Lydonia Canyon Research Articles

Benthic species diversity along a depth gradient: Boston Harbor to Lydonia Canyon

Abstract Benthic infaunal samples collected from depths ranging from 5.9 to 2180 m, from nearshore in Boston Harbor to offshore on the continental slope off the coast of Massachusetts, USA, were evaluated for changes in diversity with depth using expected species at a subsample size of 100, ES(100), as well as Fisher's log-series alpha. All samples were processed with fine mesh (0.3 mm) screens and identified by the same team of researchers, who provided a high and comparable level of expertise. Both measures of diversity were made at the single sample level. An analysis of the variation in these measures, based on a linear mixed model, showed that the largest source of variation was due to depth followed by stations within the same depth range. Variation between cruises/years was relatively small. Communities from the shallowest harbor stations out to 168 m at the edge of the continental shelf had a wide range of diversities, but exhibited no apparent pattern of change with depth or sediment type. The highest diversities were found at mid-slope depths (1220–1350 m). Diversities at 2065–2180 m overlapped with those from mid-slope depths, but were generally lower.

Metals and organic contaminants in northwest Atlantic deep-sea tilefish tissues

Data are presented on trace metal and organic hydrocarbon (PCBs, PAHs, and chlorinated pesticides) concentrations in muscle, liver, gonad, and other tissues from two small 1981–1982 collections of tilefish ( Lopholatilus chamaeleonticeps): from near Lydonia Canyon (on Georges Bank) and below Hudson Canyon (off New Jersey). Significant concentrations of trace metals and chlorinated hydrocarbons (PCBs and pesticides) were detected in the tissues, but these were generally within the ranges reported for other deep-sea and continental shelf fish in the Middle Atlantic Bight. Higher chlorinated hydrocarbon concentrations were detected in fish from the Lydonia Canyon area, compared with concentrations detected in the fish from below the Hudson Canyon. The difference appears to be statistically significant for most compounds and no satisfactory explanation can be suggested.

The structure of subtidal currents within and around Lydonia Canyon: Evidence for enhanced cross‐shelf fluctuations over the mouth of the canyon

Between October 1980 and April 1981, currents were measured within Lydonia Canyon and on the adjacent shelf and slope. The amplitude of the subtidal currents over the shelf and slope ranged between 10 and 30 cm s−1, but within the canyon, they were typically smaller than 5 cm s−1. The subtidal currents had well‐defined spatial structures over the shelf and the slope and in the middle and outer portions of the canyon. The along‐isobath flow over the shelf and slope was unaltered by the canyon. Currents within the canyon and just above it were driven up and down the canyon by the cross‐shelf pressure gradient in geostrophic equilibrium with the along‐shelf flow. The measurements suggest that the Coriolis force on the cross‐canyon flow, turbulent Reynolds stresses, and acceleration of the along‐canyon flow balanced the imposed pressure gradient for flow near the rim of Lydonia Canyon. The Coriolis force was not important in the deeper portions of the canyon, where baroclinic adjustments of the density field began to be an important factor in the momentum balance. A simple model indicates that the magnitude of the horizontal turbulent viscosity coefficient for subtidal flow in this narrow canyon is 106 to 107 cm2 s−1. The mixing indicated by the large amplitude of the viscosity coefficient was probably caused by the strong tidal currents present within Lydonia Canyon. On the shelf, along‐isobath currents were locally driven by the large‐scale component of the wind field; along‐shelf currents were equally correlated with local winds and with winds from sites 700 km northeast of Lydonia Canyon. Wind stress was not correlated with currents over the slope in water deeper than 450 m or with currents within the canyon.

Rates of Modern Sedimentary Processes in Lydonia Canyon off Southern New England: ABSTRACT

Rates of Modern Sedimentary Processes in Lydonia Canyon off Southern New England: ABSTRACT

Georges bank monitoring program: hydrocarbons in bottom sediments and hydrocarbons and trace metals in tissues

Hydrocarbons in sediments and hydrocarbons and trace metals in tissues from Georges Bank were analyzed to evaluate potential changes to the henthic environment resulting from exploratory drilling operations. Sediment hydrocarbon concentrations varied with grain size: concentrations up to 2·5μg/g dry weight total aromatic equivalents occurred in the fine-grained sediments of Lydonia Canyon and the ‘Mud Patch’ area south of Martha's Vineyard, whereas concentrations were less than I μg/g dry weight in sediments from the shallow areas of Georges Bank, at a regional control site, and at the site of drilling operations. Increases in total aromatic equivalents from approximately 0·1 μg/g dry weight to 0·4 μg/g dry weight were measured in sediments from a site 0.25 km from the drill rig concurrent with drilling operations. Petrogenic hydrocarbons were detected in both drilling fluid extracts and in sediments collected during drilling operations, suggesting short-term deposition of drilling discharges in near-rig sediments. Drilling discharge residues were not observed in the near-rig sediments one month after drilling operations were terminated. Furthermore, hydrocarbon residues from drilling discharges werenot observed in sediments from stations located at distances greater than 6 km from the drill site either during or subsequent to the drilling operations.

Composition and morphology of ferromanganese coatings on glacial erratics in Lydonia Canyon, United States East Coast

Ferromanganese coatings have been found on glacial erratics in Lydonia Canyon, off the United States northeastern coast. The coatings, which are about 17 μm thick, consist of an outer manganese-rich layer which covers the top of the erratic, a middle transitional layer, and an internal iron-rich layer that encircles the entire surface of the erratic. Chemical analyses of the coatings, when compared with similar data on abyssal marine ferromanganese deposits, reveal comparable Mn/Fe ratios, higher P and Ti concentrations, and an order of magnitude less of Co, Ni, Cu, and most other metals. A comparison of the Lydonia Canyon coatings with desert varnishes reveals obvious chemical, mineralogical, and morphological differences.

Role of submarine canyons in shaping the rise between Lydonia and Oceanographer canyons, Georges Bank

Three large submarine canyons, Oceanographer, Gilbert, and Lydonia, indent the U.S. Atlantic continental shelf and, with four additional canyons, dissect the continental slope in the vicinity of Georges Bank. On the upper rise, these canyons merge at a water depth of approximately 3100 m to form only two valleys. Differences in channel morphology of the canyons on the upper rise imply differences in relative activity, which is inconsistent with observations in the canyon heads. At present, Lydonia Canyon incises the upper rise more deeply than do the other canyons: however, seismic-reflection profiles show buried channels beneath the rise, which suggests that these other six canyons were periodically active during the Neogene. The rise morphology and the thickness of inferred Neogene- and Quaternary-age sediments on the rise are attributed to the presence and activity of the canyons. The erosional and depositional processes and the morphology of these canyons are remarkably similar to those of fluvial systems. Bear Seamount, which has approximately 2000 m of relief on the rise, has acted as a barrier to downslope sediment transport since the Late Cretaceous. Sediment has piled up on the upslope side, whereas much less sediment has accumulated in the “lee shadow” on the downslope side. Seismic-reflection profile data show that Lydonia Canyon has not eroded down to the volcanic rock of Bear Seamount.