Methane-Derived Authigenic Carbonates on the Seafloor of the Laptev Sea Shelf

Abstract

Seafloor authigenic carbonate crusts are widespread in various oceanic and marine settings, excluding high-latitude basins that are corrosive to carbonate precipitation. Newly formed carbonate formations are relatively rare in modern Arctic marine sediments. Although the first-order principles of seep carbonate formation are currently quite well constrained, little is known regarding the duration or mode of carbonate formation in the Siberian Arctic shelf. Large (massive slabs or blocks) and small crusts that were micrite cemented have been recently discovered on the seafloor of the Siberian Arctic seas within the area of known seep activity in the outer Laptev Sea shelf. Cold methane seeps were detected in the area due to the presence of an acoustic anomaly in the water column (gas flares). Microbial mats, methane gas bubbles, and carbonate crusts were observed using a towed camera platform. Here, we report new geochemical and mineralogical data on authigenic shallow Siberian Arctic cold-seep carbonate crusts to elucidate its genesis. The Laptev Sea carbonate crusts mainly consist of high-Mg calcite (up to 23 mol % MgCO3). The δ13C values in carbonates range significantly (from –40.1 to –25.9‰ VPDB), while the δ18O values vary in a narrow range (+4.4 ± 0.2‰ VPDB). The δ13C values of Corg that was determined from carbonates range from –40.2 to –31.1‰ VPDB. Using the isotope data and taking into account the geological setting, we consider that not only microbial but possibly thermogenic methane participated in the authigenic carbonate precipitation. Carbonate crust formation occurred below the water/sediment interface of the shallow Siberian Arctic shelf as a result of gas hydrate dissociation during Holocene warming events. The studied carbonate crusts were exhumated after precipitation into shallow subsurface shelf sediments.

Biogeochemistry and timing of methane-derived carbonate formation at Leirdjupet fault complex, SW Barents sea

“…The absolute dating of seep carbonates is essential to reconstruct the high-resolution history of seepage, enabling geoscientists to determine the evolution of seepage over critical climatic phases of Earth history, which can help predict future global warming scenarios. Cold seep research conducted over the years in the Barents Sea (Crémière et al, 2016;Andreassen et al, 2017;Serov et al, 2017;Yao et al, 2020) and other Arctic paleo-glaciated margins (Portnov et al, 2016;Schneider et al, 2018;Himmler et al, 2019;Kravchishina et al, 2021) revealed episodes of massive seafloor gas seepage following deglaciations. These events are highlighting the role of grounded ice sheets as "capacitors" facilitating the storage of methane into sub-glacial gas hydrates and inducing large-scale release upon ice retreat.…”

Biodegradation of Ancient Organic Carbon Fuels Seabed Methane Emission at the Arctic Continental Shelves

“…The fresher pore water shifts the methane hydrate phase boundary toward higher temperature, making methane hydrate more stable. Freshwater seepage has been detected at the continental shelves of the Laptev Sea (Kravchishina et al., 2021) and the Canadian Beaufort Sea (Gwiazda et al., 2018). Third, pore water pressure increases with the rising sea level.…”

Opportunistic consumption of marine pelagic, terrestrial, and chemosynthetic organic matter by macrofauna on the Arctic shelf: a stable isotope approach

“… Based on the data from the present study and Gebruk et al, 2003 ; Decker & Olu, 2012 ; Lee et al, 2019a ; Åström, Bluhm & Rasmussen, 2022 ; Kravchishina et al, 2021 . HMMV, Haakon Mosby Mud Volcano.…”

“…and carnivores nephtyid polychaetes were the only taxa in their respective feeding group. In the section “Seep-associated fauna” we used additional data on Oligobrachia and δ 13 C values of methane from North Atlantic and Arctic seeps for comparison on a larger scale ( Gebruk et al, 2003 ; Decker & Olu, 2012 ; Lee et al, 2019a ; Åström, Bluhm & Rasmussen, 2022 ; Kravchishina et al, 2021 ). Several taxa were not assigned to a particular feeding habit: the gastropod Frigidoalvania sp., the bivalve Montacuta spitzbergensis , and thyasirid bivalves.…”