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Globally, the largest tsunamigenic earthquakes have occurred along subduction zones. Devastating events exceeding magnitude 9, such as those in Chile, Sumatra, and Japan, struck in regions lacking instrumental records of similar events. Despite the absence of such events along the 1000-kilometer-long Mexican subduction zone, historical and geologic evidence suggests the occurrence of a magnitude 8.6 tsunamigenic earthquake. However, the Guerrero seismic gap has not experienced a high-magnitude earthquake in over 100 years. Here we present results on analyses of sediment grain size, geochemistry, microfossils, magnetic properties, and radiometric and optical stimulated luminescence dating conducted along the Guerrero coast. We provide evidence of a 2000-year history of large tsunamis triggered by potentially large earthquakes. Numerical modeling supports our findings, indicating a magnitude >8 event around the year 1300 in the Guerrero seismic gap. This evidence underscores the importance of assessing earthquake and tsunami potential using long-term evidence and instrumental observations along subduction zones globally.

This study examines textural characteristics, carbonate, organic carbon and chemical composition of sediment samples recovered in the nearshore region (~3–19 m water depth) at the Grijalva River mouth, southern Gulf of Mexico. The aim of this study is to assess the heavy metal contamination and provenance variations in sediments between the dry and northers (rainy) seasons. The proportion of sand, carbonate, and organic carbon contents were abundant at sites located near to the Grijalva River mouth, principally in northers season. Silt content is dominant in the dry season, especially in the sites located away from the Grijalva River mouth. The Chemical Index (CIX) values obtained for the dry (~76–84) and northers (~75–87) seasons indicated a moderate to high intensity of weathering and a humid climate in the source area. The low K 2 O/Al 2 O 3 ratio values (<0.5) in the dry and northers seasons indicated a higher proportion of aluminosilicates than detrital minerals, due to moderate-to-high intensity of weathering. The correlation among elemental concentrations revealed the association of Cr, Nb, Zr, Hf, Y, and rare earth elements (REE) with detrital minerals rather than aluminosilicates. The major element concentrations, Th/Sc, La/Sc, Co/Th, and Cr/Ni elemental ratios indicated the derivation of sediments from intermediate and mafic igneous rocks. A similarity in the North American Shale Composite (NASC) normalized rare earth element (REE) patterns and Eu anomaly between the dry and northers seasons suggested that the variations in sediment input played a less significant role and the provenance of sediments remained constant. The enrichment factor (EF) showed moderate to severe enrichment for Cr, Ni, and Sb (EF = ~2.63–7.57), highest in the northers season, especially at the Grijalva River mouth, although the index of geo-accumulation (I geo ) for these elements suggested as moderately polluted (I geo = 0.34–2.0). The slightly elevated EF values for Cr, Ni, and Sb during northers season were probably due to an increase in sediment discharge into the sea during the northers season. We inferred that the enrichment of Cr, Ni, and Sb in sediments was due to both lithogenic and anthropogenic origins. The sediments were influenced by the intermediate and basic igneous rocks of the Chiapas Massif Complex, and the waste generated by the urban areas located within the Grijalva River drainage basin.

The Isthmus of Tehuantepec corresponds to the shortest distance (~200 km) between the Gulf of Mexico and the Pacific Ocean in Southern Mexico, and the main economical activity of this region is oil extraction and refining. Polycyclic aromatic hydrocarbons (PAHs) and total petroleum hydrocarbons (TPHs) were determined in a 210 Pb dated sediment core collected from the continental shelf of Tehuantepec Gulf, in the vicinity of the oil refinery of Salina Cruz, Oaxaca, the main oil refining facility of the country. The sediments were mostly of coarse nature and hence PAHs and TPHs concentrations throughout the core (61–404 μg g −1 and 29–154 mg kg −1 , respectively) were below international quality benchmarks. Depth profiles of both PAHs and TPHs concentrations showed increasing trends since the early 1900s but the higher values were found from the 1950s to present. PAH congener ratios showed that these contaminants had both petrogenic and pyrolitic sources, although the former has been predominant since the 1970s. The Salina Cruz refinery started operations in 1978 but the oil industry activities in the Tehuantepec Isthmus go back to the beginning of the twentieth century with the operation of Minatitlan refinery in the Gulf of Mexico, and the Gulf of Tehuantepec being the main conduit for oil distribution in the Pacific coast. The observed changes in contaminant distributions described well the oil industry development in the area.

The southern Gulf of Mexico (sGoM) is home to an extensive oil recovery and development infrastructure. In addition, the basin harbors sites of submarine hydrocarbon seepage and receives terrestrial inputs from bordering rivers. We used stable carbon, nitrogen, and radiocarbon analyses of bulk sediment organic matter to define the current baseline isoscapes of surface sediments in the sGoM and determined which factors might influence them. These baseline surface isoscapes will be useful for accessing future environmental impacts. We also examined the region for influence of hydrocarbon deposition in the sedimentary record that might be associated with hydrocarbon recovery, spillage and seepage, as was found in the northern Gulf of Mexico (nGoM) following the Deepwater Horizon (DWH) oil spill in 2010. In 1979, the sGoM experienced a major oil spill, Ixtoc 1. Surface sediment δ13C values ranged from -22.4‰ to -19.9‰, while Δ14C values ranged from -337.1‰ to -69.2‰. Sediment δ15N values ranged from 2.8‰ to 7.2‰, while the %C on a carbonate-free basis ranged in value of 0.65% to 3.89% and %N ranged in value of 0.09% to 0.49%. Spatial trends for δ13C and Δ14C were driven by water depth and distance from the coastline, while spatial trends for δ15N were driven by location (latitude and longitude). Location and distance from the coastline were significantly correlated with %C and %N. At depth in two of twenty (10%) core profiles, we found negative δ13C and Δ14C excursions from baseline values in bulk sedimentary organic material, consistent with either oil-residue deposition or terrestrial inputs, but likely the latter. We then used 210Pb dating on those two profiles to determine the time in which the excursion-containing horizons were deposited. Despite the large spill in 1979, no evidence of hydrocarbon residue remained in the sediments from this specific time period.

The structure of the phytoplankton from the Gulf of Tehuantepec in summer is poorly known. The composition and distribution of the phytoplankton photosynthetic pigments in summer conditions are provided in this paper. Hydrographic data from nine stations, during an oceanographic cruise in June, 20013, and analysis of five major phytoplanktonic pigments, Fucoxanthin, Prasinoxanthin, Violaxanthin, Zeaxanthin (marker of Synechococcus, picoplanktonic prokaryote) and Divinyl-chlorophyll a (diagnostic of Prochlorococcus, another picoplanktonic prokaryote) are given. Column water was well-stratified: surface layers had a thickness between 20 and 35 m, with well-defined thermoclines at those depths. Values of all pigments were low, but they showed similar vertical distribution patterns, with subsurface maxima peaks (between 30 and 40 m), especially Divinyl-chlorophyll a in most stations, except 3 and 4, where Fucoxanthin was the most important pigment. These peaks did not always coincide with the depths of the main thermocline at each station, but usually they were found below the thermocline. This scenery shows the picoplankton as a very important size-fraction group in summer (at least in June), strongly contrasting with the winter-spring conditions, of intense turbulent mix and upwellings, where microplankton and diatoms appear to predominate.

There exist previous studies on phytoplankton, its taxonomic groups and species, its biomass and primary productivity, mainly in winter and spring, but the structure of the phytoplankton from the Gulf of Tehuantepec in summer is poorly known. The composition and distribution of the phytoplankton photosynthetic pigments in summer conditions are provided in this paper. Hydrographic data from nine stations, during an oceanographic cruise in June, 20013, and analysis of five major phytoplanktonic pigments, Fucoxanthin, Prasinoxanthin, Violaxanthin, Zeaxanthin (marker of Synechococcus, picoplanktonic prokaryote) and Divinyl-chlorophyll a (diagnostic of Prochlorococcus, another picoplanktonic prokaryote) are given. Column water was well-stratified: surface layers had a thickness between 20 and 35 m, with well-defined thermoclines at those depths. Values of all pigments were low, but they showed similar vertical distribution patterns, with subsurface maxima peaks (between 30 and 40 m), especially Divinyl-chlorophyll a in most stations, except 3 and 4, where Fucoxanthin was the most important pigment. These peaks did not always coincide with the depths of the main thermocline at each station, buy usually they were found below the thermocline. This scenery shows the picoplankton as a very important size-fraction group in summer (at least in June), strongly contrasting with the winter-spring conditions, of intense turbulent mix and upwellings, where microplankton and diatoms appear to predominate.

A detailed systematic study of samples from the Pliocene of the Saline Basin, Veracruz, Mexico, shows characteristic ostracode assemblages fro the Encanto, Lower and Upper Concepcion, and Agueguexquite strata. The remaining units, Filisola, Paraje Solo and Cedral, did not contain ostracodes. Ninety species belonging to 53 genera are determined and described. The ostracode assemblages of the studied units indicate a general upward shallowing trend during the Pliocene. The Encanto strata, constituting the oldest unit (N 19 or upper N 18), are characterized by Ambocythere spp., Argilloecia posterotruncata Bold, Bradleya normani (Brady), Krithe trinidadensis Bold, and Parakrithe spp. indicating a middle to upper bathyal environment. The Lower and Upper Concepcion beds (N 20) can be recognized by the presence of Actinocythereis vineyardensis (Cushman), Touroconcha lapidiscola Hartmann and the abundance of Hulingsina sp. 1, Henryhowella ex. gr. asperrima (Reuss) and Puriana spp. Encanto species persisting in the Lower Concepcion beds indicate an upper bathyal to outer neritic environment. The Upper Concepcion beds lack these species but instead possess abundant Cyprideis and Perissocytheridea spp., Basslerites? sp., Cytherura wardensis Howe and Brown and Loxoconcha sp. A Hazel. This assemblage indicates an outer to middle shelf environment. The Filisola and Paraje Solo samples were barren of ostracodes. Their foraminiferal and molluscan fauna indicates nearshore and brackish environments. The Paraje Solo may be in part contemporaneous to the Agueguexquite. The Agueguexquite strata contain the youngest (middle N 20), most abundant, and diverse fauna, indicating an inner neritic environment of deposition. They represent a local marine transgression of short duration in the northern part of the basin. By upper Agueguexquite time brackish and continental conditions had returned. A Q-mode cluster analysis utilizing Ward's method on species proportions divided the Agueguexquite and Upper Concepcion samples in two main clusters, each one subdivided into two groups representing slightly different environments. Because of their low abundance only one Encanto and 3 Lower Concepcion samples were used in the clustering. They form generally independent groups. No apparent diversity trends were found.