Oceanography and methane of waters from the Lena Delta

The Lena River is one of the largest Russian rivers draining into the Laptev Sea. The permafrost areas surrounding the Lena are predicted to thaw at increasing rates due to global temperature increases. With this thawing, large amounts of carbon - either organic or in the gaseous forms carbon dioxide and methane - will reach the waters of the Lena and the adjacent Buor-Khaya Bay (Laptev Sea). Methane concentrations and the isotopic signal of methane in the waters of the Lena Delta and estuary were monitored from 2008 to 2010. Creeks draining from permafrost soils produced hotspots for methane input into the river system (median concentration 1500 nM) compared with concentrations of 30-85 nM observed in the main channels of the Lena. No microbial methane oxidation could be detected; thus diffusion is the main process of methane removal. We estimated that the riverine diffusive methane flux is 3-10 times higher than the flux from surrounding terrestrial environment. To maintain the observed methane concentrations in the river, additional methane sources are necessary. The methane-rich creeks could be responsible for this input.

Gridded bathymetry from multibeam echosounder EM122 data of the cruise M84/2, off Kerch and the eastern Crimea (2011)

Bathymetry based on data recorded during M84-2 between 26.02.2011 and 02.04.2011 in the Black Sea. The aim of the cruise was to investigate the gas hydrate distribution in sediments of the Black Sea by using several coring technics. In addition to the coring activities the installed EM122 and the PARASOUND system were used to detect gas emissions in the water column and to map large areas of possible seep sites.

Gridded bathymetry from multibeam echosounder EM122 data of the cruise M84/2, off Georgia (2011)

Bathymetry based on data recorded during M84-2 between 26.02.2011 and 02.04.2011 in the Black Sea. The aim of the cruise was to investigate the gas hydrate distribution in sediments of the Black Sea by using several coring technics. In addition to the coring activities the installed EM122 and the PARASOUND system were used to detect gas emissions in the water column and to map large areas of possible seep sites.

Gridded bathymetry from multibeam echosounder EM122 data of the cruise M84/2, off Samsun (2011)

Bathymetry based on data recorded during M84-2 between 26.02.2011 and 02.04.2011 in the Black Sea. The aim of the cruise was to investigate the gas hydrate distribution in sediments of the Black Sea by using several coring technics. In addition to the coring activities the installed EM122 and the PARASOUND system were used to detect gas emissions in the water column and to map large areas of possible seep sites.

Gridded bathymetry from multibeam echosounder EM122 data of the cruise M84/2, off Eregli (2011)

We investigated gas bubble emissions at the Don-Kuban paleo-fan in the northeastern Black Sea regarding their geological setting, quantities as well as spatial and temporal variabilities during three ship expeditions between 2007 and 2011. About 600 bubble-induced hydroacoustic anomalies in the water column (flares) originating from the seafloor above the gas hydrate stability zone (GHSZ) at ~700 m water depth were found. At about 890 m water depth a hydrocarbon seep area named "Kerch seep area" was newly discovered within the GHSZ. We propose locally domed sediments ('mounds') discovered during ultra-high resolution bathymetric mapping with an autonomous underwater vehicle (AUV) to result from gas hydrate accumulation at shallow depths. In situ measurements indicated spatially limited temperature elevations in the shallow sediment likely induced by upward fluid flow which may confine the local GHSZ to a few meters below the seafloor. As a result, gas bubbles are suspected to migrate into near-surface sediments and to escape the seafloor through small-scale faults. Hydroacoustic surveys revealed that several flares originated from a seafloor area of about 1 km**2 in size. The highest flare disappeared in about 350 m water depth, suggesting that the released methane remains in the water column. A methane flux estimate, combining data from visual quantifications during dives with a remotely operated vehicle (ROV) with results from ship-based hydroacoustic surveys and gas analysis revealed that between 2 and 87 x 10**6 mol CH4 yr-1 escaped into the water column above the Kerch seep area. Our results show that the finding of the Kerch seep area represents a so far underestimated type of hydrocarbon seep, which has to be considered in methane budget calculations.

Gridded bathymetry from multibeam echosounder EM120 data of the cruise MSM15/2 (2011)

Bathymetry based on data recorded during MSM15-2 between 10.05.2010 and 02.06.2010 in the Black Sea. The aim of the cruise was to perform AUV and ROV pre-site surveys of potential drill sites that represent deposits where shallow gas hydrates have already been sampled by gravity and piston coring and where gas emissions to the water column have been detected.