Speciation of organic fractions does matter for aerosol source apportionment. Part 3: Combining off-line and on-line measurements
he present study proposes an advanced methodology to refine the source apportionment of organic aerosol (OA). This methodology is based on the combination of offline and online datasets in a single Positive Matrix Factorization (PMF) analysis using the multilinear engine (ME-2) algorithm and a customized time synchronization procedure. It has been applied to data from measurements conducted in the Paris region (France) during a PM pollution event in March 2015. Measurements included OA ACSM (Aerosol Chemical Speciation Monitor) mass spectra and specific primary and secondary organic molecular markers from PM10 filters on their original time resolution (30 min for ACSM and 4 h for PM10 filters). Comparison with the conventional PMF analysis of the ACSM OA dataset (PMF-ACSM) showed very good agreement for the discrimination between primary and secondary OA fractions with about 75% of the OA mass of secondary origin. Furthermore, the use of the combined datasets allowed the deconvolution of 3 primary OA (POA) factors and 7 secondary OA (SOA) factors. A clear identification of the source/origin of 54% of the total SOA mass could be achieved thanks to specific molecular markers. Specifically, 28% of that fraction was linked to combustion sources (biomass burning and traffic emissions). A clear identification of primary traffic OA was also obtained using the PMF-combined analysis while PMF-ACSM only gave a proxy for this OA source in the form of total hydrocarbon-like OA (HOA) mass concentrations. In addition, the primary biomass burning-related OA source was explained by two OA factors, BBOA and OPOA-like BBOA. This new approach has showed undeniable advantages over the conventional approaches by providing valuable insights into the processes involved in SOA formation and their sources. However, the origins of highly oxidized SOA could not be fully identified due to the lack of specific molecular markers for such aged SOA.
(Science of the Total Environment. vol. 690, n° 0048-9697, pp. 944-955, 01/11/2019)
INERIS, EPOC, EPHE, PSL, UB, INSU - CNRS, CNRS, LSCE, UVSQ, INSU - CNRS, CNRS, DRF (CEA), CEA
Uncertainties associated with in situ high-frequency long-term observations of suspended particulate matter concentration using optical and acoustic sensors
Measurement of suspended particulate matter concentration (SPMC) spanning large time and geographical scales have become a matter of growing importance in recent decades. At many places worldwide, complex observation platforms have been installed to capture temporal and spatial variability over scales ranging from cm (turbulent regimes) to whole basins. Long-term in situ measurements of SPMC involve one or more optical and acoustical sensors and, as the ground truth reference, gravimetric measurements of filtered water samples. The estimation of SPMC from optical and acoustical proxies generally results from the combination of a number of independent calibration measurements, as well as regression or inverse models. Direct or indirect measurements of SPMC are inherently associated with a number of uncertainties along the whole operation chain, the autonomous field deployment, to the analyses necessary for converting the observed proxy values of optical and acoustical signals to SPMC. Controlling uncertainties will become an important issue when the observational input comprises systems of sensors spanning large spatial and temporal scales. This will be especially relevant for detecting trends in the data with unambiguous statistical significance, separating anthropogenic impact from natural variations, or evaluating numerical models over a broad ensemble of different conditions using validated field data. The aim of the study is to present and discuss the benefits and limitations of using optical and acoustical backscatter sensors to acquire long-term observations of SPMC. Additionally, this study will formulate recommendations on how to best acquire quality-assured SPMC data sets, based on the challenges and uncertainties associated with those long-term observations. The main sources of error as well as the means to quantify and reduce the uncertainties associated with SPMC measurements are also illustrated.
(Progress in Oceanography. vol. 178, n° 0079-6611, pp. 102162, 01/11/2019)
DYNECO, IFREMER, M2C, UNICAEN, NU, INSU - CNRS, UNIROUEN, NU, CNRS, GéHCO, UT, SHOM, IRSNB / RBINS, GKSS, EPOC, EPHE, PSL, UB, INSU - CNRS, CNRS
Glacial-interglacial dust and export production records from the Southern Indian Ocean
(Earth and Planetary Science Letters. vol. 525, n° 0012-821X, pp. 115716, 01/11/2019)
OCCR, UNIBE, UFZ, EPOC, EPHE, PSL, UB, INSU - CNRS, CNRS, LSCE, UVSQ, INSU - CNRS, CNRS, DRF (CEA), CEA, CLIMAG, LSCE, UVSQ, INSU - CNRS, CNRS, DRF (CEA), CEA, PALEOCEAN, LSCE, UVSQ, INSU - CNRS, CNRS, DRF (CEA), CEA
Morphological changes in a cuspate sandy beach under persistent high-energy swells: Reñaca Beach (Chile)
The present work proposes a morphological evolution model for sandy cuspate beaches, which depends on two parameters, swash excursion (S) and offshore wave steepness (H0/L0). The model was derived from observations of morphology and wave climate at Reñaca Beach in central Chile, comprising in-situ instrumentation, topographic surveys, wave modeling, and optical imagery. It was found that wave steepness alone was unable to explain the morphological changes observed on the beach. Rather, results indicate that swash excursion is better to distinguish between erosive and accretionary events, with swash excursion exceeding 29.5 m for more than 12 h being indicative of erosive events. While morphological changes are led by S, wave steepness correlates with the erosive potential of waves, especially when H0/L0 is greater than 0.017. Although derived for a specific beach under a limited range of conditions, this work adds to the understanding of the dynamic behavior of beaches exposed to persistent high-energy swells.
(Marine Geology. vol. 417, n° 0025-3227, pp. 105988, 01/11/2019)
PUC, CIGIDEN, PUC, MERIC, UTFSM, LMFA, ECL, UCBL, INSA Lyon, INSA, CNRS, EPOC, EPHE, PSL, UB, INSU - CNRS, CNRS
Seasonal influence of parasitism on contamination patterns of the mud shrimp Upogebia cf. pusilla in an area of low pollution
(Science of the Total Environment. vol. 692, n° 0048-9697, pp. 319-332, 01/11/2019)
EPOC, EPHE, PSL, UB, INSU - CNRS, CNRS
Quantifying bioturbation across coastal seascapes: Habitat characteristics modify effects of macrofaunal communities
(Journal of Sea Research (JSR). vol. 152, n° 1385-1101, pp. 101766, 31/10/2019)
EPOC, EPHE, PSL, UB, INSU - CNRS, CNRS
Impact of freshwater release in the Mediterranean Sea on the North Atlantic climate
Sediment cores from the Mediterranean Sea have evidenced several periods of Sapropel deposition, which can be explained by events of anoxic bottom conditions. An explanation for such events calls for a very stratified sea, possibly related with freshwater input through increased precipitations and runoff discharges. It has been suggested that such a stratified Mediterranean Sea may in turn weaken the Atlantic meridional overturning circulation (AMOC) through changes in the Mediterranean overflow water (MOW). Nevertheless, models used to establish this result were relatively simple and the mechanisms leading to such an impact remained elusive. To improve on those previous studies, we analyse the impact of different freshwater releases with rates of 0.2, 0.1, 0.05 and 0.02 Sv (1 Sv=10 6 m 3 /s) in the Mediterranean Sea using the IPSL-CM5A-LR model in a few multi-centennial simulations. We focus the analysis on the impact of a decrease in the Mediterranean overflow water (MOW) on the large-scale Atlantic circulation. We find a consistent change in horizontal currents in the upper Atlantic Ocean in all simulations in the first century, with a large enhancement of the northward current west of Rockall in the northeast Atlantic. Concerning the AMOC response, we identify three different processes that impact its fate. The first is related to changes in geostrophic currents at depth induced by the disappearance of the MOW, which tends to weaken the AMOC. On the contrary, the second enhances the AMOC and is associated with the increase in northward currents in the horizontal upper circulation. The last process is due to the spread of surface freshwater anomalies out of the Mediterranean Sea that freshens the North Atlantic convection sites and weakens the AMOC. Depending on the rate of the freshwater release, the strength and balance of these three processes are different. For rates larger than 0.05 Sv, we observe a strong reduction of the AMOC, while for lower rates, we notice an enhancement in the upper cell. The climatic response follows that of the upper AMOC with a warming of the North Atlantic for rates lower than 0.05 Sv and a cooling for higher rates. Given that past estimates of freshwater release in the Mediterranean Sea indicate rates lower than 0.05 Sv, we argue that Sapropel events may have enhanced of the upper AMOC and warmed of the North Atlantic. 2
(Climate Dynamics. vol. 53, n° 0930-7575, pp. 3893-3915 (IF 4,708), 29/10/2019)
EPOC, EPHE, PSL, UB, INSU - CNRS, CNRS, GEOPS, UP11, CNRS, LSCE, UVSQ, INSU - CNRS, CNRS, DRF (CEA), CEA
Nanoplastic contamination of mangrove meiofauna communities
(21/10/2019)
ISYEB, MNHN, EPHE, PSL, SU, CNRS, UA, EPOC, EPHE, PSL, UB, INSU - CNRS, CNRS, GR, UR, INSU - CNRS, CNRS
Mediterranean Outflow Water and contourite depositional systems in the Gulf of Cadiz
The Contourite Depositional Systems (CDS) in the Gulf of Cadiz are unique archives of the Mediterranean Outflow Water (MOW) variability since the Gibraltar gateway opening. These CDS have been generated by the upper and lower paths of the MOW, MUW and MLW respectively. These CDS have been drilled during the IODP Expedition 339 (2011-2012), offering a new data set over a longer period, allowing comparisons between recent and older climatic cycles, in sites both under the MUW and MLW cores. This work provides results of a detailed sedimentological and facies analysis of different CDS in the Gulf of Cadiz, using mainly grain size, grain sources (petrography of sands and clay assemblages), natural gamma ray data, and XRF results from specific intervals. Downhole and core gamma ray data coupled to grain-size results provided a regional scale chronostratigraphic framework for the CDS contourite deposits and hiatuses at the regional scale. These long sedimentary records provide an overview of the behavior and circulation regime of the MOW over the large changes in climate and sea-level cyclicities and especially over two periods: the last climatic cycle MIS1-MIS2 and at the mid-Brunhes Event (MIS10-12) which is an analog of the last cycle. One of the defining characteristics of contourite systems is the marked cyclicity in grain-size and related sediment properties. Drilling in the Gulf of Cadiz during IODP 339 recovered over 4.5 km of contourites with over 600 distinct contourite sequences. These show irregular cyclicity, much variation in thickness (0.5-4.0 m) and estimated duration (4-10 ky). Approximately 60% are bi-gradational sequences, whereas the rest are partial sequences. Three principal controls have been considered as likely causes for the sequences: (a) long-term variation in bottom-current velocity; (b) episodic lateral influx of clastic material; and (c) variation in vertical supply of biogenic material. The bi-gradational sequence, particularly for the muddy drift sites, validate the primary control exerted by long-term variation in bottom-current velocity. The high degree of cycle correlation between adjacent sites further supports this contention. A secondary control of lateral clastic supply is more evident for the proximal sandy contourite sites, and for partial base-cut sequences. Work is in progress on cycle duration and sediment sources.
(16/10/2019)
EPOC, EPHE, PSL, UB, INSU - CNRS, CNRS, INSU - CNRS, UM, CNRS, UA, LOG, INSU - CNRS, ULCO, CNRS, IRD [Ile-de-France]
Carbon and silica megasink in deep-sea sediments of the Congo terminal lobes
Carbon and silicon cycles at the Earth surface are linked to long-term variations of atmospheric CO2 and oceanic primary production. In these cycles, the river-sea interface is considered a biogeochemical hotspot, and deltas presently receive and preserve a major fraction of riverine particles in shallow water sediments. In contrast, periods of glacial maximum lowstand were characterized by massive exports of sediments to the deep-sea via submarine canyons and accumulation in deep-sea fans. Here, we calculate present-day mass balances for organic carbon (OC) and amorphous silica (aSi) in the terminal lobe complex of the Congo River deep-sea fan as an analogue for glacial periods. We show that this lobe complex constitutes a megasink with the current accumulation of 18 and 35% of the OC and aSi river input, respectively. This increases the estimates of organic carbon burial by 19% in the South Atlantic Ocean in a zone representing less than 0.01% of the basin. These megasinks might have played a role in carbon trapping in oceanic sediments during glacial times.
(Quaternary Science Reviews. vol. 222, n° 0277-3791, pp. 105854, 15/10/2019)
LSCE, UVSQ, INSU - CNRS, CNRS, DRF (CEA), CEA, OCEANIS, LSCE, UVSQ, INSU - CNRS, CNRS, DRF (CEA), CEA, GM, IFREMER, iSTeP, INSU - CNRS, SU, CNRS, LEMAR, IRD, IFREMER, UBO EPE, CNRS, LGO, UBS, IFREMER, UBO EPE, CNRS, LEP, EEP, IFREMER, EPOC, EPHE, PSL, UB, INSU - CNRS, CNRS, LECOB, SU, CNRS, OOB, SU, CNRS, HCMR, ISTEP-PPB, iSTeP, INSU - CNRS, SU, CNRS