@article {5798, title = {Acoustic and Geomorphological Signatures of Gas Seeps on the East Siberian Margin}, year = {2016}, month = {April 11-12}, address = {University of New Hampshire, Durham, NH}, abstract = {

Rising hydrocarbon gas concentrations in the atmosphere are strongly linked to global warming. In the next century, significant amounts of hydrocarbons will be transport from the ocean to the atmosphere via thawing of flooded permafrost. The East Siberian Arctic Shelf (ESAS) holds 80\% of the world\’s flooded permafrost and is at risk of massive release due to bottom water warming. Gas released from permafrost is transported by gas seeps through the ocean; however, the magnitude of this gas flux has historically been difficult to quantify.

This research aims to estimate the total gas flux from a region of the ESAS, Herald Canyon, via acoustic and geomorphological characterization of gas seeps in the area. Data was collected with three acoustic systems (EM122 multibeam echosounder, SBP120 subbottom profiler, and EK80 split-beam sonar) onboard the Oden during the Swedish-Russian-US Arctic Ocean Investigation of Climate-Cryosphere-Carbon Interactions (SWERUS-C3) program.

53 seeps have been identified in the vicinity of Herald Canyon. Together, the EM122 high-resolution multibeam bathymetry and SBP120 chirp subbottom profiling data, provide the spatial and geologic context of the gas seeps. The EK80, which makes acoustic measurements over a broad range of frequencies, can identify individual bubble scatters. This enables estimates of bubble size distribution and rise velocity measurements in certain seeps; ultimately providing gas flux estimates. The combination of three data sets offers the opportunity to link seep flux estimates to geomorphological setting. The geomorphological setting can further be linked to local and regional geologic processes determined from seafloor morphology and subsurface structure. These links will help define our knowledge of the transport of hydrocarbon gas from flooded permafrost to the atmosphere.

}, keywords = {acoustic, east siberian margin, gas seeps, geomorphological signatures}, author = {Elizabeth Weidner and Larry A Mayer and Kevin Jerram and Thomas C Weber and Martin Jakobsson and Chernykh, D. and Ananiev, R. and Mohammad, R. and Semiltov, I.} } @article {5814, title = {Evidence for an Ice Shelf Covering the Central Arctic Ocean During the Penultimate Glaciation}, volume = {7}, year = {2016}, month = {January 18}, publisher = {Macmillan Publishers Ltd.}, abstract = {

The hypothesis of a km-thick ice shelf covering the entire Arctic Ocean during peak glacial conditions was proposed nearly half a century ago. Floating ice shelves preserve few direct traces after their disappearance, making reconstructions difficult. Seafloor imprints of ice shelves should, however, exist where ice grounded along their flow paths. Here we present new evidence of ice-shelf groundings on bathymetric highs in the central Arctic Ocean, resurrecting the concept of an ice shelf extending over the entire central Arctic Ocean during at least one previous ice age. New and previously mapped glacial landforms together reveal flow of a spatially coherent, in some regions \>1-km thick, central Arctic Ocean ice shelf dated to marine isotope stage 6 (~140\ ka). Bathymetric highs were likely critical in the ice-shelf development by acting as pinning points where stabilizing ice rises formed, thereby providing sufficient back stress to allow ice shelf thickening.

}, keywords = {Arctic Ocean, glaciation, ice shelf}, doi = {doi:10.1038/ncomms10365}, url = {http://www.nature.com/ncomms/2016/160118/ncomms10365/full/ncomms10365.html}, author = {Martin Jakobsson and Johan Nilsson and Anderson, L and Backman, Jan and Bjork, G and Cronin, Tomas and Kirchner, N. and Koshurnikov, Andrey and Larry A Mayer and Noormets, R. and O{\textquoteright}Regan, M A and Christian Stranne and Ananiev, R. and Barrientos, Natalia and Chernykh, D. and Helen K. Coxall and Bjorn Eriksson and Floden, Tom and Laura Gemery and Gustafson, Orjan and Kevin Jerram and Johansson, Carina and Khortov, Alexey and Mohammad, R. and Semiltov, I.} } @article {5999, title = {Quantification of Methane Gas Flux and Bubble Fate on the Eastern Siberian Arctic Shelf Utilizing Calibrated Split-beam Echosounder Data}, year = {2016}, month = {December 12-16}, pages = {San Francisco, CA}, abstract = {

On the Eastern Siberian Arctic Shelf (ESAS) subsea permafrost, shallow gas hydrates, and trapped free gas hold an estimated 1400 Gt of methane. Recent observations of methane bubble plumes and high concentrations of dissolved methane in the water column indicate methane release via ebullition. Methane gas released from the shallow ESAS (\<50 m average depth) has high potential to be transported to the atmosphere.

To directly and quantitatively address the magnitude of methane flux and the fate of rising bubbles in the ESAS, methane seeps were mapped with a broadband split-beam echosounder as part of the Swedish-Russian-US Arctic Ocean Investigation of Climate-Cryosphere-Carbon Interactions program (SWERUS-C3). Acoustic measurements were made over a broad range of frequencies (16 to 29 kHz). The broad bandwidth provided excellent discrimination of individual targets in the water column, allowing for the identification of single bubbles. Absolute bubble target strength values were determined by compensating apparent target strength measurements for beam pattern effects via standard calibration techniques. The bubble size distribution of seeps with individual bubble signatures was determined by exploiting bubble target strength models over the broad range of frequencies. For denser seeps, with potential higher methane flux, bubble size distribution was determined via extrapolation from seeps in similar geomorphological settings. By coupling bubble size distributions with rise velocity measurements, which are made possible by split-beam target tracking, methane gas flux can be estimated.

Of the 56 identified seeps in the SWERUS data set, individual bubbles scatterers were identified in more than half (31) of the seeps. Preliminary bubble size distribution results indicate bubble radii range from 0.75 to 3.0 mm, with relatively constant bubble size distribution throughout the water column. Initial rise velocity observations indicate bubble rise velocity increases with decreasing depth, seemingly independent of bubble radius.

}, keywords = {flux and bubble fate, methane gas, siberian arctic}, url = {https://agu.confex.com/agu/fm16/meetingapp.cgi/Paper/122698}, author = {Elizabeth Weidner and Larry A Mayer and Martin Jakobsson and Chernykh, D. and Ananiev, R. and Thomas C Weber and Kevin Jerram and Mohammad, R. and Semiltov, I.} } @article {5706, title = {On the Existence of an East-Siberian-Chukchi Ice Sheet: New Insights from the SWERUS-C3 Expedition 2014}, year = {2015}, month = {December 14-18}, address = {San Francisco, CA}, abstract = {

The glacial history of the vast Siberian continental shelf of the Laptev and East Siberian Seas is poorly known. Most of this shelf area is shallower than 120 m implying that it was exposed land during the Last Glacial Maximum (LGM) as well as during older major Quaternary glaciations. The regional glacial and deglacial history of marine transgression has greatly influenced marine conditions of today\’s Arctic Ocean continental shelves. For example, the present extent of submarine permafrost on the shallow continental shelves is tightly linked to the glacial history, because the submarine permafrost was formed during cold conditions when sea level was low enough for the shelves to be subaerially exposed. Conversely, one explanation for lack of submarine permafrost on some shelf areas is the presence of past ice sheets. Ice sheets extending over parts of the Eastern Siberian continental shelf have been proposed in literature during LGM as well as during older Quaternary glacial periods. However, the sparsely available data from the outer continental shelf and adjacent slope of the Eastern Siberian Arctic Ocean has left the glacial history in this part largely unresolved. Here we present new geophysical mapping and sediment coring data from the shallow East Siberian shelf and adjacent slope collected during the 2014 SWERUS-C3 expedition (SWERUS-C3: Swedish \– Russian \– US Arctic Ocean Investigation of Climate-Cryosphere-Carbon Interactions) with Swedish icebreaker Oden. The mapping, using multibeam sonar, chirp sub-bottom profiler, and electro magnetics, in combination with new sediment cores provide information on past glacial activities, sea-level history and permafrost extent on the Eastern Siberian Arctic Ocean. Combining the new SWERUS-C3 data with previous results from this region raises the question whether an East Siberian-Chukchi ice sheet existed during LGM and/or during older glacial periods.\ 

}, keywords = {chukchi, ice sheet, swerus-c3}, url = {http://fallmeeting.agu.org/2015/}, author = {Martin Jakobsson and O{\textquoteright}Regan, M A and Kirchner, N. and Ananiev, R. and Bachman, Jan and Barrientos, Natalia and Chernykh, D. and Helen K. Coxall and Cronin, Tomas and Koshurnikov, Andrey and Lobkovsky, Leopold and Larry A Mayer and Noormets, R. and Muschitiello, Francesco and Johan Nilsson and Pearce, Christof and Semiltov, I. and Christian Stranne} } @article {5705, title = {A Multi-Frequency Look at Gas Seeps on the East Siberian Margin}, year = {2015}, month = {December 14-18}, address = {San Francisco, CA}, abstract = {

The Swedish-Russian-US Arctic Ocean Investigation of Climate-Cryosphere-Carbon Interactions (SWERUS-C3) is a multi-investigator, multi-disciplinary program aimed at increasing our understanding of the climate-cryosphere-carbon system of the Eastern Siberian Arctic Ocean. In 2014 SWERUS-C3 carried out a two-leg field program on the Swedish Icebreaker ODEN. A component of the SWERUS-C3 program focused on water column mapping of the spatial distribution and geologic context of gas seeps using the acoustic systems on board ODEN (12 kHz EM122 multibeam echo sounder, 2-8 kHz SBP120 subbottom profiler, and an 18 kHz EK60 split-beam sonar). On Leg 2 of the 2014 expedition, a new wideband transceiver (EK80) was added to the split-beam echo sounder and calibrated, providing the ability to measure the acoustic response of the gas seeps over a much broader range of frequencies (15-30 kHz). While the broader bandwidth unquestionably provides higher target resolution a further objective of the broadband mapping was to determine whether information on bubble size distribution could be determined so as to help model the flux of gas coming from the seeps. On Leg 2 approximately 34 seeps were mapped, mostly in the vicinity of Herald Canyon. The wide-swath, high-resolution multibeam bathymetry (from the EM122) and high-resolution chirp sub-bottom profiling (from the SBP120 multibeam sub-bottom profiler) combined with water column imaging of seeps collected at both 12 kHz (from the EM122) and 15-30 kHz (from the EK80) offer an important opportunity to understand the spatial distribution of seeps and their relationship to local and regional processes as determined from seafloor and subsurface structure, as well as to explore the potential of extracting quantitative information about the magnitude of gas transport from the seeps.\ 

}, keywords = {east siberian margin, gas seeps}, url = {http://fallmeeting.agu.org/2015/}, author = {Larry A Mayer and Elizabeth Weidner and Kevin Jerram and Thomas C Weber and Martin Jakobsson and Chernykh, D. and Ananiev, R. and Mohammad, R. and Semiltov, I.} } @article {5799, title = {A Multi-Frequency Look at Gas Seeps on the East Siberian Margin}, year = {2015}, month = {December 14-18 }, publisher = {American Geophysical Union }, address = {San Francisco, CA}, abstract = {

The Swedish-Russian-US Arctic Ocean Investigation of Climate-Cryosphere-Carbon Interactions (SWERUS-C3)is a multi-investigator, multi-disciplinary program aimed at increasing our understanding of the climate-cryosphere-carbon system of the Eastern Siberian Arctic Ocean.In 2014, SWERUS-C3 carried out a two-leg field program on the Swedish Icebreaker ODEN. A component of the SWERUS-C3 program focused on water column mapping of the spatial distribution and geologic context of gas seeps using the acoustic systems on board ODEN(12kHzEM122 multibeam echosounder, 2-8kHzSBP120 subbottom profiler, and an 18kHzEK60split-beamsonar). On Leg 2 of the 2014 expedition, a new wide-band transceiver (EK80) was added to the split-beam echosounder and calibrated, providing the ability to measure the acoustic response of the gas seeps over a much broader range of frequencies (15-30kHz). While the broader bandwidth unquestionably provides higher target resolution, a further objective of the broadband mapping was to determine whether information on bubble size distribution could be determined so as to help model the flux of gas coming from the seeps. On Leg2, 53seeps were identified in the vicinity of Herald Canyon.The wide-swath, high-resolution multibeam bathymetry (from the EM122) and high-resolution chirp subbottom profiling (from the SBP120 multibeam subbottom profiler), combined with water column imaging of seeps collected at both 12kHz (from the EM122) and 15-30kHz (from the EK80) offer an important opportunity to understand the spatial distribution of seeps and their relationship to local and regional processes as determined from seafloor and subsurface structure, as well as to explore the potential of extracting quantitative information about the magnitude of gas transportfrom the seeps.

}, keywords = {east siberian margin, gas seeps}, url = {http://ccom.unh.edu/publications/multi-frequency-look-gas-seeps-east-siberian-margin}, author = {Elizabeth Weidner and Larry A Mayer and Thomas C Weber and Martin Jakobsson and Chernykh, D. and Ananiev, R. and Mohammad, R. and Semiltov, I.} }