Factors controlling frequency of turbidites in the Bengal fan during the last 248 kyr cal BP: Clues from a presently inactive channel
(Marine Geology. vol. 415, n° 0025-3227, pp. 105965, 01/09/2019)
EPOC, EPHE, PSL, UB, INSU - CNRS, CNRS, PALEOCEAN, LSCE, UVSQ, INSU - CNRS, CNRS, DRF (CEA), CEA, CLIMAG, LSCE, UVSQ, INSU - CNRS, CNRS, DRF (CEA), CEA, LOCEAN-VOG, LOCEAN, MNHN, IRD, INSU - CNRS, SU, CNRS, IPSL (FR_636), ENS-PSL, UVSQ, CEA, INSU - CNRS, X, CNES, SU, CNRS, UPCité, LMV, IRD, INSU - CNRS, UJM, UCA [2017-2020], CNRS
The Mediterranean Palynological Societies Symposium 2019. Abstract book.
(pp. 142, 30/08/2019)
EPOC, EPHE, PSL, UB, INSU - CNRS, CNRS
Geochemistry of the coccoliths: proxy of surface water conditions or of resilience of coccolithophores facing climate change ?
Coccolithophores, the pelagic calcite ocean producers, experience ocean acidification and warming of Anthropocene. Concomitantly, they can recorde changes in pH and temperature (SST) in surface waters, through the incorporation of elements (B, Sr, Li, Mg) and isotopes (d 11 B) in their biominerals (coccoliths) during biocalcification. Yet, geochemistry of coccoliths is still relatively unexplored so far, stressing the need for calibration of such proxies in coccoliths. In this work, we studied the geochemistry of coccoliths deposited on top-core sediments of worlwide ocean. Elemental and isotopic compositions of these archives were then plotted against in situ data of surface-pH and SST to investigate potential relationships. A positive relationship was found between the B/Ca ratio of large sedimentary coccoliths (5-12 µm, mainly C. leptoporus) and surface-pH as predicted by thermodynamics, indicating these biominerals could be used as an archive of surface acidification. Conversely, the relation was negative for those of small size (3-5 µm, essentially consisting of E. huxleyi and G. oceanica), suggesting an increase of pH in the internal vesicle where coccoliths are formed when pH is decreasing in surface waters. Intra-vesicular pH regulation is favourable for the precipitation of calcite. We also showed that Li/Mg in coccoliths-rich sediments could be used to estimate SST. Our work constitutes an important step towards the calibration of proxies in coccoliths either to reconstruct surface water conditions, or to explore biocalcification mechanisms that will help to better anticipate and reconstruct the evolution of the pelagic calcification.
(18/08/2019)
IPGP, INSU - CNRS, UPD7, UR, IPG Paris, CNRS, LEMAR, IRD, IFREMER, UBO EPE, CNRS, LDO, INSU - CNRS, UBO EPE, CNRS, EPOC, EPHE, PSL, UB, INSU - CNRS, CNRS, CR2P, MNHN, UPMC, CNRS, CEREGE, IRD, INRA, AMU, CdF (institution), INSU - CNRS, CNRS
Occurrence of perfluoroalkyl substances in the Bay of Marseille (NW Mediterranean Sea) and the Rhône River
Four perfluoroalkyl substances (PFAS) were analyzed in 62 duplicate surface water samples from the Rhône River and Marseille Bay (France; NW Mediterranean Sea). Perfluorooctane sulfonate (PFOS) was detected in all samples and exceeded the European Environmental Quality Standard (EQS) values in over 80% of the cases. The most contaminated samples were from the Rhône River (up to 200 ng L-1 ∑ 4 PFAS), as well as those collected near a wastewater treatment plant outlet in Marseille Bay (up to 9 ng L −1 ∑ 4 PFAS). While PFOS was the predominant PFAS in Marseille Bay, remarkably high concentrations of perfluorohexanoic acid (PFHxA) were measured in the Rhône River (8-193 ng L −1). The relative abundances of individual compounds differed thus significantly between the Rhône River and Marseille Bay, indicating different sources. A simulation made with the MARS3D model showed that PFOS inputs from the Rhône River can enter Marseille Bay at levels > EQS.
(Marine Pollution Bulletin. vol. 149, n° 0025-326X, pp. 110491, 08/08/2019)
MIO, IRD, AMU, INSU - CNRS, UTLN, CNRS, EPOC, EPHE, PSL, UB, INSU - CNRS, CNRS, OSU PYTHEAS, IRD, AMU, IRSTEA, CNRS
Responses of different herb life-history groups to a dominant shrub species along a dune stabilization gradient
Shrubs play a pivotal role in reversing desertification and in promoting ecological rehabilitation in severe environments. However, how the interactions between shrubs and their understorey species change during restoration remains unclear. Here, we report the results of an observational study conducted in the Mu Us Desert of northern China. This study explored how dune stabilization and the size of individual shrubs affect shrub–herb interactions. In particular, we aimed to determine how different life-history groups and performance indicators (e.g., biomass and richness) of subordinate species respond to shrub–herb interactions during dune stabilization. The shrub Artemisia ordosica had positive effects on understorey species in this dune system. The ability of the shrub to promote the growth of understorey species increased with dune stabilization, but decreased from small to large shrubs. This effect was due to an increase in the relative abundance and biomass of perennials and their higher sensitivity to the positive effects of the shrubs. In contrast, the ability of shrubs to improve the richness of understorey species decreased with dune stabilization, but increased from small to large shrubs. This effect occurred because perennials suffered high strain during recruitment in disturbed open patches of the semi-fixed dunes, particularly below small shrubs. Our results support the theory claiming that communities are sets of hidden interaction groups that have contrasting responses (neutral for annuals, but facilitative for perennials) to dominant neighbors in a single community, depending on their functional strategies. Furthermore, our study highlights the high efficiency of A. ordosica in facilitating ecological restoration of dry and disturbed sandy communities.
(Basic and Applied Ecology. vol. 38, n° 1439-1791, pp. 1-12, 01/08/2019)
EPOC, EPHE, PSL, UB, INSU - CNRS, CNRS
Sea Level at the Coast from Video-Sensed Waves: Comparison to Tidal Gauges and Satellite Altimetry
Nearshore complex and energetic hydrodynamic conditions make observing evolving processes during extreme and short-term events difficult. In particular, total sea levels at the coast are hard to measure with current techniques. Sea level is commonly measured with tidal gauges and spaceborne altimetry, which lack essential details of spatial and wave-related sea level variability along the coast. Hence, novel techniques, adapted to nearshore areas, are required. This paper presents the first-time use of video cameras to derive the total sea level at the coast. This novel approach consists of estimating time-varying total water levels by applying a celerity-based depth inversion method, which is conventionally used to estimate bathymetry from video. The video-derived total sea levels are compared to sea levels derived from an in situ acoustic Doppler current profiler (ADCP), the nearest tide gauge, and altimetry. A tidal harmonic analysis is performed on the video-derived water levels, yielding an accurate determination of the dominant tidal harmonics. However, it remains difficult to separate bathymetric changes due to the waves on beaches when rapid morphological changes occur under energetic conditions. Nonetheless, video-derived water-level anomalies are in good agreement with state-of-the-art altimetry products. Although there is still work to be done, the results show the potential to measure total sea level at the coast using video camera systems.
(Journal of Atmospheric and Oceanic Technology, n° 0739-0572, 01/08/2019)
LEGOS, IRD, UT3, Comue de Toulouse, INSU - CNRS, CNES, CNRS, EPOC, EPHE, PSL, UB, INSU - CNRS, CNRS, OLVAC, LEGOS, IRD, UT3, Comue de Toulouse, INSU - CNRS, CNES, CNRS
Ostracods and mollusks in northern Sfax coast: reconstruction of Holocene paleoenvironmental changes and associated forcing
The present study investigates the history of the northern Sfax coast by means of subsurface sediments of the sebkhas El Merdessia and El Awebed through a multiproxy approach. Ostracod and mollusk assemblages, diversity index, sedimentological criteria, correspondence analysis, and radiocarbon datings together provide an overview of the development of this coast over the last 5000 years. Original data give evidence for periods of predominantly lagoonal and brackish water conditions. These data testify to the emersion of sebkha El Awebed during Holocene, while sebkha El Merdessia recorded three marine transgressions toward 4599, 2225, and 1396 years cal BP. These transgressions are indicated by the richness of sediments in lagoonal and marine ostracod assemblages coupled with marine mollusks and the high values of species richness and diversity index. Sandwiched between 2225 and 1396 years BP, a period of sea-level stability and buildup of sand barriers in front of the estuaries was evidenced. Toward 250 years cal BP, a tsunami event is evidenced by the deposition of a shelly bed containing angular and sharpened Cerithium vulgatum in coarser marine sands overlaid by silts and clays rich in charcoal particles and pottery fragments. The comparison between the proxies analyzed of the studied area and those of Skhira coast leads to the conclusion that the two coasts were subjected to the same factors. However, a time shift of sedimentation is due to the uplift of Sfax northern coast favored by the activity of the faults, unlike the southern Skhira subsidence.
(Geo-Marine Letters. vol. 39, n° 0276-0460, pp. 313-336, 01/08/2019)
EPOC, EPHE, PSL, UB, INSU - CNRS, CNRS
Variability in the Northern North Atlantic and Arctic Oceans Across the Last Two Millennia: A Review
The climate of the last two millennia was characterized by decadal to multicentennial variations, which were recorded in terrestrial records and had important societal impacts. The cause of these climatic events is still under debate, but changes in the North Atlantic circulation have often been proposed to play an important role. In this review we compile available high-resolution paleoceanographic data sets from the northern North Atlantic and Nordic Seas. The records are grouped into regions related to modern ocean conditions, and their variability is discussed. We additionally discuss our current knowledge from modeling studies, with a specific focus on the dynamical changes that are not well inferred from the proxy records. An illustration is provided through the analysis of two climate model ensembles and an individual simulation of the last millennium. This review thereby provides an up-to-date paleoperspective on the North Atlantic multidecadal to multicentennial ocean variability across the last two millennia.
(Paleoceanography and Paleoclimatology. vol. 34, n° 2572-4525, pp. 1399-1436, 01/08/2019)
EPOC, EPHE, PSL, UB, INSU - CNRS, CNRS
Field data-based evaluation of methods for recovering surface wave elevation from pressure measurements
(Coastal Engineering. vol. 150, n° 0378-3839, pp. 147-159, 01/08/2019)
EPOC, EPHE, PSL, UB, INSU - CNRS, CNRS, IMB, UB, Bordeaux INP, CNRS
Climate variability of the last 2700 years in the Southern Adriatic Sea: Coccolithophore evidences
New information on palaeoenvironmental conditions over the past ~2700 years in the Central Mediterranean Sea have been acquired through the high-resolution study of calcareous nannofossils preserved in the sediment core SW104-ND14Q recovered in the Southern Adriatic Sea (SAS) at 1013-m water depth. The surface water properties at this open SAS site are sensitive to atmospheric forcing (acting both at local and regional scale) and the North Ionian Sea driven inflowing waters. Our data show a relationship between reworked coccolith abundances, flood frequency across the Southern Alps and the North Atlantic Oscillation (NAO) confirming their value as indicator of runoff/precipitation. Changes in the abundance of the opportunistic (r-strategist) species Emiliania huxleyi and deep dweller taxa Florisphaera profunda were used to reconstruct the upper water column stratification and associated changes in coccolithophorid productivity. The negative correlation between reworked coccoliths and the N-Ratio (r = −0.44; p = 6−7) suggest that fresh water induced stratification is a controlling factor of the SAS coccolithophorid production. High coccolithophorid productivity levels occurred during dry periods and/or time intervals of inflowing salty and nutrient-rich Levantine Intermediate Waters favouring convection while lower levels took place during high freshwater discharge, mainly during the ‘Little Ice Age’ and two centennial scale intervals of weakest NAO around 200 BCE and 500 CE.
(The Holocene. vol. 30, n° 0959-6836, pp. 53-64, 31/07/2019)
INGV, ISMAR-CNR, ISMAR, CNR, LOCEAN, MNHN, IRD, INSU - CNRS, SU, CNRS, IPSL (FR_636), ENS-PSL, PSL, UVSQ, CEA, INSU - CNRS, X, IP Paris, CNES, SU, CNRS, UPCité, LOCEAN-VOG, LOCEAN, MNHN, IRD, INSU - CNRS, SU, CNRS, IPSL (FR_636), ENS-PSL, UVSQ, CEA, INSU - CNRS, X, CNES, SU, CNRS, UPCité, ISMAR, CNR, EPOC, EPHE, PSL, UB, INSU - CNRS, CNRS