Sonar Estimation of Methane Bubble Flux from Thawing Subsea Permafrost: A Case Study from the Laptev Sea Shelf

Seeps found offshore in the East Siberian Arctic Shelf may mark zones of degrading subsea permafrost and related destabilization of gas hydrates. Sonar surveys provide an effective tool for mapping seabed methane fluxes and monitoring subsea Arctic permafrost seepage. The paper presents an overview of existing approaches to sonar estimation of methane bubble flux from the sea floor to the water column and a new method for quantifying CH4 ebullition. In the suggested method, the flux of methane bubbles is estimated from its response to insonification using the backscattering cross section. The method has demonstrated its efficiency in the case study of single- and multi-beam acoustic surveys of a large seep field on the Laptev Sea shelf

Pingo drilling reveals sodium-chloride dominated massive ice in Grøndalen, Spitsbergen

Drilling of a 21.8-m-deep borehole on top of the 10.5-m-high Nori pingo that stands at 32 m asl in Grøndalen Valley (Spitsbergen) revealed a 16.1-m-thick massive ice enclosed by frozen sediments. The hydrochemical compositions of both the massive ice and the sediment extract show a prevalence of Na+ and Cl� ions throughout the core. The upper part of the massive ice (stage A) has low mineralization and shows an isotopically closed-system trend in δ18O and δD isotopes decreasing down-core. Stage B exhibits high mineralization and an isotopically semi-open system. The crystallographic structure of Nori pingo’s massive ice provides evidence of several large groundwater intrusions that support the defined formation stages. Analysis of local aquifers leads to suggest that the pingo was hydraulically sourced through a local fault zone by low mineralized sodium–bicarbonate groundwater of a Paleogene strata aquifer. This groundwater was enriched by sodium and chloride ions while filtering through marine valley sediments with residual salinity. The comparison between the sodium–chloride-dominated massive ice of the Nori pingo and the sodium–bicarbonate-dominated ice of the adjacent Fili pingo that stands higher up the valley may serve as an indicator for groundwater source patterns of other Nordenskiöld Land pingos

Pingo Nori (Spitsbergen) massive ice isotope and chemical content of permafrost core Grondalen 13

The drilling of the 10.5 m high Nori pingo that stands at 32 m asl in Grøndalen Valley (Spitsbergen) performed in April 2019 reached a depth of 21.8 m bs (core #13, starting from 42.5 m asl, 77.99483 °N, 14.59009 °E) and revealed 16.1 m thick massive ice. The core was obtained with a portable gasoline-powered rotary drilling rig (UKB 12/25, Vorovskiy Machine Factory, Ekaterinburg, Russia). The core pieces with diameter 112-76 mm were lifted for sampling to the surface every 30–50 cm. After documentation and cryolithological description core pieces were sealed in zip lock bags. Ice samples were split in two parts - one part for stable isotope analyses, another part for ion content measurement. They were kept frozen for transportation while sediment samples were kept unfrozen. Moisture content was analyzed in laboratory by measuring sediment samples weight before and after drying. The stable water isotope composition (δ18O and δD) of massive pingo ice was analyzed at the Climate and Environmental Research Laboratory (CERL, Arctic and Antarctic Research Institute, St. Petersburg, Russia) using a Picarro L2120- i analyzer. After every five samples the working standard (SPB-2, δ18O = -9.66 ‰ and δD = -74.1 ‰) was measured. SPB-2 is made of distilled St. Petersburg tap water and is calibrated against the International Atomic Energy Agency (IAEA) standards VSMOW-2 (Vienna Standard Mean Ocean Water 2), GISP (Greenland Ice Sheet Precipitation), and SLAP-2 (Standard Light Antarctic Precipitation 2). The reproducibility of the results is 0.08 ‰ for δ18O and 0.4 ‰ for δD and was assessed by re-measuring a random selection of 10% of the total samples. The measurement error is thus 1-2 orders of magnitude less than the natural isotopic variability of pingo ice, which is satisfactory for the purpose of this study. The δ18O and δD values are given as per mil (‰) difference to the VSMOW-2 standard. The deuterium excess (d) is calculated as d = δD - 8δ18O29. The ion content of sedimentary permafrost samples from core #13 was estimated after water extraction at the analytical laboratory of RAE-S, Barentsburg. The material was dried and sieved at 1 mm. About 20 g of the sediment were suspended in 100 ml of de-ionized water and filtered through 0.45 μm nylon mesh within 3 minutes after stirring. Electrical conductivity (EC, measured in μS cm-1) and pH values were estimated with a Mettler Toledo Seven Compact S 220. EC values were transformed automatically by the instrument into general ion content (mineralization) values given as mg L-1. Major anions and cations in the water extracts were analyzed by an ion chromatograph (Shimadzu LC-20 Prominence) equipped with the Shimadzu CDD-10AVvp conductometric detector and ion exchange columns for anions (Phenomenex Star-ion A300) and for cations (Shodex ICYS-50). Bicarbonate content was measured by a Shimadzu TOC-L analyzer via catalytic oxidizing at +680o C and subsequent infrared detecting. Melted pingo ice samples from core #13 and spring water samples were analyzed after filtration through 0.45 μm nylon mesh on the same equipment using the same techniques for pH, EC, and ion composition as for sedimentary permafrost samples. Analyses and research were aimed at determining major characteristics of the Nori pingo including its internal structure, groundwater source, and geochemical and isotopic stages of formation

Geocryological and hydrogeological conditions of Western part of Nordenskiold Land (Spitsbergen Archipelago)

This work summarizes the archived data of geocryological and hydrogeological conditions in the west of Nordenskiold Land on the Spitsbergen Archipelago. The historical data obtained in the Soviet period during coal exploration are reviewed together with the results of our own studies performed as part of the Russian Scientific Arctic Expedition on Spitsbergen (RAE-S) in 2016–2020. With respect to geocryology, the region is assigned to the zone of continuous permafrost. The thickness of rocks and sediments with temperatures below zero is about 100 m near the coast and increases to 540 m on watersheds. The mean annual ground temperature near the zero-amplitude depth varies from –3.6 to –2.2°C. Below this layer, the temperature curve in the top part of the section tends to deviate toward positive temperatures, reflecting the modern cycle of climate warming. From the hydrogeological point of view, the area belongs to the marginal zone of the West Spitsbergen cryoadartesian basin. Seawater intrusions near the coast form saline subpermafrost aquifers, including those with temperatures below zero, reflecting the seawater (sodium chloride) composition and hydraulic heads close to sea level. Fresh and slightly saline (sodium bicarbonate on the east coast of Grønfjorden and magnesium–calcium sulfate in gypsum-bearing deposits on the west coast) subpermafrost water with hydraulic heads reaching 100 m above sea level is fed by water-saturated ice in the deep layers of large glaciers

A Complex of Marine Geophysical Methods for Studying Gas Emission Process on the Arctic Shelf

The Russian sector of the arctic shelf is the longest in the world. Quite a lot of places of massive discharge of bubble methane from the seabed into the water column and further into the atmosphere were found there. This natural phenomenon requires an extensive complex of geological, biological, geophysical, and chemical studies. This article is devoted to aspects of the use of a complex of marine geophysical equipment applied in the Russian sector of the arctic shelf for the detection and study of areas of the water and sedimentary strata with increased saturation with natural gases, as well as a description of some of the results obtained. This complex contains a single-beam scientific high-frequency echo sounder and multibeam system, a sub-bottom profiler, ocean-bottom seismographs, and equipment for continuous seismoacoustic profiling and electrical exploration. The experience of using the above equipment and the examples of the results obtained in the Laptev Sea have shown that these marine geophysical methods are effective and of particular importance for solving most problems related to the detection, mapping, quantification, and monitoring of underwater gas release from the bottom sediments of the shelf zone of the arctic seas, as well as the study of upper and deeper geological roots of gas emission and their relationship with tectonic processes. Geophysical surveys have a significant performance advantage compared to any contact methods. The large-scale application of a wide range of marine geophysical methods is essential for a comprehensive study of the geohazards of vast shelf zones, which have significant potential for economic use