DCO Project Summary

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Project Title
Eastern Siberian Arctic Ocean Seafloor
Start DateEnd Date
2014-08-17 2014-10-04
NameRoleInstitutionDCO ID
Related GrantsDCO ID
11121/4015-2040-1025-6363-CC
Description
The seafloor of the Eastern Siberian Arctic Ocean holds significant, but as yet virtually unsurveyed, methane deposits.  As part of an international collaborative effort to better understand the climate, cryosphere and carbon system of the Arctic (SWERUS-C3),  we have been invited to use newly developed acoustic water-column imaging techniques to map the distribution (and to help quantify the flux) of methane gas seeps from the seafloor. Specifically, we hope to use the multibeam sonar onboard the Swedish Icebreaker ODEN to locate and characterize gas seeps in the water column and then apply a newly developed wideband transceiver to the split-beam echosounder onboard the ODEN to constrain the size and fate of gas bubbles rising to the surface. Together, these acoustic observations will help the SWERUS-C3 team understand the flux of methane from the seafloor into the water column and potentially into the atmosphere. If successful, these techniques will allow the mapping of the gas flux in the Arctic over scales never before possible. This proposal requests support for the participation of the UNH team on this expedition and for post-cruise work-up of the data. Among problems to be addressed by the SWERUS-C3 program are: (1) Quantification of methane release from subsea permafrost and the deep sea; (2) The fate of carbon in the shelf sea released from thawing coastal permafrost; (3) The magnitude of air/sea methane exchange; (4) The recent/post-glacial/paleoclimate sediment record of permafrost carbon releases, and; and (5) The longer-term history of Arctic sea ice and its impact on carbon fluxes. The UNH contribution will provide a means (using underway acoustic systems) to broadly map the location and character of gas seeping from the seafloor into the water column.
Project UpdatesClick to add Project Update

Reporting Year 2017 Click to expand


  • Update 2017: Eastern Siberian Arctic Ocean Seafloor - submitted on ,

    Update Details:

    The Swedish-Russian-US Arctic Ocean Investigation of Climate-Cryosphere-Carbon Interactions (SWERUS-C3) was a major international, multi-disciplinary program aimed at increasing our understanding of the complex interactions among climate, Arctic ice and carbon dioxide in the atmosphere.  Our (University of New Hampshire) component of the program was to help in the detailed mapping of the seafloor using a sophisticated seafloor mapping system known as a multibeam echosounder and particularly to evaluate whether multibeam and other echosounders may be able to help us find natural gas seeps coming from the seafloor and quantify that amount of gas (methane) being put into the ocean and atmosphere.  Methane is a powerful greenhouse gas that can greatly affect the acidity of the ocean and climate.  The amount of methane being put into the ocean and atmosphere by natural gas seeps is currently unknown and we are seeking to develop tools that will allow us to detect natural gas seeps and measure the amount of gas from surface ships. 
    We were successfully able to map and identify gas seeps on the East Siberian Continental Margin (Figure 1).  We have been able to use a specialized echosounder to identify individual gas bubbles from these seeps and measure their size and rise rate (Figure 2).  Knowing this, we have been able to remotely measure the “flux” or amount of gas coming from the gas seeps.    The approaches we have developed to do this are now being used by both the oil and gas industry to search for resources and by the regulatory agencies to get a better handle on natural background levels as well as leaky oil rigs and pipelines. In the long-run we hope they will contribute to more accurate models of methane into the ocean and atmosphere and it impact on climate and ocean acidification.
    Additionally, we had an unexpected, but exciting result.  In the very high Arctic where waters from the Atlantic mix with waters from the Arctic our specialized echo-sounders recorded very fine-scale layering that turned out to be the inter-fingering of these two water masses (something called thermohaline stair steps).  We were able to match the changes in water properties measured by lowering instruments through the water column with the layers in the echosounder (Fig 3) indicating that we now have the ability to map and trace, over large distances the complex mixing processes in the ocean. With such a capability, we hope to be able to better understand the distribution of heat through the ocean, and associated oceanographic phenomena like upwelling which drives productivity.
    Finally, mapping of the seafloor during this cruise revealed two important new insights into the history of ice sheets and sea level in the Arctic.  First the discovery of the imprint of ice sheets on the seafloor in the middle of the Arctic at water depths as much as 1000m (3300ft) imply that about 140,000 years ago much of the Arctic may have been covered by a 3300-foot thick ice shelf.  This idea had been proposed more than 100 years ago but had been dismissed for lack of evidence.  Secondly, we were able to determine through detailed mapping and dating of cores recovered from the seafloor that the Beringia Land Bridge – the land bridge that connected Asia to North America approximately 18,000 years ago during the peak of the last ice age, became flooded later than previously thought (about 11,000 years ago).  This new dating of the end of the land bridge has important implications on our understanding global circulation (Pacific water could now flow into the Arctic and vice-versa) as well as on the migration of early people from Asia to North America.

Reporting Year 2015 Click to expand


  • Update 2015: Eastern Siberian Arctic Ocean Seafloor - submitted on Oct 02, 2015

    Update Details:

    Submitted by L. Mayer, September 2015

    Introduction:

    Sloan DCO Field Studies Grant 2014-3-1 provided partial support for scientists from the Center of Coastal Mapping at the University of New Hampshire to participate in the SWERUS C-3 Expedition to the East Siberian Arctic Ocean on board the Swedish Icebreaker ODEN. SWERUS-C3 (The Swedish-Russian-US Investigation of Climate, Cryosphere and Carbon interaction) was initiated as a Knut and Alice Wallenberg funded research project and then evolved into a multi-disciplinary international research program focused on investigating the historical functioning of the Climate-Cryosphere-Carbon (C3) system of the East Siberian Arctic Ocean (ESAO) (Fig. 1). The two-leg (total of 90 days) expedition included a carefully planned program of geophysical surveying, sampling (atmosphere, water, terrestrial, and sub-seafloor) and on-board and post-cruise geochemical, biogeochemical, and oceanographic measurements and analyses.  The objective of the UNH team was to use newly developed acoustic water-column imaging techniques to map the distribution (and to help quantify the flux) of methane gas seeps from the seafloor. Specifically our goal was to use the multibeam sonar on board the ODEN to locate and characterize gas seeps in the water column and then apply a newly developed wideband transceiver to the split-beam echo sounder on board the ODEN to attempt to constrain the size and fate of gas bubbles rising to the surface. Together, these acoustic observations will help the SWERUS-C3 team understand the flux of methane from the seafloor into the water column and potentially into the atmosphere.

    The UNH team participated in the second leg of the SWERUS-C3 expedition departing Barrow Alaska on 21 August 2014 and returning to Tromso Norway on 4 October 2014.  Five work areas were surveyed during this period (Fig. 2) including detailed multibeam sonar mapping of the seafloor and water column, broad-band (EK80) acoustic measurements in the water column, approximately 150 CTD stations and 35 coring stations (piston, gravity and multicores).

    As outlined above, the UNH Water Column Mapping program on Leg 2 was been designed to address the SWERUS-C3 objectives through mapping the spatial distribution and geologic context of gas seeps in the East Siberian Arctic Ocean as well as attempting a new approach that may enhance the estimates of the flux of gas emanating from the seeps by providing acoustic information related to bubble size distribution.   The UNH team used an array of tools to address these objectives including the EM122 multibeam sonar, the SBP 120 high-resolution subbottom profiler and an EK80 broad-band split-beam sonar.   The EM122 on the Oden, has, in addition to its seafloor mapping capabilities, the ability to also map acoustic targets in the water column.  Natural gas seeps have been shown to be very strong acoustic targets that can often be identified in multibeam sonar water column imagery.  From these data the areal distribution and density of natural seeps can be mapped directly in the context of seafloor bathymetry.  Additionally, data from the SBP120 high-resolution sub-bottom profiling system (as well as data from data from single channel seismic reflection profiling system) can be integrated with the midwater data to better understand the relationship of gas in the sediment column to gas seeps observed in the water column.  

    The EK60 and the EK80 were calibrated on Leg 2 making it possible to quantify the acoustic target strength of gas bubbles within an ensonified volume such as a plume of gas bubbles rising from a seep.  These observations can be used to examine the spatial (and temporal, for seeps observed multiple times) variability of gas seep ‘strength’. With knowledge of bubble size distribution, these target strength observations can then be used to make quantitative estimates of gas flux.  The EK80 provides broadband information that should provide higher (than standard narrow-band echo sounders) resolution detection of targets and most importantly, allow for estimation of bubble size distribution. Gas seep target strength measurements made across a wide range of frequencies can be inverted for estimates of bubble size distribution and, subsequently, estimates of free gas within the plume.  Frequency-dependent changes in the target strengths of gas bubbles rising through the water column may also help constrain models for the evolution and fate of gas bubbles as they rise to the surface and will help determine what fraction of gas exiting the seafloor is capable of reaching the atmosphere.

    Results

    EK80 data were collected for the entire cruise from departure off Barrow to the securing of the systems approaching Tromso. A total of ca. 7 Terabytes of EK80 data were recorded.  These data provided the primary source of identification of seeps and other midwater targets.  On Leg 2, approximately 34 individual seeps were identified in the EK80 data (some were multiple vents) almost all of them in the vicinity of Herald Canyon in Survey Box 1.  Seeps in this region ranged in water depth from 50 to 88 m.   Several other seeps were identified in slightly deeper water (100 – 118m) on the shelf end of Slope Transect 3 in Survey Box 3. Examples will be presented below.

    The first example is of a single, isolated plume found in about 85 m of water.  Figure 3 (left) show the clear representation of this seep in the EK80 data.  Above the plume a number of scatterers can be seen between the top of the plume and the sea surface.  It is most likely that these are biological scatterers (attracted by the plume activity?) but may also be small bubble packets.  Further analysis will be done to resolve this.  Using the EK80 as a guide, the equivalent time is shown in the water column data from the EM122 (Fig. 3 middle). Note that the EM122 caught the bottom of the seep while the EK80 only saw the seep when it entered its 11-degree beam (approximately 11m wide at 80 m depth). Thus, in this case, the EM122 can provide a much more accurate location for the source of the seep than the EK80.   The manual extraction of target data in commercially available software is a tedious and subjective process.  To address this issue we have written Matlab code to normalize background levels and automatically extract midwater targets.  An example of the normalized extraction for this same target is presented in Figure 3 (right).  Note that this is presented for a single ping.  The normalization software will do this extraction for the entire time series of pings (the stacked pings) and thus extract the 3-D distribution of the target.

    To establish the geomorphological and geological context, the extracted seep was combined with the EM122 bathymetry and the SBP120 high-resolution subbottom profiler data (Fig. 4).  In this example the seep is located directly in an iceberg scour that appears to have pierced a subsurface zone of gas (Fig. 4 – lower).

    The second example is of a line that appears as many small seeps in the EK80 record (Fig. 5).  While these seeps appeared quite small on the EK80, the EM122 water column imagery showed at least one of these seeps (Fig. 5 left panel) to be the largest and strongest target seen with the EM122 on Leg 2 (Fig. 6).  This difference demonstrates the fact that the two systems complement each other.  The EK80 offers the opportunity to make calibrated measurements of target strength (and perhaps flux) but its field of view is limited to its approximately 11 degree beam width.  Thus if the transducer does not pass within approximately 11 m of the target in 80 m of water, it will be missed.   Also as bubbles move up through the water column the field of view narrows (5.5 m at 40 m depth, etc.) resulting in more opportunity to miss targets.  The EM122 on the other hand with its 120 - 130 degree opening angle, ensonifies a swath of approximately four times the water depth – thus capturing targets across a swath of more than 300 m on the seafloor in 80 m of water.  A georeferenced image of the seeps along the line described above along with the seafloor bathymetry and the high-resolution subbottom image is presented in Fig. 7. In contrast to the first example, here the seeps do not seem to be associated with iceberg scours.   Two of the seeps (those on the left side) appear to be associated with broad gas blanking zones that approach the seafloor while the third (which is the large one shown in Figure 6) sits above stratified sediments.

    The final example is of a single seep that is clearly related to a subsurface feature. Here the seep has a much less coherent appearance than some of the others – perhaps indicating intermittent rather than steady release of gas.  While this seep is very clear in the EK80 image, it is much more difficult to locate in the multibeam (Fig. 8).  Georeferencing of the extracted seep with the seafloor and subsurface morphology (Fig. 9) reveals the coincidence of the seep with a clear subsurface gas structure.  The multibeam bathymetry shows a depression at the location of the seep but this depression is not apparent on either the EK80 or SBP120 and is thus most likely the result of “punch-through” (detection of the bottom deeper than the actual seafloor) of the multibeam sonar in the soft sediments disturbed by the gas expulsion.  

    Figure 1: Schematics of key components of the Arctic climate-cryosphere-carbon system that are addressed by the SWERUS-C3 Program. a,b) Sonar images of gas plumes in the water column caused by sea floor venting of methane (a: slope west of Svalbard, Westbrook et al., 2009; b: ESAO, Shakhova et al., 2010, Science). c) Coastal erosion of organic-rich Yedoma permafrost, Muostoh Island, SE Laptev Sea. d) multibeam image showing pockmarks from gas venting off the East Siberian shelf. e) distribution of Yedoma permafrost in NE Siberia. f) Atmospheric venting of CH4, CO2.      

    Figure 2: Overview map of Leg 2 cruise track starting August 21 from Barrow, Alaska. The cruise ended in Tromsö, Norway, August 4. Working Boxes 1-5 are outlined with blue boxes. Red lines=Seismic reflection profiles; purple lines=Electromagnetic profiles; yellow stars=coring stations; green dots=CTD stations (some also included water sampling).

    Figure 3: EK80 observation of single seep in 84 m of water (left).  Same seep as seen by EM122 (middle).  Same target automatically extracted targets through normalization process.  Note that the EM122 and normalization display represent a single ping.  The seep is actually seen in several pings along the track.

    Figure 4: Seep extracted from EM122 data georeferenced with EM122 bathymetry and SBP120 high-resolution subbottom profile.  Color bar on right represents seafloor depths.  Bubbles are identified to approximately 35m below the sea surface.

    Figure 5: Numerous small seeps as seen by EK80 along a single line.  Insets in middle and right images are zoomed view of seeps.

    Figure 6: EM122 water column data of seep displayed in Figure 5 left panel.

    Figure 7: Seeps shown in Figure WC-17 extracted from EM122 data georeferenced with EM122 bathymetry and SBP120 high-resolution subbottom profile.  Color bar on right represents seafloor depths.

    Figure 8: EK80 observation of single seep in 52 m of water (left).  Same seep as seen by EM122 (right side of right panel).

    Figure 9: Seep shown in Figure 8 extracted from EM122 data georeferenced with EM122 bathymetry and SBP120 high-resolution subbottom profile.  Color bar on right represents seafloor depths.

    Future Efforts:

    The seep data presented above was all collected in the Russian EEZ.  Data acquired within the Russian EEZ during SWERUS-C3 was subject to a six-month embargo by the Russian government.  This embargo was lifted in May 2015 and we will now begin the quantitative analysis of the broad-band data to determine the viability of extracting bubble-size information from it.   The results of the field work and these analyses will be initially be presented at the Fall AGU meeting in San Francisco (Mayer et al., 2015).   A special issue encompassing the simultaneous publication of SWERUS papers in four Copernicus Journals -- The Cryosphere, Ocean Sciences, Biogeosciences and Climate of the Past is also being organized and we will contribute a paper to this special effort.

    Mayer, L.A., Jerram, K., Weber, T., Jakobsson, M., Chernkh, D., Ananiev, R, Mohammad, R, and Semiletov, I., to be presented at Fall 2015 AGU meeting, A multifrequency look at gas seeps on the East Siberian Margin.


Reporting Year 2016 Click to expand


  • Update 2016: Eastern Siberian Arctic Ocean Seafloor - submitted on ,

    Update Details:

    Seagoing operations at this Site were completed in 2014, producing spectacular images of gas seeps on the Arctic Ocean seafloor, as reported last year. Data acquired within the Russian EEZ during SWERUS-C3 was subject to a six-month embargo by the Russian government.  This embargo was lifted in May 2015 and we have now begun quantitative analysis of the broad-band data to determine the viability of extracting bubble-size information.   The results of the field work and these analyses were presented at the 2015 Fall AGU meeting in San Francisco (Mayer et al., 2015), and additional results will be presented at the 2016 meeting (Weidner et al, 2016).   A special issue encompassing the simultaneous publication of SWERUS papers in four Copernicus Journals -- The Cryosphere, Ocean Sciences, Biogeosciences and Climate of the Past is also being organized and we will contribute a paper to this special effort. 
    Because Sloan funding blended with support from other sources has facilitated the development of entirely new geophysical imaging capabilities, Sloan support has led to a huge array of substantial grant funding for related research using and further developing these methods. Thus, the grant support related to this Field Site, totaling $2.5M, comprises a fifty-fold return on Sloan’s initial investment. 
Related ProjectsProject URIDCO ID
Related DatasetsDCO ID
Related PublicationsDCO ID
11121/9460-6947-3138-2804-CC
11121/4365-2632-8573-4838-CC


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