Ocean circulation promotes methane release from gas hydrate outcrops at the NEPTUNE Canada Barkley Canyon node

Abstract

[1] The NEPTUNE Canada cabled observatory network enables non-destructive, controlled experiments and timeseries observations with mobile robots on gas hydrates and benthic community structure on a small plateau of about 1 km 2 at a water depth of 870 m in Barkley Canyon, about 100 km offshore Vancouver Island, British Columbia. A mobile Internet operated vehicle was used as an instrument platform to monitor and study up to 2000 m 2 of sediment surface in real-time. In 2010 the first mission of the robot was to investigate the importance of oscillatory deep ocean currents on methane release at continental margins. Previously, other experimental studies have indicated that methane release from gas hydrate outcrops is diffusion-controlled and should be much higher than seepage from buried hydrate in semipermeable sediments. Our results show that periods of enhanced bottom currents associated with diurnal shelf waves, internal semidiurnal tides, and also wind-generated near-inertial motions can modulate methane seepage. Flow dependent destruction of gas hydrates within the hydrate stability field is possible from enhanced bottom currents when hydrates are not covered by either seafloor biota or sediments. The calculated seepage varied between 40-400 mmol CH 4 m À2 s À1 . This is 1-3 orders of magnitude higher than dissolution rates of buried hydrates through permeable sediments and well within the experimentally derived range for exposed gas hydrates under different hydrodynamic boundary conditions. We conclude that submarine canyons which display high hydrodynamic activity can become key areas of enhanced seepage as a result of emerging weather patterns due to climate change. Citation: Thomsen, L., C. Barnes, M. Best, R. Chapman, B. Pirenne, R. Thomson, and J. Vogt (2012), Ocean circulation promotes methane release from gas hydrate outcrops at the NEPTUNE Canada Barkley

Biological and environmental rhythms in (dark) deep-sea hydrothermal ecosystems

“…For instance, in the NEP, measured tides in the Barkley Canyon, another instrumented node from ONC closer to shore, were mixed semi-diurnal/diurnal at 870 m depth (Juniper et al, 2013). In the same canyon, periods of enhanced bottom currents associated with diurnal shelf waves, internal semi-diurnal tides and wind-generated near-inertial motions were shown to modulate methane seepage (Thomsen et al, 2012). While temperature variability in hydrothermal vents at Cleft Segment on the Juan de Fuca Ridge was shown to greatly diminish when current directions did not shift in direction with the tides, it was suggested that, through the modulation of horizontal bottom currents, the modulation of temperature by tides was only indirect (Tivey et al, 2002).…”

“…Several studies reveal the presence of tidal cycles in environmental variables (such as currents, fluid emission, temperature) in the deep sea, particularly in hydrothermal vents (e.g. Tivey et al, 2002;Thomsen et al, 2012;Barreyre et al, 2014;Sarrazin et al, 2014;Lelièvre et al, 2017) and the influence of tides on the deepsea organisms has been previously inferred. Additionally, an actual tidal rhythm has been revealed in visible faunal densities and appearance rate for inhabitants of various deepsea chemosynthetic environments -e.g.…”

Ecological Role of Submarine Canyons and Need for Canyon Conservation: A Review

“…The North East Pacific Time-Series Experiment, (NEPTUNE) network deployed in Barkley Canyon allows to studyin situ rhythmic behavior and species tolerance in response to tidal and inertial fluxes (which has important implications on adult dispersal rates; Sbragaglia et al, 2015;Chatzievangelou et al, 2016), and to multiple climate change variables including methane, pH, pCO2, pO2, salinity, temperature, turbidity, chlorophyll-a (for primary production) . Such monitoring capability can be to date increased by endowing fixed networks of cabled monitoring platforms with semi-mobile rovers, tethered to the nodes, extending the spatial coverage from few m2 to few tens of m2 (Thomsen et al, 2012;Aguzzi et al, 2015). In the NW Mediterranean, the Operational Observatory of the Catalan Sea (OOCS; http://www2.ceab.csic.es/oceans/index_en.html) is a permanent pelagic buoy anchored at 200 m depth at the head of Blanes Canyon (Bahamon et al, 2011).…”

Neogene strontium isotope stratigraphy, foraminifer biostratigraphy, and lithostratigraphy from offshore wells, Queen Charlotte Basin, British Columbia, Canada

“…This is recorded in real time by remotely operated vehicles, crawlers, sensors, and seabed cameras (Thomsen et al 2012;Barnes et al 2013;Purser et al 2013 ups (possibly marking stratigraphic disconformities). Further, since the methane hydrate and associated carbonate deposits are related to deep-sea temperature-pressure relationships, variations of carbonate distribution in the stratigraphy can be influenced by major eustatic and climate changes (Xu et al 2001).…”