Adam Skarke

Evidence for extensive methane venting on the southeastern U.S. Atlantic margin

We present the first evidence for widespread seabed methane venting along the southeastern United States Atlantic margin beyond the well-known Blake Ridge diapir seep. Recent ship- and autonomous underwater vehicle (AUV)–collected data resolve multiple water-column anomalies (>1000 m height) and extensive new chemosynthetic seep communities at the Blake Ridge and Cape Fear diapirs. These results indicate that multiple, highly localized fluid conduits punctuate the areally extensive Blake Ridge gas hydrate province, and enable the delivery of significant amounts of methane to the water column. Thus, there appears to be an abundance of seabed fluid flux not previously ascribed to the Atlantic margin of the United States.

Exploration of the Canyon-Incised Continental Margin of the Northeastern United States Reveals Dynamic Habitats and Diverse Communities

The continental margin off the northeastern United States (NEUS) contains numerous, topographically complex features that increase habitat heterogeneity across the region. However, the majority of these rugged features have never been surveyed, particularly using direct observations. During summer 2013, 31 Remotely-Operated Vehicle (ROV) dives were conducted from 494 to 3271 m depth across a variety of seafloor features to document communities and to infer geological processes that produced such features. The ROV surveyed six broad-scale habitat features, consisting of shelf-breaching canyons, slope-sourced canyons, inter-canyon areas, open-slope/landslide-scar areas, hydrocarbon seeps, and Mytilus Seamount. Four previously unknown chemosynthetic communities dominated by Bathymodiolus mussels were documented. Seafloor methane hydrate was observed at two seep sites. Multivariate analyses indicated that depth and broad-scale habitat significantly influenced megafaunal coral (58 taxa), demersal fish (69 taxa), and decapod crustacean (34 taxa) assemblages. Species richness of fishes and crustaceans significantly declined with depth, while there was no relationship between coral richness and depth. Turnover in assemblage structure occurred on the middle to lower slope at the approximate boundaries of water masses found previously in the region. Coral species richness was also an important variable explaining variation in fish and crustacean assemblages. Coral diversity may serve as an indicator of habitat suitability and variation in available niche diversity for these taxonomic groups. Our surveys added 24 putative coral species and three fishes to the known regional fauna, including the black coral Telopathes magna, the octocoral Metallogorgia melanotrichos and the fishes Gaidropsarus argentatus, Guttigadus latifrons, and Lepidion guentheri. Marine litter was observed on 81% of the dives, with at least 12 coral colonies entangled in debris. While initial exploration revealed the NEUS region to be both geologically dynamic and biologically diverse, further research into the abiotic conditions and the biotic interactions that influence species abundance and distribution is needed.

Opinion: Telepresence is a potentially transformative tool for field science

Field expeditions have long played a critical role in advancing our understanding of the natural world. From the voyage of the Beagle to the HMS Challenger Expedition and the Apollo Moon landings, researchers have visited remote locations to collect samples and in situ data before returning to the laboratory for further analyses.

Automatic detection of sand ripple features in sidescan sonar imagery

A novel image processing technique, based on fingerprint analysis, is applied to sidescan sonar data in order to automatically extract seabed ripple orientation, wavelength, and defect density parameters. The technique is applied to seabed imagery collected on repeat passes over the same ripple field at headings distributed over 360° in order to evaluate ripple parameter extraction across a range of relative angles between the sonar and dominant ripple orientation. The presence of ripples increases the difficulty of identifying objects of interest in sidescan sonar seabed imagery. The potential for utilizing the density of ripple defects as an objective parameter for the quantification of this difficulty in the context of object detection operations is discussed. Results suggest a number of sidescan sonar data analysis applications that are highly compatible with unsupervised detectors and autonomous mission planning processes.

Approaches for quantifying seabed morphology: techniques for utilizing rotary sonar systems

Rotary sonar instrumentation is a versatile tool for the observation of seafloor morphology with a wide variety of potential applications. Here we present a review of rotary sonar development and implementation, followed by analysis of seafloor morphological evolution based on rotary sonar observations made in two contrasting depositional environments: the Delaware Bay mouth, a non-cohesive high-energy environment, and the York River Estuary, a low-energy cohesive environment. Additionally, we present a methodological approach for rotary sonar deployment, utilization, and data analysis.