Abstract
Seafloor heat flow measurements are utilized to determine the geothermal regime of the Danube deep-sea fan in the western Black Sea and are presented in the larger context of regional gas hydrate occurrences. Heat flow data were collected across paleo-channels in water depths of 550–1460 m. Heat flow across levees ranges from 25 to 30 mW m−2 but is up to 65 mW m−2 on channel floors. Gravity coring reveals sediment layers typical of the western Black Sea, consisting of three late Pleistocene to Holocene units, notably red clay within the lowermost unit cored. Heat flow derived from the bottom-simulating reflector (BSR), assumed to represent the base of the gas hydrate stability zone (GHSZ), deviates from seafloor measurements. These discrepancies are linked either to fast sedimentation or slumping and associated variations in sediment physical properties. Topographic effects account of up to 50% of heat flow deviations from average values. Combined with climate-induced variations in seafloor temperature and sea-level since the last glacial maximum large uncertainties in the prediction of the base of the GHSZ remain. A regional representative heat flow value is ~30 mW m−2 for the study region but deviations from this value may be up to 100%.
Highlights
Accepted: 31 May 2021Gas hydrates were initially discovered in the Black Sea in 1974 [1]
Several seismic studies [9,10,11,12,13,14,15] were conducted to map bottom-simulating reflectors (BSRs), which are used as an indicator for the base of the structure I gas hydrate stability zone (GHSZ)
Just marks an onset of free gas, but the current base of the GHSZ is much shallower by ~20–30 m. These analyses focus on the upper edge of the gas hydrate zone in the Danube deep-sea fan and water depths
Summary
Accepted: 31 May 2021Gas hydrates were initially discovered in the Black Sea in 1974 [1]. A number of scientific research projects were conducted studying the general occurrence and distribution of gas hydrates along the continental margins of the Black Sea, e.g., [2,3,4,5,6,7,8]. Several seismic studies [9,10,11,12,13,14,15] were conducted to map bottom-simulating reflectors (BSRs), which are used as an indicator for the base of the structure I (sI) gas hydrate stability zone (GHSZ). The shallow feather edge of the sI gas hydrate systems in ~720 m water depth marks the onset of BSRs towards deeper water [19,20,21]. Gas venting is seen only in water depths shallower than the 720 m feather edge of the current GHSZ [17,19,20,21,22,23,24]
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