low-intensity methane seepage occurred at 19.3, 16.5, and 11.3 ka BP, respectively; and MRE III, the continuous methane seep began at 9.3 ka BP until now. The synthesis of geochemical indicators has significant implications for tracing methane seepage of varying intensity and duration.

Negative δ13C Excursions in Foraminiferal Records: The Holocene History of Methane Events in the Central Sea of Okhotsk

Abstract—Several negative δ13C excursions in benthic foraminifera from gas-bearing core LV50-05 sampled offshore on the eastern slope of Sakhalin Island, Sea of Okhotsk, in an area of active methane seepage record the local history of methane events (ME). The core chronostratigraphy has been contrained from AMS 14C ages and biostratigraphic data. Benthic foraminifera (Nonionellina labradorica and Uvigerina parvocostata) from some core intervals show normal marine δ13C values about –1‰ but some intervals are marked by extremely depleted compositions as low as –34.5‰ δ13C (relative to VPDB). The negative δ13C excursions are interpreted as a record of seabed methane emanation during primary and secondary biomineralization of carbonate foraminifera. The results reveal four Holocene methane events (ME) in the area: two brief (ME-1 at 700–900 yr BP and ME-2 at 1200–1400 yr BP) and two long (ME-3 at 2500–4700 yr BP and ME-4 at 7400–10000 yr BP) events.

Benthic Foraminifera in Arctic Methane Hydrate Bearing Sediments

Benthic foraminifera have been widely used as proxy for paleo-methane emissions, mainly based on their stable isotopic signature. In cold seeps, the ecology of these organisms remains uncertain, in particular their ability to thrive during active phases of seepage. In this study, we evaluate the benthic foraminiferal response to methane seepage in Arctic sediments. We do so by examining living and dead benthic foraminiferal assemblages (>63 µm) of eleven push cores collected in two of the most active pockmarks (Lunde and Lomvi) along Vestnesa Ridge, offshore western Svalbard. Benthic foraminiferal assemblages are interpreted in the context of sediment geochemistry, seafloor images, and pore water analyses, which are used to characterize the different microhabitats. At the sampling locations, methane is currently being released making these the ideal sites to investigate the connection between the benthic foraminiferal distribution and methane seepage in the Arctic Ocean. Our results show that benthic calcareous foraminifera live in methane charged sediments, even if the faunal density and diversity is low. We note that the eutrophic-tolerant species Melonis barleeanus withstand the methane-induced hostile geochemical conditions and that it seems to prosper on the additional food availability represented by microbial mats growing at methane seeps. We also observe that the methane transport mechanisms affect different species differently. For example, sediments characterized by advective-like conditions are distinguished by a high density of living individuals, dominated by Cassidulina neoteretis, whereas sediments characterized by methane diffusion exhibit a very low faunal density. Agglutinated foraminifera are less abundant in sediments influenced by methane seepage, suggesting that this group of foraminifera does not tolerate the geochemical conditions at seeps. A comparison between the size fractions >63 and >125 µm highlights the importance of studying the finer size fraction for ecological studies in the Arctic Ocean. In the light of our results, we conclude that benthic foraminiferal can thrive at active methane seeps, where assemblages are clearly affected by methane flux.

Characteristics and Evolution of sill-driven off-axis hydrothermalism in Guaymas Basin \u2013 the Ringvent site

The Guaymas Basin spreading center, at 2000 m depth in the Gulf of California, is overlain by a thick sedimentary cover. Across the basin, localized temperature anomalies, with active methane venting and seep fauna exist in response to magma emplacement into sediments. These sites evolve over thousands of years as magma freezes into doleritic sills and the system cools. Although several cool sites resembling cold seeps have been characterized, the hydrothermally active stage of an off-axis site was lacking good examples. Here, we present a multidisciplinary characterization of Ringvent, an ~1 km wide circular mound where hydrothermal activity persists ~28 km northwest of the spreading center. Ringvent provides a new type of intermediate-stage hydrothermal system where off-axis hydrothermal activity has attenuated since its formation, but remains evident in thermal anomalies, hydrothermal biota coexisting with seep fauna, and porewater biogeochemical signatures indicative of hydrothermal circulation. Due to their broad potential distribution, small size and limited life span, such sites are hard to find and characterize, but they provide critical missing links to understand the complex evolution of hydrothermal systems.

Seismic evidence of free gas migration through the gas hydrate stability zone (GHSZ) and active methane seep in Krishna-Godavari offshore basin

Abstract Seismic amplitude versus offset (AVO) analysis was performed on the multichannel seismic data in the vicinity of Site NGHP-01-10, where thick fracture-filled gas hydrate is reported, to understand the fluid migration in fracture dominated gas hydrate system. Amplitude preserved common image gathers (CIG) are used in extracting the seismic amplitude with offset for seafloor, bottom simulating reflectors (BSR), and different horizons within the gas hydrate stability zone (GHSZ). The extracted amplitudes are fitted with three-term Shuey's AVO approximation to estimate the intercept and gradient values. Based on the intercept and gradient values, two distinct classes of seismic AVO responses are observed; class IV AVO (decreasing negative amplitudes with increasing offsets) and class III AVO (increasing negative amplitudes with increasing offsets) for the BSR and other horizons above the BSR. The large negative intercept and gradient values which indicate class III AVO ranges from −0.2 to −1.8 for the inline seismic profile and from −0.01 to −0.3 for the crossline profile. The presence of class III AVO anomaly within the gas hydrate stability zone (GHSZ) provides evidence of existence of free gas which may be migrating along the fault system. Some of the active faults are exposed on the surface and show gas venting signatures such as gas-flares and pockmarks in the multibeam data.

The first record of active methane (cold) seep ecosystem associated with shallow methane hydrate from the Indian EEZ

Here we report the discovery of cold-seep ecosystem and shallow methane hydrates (2–3 mbsf) associated with methane gas flares in the water column from the Indian EEZ for the first time. The seep-sites are located in the Krishna–Godavari (K–G) basin at water depths of 900–1800 m and are characterized by gas flares in the water-column images. The occurrence of methane gas hydrates at very shallow depths (2–3 mbsf) at some of the seep-sites is attributed to high methane flux and conducive P–T conditions, necessary for the stability of methane hydrate. Chemosymbiont bearing Bivalves (Vesicomidae, Mytilidae, Thyasiridae and Solemyidae families); Polychaetes (Siboglinidae family) and Gastropods (Provannidae family) are also identified from seep-sites.

Methane seepage at Vestnesa Ridge (NW Svalbard) since the Last Glacial Maximum

Multiple proxies in the geological record offshore NW Svalbard track shallow subseafloor diagenesis and seafloor methane seepage during the Last Glacial Maximum (LGM) extent and the disintegration of the Svalbard Barents Sea Ice Sheet (SBIS). Vestnesa Ridge, located at 79°N and in 1200 m water depth, is one of the northernmost known active methane seep sites and is characterised by a subseafloor fluid flow system, numerous seafloor pockmarks and gas flares in the water column. In this study, we develop a Late Pleistocene and Holocene stratigraphic framework, use stable oxygen and carbon isotope signatures (δ18O, δ13C) of benthic and planktic foraminifera, the mineralogical and carbon isotope composition of methane-derived authigenic carbonate (MDAC) and sediment geochemical data of ten sediment cores to assess methane seepage variability on Vestnesa Ridge.The studied cores cover the age range between 31.9 and 10 cal ka BP and record 32 negative δ13C excursions in benthic and planktic foraminifera with amplitudes down to −29 ‰ VPDB. These δ13C excursions are often associated with elevated Ca/Ti and Sr/Ti elemental ratios in sediments and MDAC nodules. The precipitation of MDAC overgrowth on foraminiferal tests explains most of the negative δ13C excursions. In this dataset, the oldest recorded methane emission episodes on Vestnesa Ridge occurred between the LGM (24–23.5 cal ka BP) and Heinrich Event 1 (HE 1; 17.7–16.8 cal ka BP).Geological indicators for past subseafloor methane cycling and seafloor methane seepage, such as negative foraminiferal δ13C excursions, MDAC nodules, and elevated Sr/Ti elemental ratios recorded in post-LGM sediments, possibly represent vertical migration of the sulphate-methane transition zone (SMTZ) and post-date sedimentation by up to 13.4 ka. However, it is important to note that indications of post-LGM seafloor methane seepage at Vestnesa Ridge also correspond to the established methane efflux chronology for the adjacent Barents Sea shelf, implying that glacio-isostatic adjustments and associated re-activation of pre-existing deep-seated faults after disintegration of the SBIS are likely important controlling factors on fluid migration towards the seafloor.

Influences of thermal and fluid characteristics of methane and hydrothermal seeps on the stable oxygen isotopes of living benthic foraminifera

The serendipitous discovery of methane seep fluids with elevated temperatures (3.6–5.2 °C), described as a “hydrothermal seepage” by Levin et al. (2012), has led to questions about the prevalence of this previously overlooked habitat. Stable oxygen isotopic analysis of Cibicidoides wuellerstorfi (Schwager, 1866) attached to tubeworms near the hydrothermal seep described by Levin et al. (2012) reflect δ18O values consistent with elevated seepage temperatures. Temperature reconstructions, based on C. wuellerstorfi δ18O, from additional seeps in the Pacific (Mounds 11 & 12 offshore Costa Rica, and Hydrate Ridge) produced variability that is likely a result of influences of seep source, temperature and salinity. Larger ranges in δ18O (σ > 0.10) paired with traditional isotopic seep indicators, (e.g., δ13C; σ > 0.15), have the potential to geochemically discern whether foraminifera were calcifying in areas of active methane seepage or nearby surrounding off-seep environments. Elevated temperatures derived from foraminiferal reconstructions at Jaco Scar indicate that it is possible to use foraminiferal δ18O to identify the presence and extent of these recently discovered environments. Seep fluids with elevated temperatures may be common seafloor features, and benthic foraminiferal δ18O may be an effective means to detect and determine the spatial and temporal extent and possible origin of hydrothermal seepage.