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Abstract 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 Mazatlán). 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. Highlights • Trace metal enrichments were relatively small in sediment cores retrieved outside the present OMZ. • Dysoxic conditions at the OMZ core controls the authigenic enrichment of redox-sensitive metals. • Authigenic Mo and U and foraminiferal assemblages indicate that the OMZ has recently weakened. [ABSTRACT FROM AUTHOR]

Two lead-210 ( 210 Pb) 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. [ABSTRACT FROM AUTHOR]

Concentrations, temporal trends and fluxes of persistent organic pollutants (POPs: PAHs, PCBs and PBDEs) were determined in soil and 210Pb-dated sediment cores from remote lacustrine environments (El Tule and Santa Elena lakes) in rural areas of Central Mexico. In both areas, the concentrations of target analytes in soil and sediment samples were comparable and indicative of slightly contaminated environments. The prevalence of low-molecular-weight PAHs in soils suggested their mainly atmospheric origin, in contrast to the aquatic sediments where runoff contribution was also significant. Increasing contamination trends of PCBs and PBDEs were evident, showing maximum fluxes of 4.8 ± 2.1 and 0.3 ± 0.1 ng cm-2 a-1 for PCBs and PBDEs, respectively. The predominance of lower-brominated PBDEs and lower-chlorinated PCBs in soils and sediments indicated that their presence is mostly due to long-range atmospheric transport. [ABSTRACT FROM AUTHOR]

Concentrations and enrichment of major (Na, Al and Cl) and trace (V, Mn, Fe, Ni, Cu, Zn, As, Br, Mo, Hg, Pb and U) elements were evaluated in 210Pb-dated sediment cores from saltmarsh areas surrounding an anthropized lagoon at southeastern Gulf of California. A chemometric approach was used to identify the sedimentary processes that control the variability of elements among the cores; and the elemental fluxes were compared among coring sites on the basis of historical urbanization and industrial development in the area. The highest fluxes and excess concentrations of V, Ni, Hg and Pb were observed after 1960 in cores EUI and EUIII, and in 1980 at EUII. In general, the historical trends of metal enrichment coincide with the growth of urban and industrial developments around the lagoon, and particularly with the beginning and full operation of a thermoelectric power plant in 1980s. Image 1 • Metal contamination was assessed in a saltmarsh associated to an urbanized lagoon. • Hg and Ni sediment concentration might pose noxious effects for benthic biota. • Hg enrichment is strong since late 1930s. • The highest Hg, Ni, V and Pb concentrations were found after 1960. • Historical contamination trends reflected the urban and industrial growth onsite. [ABSTRACT FROM AUTHOR]

The petrochemical industry and urban activities are widely recognized worldwide as a source of pollution to mangrove environments. They can supply pollutants such as trace elements that can modify the ecosystem structure and associated services, as well as human populations. Through geochemical data, multivariate statistical analysis and pollution indices such as the enrichment factor (EF), geo-accumulation index (Igeo), adverse effect index (AEI) and the pollution load index (PLI), we evaluated the factors that control trace element distribution, punctual sources and determined the pollution level of sediments and their potential biological impact in the mangrove ecosystem of Isla del Carmen, Mexico. The factor and cluster analysis highlighted that the distribution of trace elements is influenced by the mineralogy, texture as well as urban derived sources. The pollution indices showed values in the punctual sources from the urban area of EF > 10, Igeo > 3, AEI > 3, PLI > 1 by Cu, Zn and Pb. Finally, the results revealed that mangroves from Isla del Carmen has a major influence from urban activities and natural sources rather than oil industry and also indicate a degraded environment as a result of anthropogenic activities that could have knock-on effect for human health if polluted marine organisms derived from the urban mangroves are consumed. Surface sediments show the influence of point sources on selected trace element concentrations correlated with human activities within the mangroves of Isla del Carmen, Mexico. Unlabelled Image • City sewages and boatyards act as point sources for Zn, Cu and Pb. • Ni and V contents show that oil industry has a low impact in mangroves. • Zn, Cu, and Pb contents exceed adverse effect index (AEI) in two urban point sources. [ABSTRACT FROM AUTHOR]