Diatom-based inference model for paleosalinity reconstructions in estuaries along the northeastern coast of Argentina Gabriela S. Hassan ⁎, Marcela A. Espinosa, Federico I. Isla CONICET-Instituto de Geología de Costas y del Cuaternario, Universidad Nacional de Mar del Plata, CC 722, 7600 Mar del Plata, Argentina abstract article info Article history: Received 2 May 2008 Received in revised form 2 February 2009 Accepted 8 February 2009 Keywords: Diatoms Estuaries Salinity Sea-level change Transfer function Holocene The relationship between benthic diatom assemblages and environmental variables was analyzed in 40 sites at three estuaries from the northeastern coast of Argentina by using multivariate analyses. Surface sediment samples were collected along the estuarine gradient and analyzed for diatoms, organic matter, water content and grain size. Water salinity, pH, turbidity and temperature were measured seasonally at every sampling site. Canonical Correspondence Analysis (CCA) was applied in order to recognize which environmental variables correlated most closely with the distributions of diatom taxa. Salinity and sediment properties were identified as the most important variables influencing diatom distribution in the studied estuaries. A two-component Weighted-Averaging Partial Least Squares (WA–PLS) calibration model was developed to infer salinity based on diatom assemblages. The reliability of the model was evaluated by the error of prediction (RMSEP jack-knifed = 4.42‰) and the correlation (r 2 jack-knifed = 0.75) between observed and diatom- inferred values. The transfer function was applied to fossil diatom assemblages recovered from a Holocene sequence from the Argentinean coast. The application of the model to the fossil record allowed quantitative inferences of salinity changes in southern South America, improving the quality of the inferences performed from diatom analysis. © 2009 Elsevier B.V. All rights reserved. 1. Introduction Diatoms are useful indicators for the study of late Quaternary environmental changes because of their abundance in sediments and their sensitivity to environmental variables (Cooper, 1999). Studies based on diatom distributional ecology began in the late 1880s (e.g. Cleve, 1894–1895) and demonstrated that benthic diatom assem- blages from surface sediments faithfully reflect the physical and chem- ical characteristics of the overlying water masses, allowing their use to reconstruct past environments (Maynard, 1976). However, it was not until the 1920s that the value of diatom analysis in paleoenvironmental reconstructions was recognized (Denys and de Wolf, 1999). The classical method of inferring environmental conditions from fossil diatoms had consisted on the analysis of the assemblage composition and the consideration of the relevant autoecological characteristics of the taxa present (e.g. Vos and De Wolf, 1993). On the other hand, statistical inference models derived from modern species–environment relations take optimal advantage of the ecolo- gical information that can be obtained from the assemblage allowing quantitative inferences of important parameters (Denys and de Wolf, 1999). Therefore, transfer functions are a reliable method for generating high-resolution, quantitative paleoenvironmental estima- tions (Birks, 1998). In the last decade, a considerable number of diatom-based transfer functions have been developed to infer a wide range of environmental variables in lacustrine systems (e.g., Sylvestre et al., 2001; Bigler and Hall, 2002). In brackish and marine habitats, however, precise inferences have been more difficult to apply because of the adaptation of many taxa to a wide range of ecological conditions (Vos and De Wolf, 1993; Denys and de Wolf, 1999). Nevertheless, the calibration of the relationship between sedimentary diatom species composition and environmental variables in some estuaries has allowed the development of inference models useful to coastal reconstructions (Juggins, 1992; Campeau et al., 1999; Sherrod, 1999; Zong and Horton, 1999; Gehrels et al., 2001; Ng and Sin, 2003; Sawai et al., 2004; Horton et al., 2006). A considerable number of studies using diatoms to reconstruct changes in salinity, depth and trophic status related to fluctuations in shoreline positions in southern South America have been published in recent years (e.g., Espinosa, 1994, 1998; Espinosa et al., 2003; García-Rodríguez et al., 2004a,b; Inda et al., 2006). However, the use of modern diatom assemblages to quantitatively reconstruct past salinity changes in the region has not been explored, mainly because the distribution optima of individual taxa with respect to environ- mental factors have been poorly documented. Along the Argentinean Palaeogeography, Palaeoclimatology, Palaeoecology 275 (2009) 77–91 ⁎ Corresponding author. Centro de Geología de COSTAS y del Cuaternario, Universidad Nacional de Mar del Plata, C.C. 722, 7600, Mar del Plata, Argentina. Tel.: +54 0223 4754060; fax: +54 0223 4753150. E-mail addresses: ghassan@mdp.edu.ar (G.S. Hassan), maespin@mdp.edu.ar (M.A. Espinosa), fisla@mdp.edu.ar (F.I. Isla). 0031-0182/$ – see front matter © 2009 Elsevier B.V. All rights reserved. doi:10.1016/j.palaeo.2009.02.020 Contents lists available at ScienceDirect Palaeogeography, Palaeoclimatology, Palaeoecology journal homepage: www.elsevier.com/locate/palaeo