Sensitivity of Holocene East Antarctic productivity to subdecadal variability set by sea ice
(Nature Geoscience. vol. 14, n° 1752-0894, pp. 762-768, 01/10/2021)
EPOC, EPHE, PSL, UB, INSU - CNRS, CNRS
Origin and preservation conditions of organic matter in the Mozambique Channel: Evidence for widespread oxidation processes in the deep-water domains
The Mozambique and Madagascar margins present major rivers that are responsible for the discharge of large amounts of terrestrial organic matter (OM) which can influence carbon cycling in marine environments. Therefore, the Mozambique channel represents a unique case to study the fate of the organic carbon in deepwater domains. Using a new and extensive data set of sedimentary OM collected from sediment traps, seafloor sediments and core sediments, we address the origin of the OM that is transported and deposited in the Mozambique Channel, its degradation state and preservation conditions. A Rock-Eval 6 survey allowed us to characterize the origin and amount of OM from shallow to deep-water turbidite systems, between 500 and 4400 m water depth. Rock-Eval 6 performed on suspended sediments within particle traps at 47 m above the seabed show that the OM is transported into the deep-water domain with relatively high TOC (between 1.5 and 2.5%). However, the OM is largely oxidized close to the water-sediment interface (Oxygen Index >300 mg CO 2 /g TOC). Seafloor sediments sampled to a maximum depth of 40 cm show lower TOC values compared to those collected from particle traps suggesting that the degradation of the OM is mainly active at the water-sediment interface. Small concentrations of OM are preserved within the recent sediments of the distal area of the Zambezi turbidite system below 2500 m water depth (TOC < 0.5%). Rock-Eval results show that core sediments from the Majunga slope (NW margin of Madagascar) and the Zambezi slope (Mozambique margin) contain the highest concentration of terrestrial OM (TOC between 1 and 2%). However, the OM within core sediments from the deep-water domain is largely oxidized and degraded, probably due to the conjugate effect of low sediment accumulation rates (SARs) and high permeabilities of the coarse-grained sediments. Consequently, the deep-water domain of the Mozambique Channel does not seem to be an important sink of terrestrial OM. This process is reinforced by important bottom water currents which induce the remobilization and transport of seafloor sediments that lead to higher oxygen exposure time in the uppermost centimeters of sediments.
(Marine Geology. vol. 440, n° 0025-3227, pp. 106589, 01/10/2021)
IFPEN, LFCR, UPPA, CNRS, IFREMER, EPOC, EPHE, PSL, UB, INSU - CNRS, CNRS
Sediment dynamics and morphological evolution in the Tagus Estuary inlet
The morphological evolution of the Tagus estuary inlet in the last century is analyzed in order to characterize its dynamics, explain its behavior and anticipate its future evolution. First, the evolution is characterized through a literature review, complemented by new data analyses. This review synthesizes the present understanding of the inlet's dynamics and highlights some key questions that remain unanswered. To address these questions, a 2DH process-based morphodynamic model is implemented and validated, and then used to refine the previous understanding of the inlet's dynamics. A new conceptual model, which highlights a seasonal behaviour of the inlet's morphodynamics, is proposed. During winter time, the residual sediment transport is directed seaward along the navigation channel, towards the inlet mouth along the beaches adjacent to the inlet, and towards the estuary over the southern part of the ebb delta (Cachopo Sul). During the maritime summer, residual sediment fluxes are approximately half those occurring during winter. The relative importance of tidal flows increases, leading to sediment fluxes directed towards the southwest over the Cachopo Sul. The sediment deposits formed during the summer can be mobilized under specific wave conditions and transported to the northern stretch of the beaches to the south of the inlet. A positive feedback between the erosion of the Cachopo Sul-or, similarly, sea level rise-and the sediment fluxes over this bank suggests that the evolution of the bank observed during the last decades will continue in the foreseeable future.
(Marine Geology. vol. 440, n° 0025-3227, pp. 106590, 01/10/2021)
LNEC, LIENSs, INSU - CNRS, ULR, CNRS, IRSTEA, EPOC, EPHE, PSL, UB, INSU - CNRS, CNRS
Remotely-sensed rip current dynamics and morphological control in high-energy beach environments
Understanding the surf zone circulation and the morphological changes within the nearshore is essential for both scientific and societal interests. However, direct measurements with in-situ instruments are logistically challenging and expensive. The development of optical remote sensing techniques in combination with low-cost image platforms and open-source algorithms offers the possibility of collecting large amounts of information at a reasonable instrumental and computational cost. This work builds on existing and new video monitoring techniques to remotely sense the nearshore bathymetry as well as the surf zone circulation in a high-energy meso-macro tidal beach environment, including storm events. The methods are validated against a dense data set acquired during an intensive field campaign conducted at Anglet beach, SW France. For the first time the temporal and spatial variability of concurrent nearshore bathymetry and surface currents are addressed under high-energy wave forcing.
(30/09/2021)
EPOC, EPHE, PSL, UB, INSU - CNRS, CNRS
Are past sea‐ice reconstructions based on planktonic foraminifera realistic? Study of the last 50 ka as a test to validate reconstructed paleohydrography derived from transfer functions applied to their fossil assemblages
Since its existence, paleoceanography has relied on fossilized populations of planktonic foraminifera. Except for some extreme environments, this calcareous protist group composes most of the silty‐to‐sandy fraction of the marine sediments, i.e., the foraminiferal oozes, and its extraction is probably the simplest among the currently existing set of marine fossil proxies. This tool has provided significant insights in the building of knowledge on past climates based on marine ar-chives, especially with the quantification of past hydrographical variables, which have been a turning point for major comprehensive studies and a step towards the essential junction of modelling and paleodata . In this article, using the modern analog technique and a database compiling modern analogs (n = 1007), we test the reliability of this proxy in reconstructing paleohydro-graphical data other than the classical sea‐surface temperatures, taking advantage of an update regarding a set of extractions from the World Ocean Atlas for transfer functions. Our study focuses on the last glacial period and its high climatic variability, using a set of cores distributed along the European margin, from temperate to subpolar sites. We discuss the significance of the reconstructed parameters regarding abrupt and extreme climate events, such as the well‐known Heinrich events. We tested the robustness of the newly obtained paleodata by comparing them with older published reconstructions, especially those based on the complementary dinoflagellate cyst proxy. This study shows that the potential of planktonic foraminifera permits going further in reconstructions, with a good degree of confidence; however, this implies considering ecological forcings in a more holistic perspective, with the corollary to integrate the message of this fossil protist group, i.e., the obtained parameters, in light of a cohort of other data. This article constitutes a first step in this direction. © 2021 by the authors. Licensee MDPI, Basel, Switzerland.
(Geosciences. vol. 11, n° 2076-3263, 28/09/2021)
EPOC, EPHE, PSL, UB, INSU - CNRS, CNRS
Skillful decadal prediction of unforced southern European summer temperature variations
Abstract We assess the capability of decadal prediction simulations from the Coupled Model Intercomparison Project phase 6 (CMIP6) archive to predict European summer temperature during the period 1970–2014. Using a multi-model ensemble average, we show that Southern European (SEU) summer temperatures are highly predictable for up to ten years in CMIP6. Much of this predictive skill, is related to the externally forced response: historical simulations explain about 90% of observed SEU summer temperature variance. Prediction skill for the unforced signal of SEU summer temperature is low: initialized model simulations explain less than 10% of observed variance after removing the externally forced response. An observed link between unforced SEU summer temperature and preceding spring Eastern North Atlantic—Mediterranean sea surface temperature (SST) motivates the application of a dynamical-statistical model to overcome the low summer temperature skill over Europe. This dynamical-statistical model uses dynamical spring SST predictions to predict European summer temperature, and significantly increases decadal prediction skill of unforced European summer temperature variations, showing significant prediction skill for unforced Southern European summer temperature 2–9 years ahead. As a result, dynamical-statistical models can benefit the decadal prediction of variables with initially limited skill beyond the forcing, such as summer temperature over Europe.
(Environmental Research Letters. vol. 16, n° 1748-9326, pp. 104017, 23/09/2021)
GKSS, UHH, LOCEAN-VARCLIM, LOCEAN, MNHN, IRD, INSU - CNRS, SU, CNRS, IPSL (FR_636), ENS-PSL, UVSQ, CEA, INSU - CNRS, X, CNES, SU, CNRS, UPCité, EPOC, EPHE, PSL, UB, INSU - CNRS, CNRS
Coastal dynamics and the evolution of the Acholla lagoon (Gulf of Gabes, Tunisia): a multiproxy approach
This study explores the paleoenvironmental changes of the Acholla coast over the last 2000 years by means of subsurface sediment analyses of lagoonal deposits via a multiproxy approach. A sequence of 5 steps is shown to have shaped the coastal development at Acholla and includes (i) the settlement of an open marine embayment during the Upper Pleistocene (substage 5e) in response to a transgressive event as evidenced by the deposition of carbonate sandstones rich in mollusc associations and marine elemental ratios Sr/Al, Ca/Al, Cl/Al, and S/Al; (ii) a sea-level rise towards183 AD, after a long period of emergence of the coast, leading to transgressive deposits of poorly sorted fine sands that are rich in diversified mollusc and ostracod taxa; (iii) a high-energy event (towards 417AD) with a peculiar biofacies characterized by coarse bioclastic mollusc-rich sands, charcoal particles, Tyrrhenian lithoclasts, and high values of marine elemental ratios Cl/Al, S/Al, and Ca/Al; (iv) a progradation of coastal habitats (between 417 and 1577 AD), favored by a period of flooding/detrital input and longshore current drifts, resulting in the development of an extensive sandspit and the formation of the Acholla lagoon. The construction of a Roman pier, originally constructed to protect the Acholla harbor from sedimentation, was counterproductive and favored the expansion of coastal swash bars and extension of the sandspit, ultimately resulting in the abandonment of the Acholla harbor; (v) the closure of the lagoon (from 1577 AD onward) and the built-up of well-sorted silt deposits are marked by the decrease of detrital elemental ratios (Ti/Al, Si/Al, and K/Al) and by reduced ostracod species richness values. The inferred scenario for the evolution at Acholla coast matches those for Sfax and Skhira coast in the Gulf of Gabes (Tunisia). Unlike Sfax and Skhira, however, the Acholla coast has been subjected to uplift by active faults, resulting in a time shift of depositional patterns. © 2021, Saudi Society for Geosciences.
(Arabian Journal of Geosciences. vol. 14, n° 1866-7511, 16/09/2021)
EPOC, EPHE, PSL, UB, INSU - CNRS, CNRS
Impacts d'un agent de désinfection sur les communautés périphytiques d'eau douce
(14/09/2021)
UR EABX, INRAE, EPOC, EPHE, PSL, UB, INSU - CNRS, CNRS
Improving the chronology of marine cores: IRSL dating and Bayesian modelling of a core from the Bay of Biscay (NE Atlantic)
(13/09/2021)
IRAMAT-CRP2A, IRAMAT, UTBM, UO, UBM, CNRS, EPOC, EPHE, PSL, UB, INSU - CNRS, CNRS, EPHE, PSL, LMJL, UN UFR ST, UN, CNRS
Revision of the French Terebellidae sensu stricto (Annelida, Terebelliformia), with descriptions of nine new species
This work is the last of four papers of the Spaghetti Project, aiming to revise the species of terebellids, a.k.a. “spaghetti” worms, present in the European French waters. In this last paper the Terebellidae, sensu stricto, from French waters are revised based, on material available in the French marine stations, type materials stored in the MNHN collection and newly collected specimens. Nine new species are described using both morphological and molecular tools: Eupolymnia gili n. sp., E. lacazei n. sp., E. meissnerae n. sp., Lanice kellyslateri n. sp., Paramphitrite dragovabeci n. sp., Pista labruneae n. sp., P. miosseci n. sp., P. sauriaui n. sp., and Terebella banksyi n. sp. European species of Eupolymnia are distinguished mainly by the shape of the lateral lobes and the size of the branchial stems. The two species belonging to Lanice genus are distinguished by the fusion of the first ventral shields, the shape of both noto- and neuropodia, and the pigmentation of the upper lip. The two species of Paramphitrite are distinguished by the presence or absence of a medial dorsal gap between the pairs of branchiae, by the shape of the lateral lobes and the presence or absence of a nephridial papilla on segment 4. The different species of Pista are distinguished by the number of pairs of branchiae, the shape of the lateral lobes and uncini. Finally, the two species of Terebella are distinguished by the number of segments with nephridial and genital papillae and the segments on which the branchiae occur. An identification key for European species of Terebellidae sensu stricto is also provided.
(Zootaxa. vol. 5038, n° 1175-5326, pp. 1-63, 13/09/2021)
EPOC, EPHE, PSL, UB, INSU - CNRS, CNRS, UMS POREA, INSU - CNRS, CNRS, INRAE