https://hdl.handle.net/10481/75029 Sat, 18 Apr 2026 22:44:03 GMT 2026-04-18T22:44:03Z https://hdl.handle.net/10481/112782 Late Pleistocene–Holocene environmental conditions in Lanzarote (Canary Islands) inferred from calcitic and aragonitic land snail shells and bird bones Yanes, Yurena; García-Alix Daroca, Antonio; Asta Andrés, María Pilar; Ibáñez, Miguel; Alonso, María R.; Delgado, Antonio Aragonitic and calcitic land snails from carbonate-rich paleosols in northwestern Lanzarote (Canary Islands) were analyzed for 13C/12C and 18O/16O ratios to deduce the Pleistocene–Holocene transition in the western- most Sahara zone. Modern, mid-late Holocene (~ 2.1–5.5 cal ka BP) and late Pleistocene (~ 23.3–24.0 cal ka BP) aragonitic shells exhibited respective values of −9.5 ± 1.6‰, −7.7 ± 1.5‰, and −2.3 ± 2.8‰ for δ13C; and +0.3 ± 0.3‰, +0.1 ± 0.7‰, and +2.5 ± 0.4‰ for δ18O. Holocene and Pleistocene calcitic shells of the endemic slug Cryptella canariensis showed respective values of −0.7 ± 2.6‰ and −8.5 ± 2.5‰ for δ13C; and +0.8 ± 1.5 and +3.6 ± 0.4‰ for δ18O. Both aragonitic and calcitic shells showed equivalent temporal isotopic trends. Higher δ13C values during ~ 23.3–24.0 cal ka BP suggest higher abundance of C4 and/or CAM plants, likely associated with drier conditions and/or lower atmospheric CO2 concentration. Maximum shell δ18O values during ~ 23.3–24.0 cal ka BP opposes minimal values of Greenland ice cores and probably reflect the combined effects of (1) higher rain δ18O values linked to higher glacial seawater δ18O values and/or larger snail activity during summer seasons; (2) relative humidity values similar or slightly lower than at present; (3) higher evaporation rates; and (4) cooler temperatures. Bone remains of the extinct Dune Shearwater Puffinus holeae were only recovered from the Holocene bed. Collagen δ13C and δ15N values (−13.5 ± 0.2‰[PDB] and +13.7 ± 1.0‰[air], respectively) match with the signature of a low trophic level Macaronesian seabird that fed upon local fish. Bone carbonate δ13C (−7.4 ± 1.0‰[PDB]) and phosphate δ18O (+ 18.2 ± 0.4‰[SMOW]) values exhibited pristine signals denoting their potential value in future paleoenvironmental studies in the region. The age of P. holeae (~ 2.1–2.7 cal ka BP) supports that the aborig- inal population possibly caused its extinction. In contrast, the extinction of the endemic helicid Theba sp. (~ 23.3–24.0 cal ka BP) was likely caused by environmental change. This research was funded by the Spanish Ministry of Economía y Competitividad (Mineco) research grant CGL2011-29898/BTE to YY. The Spanish Mineco also supports AGA and MPA through the Juan de la Cierva program. https://hdl.handle.net/10481/112782 https://hdl.handle.net/10481/112759 Arsenic Speciation in Mekong Delta Sediments Depends on Their Depositional Environment Wang, Yuheng; Le Pape, Pierre; Morin, Guillaume; Asta Andrés, María Pilar; Bártová, Barbora; Suvorova, Elena; Frutschi, Manon; Ikogou, Maya; Pham, Vu Hoai; Le Vo, Phu; Herman, Frédéric; Charlet, Laurent; Bernier-Latmani, Rizlan Arsenic contamination in groundwater is pervasive throughout deltaic regions of Southeast Asia and threatens the health of millions. The speciation of As in sediments overlying contaminated aquifers is poorly constrained. Here, we investigate the chemical and mineralogical compositions of sediment cores collected from the Mekong Delta in Vietnam, elucidate the speciation of iron and arsenic, and relate them to the sediment depositional environment. Gradual dissolution of ferric (oxyhydr)oxides with depth is observed down to 7 m, corresponding to the establishment of reducing conditions. Within the reduced sediment, layers originating from marine, coastal or alluvial depositional environments are identified and their age is consistent with a late Holocene transgression in the Mekong Delta. In the organic matter- and sulfur-rich layers, arsenic is present in association with organic matter through thiol-bonding and in the form of arsenian pyrite. The highest arsenic concentration (34−69 ppm) is found in the peat layer at 16 m and suggests the accumulation of arsenic due to the formation of thiol-bound trivalent arsenic (40−55%) and arsenian pyrite (15−30%) in a paleo-mangrove depositional environment (∼8079 yr BP). Where sulfur is limited, siderite is identified, and oxygen- and thiol-bound trivalent arsenic are the predominant forms. It is also worth noting that pentavalent arsenic coordinated to oxygen is ubiquitous in the sediment profile, even in reduced sediment layers. But the identity of the oxygen-bound arsenic species remains unknown. This work shows direct evidence of thiol-bound trivalent arsenic in the Mekong Delta sediments and provides insight to refine the current model of the origin, deposition, and release of arsenic in the alluvial aquifers of the Mekong Delta. https://hdl.handle.net/10481/112759 https://hdl.handle.net/10481/111221 Associations between inorganic arsenic in rice and groundwater arsenic in the Mekong Delta Reid, Matthew C.; Asta Andrés, María Pilar; Falk, Lily; Maguffin, Scott C.; Cong Pham, Vu Hoai; Hoang Anh, Le; Bernier-Latmani, Rizlan; Le Vo, Phu https://hdl.handle.net/10481/111221 https://hdl.handle.net/10481/111220 Monitoring a Mechanochemical Reaction Reveals the Formation of Stable Alkaline Earth (Ca, Sr, Ba) Hydrogen Carbonates En-capsulated by an Amorphous Phase Opitz, Phil; Asta Andrés, María Pilar; Fernandez-Martinez, Alejandro; Martin, Panthöfer; Kabelitz, Anke; Emmerling, Franziska; Mondeshki, Mihail; Tremel, Wolfgang https://hdl.handle.net/10481/111220 https://hdl.handle.net/10481/111164 Microbially-mediated release of As from Mekong Delta peat sediment Asta Andrés, María Pilar; Frutschi, Manon; Viacava, Karen; Loreggian, Luca; Le Pape, Pierre; Le Vo, Phu; Fernández, Ana María; Morin, Guillaume; Bernier-Latmani, Rizlan Peat layers within alluvial sediments are considered effective arsenic (As) sinks under reducing conditions due to the binding of As(III) to thiol groups in natural organic matter (NOM) and the formation of As-bearing sulfide phases. However, their possible role as sources of As for anoxic groundwaters remains unexplored. Here, we perform laboratory experiments to provide evidence for the role of a sediment peat layer in releasing As. Our results show that the peat layer, deposited about 8,000 years ago in a paleomangrove environment in the nascent Mekong Delta, could be a source of As to porewater under reducing conditions. X-ray absorption spectroscopy (XAS) analysis of the peat confirmed that As was bound to NOM thiol groups and incorporated into pyrite. Nitrate was detected in peat layer porewater, and flow-through and batch experiments evidenced the release of As from NOM and pyrite in the presence of nitrate. Based on poisoning experiments, we propose that the microbially mediated oxidation of arsenic-rich pyrite and organic matter coupled to nitrate reduction releases arsenic from this peat. Although peat layers have been proposed as As sinks in earlier studies, we show here their potential to release depositional- and/or diagenetically-accumulated As. This study is funded by the Swiss National Science Foundation (grant number 200021_157007), by the CODEV-EPFL Seed Money Fund, and by RESCIF-EPFL under the framework of a CARE-RESCIF initiative. Use of the Stanford Synchrotron Radiation Lightsource, SLAC National Accelerator Laboratory, is supported by the U.S. Department of Energy, Office of Science, and Office of Basic Energy Sciences under Contract No. DE-AC02-76SF00515. https://hdl.handle.net/10481/111164