Analysis of a longitudinal ripple from the Nova Scotian continental rise

McCave, I Nick; Hollister, Charles D.; DeMaster, David J.; Nittrouer, Charles A.; Silva, A.J.; Yingst, Josephine Y.

doi:10.1016/0025-3227(84)90205-6

Cited by 38 publications

(7 citation statements)

References 14 publications

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“…Like the first report based on these samples (GAGE et a/., this volume), the present study also includes comparison, where appropriate, with a set of six (non-"vegematic") box cores taken in 1975 from the southern Rockall Trough Permanent Station (GAGE, 1977) and in box core samples (see THISTLE et al, 1985) from a site on the Nova Scotian Rise which experiences periodic major disturbance from sediment resuspension during benthic "storms" (KERR, 1980;MCCAVE et al, 1984;GROSS and WILLIAMS, 1991).…”

Section: --mentioning

confidence: 99%

“…Areas intermittently experiencing energetic flow resulting from eddy kinetic energy generated at the sea surface and transmitted to great depths may comprise surprisingly large areas of the deep-sea floor (see HOLLISTER and NOWELL, 1991). The High Energy Benthic Boundary Layer Experiment (HEBBLE), at 4,820m depth on the Nova Scotia continental rise (N. W. Atlantic), has provided evidence of periods of massive erosion during benthic "storms" followed by deposition of sediment during quiescent intervals (HOLLISTER and MCCAVE, 1984). THISTLE et a/.…”

Section: Introductionmentioning

confidence: 99%

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Deep‐Sea Macrobenthic Communities at Contrasting Sites off Portugal, Preliminary Results: II Spatial Dispersion

Lamont

Gage

Tyler³

1995

Intl Review of Hydrobiology

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Small-scale, biogenic processes are thought to be important in creating a mosaic of microhabitats that allow co-existence of the large numbers of rare species found in deep-sea sediments. However, the large-scale effects of hydrodynamic disturbance seem likely to be important in high-energy settings on the deep-sea bed. This is investigated by examining spatial dispersion patterns in the macrobenthic populations at two deep-sea sites off Portugal. The widely differing conditions of sediment disturbance at the two sites are related to differences in macrobenthic species diversity and dominance.Closely grouped, transponder-mapped, replicate box core samples, each divided into 25 "vegematic" subcores permitted analysis of dispersion patterns at two spatial scales at each site. One site was located on the Tagus Abyssal Plain (TAP), and the other in the nearby Setubal Canyon (SC) where ripple bedfoms indicate vigorous bed flow, probably with a tidal periodicity. Greater aggregation at the scale of tens of metres is indicated from the observed numbers of SC species per box core being wide underestimates of the value predicted by rarefaction of the pooled total compared to those from TAP. Variancehean ratios for individual species of bivalves and tanaids indicated more aggregation in spatial distribution between box cores from SC than from TAP. Dispersion chi-square analysis also indicated more non-randomness at SC between box cores than for the TAP cores. However, low faunal abundances in the TAP samples render the results of analyses for this site somewhat inconclusive and therefore the trend indicating less aggregation at TAP compared to SC must be regarded as weak for the groups examined. Analyses of the distribution of tanaids, and bivalves at a 100 x 100mm subcore scale showed no convincing significant departure from random expectation, but low abundances in these groups reduces the sensitivity of the tests applied. Between-core aggregation detected at SC may reflect habitat variation resulting from the varying depth within the area of sampling, while within-core patchiness could be influenced by the ripple bed forms on the sediment.

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Section: --mentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Deep‐Sea Macrobenthic Communities at Contrasting Sites off Portugal, Preliminary Results: II Spatial Dispersion

Lamont

Gage

Tyler³

1995

Intl Review of Hydrobiology

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“…surface few centimetres of seafloor sediments, which are extremely mobile and subject to very rapid erosion and deposition McCave et al 1984;Gross & Williams 1991;Gross & Dade 1991). In a matter of days to weeks, seafloor conditions can change from a state of tranquil deposition and sediment reworking by benthic organisms to a state of extreme storm scour.…”

Section: Geological and Oceanographic Settingmentioning

confidence: 99%

“…largest bedforms photographed are longitudinal ripples (LRs) (Figs 9D-F & 10) which parallel the direction of flow and have roughly symmetrical, triangular cross-sections (Flood 1981;Tucholke 1982;McCave et al 1984;Swift et al 1985). LRs often appear in bottom photographs as apparently consolidated sediment that is tool marked by bedload debris (Fig.…”

Section: Bottom Currents Interpreted From Seafloor Photographymentioning

confidence: 99%

“…This unit is of sandy mud, the sand being chiefly planktonic foraminifera and c.10.0%. The material is stiffer than the surface sediment (shear strength up to 4 kPa, McCave et al 1984) and has <47% water content. The unit is extensively burrowed and the upper part with current lamination and fine-scale burrows has little preservation potential, so the resulting deposit is pervasively bioturbated (Fig.…”

Section: Sediment Properties: H E B B L E Areamentioning

confidence: 99%

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Contourites of the Nova Scotian continental rise and the HEBBLE area

McCave

Chandler

Swift

et al. 2002

Memoirs

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The Nova Scotian continental rise is swept by a Deep Western Boundary Current system comprising layers of Labrador Sea Water overlying a core of Norwegian Sea Overflow Water at depths of 3100-3900 m, and below about 4600 m a cold stream of southern-source water. Seismic-reflection data show that the rise contains sediments transported downslope in channels and debris lobes, but there is also evidence of current-controlled deposition and erosion in the post-Eocene sequence. The rise is now mantled by Holocene contourites that have accumulated at a rate of c. 6 cm ka -1 and are <1 m thick. Bottom photographs show a zonation in current effects and bedform types, with longitudinal ripples and strong currents prevalent at 4800-5000 m, smaller bedforms and progressively weaker currents up to c. 4000 m, and mostly tranquil seafloor above 4000 m. Bedform scales and orientations also suggest significant short-term (hours to weeks) variability in current velocity but a mean contour-following flow to the southwest at longer time scales (months to years). These structures are not preserved in the sediment because of pervasive bioturbation and the uppermost layers have negligible preservation potential. The sediments display clear current controlled effects in their grain-size structure involving both percentage of (foraminiferal) sand, and size and percentage in the 10-63 pm range, the 'sortable silt'. There is a sand-rich zone at 4800-4900 m and below 5000 m, and a decreasing silt/clay ratio from 5100 m up to 4000 m. Although much of the sedimentary sequence probably has been emplaced by downslope processes, it has been significantly modified by the Deep Western Boundary Current. Particularly strong and variable currents which rework sediments below c. 4800 m probably are engendered by interaction of Gulf Stream eddies with the DWBC. Although strong currents and upstream input from turbidites and debris flows might be thought to favour a coarse-grained deposit, the facies at the HEBBLE (High Energy Benthic Boundary Layer Experiment) site is muddy contourite with < 12% sand.This was to have been Charley Hollister's paper. He led many cruises to the HEBBLE area between 1979 and 1986, and insights gained from studies of the area are an important part of his scientific legacy. We might have expected to have to help out with production of this paper via some last minute cajoling, but we certainly did not expect the sad task of doing it without him. So this is the best we can do, without his insight, and we dedicate it to Charley's memory.

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Deep‐Sea Macrobenthic Communities at Contrasting Sites off Portugal, Preliminary Results: I Introduction and Diversity Comparisons

Gage

Lamont

Tyler³

1995

Intl Review of Hydrobiology

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Species diversity, faunal composition and abundance in the deep-sea macrobenthos are investigated at two, adjoining deep-sea areas off Portugal experiencing contrasting hydrodynamic conditions in order to test for the importance of disturbance in structuring the community. The first was located at 5,035 m depth on a presumably low current-energy site on the Tagus Abyssal Plain (TAP) and the second was centered in the lower end of the Setubal Canyon (SC) at 3,400111 depth where high levels of hydrodynamic activity are inferred from ripple bedforms visible in sea bed photographs. Closely grouped, transponder-mapped, "vegematic" box core samples were taken at each site. Agglutinated foraminifers numerically dominate the macrofauna (retained by 300 pm sieve) at both sites. Seagruss content in the SC cores indicates downslope detrital input from shallow water which is absent in the TAP samples. This must contribute, possibly with high levels of resuspended particles in near-bed flow, to the almost tenfold difference in abundance of metazoan macrofauna at the two sites. Expected species diversity measured from rarefaction is highest at TAP, both for pooled data and when foraminifers, tanaids and bivalve are considered separately. Evenness (equitability) in species' abundances is also higher at TAP than at SC. These differences are compared with benthic community data from the hydrodynamically disturbed High Energy Benthic Boundary Layer (HEBBLE) site on the Nova Scotia continental rise, and from the Rockall Trough (N.E. Atlantic). In common with these sites, strong bed flow at SC is thought to result in relatively high abundances, lower species richness and greater unevenness by acting to periodically disturb and reduce populations. Differences in the degree to which different faunal groups seem to be affected might be related to differences in lifestyle, particularly burrowing depth.

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Analysis of a longitudinal ripple from the Nova Scotian continental rise

Cited by 38 publications

References 14 publications

Deep‐Sea Macrobenthic Communities at Contrasting Sites off Portugal, Preliminary Results: II Spatial Dispersion

Deep‐Sea Macrobenthic Communities at Contrasting Sites off Portugal, Preliminary Results: II Spatial Dispersion

Contourites of the Nova Scotian continental rise and the HEBBLE area

Deep‐Sea Macrobenthic Communities at Contrasting Sites off Portugal, Preliminary Results: I Introduction and Diversity Comparisons

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