Norfolk Canyon Research Articles

Parasitism of Galatheid Crustaceans From the Norfolk Canyon and Middle Atlantic Bight By Bopyrid Isopods 1,2)

Among twelve species of galatheid and one species of chirostylid Crustacea collected in the vicinity of Norfolk Canyon off eastern U.S.A., four galatheids, Munida iris iris, M. longipes, M. microphthalma and Munidopsis rostrata were found to be infested with bopyrid isopod parasites Munida iris iris was the most heavily parasitized host species with incidence of infestation by Anuropodione carolinensis ranging from 2.0-5.0%. Male M. iris iris were significantly more numerous than females and also had a greater incidence of infestation by bopyrids than females. The size of female A. carolinensis was found to be related to size of the host, which suggests simultaneous molts for both species. Male A. carolinensis were found to have pleons which were either fused, completely segmented, partly segmented or with slight lateral undulations. Significant size differences between males with fused, undulate, and segmented pleons may indicate impending feminization of males with segmented pleons. Single occurrences of bopyrids were observed on the other host species. Munida microphthalina was infested with Bonnieria americana. Munidion longipedis was found on Munida longipes and an undescribed bopyrid was found on Munidopsis rostrata.

Distribution, Morphology, Mechanisms, and Ages of Sediment Slides on Eastern Continental Margin--Cape Cod to Florida: ABSTRACT

Recent mapping off eastern North America has revealed four areally extensive slide zones between the Blake-Bahama Outer Ridge and Long Island. These slide zones are recognized on the basis of 3.5-kHz records and by the structures present in piston and box cores. The distribution of piston cores containing slump and debris-flow structures indicates that mass movements have taken place in this region on a wide scale and that slumping and sliding of sediments from the slope and upper rise onto the middle and lower rise are ubiquitous in the region during recent geologic time. The slides appear to originate on the continental slope and upper rise and appear to have occurred in multiphase events. In the area south of Baltimore Canyon a series of apparently disconnected 20 to 30° scarps are present within the stratified hemipelagic sediments of the upper rise and slope. Large volumes of sediment which now cover an area of at least 2,000 sq km moved down through the valleys onto the middle rise (~3,100 m). The sudden loading of material appears to have triggered a series of smaller slides in deeper water (3,100 to 3,600 m), and this sediment then moved down onto the lower rise to depths as great as 4,200 m, forming a narrow mudflow tongue 10 km wide and 100 km long which appears to be disconnected from the shallower flows. Three very large slide zones, each in excess of 10,000 sq km, occur on the slope and rise: (1) north of the End_Page 444------------------------------ Blake Outer Ridge, (2) between Washington and Norfolk canyons, and (3) southeast of Long Island. Deposits resulting from these events extend across the rise to depths greater than 4,000 m. In the zone north of the Blake Outer Ridge, the deposits extend onto the Hatteras Abyssal Plain to a water depth of 5,400 m. The distribution of most of the major slide zones appears to relate to the position of canyon systems and may be due to the rapid buildup of sediment over-flowing from the canyons during the last glacial stage. Occasional large intraplate earthquakes such as the 1886 Charleston or the 1929 Grand Banks events may be the direct triggering mechanism. The ages of the slides are as young as middle Holocene. In time, the slope and rise probably will reach an equilibrium point (this may already be the situation), and the frequency of large-scale slides will decrease drastically until the next glacial stage. End_of_Article - Last_Page 445------------

Biology of the Morid Fish Antimora rostrata in the Western North Atlantic

From otter trawl catches in the Middle Atlantic Bight, blue hake, Antimora rostrata, were found at depths of 790 to at least 2930 m in the Norfolk Canyon area; maximum abundance was between 1300 and 2500 m. Available data indicate that the blue hake is more abundant in the western than the eastern North Atlantic. Males were smaller in average size than females and a skewed sex–depth relationship was found with a larger percentage of the catch in shallower depths being male. In Canadian Atlantic waters A. rostrata live in water at least 500 m shallower. The Middle Atlantic continental slope may serve as a feeding habitat for this species; the reproductive and larval portions of its life history are probably completed in the northern part of its range. Key words: Antimora rostrata, bathymétrie distribution, reproduction

Aspects of the Biology and Morphology of the Snake Eel, Pisodonophis cruentifer (Pisces, Ophichthidae)

Variability in meristic and morphometric characters and dentition of the snake eel, Pisodonophis cruentifer, is presented. Pisodonophis cruentifer is distributed from the Laurentian Channel in the north to just north of Cape Hatteras in the south and is most abundant between 150 and 400 m in the Norfolk Canyon area. Males collected in June 1973 possessed mature spermatozoa in testicular tissue while females had yolk-laden eggs 0.6–1.0 mm in diameter. The total length−fecundity relation is log10 y = 4.28696 (log10 x) − 7.33402, where y = total fecundity and x = total length in millimeters. Gross and microscopic morphology of the gonads is presented. Morphological adaptations of P. cruentifer for burrowing into the substrate are contrasted with the benthopelagic eel, Synaphobranchus qffinis, and actual burrowing into the substrate is documented.

Mineralogic Composition of Sand-Sized Sediment on the Outer Margin off the Mid-Atlantic States: Assessment of the Influence of the Ancestral Hudson and Other Fluvial Systems

The mineralogic composition of surface and core sand samples from the outer shelf, slope, and rise between Hudson and Norfolk Canyons off the mid-Atlantic states has been determined to evaluate the relative contributions of major drainage areas lying to the north and west. The observed mineralogic uniformity in space and time is largely attributable to the fact that the principal fluvial supply to this sector during the Pleistocene and Holocene Epochs was through river systems, all of which drain some part of a large and geologically variable glaciated region. Further complications in distinguishing specific sources probably result from the extensive migration of the Hudson River across the subaerially exposed continental shelf during various Pleistocene low sea-level stands, which produced considerable homogenizing of shelf sediment prior to their downslope transfer onto the continental rise. Trends of the major light and heavy mineral groups on this outer continental margin show that the ancestral Hudson probably extended at least to the head of Baltimore Canyon. The distribution of a distinctive variety of the mineral axinite suggests that the Hudson may have even exerted its influence as far south as the head of Washington Canyon, or some 140 km farther to the south than previously postulated. Vertical time-related changes in the mineral assemblages in slope and rise cores show a broadly similar pattern throughout the region. Vertical variability is particularly notable in cores on the slope off the Norfolk-Washington Canyon pair, where there appears to be a progressive increase in the influence of a western (Delaware-Susquehanna) supply in recent time. The marked compositional variation of sand with depth in cores from the lower rise is best explained by fluctuations in materials transported from adjacent shelf sources downslope to the southeast (lateral input and transport model) rather than by significant long-term dispersal parallel to isobaths (contour-current transport model).

Seismic profiling survey of the east coast submarine canyons Part 1. Wilmington, Baltimore, Washington and Norfolk Canyons

Seismic profiler recordings indicate that the morphology of Wilmington, Baltimore, Washington, and Norfolk Canyons are erosional not structural in origin. No evidence of folding or faulting was observed on any of the profiles.