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The NW Iberian continental margin is characterised by a complex morphology and by a sedimentary system which was highly dynamic over glacial to interglacial times. The sedimentary history of the continental slope was strongly influenced by the interaction of bottom currents with topographic highs of structural origin leading to the accumulation of several sediment drifts. A combined analysis of gravity cores from different water depth with hydroacoustic data reveals the vertical behaviour of the upper Mediterranean Outflow Water (MOW) core after the Last Glacial Maximum (LGM). A coarser grained interval during Deglacial and early Holocene times (17.2 to 9.9 cal ka BP) points to an increase in bottom current strength. This increase in velocity was probably related to oceanic density fronts, which migrated through the 300 m thick transition zone between the underlying Labrador Sea Water and the overlying MOW. Radiocarbon dates timed the current strengthening to 17.2 cal ka BP, and a following weakening of the bottom current to 13.3 cal ka BP at 1965 m water depth and to 9.9 cal ka BP at 1885 m water depth. The depth-dependent current weakening suggests an upward shifting of the transition zone by 80 m that was related either to an overall shallowing of MOW or a vertical contraction of this water mass. The upward movement happened over a time interval of approximately 3.4 thousand years. In addition sediment core analysis reveals significant lateral heterogeneities within cm to dm thick sediment layers in the contourite drift. These heterogeneities suggest a need of a detailed core coverage across current-influenced deposits for palaeoceanographic studies to minimize misinterpretations.

The Río de la Plata estuary (RdlP) and adjacent continental shelf exhibit complex hydrological processes as a result of a highly variable fluvial discharge and associated terrigenous supply, which are primarily controlled by regional climatic forcing in interaction with the oceanographic system. Previous hydrological studies indicate that Little Ice Age and Medieval Climate Anomaly resulted in increased/decreased river runoff due to an enhanced/weakened precipitation regime. This study aims to analyze the cyclicity in the runoff-related continental supply and the associated climatic oscillation behind it over the past 1,000 cal yr BP. To achieve this, we used a 10-m-long sediment core retrieved from the RdlP mud depocenter, which exhibits an extremely high and fairly constant linear sedimentation rate of 1.1 cm yr-1. We performed continuous 1-cm XRF element intensity scans and performed time series analysis on Fe/K, Ti/Al, Fe/Ca, Ti/Ca and Si/Al ratios, considered as regional proxies for inferring fluvial supply. The most significant cyclicities occur at 215, 192, 115, 100, 49, 47, 37, 35, and 2.5-8 yrs recurrence times. The long-term cyclicity is persistent throughout the whole record for all ratios, and it is probably related to solar forcing, i.e., the 200 yr Vries/Suess cycle, which determines the activity of the South American Monsoon System activity. The shorter climate-related cyclicities (˂100 yr) are probably related to the Atlantic Multidecadal Oscillation, the Pacific Decadal Oscillation and the El Niño Southern Oscillation climatic modes, and were registered only for Ti/Al, Fe/K and Si/Al ratios. We further identified an intensification of such shorter climate-related cyclicities over the past 500 yr BP. This study provides new evidence that both tropical Pacific and Atlantic SSTs and solar forcing are the main drivers of changes in rainfall over Southeastern South America on interannual to decadal, multidecadal and centennial scales, and thus modulates the RdlP river discharge. ResumoO estuário do Río de la Plata (RdlP) e a plataforma continental adjacente exibem processos hidrológicos complexos, controlados principalmente pela forçante climática regional em interação com o sistema oceanográfico, o que resulta em grande variabilidade da descarga fluvial e do fornecimento de materiais terrígenos ao sistema oceânico. Estudos hidrológicos anteriores indicam que a Pequena Idade do Gelo e a Anomalia Climática Medieval resultaram no aumento / diminuição do escoamento do rio devido a um regime de precipitação aumentado/ enfraquecido. Este estudo tem como objetivo analisar a ciclicidade no fornecimento continental condicionada por oscilações climáticas nos últimos 1.000 anos e com mudanças no caudal do RdlP. Com este objetivo, foi estudado um testemunho de sedimentos, com 10 m de comprimento, obtido no depósito lodoso do RdlP. O testemunho apresenta uma taxa de acumulação extremamente alta e razoavelmente constante de 1,1 cm ano-1. Foram efetuadas análises elementares de XRF, com resolução de 1 cm, das razões Fe/K, Ti/Al, Fe/Ca, Ti/Ca e Si/Al, consideradas como proxies regionais para inferência de suprimento fluvial. As ciclicidades de recorrência mais significativas ocorreram há 215, 192, 115, 100, 49, 47, 37, 35 e 2,5-8 anos. A ciclicidade mais longas, persentes ao longo de todo o registro, estão provavelmente relacionadas com o forçamento solar, ou seja, com o ciclo de 200 anos de Vries/Suess, que determina a atividade do Sistema de Monção Sul-Americana. As ciclidades mais curtas (˂100 anos) estão provavelmente relacionadas com a Oscilação Multidecadal Atlântica, Oscilação Decadal do Pacífico e fenômeno El Niño-Oscilação Sul, tendo sido registrados por mudanças nos valores das razões Ti/Al, Fe/K e Si/Al. Além disso, identificámos uma intensificação de tais ciclicidades, relacionadas com o clima, nos últimos 500 anos BP. Este estudo fornece novas evidências de que tanto as temperaturas superficiais do oceano Pacífico e Atlântico tropicais, como o forçamento solar, são as causas principais responsáveis pelas mudanças na precipitação no sudeste da América do Sul, á escala interanual a decadal, multidecadal e centenária, e modulam a descarga do Río de la Plata.

In order to strengthen and update knowledge on climatic, environmental and oceanographic changes on the inner Uruguayan continental shelf, w e studied pollen, dinocyst and other non-pollen palynomorph assemblages on the sediment core GeoB13813-4. This core was taken from the mud depocenter and its remarkable high sedimentation rate for the last ca. 1000 yr cal BP reflects the high terrigenous supply from the Rio de la Plata (RdlP). Most pollen and spores are originated from the RdlP grasslands, the vegetation that covers the lower reaches of the La Plata Drainage Basin (LPDB). They mainly represent the regionally dominant grasslands, but also the riparian forests, Butia yatay palm populations, and the herbaceous-bushy marshes around the mouth of the estuary. Pollen from salt marshes, Atlantic rainforest, and Araucaria forests located in southern Brazil reached the study site, probably transported by coastal ocean currents, whereas pollen from Andean regions would represent a long-distance transport by wind. Changes in both proportion and concentration of freshwater and marine palynomorphs indicate variability in freshwater input to the inner Uruguayan shelf. From ca. 1000 to 230 yr cal BP, significant marine influence of Subtropical Shelf Waters (STSW) was inferred, which was diluted by the freshwater supply from the Uruguayan mainland. This time interval was interrupted between ca. 690 to 575 yr cal BP by an increased freshwater contribution to the study area under the influence of Subantarctic Shelf Waters (SASW). From ca. 230 to 25 yr cal BP, a strong influence of RdlP waters was detected, only followed by another phase of dominant STSW during the past century. Such changes were related to regional climatic variability, i.e., Medieval Climate Anomaly, Little Ice Age and Current Warm Period. After ca. 1960 AD, the anthropogenic impact within the LPDB was clearly evidenced both by eutrophication and the first occurrence of Pinus pollen. Resumo A fim de melhorar e atualizar o conhecimento sobre mudancas climaticas, ambientais e oceanograficas na Plataforma Continental Uruguaia, foi estudado o polen, os dinocistos e outras associacoes de palinomorfos nao polinicos no testemunho de sedimentos GeoB13813-4. Este testemunho foi recolhido no deposito lodoso e a sua taxa de sedimentacao durante os ultimos ≈1000 anos antes do presente (BP; before present ) reflete o elevado contributo terrigeno do Rio de la Plata (RdlP) a area de estudo. Os resultados obtidos revelam que a maioria dos polenes e esporos e originaria das pastagens e da vegetacao que cobre o curso inferior da Bacia de Drenagem do Rio de la Plata (LPDB). Representam principalmente as pastagens, as quais sao regionalmente dominantes, mas tambem matas ciliares, populacoes da palmeira Butia yatay e sapais herbaceos ao redor da foz do estuario. Polen de sapais, Mata Atlântica e florestas de Araucaria localizadas no sul do Brasil chegaram ao local de estudo, provavelmente transportados por correntes oceânicas costeiras. O polen das regioes andinas podera representar um transporte de longa distância pelo vento. Mudancas na proporcao e concentracao de palinomorfos de agua doce e marinhos indicam variabilidade na entrada de agua doce na plataforma continental interna uruguaia. Entre ≈1000-230 anos BP, os dados indicam a ocorrencia de uma significativa influencia marinha das Aguas Subtropicais da Plataforma (STSW), misturadas com agua doce do continente uruguaio. Este intervalo foi marcado, entre ≈690-575 anos BP, com uma maior contribuicao de agua doce para a area de estudo sob a influencia de Aguas Subantarticas (SASW). Entre ≈230-25 anos BP, foi detectada uma forte influencia das aguas do RdlP. Esta fase foi seguida, durante o seculo passado, por outra em que as STSW foram dominantes. Tais mudancas poderao ter sido causadas pela variabilidade climatica regional, ou seja, Anomalia Climatica Medieval, Pequena Idade do Gelo e Periodo Quente Atual. Desde ≈1960, o impacto antropogenico no LPDB esta claramente evidenciado tanto pela eutrofizacao quanto pela primeira ocorrencia de polen de Pinus .

In order to strengthen and update knowledge on climatic, environmental and oceanographic changes on the inner Uruguayan continental shelf, we studied pollen, dinocyst and other non-pollen palynomorph assemblages on the sediment core GeoB13813-4. This core was taken from the Rio de la Plata (RdlP) mud depocenter and its remarkable high sedimentation rate for the last ca. 1000 cal yr BP reflects the high terrigenous supply from RdlP. Most pollen and spores are originated from the RdlP grasslands, the vegetation that covers the lower reaches of the La Plata Drainage Basin (LPDB). They mainly represent the regionally dominant grasslands, but also the riparian forests, Butia yatay palm populations, and the herbaceous-bushy marshes around the mouth of the estuary. Pollen from salt marshes, Atlantic rainforest, and Araucaria forests located in southern Brazil reached the study site, probably transported by coastal ocean currents, whereas pollen from Andean regions would represent a long-distance transport by wind. Changes in both proportion and concentration of freshwater and marine palynomorphs indicate variability in freshwater input to the inner Uruguayan shelf. From ca. 1000 to 230 cal yr BP, significant marine influence of Subtropical Shelf Waters (STSW) was inferred, which was diluted by the freshwater supply from the Uruguayan mainland. This time interval was interrupted between ca. 690 to 575 cal yr BP by an increased freshwater contribution to the study area under the influence of Subantarctic Shelf Waters (SASW). From ca. 230 to 25 cal yr BP, a strong influence of RdlP waters was detected, only followed by another phase of dominant STSW during the past century. Such changes were related to regional climatic variability, i.e., Medieval Climate Anomaly, Little Ice Age and Current Warm Period. After ca. 1960 AD, the anthropogenic impact within the LPDB was clearly evidenced both by eutrophication and the first occurrence of PINUS pollen.

The Río de la Plata estuary (RdlP) and adjacent continental shelf exhibit complex hydrological processes as a result of a highly variable fluvial discharge and associated terrigenous supply, which are primarily controlled by regional climatic forcing in interaction with the oceanographic system. Previous hydrological studies indicate that Little Ice Age and Medieval Climate Anomaly resulted in increased/decreased river runoff due to an enhanced/weakened precipitation regime. This study aims to analyze the cyclicity in the runoff-related continental supply and the associated climatic oscillation behind it over the past 1,000 cal yr BP. To achieve this, we used a 10-m-long sediment core retrieved from the RdlP mud depocenter, which exhibits an extremely high and fairly constant linear sedimentation rate of 1.1 cm yr-1. We performed continuous 1-cm XRF element intensity scans and performed time series analysis on Fe/K, Ti/Al, Fe/Ca, Ti/Ca and Si/Al ratios, considered as regional proxies for inferring fluvial supply. The most significant cyclicities occur at 215, 192, 115, 100, 49, 47, 37, 35, and 2.5-8 yrs recurrence times. The long-term cyclicity is persistent throughout the whole record for all ratios, and it is probably related to solar forcing, i.e., the 200 yr Vries/Suess cycle, which determines the activity of the South American Monsoon System activity. The shorter climate-related cyclicities (˂100 yr) are probably related to the Atlantic Multidecadal Oscillation, the Pacific Decadal Oscillation and the El Niño Southern Oscillation climatic modes, and were registered only for Ti/Al, Fe/K and Si/Al ratios. We further identified an intensification of such shorter climate-related cyclicities over the past 500 yr BP. This study provides new evidence that both tropical Pacific and Atlantic SSTs and solar forcing are the main drivers of changes in rainfall over Southeastern South America on interannual to decadal, multidecadal and centennial scales, and thus modulates the RdlP river discharge.

We conducted a multidisciplinary study to provide the stratigraphic and palaeoclimatic context of monsoonal rainfall dynamics and their responses to orbital forcing for the Bay of Bengal. Using sediment lightness we established an age model at orbital resolution for International Ocean Discovery Programme (IODP) Core U1452C-1H that covers the last 200 ka in the lower Bengal Fan. The low-resolution δ18O of G. sacculifer is consistent with global δ18O records, at least for major glacial-to-interglacial transitions. The variability of total organic carbon, total nitrogen, and the δ13C composition of organic matter indicate the marine origin of organic matter. Marine primary productivity likely increased during insolation minima, indicative for an enhanced NE monsoon during glacials and stadials. Pristine insolation forcing is also documented for wet-bulk density, red-green color variability, and grain-size variations, indicating that darker and coarser-grained material deposited at higher sedimentation rates during insolation minima. Stronger NE monsoon likely amplified ocean-atmosphere interactions over the Indian Ocean, leading to stronger upwelling through shoaling the thermocline, and higher delivery of sediment to the Bay of Bengal due to higher soil erosion on land. In addition, lower glacial and stadial sea levels as well as stronger westward surface circulation favored delivery of coarser-grained fluvial material to the lower Bengal Fan. At the same time the stronger NE monsoon might have increased the aeolian supply. Total inorganic carbon, the Ca/Ti ratio, and biogenic silica vary dominantly on obliquity frequencies, suggesting mobilization and transport of lithogenic material primarily during lowered sea levels and/or higher influence of the Northern Hemisphere westerlies on the dust transport from the Tibetan Plateau. The close resemblance of sediment lightness and the climate record of Antarctic ice cores over multiple glacial cycles indicate close relationship between high southern latitude and tropical Asian climate through shifts in position of the Intertropical Convergence Zone. The Bengal Fan monsoonal record shows very clear and strict responses to insolation forcing in the lower part from ~200 ka to the Younger Toba Tuff during Marine Isotope Stage (MIS) 7 – 5, and less distinct response patterns after deposition of the ash during MIS 4 – 2, consistent with low-amplitude changes in insolation.

High-resolution sediment echosounder data combined with radiocarbon-dated sediment cores allowed us to reconstruct the Late Quaternary stratigraphic architecture of the Kveithola Trough and surrounding Spitsbergenbanken. The deposits display the successive deglacial retreat of the Svalbard-Barents Sea Ice Sheet. Basal subglacial till indicates that the grounded ice sheet covered both bank and trough during the Late Weichselian. A glaciomarine blanket inside the trough coinciding with laminated plumites on the bank formed during the initial ice-melting phase from at least 16.1 to 13.5 cal ka BP in close proximity to the ice margin. After the establishment of open-marine conditions at around 13.5 cal ka BP, a sediment drift developed in the confined setting of the Kveithola Trough, contemporary with crudely laminated mud, an overlying lag deposit, and modern bioclastic-rich sand on Spitsbergenbanken. The Kveithola Drift shows a remarkable grain-size coarsening from the moat towards the southern flank of the trough. This trend contradicts the concept of a separated drift (which would imply coarser grain sizes in proximity of the moat) and indicates that the southern bank is the main sediment source for the coarse material building up the Kveithola Drift. This depocenter represents, therefore, a yet undescribed combination of off-bank wedge and confined drift. Although the deposits inside Kveithola Trough and on Spitsbergenbanken display different depocenter geometries, time-equivalent grain-size changes imply a region-wide sediment-dynamic connection. We thus relate a phase of coarsest sediment supply (8.8–6.3 cal ka BP) to an increase in bottom current strength, which might be related to a stronger Atlantic Water inflow from the Southeast across the bank leading to winnowing and off-bank export of sandy sediments.

The deep southern component water (SCW), comprising Lower Circumpolar Deep Water (LCDW) and Antarctic Bottom Water (AABW), is a major component of the global oceanic circulation. It has been suggested that the deep Atlantic water mass structure changed significantly during the last glacial/interglacial cycle. However, deep SCW source-proximal records remain sparse. Here we present three coherent deep SCW paleocurrent records from the deep Argentine continental margin shedding light on deep water circulation and deep SCW flow strength in the Southwest Atlantic since the Last Glacial Maximum (LGM). Based on increased sortable silt values, we propose enhanced deep SCW flow strength from 14 to 10 cal ka B.P. relative to the early deglacial/LGM and the Holocene. We propose a direct influence of deep northern component water (NCW) on deep SCW flow strength due to vertical narrowing of deep SCW spreading, concurrent with a migration of the high-energetic LCDW/AABW interface occupying our core sites. We suggest a shoaled NCW until 13 cal ka B.P., thereby providing space for deep SCW spreading that resulted in reduced carbonate preservation at our core sites. Increased carbonate content from 13 cal ka B.P. indicates that the NCW expanded changing deep water properties at our core sites in the deep Southwest Atlantic. However, southern sourced terrigenous sediments continued to be deposited at our core sites, suggesting that deep SCW flow was uninterrupted along the Argentine continental margin since the LGM.

PARASOUND (3.5 kHz) subbottom echosounder profiles acquired on the southern Spitsbergenbanken, NW Barents Sea, show iceberg-keel scouring features which are buried by sediment that accumulated during the post Last Glacial Maximum (LGM) sea-level rise. Four acoustic units (Units 1 to 4 in stratigraphic order) were differentiated, based on the characterization of their acoustic facies and reflection surfaces. Unit 1 shows a chaotic internal structure and is interpreted as a glacial till, whereas the laminated Units 2 to 4 accumulated by sediment settling from suspension clouds and bottom currents during the last deglaciation phase. The top of Unit 2 was frequently incised by iceberg keels, resulting in up to 12 m deep ploughmarks which were later filled and buried by Unit 3 and 4 sediments. Three main paleo-evironmental changes controlled the evolution of the facies succession: (1) The major shift from till formation (Unit 1) below grounded ice to the accumulation of laminated sediments (Unit 2) which are inferred to reflect ice lifting and meltwater release; (2) Iceberg-keel scouring after sedimentation of Unit 2; (3) the probable abrupt termination of iceberg-keel scouring related to the glacio-eustatic sea-level rise. A linkage between these episodes of changes and short-lasting phases of rapid post LGM sea-level rise, such as meltwater pulses, is inferred, although further studies are needed to better understand the temporal and genetic relationships between the sedimentary events recognized in the Barents Sea and climate changes.

Rebesco, Michele ... et al.-- Special Issue: PAST Gateways (Palaeo-Arctic Spatial and Temporal Gateways).-- 16 pages, 12 figures, 2 tables, supplementary data http://dx.doi.org/10.1016/j.quascirev.2016.02.007, Kveithola is a glacially-carved, E-W trending trough located in the NW Barents Sea, an epicontinental shelf sea of the Arctic Ocean located off northern Norway and Russia. A set of confined sediment drifts (the “Kveithola Drift”) is located in the inner part of the trough. In general, drift deposits are commonly characterized by high lateral continuity, restricted occurrence of hiatuses and relatively high accumulation rates, and thus represent excellent repositories of paleo-environmental information. We provide for the first time a detailed morphological and seismostratigraphic insight into this sediment drift, which is further supported by some preliminary lithological and sedimentological analyses. The complex morphology of the drift, imaged by combining all available multibeam data, includes a main and a minor drift body, two drift lenses in the outer part of the trough, more or less connected drift patches in the innermost part and small perched sediment patches in a structurally-controlled channel to the north. The seismic (PARASOUND) data show that the main and minor drift bodies are mainly well-stratified, characterized by sub-parallel reflections of moderate to high amplitude and good lateral continuity. The reflectors show an abrupt pinch-out on the northern edge where a distinct moat is present, and a gradual tapering to the south. Internally we identify the base of the drift and four internal horizons, which we correlate throughout the drift. Two units display high amplitude reflectors, marked lensoidal character and restricted lateral extent, suggesting the occurrence of more energetic sedimentary conditions. Facies typical for contourite deposition are found in the sediment cores, with strongly bioturbated sediments and abundant silty/sandy mottles that contain shell fragments. These characteristics, along with the morphological and seismic information, suggest a strong control by a bottom current flowing along the moat on the northern edge of the drift. Though both Atlantic and Arctic waters are known to enter the trough, from the west and the north respectively, brine-enriched shelf water (BSW) produced during winter and flowing westward in the moat, is suggested to be responsible for the genesis of the Kveithola Drift. The formation of BSW is inferred to have started around 13 cal ka BP, the onset of drift deposition, suggesting that conditions leading to atmospheric cooling of the surface waters and/or the presence of coastal polynyas and wind or floating ice shelves have persisted on the western Barents Shelf since that time. The units inferred to have been deposited under more energetic sedimentary conditions (tentatively dated to the Younger Dryas and to 8.9–8.2 cal ka BP) are suggestive of stronger BSW formation. In general, we infer that variations in the bottom current regime were mainly related to BSW formation due to atmospheric changes. They could also have been a response to successive episodes of grounded and sea ice retreat that allowed for a first limited, later open shelf current, which progressively established on the western Barents Sea shelf, The research cruise MSM30 CORIBAR and this study were partly funded through the MARUM DFG-Research Center/Cluster of Excellence “The Ocean in the Earth System” as part of MARUM project SD-2. This study contributes to the IPY initiative 367 NICESTREAM (Neogene Ice Streams and Sedimentary Processes on High- Latitude Continental Margins). The work was funded by the Italian projects OGS-EGLACOM, PNRA-CORIBAR-IT (PdR 2013/C2.01), ARCA (grant n. 25_11_2013_973) and PNRA-VALFLU, by the Council of Norway through its Centres of Excellence funding scheme (project number 223259), by the Spanish projects DEGLABAR (CTM2010-17386) and CORIBAR-ES (CTM2011-14807-E) funded by the “Ministerio de Economia y Competitividad”. The “Generalitat de Catalunya” is acknowledged for support through an excellence research group grant (2014SGR940). J.L. was funded by an FPI grant BES-2011-043614

27 pages, 14 figures, 4 tables, supporting information https://doi.org/10.1111/bre.12331, Using a combination of geophysical and geotechnical data from Storfjorden Trough Mouth Fan off southern Svalbard, we investigate the hydrogeology of the continental margin and how this is affected by Quaternary glacial advances and retreats over the continental shelf. The geotechnical results show that plumites, deposited during the deglaciation, have high porosities, permeabilities and compressibilities with respect to glacigenic debris flows and tills. These results together with margin stratigraphic models obtained from seismic reflection data were used as input for numerical finite element models to understand focusing of interstitial fluids on glaciated continental margins. The modelled evolution of the Storfjorden TMF shows that tills formed on the shelf following the onset of glacial sedimentation (ca. 1.5 Ma) acted as aquitards and therefore played a significant role in decreasing the vertical fluid flow towards the sea floor and diverting it towards the slope. The model shows that high overpressure ratios (up to λ ca. 0.6) developed below the shelf edge and on the middle slope. A more detailed model for the last 220 kyrs accounting for ice loading during glacial maxima shows that the formation of these aquitards on the shelf focused fluid flow towards the most permeable plumite sediments on the slope. The less permeable glacigenic debris flows that were deposited during glacial maxima on the slope hinder fluid evacuation from plumites allowing high overpressure ratios (up to λ ca. 0.7) to develop in the shallowest plumite layers. These high overpressures likely persist to the Present and are a critical precondition for submarine slope failure, This study is funded by the ‘Ministerio Economia y Competitividad’ through grants DEGLABAR, (CTM2010‐17386), CORIBAR‐ES (CTM2011‐14807‐E) and SVAIS (POL2006‐07390). UNESCO and IUGS are also acknowledged for funding through projects IGCP‐585 and IGCP‐640. The Italian contribution was supported by PNRA project 2013/B2.08 VALFLU

Mud accumulates on continental shelves under a variety of environmental conditions and results in a diverse formation of mud depocenters (MDCs). Their three-dimensional architectures have been in the focus of several recent studies. Due to some terminological confusion concerning MDCs, the present study sets out to define eight individual MDC types in terms of surface sediment distribution and internal geometry. Under conditions of substantial sediment supply, prodeltas (distal zones off river deltas; triangular sheets), subaqueous deltas (disconnected from deltas by strong normal-to-shore currents; wedge-like clinoforms), and mud patches (scattered distribution) and mud blankets (widespread covers) are formed. Forced by hydrodynamic conditions, mud belts in the strict sense (detached from source; elongated bodies), and shallow-water contourite drifts (detached from source; growing normal to prevailing current direction; triangular clinoforms) develop. Controlled by local morphology, mud entrapments (in depressions, behind morphological steps) and mud wedges (triangular clinoforms growing in flow direction) are deposited. Shelf mud deposition took place (1) during early outer-shelf drowning (~14 ka), (2) after inner-shelf inundation to maximum flooding (9.5–6.5 ka), and (3) in sub-recent times (

In paleoenvironmental studies, the mineralogical composition of sediments is an important indicator. In combination with other indicators, they contribute to the understanding of changes in sediment sourcing as well as in weathering and depositional processes. Fourier transform infrared spectroscopy (FTIRS) spectra contain information on mineralogical composition because each mineral has a unique absorption pattern in the mid-IR range. Although easily obtained, FTIR spectra are often too complex to infer mineral concentrations directly. In this study, we use a calibration set of ca. 200 sediment samples conventionally measured using X-ray diffraction (XRD) in order to develop multivariate, partial least squares (PLS) regression models relating mineral contents to sediment spectra. Good correlations were obtained for the most common minerals (e.g. quartz, K-feldspar, illite, plagioclase, smectite, calcite). Correlation coefficients ranged from 0.85 to 0.92, coefficients for the validation varied from 0.64 to 0.80, the number of latent variables (PLS regression components) in the models ranged between 3 and 7 and the range of variation of the RMSEcv gradient was from 15.28 to 5.7.

The Mar del Plata (MdP) Canyon at the Argentine continental margin is incorporated into a major contourite depositional system, built by the incursion of southern-sourced water masses affecting the seafloor at different waters depths. The new sedimentological, morphological and hydro acoustic data provide novel insights into contour and turbidity current interactions in mid-slope (blind) canyons, which do not have a connection to the shelf or an onshore river system. Such canyons are capable to record climate-related ocean stratification changes, current variability, and slope stability. Three sediment cores were obtained along the MdP Canyon thalweg covering the last 20,000 years and compiled with two cores from the adjacent Ewing Terrace. Turbidity-current activity within the MdP Canyon was limited to the time interval from Last Glacial Maximum (LGM) to the late deglacial. During the LGM and early deglacial, turbidites reached both the proximal sector and the distal northern flank of the canyon. During the late deglacial only the proximal sector was characterized by turbidite deposition. Similarities in mineralogy and grain-size data indicate that the material transported by the turbidity currents originated from the mid-slope Ewing Terrace. Glacial turbidity-current activity was most probably favored by increased sediment supply along the Ewing Terrace from a shallowed and/or enhanced glacial Antarctic Intermediate Water (AAIW) nepheloid layer. These sediments were trapped by the MdP Canyon, in particular at the head area. During the late deglacial, a displacement or limited AAIW nepheloid layer resulted in less sediment transfer along the Ewing Terrace and immediate accumulation in the MdP Canyon head restricting turbidite deposition to the proximal sector of the canyon. In general, contourite-turbidite interactions provide valuable information on variations in thermohaline circulation such as AAIW distribution and current strength.

Based on a well-established stratigraphic framework and 47 AMS-14C dated sediment cores, the distribution of facies types on the NW Iberian margin is analysed in response to the last deglacial sea-level rise, thus providing a case study on the sedimentary evolution of a high-energy, low-accumulation shelf system. Altogether, four main types of sedimentary facies are defined. (1) A gravel-dominated facies occurs mostly as time-transgressive ravinement beds, which initially developed as shoreface and storm deposits in shallow waters on the outer shelf during the last sea-level lowstand; (2) A widespread, time-transgressive mixed siliceous/biogenic-carbonaceous sand facies indicates areas of moderate hydrodynamic regimes, high contribution of reworked shelf material, and fluvial supply to the shelf; (3) A glaucony-containing sand facies in a stationary position on the outer shelf formed mostly during the last-glacial sea-level rise by reworking of older deposits as well as authigenic mineral formation; and (4) A mud facies is mostly restricted to confined Holocene fine-grained depocentres, which are located in mid-shelf position. The observed spatial and temporal distribution of these facies types on the high-energy, low-accumulation NW Iberian shelf was essentially controlled by the local interplay of sediment supply, shelf morphology, and strength of the hydrodynamic system. These patterns are in contrast to high-accumulation systems where extensive sediment supply is the dominant factor on the facies distribution. This study emphasises the importance of large-scale erosion and material recycling on the sedimentary buildup during the deglacial drowning of the shelf. The presence of a homogenous and up to 15-m thick transgressive cover above a lag horizon contradicts the common assumption of sparse and laterally confined sediment accumulation on high-energy shelf systems during deglacial sea-level rise. In contrast to this extensive sand cover, laterally very confined and maximal 4-m thin mud depocentres developed during the Holocene sea-level highstand. This restricted formation of fine-grained depocentres was related to the combination of: (1) frequently occurring high-energy hydrodynamic conditions; (2) low overall terrigenous input by the adjacent rivers; and (3) the large distance of the Galicia Mud Belt to its main sediment supplier.

The high-energy, low-accumulation NW Iberian shelf features three confined Holocene mud depocentres. Here, we show that the evolution of such depocentres follows successive steps. The flooding of inner shelf zones and river catchment areas by the late deglacial sea-level rise provided the precondition for shelf mud deposition. Following this, the Holocene deceleration of the sea-level rise caused a rapid refill of the accommodation space within river valleys. Subsequently, the export of major amounts of fines was initiated. The initial onset and loci of shelf mud deposition were related to deposition-favouring conditions in mid-shelf position or to the presence of morphological highs, which act as sediment traps by providing protection against stronger hydrodynamic energy. The detailed reconstruction of the Holocene depocentre evolution shows for the first time that the expansion of such shelf mud deposits cannot only occur by linear growth off the associated sediment source. Rather, they might develop around centres that are fully disconnected from the source of original sediment supply, and expand later into specific directions. Based on these differences and on the connection of the individual mud depocentres to the material source we propose a conceptual subdivision of the group “mid-shelf mud depocentres”.

Continental shelves represent areas of highest economical and ecological importance. Nevertheless, these sedimentary systems remain poorly understood due to a complex interplay of various factors and processes which results in highly individual construction schemes. Previous studies of sedimentary shelf systems have mainly focused on a limited number of cores, retrieved from Holocene fine-grained depocentres. As such, the relation between shelf architecture and sedimentary history remains largely obscure. Here, we present new data from the NW Iberian shelf comprising shallow-seismic profiles, a large number of sediment cores, and an extended set of radiocarbon dates to reveal the Late Quaternary evolution of a low-accumulation shelf system in detail. On the NW Iberian shelf, three main seismic units are identified. These overly a prominent erosional unconformity on top of the basement. The lowermost Unit 1 is composed of maximal 75-m thick, Late Tertiary to Pleistocene deposits. The youngest sediments of this unit are related to the last glacial sea-level fall. Unit 2 was controlled by the deglacial sea-level rise and shows a maximum thickness of 15 m. Finally, Unit 3 comprises deposits related to the late stage of sea-level rise and the modern sea-level highstand with a thickness of 4 m in mid-shelf position. Two pronounced seismic reflectors separate these main units from each other. Their origin is related to (1) exposure and ravinement processes during lower sea level, and (2) to reworking and re-deposition of coarse sediments during subsequent sea-level rise. According to the sediment core ground-truthing, sediments of the Late Tertiary to Pleistocene unit predominantly display homogenous fine sands with exceptional occurrences of palaeosols that indicate an ancient exposure surface. Fine sands which were deposited in the run of the last sea-level rise show a time-transgressive retrogradational development. The seismic reflectors, bounding the individual units, appear in the cores as 0.1 to 1-m thick deposits consisting either of shell gravels or siliceous coarse sands with gravels. The modern sea-level highstand stage is characterised by zonal deposition of mud forming a mud belt in mid-shelf position, and sediment starvation on outer shelf zones. Radiocarbon ages indicate that this mud belt was the main depocentre for river-supplied fine material on the NW Iberian shelf at least over the past 5.32 ka BP. The initial onset of this depocentre is proposed to be related to a shift in the balance between rate of sea-level rise and amount of terrigenous sediment supply. Various other stratigraphical shelf reconstructions reveal analogies in architecture which indicate that timing and shaping of the individual units on low-accumulation shelves is fundamentally controlled by eustatic sea-level changes. Other factors of local importance such as differential elevation of the basement and the presence of morphological barriers formed by rocky outcrops on the seafloor have additionally modifying influence on the sedimentary processes.

The sedimentation on the Mauritanian shelf off the western Saharan desert is strongly influenced by dust supply and is investigated in this study by combining surface mapping, shallow-acoustic profiling and the analysis of sediment cores. Coarse-grained carbonates dominate wide areas of the open shelf at places where the shelf is exposed to the Atlantic Ocean. The sheltered Golfe d'Arguin, in contrast, is characterized by muddy shoals in its inner area, and locally restricted and wedge-shaped muddy depocenters which extend contour-parallel in mid-shelf settings. In both cases, cross-shelf currents control sediment distribution and accumulation, not location or amount of primary eolian input. A major discontinuity on the outer shelf is located in 85–110 m water plus sediment depth and is refilled by a sedimentary facies succession of shoreface, tidal and open-shelf deposits. This succession has formed during temporary lower sea levels along the last overall regression (MIS-4 and MIS-3), the Last Glacial Maximum, and during the past deglacial sea-level rise. Significant sediment deposition and preservation is limited to very restricted areas. Concerning the overall shelf architecture, sea level was the main factor enabling or suppressing deposition in terms of 1) creating local erosional swales which have favored subsequent trapping and preservation of sediments; 2) determining the type of sedimentary facies refilling these depressions under a variety of nearshore conditions; 3) interacting with the seafloor morphology and, by this, controlling timing of initiation and growth geometry of mud wedges. These mud wedges have formed since ca. 9 cal. ka under a continuous sedimentation regime. These bodies must have formed in hydraulic equilibrium but they are detached from a defined sediment point source which is in contrast to common mudbelt formation on shelves. In general, sediment storage on shelves under hyperarid conditions seems to be very limited due to comparably low sediment input, strong ravinement activity during changing sea levels, significant bypassing and winnowing processes, and a low preservation potential of the non-cohesive materials. These conditions lead to the development of almost sediment-starved systems with low subsidence rates over longer geological timescales.

Middle Pleistocene to Holocene sediment variations observed in a 26 metre long core taken during a cruise of the RV Marion Dufresne are presented. Core MD992202 was retrieved from the northern slope of Little Bahama Bank and provides an excellent example for sedimentation processes in a mid-slope depositional environment. The sediment composition indicates sea-level related deposition processes for the past 375000 years (marine isotope stages 1 to 11). The sediments consist of: (i) periplatform ooze (fine-grained particles of shallow-water and pelagic origin) with moderate variations in carbonate content, carbonate mineralogy and grain-size; and (ii) coarser intervals with cemented debris consisting of massive, poorly sorted, mud-supported or clast-supported deposits with an increased high-magnesium calcite content. During interglacial stages (marine isotope stages 1, 5, 7, 9 and 11) periplatform oozes (i) are characterized by higher aragonite contents, finer grain-size and higher organic contents, whereas during glacial stages (marine isotope stages 2 to 4, 6, 8 and 10), increased low-magnesium and high-magnesium calcite values, coarser grain-size and lower organic contents are recorded. These glacial to interglacial differences in mineralogy, grain-size distribution and organic content clearly show the impact of climatically controlled sea-level fluctuations on the sedimentation patterns of the northern slope of Little Bahama Bank. The coarser deposits (ii) occur mainly at the transitions from glacial to interglacial and interglacial to glacial stages, and are interpreted as redeposition events, indicating a direct link between sediment properties (changes in mineralogy, grain-size distribution, variations in organic contents) and sea-level fluctuations. Changes in hydrostatic pressure and the wave base position during sea-level changes are proposed to have triggered these large-scale sediment redepositions. © 2007 The Authors. Journal compilation © 2007 International Association of Sedimentologists.

The continental margin off the La Plata Estuary (SE South America) is characterized by high fluvial sediment supply and strong ocean currents. High-resolution sediment-acoustic data combined with sedimentary facies analysis, AMS-14C ages, and neodymium isotopic data allowed us to reconstruct late Quaternary sedimentary dynamics in relation to the two major sediment sources, the La Plata Estuary and the Argentine margin. Sediments from these two provinces show completely different dispersal patterns. We show that the northward-trending La Plata paleo-valley was the sole transit path for the huge volumes of fluvial material during lower sea levels. In contrast, material from the Argentine margin sector was transported northwards by the strong current system. Despite the large sediment volumes supplied by both sources, wide parts of the shelf were characterized by either persistent non-deposition or local short-term depocenter formation. The location and formation history of these depocenters were primarily controlled by the interplay of sea level with current strength and local morphology. The high sediment supply was of secondary importance to the stratigraphic construction, though locally resulting in high sedimentation rates. Thus, the shelf system off the La Plata Estuary can be considered as a hydrodynamic-controlled end-member.