Extreme events: impact and recovery
Sandy coast changes on timescales from days to years and sometimes decades, primarily result from the erosion-recovery (im)balance that is controlled by the respective contributions of storms and recovery conditions. Over the last decade, our understanding and predictive ability of storm-driven erosion and subsequent multi-day to multi-annual recovery has greatly improved, notably thanks to long-term and rapidresponse coastal monitoring programs. This chapter gives a broad overview of the definitions and processes that control storm-driven beach and dune erosion and subsequent (partial, complete or excess) recovery. Key conceptual concepts are illustrated using two well-documented case studies: response and (partial) multi-annual recovery from (1) over a severe winter period along the Atlantic coast of Europe characterised by unusually strong storm clustering episode; and (2) from a single severe storm with an anomalous wave direction along the southeast coastline of Australia. Finally, future perspectives and knowledge gaps in relation to impacts and recovery from extreme events are discussed.
(20/05/2020)
EPOC, EPHE, PSL, UB, INSU - CNRS, CNRS
Carbon 13 Isotopes Reveal Limited Ocean Circulation Changes Between Interglacials of the Last 800 ka
Ice core data have shown that atmospheric CO2 concentrations during interglacials were lower before the Mid-Brunhes Event (MBE, ~430 ka), than after the MBE by around 30 ppm. To explain such a difference, it has been hypothesized that increased bottom water formation around Antarctica or reduced Atlantic Meridional Overturning Circulation (AMOC) could have led to greater oceanic carbon storage before the MBE, resulting in less carbon in the atmosphere. However, only few data on possible changes in interglacial ocean circulation across the MBE have been compiled, hampering model-data comparison. Here we present a new global compilation of benthic foraminifera carbon isotopic (δ13C) records from 31 marine sediment cores covering the last 800 ka, with the aim of evaluating possible changes of interglacial ocean circulation across the MBE. We show that a small systematic difference between pre- and post-MBE interglacial δ13C is observed. In pre-MBE interglacials, northern source waters tend to have slightly higher δ13C values and penetrate deeper, which could be linked to an increased northern sourced water formation or a decreased southern sourced water formation. Numerical model simulations tend to support the role of abyssal water formation around Antarctica: Decreased convection there associated with increased sinking of dense water along the continental slopes results in increased δ13C values in the Atlantic in agreement with pre-MBE interglacial data. It also yields reduced atmospheric CO2 as in pre-MBE records, despite a smaller simulated amplitude change compared to data, highlighting the need for other processes to explain the MBE transition.
(Paleoceanography and Paleoclimatology. vol. 35, n° 2572-4525, pp. e2019PA003776, 10/05/2020)
LSCE, UVSQ, INSU - CNRS, CNRS, DRF (CEA), CEA, EPOC, EPHE, PSL, UB, INSU - CNRS, CNRS, CLIM, LSCE, UVSQ, INSU - CNRS, CNRS, DRF (CEA), CEA, GM, IFREMER, CLIMAG, LSCE, UVSQ, INSU - CNRS, CNRS, DRF (CEA), CEA, EPHE, PSL
Assessment of PCB trajectories along French river corridors between 1945 and 2018
The reconstruction and modelling of contamination trajectories in rivers is a key concern to investigate spatio-temporal impacts of long-term anthropogenic activities. This issue is highly significant for persistent organic pollutants, such as polychlorinated biphenyls (PCBs), known for their toxicity, their low degradation rates and their hydrophobic properties leading to their accumulation in sediments and biota. Increasingly produced and released worldwide from the 1930s to the 1970-1980s, PCBs were analysed in numerous studies dealing with river sediment quality. However, data syntheses are uncommon at the scale of large hydrosystems, and source-to-estuary approaches along rivers are still needed. Accordingly, we propose an original work integrating PCBs analyses on different solid matrices (sediment cores, bed and flood deposits, suspended particulate matters, and dredged sediments) originating from both research programmes and monitoring. Based on more than 1400 validated analyses, temporal trends of the PCB contamination were reconstructed since 1945 along the four main fluvial corridors in France (Rhône, Seine, Loire and Garonne Rivers). The relationships with socio-environmental factors were also deciphered by integrating hydrological and human spatio-temporal data (cumulative river discharge, population hot spots, urban and industrial surfaces). This work highlighted that the main contaminant trends were driven by regulation, but also by sediment transport and accidental releases (especially since the 1990s). In general, urban and industrial areas were the main contributors to the PCB contamination of rivers: around and downstream of Paris and Rouen (Seine River), Lyon and its "Chemical Valley" (Rhône River), Saint-Etienne and Nantes conurbations (Loire River), and probably downstream of Toulouse and Bor3deaux (Garonne River). Relatively high concentrations persisted after the end of the PCB production due to chronic diffuse inputs and accidental releases, particularly on the Rhône River. Moreover, the estimation of specific fluxes revealed that up to 12 µg/m²/yr (i.e. 0.9 t/yr on average) of PCBs were brought by French rivers, especially by the Rhône, Seine and Loire Rivers (ranked in order of importance) to Western European seas since the 1970s.
(04/05/2020)
LEHNA, UCBL, ENTPE, CNRS, EPOC, EPHE, PSL, UB, INSU - CNRS, CNRS, LSCE, UVSQ, INSU - CNRS, CNRS, DRF (CEA), CEA, GEDI, LSCE, UVSQ, INSU - CNRS, CNRS, DRF (CEA), CEA, M2C, UNICAEN, NU, INSU - CNRS, UNIROUEN, NU, CNRS, GéHCO, UT
Surf Zone Wave Measurements from Lidar Scanners: Analysis of Non-hydrostatic Processes
(Journal of Coastal Research. vol. 95, n° 0749-0208, pp. 1189, 01/05/2020)
EPOC, EPHE, PSL, UB, INSU - CNRS, CNRS, LEGI, CNRS, Fédération OSUG, UGA, Grenoble INP, UGA
Beach-dune Recovery from the Extreme 2013-2014 Storms Erosion at Truc Vert Beach, Southwest France: New Insights from Ground-penetrating Radar
(Journal of Coastal Research. vol. 95, n° 0749-0208, pp. 588, 01/05/2020)
ACTES, UA, CEFREM, UPVD, INSU - CNRS, CNRS, BRGM, EPOC, EPHE, PSL, UB, INSU - CNRS, CNRS, ONF
Recent Advances in Tidal Inlet Morphodynamic Modelling
(Journal of Coastal Research. vol. 95, n° 0749-0208, pp. 1016, 01/05/2020)
LIENSs, INSU - CNRS, ULR, CNRS, TU Delft, EPOC, EPHE, PSL, UB, INSU - CNRS, CNRS
A 3800 yr paleoseismic record (Lake Hazar sediments, eastern Turkey): Implications for the East Anatolian Fault seismic cycle
The East Anatolian Fault (EAF) in Turkey is a major active left-lateral strike-slip fault that was seismically active during the 19th century but mostly quiet during the 20th century. Geodetic data suggests that the fault is creeping along its central part. Here we focus on its seismic history as recorded in the sediments of Lake Hazar in the central part of the EAF. Sediment cores were studied using X-ray imagery, magnetic susceptibility, grain-size, loss-on-ignition and X-ray fluorescence measurements. Recurring thin, coarse-grained sediment units identified as turbidites in all cores were deposited synchronously at two deep study sites. The turbidite ages are inferred combining radiocarbon and radionuclide (137Cs and 210Pb) dating in an Oxcal model. A mean recurrence interval of ∼190 yrs is obtained over 3800 yrs. Ages of the recent turbidites correspond to historical earthquakes reported to have occurred along the EAF Zone or to paleoruptures documented in trenches just northeast of Lake Hazar. The turbidites are inferred to be earthquake-triggered. Our record demonstrates that Lake Hazar has been repeatedly subjected to significant seismic shaking over the past 3800 yrs. The seismic sources are variable: ∼65% of all turbidites are associated with an EAF source. The seismic cycle of central EAF is thus only partly impacted by creep.
(Earth and Planetary Science Letters. vol. 538, n° 0012-821X, pp. 116152, 01/05/2020)
ULiège, ULiège, EPOC, EPHE, PSL, UB, INSU - CNRS, CNRS, ITÜ
Upstream migrating knickpoints and related sedimentary processes in a submarine canyon from a rare 20-year morphobathymetric time-lapse (Capbreton submarine canyon, Bay of Biscay, France)
The Capbreton submarine canyon is a striking feature of the south-east of the Bay of Biscay. This canyon forms a deep incision through the continental shelf and slope, and displays remarkable structures linked to its present-day hydrosedimentary activity. Its head has been disconnected from the Adour River since 1310 CE, but remains close enough to the coast to be supplied with sediment by longshore drift. Gravity processes in the canyon body are abundantly described and documented, but activity in the head and the fan of the canyon is poorly constrained. Furthermore, many questions remain regarding the details of processes affecting the head, the body and the fan of the Capbreton canyon. In this work, we address the paucity of documentation concerning (1) the temporal evolution of sediment transfer between the head and the deep reaches of the canyon, and (2) the interaction between gravity processes and the morphology of the canyon floor, including both shaping and feedback mechanisms.This study is based on the analysis and comparison of eight multibeam bathymetric surveys acquired in the upper part of the Capbreton canyon between 1998 and 2018, in depths ranging 10–320 m below sea level. This rare time series exposes the morphological evolution of this outstanding dynamic area over the last 20 years. Our work shows that much of the changes are located in the canyon floor and head. Following a period characterized by a unique flat floor thalweg, the canyon was affected by an incision with low lateral terraces which resulted in a narrow axial thalweg. The deepening of the narrow thalweg was induced by retrogressive erosion according to the presence of upstream-migrating knickpoints, while low elevation residual terraces formed as the canyon reached a local equilibrium profile.The flat thalweg observed in 1998 is likely a result of a partial filling of the canyon thalweg by a substantial emptying of the canyon head and significant mass transfer to the proximal part of the canyon. A flat floor thalweg was not observed again in the remaining of our time series (since 2010), suggesting a possible quieter working mode of the canyon. We also propose the first accurate volume quantification of sediment displacement on the canyon floor. Our findings underline the alternation of filling and erosive periods in the canyon axis and an unexpected continuous sediment deposition in the canyon head during the last 20 years.
(Marine Geology. vol. 423, n° 0025-3227, pp. 106143, 01/05/2020)
EPOC, EPHE, PSL, UB, INSU - CNRS, CNRS, GM, IFREMER
Biomarker responses and accumulation of polycyclic aromatic hydrocarbons in Mytilus trossulus and Gammarus oceanicus during exposure to crude oil
In the brackish water Baltic Sea, oil pollution is an ever-present and significant environmental threat mainly due to the continuously increasing volume of oil transport in the area. In this study, effects of exposure to crude oil on two common Baltic Sea species, the mussel Mytilus trossulus and the amphipod Gammarus oceanicus, were investigated. The species were exposed for various time periods (M. trossulus 4, 7, and 14 days, G. oceanicus 4 and 11 days) to three oil concentrations (0.003, 0.04, and 0.30 mg L-1 based on water measurements, nominally aimed at 0.015, 0.120, and 0.750 mg L-1) obtained by mechanical dispersion (oil droplets). Biological effects of oil exposure were examined using a battery of biomarkers consisting of enzymes of the antioxidant defense system (ADS), lipid peroxidation, phase II detoxification (glutathione S-transferase), neurotoxicity (acetylcholinesterase inhibition), and geno- and cytotoxicity (micronuclei and other nuclear deformities). In mussels, the results on biomarker responses were examined in connection with data on the tissue accumulation of polycyclic aromatic hydrocarbons (PAH). In M. trossulus, during the first 4 days of exposure the accumulation of all PAHs in the two highest exposure concentrations was high and was thereafter reduced significantly. Significant increase in ADS responses was observed in M. trossulus at 4 and 7 days of exposure. At day 14, significantly elevated levels of geno- and cytotoxicity were detected in mussels. In G. oceanicus, the ADS responses followed a similar pattern to those recorded in M. trossulus at day 4; however, in G. oceanicus, the elevated ADS response was still maintained at day 11. Conclusively, the results obtained show marked biomarker responses in both study species under conceivable, environmentally realistic oil-in-seawater concentrations during an oil spill, and in mussels, they are related to the observed tissue accumulation of oil-derived compounds.
(Environmental Science and Pollution Research. vol. 27, n° 0944-1344, pp. 15498-15514, 01/05/2020)
NORCE, EPOC, EPHE, PSL, UB, INSU - CNRS, CNRS
Holocene fire and vegetation dynamics in the Central Pyrenees (Spain)
Fire-vegetation relationships are critical to understand transient mountain ecosystems and their long-term landscape dynamics, which is essential for alpine forest conservation. In this paper we aim to (1) reconstruct the Holocene fire history at high altitudes of the southern Central Pyrenees, (2) add evidence to the debate on fire origin, naturally or anthropogenically produced, (3) determine the importance of fire as a disturbance agent for sub-alpine and alpine vegetation, in comparison with the plant community internal dynamics applying conditional inference trees. We present and compare microcharcoal and pollen data series, from two lacustrine se-dimentary sequences in the Central Pyrenees: Basa de la Mora (BSM), within the treeline ecotone at the sub-alpine belt (1914 m a.s.l.) and Marboré Lake, above the treeline at the alpine belt (2612 m a.s.l.). We evidence that, fire activity was not the most important factor in driving vegetation dynamics regionally. Our results suggest that spatially, the fire signal might be site-dependent while over time, climate exerted a strong influence on fire activity during the early-to-mid Holocene, showing more fires during the Holocene Thermal Maximum (HTM) (ca. 7000-6000 cal yr BP) whereas fire activity decreased with the cold Neoglacial period. At ca. 3700 cal yr BP, fire activity increased coinciding with a regional landscape opening, suggesting that human activities may have strengthened the importance of fire. Fire activity remained low over the last two millennia but a remarkable Holocene maximum for the last centuries in both sequences is observed, likely related to increasing human pressure.
(CATENA. vol. 188, n° 0341-8162, pp. 104411, 01/05/2020)
EPOC, EPHE, PSL, UB, INSU - CNRS, CNRS, UiB