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Sea level rise (SLR) has been evaluated using data acquired from two Tagus estuary salt marshes. Sediment accumulation rates over a 40-year study period were determined using 137Cs along with an evaluation of several geochemical indices and ratios as proxies of the mechisms underlying these SAR variations. Correlating SLR data from 1963 to 2001 with the sediment accretion rates (SARs) an inverse pattern of interaction was observed, with lower SAR associated to periods of higher mean sea level (MSL) heights. This pointed out to an erosion effect of the salt marsh during higher tidal flooding. Although SLR apparently slows down SAR, it still presents a positive balance with SLR, similar to that identified in most mesotidal estuaries. The geochemical analysis of sediments and chemical alteration index (CAI) also suggest that the major processes inherent to the SAR vary inversely, being mostly based by physical disturbances. Geochemical ratio-based indices showed that both salt marshes presented enhanced highenergy transport driven inputs of sediments, although in Pancas salt marsh there is a slight evidence of chemical weathering of the sediments. Anthropogenic contamination of the sediments by heavy metals was identified and has been decreasing from 1963 to 2001, mostly linked to a marked reduction of industrial activities in some areas surrounding the Tagus estuary, rather than the sedimentary history of the estuary. The authors would like to thank to the “Fundac¸ ão para a Ciência e Tecnologia (FCT)” for funding the research in the Centre of Oceanography (CO) throughout the project PEst-OE/MAR/UI0199/2011, the Institute of Marine Research (IMAR) throughout the project PEst-C/MAR/UI0284/2011 and this specific work throughout the ECOSAM project (PTDC/AAC-CLI/104085/2008). B. Duarte investigation was supported by FCT throughout a PhD grant (SFRH/BD/75951/2011).

et al., Sea-level rise (SLR) is one of the most conspicuous examples of the environmental impact of recent climate change. Since SLR rates are not uniform around the planet, local and regional data are needed for proper adaptation plans. Pb-dated sediment cores were analyzed to determine the trends of sediment accretion rates (SARs) at three tropical saltmarshes in the Estero de Urias lagoon (Gulf of California, Mexico), in order to estimate the SLR trends during the past ~100 years, under the assumption that these ecosystems accrete at a similar rate to SLR. A chemometric approach, including multivariate statistical analysis (factor analysis) of geochemical data (including δC; δN; C/N ratios; and Br, Na, and Cl as proxies for marine transgression) was used to identify the marine transgression in the sediment records. Based on core geochemistry, only one of the three cores provided a long-term record attributable to marine transgression. SLR trends, estimated from SARs, showed increasing values, from a minimum of 0.73 ± 0.03 mm yr at the beginning of the 20th century and up to 3.87 ± 0.12 mm yr during the period 1990–2012. The estimated SLR trend between 1950 and 1970 was comparable to the tide gauge records in Mazatlan City for the same period. Results showed the caveats and strengths of this methodology to reconstruct decadal SLR trends from the sedimentary record, which can be used to estimate long-term SLR trends worldwide in regions where monitoring data are scarce or absent., This work has been supported by the grants CONACyT CB2010-153492, PAPIIT-IN203313, CONACYT PDCPN2013-01/214349, and the CONACYT fellowship to JLSP.