Can pesticides, copper and seasonal water temperature explain the seagrass Zostera noltei decline in the Arcachon bay?
(Marine Pollution Bulletin. vol. 134, n° 0025-326X, pp. 66-74, 01/09/2018)
EPOC, EPHE, PSL, UB, INSU - CNRS, CNRS, LERAR, COAST, IFREMER, PSL, LPTC, UB, CNRS
Genesis and growth of a carbonate Holocene wedge on the northern Little Bahama Bank
The study focuses on the sedimentary dynamics at the transition between the modern Bahamas carbonate platform and related adjacent slopes and deeper environments. A Holocene carbonate sedimentary wedge is developed at the edge of the carbonate platform extending along the northern Little Bahamas Bank (LBB; Bahamas). The transition area between the platform and the wedge shows superposed terraces. The Holocene wedge thickness varies from 0 to 35 m. Its surface is dominated by homogeneous, fine-grained, soft sediments. It lies on a Pleistocene substratum and fills depressions corresponding to lowstand erosional surfaces. On the uppermost slope, this wedge represents the main depocenter of fine-grained bank-derived sediments since the last bank flooding.Twelve gravity cores were sampled from this wedge and allow the identification of both the processes that can supply this wedge and the wedge evolution based on content analyses and 19 radiocarbon ages.At present, particle export from the LBB margins mostly occurs during episodes of winter cold fronts but also occurs during hurricanes. Evidence of hurricane impact in the sedimentary record is suggested by the recovery of two laminated sequences showing both decreasing sedimentation rates and varying velocities during platform export. The local morphology of the platform edge allows the better sorting and export of sediments according to the presence of tidal outlets and sediment sorting on the wedge. However, because no ooids from tidal deltas located on the platform edge were found in cores, tidal currents are probably not energetic enough to both mobilize and export sediment, even if tide–induced currents may help the export of fine-grained carbonate particles remobilized by either cold fronts or hurricanes on the platform and upper slope.The formation of the wedge started at 13.6 ± 3.5 kyr cal BP following the meltwater pulse 1 A. It was supplied by shallow environment-derived particles produced on four narrow terraces between 60 and 20 mbsl after meltwater pulses. Since the LGM (Last Glacial Maximum), terrace formation seems to correspond to periods of sea-level stillstands and wedge formation, whilst escarpments correspond to periods of high rates of rising sea-level due to meltwater pulses. The main period of wedge growth started around 6.5 ± 0.9 kyr cal BP, when sea level finally reached the platform margins. The maximum flooding period around 4 kyr cal BP is characterized by the highest contents of aragonite needles exported from the platform.
(Marine and Petroleum Geology. vol. 96, n° 0264-8172, pp. 602-614, 01/09/2018)
EPOC, EPHE, PSL, UB, INSU - CNRS, CNRS, CSTJF, [Total Energies. Anciennement : Total, TotalFina, TotalFinaElf], CEREGE, IRD, INRA, AMU, CdF (institution), INSU - CNRS, CNRS
A 2000-year record of ocean influence on Jakobshavn Isbræ calving activity, based on marine sediment cores
(The Holocene. vol. 28, n° 0959-6836, pp. 1731-1744, 30/08/2018)
GEUS, EPOC, EPHE, PSL, UB, INSU - CNRS, CNRS
Field observations of alongshore runup variability under dissipative conditions in presence of a shoreline sandwave
Video measurements of runup were collected at low tide along several profiles covering an alongshore distance of 500 m. The morphology displayed a complex shape with a shoreline sandwave in the lower beach face of about 250 m long mirrored in the inner sandbar. Wave conditions were stationary and moderate (offshore height of 2 m and peak period of nearly 13 s) but yet dissipative. Runup energy was dominated by infragravity frequencies. Alongshore variations in runup (by a factor up to 3) observed both in the incident and infragravity bands were much higher than reported previously (e.g., Guedes et al., 2012, https://doi.org/10.1016/j.csr.2012.08.022; Ruggiero et al., 2004, https://doi.org/10.1029/2003JC002160) while the alongshore variations in other environmental parameters (e.g., foreshore beach slope) appear to be much lower. Our data suggest that the beach morphology in the inner surf zone plays a crucial role by inducing rapid and significant modification in the incident wave pattern and the alongshore coherence length scales were consistent with the typical alongshore length scale of the morphology.
(Journal of Geophysical Research. Oceans. vol. 123, n° 2169-9275, pp. 6800-6817, 28/08/2018)
EPOC, EPHE, PSL, UB, INSU - CNRS, CNRS
Microplastic contamination in the Seine River estuary
(23/08/2018)
LEESU, ENPC, UPEC UP12, LERN, COAST, IFREMER, IFREMER, EPOC, EPHE, PSL, UB, INSU - CNRS, CNRS
Benefactor facilitation and beneficiary feedback effects drive shrub-dominated community succession in a semi-arid dune ecosystem
Questions (a) How do the facilitative effects of benefactors on understorey species change along a successional gradient; (b) what are the feedback effects of the beneficiary species on the benefactor; and (c) how do these bidirectional interactions drive community dynamics of a shrub‐dominated ecosystem. Location A sand‐fixing community, Mu Us Desert, China. Methods We quantified the effects of the shrub Artemisia ordosica on understorey herb abundance, biomass and richness using an observational procedure at four positions along a successional gradient, i.e., semi‐fixed dunes (D1 stage), fixed dunes (D2 stage), fixed dunes covered with biological crusts (D3 stage) and fixed dunes with herbs (D4 stage). The relative interaction index (RII) was used to calculate the effect of the shrub on the herbs. Additionally, we conducted a removal experiment at the latest successional stage to assess the beneficiary feedback effects on the growth of the shrub's vegetative and reproductive twigs. Results The response of herbs to the effect of the benefactor shrub showed a humped‐back curve for abundance and biomass along the successional gradient, supporting the collapse of the interaction model, but a linear curve for richness, thus supporting the stress‐gradient hypothesis. This difference could likely be explained by a turnover of life‐history groups of understorey species from annuals to perennials along the successional gradient, with the growth of the latter group being more susceptible to shrub facilitation than the former. The herbs had a negative feedback effect on the growth of the shrub's reproductive twigs. Conclusions Our results suggest that the relationship between the shrub A. ordosica and the associated herbs was antagonistic, and the absence of shrub seedling recruitment at the end of succession suggests that this antagonistic relationship was a crucial driver of a successional shift from a shrub‐dominated to a herb‐dominated community.
(Applied Vegetation Science. vol. 21, n° 1402-2001, pp. 595-606, 08/08/2018)
EPOC, EPHE, PSL, UB, INSU - CNRS, CNRS
Deformation bands in volcaniclastic rocks – Insights from the Shihtiping tuffs, Coastal Range of Taiwan
Deformation bands have been extensively studied in sandstones, whereas far less is known about bands occurring in porous volcaniclastic rocks. Here we investigate spectacular outcrop exposures of late Miocene tuffaceous rocks in the Coastal Range of Taiwan, which host several deformation band types: (i) disaggregation-dominated, layer-bound, sub-vertically-dipping pure compaction bands (PCB); (ii) cataclastic, layer-bound, reverse-sense compactional shear bands (RCSB); and (iii) non-layer-bound and intensely cataclastic transverse-sense compactional shear bands (TCSB). RCSBs and TCSBs host discrete slip surfaces on individual bands. The bands formed in an overall compressive stress regime related to convergence of the Eurasian and Philippine Sea plates. PCBs and RCSBs formed first, whereas progressive burial caused a shift to a transverse stress state and formation of TCSBs. The occurrence of cataclasis in RCSBs but not PCBs is inferred to be shear-driven, rather than confining-pressure-driven. Our findings suggest that cataclasis in deformation bands in volcaniclastic rocks is bimodal. Shear localization preferentially affects weak glass shards, causing intense comminution of volcanic glass. Feldspar, pyroxene and amphibole phenocrysts are comparatively less crushed, and cataclasis is strongly controlled by mineralogic cleavage planes. We conclude that increasing glass content reduces shear resistance, and that deformation bands in volcaniclastic rocks effectively exhibit a strain-weakening behavior.
(Journal of Structural Geology. vol. 113, n° 0191-8141, pp. 155-175, 01/08/2018)
EPOC, EPHE, PSL, UB, INSU - CNRS, CNRS
Hydro- and sediment dynamics in the Gironde estuary (France): Sensitivity to seasonal variations in river inflow and sea level rise
Understanding estuarine hydrodynamics and sediment dynamics is of key importance to provide the foundation for sound management of these coastal systems. Turbidity maxima, which are zones of elevated suspended sediment concentration (SSC), are of particular interest as they control biogeochemical cycling and affect the overall environmental quality of the estuary. These turbidity maxima, however, are complex dynamic features that respond to changes in forcing conditions. In this study we use a 3D numerical model to investigate the response of hydrosedimentary dynamics to variations in river inflow and sea level rise in the Gironde estuary, which is one of the largest estuarine systems in Europe. Yearly simulations and comparisons with satellite data and measurements of salinity and SSC show that the model reproduces variations in salinity intrusion and the migration of the turbidity maximum driven by seasonal fluctuations in river inflow. Numerical experiments indicate that the formation of this dynamic turbidity maximum is mainly driven by tidal asymmetry. Density gradients play a secondary role by maintaining the stability of the suspended sediment mass. The model also simulates the presence of a secondary turbidity maximum which is more stable, consistent with observations. Evaluation of the sediment budget shows that sediment export mainly occurs during spring tides and when river discharge is high. Simulations including sea level rise suggest that salinity levels in the middle estuary will increase and rising water levels cause tidal amplification, strengthening of tidal currents and enhanced SSC levels in the upper estuary. On the other hand, the locations of the salinity front and the turbidity maximum remain relatively stable under rising water levels. Overall, our simulations suggest that decadal changes in river inflow can potentially have a larger effect on turbidity maximum dynamics than sea level rise.
(Continental Shelf Research. vol. 165, n° 0278-4343, pp. 37-50, 01/08/2018)
EPOC, EPHE, PSL, UB, INSU - CNRS, CNRS
Transient early diagenetic processes in Rhône prodelta sediments revealed in contrasting flood events
Floods carry sediments to river deltas and the coastal zone, but little is known about the geochemical evolution of this particulate material deposited over a short period of time. Here, we studied two recent contrasting flood deposits in the Rhône River prodelta area (northwestern Mediterranean Sea). We monitored the porewater and solid-phase chemistry over periods ranging from a few days to 6 months after deposition. Non-steady state diagenetic processes associated with episodic deposition promote a wide spectrum of transient redox conditions in the shallow prodelta region of the Rhône. Specific attributes of diagenetic responses depend on the sources of flood material and scale (thickness) of deposition. The first flood unit of 20-30 cm was composed of light gray mud, poor in organic carbon and rich in reactive manganese oxides. The short-term responses of early diagenetic processes contrasted with a rapid consumption of O2 and NO3-over a few hours just after the deposition event, accompanied by a slower build-up of Mn2+ concentration, and a lagged response in Fe2+ concentration over a few days or weeks. This difference was due to the redox capacity of the sediment, evolving from oxidized, during the flood layer deposition, to more reducing conditions, after a few days or weeks, allowing Fe2+ to build up and remain in solution. Sulfate reduction may have started within a few days within the flood deposit and was greatly enhanced just below the former redox front due to a fresh input of organic matter (OM). This large production of H2S probably led to the precipitation of sulfide minerals in close vicinity to the former redox front, limiting the accumulation of Fe2+ and H2S. The unit was sampled repeatedly three times during the six months following the flood event, and showed that manganese oxides were reduced at a rate of 1.8 mmol m−2 d−1, whereas the iron oxide concentration did not vary substantially.
(Continental Shelf Research. vol. 166, n° 0278-4343, pp. 65-76, 01/08/2018)
IPGP, INSU - CNRS, UPD7, UR, IPG Paris, CNRS, LSCE, UVSQ, INSU - CNRS, CNRS, DRF (CEA), CEA, OCEANIS, LSCE, UVSQ, INSU - CNRS, CNRS, DRF (CEA), CEA, LPG-ANGERS, LPG, UA, UN UFR ST, UN, INSU - CNRS, CNRS, IPGP, INSU - CNRS, UPD7, UR, IPG Paris, CNRS, EPOC, EPHE, PSL, UB, INSU - CNRS, CNRS
Influence of the bioturbator Upogebia cf. pusilla on trace metal remobilization: Does parasitism matter?
(Marine Environmental Research. vol. 139, n° 0141-1136, pp. 87-98, 01/08/2018)
EPOC, EPHE, PSL, UB, INSU - CNRS, CNRS, LEFE, INEE-CNRS, CNRS, UT3, Comue de Toulouse, CNRS, Toulouse INP, Comue de Toulouse, LOBB, OOB, UPMC, CNRS, UPMC, INSU - CNRS, CNRS