Climate change facilitated the early colonization of the Azores Archipelago during medieval times.

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.

Influence of agricultural system transition on trace element contamination in salt marsh and seagrass sediments from a coastal Ramsar site.

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 Quintín 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.

Biomagnification of Mercury in Fish from Two Gold Mining-Impacted Tropical Marshes in Northern Colombia.

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 < 0.05) between marshes in δ15N, δ13C, and T-Hg, as well as significant seasonal differences (p < 0.05) in T-Hg values for some species, suggesting the possible influence of factors, such as differences in length of food chains between marshes and different degree of anthropogenic impact in relation to human settlements, farmland, livestock (higher in Ayapel marsh), and gold mining activity (higher in La Raya marsh). Correlations analysis showed significant (p < 0.05) relationships between T-Hg concentrations and δ15N values, as well as trophic level, evidencing a T-Hg biomagnification process in the fish food chain from both marshes and consequently a potential health risk for human riverside inhabitants who eat these fish.

First report of fossilized cysts produced by the benthic Bysmatrum subsalsum (Dinophyceae) from a shallow Mexican lagoon in the Gulf of Mexico.

Cysts belonging to the benthic dinoflagellate Bysmatrum subsalsum were recovered from palynologically treated sediments collected in the Alvarado Lagoon (southwestern Gulf of Mexico). The cysts are proximate, reflecting the features of the parent thecal stage, and their autofluorescence implies a dinosporin composition similar to the cyst walls of phototrophic species. This finding is important for our understanding of B. subsalsum life cycle transitions and ecology. Encystment may play an important role in the bloom dynamics of this species as it can enable the formation of a sediment cyst bank that allows reinoculation of the water column when conditions become favorable. This is the first report of a fossilized cyst produced by a benthic dinoflagellate recovered from sub-recent sediments.

Accelerating microplastic contamination in 210Pb dated sediment cores from an urbanized coastal lagoon (NW Mexico) since the 1990s.

The ubiquity of microplastics (MP) across all ecosystems raises concerns about their potential harm to the environment and living organisms. Sediments are a MP sink, reflecting long-term accumulation and historical anthropogenic impacts. Three 210Pb-dated sediment cores were used to understand the temporal variations of MP abundances (particles kg-1) and fluxes (particles m-2 year-1) within the past century in Estero de Urías Lagoon, an urbanized coastal lagoon in the Mexican Pacific. MP particles, extracted from sediments by density separation (saturated NaCl solution) were counted using a stereomicroscope, under visible and ultraviolet light on Nile red (NR) stained filters. The polymer composition was determined in ∼10 % of the suspected MP particles using Fourier Transform Infrared spectrometry. Fibers (66 to 89 % of the total particles) predominated over fragments (11 to 34 %). Before 1950, no MP particles were detected. Polyethylene terephthalate (PET) was the prevalent synthetic polymer (up to 50 % of the particles), while semisynthetic cellulosic fibers were predominant, underscoring the broader scope of anthropogenic contamination. Suspected MP abundances (NR stained filters) were highest in the core collected at the innermost area, which was attributed to the lagoon's hydrodynamics, since current velocities decrease from the proximal to the distal area to the sea. From the regression between MP fluxes and time elapsed since sediments deposited, the cores showed consistent accelerated increases of MP burial since mid-20th century, most likely because of the increasing availability of plastic products and population growth, with the consequent increment in plastic waste and wastewater releases. Our findings emphasize the growing MP pollution challenges at EUL, which may directly impact subsistence fishing and shrimp aquaculture activities, threatening local livelihoods and food sources; and also highlight the need for improved waste management and pollution control strategies in rapidly industrializing regions, to protect both aquatic ecosystems and human populations dependent on fishing products.

Potentially toxic elements fluxes in 210Pb-dated sediment cores from a large coastal lagoon (southern Gulf of Mexico) under environmental stress.

Terminos Lagoon (TL), in the southern Gulf of Mexico, has been under intensive anthropogenic pressure (e.g., oil-industry development) since the 1970s. Historical changes in flux ratios of potentially toxic elements (PTEs; As, Cd, Cr, Cu, Ni, Pb, V, Zn) were, for the first time, assessed inside TL by using 210Pb-dated sediment cores. Sediments showed minor enrichments for Cd, Ni, Pb, and V. However, according to international benchmarks, the As, Cr, Cu, and Ni concentrations could pose a risk for benthic biota. Sedimentary processes involved in the accumulation of PTEs were identified through a chemometric approach. Increments in PTEs flux ratios concur with the recent (⁓50 years) and extensive land-use changes, particularly the transport and deposit of materials delivered by rivers. These findings are expected to be used in managing this crucial natural resource, the larger Mexican coastal lagoon ecosystem, to mitigate the effects of global change.

Regional assessment of the historical trends of mercury in sediment cores from Wider Caribbean coastal environments.

Spatial and temporal variations of mercury (Hg) concentrations, enrichment, and potential ecological risks were studied in a suite of lead-210 (210Pb) dated sediment cores from 13 Wider Caribbean Region coastal environments. Broad variability of Hg concentrations (19-18761 ng g-1) was observed, encompassing even background levels (38-100 ng g-1). Most Hg concentration profiles exhibited a characteristic upward trend, reaching their peak values in the past two decades. Most of the sediment sections, showing from moderately to very severe Hg enrichment, were found in cores from Havana Bay and Sagua River Estuary (Cuba), Port-au-Prince Bay (Haiti), and Cartagena Bay (Colombia). These were also the most seriously contaminated sites, which can be considered regional Hg 'hotspots'. Both Havana Bay and Port-au-Prince Bay reportedly receive waste from large cities with populations exceeding 2 million inhabitants, and watersheds affected by high erosion rates. The records from the Sagua River Estuary and Cartagena Bay reflected historical Hg contamination associated with chloralkali plants, and these sites are of very high ecological risk. These results constitute a major contribution to the scarce regional data on contaminants in the Wider Caribbean Region and provide reference information to support the evaluation of the effectiveness of the Minamata Convention.

Vertical distribution and trace element contamination in sediment cores affected by gold mining in Colombia.

The vertical distribution, level of contamination, potential ecological risks, and historical fluxes of trace elements (Pb, As, and Hg) were evaluated from 210Pb-dated sediment cores in three different areas with gold mining impacts in northern Colombia: the Atrato River (AR), the Delicias Marsh (DM) and the Encaramada Marsh (EM). All cores spanned ∼100 years; the mass accumulation rates followed the order AR > DM > EM. The average trace elements concentrations in the sediment cores were: Pb 2.41 ± 0.72, As 0.65 ± 0.32, Hg 0.07 ± 0.02 µg g-1 in the Atrato River; Pb 23.49 ± 2.59, As 2.46 ± 0.88, Hg 0.10 ± 0.02 µg g-1 in the Delicias Marsh; and Pb 9.76 ± 4.18, As 2.44 ± 1.26, Hg 0.17 ± 0.06 µg g-1 in the Encaramada Marsh. Sediments are classified according to the contamination factor (CF) and geoaccumulation index (Igeo) as low to very highly contaminated. The Pollution load index (PLI) indicates environmental deterioration (PLI> 1), and the Sediment quality guidelines (SQGs) indicate that only Hg may produce adverse biological effects in the EM core. This study is an example of the reconstruction of temporal changes in pollution levels and impacts of potentially toxic elements caused by gold mining in remote ecosystems, which can be reproduced in other areas where environmental monitoring is scarce or non-existent.

Microplastics transport in a low-inflow estuary at the entrance of the Gulf of California.

Microplastics (MPs) are recognized as a global emergent pollution impact, which can affect all food chains. Estimating MPs transport pathways in coastal ecosystems is needed to assess their likely effects. Here, we studied MPs accumulation and transport pathways in the Estero de Urias lagoon system (low-inflow estuary) using field data and a 3D particle model. Field results showed that the MPs present similar abundances throughout the study area during the dry and rainy seasons. Model simulations indicated that i) morphology and tidal currents caused the MPs discharged in the lagoon to remain inside, and ii) wind-induced currents caused the MPs in the coastal area to be transported to the southwest. These transport processes may be responsible for homogenizing MPs concentrations through the studied area. In addition, model simulations suggested that EUL-dense waters can export MPs from the coastal area to the sea bottom.

210Pb geochronology and metal concentrations in sediment cores recovered in the Alvarado Lagoon system, Veracruz, Mexico.

Three sediment cores recovered from the Alvarado Lagoon System (ALS) in the Gulf of Mexico were used to reconstruct the history of metals and metalloids and their environmental importance. The sedimentary profiles were dated with 210Pb and verified with 137Cs. Maximum ages of 77 and 86 years were estimated. Sediment provenance was described by sedimentological and geochemical proxies. The chemical alteration index (CIA) and weathering index (CIW) revealed moderate to high intensity of weathering in the source area that is controlled tropical climatic conditions, runoff, and precipitation in the basin that feeds sediments to this coastal lagoon. The Al2O3/TiO2 ratios indicated that the sediments were derived from intermediate igneous rocks. The enrichment factor values revealed the lithogenic and anthropic contribution of metals and metalloids. Cd is classified under the category extremely severe enrichment; agricultural activities, fertilizers, herbicides, and pesticides containing Cd are expected to supply this metal to the ecosystem. Factor Analysis and Principal Components provided two main factors, terrigenous and biological origins; ANOVA indicated that there are significant differences between the cores for the parameters analyzed and revealed that there are differences in depositional environments between the recovery zones of the cores. The ALS presented natural variations associated with the climatic conditions, terrigenous input, and its relationship with the hydrological variations of the main rivers. The contribution of this work was to identify the magnitude of the natural component versus the human contribution, mainly of risk metals such as Cd, to support better management of the hydrological basin that affects the ALS.

Reconstruction of Pyrodinium blooms in the tropical East Pacific (Mexico): are they related to ENSO?

Some microplanktonic species, mostly dinoflagellates, causing Harmful Algal Blooms (HABs), produce toxins which may affect the environment and human health, thus causing important economic losses. The dinoflagellate Pyrodinium bahamense var. compressum is one of the main species causing harmful algal blooms along the tropical Pacific. Although it was first reported along the Mexican coast in the 1970s, here we report that a sedimentary record of Pyrodinium cysts from the Gulf of Tehuantepec in the tropical East Pacific (Mexico), which spans from the 1860s, showed the continuous occurrence of Pyrodinium cysts and that their presence has been declining in the last few decades. Although Pyrodinium HABs have been attributed to El Niño events in the tropical Indo-West Pacific, the record shows that most blooms in the tropical East Pacific appear in periods of low sea surface temperature and higher rainfall, as can be observed during rapid shifts from cold (La Niña) to warm (El Niño) conditions in that region. This mechanism offers new ways to better predict and facilitate early detection of Pyrodinium HABs worldwide.

Accumulation and fluxes of potentially toxic elements in a large coastal lagoon (southern Gulf of Mexico) from 210Pb sediment chronologies.

Three 210Pb-dated sediment cores were used to evaluate the contamination degree and flux ratios of potentially toxic elements (PTEs; As, Cd, Cr, Cu, Ni, Pb, V, and Zn) in seagrass meadows from the northern margin of Términos Lagoon (TL), southern Gulf of Mexico. The sediments displayed minor Cd, Ni, V, and Zn enrichments but moderate to strong enrichment by As. Results from a chemometric analysis revealed that: 1) salinization and grain size, along with 2) the terrigenous inputs are the major factors influencing the PTEs accumulation. The historical trends of PTEs flux ratios nearly follow the large-scale land-use changes around TL, linked to the growth of the Mexican oil industry in the area since the 1970s. Our findings showed the critical role of seagrass meadows as PTEs sinks. This information is useful for decision-makers to develop restoration projects for a vulnerable site within the largest coastal lagoon ecosystem in Mexico.

Contrasting nutrient distributions during dry and rainy seasons in coastal waters of the southern Gulf of Mexico driven by the Grijalva-Usumacinta River discharges.

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-1 6893 t P yr-1 and 928,904 t Si yr-1 to SGoM. These results contribute with a nutrient baseline in the SGoM that could be useful for GURS decision-makers.

Microplastic contamination and fluxes in a touristic area at the SE Gulf of California.

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 Mazatlán, 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 Mazatlán (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.

Plutonium in coral archives: A good primary marker for an Anthropocene type section.

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.

Anthropogenic and climate induced trace element contamination in a water reservoir in northwestern Mexico.

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.

Sedimentary record of the impact of management actions on pollution of Cartagena bay, Colombia.

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.

Calibration and use of well-type germanium detectors for low-level gamma-ray spectrometry of sediments using a semi-empirical method.

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.

Sand deposits reveal great earthquakes and tsunamis at Mexican Pacific Coast.

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.