Deep-water Mid-Atlantic Canyons
Steve W. Ross and Sandra Brooke
Submarine canyons are dominant features of the outer continental shelf and slope of the US East coast from Cape Hatteras to the Gulf of Maine. There are 13 major canyons in the Middle Atlantic Bight (MAB) region, and minor canyons are abundant. The canyons vary in size, shape, and morphological complexity; some were scoured by the flow of rivers during past low sea level periods, but most formed via other erosional processes, such as mud-slides, debris flows, and turbidity currents.
Cutting deeply into the bottom and linking the shelf to the deep sea, these conduits funnel anthropogenic pollutants, organic carbon, and sediments from shallow to deeper waters. The most southerly of these canyons (just north of Cape Hatteras) occur in an extremely dynamic and productive area known as The Point. The Point has been characterized as one of the hottest fishing spots on the east coast, apparently fueled by upwelling generated by the collision of several major currents over complex bottom topography. Further north, large canyons (e.g., Norfolk, Baltimore, Washington, Hudson, Lydonia) occur at regular intervals (Figure 1).
The geology of these features has been well-studied; however, despite their well-known biological productivity, biological data are quite limited (particularly deeper than 200 m). While there are studies on fishes at The Point and a few of the canyons to the north, there is very little information on the benthic invertebrate communities of the slope. We know that vulnerable and productive habitats such as deep-sea corals and hydrocarbon seeps occur in and around some of these canyons, yet these habitats are poorly explored. The canyons between Cape Hatteras and Cape Cod are less well-known than those further north, and yet these are the subject of potential oil exploration, intensive fisheries, and are possible National Marine Sanctuary (NMS) candidates. Some of the areas around the Mid-Atlantic canyons, as well as The Point, have been designated as Essential Fish Habitat by the Fishery Management Councils.
The middle Atlantic includes some of the most historically significant waters in the US. The approaches to Chesapeake and Delaware Bays have a long history of exploration, warfare, commerce, fishing, and recreation, leaving a rich, but poorly understood, repository of cultural material on the seafloor. This diversity and intensity of human activity along the middle Atlantic region has created an important submerged cultural landscape. The ocean floor is marked by fishing vessels (and their gear), warships, military experiments and ammunition, and the remnants of commercial shipping dating back 400 years. While the area is historically significant and archaeologically sensitive, gaps in our knowledge are extensive and much of the reported information about shipwreck locations is incorrect and/or inaccurate
Our first activity in this project was to conduct Seafloor Mapping of major canyons and potential shipwreck sites using the NOAA Vessel Nancy Foster, and this was completed in June 2011. The 2012 mission is divided into 3 legs, all of which will have specific related activities. During daylight hours we will use the ROV Kraken II (Univ. Conn) for 12-hour ROV surveys and sampling. At night we will conduct non-ROV sampling, including box coring, bottom and mid-water trawling, deployment of four benthic landers and two moorings, multibeam mapping, CTD and water sampling (using CTD with niskin rosette). Work in Legs I and II will emphasize biological objectives in Baltimore Canyon, with some sampling in Norfolk Canyon en route to and from the port in Norfolk. Leg III will focus on archaeological targets in and around the Norfolk Canyon area, with some emphasis on biological objectives.
These canyon ecosystems are important targets of study for the following reasons:
They appear to be biodiversity and productivity hotspots, yet biological studies are lacking.
They harbor the only known natural hard substrata and deep-sea coral communities in the region.
They may be impacted by proposed hydrocarbon leases
They are sites of intense recreational and commercial fishing activity (e.g., tilefish, lobsters, red crab, tuna, swordfish).
They include sites of cultural historical interest (i.e., shipwrecks).
They may include the only known cold seep sites north of Cape Hatteras.
This new project represents a collaborative effort among the Bureau of Ocean Energy Management (BOEM), Continental Shelf Associates (the BOEM contractor) and their academic partners, NOAA Office of Ocean Exploration and Research (provider of ship time and equipment), and the US Geological Survey. The study concept, oversight, and funding were provided by the U.S. Department of the Interior, BOEM, Environmental Studies Program under U.S. Department of the Interior, BOEM, Environmental Studies Program Contract No. M10PC00100.