Benthic Foraminiferal response to sea level change in the mixed siliciclastic-carbonate system of southern Ashmore Trough (Gulf of Papua)

Ashmore Trough in the western Gulf of Papua (GoP) represents an outstanding modern example of a tropical mixed siliciclastic-carbonate depositional system where significant masses of both river-borne silicates and bank-derived neritic carbonates accumulate. In this study, we examine how benthic foraminiferal populations within Ashmore Trough vary in response to sea level–driven paleoenvironmental changes, particularly organic matter and sediment supply. Two 11.3-m-long piston cores and a trigger core were collected from the slope of Ashmore Trough and dated using radiocarbon and oxygen isotope measurements of planktic foraminifera. Relative abundances, principal component analyses, and cluster analyses of benthic foraminiferal assemblages in sediment samples identify three distinct assemblages whose proportions changed over time. Assemblage 1, with high abundances of Uvigerina peregrina and Bolivina robusta, dominated between ∼83 and 70 ka (early regression); assemblage 2, with high abundances of Globocassidulina subglobosa, dominated between ∼70 and 11 ka (late regression through lowstand and early transgression); and assemblage 3, with high abundances of neritic benthic species such as Planorbulina mediterranensis, dominated from ∼11 ka to the present (late transgression through early highstand). Assemblage 1 represents heightened organic carbon flux or lowered bottom water oxygen concentration, and corresponds to a time of maximum siliciclastic fluxes to the slope with falling sea level. Assemblage 2 reflects lowered organic carbon flux or elevated bottom water oxygen concentration, and corresponds to an interval of lowered siliciclastic fluxes to the slope due to sediment bypass during sea level lowstand. Assemblage 3 signals increased off-shelf delivery of neritic carbonates, likely when carbonate productivity on the outer shelf (Great Barrier Reef) increased significantly when it was reflooded. Benthic foraminiferal assemblages in the sediment sink (slopes of Ashmore Trough) likely respond to the amount and type of sediment supplied from the proximal source (outer GoP shelf)

Deltaic and Coastal Sediments as Recorders of Mediterranean Regional Climate and Human Impact Over the Past Three Millennia

This work was financially supported by the MISTRALS/PaleoMex program and by the Project of Strategic Interest NextData PNR 2011–2013 (www. nextdataproject.it). Lionel Savignan is thanked for his participation in the biomarker analysis. Radiocarbon datings for core KESC9-14 have been funded by Institut Carnot Ifremer-EDROME (grant A0811101). We also thank the Holocene North-Atlantic Gyres and Mediterranean Overturning dynamic through Climate Changes (HAMOC) project for financial support. The biomarker data presented here are available in the supporting information.Peer reviewedPublisher PD

Millennial-Scale Response of a Western Mediterranean River to Late Quaternary Climate Changes: A View from the Deep Sea

Although it is widely accepted that erosion and sediment transfer respond to millennial-scale climatic variability, these changes remain difficult to detect in marine sedimentary archives. In the Var sediment-routing system, northwestern Mediterranean Sea, the absence of a continental shelf results in a direct connection between the Var River mouth and the deep basin during both highstand and lowstand conditions. This makes the Var sediment-routing system an ideal target to test whether rivers can transmit climate-driven high-frequency changes in sediment flux to the ocean. On the basis of an unprecedented (centennial-to-millennial-scale) resolution in turbidite sequences, we reconstructed the activity of turbidity current overflows along the deep-sea Var Sedimentary Ridge over the past 75 kyr. The overflow activity is highest (one event every 10-30 yr) during maximum glacial conditions (30 kyr-16 kyr ago [ka]) and rapidly decreases (down to one event every 100-500 yr) during the last glacial-interglacial transition (Termination 1). During marine isotope stage (MIS)4 and MIS3 (75-30 ka), peaks in the overflow activity occurred synchronously with cold and arid Dansgaard-Oeschger stadials, while warmer and wetter interstadial conditions correspond to low overflow activity. We conclude that overflow activity on the Var Sedimentary Ridge mainly reflects changes in the magnitude of hyperpycnal currents flowing in the turbiditic channel-levee system in relation with variations in suspended-sediment concentration during Var River floods. We show that this signal is sensitive to changes in pure sediment flux induced by climatic perturbations occurring inland: (1) the decrease in glacier-derived sediment input after glacier retreat and (2) changes in erosion induced by shifts in the vegetation cover in response to Dansgaard-Oeschger climate swings

Sea-level fluctuations control the distribution of highly liquefaction-prone layers on volcanic-carbonate slopes

Understanding and quantifying the hazards related to earthquake-induced submarine liquefaction and landslides are particularly significant offshore of tropical volcanic-carbonate islands, where carbonate production competes with volcanism to create highly contrasted lithological successions. To improve the detection of liquefaction-prone layers, we analyzed physical properties and mineralogy and performed 70 dynamic triaxial tests on 25 sediment cores offshore of the eastern side of Mayotte (Comoros archipelago in the western Indian Ocean) in an area that has experienced significant seismicity since 2018. We found that the main parameter controlling the liquefaction potential offshore of Mayotte is the presence of low-density layers with high calcite content accumulating along the slope during lowstands. This phasing with sea-level fluctuations implies a significant recurrent geohazard for tropical volcanic-carbonate islands worldwide. Furthermore, the relationship we found between the cyclic resistance of sediment and its density and magnetic susceptibility represents a time-effective approach for identifying the hazards related to earthquake-induced liquefaction

Bundled turbidite deposition in the central Pandora Trough (Gulf of Papua) since Last Glacial Maximum: Linking sediment nature and accumulation to sea level fluctuations at millennial timescale

Since Last Glacial Maximum (23-19 ka), Earth climate warming and deglaciation occurred in two major steps (Bølling-Allerød and Preboreal), interrupted by a short cooling interval referred to as the Younger Dryas (12.5-11.5 ka B.P.). In this study, thre

Late Quaternary geomorphology and sedimentary processes in the Zambezi turbidite system (Mozambique Channel)

International audienceThe morphology and present-day sediment distribution of the Zambezi turbidite system was investigated using new bathymetric and sub-bottom profiler data as part of the PAMELA research project. The Zambezi turbidite system is composed of two depositional systems: a channelized fan (the Zambezi Fan) and a semi-confined fan (in the Intermediate Basin). The Zambezi Fan includes the Zambezi Valley, which is deeply incised in the Mozambique Channel and is more than three times as large and deep as the great Tanzanian and North Atlantic Mid-Ocean channels. The erosion in the Zambezi Valley is evidenced by its V-shaped morphology and the existence of a U-shaped thalweg affected by several generations of incisions. Based on echo facies and cores from literature, sediments of the Zambezi Fan are dominantly coarse-grained and fine-grained overbank deposits are infrequent. The distal portion of the Zambezi Fan is a main depositional area where typical transparent wedged-shape seismic bodies are interpreted as terminal lobes. Seismic facies in the Intermediate Basin are thought to represent mostly fine-grained turbidites intercalated with infrequent coarse-grained sheet-like turbidites. Hydrodynamic circulation (from surface eddies to the deep circulation of NADW) appears to have a great impact on the Mozambique Channel sedimentation and is suggested (1) to be involved in the delivery of the Zambezi River sediments along the Mozambique margin, (2) to entrain the upper suspended load of turbidity currents, contributing to the absence of fine-grained sedimentation and (3) to contribute to the erosion of the valley flanks leading to the exceptionally great dimensions of the valle

Deglacial to Holocene environmental changes in the northern Ligurian Sea: The dual influence of regional climate variability and large-scale intermediate Mediterranean circulation

The sedimentary archives of the Mediterranean Sea record periodic deposits of organic-rich deposits, called sapmpels in the eastern basin and organic-rich layers (ORL) in the western basin. Changes in both the Mediterranean circulation and inputs of fresh water through borderlands rivers under more humid climate, are important mechanisms to explain those events. The last ORL and sapropel 51 have different timing, respectively from similar to 14.5 to 9 Ka and from similar to 10 to 6 Ka, presumably due to different forcing factors in the western basin (i.e., melting of Alps ice). Here we present a high-resolution study of a marine sediment core located off the mouth of the Var River, one of the most dynamic river system of the northern borderland of the western Mediterranean Sea. We applied a multi-proxy approach based on benthic foraminiferal assemblages, foraminiferal delta O-18 and delta O-13, grain size analyses, organic carbon content and XRF elemental data to decipher the regional climate signals from the basin-scale intermediate circulation signature. Our results do not show large river inputs at the timing of the last ORL deposit. On the opposite, foraminiferal and geochemical evidence indicate that the 11-6 kyr period, concomitant to Sapropel S1 event in the Eastern Mediterranean, was characterised by high river activity and low ventilated bottom waters at the studied location. Additionally, our results characterized the last 6 ka with large scale episodes of more active bottom water ventilation due perhaps to enhanced wind activity under an overall cooler climate. Time series analyses were computed from stable isotopes, Ca/Ti XRF ratio and foraminifera abundances. They show common frequencies peaks (2.2-3, 1.1-1.2, 0.9-1.0, and 0.4-0.5 kyr) most likely related to the solar activity. Also, a specific frequency band (1.5-1.6 kyr) was only recorded in benthic foraminiferal abundance and stable isotopic records. This was preferentially attributed to an oceanic-driven internal forcing