Angola Basin Research Articles

Three new species of free-living nematodes from the South-East Atlantic Abyss (DIVA I Expedition)

Three new nematode species were found in the Angola Basin (south-east Atlantic Ocean) at depths of about 5500 m. Paracyatholaimus diva sp. nov. (Cyatholaimidae) is characterised by outer labial and cephalic setae of about 3–5 μm, multispiral amphidial fovea with six turns in males and four turns in females situated at the level of the dorsal tooth, buccal cavity armoured with only one prominent dorsal tooth, tail consisting of anterior conical and posterior slender cylindrical half portions, and six preanal midventral setose supplementary organs. Paracyatholaimus diva sp. nov. is most similar to Paracyatholaimus rotundus Gerlach, 1964 but differs by slightly longer body (936–1176 μm versus 705 μm), tail shape (with clearly narrowed posterior half versus conical), six versus four supplementary organs of different shape. The genus Paracyatholaimus Micoletzky, 1923 is briefly reviewed. The genus now includes twenty-four valid species. Five species are considered as species inquirendae, mainly because of inadequate type material lacking adult stages and/or incomplete descriptions. A pictorial guide for identification of the valid species of Paracyatholaimus is provided. Pomponema proximamphidum sp. nov. shares subapical position of the amphidial fovea and distinct lateral differentiation of the somatic cuticle with five Pomponema species: P. concinnum Wieser, 1954, P. corniculata Gourbault, 1980, P. mirabile Cobb, 1917, P. multipapillatum Filipjev, 1922 and P. stomachor Wieser, 1954 but differs from them by tail length, longer posterior cylindrical portion of the tail, relative width of the amphidial fovea, position of the ventral pore and lesser number of supplementary organs. Desmodora striatocephala sp. nov. is well characterized by a combination of very large amphidial fovea occupying nearly the entire lateral surface of the cephalic capsule and thickened midventral preanal cuticle with a few supplementary papillae inserted therein in males. D. striatocephala sp. nov. differs from related species D. cuddlesae Inglis, 1963 and to some lesser degree with D. inflexa Wieser, 1954 with shorter body, relative tail length, bigger size of the amphidial fovea and lesser number of supplementary papillae.

Argestes angolaensis sp. nov. (Copepoda: Harpacticoida: Argestidae) from theAngola Basin (Southeast Atlantic), and the phylogenetic characterization of thetaxon Argestes Sars, including the redescription of A. mollis Sars, 1910, and A.reductus (Itô, 1983)

Argestes angolaensis sp. nov. (Copepoda, Argestidae) is described from the Angola Basin. Detailed comparison with the other Argestes species, A. mollis Sars, 1910 and A. reductus (Itô, 1983), which are redescribed in the present contribution, reveals autapomorphies for the genus, finally enabling the characterization of Argestes as a monophylum: 1) body densely covered with fine small cuticular spinules, 2) sensilla of cephalothorax and free thoracic somites arising from long tubercles, 3) antennula with very strong seta terminally on 6th segment in female (9th–10th in male). This investigation, concentrating on the systematic status of Argestes and first remarks on its relationships to Parargestes Lang, is the first in a series dedicated to the phylogeny of Argestidae Por, 1986.

New Acanthomeniidae (Solenogastres, Cavibelonia) from the abyssal Angola Basin

Solenogastres are a small class of vermiform Mollusca that present a mantle with calcareous sclerites and a ventral pedal groove. During the expedition Me48/1 DIVA 1, carried out in the abyssal Angola Basin between 5100-5500 m depth, several specimens of Solenogastres were collected. Their study has made possible to describe two new species and a new genus of the family Acanthomeniidae Salvini-Plawen, 1978, whose anatomical features have caused the modification of the family definition.

Results of the DIVA-1 Expedition of RV “Meteor” (Cruise M48:1):Three new species of Munnopsidae Sars, 1864 from abyssal depths of the AngolaBasin (Crustacea: Isopoda: Asellota)

Three new species of Munnopsidae, Eurycope monodon sp. nov., E. denticollis sp. nov. and Munneurycope Persephone sp. nov. are described from the deep sea of the Angola Basin in the southeast Atlantic. E. monodon and E. denticollis closely resemble E. glabra Kensley, 1978 in general appearance and in the peculiar shape of the female operculum with an apex shifted far frontally, but with a less pronounced medial lobe of antenna 1 article 1, presence of dorsal tubercles on the pleotelson and uropods with less reduced exopods. Eurycope monodon has a rostrum bearing a single anteromedian spinelike seta and a male pleopod 1 with a subapical, hook-like cusp of the distolateral lobe curved anteriolaterally. Eurycope denticollis has paired and relatively shorter spine-like setae on the rostrum, and the cusp of pleopod 1 distolateral lobe is curved caudolaterally. M. persephone is the first species of the genus recorded from the South Atlantic. It differs from the most similar species, M. nodifrons (Hansen, 1916), in antenna 1 with elongated third article, a maxilliped with more distinctly truncate endite, and a different dentation on the retinacula.

The Cenomanian/Turonian oceanic anoxic event in the South Atlantic: New insights from a geochemical study of DSDP Site 530A

One of the key objectives of Deep Sea Drilling Project (DSDP) Leg 75 was to shed light on the underlying causes of Cretaceous oceanic anoxia in the South Atlantic by addressing two major hypotheses: productivity productivity-driven anoxia vs. enhanced ocean stratification leading to preservation of organic matter and black shale deposition. Here we present a detailed geochemical dataset from sediments deposited during the Cenomanian/Turonian (C/T) transition and the global oceanic anoxic event 2 (OAE 2) at DSDP Site 530A, located off-shore Namibia (southeast Angola Basin, north of Walvis Ridge). To characterise the succession of alternating black and green shales at this site and to reconstruct the evolution of their paleoenvironmental setting, we have combined data derived from investigations on bulk organic matter, biomarkers and the inorganic fraction. The location of the C/T boundary itself is biostratigraphically not well constrained due to the carbonate-poor (but organic matter-rich) facies of these sediments. The bulk δ 13C org record and compound-specific δ 13C data, in combination with published as well as new biostratigraphic data, enabled us to locate more precisely the C/T boundary at DSDP Site 530A. The compound-specific δ 13C record is the first of this kind reported from C/T black shales in the South Atlantic. It is employed for paleoenvironmental reconstructions and chemostratigraphic correlation to other C/T sections in order to discuss the paleoceanographic aspects and implications of the observations at DSDP Site 530A in a broader context, e.g., with regard to the potential trigger mechanisms of OAE 2, global changes in black shale deposition and climate. On a stratigraphic level, an approximation and monitoring of the syndepositional degree of oxygen depletion within the sediments/bottom waters in comparison to the upper water column is achieved by comparing normalised concentrations of redox-sensitive trace elements with the abundance of highly source specific molecular compounds. These biomarkers are derived from photoautotrophic and simultaneously anoxygenic green sulphur bacteria (Chlorobiacea) and are interpreted as paleoindicators for events of photic zone euxinia. In contrast to a number of other OAE 2 sections that are characterised by continuous black shale sequences, DSDP Site 530A represents a highly dynamic setting where newly deposited black shales were repeatedly exposed to conditions of subtle bottom water re-oxidation, presumably leading to their progressive alteration into green shales. The frequent alternation between both facies and the related anoxic to slight oxygenated conditions can be best explained by variations in vertical extent of an oxygen minimum zone in response to changes in a highly productive western continental margin setting driven by upwelling.

Analysis of light hydrocarbons in marine sediments by headspace technique: Optimization using design of experiments

Headspace technique is a common method to analyze light hydrocarbons in deep marine sediments. The use of an automatic headspace sampler instead of a manual injection is the guarantee for a better repeatability and furthermore it is less time consuming. But to increase the sensitivity and therefore, to achieve a better detection limit, it is necessary to optimize the automatic headspace sampler parameters. The theory of design of experiments was applied here by studying them. As a response, methane, which is an important gas in marine sediments, was chosen for its short analysis time. Regarding the parameters for automatic headspace sampler, eight variables were selected and then, a screening of them was carried out with a fractional factorial design to determine the influential factors. Finally, optimization was conducted with four factors: Sample Loop Fill time ( t slf), Oven temperature ( T° o), Vial Pressurization time ( t vp) and Vial pressure ( P v). They were modeled with a Doehlert experimental design. Then, the model was validated by a conventional statistical test (analysis of variance) and the optimum has been found and checked by three experiments. Results on light hydrocarbons measured in sediments from the Congo–Angola Basin are given, as an example.

Pericontinental petroliferous basins of the South Atlantic Ocean

Sedimentary basins located at Atlantic margins of South America and Africa (Brazil, Congo, and Angola) are composed of thick Cretaceous-Pleistocene rocks (7–9 km). The principal oil-bearing complexes of both regions are dominated by terrigenous rocks. Their accumulation took place at the rifting stage, ended with precipitation of evaporites in the Aptian at the oceanic stage of evolution. Starting with Coniacian and Campanian, the accumulation of terrigenous clastic formations in the Santos and Campos basins was governed by main phases of orogenesis in the Peruvian Andes. In the Angola and Lower Congo basins, the sedimentation was governed by movements related to the development of the East African Rift System. The formation of carbonate and carbonate-clayey sediments prevailed here at early (Albian-Late Eocene) stages of the South Atlantic opening.

Advection and scavenging: Effects on 230Th and 231Pa distribution off Southwest Africa

We investigated the controls of hydrography and of scavenging on the distribution of the particle reactive radionuclides 231Pa and 230Th in the water column and in surface sediments off Southwest Africa (Angola and Cape basins). Based on a vertical section of total 230Th ex concentrations in the water column we show that small differences in the salinity between the North Atlantic Deep Water (NADW) in the Angola Basin and the NADW in the Cape Basin as well as the advection of NADW associated with the Namib Col Current are reflected in total 230Th ex concentrations. These variable total concentrations are believed to reflect the flow path and mixing history of NADW with the NADW in the Angola Basin being relatively older and 230Th enriched compared to the NADW in the Cape Basin. In the area investigated we found high 231Pa ex/ 230Th ex ratios ( 231Pa ex/ 230Th ex > 0.093) in surface sediments at the continental margin and lower ones ( 231Pa ex/ 230Th ex < 0.093) in the open ocean. Such a distribution is normally interpreted to result from high particle flux at ocean margins (boundary scavenging). However, the lack of any significant depletion of dissolved 230Th and 231Pa in the water column does not indicate extensive scavenging at the continental margin. High 231Pa ex/ 230Th ex ratios are constrained to shallow waters depths (< 2000 m) only and coincide with low fractionation between 231Pa and 230Th indicating that preferential scavenging of 231Pa on opal may have caused high 231Pa ex/ 230Th ex ratios in the sediments. The observed close negative correlation ( r 2 = 0.82) between 231Pa ex/ 230Th ex ratios in sediments and water depths is believed to reflect changes in the particle composition, i.e. a decrease in opal content with water depth. In the Angola and Cape basins the total 231Pa ex concentrations in NADW were the highest observed so far in the Atlantic Ocean, and they are attributed to the meridional export of 231Pa from the North Atlantic. This caused the average dissolved 231Pa/ 230Th in the Southeast Atlantic to be about a factor 2 higher when compared to the North Atlantic (Labrador Sea). These differences in the dissolved 231Pa/ 230Th were not reflected in 231Pa/ 230Th ratios of surface sediments because the fractionation is lower in the Labrador Sea compared to the Southeast Atlantic, i.e. fractionation counteracts changes in the dissolved 231Pa/ 230Th. This suggests that fractionation is more important for the determination of 231Pa ex/ 230Th ex ratios in sediments than the meridional export of 231Pa from the North Atlantic.

Two new species of the genus Pseudomesus Hansen, 1916 (Isopoda, Asellota) from the Southern hemisphere: Pseudomesus pitombo sp. nov. and Pseudomesus satanus sp. nov.

Two new species of the genus Pseudomesus Hansen, 1916 (Isopoda, Asellota) are described from the Southern hemisphere: Pseudomesus pitombo sp. nov. and Pseudomesus satanus sp. nov. Specimens of the new species were collected during DIVA-1 (DIVersity of the abyssal Atlantic Ocean) in the deep Angola Basin (P. pitombo) and a cruise to the Australian continental slope (P. satanus), respectively. They differ from the remaining species of this genus by the presence of a mandibular palp. P. pitombo can be distinguished from P. satanus by the shape of the anterior margin of the cephalothorax of the female, in the number of articles of the antenna, and the length of the maxilliped´s exopodite.

Sipunculans and echiurans from the deep Angola Basin

Sipunculans and echiurans collected by the “DIVA 1” expedition by RV Meteor (Cruise M48/1) to the deep‐sea bottom of the Angola Basin are recorded. Seven species from five genera and two separate phyla are recognized; only the echiuran Pseudoikedella achaeta has not been recorded hitherto in the southern sector of the Atlantic Ocean. A gradient analysis using redundancy analysis (RDA) under the CANOCO package indicates the existence of a neat latitudinal gradient of sipunculans along the Angola Basin from the southernmost stations towards the northern ones. The local abundance of abandoned horny tubes of polychaetes at some of the sampling sites of the northernmost stations explains the dense aggregations of Nephasoma diaphanes. This species exhibits an opportunistic lifestyle inside empty polychaete tubes on the abyssal plains of the Angola Basin.

Neodymium isotopes in benthic foraminifera: Core-top systematics and a down-core record from the Neogene south Atlantic

Records of the past neodymium (Nd) isotope composition of the deep ocean can resolve ambiguities in the interpretation of other tracers. We present the first Nd isotope data for sedimentary benthic foraminifera. Comparison of the ɛ Nd of core-top foraminifera from a depth transect on the Cape Basin side of the Walvis Ridge to published seawater data, and to the modern dissolved SiO 2–ɛ Nd trend of the deep Atlantic, suggests that benthic foraminifera represent a reliable archive of the deep water Nd isotope composition. Neodymium isotope values of benthic foraminifera from ODP Site 1264A (Angola Basin side of the Walvis Ridge) from the last 8 Ma agree with Fe–Mn oxide coatings from the same samples and are also broadly consistent with existing fish teeth data for the deep South Atlantic, yielding confidence in the preservation of the marine Nd isotope signal in all these archives. The marine origin of the Nd in the coatings is confirmed by their marine Sr isotope values. These important results allow application of the technique to down-core samples. The new ɛ Nd datasets, along with ancillary Cd/Ca and Nd/Ca ratios from the same foraminiferal samples, are interpreted in the context of debates on the Neogene history of North Atlantic Deep Water (NADW) export to the South Atlantic. In general, the ɛ Nd and δ 13C records are closely correlated over the past 4.5 Ma. The Nd isotope data suggest strong NADW export from 8 to 5 Ma, consistent with one interpretation of published δ 13C gradients. Where the ɛ Nd record differs from the nutrient-based records, changes in the pre-formed δ 13C or Cd/Ca of southern-derived deep water might account for the difference. Maximum NADW-export for the entire record is suggested by all proxies at 3.5–4 Ma. Chemical conditions from 3 to 1 Ma are totally different, showing, on average, the lowest NADW export of the record. Modern-day values again imply NADW export that is about as strong as at any stage over the past 8 Ma.

Rediscovery of Bathypsammis Huys &amp;amp; Gee, 1993 (Copepoda, Harpacticoida, Pseudotachidiidae) with description of a new species from the Antarctic deep sea

The species diversity of Copepoda Harpacticoida in the deep sea of the Angola Basin (DIVA I expedition with RV Meteor) and in the Weddell Sea (ANDEEP II expedition with RV Polarstern) have been investigated. From the obtained multicorer samples two female specimens of Bathypsammis Huys &amp; Gee, 1993 were collected. The only specimen known before was described as Psammis longifurca by Bodin in 1968 from the northern Atlantic. In the present paper a new species Bathypsammis polaris sp. n. from the Antarctic Weddell Sea is described. The monophyly of Bathypsammis within the Paranannopinae Por, 1986 can be confirmed by several new autapomorphies whereas the relation to other paranannopid taxa must remain open for the moment. The new findings implicate a widespread distribution of Bathypsammis from the northern to the southern Atlantic and even to the southern polar regions. Up to now all individuals that have been found occur exclusively at deep-sea sites and in very low abundances.

Composition, abundance and distribution of Peracarida from the Southern Ocean deep sea

Abstract Peracarida are an important component of both the deep-sea fauna and the fauna known from the Antarctic shelf. The peracarid composition from epibenthic-sledge samples obtained during the expeditions ANDEEP I–III is shown and compared to that of other deep-sea basins and the Antarctic shelf. The Amphipoda were the most abundant taxon in the samples, with 43% of all peracarid individuals, followed by the Isopoda (35%), Cumacea (16%), Tanaidacea (5%) and Mysidacea (1%). Highest abundances were found at the shallower stations, but a clear trend towards decreasing abundances with depth could not be confirmed. Although the decrease of amphipod numbers and the increase of isopod numbers with depth in general correspond to other areas, e.g., the Angola Basin, the Southern Ocean deep sea seems to be special by harboring more amphipod specimens at medium depths, thus reflecting the situation on the Antarctic shelf. Outstanding by their number of specimens were the samples from station 133-2 at about 1500 m depth in the Powell Basin, which contained the highest number of specimens, and from station 152-6 in the Bransfield Strait, where the number of specimens was strikingly low despite the moderate depth of about 2000 m.

A new species of Parabradya Lang, 1944 (Copepoda: Harpacticoida: Ectinosomatidae) from the abyssal plain of the Angola Basin

Parabradya samsoni sp. nov. is described from deep-sea samples collected from the Angola Basin during the DIVA-1 campaign in July 2000. Parabradya samsoni can be distinguished from its congeners by: its bigger size, the ornamentation of the body, the cuticula (except for that of the cephalic shield and the genital field) is covered with spinules, the multipinnate setae of A1, A2, mouthparts, P1–P5 and caudal rami, and the position of the innermost seta of P5, which is not directly situated at the inner distal corner, but displaced towards the outer edge. Full generic rank is assigned to both Bradya Boeck, 1873 and Parabradya Lang, 1944. With P. samsoni sp. nov. Parabradya includes five species.

Crinoidea and Holothuroidea (Echinodermata) of the abyssal Angola Basin—Results of the DIVA­ 1 expedition of FS " Meteor " (Cruise M 48 / 1)

Crinoidea and Holothuroidea (Echinodermata) of the abyssal Angola Basin—Results of the DIVA­ 1 expedition of FS " Meteor " (Cruise M 48 / 1)

Carbonate dissolution revealed by silt grain‐size distribution: comparison of Holocene and Last Glacial Maximum sediments from the pelagic South Atlantic

AbstractThe current issue of global warming and the role of the ocean in global exchange of CO2 increases the interest in solid budgets of marine carbonate production and dissolution. The present study utilizes grain‐size composition of pelagic sediments in order to trace spatial and temporal variability of carbonate sedimentation in the South Atlantic for the Holocene and Last Glacial Maximum (LGM, 19–23 cal kyr BP). A decrease in grain size (e.g. sand content, mean grain size of coarse carbonate silt) indicates increased carbonate dissolution as a result of increased fragmentation of calcareous microfossils. The spatial grain‐size pattern suggests a threshold water depth below which a gradual grain‐size decrease becomes increasingly rapid. This water depth is considered as the sedimentary lysocline. For the Holocene time slice, a constant, gradual decrease of foraminifer carbonate of about 5–10% per 1000 m water depth above the lysocline gives evidence for supra‐lysoclinal dissolution. The water depth of the lysocline for the Holocene is tied to the interface of North Atlantic Deep Water and Antarctic Bottom Water (AABW) (ca 4100 m). Submarine ridges which restrict intrusion of AABW into the Angola Basin cause an asymmetry in carbonate preservation across the Mid‐Atlantic Ridge. The lysocline was reconstructed at ca 3100 m for the LGM. These data suggest that the ca 1000 m rise of the lysocline eradicated the Holocene east–west asymmetry.

Structure and function of macrofaunal communities influenced by hydrodynamically controlled food availability in the Wadden Sea, the open North Sea, and the Deep-sea. A synopsis

The study areas were situated in the East Frisian Wadden Sea, in the south-eastern North Sea, the Skagerrak and the Kattegat, and in the deep-sea of the Arctic Ocean (Eurasian Basin), the eastern Mediterranean and the Angola Basin.

Glacial/interglacial changes in southern Africa: Compound‐specific δ13C land plant biomarker and pollen records from southeast Atlantic continental margin sediments

This is part 2 of a study examining southwest African continental margin sediments from nine sites on a north‐south transect from the Congo Fan (4°S) to the Cape Basin (30°S) representing two glacial (MIS 2 and 6a) and two interglacial stages (MIS 1 and 5e). Contents, distribution patterns, and molecular stable carbon isotope signatures of long‐chain n‐alkanes (C27‐C33) and n‐alkanols (C22‐C32) as indicators of land plant vegetation of different biosynthetic types were correlated with concentrations and distributions of pollen taxa in sediments of the same time horizons. Selected single pollen type data reveal details of vegetation changes, but the overall picture is best illustrated by summing pollen known to predominantly derive from C4 plants or C4 plus CAM plants. The C4 plant signals in the biomarkers are recorded in the δ13C data and in the abundances of C31 and C33n‐alkanes, and the C32n‐alkanol. Calculated clusters of wind trajectories for austral summer and winter situations for the Holocene and the Last Glacial Maximum afford information on the source areas for the lipids and pollen and their transport pathways to the ocean. This multidisciplinary approach provides clear evidence of latitudinal differences in leaf wax lipid and pollen composition, with the Holocene sedimentary data paralleling the current major phytogeographic zonations. The northern sites (Congo Fan area and northern Angola Basin) get most of their terrestrial material from the Congo Basin and the Angolan highlands dominated by C3 plants. Airborne particulates derived from the western and central South African hinterland dominated by deserts, semideserts, and savannah regions are rich in organic matter from C4 plants. As can be expected from the present and glacial positions of the phytogeographic zones, the carbon isotopic signatures of n‐alkanes and n‐alkanols both become isotopically more enriched in 13C from north to south. In the northern part of the transect the relative importance of C4 plant indicators is higher during the glacials than in the interglacials, indicating a northward extension of arid zones favoring grass vegetation. In the south, where grass‐rich vegetation merges into semidesert and desert, the difference in C4 plant indicators is small.

Crinoidea and Holothuroidea (Echinodermata) of the abyssal Angola Basin—Results of the DIVA-1 expedition of FS "Meteor" (Cruise M48/1)

Agassiz trawl and epibenthic sledge samples taken at abyssal depths in the Angola Basin (south-eastern Atlantic Ocean) during the expedition DIVA-1 with FS "Meteor" in July 2000 yielded a rich variety of Echinodermata: inter alia one stalked crinoid (Bathycrinus cf. aldrichianus Wyville Thomson, 1876) and altogether nine holothurian species, two of which are subspecies. One of these, Achlyonice longicornis spec. nov., is new to science, while all others have been described earlier: Deima validum validum Théel, 1879, Psychropotes semperiana Théel, 1882, Peniagone purpurea (Théel, 1882), Molpadiodemas atlanticus (R. Perrier, 1898), Molpadia liska Pawson, 1977, Protankyra brychia (Verrill, 1885), Siniotrochus myriodontus Gage &amp; Billett, 1986 and Neolepidotrochus parvidiscus angolensis Bohn, 2005. All species collected are described and their known distributions are given. Finally, two crinoids and 21 holothurian species, so far known from the abyssal Angola Basin, are listed and their zoogeographical relationships are discussed.

Reply to the letter submitted by S.M. Zverev to the Editorial Board of the Journal Fizika Zemli (Izvestiya, Physics of the Solid Earth) regarding the paper “Geological Origin of Distinctions in Seismic Fields along Various Directions in the Angola Basin” by Yu.V. Tulina, V.Yu. Burmin, and I.B. Shemeleva in No. 6 of the Journal in 2003

Reply to the letter submitted by S.M. Zverev to the Editorial Board of the Journal Fizika Zemli (Izvestiya, Physics of the Solid Earth) regarding the paper “Geological Origin of Distinctions in Seismic Fields along Various Directions in the Angola Basin” by Yu.V. Tulina, V.Yu. Burmin, and I.B. Shemeleva in No. 6 of the Journal in 2003