Acoustically detected hydrocarbon plumes rising from 2‐km depths in Guaymas Basin, Gulf of California

Abstract

Plumes extending nearly 1000 m from the 1500–2000 m deep seafloor of Guaymas Basin were detected from below by the 23.5‐kHz inverted echo‐sounder of the Scripps Deep Tow vehicle. Individual sound reflectors (bubbles or drops) rise at approximately 17 cm/s in one plume. The Deep Tow side scan records provide more information on the plumes' structure at the altitude of the vehicle (75 m), where some form multiple side scan targets, one 20 m across. Near‐bottom 4‐kHz profiles show that plumes overlie either young fault traces associated with extensional faulting at the basin's spreading centers or outcrops of tilted beds beside strike‐slip faults. We infer from analysis of the Deep Tow observations, field relationships, and knowledge of the geology of this basin that the plumes are made of light hydrocarbons, perhaps mainly methane, that emanate from seabed seeps. One of the acoustically detected plumes was at a spreading‐axis hydrothermal field, which has many buoyant, acoustically transparent thermal plumes, some of which are rich in dissolved hydrocarbons.

Determination of gas bubble fractionation rates in the deep ocean by laser Raman spectroscopy

“…Our purpose was to test under field condition s a propo sal for ocean CO 2 sequestr ation witho ut prior CO 2 capture (Kajishi ma et al, 1997;Sait o et al, 2000) based upon the marked difference i n solubiliti es of CO 2 (Aya et al, 1997;Haugan and Dr ange, 19 92) and N 2 (Wiebe et al, 1933) gases in cold sea wat er at high pressure. The dissolution b ehavi or of gas bubbles is of f undament al interest to o cean sci entists for reasons as div erse as their role in air-sea gas exchange (Keel ing, 1993), to the fate of gases vent ed from the deep ocean floor (Massoth et al, 1989 ;Merewether et al, 1985;Rehder et al, 2002). Additionally we soug ht t o advance the u se of newly develop ed Ram an spectrometric techniques Past eris et al, 2004) for deep-sea g eochemical studies.…”

Dissolved methane in the sills region of the Gulf of California

“…The rate of thermogenic methane production in Guaymas Basin was found to be so great that it completely masked the abiogenic methane production that would be expected in this active spreading center based on observed 3 He anomalies (Whelan and Lupton 1987). As a consequence of the high methane production rate, many methane-rich thermal plumes have been documented in Guaymas Basin, some extending at least 900 m above the 1500-2000 m deep seafloor (Merewether et al 1985). More recently, massive seafloor gas seepage from depths of 65 to 150 m was reported in the pull-apart Wagner and Consag basins (Canet et al 2010), which are located about 100 km northwest of our study area.…”

“…These pull-apart basins were formed at short spreading centers, many of which are still active, including Guaymas Basin, which is about 100 km southeast of our study area. A combination of highly productive surface waters and input of riverine clastic sediments has led to a high rate of sedimentation and a 1.5-to 2-km-thick deposit of organic-rich sediments in Guaymas Basin (Merewether et al 1985). This rapid deposition of sediments inhibits seafloor eruption, such as that observed at mid-ocean ridges, and intrusion of hot basaltic sills and dikes into the organic-rich sediments is the main igneous activity (Lonsdale and Becker 1985).…”

Modeling of methane bubbles released from large sea-floor area: Condition required for methane emission to the atmosphere

“…Within the hydrate stability zone (HSZ), bubble dissolution is much slower than that above the HSZ Rehder et al, 2002;Merewether et al, 1985), since the formation of a hydrate rim around the bubble has already been proposed and observed .…”