Date of Award

Winter 2020

Project Type

Dissertation

Program or Major

Oceanography

Degree Name

Doctor of Philosophy

First Advisor

Larry A Mayer

Second Advisor

Mark Finkbeiner

Third Advisor

David Mosher

Abstract

Accurate maps of ocean bathymetry and seafloor habitats are needed to support effective marine ecosystem-based management (EBM) approaches. The central premise of this thesis was to synthesize geomorphological elements of large regions of the deep ocean seafloor to establish standards of characterization for ecosystem-based classification. The approach was to apply semi-automated characterization techniques on seafloor bathymetric data that were originally collected for other purposes. The purpose of generating these maps is ultimately to apply to informing ecosystem-based management for large marine regions. While seafloor classification techniques for habitat classification have been applied in shallow water and generally over more local regions, these techniques have never before been applied at continental-margin scales in such deep water. Over the past decade, the United States has made a substantial investment in seafloor mapping efforts covering over 2.5 million square kilometers of the nation’s potential extended continental shelf (ECS) regions, which extend into deep ocean areas beyond 200 nautical miles from the nation’s shoreline. The entire potential ECS region off the U.S. Atlantic margin has been mapped by researchers at the University of New Hampshire’s Center for Coastal and Ocean Mapping/Joint Hydrographic Center (CCOM/JHC). Extensive complimentary mapping datasets collected by the National Oceanic and Atmospheric Administration’s Office of Ocean Exploration and Research (NOAA OER) have been acquired in adjacent U.S. waters off the East Coast covering the continental slope submarine canyons region and a majority of the Blake Plateau. The focus of this thesis is on demonstrating that data gathered with the initial purpose of establishing a potential extended continental shelf claim can further be used to support EBM efforts and sound marine spatial planning. The approaches developed here could be effectively applied to ECS and ocean exploration data sets collected world-wide to leverage substantial additional value from broad-scale ocean mapping efforts. This thesis posited and tested three hypotheses: 1) Broad-scale bathymetric data of the U.S. Atlantic margin collected for ECS and deep sea exploration purposes are useful to consistently classify ecological marine units of the seafloor and generate value-added characterization maps of large regions. 2) Transparent, repeatable, and efficient semi-automated geomorphic analysis methods employing the Coastal and Marine Ecological Classification Standard (CMECS) as an organizational framework produce useful habitat characterization maps of the U.S. Atlantic margin. 3) Vulnerable cold-water coral (CWC) habitats are identifiable and able to be inventoried and characterized using geomorphic analysis and CMECS classification of bathymetric data. These three research hypotheses were tested through classification and characterization studies of three distinct regions of the U.S. Atlantic margin at different scales (an individual seamount feature, the continental slope and abyssal plains, and a continental margin borderland) ranging across a diversity of marine habitats. An automatic segmentation approach to initially identify landform features from the bathymetry of these study areas was completed and then translated into CMECS classification terminology. Geomorphic terrain classification methods were applied to the continental slope and the abyssal plain of the U.S. Atlantic margin ECS region covering a 959,875 km2 area. Landform features derived from the bathymetry were then translated into complete coverage geomorphology maps of the region utilizing CMECS to define geoforms. Abyssal flats made up more than half of the area (53%), with the continental slope flat class making up another 30% of the total area. Flats of any geoform class (including continental shelf flats and guyot flats) made up 83.06% of the study area. Slopes of any geoform classes make up a cumulative total of 13.26% of the study region (8.27% abyssal slopes, 3.73% continental slopes, 1.25% seamount slopes), while ridge features comprise only 1.82% of the total study area (1.03% abyssal ridges, 0.63 continental slope ridge, and 0.16% seamount ridges). Using methods developed to classify the ECS dataset, bathymetric data from twenty multibeam sonar mapping surveys of the Blake Plateau region were used to derive a standardized geomorphic classification capable of quantifying cold-water coral (CWC) mound habitats. Results documented the most extensive CWC mound province thus far discovered and reported in the literature. Nearly continuous CWC mound features span an area up to 472 km long and 88 km wide, with a core area of high density mounds up to 248 km long by 35 km wide. A total of 59,760 individual peak features were delineated, providing the first estimate of the overall number of potential CWC mounds mapped in the Blake Plateau region to date. Five geomorphic landform classes were mapped and quantified: peaks (342 km2), valleys (2,883 km2), ridges (2,952 km2), slopes (15,227 km2), and flats (49,003 km2). The complex geomorphology of eight subregions was described qualitatively with geomorphic “fingerprints” and quantitatively by measurements of mound density and vertical relief. Ground-truth from 23 submersible dive videos revealed coral rubble to be the dominant substrate component within the peak, ridge, and slope landforms explored, thereby validating the interpretation of these bathymetric features as CWC mounds. Results indicated that the Blake Plateau supports a globally exceptional CWC mound province of heretofore unprecedented scale (at least for now) and diverse morphological complexity. This dissertation has successfully characterized the geomorphology of vast regions of the deep ocean floor off the U.S. Atlantic margin for ecosystem-based management purposes. It has applied techniques and established standards of classification that can be applied to other regions throughout the World. This latter point is critical as there are ongoing international efforts today to map the entirety of the World's oceans at meaningful scales and these techniques can synthesize this information in meaningful ways. Furthermore, the need for such syntheses is paramount in order to successful manage (conserve and preserve) the living and non-living resources of the ocean. This thesis shows a way forward for such endeavors, and emphasizes 1) the applicability of data acquired for other purposes to be applied to this purpose, and 2) the need for standards to define and describe marine habitats so that all governments, managers, biologists, geoscientists, and other ocean stakeholders communicate using the same language.

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