Fast deep water warming of a subtropical crater lake

Water temperature of deep lakes is often used to evaluate climate variability over long periods. Santa Maria del Oro Lake is a sub-tropical crater-lake (60 m maximum depth) almost confined by surrounding mountains, which only receives seasonal fresh water input. In order to evaluate lake thermal variations, we measured water temperatures at bottom, 4 m, 10 m, 25 m, and 32 m depth. To study lake vertical mixing process, we implemented a 3D high-resolution model forced with atmospheric variables. Field data analysis indicate an hypolimnetic warming rate of 0.1136 ± 0.0001 °C y−1, about ten times larger than the mean global warming rate, and model results indicated that this was mainly caused by thermal diffusion between surface and bottom water layers. The lake presents a stable temperature stratification, which can reach 40 m depth during the windiest and coolest nights, indicating that the lake is oligomictic (i.e. mixes only occasionally). Inter-annual climate variability and global warming can alter the frequency of full vertical water mixing and, therefore, deep water warming. The used methodology can be useful to evaluate bottom trend temperature of subtropical lakes worldwide, and results may contribute to the use of deep lake waters as sentinels of multi-annual climate variability. As deep water mixing affects water quality, this may also be useful to better manage lake environmental services. © 2019 Elsevier B.V.This work was supported by Universidad Nacional Autónoma de México (UNAM) through PAPIIT [grant number IN104718 ].Peer reviewe

Anthropogenic drivers of increasing sediment accumulation in contrasting Mexican mangrove ecosystems

International audienc

Historical reconstruction of sediment accumulation rates as an indicator of global change impacts in a tropical crater lake

Lakes are effective sentinels of global change owing to their sensitivity to land-use changes and climate variability in their catchment. Santa María del Oro Lake (SAMO, NW Mexico) is of interest both for global change studies and as a natural resource to sustain the economy of local communities. Four sediment cores were used to evaluate the temporal variations of sediment accumulation, under the hypothesis that changes in sediment input are mostly driven by anthropic activities developed in the lake surroundings. Radiocarbon (14C) dating of SAMO sediments was precluded by a large and variable reservoir effect, inducing an age offset of ~ 4000 years. Well-constrained chronologies over the past century were obtained by 210Pb dating, corroborated by the stratigraphic markers 137Cs, 239+240Pu, and 14C-fraction modern. Geochemical, magnetic susceptibility, and meteorological data were used to elucidate the main controls of sedimentation processes in the lake. Mass accumulation rates were high, likely because of the natural vulnerability of catchment soils to hydric and aeolian erosion. The highest values, observed towards the lakeshore, were attributed to the influence of seasonal runoff from the surrounding steep hills, and the proximity of human settlements and agricultural fields. Mean mass accumulation rates increased with time (from 0.03 ± 0.01 g cm−2 year−1 between 1900 and 1950, to 0.14 ± 0.10 g cm−2 year−1 after the 1950s), although the most recent values were comparable to the mean values during the pre-1950 period. Accumulation maxima across the lake, occurring mostly since the 1980s, concurred with precipitation minima and were related to terrigenous pulses associated with soil erosion, likely favored by lower soil humidity and the occurrence of wildfires during dryer years. Controls on the development of human settlement and agriculture practices should be included in the long-term environmental management plans for the conservation of the lake resources.This work was supported by the grants UNAM DGAPA-PAPIIT/104718 and Newton Mobility Grant NMG\R2\170126

Mercury in Sediment Cores from the Southern Gulf of Mexico: Preindustrial Levels and Temporal Enrichment Trends

Spatial and temporal variability of mercury concentrations in sediments was evaluated in 210Pb-dated sediment cores from offshore and intertidal areas in the southern Gulf of Mexico. In offshore cores, mercury concentrations were comparable (11.2–69.2 ng g−1), and intermediate between concentrations in intertidal cores from the eastern (6.0–34.4 ng g−1) and the western (34.9–137.7 ng g−1) inlets of Términos Lagoon. The enrichment factor (EF) indicated minimal contamination (EF  \u3c  2) in most offshore cores, whereas in some intertidal cores steadily increasing mercury enrichment and fluxes were observed along the past century. No evidence of oil industry related mercury contamination was found, as the minor but increasing enrichment in intertidal cores is most likely related to land-derived sources such as catchment eroded soils and waste water runoff. Results highlight the importance to control catchment erosion and untreated sewage releases to reduce mercury loadings to the coastal zone

Multi-messenger Observations of a Binary Neutron Star Merger

International audienceOn 2017 August 17 a binary neutron star coalescence candidate (later designated GW170817) with merger time 12:41:04 UTC was observed through gravitational waves by the Advanced LIGO and Advanced Virgo detectors. The Fermi Gamma-ray Burst Monitor independently detected a gamma-ray burst (GRB 170817A) with a time delay of $\sim 1.7\,{\rm{s}}$ with respect to the merger time. From the gravitational-wave signal, the source was initially localized to a sky region of 31 deg(2) at a luminosity distance of ${40}_{-8}^{+8}$ Mpc and with component masses consistent with neutron stars. The component masses were later measured to be in the range 0.86 to 2.26 $\,{M}_{\odot }$. An extensive observing campaign was launched across the electromagnetic spectrum leading to the discovery of a bright optical transient (SSS17a, now with the IAU identification of AT 2017gfo) in NGC 4993 (at $\sim 40\,{\rm{Mpc}}$) less than 11 hours after the merger by the One-Meter, Two Hemisphere (1M2H) team using the 1 m Swope Telescope. The optical transient was independently detected by multiple teams within an hour. Subsequent observations targeted the object and its environment. Early ultraviolet observations revealed a blue transient that faded within 48 hours. Optical and infrared observations showed a redward evolution over ∼10 days. Following early non-detections, X-ray and radio emission were discovered at the transient’s position $\sim 9$ and $\sim 16$ days, respectively, after the merger. Both the X-ray and radio emission likely arise from a physical process that is distinct from the one that generates the UV/optical/near-infrared emission. No ultra-high-energy gamma-rays and no neutrino candidates consistent with the source were found in follow-up searches. These observations support the hypothesis that GW170817 was produced by the merger of two neutron stars in NGC 4993 followed by a short gamma-ray burst (GRB 170817A) and a kilonova/macronova powered by the radioactive decay of r-process nuclei synthesized in the ejecta