Heat Flow on the U.S. Beaufort Margin, Arctic Ocean: Implications for Ocean Warming, Methane Hydrate Stability, and Regional Tectonics

Hornbach, Matthew J.; Harris, Robert N.; Phrampus, B. J.

doi:10.1029/2020gc008933

Cited by 8 publications

(6 citation statements)

References 139 publications

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“…Geochemical methods (isotope analysis) can be used to assess past destabilizations such as in the Krishna-Godavari Basin consecutive to a sea level drop (Joshi et al, 2014). Other examples of ongoing GH destabilization include Lake Baikal (De Batist et al, 2002) and the U.S. Beaufort margin (Hornbach et al, 2020).…”

Section: Introductionmentioning

confidence: 99%

Irregular BSR: Evidence of an Ongoing Reequilibrium of a Gas Hydrate System

Colin

Ker

Riboulot

et al. 2020

Geophysical Research Letters

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Gas hydrate (GH) systems constitute methane sinks sensitive to environmental changes such as pressure, temperature, and salinity. It remains a matter of debate as to whether the large GH system of the Black Sea has reached a steady state since the last glacial maximum (LGM). We report on an irregular free gas distribution in specific sediment layers marking an irregular bottom-simulating reflector (BSR). This anomalous free gas distribution revealed by very high resolution seismic images, acquired by a deep-towed multichannel seismic system, might be evidence of an ongoing migration of the base of the GH stability zone (GHSZ). We show that the reequilibrium is not occurring homogeneously as overpressure from hydrate dissociation slows their decomposition in specific sedimentary layers. The Black Sea example highlights that dissociation and the associated methane release in the water column or even in the atmosphere could be largely delayed by overpressure accumulation. Plain Language Summary Methane hydrate is an ice-like compound composed of a cage of water molecules enclosing a methane molecule. Hydrates can form where water and methane are present under high pressure and low temperatures, for example, in deep-sea sediments. As a result of climate change (e.g., seawater temperature increase), hydrates can melt and release free gas and water. Yet we observe that hydrates are present where they should have melted according to modeling. We explain this irregular melting by differing properties of the host sediments and different quantities of hydrate in the sediments. Methane in the Earth's atmosphere is a strong greenhouse gas. The release of methane from hydrate melting has been proposed as a runaway process where the methane released increases global warming, which further increases hydrate melting and methane release, repeating the cycle. Our results show that the destabilization of a hydrate system is actually a slow process, spanning several millennia. As such, a catastrophic destabilization of a gas hydrate system is unlikely.

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Section: Introductionmentioning

confidence: 99%

Irregular BSR: Evidence of an Ongoing Reequilibrium of a Gas Hydrate System

Colin

Ker

Riboulot

et al. 2020

Geophysical Research Letters

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“…Temperature within the subsurface was determined by calculating a geothermal gradient derived from predicted heat flow at the seafloor using observations primarily from the Global Heat Flow Compilation Group (2013). We assimilated several new observations from Hornbach et al (2020) and Riedel and Collett (2017). Using these observations, we predicted heat flow and uncertainty at the seafloor using a KNR machine learning algorithm following the workflow outlined in Lee et al (2019).…”

Section: Organic Carbon Calculation Detailsmentioning

confidence: 99%

Global Estimates of Biogenic Methane Production in Marine Sediments Using Machine Learning and Deterministic Modeling

Lee

Phrampus

Skarke

et al. 2022

Global Biogeochemical Cycles

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Organic carbon burial and degradation in marine sediments is an important factor in the regulation of Earth's climate on geologic time scales (LaRowe et al., 2020) and has been suggested as a possible carbon sink, which can explain observed decreases in atmospheric CO 2 over the past 50 million years (IPCC, 2021). Therefore, quantifying the amount and spatial distribution of organic carbon sequestered in marine sediments is fundamental to understanding global carbon cycling associated with climate variability via source and sink carbon interactions with the biosphere. Organic carbon is initially deposited on the seafloor through the outflow of terrestrial sources (i.e., rivers) and/or sinking of dead and decaying organisms (e.g., marine snow). Over time, this pool of shallow organic carbon deposited at the seafloor is either oxidized or buried where it can undergo a series of microbially driven redox reactions ultimately rendering methane (CH 4 ) (Middelburg, 2019). The majority of methane found in the subsurface is hypothesized to be of microbial origin (Kvenvolden, 1995), but abiotic thermogenic reactions also occur (Etiope & Sherwood Lollar, 2013).Methane produced in the subsurface is commonly incorporated into one of the largest estimated free carbon pools on Earth, methane hydrate (Ruppel & Kessler, 2017). Methane at a concentration level that exceeds local solubility and occurs within a specific pressure-temperature regime, referred to herein as the hydrate stability zone (HSZ), may form methane hydrates. The carbon sequestered in this ice-like substance is estimated to comprise ∼15%-50% of all global free carbon (Ruppel & Kessler, 2017). The HSZ generally occurs in water depths >300 m below sea level (mbsl), where pressures are high (∼3-30 MPa) and seafloor temperatures are low (<25°C) (Max et al., 2006;Ruppel & Waite, 2020). The thickness of the HSZ is controlled by the temperature, pressure, and salinity gradients in the subseafloor. Direct, global subseafloor observations of the HSZ are sparse, therefore the identification of the HSZ is first-order dependent upon accurate estimates of input parameters such as pressure, temperature, and geothermal gradient.

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“…BSRs have already been demonstrated to help derive heat flow by past authors Horai & Von Herzen, 1985;Hornbach et al, 2020;Uyeda & Horai, 1982). Thus, the shallow heat flow output is not particularly novel.…”

Section: Scientific Applicationsmentioning

confidence: 99%

Reflection seismic thermometry

Sarkar

Huuse

2021

Basin Research

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The North Viking Graben (NVG) is part of the mature North Sea Basin petroleum province and designated as a major carbon storage basin for NW Europe. It has been extensively drilled over five decades with an abundance of well and seismic data in the public domain. As such it serves as an excellent setting to demonstrate the efficacy of a reflection seismic data led approach to predicting subsurface temperatures using a state-of-the-art, fullwaveform inversion velocity model covering the entire NVG. In a forward modelling approach, an empirical velocity to thermal conductivity transform is used in conjunction with predefined heatflow to predict subsurface temperature. The predefined heatflow parameters are set based on the range of values from previous studies in the area. Abundant well data with bottom hole temperature (BHT) records provide calibration of results. In the second step of inverse modelling, BHTs and the velocity derived thermal conductivity are used to derive heat flow based on a 1D steady-state approximation of Fourier's law. In this way, heatflow is estimated over the 12,000 km 2 model area at a km scale (lateral) resolution, highlighting lateral variability in comparison with the traditional point-based heatflow data sets. This heatflow is used to condition a final iterative loop of forward modelling to produce a temperature model that is best representative of the subsurface temperature.Calibration against 139 exploration wells indicate that the predicted temperatures are on average 0.6℃ warmer than the recorded values. BHT for the recently completed Northern Lights carbon sequestration 31/5-7 (Eos) modelled to be 97℃, which is 6℃ below the recorded BHT. This highlights the applicability of this workflow not only towards enhancing petroleum systems modelling work but also for use in the energy transition and for fundamental scientific purposes.

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Heat Flow on the U.S. Beaufort Margin, Arctic Ocean: Implications for Ocean Warming, Methane Hydrate Stability, and Regional Tectonics

Cited by 8 publications

References 139 publications

Irregular BSR: Evidence of an Ongoing Reequilibrium of a Gas Hydrate System

Irregular BSR: Evidence of an Ongoing Reequilibrium of a Gas Hydrate System

Global Estimates of Biogenic Methane Production in Marine Sediments Using Machine Learning and Deterministic Modeling

Reflection seismic thermometry

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