Dissolved Gases in Black Sea Sediments

Abstract

Most Black Sea cores contained dissolved gases which expanded as the cores were brought to the surface. This caused the core sections to be separated at various points. Some cores contained sufficient gas to blow the core out the end of the barrel upon removal of the core catcher. The gases, which were sampled and analyzed on shipboard, were mostly methane with small amounts of carbon dioxide and other hydrocarbon gases. The equipment on the ship was not sensitive enough to analyze the higher hydrocarbon gases in detail so this was done at Woods Hole Oceanographic Institution. About 300 gas samples were analyzed from Holes 379, 38O/38OA, and 381. Data for the higher hydrocarbons, ethane through the pentanes are shown in

Basin-wide estimates of the input of methane from seeps and clathrates to the Black Sea

“…While a few direct observations of individual seeps have led to a regional estimate of fluxes of CH 4 from seeps to the atmosphere [7], there are no estimates of the quantity of CH 4 contributed to the entire Black Sea by these sources. Recent discoveries of globally distributed seeps suggest that CH 4 released from seeps and clathrates may play a role in the global and oceanic CH 4 budget [10,20,21] and climate change [22][23][24]. One of the limitations to understanding the role of these reservoirs in global carbon cycles and climate change is that there have been few attempts to extend individual observations to larger spatial scales.…”

“…During the last decade, numerous seeps and mud volcanoes, emitting or capable of emitting CH 4 , have been identified on the shelf and slope of the northern Black Sea [7][8][9][10][11]. Methane clathrate hydrates (clathrates), an important global CH 4 reservoir estimated to contain over 10 3 times more CH 4 than the atmosphere [15], are also present in deep Black Sea sediments [11,12], and represent an unknown CH 4 source.…”

“…Methane clathrate hydrates (clathrates), an important global CH 4 reservoir estimated to contain over 10 3 times more CH 4 than the atmosphere [15], are also present in deep Black Sea sediments [11,12], and represent an unknown CH 4 source. The stability of clathrates is governed by pressure, temperature, and CH 4 concentration [16][17][18][19].…”

“…The stability of clathrates is governed by pressure, temperature, and CH 4 concentration [16][17][18][19]. Even in a pressure-temperature zone where clathrates are stable, a clathrate will decompose if the water surrounding it contains a CH 4 concentration below what is necessary to form clathrates. This condition is not met for clathrates outcropping at the seafloor and in some sediments.…”

“…[1][2][3][4][5][6][7][8][9][10][11][12][13][14]). Concentration and oxidation rate measurements of CH 4 dissolved in the water column and sediments [1][2][3][4][5][6] have been used to assemble CH 4 geochemical budgets for the entire Black Sea [1] and the north-western shelf [5]. These studies indicate that the Black Sea is the largest surface water reservoir of dissolved CH 4 (96 Tg) of which 0.066 Tg yr − 1 are emitted into the atmosphere [1].…”