Abstract Biologic studies along the Atlantic coast of North America, as well as elsewhere in the world, have been far more numerous than studies of other aspects of oceanography. Similarly, ease of access has led to a dominance in knowledge of shore and shallow-water forms. The requirements for ships, expensive equipment, and research coordination effectively restrict deep-water biology to large organizations. Thus, the more important early collections and studies of the offshore area were made by the U.S. Fish Commission (now the National Marine Fisheries Service) because of the interests of a succession of farsighted directors and active scientists. Detailed studies of benthic animals and their ecology, such as those of Verrill (1873) in Vineyard Sound, led to the establishment of such regional bureau laboratories as the one at Woods Hole (Galtsoff, 1962), which was founded in 1885, and permitted even more detailed ecologic and other studies (Sumner et al., 1913). Completion of similar work at other laboratories along the coast resulted in the recognition of broad zoogeographic coastal zones that are based chiefly on optimum temperatures for reproduction and both higher and lower limiting temperatures for survival (Dana, 1853; Verrill, 1874; Hutchins, 1947). The generally accepted zoogeographic zones (C. W. Johnson, 1934; Hedgpeth, 1953; Valentine, 1963; Hazel, 1970) are: Arctic—Arctic to Newfoundland; Boreal—Newfoundland to Cape Cod; Virginian—Cape Cod to Cape Hatteras; Carolinian— Cape Hatteras to Cape Canaveral; Caribbean— Cape Canaveral to Tampa; Northeast Gulf— Tampa to Mississippi River; Northwest Gulf— Mississippi River to Matagorda Island; and Texas Transitional—Matagorda Island to

Abstract Although the study of Atlantic continental margin physiog- raphy (Plate la) started with lead-line sounding data centuries ago, it was the development and automation of precision echo sounding in the second quarter of the twentieth century that fostered modern investigation and interpretation (Veatch and Smith, 1939; Emery and Uchupi, 1972). Bottom samples ga- thered in the last four decades have strongly influenced the ex- planations for the development of submarine topography (Field and others, 1979; Hollister, 1973; Knebel, 1981; Milliman and others, 1972; Schlee and Pratt, 1970). High-resolution seismic profiling, side-scan sonar, bottom photography, current meters, and submersibles have allowed more detailed examination and interpretation of selected areas. Key recent articles cited in this chapter, from the vast literature about the Atlantic margin, pro- vide references for an up-to-date understanding of the major physiographic features of the shelf, slope, and rise. In addition, controversies and unresolved questions have been identified. For readers less familiar with the location of physiographic features discussed in the text, the map provided should be of considerable assistance. Because the nature of the shelf physiography and the proc- esses responsible for creating the submarine landforms differ markedly along the U.S. Atlantic shelf (Burk and Drake, 1974; Nairn and Stehli, 1974; Emery and Uchupi, 1972; and Uchupi, 1968), six areas are recognized. From north to south they are: 1) Gulf of Maine, 2) Georges Bank, 3) Southern New England,4) Mid-Atlantic from Rhode Island to Cape Hatteras, 5) South-Atlantic from Cape Hatteras to Southern Florida, and 6) the Bahamas. A seventh section introduces the recent literature on microtopography and related sediment transpont.

Pea Island, Oregon Inlet, and Bodie Island, North Carolina, are severely human-modified barrier-island segments that are central to an age-old controversy pitting natural barrier-island dynamics against the economic development of coastal North Carolina. Bodie Island extends for 15 km from the Nags Head–Kitty Hawk urban area to the north shore of Oregon Inlet and is part of Cape Hatteras National Seashore. Pea Island extends 19.3 km from the southern shore of Oregon Inlet to Rodanthe Village and is the Pea Island National Wildlife Refuge. Bodie and Pea Islands evolved as classic inlet- and overwash-dominated (transgressive) simple barrier islands that are now separated by Oregon Inlet. The inlet was opened in 1846 by a hurricane and subsequently migrated 3.95 km past its present location by 1989. With construction of coastal Highway 12 on Bodie and Pea Islands (1952) and the Oregon Inlet bridge (1962–1963), this coastal segment has become a critical link for the Outer Banks economy and eight beach communities that occur from Rodanthe to Ocracoke. The ongoing natural processes have escalated efforts to stabilize these dynamic islands and associated inlet in time and space by utilizing massive rock jetties and revetments, kilometers of sand bags and constructed dune ridges, and extensive beach nourishment projects. As the coastal system responds to ongoing processes of rising sea level and storm dynamics, efforts to engineer fixes are increasing and now constitute a “human hurricane” that pits conventional utilization of the barriers against the natural coastal system dynamics that maintain barrier-island integrity over the long term.

Abstract A detailed magnetic study of the U.S. Atlantic continental margin north of Cape Hatteras delineates the pattern of basins and platforms that form the basement structure. A 185,000-km, high-sensitivity aeromagnetic survey acquired in 1975 over the entire U.S. Atlantic continental margin forms the basis of this study. Magnetic depth-to-source estimates were calculated for the entire survey using a Werner "deconvolution" type method. These depth-to-basement estimates are integrated with multichannel seismic reflection profiles to interpolate basement structures between seismic profiles. The deep sediment-filled basins along the margin are bounded on their landward sides by blockfaulted continental crust; their seaward sides are marked by the East Coast magnetic anomaly. The trends of the landward sides of these basins vary from 030° in the south to 040° in the north, consistent with a common pole of opening for all of the basins. The ends of these basins are controlled by sharp offsets in the continental crust that underlie the various platforms. These offsets are the result of the initial breakup of North America and Africa and are preserved as fracture zones under the continental rise. The regions west of the various basins are comprised of platforms of Paleozoic and older crust and embayments of Triassic-Jurassic age. The Long Island platform is a series of ridges and troughs. These troughs are oriented northeastward, parallel with the Baltimore Canyon trough and the Georges Bank trough. The Connecticut Valley Triassic basin has a broad magnetic low associated with it that can be traced across Long Island. A similar magnetic signature is associated with the trough between Martha's Vineyard and Nantucket Island, suggesting that it also may be a Triassic basin. The Salsbury Embayment with its Triassic-Jurassic age sediments lies just west of the Baltimore Canyon trough while the Carolina platform, which has a few smaller Triassic basins within predominantly Paleozoic and older crust, lies landward of the Carolina trough. The area around Charleston is another major embayment of Triassic-Jurassic age, and west of the Blake Plateau is the Florida platform with Paleozoic and older crust. A magnetic basement high associated with the East Coast magnetic anomaly separates oceanic crust from the deep sediment-filled troughs. The minimum depth of this high ranges from 6 to 8 km and the susceptibility contrast suggests that it is more likely an uptilted block of oceanic crust than a massive intrusive body. The magnetic anomaly probably is produced by a combination of a basement high and an "edge effect," where the edge is between the uptilted block and flat-lying, nonmagnetic sediments to the west.