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Se presentan las características principales del método de datación de sedimentos recientes mediante el radioisótopo natural ²¹⁰Pb y su validación utilizando radionucleidos artificiales tales como ¹³⁷Cs y ²³⁹,²⁴⁰Pu. Se hace una revisión de los principios generales de esta metodología, se aportan recomendaciones prácticas para la recogida de testigos sedimentarios en el campo y su posterior procesamiento en el laboratorio, se describen diferentes técnicas analíticas utilizadas en la determinación de sus concentraciones y se explican brevemente varios modelos para la interpretación de los perfiles obtenidos. Por último, se incluyen ejemplos prácticos de su aplicación en secuencias sedimentarias procedentes de distintos ambientes marinos (estuario, bahía y plataforma continental) en el norte de la Península Ibérica. The main characteristics of the dating method of recent sediments using the natural radioisotope ²¹⁰Pb and its validation with artificial radionuclides such as ¹³⁷Cs and ²³⁹,²⁴⁰Pu are presented. A review of the general principles of this methodology is made, practical recommendations for the collection of sedimentary cores in the field and their subsequent processing in the laboratory are provided, several analytical techniques used to measure their concentrations are described and several models for the interpretation of the profiles are briefly explained. Finally, practical examples of its application in sedimentary sequences from different marine environments (estuary, bay and continental shelf) in the northern Iberian Peninsula are also included. Agradecimientos: Este artículo se ha inspirado en el manual de referencia publicado por Sanchez-Cabeza, J.A., Díaz-Asencio, M., Ruiz-Fernández, A.C., eds. (2012). Radiocronología de sedimentos costeros utilizando 210Pb: Modelos, Validación y Aplicaciones. Organismo Internacional de Energía Atómica, Viena, 105 pp., donde se profundizan diferentes aspectos tratados aquí. Trabajo financiado por los proyectos RTI2018-095678-B-C21, MCIU/AEI/FEDER, UE (MINECO) e IT976-16 (EJ/GV). Dos revisoras/es anónimas/os mejoraron el manuscrito original con sus comentarios y sugerencias. Contribución nº 56 de la Unidad de Investigación Geo-Q Zentroa (Laboratorio Joaquín Gómez de Llarena).

espanolLos manglares, junto con los pastizales marinos y las marismas, se encuentran entre los ecosistemas costeros conocidos como ecosistemas de carbono azul. Estos ecosistemasson sumideros naturales de carbono, relevantes para la mitigacion del calentamiento global debido a que son capaces de secuestrar importantes cantidades de CO2 para produccion de biomasa, asi como de almacenar materia organica en sus sedimentos durante muy largo plazo. Se presentan los resultados de la evaluacion temporal de los flujos (g m-2ano-1) e inventarios (Mgha-1) de carbono organico (Corg) en nucleos sedimentarios recolectados en areas de manglar asociados a la laguna costera Estero de Urias (Mazatlan, Sinaloa). La estrategia de trabajo incluyo la caracterizacion geoquimica de los sedimentos mediante el analisis de composicion elemental por espectrometria de fluorescencia de rayos-X para evaluar cambios en el origen de los sedimentos (terrigeno o marino); la determinacion de la distribucion de tamano de grano para evaluar cambios en la hidrodinamica de los sitios de estudio; y la cuantificacion de las concentraciones de Corg mediante un analizador elemental. Por ultimo, se presenta una estimacion del costo economico de los impactos de las emisiones potenciales de CO2como consecuencia de la oxidacion del Corg,debido a las potenciales perturbaciones de los sitios de estudio. La informacion generada representa una componente mas de los beneficios economicos de la preservacion de los ecosistemas de manglar, relevante en los planes de manejo de humedales costeros,cuya conservacion contribuye a la reduccion de emisiones de gases de efecto invernadero, y podria ser aprovechada como parte de una estrategia de adaptacion al cambio climatico basada en ecosistemas, en zonas tropicales y subtropicales alrededor del mundo EnglishMangroves, along with seagrasses and saltmarshes, are among the coastal ecosystems known as blue carbon ecosystems. These ecosystems are natural carbon sinks, relevant to mitigate global warming because they are able to sequester significant amounts of CO2for biomass production, andto store organic matter in sediments for a very long time. We present the temporal evaluation of fluxes (g m-2year-1) and inventories (Mg ha-1) of organic carbon (Corg) from sediment cores collected in mangroves areas associated with the coastal lagoon Estero de Urias, in Mazatlan, Sinaloa. The work strategy included the geochemical characterization of sediments by elemental composition analysis through X-ray fluorescence spectrometry to evaluate changes in sediment origin (terrestrial or marine); the determination of the grain size distribution to evaluate changes in the hydrodynamics of the study sites; and the quantification of Corgconcentrations with an elemental analyzer. Finally, we estimated theeconomic cost of the impacts of CO2 emissions caused by the oxidation of Corgdue to potential perturbations of the study sites. This information isan additional component of the economic benefits of the preservation of mangrove ecosystems, relevant in coastal wetland management plans, since mangrove conservation contributes to the reduction of greenhouse gas emissions and could be used as part of an ecosystem-based adaptation to climate change strategy in tropical andsubtropical zones around the world.

Sea-level rise (SLR) is one of the most pervasive consequences of global warming, and the Cuban Archipelago is threatened by current and future SLR. In order to support adaptation plans, it is essential to have reliable information about sea-level change during the last decades at the local scale, particularly in the most vulnerable regions. Here, we use sedimentary records to evaluate coastal accretion and to estimate the relative sea-level rise (RSLR) in two vulnerable coastal sites in central Cuba: Cayo Santa María (CSM) and Península de Ancón (PA). Both sites showed sediment sections with a continuous record of sediment accretion as a result of relative SLR and tropical storms. The sedimentary process was different between CSM and PA owing to differences in geomorphology and primary mineral composition. Sedimentary records also showed recent impacts of anthropogenic activities, likely increasing the vulnerability of the shoreline to SLR. The estimated RSLR values agreed with tidal gauge records, although they spanned a much longer time period (CSM: 0.5 ± 0.1 mm a−1, span of 38 years; PA: 1.5 ± 0.3 mm a−1, span of 92 years). Our results confirm that this methodology may be used to estimate the RSLR in places where data by instrumental records do not exist.

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Despite the multidisciplinary and comprehensive approach taken in ref. 1, we acknowledge that there are still open questions that require further research. We emphasize that our study relies on multiple records that show the synchronous arrival of humans on multiple islands before ca. 1400 CE. Elias et al. (2) raise specific concerns about the record from Peixinho Lake, one of the five lakes included in the study, while ignoring the other multiproxy lake sediment records. The arguments presented by Elias et al. (2) do not undermine in any way the main conclusions of our paper, but still we would like to explicitly address the main criticisms with regard to the only record in question

Globally, nutrient river discharges drive water quality of coastal ecosystems, and excess nutrients can cause eutrophication impacts. The Grijalva-Usumacinta River System (GURS) discharges in the southern Gulf of Mexico (SGoM) and it is the second largest riverine input to the Gulf. To study how contrasting GURS freshwater flow between rainy and dry seasons affects nutrients concentrations in the receiving coastal ecosystem, we evaluated nutrient variability in the water column during both seasons. High inorganic nutrients and total phosphate outline the rivers discharge plumes during rainy season, and were significantly higher than during the dry season throughout the study area, suggesting contrasting seasonal nutrient discharge of the GURS to coastal waters. On average the GURS discharged 141,123 t N yr

Humans have made such dramatic and permanent changes to Earth's landscapes that much of it is now substantially and irreversibly altered from its preanthropogenic state. Remote islands, until recently isolated from humans, offer insights into how these landscapes evolved in response to human-induced perturbations. However, little is known about when and how remote systems were colonized because archaeological data and historical records are scarce and incomplete. Here, we use a multiproxy approach to reconstruct the initial colonization and subsequent environmental impacts on the Azores Archipelago. Our reconstructions provide unambiguous evidence for widespread human disturbance of this archipelago starting between 700-60+50 and 850-60+60 Common Era (CE), ca. 700 y earlier than historical records suggest the onset of Portuguese settlement of the islands. Settlement proceeded in three phases, during which human pressure on the terrestrial and aquatic ecosystems grew steadily (i.e., through livestock introductions, logging, and fire), resulting in irreversible changes. Our climate models suggest that the initial colonization at the end of the early Middle Ages (500 to 900 CE) occurred in conjunction with anomalous northeasterly winds and warmer Northern Hemisphere temperatures. These climate conditions likely inhibited exploration from southern Europe and facilitated human settlers from the northeast Atlantic. These results are consistent with recent archaeological and genetic data suggesting that the Norse were most likely the earliest settlers on the islands., This research is funded by Fundação para a Ciência e Tecnologia (DL57/2016/ ICETA/EEC2018/25) grant, DISCOVERAZORES research project (PTDC/CTA-AMB/28511/2017), the Spanish Ministry of Economy and Competitiveness research projects PaleoNAO (CGL2010-15767), RapidNAO (CGL2013-40608-R), and PaleoModes (CGL2016-75281-C2), and by the Luso-American Foundation. This work is contributing to the Institut de Ciència i Tecnologia Ambiental (ICTA) - Universitat Autonoma de Barcelona “Unit of Excellence” Maria de Maetzu (CEX2019-000940-M) grant. The International Atomic Energy Agency is grateful for the support provided to its Environment Laboratories by the Government of the Principality of Monaco.

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 ].

Testate amoebae are bioindicators sensitive to environmental change, which show good preservation in sediments of low pH environments, such as high mountain lakes (LAM). The presence and diversity of testate amoebae were documented in surface sediments and sediment cores, dated with 210Pb, from the only 2 LAMs in Mexico (El Sol and La Luna), which have shown signs of recent human-induced changes. A total of 18 taxa were recorded and the main species observed in both lakes were Difflugia glans “glans” and D. globulosa. Specific richness and Shannon’s diversity index were higher in Lake El Sol than in the smaller, acidic and ultraoligotrophic Lake La Luna. The sediment cores recorded changes, during the last 20 to 25 years, in the composition of the testate amoebae communities (El Sol) and in their dominance (La Luna), as well as increased accumulation rate and concentrations of iron and organic carbon. These are signs of anthropogenic impact on the lakes, which should alert us to improve protection measures for these unique ecosystems, not only at the local (crater) level, but also with a more regional perspective.

While we officially live in the Holocene epoch, global warming and many other impacts of global change have led to the proposal and wide adoption of the Anthropocene to define the present geological epoch. The Anthropocene Working Group (AWG) established that it should be treated as a formal stratigraphic unit, demonstrated by a reference level commonly known as “golden spike”, still under discussion. Here we show that the onset of bomb-derived plutonium recorded in two banded massive corals from the Caribbean Sea is consistent (1955–1956 CE), so sites far from nuclear testing grounds are potentially suitable to host a type section of the Anthropocene. Coastal coral demonstration sites are feasible, could foster economic development, and may serve as focal points for scientific dissemination and environmental education.

Chronologies are an essential tool to place natural archives of environmental changes on a calendar scale. Because of this, studies that compare and assess the accuracy and precision of available dating models are essential. 210Pb is a radioactive isotope which is used to date recent sediments (210Pb dating models: the Constant Flux model (also known as the Constant Rate of Supply model) and the recently developed Bayesian Plum model. This comparison was implemented by using four sediment cores from contrasting environmental settings, and showed several benefits of using a Bayesian approach. This allows to infer variables, such as the supported levels of 210Pb, crucial to the chronology and commonly estimated through either samples where an asymptotic behaviour is observed or through 226Ra measurements, which themselves contain some level of uncertainty. Another step of traditional methods is the selection of the equilibrium depth in order to calculate total inventories, which carries strong consequences for the resulting age depth model. Plum, on the other hand, infers the 210Pb flux, which eliminates the need to select an equilibrium depth and allows for dating cores with incomplete inventory. When traditional methods address cores with missing inventory, 137Cs time markers are commonly used to correct the chronology, but Plum can use these time markers to improve the chronology and to reduce the uncertainty. These aspects show that the Bayesian approach results in more robust and objective chronologies, and thus in better reconstructions of environmental change over the past centuries.

Vegetated coastal ecosystems have an important role as contaminant filters. Temporal variations in concentrations, enrichment factors (EF), and fluxes of trace elements (As, Cd, Co, Cr, Cu, Ni, Pb, V, and Zn) were evaluated in 210Pb-dated sediment cores from salt marsh and seagrass ecosystems at San Quintin Bay (Mexican northern Pacific). Trace element contamination was negligible in seagrass sediments, but minor to severe, depending on the element, in salt marsh cores, owing to higher organic carbon and fine sediment contents. EF temporal variation in salt marsh cores was attributed to agriculture technology changes (e.g. installation of greenhouses, and improved irrigation and fertilization systems). Trace element flux ratios increased during the past 100 years, likely caused by steadily increasing sediment accumulation rates promoted by land-use changes in the catchment. The conservation of salt marsh areas is important to preserve their function as contaminants biofilters and the health of adjacent ecosystems.

Water reservoirs are essential for regional economic development, as populations depend on them for agriculture irrigation, flood control, hydroelectric power generation, water supply for human consumption, and subsistence fishing activities. However, the reservoir environmental quality can be disturbed by enhanced sediment input and trace metal contamination, affecting human health as a consequence of contaminated water and fish consumption. With the purpose to understand the trends and extent of sediment accumulation and trace element contamination in the Oviachic reservoir (OV, northwestern Mexico) since its construction, the temporal variations of sediment accumulation, and As, Cr, Cu, Hg, Ni, Pb, and Zn concentrations, enrichment, and fluxes, were evaluated through the study of two 210Pb-dated sediment cores. We assumed that siltation and trace element contamination were driven by the development of anthropogenic activities in the region within the past ~ 70 years. Elemental concentrations accounted from null to minor enrichment for most elements, but moderate to significant enrichment by Hg. Mercury, As, and Cu fluxes have notably increased since the past decade, most likely because of a combination of anthropogenic and natural processes, including catchment erosion, artisanal gold mining, and recent drought conditions in the region. Arsenic and Hg concentrations may pose deleterious risks to biota in the reservoir, and consequently to humans through fish consumption, for which further biological and toxicological tests are advisable. This study highlights the importance of using sediment dating to assess historical trends of metal contamination and identify possible sources, to support decision-making in programs addressed to reduce environmental and health risks in aquatic ecosystems.

Globally, instrumentally based assessments of tsunamigenic potential of subduction zones have underestimated the magnitude and frequency of great events because of their short time record. Historical and sediment records of large earthquakes and tsunamis have expanded the temporal data and estimated size of these events. Instrumental records suggests that the Mexican Subduction earthquakes produce relatively small tsunamis, however historical records and now geologic evidence suggest that great earthquakes and tsunamis have whipped the Pacific coast of Mexico in the past. The sediment marks of centuries old-tsunamis validate historical records and indicate that large tsunamigenic earthquakes have shaken the Guerrero-Oaxaca region in southern Mexico and had an impact on a bigger stretch of the coast than previously suspected. We present the first geologic evidence of great tsunamis near the trench of a subduction zone previously underestimated as potential source for great earthquakes and tsunamis. Two sandy tsunami deposits extend over 1.5 km inland of the coast. The youngest tsunami deposit is associated with the 1787 great earthquake, M 8.6, producing a giant tsunami that poured over the coast flooding 500 km alongshore the Mexican Pacific coast and up to 6 km inland. The oldest event from a less historically documented event occurred in 1537. The 1787 earthquake, and tsunami and a probable predecessor in 1537, suggest a plausible recurrence interval of 250 years. We prove that the common believe that great tsunamis do not occur on the Mexican Pacific coast cannot be sustained.

Oxygen minimum zones (OMZs) are predicted to expand in the near future due to continued global warming, with largest declines in oxygen occurring within the strong tropical OMZs. In this study, shifts in the position and intensity of the OMZ in the Eastern Tropical North Pacific (ETNP) were examined using three 210Pb-dated sediment cores collected along the continental shelf and slope of the NW Mexican Margin (southwest of Mazatlan). Using a suite of redox sensitive elements, bulk element and physical analyses, three main factors were identified as driving the geochemical signatures of trace elements across the NW Mexican Margin: 1) terrigenous input, 2) organic matter scavenging and 3) bottom water oxygen content. Downcore trends in benthic foraminiferal assemblages and authigenic concentrations of Mo and U suggest that dysoxic conditions were more intense and covered a larger depth range prior to the 20th century followed by a reduction in both size and strength of the OMZ over the last century.

The profile of 11 trace metals in two commonly used biomonitors (the native oyster Crassostrea palmula and mussel Mytella strigata) from Estero de Urias lagoon, Gulf of California, were studied for six months, covering both dry and wet seasons. Metal concentrations in these two bivalves were compared with concentrations accumulated by Artificial Mussels (AMs) deployed alongside during the same period. Significant temporal variations in Cd, Cr and Mn were observed in both bivalve species and AMs. Temporal changes were observed for Fe in both bivalve species, Pb in oyster only and Cu in both AMs and oysters, revealing seasonal changes in inputs and/or chemical forms of these metals in the lagoon. Significant correlations for Cd, Cr and Cu were found in mussels and oysters, but their Co, Fe, Mn and Zn profiles were very different, despite these two species being taxonomically closely related and often used as biomonitors for metals. Interestingly, Hg and U were detected in AMs but not in oysters and mussels. The difference in metal profile in oysters, mussels and AMs revealed in the present study clearly showed that different biomonitors and AM take up metals differentially from the same environment, and metal profile in a single biomonitor or AM alone therefore, cannot provide a good estimate on metal concentrations in the ambient environment. As such, different biomonitors and AM should be used in metal monitoring, in order to provide a comprehensive picture on metal levels in aquatic ecosystems. Concentrations of Ni and Pb in oysters, and Cr, Fe and Mn in mussels were among the highest reported in coastal waters worldwide. Concentrations of Pb in oysters exceeded legal limits set for bivalve mollusks in EU. Concentrations of Cr in mussels and oysters exceeded or were very close to, respectively, the legal limit for fish, crab-meat, oysters, prawns, and shrimps in Hong Kong. The results indicate a potential public health risk on human consumption of oysters and mussels commonly harvested from the Estero de Urias lagoon, and corresponding pollution control measures are deemed necessary.

The identification and quantification of global change, including climate change, requires long time series of key variables. In this work, the fundamentals and operation of low-cost long-term coastal observatories are described, and preliminary data are shown. The vision is to offer a scientific platform of physicochemical data for at least the next 100 years, what requires establishing sustainable strategies, training human resources, strong institutional support, and long-term funding sources. The network formally operates since 2013 and has generated more than 6 million data points, continuously growing, of which >1.5 million data points are permanently stored and available through a public access web platform. The strategies and methodologies are described and, in the Mazatlan observatory, data recovery and basic statistics of eight environmental variables are presented. During 2015, an extreme El Nino year, marine temperatures increased from the bay to the middle Urias coastal lagoon, were h...

Coastal vegetated habitats can be important sinks of organic carbon (Corg) and mitigate global warming by sequestering significant quantities of atmospheric CO2 and storing sedimentary Corg for long periods, although their Corg burial and storage capacity may be affected by on-going sea level rise and human intervention. Geochemical data from published 210Pb-dated sediment cores, collected from low-energy microtidal coastal wetlands in El Salvador (Jiquilisco Bay) and in Mexico (Salada Lagoon; Estero de Urias Lagoon; Sian Ka'an Biosphere Reserve) were revisited to assess temporal changes (within the last 100years) of Corg concentrations, storage and burial rates in tropical salt marshes under the influence of sea level rise and contrasting anthropization degree. Grain size distribution was used to identify hydrodynamic changes, and δ13C to distinguish terrigenous sediments from those accumulated under the influence of marine transgression. Although the accretion rate ranges in all sediment records were comparable, Corg concentrations (0.2-30%), stocks (30-465Mgha-1, by extrapolation to 1m depth), and burial rates (3-378gm-2year-1) varied widely within and among the study areas. However, in most sites sea level rise decreased Corg concentrations and stocks in sediments, but increased Corg burial rates. Lower Corg concentrations were attributed to the input of reworked marine particles, which contribute with a lower amount of Corg than terrigenous sediments; whereas higher Corg burial rates were driven by higher mass accumulation rates, influenced by increased flooding and human interventions in the surroundings. Corg accumulation and long-term preservation in tropical salt marshes can be as high as in mangrove or temperate salt marsh areas and, besides the reduction of Corg stocks by ongoing sea level rise, the disturbance of the long-term buried Corg inventories might cause high CO2 releases, for which they must be protected as a part of climate change mitigation efforts.

Two lead-210 (210Pb) dated sediment cores from Chapala Lake were studied to identify the mineral composition of the sediments and to discuss its relation with trace metals. Minerals and trace metals reflected the domain of volcanic rocks (i.e. basalts, rhyolite and andesite) that characterize Chapala Lake and the Lerma River watershed. Redundancy analyses (RDA) were used to identify the sedimentary variables (magnetic susceptibility, organic matter, sand content, and mineral composition) that could be related to elemental composition. Despite the distance between the two cores (7.3 km) and hydrodynamic circulation the RDA showed that the main mechanism that controls the input of mineral species, and, therefore, element distributions in the lacustrine sediment of Chapala Lake, is related to the weathering of volcanic rocks in the Lerma-Chapala watershed, the consequent runoff and transport of fine grained catchment materials, and later in-lake processes. These findings highlight the importance of controlling watershed erosion to contribute to the improvement of the environmental quality of the lake.

Anthropogenic salinization impacts the health of aquatic and terrestrial ecosystems worldwide. In tropical and subtropical areas, shrimp farm aquaculture uses water from adjacent ecosystems to fill the culture ponds, where enhanced evaporation cause salinization of discharged water. In this study, we studied water salinity before and after shrimp farm harvest and implemented a three-dimensional hydrodynamic model to assess the impact on a subtropical coastal lagoon that receives water releases from shrimp ponds. The shrimp pond discharge significantly increased the salinity of receiving waters, at least 3 psu over the local variation. In the worst-case salinization scenario, when harvest occurs after a long dry season, salinity could increase by up to 6 psu. The induced salinization due to shrimp pond effluents remained up to 2 tidal cycles after harvest, and could affect biota. The methodology and results of this study can be used to assess the impacts of shrimp aquaculture worldwide.

International audience; Coastal areas are inhabited by a large fraction of the human population and provide many important ecosystem services, notably those related to fisheries. Hypoxia occurs when dissolved oxygen (DO) levels are so low that affect metabolic processes of many organisms, causing stress or even death. During the last decades, coastal hypoxia events have increased and nowadays these are one of the largest impacts of global change on coastal ecosystems. The entrance area of the Gulf of California is a region characterized by a shallow oxygen minimum zone and seasonal coastal upwelling events that may cause hypoxia by shoaling the oxycline. Under the hypothesis that some of the observed hypoxia episodes are controlled by coastal upwelling events, the objective of this work was to propose a novel statistical methodology to identify these events. From two oceanographic cruises, we observed the top of the oxycline depth at ∼30 m near the coast, while hypoxia was reached at ∼55 m. Also, DO time-series were recorded with autonomous sensors from early 2014 to late 2016 every 30 min in surface waters (5 m depth) off the Mazatlán City coastal zone (Mexico). This time series showed hypoxia events (and even anoxia, DO < detection limit = 0.06 mg L-1) at surface waters lasting from days to weeks. We propose a novel methodology to identify coastal hypoxia events controlled by coastal upwelling, which involves statistical and frequency analyses performed in conjunction with other physical variables such as sea surface temperature (SST), sea level, and the coastal upwelling index (CUI). Results confirmed that coastal wind-induced upwelling controls at least half of the hypoxia events identified. Further research is needed to understand the processes responsible for the other events, likely including mesoscale processes (such as eddies and internal waves) and the degradation of organic matter during eutrophic conditions. The methodology could be used in other eastern boundary upwelling systems of the world. These results should be of interest to coastal zone managers, local fishing communities, and the large fishing industry of this region to discriminate between natural and anthropogenic hypoxia events.

Sea level rise, one of the most evident effects of recent climate change, is already impacting coastal ecosystems. Because of its low relief, population increase and economic development during the last century, the Celestun lagoon is highly vulnerable to global change, including sea level rise. Here, we study a sediment core from a tropical saltmarsh to evaluate the impact of sea level rise on sediment accretion and carbon fluxes. Some geochemical indicators in a 210Pb dated sediment core showed clear signals of marine influence. This was reflected on increased accretion rates, from 0.3 ± 0.1 mm yr− 1 in ≈ 1941 to 2.9 ± 1.2 mm yr− 1 in 2012. These accretion rates were similar to eustatic sea level rise, and mean acceleration ranged from 0.037–0.22 mm yr− 2, implying a SLR by 2100 ranging from 14 to 86 cm. The one-century (1917–2013) organic carbon stock in sediments was calculated to be 10.1 ± 0.2 Mg C ha− 1. During the same period, the organic carbon flux, corrected for organic carbon degradation, increased from 7 ± 3 g C m− 2 yr− 1 to 73 ± 26 g C m− 2 yr− 1, attributed to the impact of sea level rise in this ecosystem. This work shows that tropical saltmarshes may provide useful information on sea level rise, and the presented methodology may be used where instrumental records do not exist or they are too short.

The reconstruction of pollution in aquatic ecosystems is a useful tool to evaluate the effectiveness of management actions. Cartagena Bay (Colombia, Caribbean Sea) is one of the most impacted coastal zones in Colombia by a wide variety of human activities. A sediment core was dated using 210Pb and used to reconstruct the historical input of heavy metals, polycyclic aromatic hydrocarbons (PAHs), and organochlorinated pesticides to the bay. The highest pollutant concentrations were observed in the deeper core layers. The maximum mercury concentration (18.76 μg g−1) was observed at 61 cm depth, corresponding to 1967, when a chlor-alkali plant was operating. Since all pollutant concentrations have decreased due to better industrial management policies, their presence is a potential contamination risk through sediment remobilization and pollutant resuspension.

We evaluated the forest structure, pore water salinity, geochemical characteristics, grain-size distribution and sediment accumulation rates (SAR) in 15 mangrove sites along the San Pedro Mezquital River, one of the major sources of fresh water supply to the Marismas Nacionales System. Sediments were sandy-silty with high organic matter content (5.8 ± 1.5% to 23.6 ± 1.7%). The marine (Na, Cl and Br) and terrigenous (Al, Ti, Rb and Zr) elements indicated that sediments were mostly of continental provenance, with small marine contribution. SAR ranged from 0.08 ± 0.01 to 2.29 ± 0.28 cm yr−1. Laguncularia racemosa was the dominant species in the northern sites (between Toluca Lagoon and Mexcaltitan Lagoon), with a mean basal area of 11.1–49.3 m2 ha−1, whereas Rhizophora mangle prevailed in the southern sites, closer to the river mouth (between Boca Camichin and Los Limones River, mean basal area of 2.0–11.0 m2 ha−1). The southern area was characterized by lower forest attributes, and higher pore water salinity and sediment accumulation rates than the northern area. We concluded that mangrove preservation along SPMR requires insuring appropriate fresh water and sediment supply, and the control of organic matter pollution sources.

The Salada coastal lagoon is located in Veracruz (Mexico) near the Laguna Verde Nuclear Power Plant (LVNPP). Currently, the lagoon receives the cooling waters used in the LVNPP. To evaluate the fluxes and mobilization of trace elements due to human activities in the area, two sediment cores from the coastal flood plains of Salada Lagoon were analysed. Cores were collected using PVC tubes. Sediments cores were analysed every centimetre for dating ( 210 Pb by alpha detector) and trace metal analysis using ICP-Mass Spectrometry. The dating of both sediment cores covers the period from 1900 to 2013, which includes the construction of the LVNPP (1970's). The Normalized Enrichment Factor shows enrichment of Ag, As and Cr in both sediment cores. These enrichments correspond to the extent of mining activity (which reached a maximum in the 1900's) and to the geological setting of the coastal zone. The profiles of the element fluxes in both sediment cores reflected the construction and operation of the LVNPP; however, the elements content did not show evidence of pollution coming from the LVNPP.

Total mercury concentrations (T-Hg) and stable isotope ratios (δ15N and δ13C) were analyzed in the muscle of fish, collected at two marshes impacted by gold mining in Northern Colombia, to evaluate the seasonal and spatial behavior of these variables and mercury biomagnification based on their relationship with δ15N ratios in the fish. There was not significant (p > 0.05) seasonal differences (dry and rainy season) in δ15N and δ13C values in none marsh, suggesting that these fish species keep a similar feed pattern within each marsh along the year. However, there were significant differences (p

Gamma-ray spectrometry is a widely used technique to quantify the presence of numerous radionuclides in environmental samples. In this work, we describe a methodology for efficiency calibration of four well-type germanium detectors and their use for the determination of low-level activities of gamma emitters in sediment samples. An experimental efficiency calibration for each detector was built with three materials for 17 energies, ranging from 46.5 keV to 1460 keV. For efficiency transfer to different geometries and sample types, we used the effective solid angle approach (ET-Ω method). Final calibrations were calculated for all detectors, several counting geometries, and elemental composition of selected sample types. Calibrations were validated with six reference materials. This methodology allowed to reliably analyze nine gamma emitters (210Pb, 241Am, 234Th, 228Ac, 214Pb, 208Tl, 137Cs, 134Cs and 40K) in sediment samples. Using these calibrations, gamma emitter profiles of sediment cores from contrasting aquatic systems (lake, intertidal, marine and deep-sea areas) provided reliable profiles of 210Pb and artificial radionuclides useful for dating and stratigraphic interpretation. A protocol to implement this methodology is also presented.

The coral Li/Mg temperature proxy is revisited through an in-depth trace element analysis of scleractinians collected live from tropical to polar environments. The dataset consists of Li/Ca, Mg/Ca, Sr/Ca and Li/Mg ratios from 64 coral specimens belonging to 8 different taxa, including both reef-building zooxanthellate and cold-water non-zooxanthellate species, from a wide range of water temperature (-1 to 29.5 degrees C), salinity (34.71 to 38.61), and depth (3 to 670m). Our results showed that the reliability of the Li/Mg temperature proxy is strongly limited by the organic matter associated with the coral skeleton, which is most evident within the green bands observed in tropical corals. Organic-rich bands can double the Mg content otherwise present in the skeleton, which may ultimately lead to a temperature overestimation exceeding 15 degrees C. We found that this bias can be overcome by the treatment of coral skeletons with a specific oxidizing cleaning protocol. We also detected the presence of calcite deposits within the aragonite skeleton of some Antarctic living coral specimens, which strongly affects the robustness of the Li/Mg proxy given its temperature sensitivity of similar to 1.5 degrees C/1% calcite. Therefore, to obtain reliable reconstructions a correction needs to be applied when organic matter and/or calcite contamination is present, which requires the scrupulous assessment of the integrity of the aragonite prior to geochemical analyses. Given that some species entrap more organic matter than others, and that some are more prone to calcite contamination, a taxon-related effect is apparent. Here we show that the tropical species Porites spp., Pseudodiploria strigosa and Orbicella annularis, and the cold-water species Madrepora oculata, Caryophyllia antarctica and Flabellum impensum, are all suitable candidates for reconstructing seawater temperatures. The integrated results across a wide temperature range, from extreme cold to tropical shallow waters, yield an overall precision for the Li/Mg-temperature proxy of +/- 1.0 degrees C, as quantified by the standard error of estimates. If calculated from the 95% prediction intervals, the uncertainty of the temperature estimates is +/- 0.9 degrees C at 1 degrees C, +/- 1.5 degrees C at 12 degrees C and +/- 2.6 degrees C at 25 degrees C. However, the uncertainty for the tropical corals (e.g. Porites) can be reduced to +/- 0.6 degrees C if a Li/Mg and Sr/Ca multi-regression approach is applied.

The Bilbao estuary is one of themost polluted areas on the northern coast of Spain, owing to the direct disposal of urban effluents and wastewaters frommining and industrial activities that has occurred during the last 170 years. Recent sediment records collected fromthe inner Abra of Bilbao baywere examined using amultidisciplinary approach including geochemical,micropaleontological and isotopic proxies to evaluate heavy metal contamination (Pb, Zn and Cd), ecological condition (benthic foraminifera), and sediment accumulation variability (210Pb). Results evidenced the interplay of both human activities and extremeweather events.Most contaminatedmaterials are buried belowa thin layer (1?21 cm) of cleaner sedimentswhich have been deposited since contaminant discharges have substantially decreased, due to industrial reconversion and environmental regulations. However, the fingerprint left in the sedimentary record by the catastrophic floods of 1983 confirms the potential of natural events for sediment relocation, showing catastrophic eventsmay endanger recently-achieved environmental improvements in historically contaminated coastal areas. Acknowledgements: This research was funded by Spanish MINECO (CGL2013-41083-P), UPV/EHU (UFI11/09) and EJ/GV (IT976-16) projects. Microfossil samples of cores Abra1, Abra4 and Abra6 were prepared and analyzed initially by I. Kortabitarte and A. González-Lanchas. L.H. Pérez-Bernal (UNAM) contributed to 210Pb and sediment characterization analyses. This is contribution 48 of the Geo-Q Zentroa Research Unit (Joaquín Gómez de Llarena Laboratory).

Following the blowout of the Macondo well, a sedimentation pulse resulted in significant changes in sedimentary redox conditions. This is demonstrated by downcore and temporal changes in the concentration of redox-sensitive metals: Mn and Re. Sediment cores collected in the NE Gulf of Mexico reveal increased sedimentation after the Deepwater Horizon (DWH) blowout. The formation of mucous-rich marine snow in surface waters and subsequent rapid deposition to sediments is the likely cause. Respiration of this material resulted in decreased pore-water oxygen and a shoaled redoxcline, resulting in two distinct Mn peaks in sediments following the event, one typically in the top 5–7 mm, with the other at 20–30 mm. Cores near the wellhead reveal this nonsteady-state behavior for 3–5 years after the event. A time series reveals that bulk sediment Re increased 3–4 times compared to the pre-impact baseline value for 2–3 years indicating sediments are increasingly more reducing. Three years after the blowout, subsurface Re reaches a plateau suggesting a return to steady-state conditions. In select sites where benthic foraminifera were counted, an assemblage-wide decrease is coincident with reducing conditions, demonstrating the important consequences of changing redox conditions on benthic ecosystems.

Microplastics (MPs) are long-lasting anthropogenic pollutants, observed in all types of natural environments. The MPs abundance and their temporal variability in beach sands, surface waters (manta trawl), and suspended sediments (sediment trap) were assessed in Mazatlan, Mexico, a tourism destination on the northern Pacific coast, under the hypothesis that MP contamination is influenced by rainfall and population density. The MP concentrations in beach sands from urban and rural areas nearby Mazatlan (4–36 MPs m−2) and in surface waters (1.7–2.0 MPs m−3) were comparable between type of sampling sites; whereas the MP fluxes in sediment trap samples varied widely (40–782 MPs m−2 day−1) with highest values during the rainfall season. The MPs recovered were mostly white/clear (48–54%), and the prevailing shapes were fragments in beach sands and surface waters (59–80%), and fibers (75%) in suspended sediments. The synthetic polymers polypropylene, polyethylene, and polyethylene terephthalate were the most abundant in the study area.

The Ixtoc-1 oil spill (1979–80) released 475 million liters of petroleum into the Southern Gulf of Mexico (sGoM) likely causing Marine Oil Snow Sedimentation and Flocculent Accumulation (MOSSFA) to occur. A multiproxy approach including short-lived radioisotopes (210Pbxs), benthic foraminifera stable isotopes (δ13CCaCO3), and volcanic sediment grains was used to investigate regional events (e.g. oil spills and volcanic eruptions) recorded in sedimentary records. Depleted δ13CCaCO3 from 1979 to 80 outside of natural variability most likely results from petrogenic carbon deposition 100–250 km west of Ixtoc-1, possibly associated with MOSSFA. An event, characterized by increased volcanic input, depleted δ13CCaCO3, and increased mass accumulation rates was consistent with the El Chichon eruption (1982) 80–100 km north of Ixtoc-1. Many factors confound the uniform distribution and preservation of these events in the sGoM. However, a multiproxy approach may aid to distinguish multiple events in the sGoM sedimentary record.

The Gulf of California (GC) is an unique large ecosystem characterized by its rich biodiversity, high biological productivity and endemism of marine life. However, as many other large ecosystems worldwide, it is subject to diverse anthropogenic pressures (overfishing, climate change, losses of biodiversity and habitats, and pollution). We reviewed over 150 studies dealing with contaminants in water, sediments and representative organisms from the GC, and here we discuss the main issues associated to the presence of metals, metalloids, persistent organic pollutants (POPs, including polycyclic aromatic hydrocarbons (PAHs), polychlorinated biphenyls (PCBs), brominated diphenyl ethers (deca tri-a) (PBDEs), and several other pesticides), plastics, nutrients and algal blooms. The GC ecosystems have been subject to a wide range of pollution sources. Nevertheless, the pollution levels remain relatively low to moderate depending on the location and contaminant type. Contamination hotspots are found i) for metals and metalloids, in sites where mining spills have occurred and ii) for nutrients and pesticides, in wetlands that receive discharges from intensive agricultural and shrimp farming. We also identified sites where harmful algal blooms (HABs) have been observed. However, numerous coastal environments in GC, affected by pollution sources and events have yet been poorly studied. More detailed, extensive and comprehensive studies on the pollution levels and trends, transfer and toxic effects are still needed.

Sedimentary records are useful to evaluate environmental changes, either from natural or anthropogenic causes, such as global and climate change. The recent changes in accumulation rates and geochemical characteristics (grain size distribution, elemental composition, organic carbon and carbonate concentrations) recorded in a sediment core from San Jose Island Lagoon (SJIL, Gulf of California) were evaluated to determine its relationship with anthropogenic impacts and climatic variability. The 210 Pb-derived chronology was corroborated with 239+240 Pu and 137 Cs stratigraphic markers. The mass accumulation rate increased up to ∼3 times during the past ∼100 years (0.16 ± 0.03 to 0.51 ± 0.06 g cm −2 yr −1 ). The contents of terrigenous and marine (salinity) indicator elements, as well as fine-grained sediments, also increased considerably, although no anthropization evidences were observed; indeed, the enrichment factor of trace elements indicated that the ecosystem is still a pristine environment. By using multivariate statistical techniques, we inferred that the larger input of fine-grained terrigenous sediments could be related to the enhancement of soil erosion from the catchment, under the influence of higher rainfall rates, especially during the last 20 years. In addition, the higher concentrations of salinity indicator elements most likely resulted from higher evaporation rates in the lagoon, caused by higher minimum atmospheric temperatures. We concluded that recent climate variability has become the main driver for sedimentary geochemical changes in San Jose Island Lagoon. These observations confirmed the usefulness of 210 Pb-dated geochemical sediment records to study the impacts of recent climate variability where long-term environmental data is scarce or non-existent.