Description: Purpose of the cruise M114 At the so-called asphalt volcanoes in the southern Gulf of Mexico heavy oil is seeping at the seafloor where it remains as asphalt deposits. Discovered and preliminarily surveyed during SO174 and M67/2 expeditions, these sites are subject for detail studies during M114 focusing on mapping with autonomous underwater vehicle (AUV MARUM-SEAL), deep-towed sidescan sonar (DTS-1), sediment echosounder (Parasound), multibeam echosounder (EM122), and remotely operated vehicle MARUM-ROV Quest. The overarching objective is to better understand the impact, fate, and decay rates of oil in the deep-sea environment. Heavy oil and gas bubbles are emitted from the 1200 to 2900 m deep seafloor in the hy-drocarbon province Campeche Knolls in the southern Gulf of Mexico. The viscous heavy oil flows across the seafloor, loses volatile compounds, solidifies, and is converted to asphalt with time. Due to the fact that the heavy oil remains at the seafloor, these sites are natural laboratories to study the impact of oil on deep-sea ecosystems, and the time scales of oil and asphalt degradation. These subjects are very timely, and can help understanding effects of deep water oil spills as caused by the 2010 Deepwater Horizon accident in the northern Gulf of Mexico. We propose to study the extent of oil emissions and asphalt deposits using sidescan sonar and to investigate them further employing ROV Quest. A further major topic of the proposed cruise addresses the question whether or not methane can reach the sea surface and may contribute to the pool of greenhouse gases. The fact that seepage of oil-coated gas bubbles leads to oil slicks at the sea surface and enhanced methane concentrations was recently shown in the north-ern Gulf. It can be assumed that similar efficient transport processes for methane exists in the area of the Campeche Knolls, where oil slicks have been observed in association with about ~30 individual seafloor structures.

Description: Abstract & Purpose of the cruise M114 At the so-called asphalt volcanoes in the southern Gulf of Mexico heavy oil is seeping at the seafloor where it remains as asphalt deposits. Discovered and preliminarily surveyed during SO174 and M67/2 expeditions, these sites are subject for detail studies during M114 focusing on mapping with autonomous underwater vehicle (AUV MARUM-SEAL), deep-towed sidescan sonar (DTS-1), sediment echosounder (Parasound), multibeam echosounder (EM122), and remotely operated vehicle MARUM-ROV Quest. The overarching objective is to better understand the impact, fate, and decay rates of oil in the deep-sea environment. Heavy oil and gas bubbles are emitted from the 1200 to 2900 m deep seafloor in the hy-drocarbon province Campeche Knolls in the southern Gulf of Mexico. The viscous heavy oil flows across the seafloor, loses volatile compounds, solidifies, and is converted to asphalt with time. Due to the fact that the heavy oil remains at the seafloor, these sites are natural laboratories to study the impact of oil on deep-sea ecosystems, and the time scales of oil and asphalt degradation. These subjects are very timely, and can help understanding effects of deep water oil spills as caused by the 2010 Deepwater Horizon accident in the northern Gulf of Mexico. We propose to study the extent of oil emissions and asphalt deposits using sidescan sonar and to investigate them further employing ROV Quest. A further major topic of the proposed cruise addresses the question whether or not methane can reach the sea surface and may contribute to the pool of greenhouse gases. The fact that seepage of oil-coated gas bubbles leads to oil slicks at the sea surface and enhanced methane concentrations was recently shown in the north-ern Gulf. It can be assumed that similar efficient transport processes for methane exists in the area of the Campeche Knolls, where oil slicks have been observed in association with about ~30 individual seafloor structures.

Description: Hydrocarbon seepage is a widespread process at the continental margins of the Gulf of Mexico. We used a multidisciplinary approach, including multibeam mapping and visual seafloor observations with different underwater vehicles to study the extent and character of complex hydrocarbon seepage in the Bay of Campeche, southern Gulf of Mexico. Our observations showed that seafloor asphalt deposits previously only known from the Chapopote Knoll also occur at numerous other knolls and ridges in water depths from 1230 to 3150 m. In particular the deeper sites (Chapopopte and Mictlan knolls) were characterized by asphalt deposits accompanied by extrusion of liquid oil in form of whips or sheets, and in some places (Tsanyao Yang, Mictlan, and Chapopote knolls) by gas emission and the presence of gas hydrates in addition. Molecular and stable carbon isotopic compositions of gaseous hydrocarbons suggest their primarily thermogenic origin. Relatively fresh asphalt structures were settled by chemosynthetic communities including bacterial mats and vestimentiferan tube worms, whereas older flows appeared largely inert and devoid of corals and anemones at the deep sites. The gas hydrates at Tsanyao Yang and Mictlan Knolls were covered by a 5-to-10 cm-thick reaction zone composed of authigenic carbonates, detritus, and microbial mats, and were densely colonized by 1-2 m-long tube worms, bivalves, snails, and shrimps. This study increased knowledge on the occurrences and dimensions of asphalt fields and associated gas hydrates at the Campeche Knolls. The extent of all discovered seepage structure areas indicates that emission of complex hydrocarbons is a widespread, thus important feature of the southern Gulf of Mexico.