IMMeRSS-- Interagency Mission for Methane Research on Seafloor Seeps Completed

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Background

Starting in 2012, an emerging set of water column acoustic images from the National Ocean and Atmospheric Administration’s (NOAA’s) ship Okeanos Explorer hinted at the existence of dozens of previously-unknown seafloor methane seeps on the U.S. Atlantic margin from Cape Hatteras to Georges Bank.  At that time, discussions between NOAA’s Office of Ocean Exploration and Research (OER) and the U.S. Geological Survey (USGS) focused on the subset of deep water (>1000 meters; 3280 feet) seeps, which had no clear explanation. 

Continued U.S. Atlantic margin surveying by the Okeanos Explorer in 2013 revealed hundreds of upper continental slope seeps at water depths of 200 to 600 meters (about 655-1970 feet), a zone that brackets the landward limit of methane hydrate stability on this margin.  By 2014, researchers had identified more than 550 newly-discovered methane seeps on the northern U.S. Atlantic margin, with over two-thirds located on the upper continental slope.  Prior to these discoveries, indirect indicators in Hudson Canyon and direct observations in Baltimore Canyon provided the only evidence of methane seepage on this part of the U.S. Atlantic margin.  

The May 2017 IMMeRSS Mid-Atlantic margin expedition will focus on critical questions related to the timing and source of seep methane emissions, the ecology of benthic communities, and the distribution of active and inactive methane seeps.  The expedition is sponsored by OER, the USGS, the British Geological Survey (BGS), and the U.S. Department of Energy and will use Oceaneering’s Global Explorer remotely-operated vehicle (ROV) to explore seafloor features at methane seeps in the sector from Baltimore Canyon on the north to Cape Hatteras on the south.  Over 250 seeps have been identified in this area, but only five have previously been visited by ROVs or by the DSV Alvin submersible.  IMMeRSS will acquire samples of rocks, sediment, seep organisms, and bottom water at several previously-explored seeps and will also explore seeps that have never before been visited. 

Scientific Goals

The IMMeRSS Mid-Atlantic expedition focuses on the geology, ecology, chemistry, and physics of northern U.S. Atlantic margin methane seeps across the full range of water depths where these seeps have been recognized and over a relatively narrow latitude range (~35.5°N to 38.25°N), where oceanographic conditions should not vary widely.   During the cruise, scientists will:

• Collect special rocks that form near seeps for use in determining the age of methane emissions.
• Sample chemosynthetic organisms (like deep-sea mussels) that live at the seeps to understand these unique communities, their metabolic processes, and their similarities to seep ecosystems in other parts of the Atlantic and in other ocean basins.
• Retrieve seafloor sediment samples to determine pore water characteristics, collect small fauna, and support biomarker studies.
• Record high-resolution imagery of bubble emissions to permit estimation of methane flux across the sediment-water interface.
• Map the seafloor near the seeps with high-resolution methods and image methane plumes in the water column to distinguish active methane seeps sites and locate previously-unknown seeps.Cruise Plan

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Cruise Plan

Between May 3 and 11, 2017, scientists will conduct research aboard the R/V Hugh R. Sharp, which is a 146-ft-long ship in the University-National Oceanographic Laboratory System (UNOLS) fleet.  Depending on the sea state and other factors, the cruise will visit targeted seeps from north to south in the study area. The first dive will explore seeps at the promontory south of Baltimore Canyon, and the final dive in the Cape Hatteras area will visit seeps discovered in March 2016.

Weather-permitting, the ROV Global Explorer will leave the deck early each morning, descend through the water column, and come to a stop hovering above the seafloor at a methane seep site.  Oceaneering’s technical staff will pilot the Global Explorer from a shipboard control van, and scientists will use the ROV’s high-resolution video cameras and sonars, whose outputs are visible on shipboard monitors, to direct the pilot to features of interest on the seafloor.  Global Explorer is equipped with instrumentation to sample seafloor sediments, organisms that live near the seep site, and special rocks that develop due to the presence of methane and to continuously monitor pressure and temperature during the dive.  Following retrieval of the ROV in the afternoon, USGS scientists will commence overnight survey programs to map the seafloor at the site of the next day’s ROV dive and to image methane plumes in the water column to locate actively seeping features.

Outreach

In recent years, OER has been a leader in operating telepresence-enabled discovery cruises, and USGS scientists have been both shipboard and shore-based participants in these OER-led activities.  Telepresence allows scientists onshore to view high-resolution video of the seafloor in real time during ROV dives and to participate in conversations with shipboard scientists about the features being explored.  The audio and video are also available to the public and are sometimes broadcast in classrooms, at aquaria, and during science outreach events. 

The IMMeRSS Mid-Atlantic program will used a streamlined version of telepresence.  During the Global Explorer dives, video of the seafloor will be transmitted to shore in real-time via satellite.  The public can access the video at the NOAA OER portal or on this dedicated YouTube channel.  Instead of an audio link to the ship, the USGS will use social media platforms to describe key features being transmitted in the video and to explain the scientists’ activities. 

Complementary Activities

The 2017 IMMeRSS Mid-Atlantic expedition builds on the discoveries made by the Okeanos Explorer and earlier explorations at the Baltimore Canyon and Norfolk Seep sites by both the Okeanos Explorer and the National Oceanographic Partnership Program –sponsored study funded by the U.S. Bureau of Ocean Energy Management, NOAA, and the USGS.  BGS scientists have carried out reconnaissance geochronologic studies with rock samples obtained by Cindy Van Dover during the 2015 NSF-sponsored SeepC Atlanticexpedition, and these preliminary results will guide the IMMeRSS cruise in acquisition of targeted samples at specific seep sites and in specific locations.  With sponsorship from DOE, the USGS Gas Hydrates Project acquired high-resolution geophysical data in the study area in April 2015 and mapped new seep locations, particularly on the upper slope.  Later in 2015, the USGS collaborated with Oregon State University, UCLA, and GEOMAR (Kiel, Germany) under DOE sponsorship to conduct piston coring, multicoring, water sampling, and geophysical mapping over seep sites from Washington Canyon to the southern New England margin.  In March 2016, the USGS obtained additional data in the area from Cape Hatteras to Baltimore Canyon during a science verification cruise for the new WHOI-operated UNOLS vessel, R/V Neil Armstrong.