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Impact of Large-Scale Natural Physical Disturbance on the Diversity of Deep-Sea North Atlantic Nematodes
MARINE ECOLOGY PROGRESS SERIES Vol. 214: 121–126, 2001 Published April 26 Mar Ecol Prog Ser Impact of large-scale natural physical disturbance on the diversity of deep-sea North Atlantic nematodes P. J. D. Lambshead1,*, J. Tietjen2, A. Glover1, T. Ferrero1, D. Thistle3, A. J. Gooday4 1Department of Zoology, The Natural History Museum, London SW7 5BD, United Kindom 2Department of Biology, City College of New York, New York, New York 10031 & Division of Invertebrates, American Museum of Natural History, New York, New York 10024, USA 3Department of Oceanography, Florida State University, Tallahassee, Florida 32306-3048, USA 4Southampton Oceanography Centre, George Deacon Division for Ocean Processes, Empress Dock, Southampton SO14 3ZH, United Kindom ABSTRACT: Nematode alpha diversity from 3 physically disturbed sites in the deep North Atlantic was compared with reference sites. Nematode diversity at the HEBBLE benthic storm site was statis- tically, and significantly, lower than at reference sites. Nematode diversity at the Madeira Abyssal Plain site, which was subject to a turbidite dated at 930 BP, also showed a significantly lower diver- sity than reference sites. However, limited data suggest that diversity was not low at a Venezuela Basin turbidite site. The difference in nematode diversity between the 2 turbidite sites is ascribed to a long term change in sediment conditions at the Madeira site. The Venezuela Basin turbidite site has a sedimentation rate greater than the Maderia site by 1 to 2 orders of magnitude, and this was reflected in the sediment profiles. Another possibility is that the Venezuela Basin turbidite is consid- erably older, by at least 1000 yr, than the Madeira turbidite, allowing more time for recolonisation. -
The Long-Term Evolution of the Congo Deep-Sea Fan: a Basin-Wide View of the Interaction Between a Giant Submarine Fan and a Mature Passive Margin (Zaiango Project)
The Congo deep-sea fan: how far and for how long? A basin-wide view of the interaction between a giant submarine fan and a mature passive margin Zahie Anka 1,*, Michel Séranne 2,**, Michel Lopez 2, Magdalena Scheck-Wenderoth 1, Bruno Savoye 3,†. 1. GFZ German Research Centre for Geosciences. Telegrafenberg, 14473 Potsdam, Germany. 2. CNRS-Université Montpellier II. cc 060, Geosciences Montpellier. 34095 Montpellier, France. 3. IFREMER, Geosciences Marines, BP 70 — 29280 Plouzané, France. (*) [email protected] (**) [email protected] (†) deceased 1.- Introduction The Congo deep-sea fan is one of the largest submarine fan systems in the world and one of the most important depocentre in the eastern south Atlantic. The present-day fan extends over 1000 km offshore the Congo-Angola continental margin and it is sourced by the Congo River, whose continental drainage area is the second largest in the world (3.7 106 km²) (Droz et al., 1996) (Fig.1). There is a direct connexion between the river’s drainage basin and the deep basin through an impressive submarine canyon, which cuts down about 950 m at the shelf-break and more than 1300 m at 100 km offshore the coastline (Babonneau et al., 2002). Hence, the direct transfer of terrigenous material onto the abyssal plain takes place through the canyon, by-passing the shelf and upper slope. The submarine fan covers a surface of about 300,000 km² and contains at least 0.7 Mkm³ of Tertiary sediments (Anka and Séranne, 2004; Droz et al., 2003; Savoye et al., 2000). -
SÉRANNE, M., and ANKA, Z., 2005
ARTICLE IN PRESS Journal of African Earth Sciences xxx (2005) xxx–xxx www.elsevier.com/locate/jafrearsci South Atlantic continental margins of Africa: A comparison of the tectonic vs climate interplay on the evolution of equatorial west Africa and SW Africa margins Michel Se´ranne *, Zahie Anka UMR 5573 Dynamique de la Lithosphe`re, CNRS/Universite´ Montpellier 2, 34095 Montpellier cedex 05, France Received 5 February 2005; accepted 18 July 2005 Abstract Africa displays a variety of continental margin structures, tectonic styles and sedimentary records. The comparative review of two representative segments: the equatorial western Africa and the SW Africa margins, helps in analysing the main controlling factors on the development of these margins. Early Cretaceous active rifting south of the Walvis Ridge resulted in the formation of the SW Africa volcanic margin that displays thick and wide intermediate igneous crust, adjacent to a thick unstretched continental crust. The non-vol- canic mode of rifting north of the Walvis ridge, led to the formation of the equatorial western Africa margin, characterised by a wide zone of crustal stretching and thinning, and thick, extensive, syn-rift basins. Contrasting lithologies of the early post-rift (salt vs shale) determined the style of gravitational deformation, whilst periods of activity of the decollements were controlled by sedimentation rates. Regressive erosion across the prominent shoulder uplift of SW Africa accounts for high clastic sedimentation rate during Late Creta- ceous to Eocene, while dominant carbonate production on equatorial western Africa shelf suggests very little erosion of a low hinterland. The early Oligocene long-term climate change had contrasted response in both margins. -
Provenance and Pathways of Late Quaternary Turbidites in the Deep-Water Agadir Basin, Northwest African Margin
Int J Earth Sci (Geol Rundsch) (2009) 98:721–733 DOI 10.1007/s00531-008-0313-4 ORIGINAL PAPER Provenance and pathways of late Quaternary turbidites in the deep-water Agadir Basin, northwest African margin Michael Frenz Æ Russell B. Wynn Æ Aggeliki Georgiopoulou Æ Vera B. Bender Æ Gayle Hough Æ Douglas G. Masson Æ Peter J. Talling Æ Bryan T. Cronin Received: 29 January 2007 / Accepted: 11 March 2008 / Published online: 28 March 2008 Ó Springer-Verlag 2008 Abstract A series of individual turbidites, correlated volume volcaniclastic turbidites are attributed to a Canary over distances[100 km, are present in the recent fill of the Islands landslide source, while several small mud-domi- Agadir Basin, offshore northwest Africa. The aim here is to nated turbidites are interpreted to be locally sourced from unravel multiple turbidite source areas and flow pathways, hemipelagic-draped seamounts (e.g. Turbidite AB10). and show how turbidite provenance studies contribute to Finally, Turbidite AB1 (*1 ka) is only present in the interpretation of flow processes. Agadir Basin turbidites are western Agadir Basin, and is linked to recent ‘‘re-activa- sourced from four main areas, with the majority originating tion’’ of the Sahara Slide headwall. The muddy suspension from the siliciclastic Morocco Shelf; their sand-mud dis- clouds of three large-volume flows, all linked to large-scale tribution is strongly controlled by flow sediment volume, landslides, have covered huge areas of seafloor and flowed with relatively low-volume flows dying out within the along or even slightly upslope for long distances. It is Agadir Basin and large-volume flows bypassing significant proposed that northeastwards-flowing bottom currents have sediment volumes to basins further downslope. -
Sea Experience in Developing Countries
Chapter 6 SEA EXPERIENCE IN DEVELOPING COUNTRIES Increasingly, developing countries are experimenting with SEA and some have SEA-type approaches and elements in place already. There is also considerable experience with using a variety of strategic planning processes that display many of the characteristics of SEA (para SEA). We focus first on SEA in southern Africa where a dedicated regional workshop on SEA was organised to feed into this review (SAIEA 2003a), followed by sections covering francophone Africa, the rest of sub-Saharan Africa, Latin America, Asia and elsewhere. But our survey of this field represents no more than a preliminary reconnaissance. Selected examples of SEA and para SEA illustrate some of the indigenous approaches that have been adopted. These are less common than SEAs promoted and funded by development assistance agencies (which are reviewed in Chapter 4). In most cases where formal SEA has been undertaken in developing countries, the basic aim and approach has mirrored that in the north – namely to identify the environmental consequences (and associated social and economic effects) of existing, new or revised policies, plans and programmes. These represent only a small number of the broad family of SEA approaches. But they are a highly visible sub-set of the large suite of informal or para-SEAs which form part of development policy-making, land use planning or resource management. No strict boundaries can be drawn for this latter area of application. Only the more evident SEA type elements and approaches are introduced in this chapter. Nevertheless, they indicate the scope and diversity of the extended SEA family in developing countries, where political and economic realities constrain what can be done. -
Hafnium and Neodymium Isotopes in Surface Waters of the Eastern Atlantic Ocean: Implications for Sources and Inputs of Trace Metals to the Ocean
Available online at www.sciencedirect.com Geochimica et Cosmochimica Acta 74 (2010) 540–557 www.elsevier.com/locate/gca Hafnium and neodymium isotopes in surface waters of the eastern Atlantic Ocean: Implications for sources and inputs of trace metals to the ocean J. Rickli a,*, M. Frank b, A.R. Baker c, S. Aciego a, G. de Souza a, R.B. Georg d, A.N. Halliday d a ETH Zurich, Institute for Isotope Geochemistry and Mineral Resources, Clausiusstrasse 25, CH-8092 Zurich, Switzerland b IFM-GEOMAR, Leibniz Institute of Marine Sciences, 24148 Kiel, Germany c School of Environmental Sciences, University of East Anglia, Norwich NR4 7TJ, UK d Department of Earth Sciences, University of Oxford, Parks Road, Oxford OX1 3PR, UK Received 14 January 2009; accepted in revised form 30 September 2009; available online 7 October 2009 Abstract We present hafnium (Hf) and neodymium (Nd) isotopic compositions and concentrations in surface waters of the eastern Atlantic Ocean between the coast of Spain and South-Africa. These data are complemented by Hf and Nd isotopic and con- centration data, as well as rare earth element (REE) concentrations, in Saharan dust. Hafnium concentrations range between a maximum of 0.52 pmol/kg in the area of the Canary Islands and a minimum value of 0.08 pmol/kg in the southern Angola Basin. Neodymium concentrations also show a local maximum in the area of the Canary Islands (26 pmol/kg) but are even higher between ~20°N and ~4°N reaching maximum concentrations of 35 pmol/kg. These elevated concentrations provide evidence of inputs from weathering of the Canary Islands and from the partial dissolution of dust from the Sahara/Sahel region. -
Deep Sea Drilling Project Initial Reports Volume 40
28. LEG 40 RESULTS IN RELATION TO CONTINENTAL SHELF AND ONSHORE GEOLOGY William G. Siesser, Department of Geology, University of Cape Town, Rondebosch, South Africa INTRODUCTION tion of basins; instead a sediment wedge has prograded seaward in a deltaic fashion (Scrutton and Dingle, This study compares and contrasts the sedimentary 1974). However, there is some suggestion that history of the onshore coastal region and the continen- marginal-fracture zones striking perpendicular to the tal shelf along the west coast of South Africa, South coast have acted as lines of differential subsidence, thus West Africa, and Angola with that of the outer con- exercising some control over the movement of tinental margin of those countries (Figure 1), as shown sediments parallel to the coast (Scrutton and Dingle, by Leg 40 drilling. 1974). This situation is in contrast to the Cuanza Basin of Geologic Setting: Mesozoic and Tertiary Sedimentation Angola, where sedimentation has been controlled by a Southern Africa underwent its last orogenic phase marginal basement plateau, a number of basement during the Triassic, raising up the Cape Fold Belt. highs, and salt structures (Scrutton and Dingle, 1974). Although no further orogenies occurred, southern Africa remained a high continental mass throughout Onshore the Mesozoic and Cenozoic owing to repeated epeiro- Only two Cretaceous exposures have been reported genic uplift. Epeirogenesis had a characteristic and between Cape Agulhas and the Kunene River. The repeated pattern: maximum uplift occurred in a zone southernmost is a deposit of nonmarine clayey sands near the coastal margin (somewhat seaward of what is (with calcareous concretions) containing bones of the now the Great Escarpment), resulting in a steep dinosaur Kangnasaurus coetzeei, calcified and silicified seaward tilting on the outer side and a gentler inland wood, and streaks of lignite (Rogers, 1915). -
Deep Sea Drilling Project Initial Reports Volume 47 Part 2
INDEX Acaeniotyle umbilicata Zone, 668 Background and objectives, Site 398, 26 Acoustic Bacterial, sulfate reduction, 733 anisotropy, 59, 585 activity, 44 basement, 86, 639 Base-of-slope province, 374 impedance, computation of, 625, Site 398, 63 Basement, 639 pseudologs, 623 Basins and Site 398, correlation between regional, 647 stratigraphy, 91, 639 Bedoulian group, 290 Site 398, 761 Bejaouaennsis Zone (MCi 23), 292 unit 3, nature of, 86 Belemnites, 55, 297 velocity, 585 Benthic, foraminifers, 729 Age of opening of North Atlantic, 28 assemblages, 293 Agglutinated foraminifers, 290, 294, 691 residual, 290, 293, 295 residual, 292 Betic system, 658 Algerianus Zone (Mci 21), foraminifers, 291 Biogenic activity, indexes of organic matter, 419 Alkalinity, 578 minerals, Lower Cretaceous sediments, 686 Alteration indexes, 543 Biostratigraphy, 69 Ammonites, 56, 75, 290, 297 Cenozoic foraminifers, 69, 255 Douvilleiceras mammilatum Zone, 362 Lower Cretaceous, 688 Euhoplites lautus Zone, 362 nannofossils, 327 loricatus Zone, 362 Bioturbation: See Burrows Hoplites dentatus Zone, 362 evidence for, 258 Lower Cretaceous, 361 Bitumen content, Hole 397 sediments, 543 systematic descriptions, 362 Black shale deposition, 30, 55, 56, 405, 437, 665, 667 Amorphous kerogen, 550 719 Ampere Bank, 659 analysis of, 472 Angola Basin, 575, 735 organic matter in, 719 Angular unconformity, 56, 93 Block-faulting, 93 Anistropy, degree of cementation, relationship to, 585 Bottom currents, 375, 380 Anomaly /, 639 temperatures, 511 MO, 639 water, formation of, Antarctic, -
Sea Experience in Developing Countries
Chapter 6 SEA EXPERIENCE IN DEVELOPING COUNTRIES Increasingly, developing countries are experimenting with SEA and some have SEA-type approaches and elements in place. There is also considerable experience of using a variety of strategic planning processes which display many of the characteristics of SEA (para SEA). We focus first on SEA in southern Africa where a dedicated regional workshop on SEA was organised to feed into this review (SAIEA 2003a), followed by sections covering francophone Africa, the rest of sub-Saharan Africa, Latin America, Asia and elsewhere. Selected examples of SEA and para SEA illustrate some of the indigenous approaches that have been adopted. These are less common than SEAs promoted and funded by development assistance agencies (which are reviewed in Chapter 4). In most cases where formal SEA has been undertaken in developing countries, the basic aim and approach has mirrored that in the north – namely to identify the environmental consequences (and associated social and economic effects) of existing, new or revised policies, plans and programmes. 6.1 SEA in Southern Africa1 EIA is now used extensively in most countries in southern Africa. However, many of the governments tend to be ad hoc in their planning and, as a result, EIA is often regarded as an ‘add on’ process “that gets done ‘later on’, after the government, board of directors or other body has decided that the intended initiative is viable and thus worthy of detailed planning” (Tarr, 2003). In recent years, there has been rapid progress in the formulation of policies, legislation and guidelines for EIA (SAIEA 2003b). -
Formation and Collapse of the Kalahari Duricrust ['African Surface
Formation and Collapse of the Kalahari Duricrust [‘African Surface’] Across the Congo Basin, 10 with Implications for Changes in Rates of Cenozoic Off-Shore Sedimentation Bastien Linol, Maarten J. de Wit, Francois Guillocheau, Michiel C.J. de Wit, Zahie Anka, and Jean-Paul Colin{ 10.1 Introduction margins, and to the east by the East African Rift System (EARS). Their relatively flat interior is covered by an exten- The Congo Basin (CB) of central Africa lies at about 400 m sive Upper Cretaceous-Cenozoic succession of sand dunes, above mean sea level (amsl), and is linked to the south, pan-lacustrine sediments and alluviums with hard-caps across a central African drainage divide, to the high interior (duricrusts) of calcrete, silcrete and ferricrete, collectively Kalahari Plateau (KP) at ca. 1,100 m amsl (Fig. 10.1). The named the Kalahari Group (SACS, 1980). This succession CB and KP are flanked by distinct marginal escarpments reaches a maximum thickness of about 500 m, but across along the South Atlantic and southwest Indian Ocean southern and central Africa is generally less than 100 m thick, representing one of the world’s most extensive, long- lived condensed stratigraphic sequences. The Kalahari Group directly overlies Precambrian base- ment of the Kalahari and Central African Shields (Fig. 10.1b), late Paleozoic to mid-Mesozoic sequences of {Author was deceased at the time of publication. the Karoo Supergroup including Lower Jurassic flood basalts in southern Africa, dated at 178–183 Ma (the B. Linol (*) AEON-ESSRI (African Earth Observatory Network – Earth Stormberg Group; Jourdan et al. -
Ocean Drilling Program Initial Reports Volume
Schmincke, H.-U., Weaver, P.P.E., Firth, J.V., et al., 1995 Proceedings of the Ocean Drilling Program, Initial Reports, Vol. 157 5. SITE 9511 Shipboard Scientific Party2 HOLE 951A Principal results: Site 951 is located in the northwestern Madeira Abyssal Plain at 32°1.90'N, 24°52.23'W, at a water depth of 5436.8 m in the Date occupied: 11 August 1994 Chads Fracture Zone Valley. Seismic profiles for the area show the same major units as at Site 950: an upper unit showing relatively high amplitude Date departed: 13 August 1994 parallel reflectors that onlap onto basement highs, and a lower unit that Time on hole: 2 days, 2 hr, 49 min drapes the basement highs. A third unit is present in the deepest part of the fracture zone and it shows reflectors with low coherency. The upper unit Position: 32°1.896'N, 24°52.232'W can be subdivided into three subunits by relatively strong reflectors at 180 Bottom felt (drill-pipe measurement from rig floor, m): 5447.7 ms and 235 ms. Reflectors within the lower two subunits are weaker than Distance between rig floor and sea level (m): 10.90 in the upper subunit. This seismic pattern, previously described by Searle (1987), is interpreted as pelagic drape over basement, with the deeper Water depth (drill-pipe measurement from sea level, m): 5436.8 draped sequences being later infilled by rapidly accumulated turbidites. Total depth (from rig floor, m): 5704.30 In combination with the other two abyssal plain sites, the primary ob- Penetration (m): 256.60 jective of this site was to determine the nature of the turbidite fill and to distinguish discrete sources for the various compositional groups of sedi- Number of cores (including cores having no recovery): 28 ment flows. -
Turbidity Flows – Evidence for Effects on Deep- Sea Benthic Community Productivity Is Ambiguous but the Influence on Diversity Is Clearer Katharine T
https://doi.org/10.5194/bg-2020-359 Preprint. Discussion started: 14 October 2020 c Author(s) 2020. CC BY 4.0 License. Review and syntheses: Turbidity flows – evidence for effects on deep- sea benthic community productivity is ambiguous but the influence on diversity is clearer Katharine T. Bigham1, 2, Ashley A. Rowden1, 2, Daniel Leduc2, David A. Bowden2 5 1School of Biological Sciences, Victoria University of Wellington, Wellington, 6140, New Zealand 2National Institute of Water and Atmospheric Research, Wellington, 6021, New Zealand Correspondence to: Katharine T. Bigham ([email protected]) Abstract. Turbidity flows – underwater avalanches – are large-scale physical disturbances that are believed to have profound and lasting impacts on benthic communities in the deep sea, with hypothesised effects on both productivity and 10 diversity. In this review we summarize the physical characteristics of turbidity flows and the mechanisms by which they influence deep sea benthic communities, both as an immediate pulse-type disturbance and through longer term press-type impacts. Further, we use data from turbidity flows that occurred hundreds to thousands of years ago as well as three more recent events to assess published hypotheses that turbidity flows affect productivity and diversity. We found, unlike previous reviews, that evidence for changes in productivity in the studies was ambiguous at best, whereas the influence on regional 15 and local diversity was more clear-cut: as had previously been hypothesized turbidity flows decrease local diversity but create mosaics of habitat patches that contribute to increased regional diversity. Studies of more recent turbidity flows provide greater insights into their impacts in the deep sea but without pre-disturbance data the factors that drive patterns in benthic community productivity and diversity, be they physical, chemical, or a combination thereof, still cannot be identified.