Ongoing methane discharge at well site 22/4b (North Sea)and discovery of a spiral vortex bubble plume motion

Highlights • Mega ebullition of biogenic methane from an abandoned offshore gas well, North Sea. • Evidence for midwater bubble plume intrusion, fallback, and short-circuiting of the plume. • Effective trapping of seabed released methane underneath the thermocline. • First observation of a spiral vortex methane plume and marginal turbulences. • Megaplumes appear less efficient in terms of vertical methane transport than previously thought. Abstract First direct evidence for ongoing gas seepage activity on the abandoned well site 22/4b (Northern North Sea, 57°55′ N, 01°38′ E) and discovery of neighboring seepage activity is provided from observations since 2005. A manned submersible dive in 2006 discovered several extraordinary intense seepage sites within a 60 m wide and 20 m deep crater cut into the flat 96 m deep seafloor. Capture and (isotope) chemical analyses of the gas bubbles near the seafloor revealed in situ concentrations of methane between 88 and 90%Vol. with δ13C–CH4 values around −74‰ VPDB, indicating a biogenic origin. Bulk methane concentrations throughout the water column were assessed by 120 Niskin water samples showing up to 400.000 nM CH4 in the crater at depth. In contrast, concentrations above the thermocline were orders of magnitude lower, with a median value of 20 nM. A dye tracer injection into the gas seeps revealed upwelling bubble and water motion with gas plume rise velocities up to ∼1 ms−1 (determined near the seabed). However, the dissolved dye did not pass the thermocline, but returned down to the seabed. Measurements of direct bubble-mediated atmospheric flux revealed low values of 0.7 ± 0.3 kty−1, much less than current state-of-the-art bubble dissolution models would predict for such a strong and upwelling in situ gas bubble flux at shallow water depths (i.e. ∼100 m). Acoustic multibeam water column imaging data indicate a pronounced 200 m lateral intrusion at the thermocline together with high methane concentration at this layer. A partly downward-orientated bubble plume motion is also visible in the acoustic data with potential short-circuiting in accordance to the dye experiment. This observation could partly explain the observed trapping of most of the released gas below the well-established thermocline in the North Sea. Moreover, 3D analyses of the multibeam water column data reveal that the upwelling plume transforms into a spiral expanding vortex while rising through the water column. Such a spiral vortex motion has never been reported before for marine gas seepage and might represent an important process with strong implication on plume dynamics, dissolution behavior, gas escape to the atmosphere, and is considered very important for respective modeling approaches

Physical properties of methane-enriched plumes along the Hikurangi margin of New Zealand: Thoughts on sources and life spans of water column methane anomalies

We explored methane distribution and physical mixing processes at active areas with CTD measurements utilizing a methane sensor combined with discrete water samples collected in Niskin bottles (24 bottle carrousel). Evidence of a methane plume injection was obtained during a CTD cast. The plume injection is thought to be the result of a vertical advective flow driven by a source of buoyancy (e.g., heat flux, bubbles, high dissolved methane concentration). Thorpe scale analyses on the high-resolution temperature data allow us to locate turbulent overturns and the associated small- to large-scale temperature inversions. Thorpe displacement analysis shows substantial overturns of ca. 30 m at around 720 m depth that perfectly correspond with a large peak (ca. 600 nM) of methane. This is likely the final intrusion depth of a methane plume originating from the sea floor. However, it is inconclusive which buoyancy source(s) are driving the plume (e.g. heat flux, bubbles, etc.). In the corresponding profiles, a completely well-mixed ca. 35 m thick layer (in T and Sal) is observed at this location. This further suggests a local buoyancy source. Substantial energy input is required to maintain such a well-mixed structure. In absence of a supporting energy source, this signal would be vertically diffusively smeared within several days (t = z/Kz), and much faster horizontally. Energy balances suggest that the source and resulting upwelling are a dissolved methane-enriched thermal plume, as the number of bubbles required to produce such a plume and maintain the deep-mixed layer is too substantial

Submarine flatulence along the Hikurangi margin of New Zealand: Linking geochemical methane anomalies in the water column with hydroacoustic evidence of bubble transport

High methane concentrations of up to 3200 nM have been measured in the water column along the Hikurangi margin. The methane is a manifestation of common and wide spread cold fluid seepage that is linked to considerable gas hydrate resources. Three methods were utilised to explore for active seeps: by continuous, qualitative measurement of dissolved methane gas in the water column, using a methane sensor (METS) which was attached to a CTD; by qualitative measurement of discrete water samples collected in niskin bottles on the CTD; and by hydroacoustic detection of gas bubbles with a single beam echosounder. Prior to cruises on the TANGAROA RV in 2006 and the SONNE RV in 2007, only a few studies have been performed in this region. Here we present data of methane distribution from three different seep locations along the Hikurangi Margin. The Rock Garden seep site is in the northern part of the Hikurangi margin and occurs at the gas hydrate stability boundary (about 700m water depth in this area). The Omakere Ridge site is also in the northern Hikurangi margin, but occurs within deeper waters (1200m). The Wairarapa area is in the southern Hikurangi margin and is only 6 miles offshore (about 1200m depth) in the Cook Strait. Qualitative methane data have been obtained by onboard GC-based analyses using head-space equilibrium and vacuum extraction methods. The ability to define and corroborate by direct measurement, narrow (10-15m wide) methane anomalies in the water column was made possible only by the availability of a very responsive METS. Hydroacoustic flare imaging shows that bubble release is a common process at almost all of the 12 studied seep sites. Particularly at Rock Garden, ROV observations show pulsed bubble release with outbursts lasting minutes. The fate of methane along the Hikurangi margin will be discussed based on CTD-cast sections across seep sites and detailed sampling at seeps and in flares. The results are linked with bubble dissolution models, incorporating ADCP current data, physical water column properties, bubble-induced advection as studied by thermistor-moorings and knowledge about currents and eddies in the area

Distribution of methane in the water column of the Baltic Sea

The distribution of dissolved methane in the water column of the Baltic Sea was extensively investigated. A strong correlation between the vertical density stratification, the distribution of oxygen, hydrogen sulfide, and methane has been identified. A widespread release of methane from the seafloor is indicated by increasing methane concentrations with water depth. The deep basins in the central Baltic Sea show the strongest methane enrichments in stagnant anoxic water bodies (max. 1086 nM and 504 nM, respectively), with a pronounced decrease towards the pelagic redoxcline and slightly elevated surface water concentrations (saturation values of 206% and 120%, respectively). In general the more limnic basins in the northern part of the Baltic are characterized by lower water column methane concentrations and surface water saturation values close to the atmospheric equilibrium (between 106% and 116%). In contrast, the shallow Western Baltic Sea is characterized by high saturation values up to 746%

Flare imaging with multibeam sonar systems: data processing for seep bubble detection

Multibeam sonar surveys have been conducted since their invention in the 1970s; however, mainly reflections from the seafloor were considered so far. More recently, water column imaging with multibeam is becoming of increasing interest for fisheries, buoy, mooring, or gas detection in the water column. Using ELAC SEABEAM 1000 data, we propose a technique to detect gas bubbles (flares) although this system is originally not designed to record water column data. The described data processing represents a case study and can be easily adapted to other multibeam systems. Multibeam data sets from the Black Sea and the North Sea show reflections of gas bubbles that form flares in the water column. At least for reasonably intense gas escape the detection of bubbles is feasible. The multibeam technique yields exact determination of the source position and information about the dimension of the gas cloud in the water. Compared to conventional flare imaging by single-beam echo sounders, the wide swath angle of multibeam systems allows the mapping of large areas in much shorter time

A low frequency multibeam assessment: Spatial mapping of shallow gas by enhanced penetration and angular response anomaly

This study highlights the potential of using a low frequency multibeam echosounder for detection and visualization of shallow gas occurring several meters beneath the seafloor. The presence of shallow gas was verified in the Bornholm Basin, Baltic Sea, at 80 m water depth with standard geochemical core analysis and hydroacoustic subbottom profiling. Successively, this area was surveyed with a 95 kHz and a 12 kHz multibeam echosounder (MBES). The bathymetric measurements with 12 kHz provided depth values systematically deeper by several meters compared to 95 kHz data. This observation was attributed to enhanced penetration of the low frequency signal energy into soft sediments. Consequently, the subbottom geoacoustic properties contributed highly to the measured backscattered signals. Those appeared up to 17 dB higher inside the shallow gas area compared to reference measurements outside and could be clearly linked to the shallow gas front depth down to 5 meter below seafloor. No elevated backscatter was visible in 95 kHz MBES data, which in turn highlights the superior potential of low frequency MBES to image shallow sub-seafloor features. Small gas pockets could be resolved even on the outer swath (up to 65°). Strongly elevated backscattering from gassy areas occurred at large incidence angles and a high gas sensitivity of the MBES is further supported by an angular response analysis presented in this study. We conclude that the MBES together with subbottom profiling can be used as an efficient tool for spatial subbottom mapping in soft sediment environments

EpiDiP/NanoDiP: a versatile unsupervised machine learning edge computing platform for epigenomic tumour diagnostics.

DNA methylation analysis based on supervised machine learning algorithms with static reference data, allowing diagnostic tumour typing with unprecedented precision, has quickly become a new standard of care. Whereas genome-wide diagnostic methylation profiling is mostly performed on microarrays, an increasing number of institutions additionally employ nanopore sequencing as a faster alternative. In addition, methylation-specific parallel sequencing can generate methylation and genomic copy number data. Given these diverse approaches to methylation profiling, to date, there is no single tool that allows (1) classification and interpretation of microarray, nanopore and parallel sequencing data, (2) direct control of nanopore sequencers, and (3) the integration of microarray-based methylation reference data. Furthermore, no software capable of entirely running in routine diagnostic laboratory environments lacking high-performance computing and network infrastructure exists. To overcome these shortcomings, we present EpiDiP/NanoDiP as an open-source DNA methylation and copy number profiling suite, which has been benchmarked against an established supervised machine learning approach using in-house routine diagnostics data obtained between 2019 and 2021. Running locally on portable, cost- and energy-saving system-on-chip as well as gpGPU-augmented edge computing devices, NanoDiP works in offline mode, ensuring data privacy. It does not require the rigid training data annotation of supervised approaches. Furthermore, NanoDiP is the core of our public, free-of-charge EpiDiP web service which enables comparative methylation data analysis against an extensive reference data collection. We envision this versatile platform as a useful resource not only for neuropathologists and surgical pathologists but also for the tumour epigenetics research community. In daily diagnostic routine, analysis of native, unfixed biopsies by NanoDiP delivers molecular tumour classification in an intraoperative time frame

Using the past to constrain the future: how the palaeorecord can improve estimates of global warming

Climate sensitivity is defined as the change in global mean equilibrium temperature after a doubling of atmospheric CO2 concentration and provides a simple measure of global warming. An early estimate of climate sensitivity, 1.5-4.5{\deg}C, has changed little subsequently, including the latest assessment by the Intergovernmental Panel on Climate Change. The persistence of such large uncertainties in this simple measure casts doubt on our understanding of the mechanisms of climate change and our ability to predict the response of the climate system to future perturbations. This has motivated continued attempts to constrain the range with climate data, alone or in conjunction with models. The majority of studies use data from the instrumental period (post-1850) but recent work has made use of information about the large climate changes experienced in the geological past. In this review, we first outline approaches that estimate climate sensitivity using instrumental climate observations and then summarise attempts to use the record of climate change on geological timescales. We examine the limitations of these studies and suggest ways in which the power of the palaeoclimate record could be better used to reduce uncertainties in our predictions of climate sensitivity.Comment: The final, definitive version of this paper has been published in Progress in Physical Geography, 31(5), 2007 by SAGE Publications Ltd, All rights reserved. \c{opyright} 2007 Edwards, Crucifix and Harriso

Trajectories of the Earth System in the Anthropocene

This is the final version of the article. Available from National Academy of Sciences via the DOI in this record.We explore the risk that self-reinforcing feedbacks could push the Earth System toward a planetary threshold that, if crossed, could prevent stabilization of the climate at intermediate temperature rises and cause continued warming on a "Hothouse Earth" pathway even as human emissions are reduced. Crossing the threshold would lead to a much higher global average temperature than any interglacial in the past 1.2 million years and to sea levels significantly higher than at any time in the Holocene. We examine the evidence that such a threshold might exist and where it might be. If the threshold is crossed, the resulting trajectory would likely cause serious disruptions to ecosystems, society, and economies. Collective human action is required to steer the Earth System away from a potential threshold and stabilize it in a habitable interglacial-like state. Such action entails stewardship of the entire Earth System-biosphere, climate, and societies-and could include decarbonization of the global economy, enhancement of biosphere carbon sinks, behavioral changes, technological innovations, new governance arrangements, and transformed social values.W.S. and C.P.S. are members of the Anthropocene Working Group. W.S., J.R., K.R., S.E.C., J.F.D., I.F., S.J.L., R.W. and H.J.S. are members of the Planetary Boundaries Research Network PB.net and the Earth League’s EarthDoc Programme supported by the Stordalen Foundation. T.M.L. was supported by a Royal Society Wolfson Research Merit Award and the European Union Framework Programme 7 Project HELIX. C.F. was supported by the Erling– Persson Family Foundation. The participation of D.L. was supported by the Haury Program in Environment and Social Justice and National Science Foundation (USA) Decadal and Regional Climate Prediction using Earth System Models Grant 1243125. S.E.C. was supported in part by Swedish Research Council Formas Grant 2012-742. J.F.D. and R.W. were supported by Leibniz Association Project DOMINOES. S.J.L. receives funding from Formas Grant 2014-589. This paper is a contribution to European Research Council Advanced Grant 2016, Earth Resilience in the Anthropocene Project 743080