Abstract
We report striking discoveries of numerous seafloor seeps of climate-reactive fluid and gases in the coastal Ross Sea, indicating this process may be a common phenomenon in the region. We establish the recent emergence of many of these seep features, based on their discovery in areas routinely surveyed for decades with no previous seep presence. Additionally, we highlight impacts to the local benthic ecosystem correlated to seep presence and discuss potential broader implications. With these discoveries, our understanding of Antarctic seafloor seeps shifts from them being rare phenomenon to seemingly widespread, and an important question is raised about the driver of seep emergence in the region. While the origin and underlying mechanisms of these emerging seep systems remains unknown, similar processes in the paleo-record and the Arctic have been attributed to climate-driven cryospheric change. Such a mechanism may be widespread around the Antarctic Continent, with concerning positive feedbacks that are currently undetermined. Future, internationally coordinated research is required to uncover the causative mechanisms of the seep emergence reported here and reveal potential sensitivities to contemporary climate change and implications for surrounding ecosystems.
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Introduction
In recent years, global methane sources and sinks have received increased attention owing to the rapid increase in atmospheric methane over the past decade and the high warming potential of methane (~80 times CO2 over a 20-year period1). There is a continued gap between the measured increase in atmospheric methane and the total emissions predicted from currently known methane sources – this underpins global efforts to better understand potential methane release from sources with the highest uncertainties, including the ocean and coasts2. Polar regions are increasingly recognized as containing globally significant volumes of methane in subglacial and marine reservoirs, with research in the geologic record3,4 and the contemporary Arctic5,6,7 illustrating the climate sensitivity of these systems.
One such mechanism of release from these reservoirs is from seeps in the marine8,9,10,11,12,13 or terrestrial4,6,14 environment, in addition to direct subglacial flux5,7. Seeps are areas of the seafloor where there is seepage of fluids rich in hydrocarbons (e.g., methane) or other chemicals (e.g., sulfide), often creating distinct marine habitats. Tens of thousands of methane seeps have been identified in the Arctic to date, with linkages to ice mass loss since the Last Glacial Maximum (LGM)4,8,13,15,16 as well as more recent climate change impacts5,7,17. The degradation of cryospheric caps, such as glacial ice, permafrost, and gas hydrates (methane and carbon dioxide gas trapped in an ice matrix) has been attributed3,4,5,6,7,15 as drivers for changes in methane flux in these instances. In these scenarios, rising atmospheric temperature enhances glacial ice melt in the terrestrial realm, reducing the weight of ice sheets and glaciers, which can decrease hydrostatic pressure on subglacial hydrate reservoirs (causing their dissociation), as well as contributing to subglacial recharge which can enhance subglacial flux and subsequent methane discharge at the coast3,4,5,7,18. Similarly, in the marine realm, the reduction in ice mass loading can result in isostatic rebound outpacing eustatic sea-level rise and lowering coastal sea-level; decreasing hydrostatic pressure and contributing to dissociation of marine methane hydrate deposits, resulting in both direct release of methane from hydrate deposits in addition opening flow pathways for methane from depth15,19. Impacts in the marine realm may also be further intensified by the local effect of ocean warming.
While the climate sensitivity and importance of subsurface fluid and gas reservoirs has received attention in the paleo-record and the Arctic, the role of Antarctica in global methane emissions has largely been overlooked. There are however indications of methane release following the LGM20 in the Antarctic, and a few reports of modern-day seepage12,21. The full extent of marine and subglacial fluid and gas reservoirs remain unquantified in the region, but hydrates and free gas have been identified in the marine22,23 and subglacial24,25 environment, and dissolved methane or evidence of methanogenesis have been detected in sediment cores collected around the Antarctic margin26,27,28,29,30,31,32.
Indeed, significant hydrate and carbon reservoirs have also been predicted in modeling work33,34 in the marine and subglacial environment (Fig. 1). An estimated 21,000 Gigatons of carbon (GtC) has been predicted to occur below Antarctic ice sheets, with up to 400 GtC immobilized as gas hydrates33 and a further 400 GtC of methane in subsurface marine reservoirs12 – magnitudes comparable to Arctic reservoirs of permafrost and marine hydrates35. Notably, in the marine realm, the uniquely persistently cold (down to −2 °C) temperatures of the Southern Ocean create the potential for a shallow Gas Hydrate Stability Zones (GHSZ) on the coastal margins34, a contrast from GHSZ’s in other regions which tend to be at much deeper water depth (> 400 m), and thus less likely to exchange across the sea-air interface. Gas hydrates are vulnerable to short-term warming or pressure changes, which are ongoing climate impacts in areas with shallow GHSZ like the Antarctic36. In addition to the carbon stored in gas hydrates in the Antarctic, permafrost reservoirs in ice-free regions of the Antarctic, as well as subsea permafrost reservoirs, are similarly vulnerable to contemporary climate change4,37. Concurrently, extensive subsurface fluid reservoirs have been identified in geophysical surveys38,39,40 which provide connections across the land-ocean continuum. These subglacial fluid reservoirs have been found to contain highly saline brines (ranging from 1,375 mM Cl-1 in brines isolated from Blood Falls41 to 536,400 mM Cl- in deep groundwater isolated by the Dry Valleys Drilling Program42) enriched in trace metals, nutrients, and gases, as a result of extended rock-water interaction times and cryo-concentration39,43,44. Together, these reservoirs may provide an intersecting network of groundwater, hydrate, permafrost, and glacial ice systems, that connects across the land-ocean continuum (as illustrated in Fig. 1).
Connectivity across the land-sea continuum is indicated along (a) glaciated and (b) non-glaciated margins. Potential reservoirs and connectivity are modelled after5,6,33,38,40, and the conceptual model is not drawn to scale. The theoretical gas hydrate stability zones (GHSZ) are based on3,8,33,34,80 and broader methane sources are from33,81,82. The subglacial hydrology is informed by38,39,40 and permafrost and subsea permafrost (SS-P) distribution is informed by83,84,85.
The increasing climate impacts in the Antarctic, including the widespread reduction in ice mass45,46, highlights the importance of understanding the current and future dynamics of fluid and gas release from the significant reservoirs predicted in the region. Here, with a suite of empirical data, we report discoveries of emergent and diverse seafloor fluid and gas seeps across the coastal Ross Sea region. Prior to this publication, only one seep site (Cinder Cones12) was known to occur in the Ross Sea region and to our knowledge all other reports were isolated to a low-activity seep off the Antarctic peninsula21 or in the sub-Antarctic11,47. Several of the seeps we establish to be recently emergent, having been discovered at locations which have been repeatedly studied for years to decades with seeps not previously observed. This process of seep emergence may indicate a fundamental shift in regional methane release, which we posit are linked to regional climate impacts.
Results
Through primarily opportunistic surveys offshore Northern Victoria Land and McMurdo Sound, both in the Ross Sea of Antarctica, we identified numerous seafloor seeps of fluid and gas in the shallow coastal environment (Fig. 2). Offshore Northern Victoria Land these features were identified with shipboard water column acoustic surveys, while in McMurdo Sound they were discovered with SCUBA diver or Remotely Operated Vehicle (ROV) surveys. These sites range in depth from ~5 m–240 m water depth, with surveys to date in deeper depths not indicating active fluid or gas flux. Identification was coupled to benthic surveys or chemical sampling of fluids/gasses or the surrounding water column when possible.
McMurdo Sound
We discovered the emergence of seep sites during routine surveys in the McMurdo Sound region at well-studied locations, including Cape Evans, Turtle Rock, Granite Harbor, Cape Barne and Dunlop Island (Fig. 3; S1). These were identified during ROV and SCUBA diver surveys visually by the presence of distinctive, white, microbial mats. Prior to the discovery of seafloor seepage at these sites, no indications of seep activity were seen in the survey areas. This adds to the first report12 of emergent seepage in the region (Cinder Cones, 10 m deep; Fig. 3c) which was initially observed in 2011 at a location that had been repeatedly visited by SCUBA diving surveys since 196712. Seep sites discovered in this region to date range in depth from ~5 m to 30 m water depth, the limit of most SCUBA surveys in the region.
a Microbial mats (x and y) on the seafloor identified near Dunlop Island (30 m water depth), with a Digital Elevation Model (DEM) showing depressions in the seafloor, apparent seafloor pockmarks, associated with the seep site - the locations of the microbial mats are indicated in the DEM with x and y. b A seep site at Cape Evans (23 m water depth), showing the seafloor with microbial mats and gas bubbles escaping into the water column (see Supplemental Video 1). c–e Images of microbial mats correlated to seafloor seepage at Cinder Cones, Turtle Rock (image taken by Rob Robbins), and Cape Barne.
Point-source methane flux from these seep sites was determined with sampling from benthic flux chambers deployed on the seafloor for 24-48 hours at seep and non-seep locations. Since 2011, and to the time of writing, Cinder Cones seep has been continuously releasing methane, with methane flux measurements in 2022 averaging 0.8 ± 0.3 mmol/m2/d (n = 6). Another seep site at 7 m depth at Cinder Cones (Figure S1) was discovered in 201612 and also has continuous methane release with measurements in 2022 revealing 5.0 ± 0.28 mmol/m2/d (n = 4). In background (non-seep) sediments at both sites, methane concentrations were below our minimum detection limit of 30 nM. Similarly, a benthic flux measurement from the emergent seep at Turtle Rock (Fig. 3d) in 2022 revealed a methane flux of 8 mmol/m2/d (n = 1), again with background (non-seep) fluxes below detection limit.
Microbial mats identified at Dunlop Island in 2021 were associated with seafloor pockmarks, potentially indicating fluid or gas expulsion if formed via similar mechanisms as other globally known features48 (Fig. 3a). Intriguingly, video obtained using ROV at a seep site identified at Cape Evans in October 2023 shows gas bubbles escaping the seafloor and accumulating on the under-side of sea-ice above the seep site (Fig. 3b; S2; Supplemental Video 1) highlighting the potential for rapid transfer to the atmosphere.
Northern Victoria Land
Simultaneous with these increasing discoveries of emergent seepage at many routinely visited locations in the McMurdo Sound region, we have identified > 28 fluid and bubble plumes in 2021 and 2023 using shipboard acoustic techniques along the Northern Victoria Land coast (Figs. 1; 4; and S5–S9). These features were discovered between 40 m (the shallowest extent of shipboard surveys) and 240 m water depth, with surveys in deeper waters not revealing any seep features. As these locations are not as well-studied as those in the McMurdo Sound region, we are unable to confirm if these features are emergent – however, the number (> 28) discovered in the rather limited area (14 km2 of seafloor <250 m) that was surveyed is notable.
The bubble plumes were temporally variable ‘bubble bursts’ best observed at lower frequencies (< 38 kHz) indicative of bubbles > 1 mm in size. These were first detected in 2023 and not seen in the 2021 survey (Fig. 4b, c; S8–S10). Camera surveys found the bubble plumes were associated with small, white, microbial mats, consistent with our observations from the shallower sites further south in McMurdo Sound (Fig. 3; and S1) and also shallow marine gas seeps in other regions49,50.
a Fluid plume at 190 m water depth at Cape Wheatstone. Associated imagery shows the transition of seafloor biological communities corresponding to the fluid plumes (image description: [background] demosponges, bryozoans, Sabellid tubeworms, asteroids, holothurians, ophiuroids and stalked tunicates; [periphery] stalked ascidians, bryozoans, demosponges and ophiuroids on bryozoan mats; [seep center] thick, brown bryozoan mats with holothurians, small white ophiuroids, and stalked ascidians. b Bubble plumes at 50–60 m water depth at Cape Hallett with images of the seafloor microbial mats corresponding to the bubble plumes (indicated with i, ii and iii). c Acoustic transect beginning 100 m north (indicated with yellow dot) of the Tucker Glacier Ice Tongue and transiting ~8 km north (indicated with orange dot), running parallel to shore. Interpretations of meltwater from the ice tongue, subglacial flux emanating from below the ice tongue, and fluid and gas seeps along the seafloor are indicated.
The fluid plumes were observed rising from the seafloor to approximately mid-water column height before being transported presumably by prevailing currents, as indicated in the directionality of the feature and literature51 (Fig. 4a, C; S5–S9). Features off Cape Hallett Peninsula gave a similar reflectivity to subglacial discharge measured from the nearby Tucker Glacier (Fig. 4c; and S8) and to signals obtained from stratified turbulences in other global regions52,53,54, but are inconsistent with that associated with other acoustic anomalies, such as plankton55. Additionally, acoustic anomalies were often correlated to shifts in water column properties including temperature, salinity, and oxygen (for examples see Figures S11–S13).
We consistently found metazoan dead zones at the center of fluid seeps, with transition zones dominated by opportunistic mega-epifaunal taxa that were relatively rare in the surrounding biologically rich areas at these sites (Fig. 4a; and S3; S4). In the seafloor images at the fluid plume sites, the background ‘non-seep’ areas were dominated by fauna such as primnoid corals, demosponges, and assorted echinoderms. In contrast, the peripheries were dominated by stalked ascidians and comatulid crinoids, and the seep centers had only sparse fauna including assorted echinoderms, stalked ascidians and patches of bryozoan mats (see Supplemental for more examples). Repeat transects in 2021 and 2023 at a fluid plume site at Cape Hallett indicate continued fluid seepage over this time-period, as well as a prolonged impact on the benthic community (Figure S3; S7).
Discussion
Methane is a powerful greenhouse gas of global importance – if methane release from seafloor seeps in the Ross Sea is indicative of the wider Antarctic continent, there is the potential to initiate, or contribute to, positive climate feedbacks with global consequences56,57. If the shallow water methane seeps reported here follow the behavior of other global seep systems, there is the potential for rapid transfer of methane to the atmosphere, as reported at other shallow seep systems58,59,60,61. Recent work has illustrated the potential for atmospheric exchange from shallow, coastal, seeps in the Arctic and Sub-Antarctic, with up to 255 µmol m-2 d-1 methane measured fluxing to the atmosphere in regions of the Southern Ocean with known seep sites62. Equally important, the presence of these seeps indicates subglacial fluid routing that could be transporting key trace elements and nutrients to the ocean39, with potential to alter regional productivity.
Seeps can also have significant local impacts on the overall function of marine ecosystems and shift larger-scale biogeochemical cycles63,64, although some mechanisms remain unclear. In addition to the biological dead-zones at the fluid plume sites in Northern Victoria Land, the Ross Island seep sites have seen an outbreak of sea star wasting disease, potentially related to subdermal hypoxia or organic matter enrichment on sea star health65. Indeed, studies at global seep sites have shown benthic oxygen demand that is two orders of magnitude greater than non-seep sites64. Seafloor seeps on the Arctic shelf are not only recognized sites of oxygen depletion64, but also ocean acidification66, and are sources of dissolved iron67 that may enhance primary production68. While seafloor seeps are known to influence benthic systems and biogeochemistry at seep sites globally63,64,67,68,69, this is the first evidence of an impact on benthic fauna in the Antarctic.
The coincidence of warming, glacial thinning and retreat, and recent emergence of seafloor seeps in the Ross Sea12, highlights the critical, time-sensitive need to understand the mechanisms driving seepage and associated impacts in coastal waters. In addition to mechanisms related to cryospheric change that can regulate fluid and gas release in polar regions, seafloor seepage is known to be regulated globally by a variety of mechanisms including variabilities in migration pathways (e.g., tectonic processes70,71,72), methane availability (e.g., organic carbon burial), fluid flow dynamics (e.g., pressure changes from longer term variations in sea-level and shorter-term processes such as tidal cycles73), and temperature (e.g., bottom-water temperature10,57,66 and seasonal cycles74). Indeed, our study area is near to the West Antarctic Rift System and there are several active volcanoes in the area. Despite the active volcanism in the area, the methane gas analyzed at the sites reported here has been found to be microbial in origin12. However, this dynamic geologic environment could certainly be playing a role in the creation of fluid migration pathways for the seeps described here.
Regardless of the formative mechanism, the novel, yet widespread, discoveries of Antarctic seafloor seeps highlight the significant gaps in understanding of what appears to be an increasingly common phenomenon. Whether this is indicative of ongoing climate impacts in the region, as has occurred in the geologic record and in the Arctic, or a regime shift with local impacts on the ecology of the region, should be a focus of research in both the Ross Sea and Antarctica, in general. Only through future, interdisciplinary work can we elucidate the mechanisms that are leading to the seep emergence observed, and more broadly the drivers and sensitivities of seafloor seepage along Antarctic coastal margins. We recommend coordinated, international research efforts to address this important topic.
Methods
Field surveys
The data presented here is a compilation of photo, video, and sample collection from SCUBA or Remotely Operated Vehicle (ROV) surveys in the McMurdo Sound region and ship-based work aboard the R/V Tangaroa offshore Northern Victoria Land. The details of specific data acquisition is described below.
Sediment geochemistry
Sediment methane flux was determined with benthic chambers deployed by SCUBA divers and left for 24 - 48-hour intervals. Benthic chambers were sediment cores with an internal diameter of 10 cm (sampling 0.08 m2 of the seafloor), with a gas-tight lid and septa for syringe sample collection. Samples were taken through the gas-tight septas on the top of the benthic chambers every 12–24 hours, and magnetic stirrers were activated prior to sampling to ensure water mixing before sample collection (outside of this sampling, the chambers remained with a gas tight seal during flux incubations). Each chamber had its exposed chamber volume measured (i.e., the distance from sediment surface to the bottom of the chamber lid) and at each sampling point 3 ml of sample was removed and placed in a serum vial with 2 ml 1 M NaOH or transported at ambient seawater temperature (-1.8 C) within the sample syringe to the lab. Once in the lab the sample was allowed to come to ambient temperature and equilibrate with a quantified volume of air and then that air was analyzed directly. Methane emission is taken as the change over time from initial sampling until final sampling, after accounting for chamber water volume, to minimize any methodological artifacts impact on total methane values. Methane samples were analyzed with a HP 5890 gas chromatograph with an AllTech Porapak N8/100 column at Oregon State University or with a Picarro G2301i Cavity Ring Down Spectrometer at McMurdo Station, Antarctica.
Remotely operated vehicle (ROV) surveys and digital elevation models
The ROV was used to record footage by navigating multiple back and forth passes across the seabed along relatively tight depth contours (every 0.5 m) and from multiple angles (highly overlapping imagery). These recordings were used to create 2D orthomosaic images and 3D digital elevation models of the seafloor terrain and habitat features such as rugosity and vertical relief75 using the software application Photoscan (Agisoft©). Parallel scaling lasers on the ROV were used to assign a scale to individual images (between 4-6 individual images spaced evenly across the transect) and provide an accurately scaled map.
Seafloor imagery collection from R/V Tangaroa
Seafloor imagery was collected with NIWAs Deep Towed Instrument System (DTIS), a towed camera frame which records continuous digital video and simultaneously takes high definition still images. The position and depth of DTIS were tracked using the KONGSBERG ultra-short baseline (USBL) transponder system. The seabed position of DTIS was plotted using OFOP software (Ocean Floor Observation Protocol, www.ofop-by-sams.eu), with all data, recorded to OFOP log files and captured by the ship’s Data Acquisition System (DAS), and correlated to the location of water column acoustic anomalies.
Water column acoustic analysis from R/V Tangaroa data
Data were collected using the R/V Tangaroa suite of multi-frequency echosounders (18, 38, 70, 120, and 200 kHz) throughout the voyage. The 38, 120, and 200 kHz echosounders were narrow-band EK60 echosounders, while the 18 and 70 kHz echosounders were wide-band, operating over the frequency range of 12–27 kHz and 45–90 kHz respectively. Echosounder models and main acquisition parameters are summarized in Table 1. In the area of seep exploration which includes Cape Hallett, Cape Wheatstone, Cape Adare, Possession Islands, and Robertson Bay, 55 km2 of the seafloor was insonnified by split-beam systems, of which 14 km2 was shallower than 250 m (the deepest depth which seeps were observed).
All echosounders were calibrated in similar water conditions at the arrival in the Ross Sea so that acoustic backscatter measurement could be used quantitatively. Wideband measurements (FM) were obtained on the 12–27 kHz and 45-90 kHz frequency bands, while other echosounders (38 kHz, 120 kHz and 200 kHz) were operated using narrow band pulses (CW).
Acoustic data was scrutinized and post-processed using the open-source software ESP376. Fluid plumes were identified as “hazy” signal connected to the seafloor (Fig. 1d; and S5–S9), with some phase coherence associated to the boundaries of the plumes. The plumes are reflecting strongly at higher frequencies but are easier to identify using the 38 kHz or the 45–90 kHz bands, as they are easier to separate to other reflectors in the water-column (micronekton, biological targets).
Bubble plumes were identified as small groups of single targets consistently rising from the seafloor, with a clear phase coherence associated to them of single-target nature (Fig. 1d; and S8–S10)77. Radiuses of targets were independently estimated from measurements of rising rates78 and target strength frequency response79 which gave comparable results.
Data availability
The water column acoustic data that was used for seep identification in Northern Victoria Land and is discussed and visualized throughout the manuscript and in the Supplemental Information has been deposited in the Open Science Framework repository and is available for download at: (https://osf.io/3u69v/). All remaining data supporting the study is either included in the manuscript or supplemental information, or available upon request to the corresponding author.
Code availability
The code used to analyse the water column acoustic data is available at: https://bitbucket.org/yladroit/esp3/src/master/
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Acknowledgements
We extend our appreciation to Antarctica New Zealand and the US Antarctic Program for logistical support. S.S., V.C., C.L., L.T., and I.H. acknowledge funding support from the New Zealand Antarctic Science Platform, Ministry of Business, Innovation, and Employment Grant (MBIE ANTA1801). S.S., V.C., and C.L. acknowledge funding from the Royal Society of New Zealand Marsden Research Fund (MFP-NIW23303). S.S. additionally acknowledges co-funding from the New Zealand Ministry of Business, Innovation, and Employment Endeavour Programme (CO1X1710, Ross-RAMP). ART acknowledges funding from the National Science Foundation Office of Polar Programs (NSF OPP 1103428, 2046800, 2325046). We thank Rob Robbins, Steve Rupp, Lila Ardor Bellucci and Dr Rowan McLachlan for their time and effort with the diving-based discoveries presented here. We thank Peter Marriot, Jack Massuger, David Bremner, and Lily Pryor Rodgers for help with Remotely Operated Vehicle field work in McMurdo Sound. We also thank Dr Matt Druce for his contributions to this work as well as the captain, crew, and scientists aboard the R/V Tangaroa TAN2101 and TAN2302 voyages offshore Northern Victoria Land.
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S.S. conceived of and wrote the manuscript. A.R.T., Y.L., V.C., L.T., A.M., I.H., and C.S.L. contributed to discussion of the content and results, as well as editing and revision of the manuscript. A.R.T. collected and compiled methane flux data and seafloor photographs of Cinder Cones and Turtle Rocks seeps. V.C. and L.T. collected and compiled seafloor video and photographs of Dunlop Island, Cape Evans, Cape Barnes, and Granite Harbor seeps. L.T. created the digital elevation model of Dunlop Island. S.S., C.S.L., L.T., Y.L., and A.M. collected and compiled the shipboard observations from Northern Victoria Land. Y.L. and A.M analysed and visualized the water column acoustic data from Northern Victoria Land.
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Seabrook, S., Law, C.S., Thurber, A.R. et al. Antarctic seep emergence and discovery in the shallow coastal environment. Nat Commun 16, 8740 (2025). https://doi.org/10.1038/s41467-025-63404-3
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DOI: https://doi.org/10.1038/s41467-025-63404-3