Coral Ba/Ca molar ratios as a proxy of precipitation in the northern Yucatan Peninsula, Mexico Guillermo Horta-Puga a,1 , José D. Carriquiry a,⇑ a Instituto de Investigaciones Oceanológicas, Universidad Autónoma de Baja California, Apdo. Postal #453, Ensenada, Baja California 22800, Mexico article info Article history: Received 4 October 2011 Accepted 14 May 2012 Available online 22 May 2012 Editorial handling by R. Fuge abstract The Yucatan Peninsula consists of a karstic terrain that allows the aquifer to directly recharge from rainfall. Due to the various dissolution/precipitation reactions occurring during groundwater flow, the groundwater discharge in the coastal zone becomes a source of trace elements including Ba. The aim of this study was to use the coralline Ba/Ca record as a proxy of precipitation under the consideration that rainfall rates vary at inter-annual time scales. Annual Ba/Ca ratios, both the total content (Ba/Ca TC ) and the Ca-substitutive frac- tion (Ba/Ca CaF ), were quantified in a 52-a old coral colony of Montastraea annularis from the Punta Nizuc Reef, Mexican Caribbean. Average Ba/Ca TC (5.90 ± 0.56 lmol/mol) was 20% higher than Ba/Ca CaF (4.85 ± 0.33 lmol/mol) indicating that Ba is also incorporated in other fractions. Correlation between annual precipitation and Ba/Ca TC time-series is significant (r = 0.77, p < 0.05), allowing the use of the Ba/Ca TC ratio as a proxy of precipitation, and hence, enabling the reconstruction of precipitation patterns through time. Likewise, the Ba/Ca CaF ratio can be used for the reconstruction of dissolved Ba in coastal seawater. Ó 2012 Elsevier Ltd. All rights reserved. 1. Introduction The geochemical record contained in annually banded herma- typic corals has been extensively used as a reliable tool for the reconstruction of recent climate variability at weekly, seasonal, in- ter-annual, decadal, and even secular time-scales; and has been especially important in tropical areas where there are no available instrumental meteorological/oceanographical data (Druffel, 1997; Gagan et al., 2000; Evans et al., 2001; Mann, 2002). Sea surface temperature (SST) from tropical reef areas has been reconstructed using the coralline ratios of: Sr/Ca (Smith et al., 1979; Beck et al., 1992; de Villiers et al., 1994; McCulloch et al., 1994; Corrège et al., 2000; Marshall and McCulloch, 2002), Mg/Ca (Mitsuguchi et al., 1996; Sinclair et al., 1998; Fallon et al., 1999; Wei et al., 2000), U/Ca (Min et al., 1995), and Ba/Ca (Allison and Finch, 2007). The O stable isotopic record (d 18 O) has also been used for the reconstruction of SST, salinity and the hydrological regime (precipitation and evaporation) (Cole et al., 1993; Carriquiry et al., 1994; McCulloch et al., 1994; Gagan et al., 2000). As previ- ously suggested by Shen and Sanford (1990), the variability of the coralline Ba/Ca molar ratio from corals growing near coastal areas has been successfully used to infer: salinity and sediment load changes associated with river runoff and soil erosion; volume of fluvial discharge; and even to calculate the concentration of Ba in river water (dissolved + desorbed from particulate phases) using the effective river’s end-member concentration (Alibert et al., 2003; McCulloch et al., 2003; Sinclair and McCulloch, 2004; Ramos et al., 2004; Sinclair, 2005; Fleitmann et al., 2007; Lewis et al., 2007; Jupiter et al., 2008; Carrilli et al., 2010; Carriquiry and Horta-Puga, 2010; Prouty et al., 2010). Because the volume of freshwater flow from mainland to coastal areas is highly depen- dent on rainfall, and the levels of coastal Ba increase with increases in river outflow, the coralline Ba/Ca geochemical record could be used as a tracer of precipitation. The northeastern part of the Yucatan Peninsula (NYP) is a rela- tively flat, low-lying platform consisting of Cretaceous-Tertiary car- bonate rocks, predominantly limestone that has evolved into a highly permeable and complex karstic system; hence, surface flow and streams are absent (Ward, 1985; Morán, 1985). Rainwater infil- trates through the porous limestone framework forming groundwa- ter aquifers that flow into the coastal zone and discharge as submarine springs (Back and Hanshaw, 1970; Back et al., 1986; Perry et al., 1989, 2002; Crook et al., 2011). By reacting with atmo- spheric CO 2 , rainwater becomes slightly acidified enhancing the dis- solution of limestone (Hanshaw and Back, 1980; Back et al., 1986; Beach, 1998), and during the process different minerals (mainly car- bonates and sulfates) and trace elements released from the dissoci- ation of these minerals reach the coastal ocean, both in solution or adsorbed to particles (Reeve and Perry, 1994; Carruthers et al., 2005; Young et al., 2008). Also, as freshwater approaches the conti- nental margin, the mixing with seawater generates a highly reactive geochemical zone that enhances dissolution of the carbonate rock 0883-2927/$ - see front matter Ó 2012 Elsevier Ltd. All rights reserved. http://dx.doi.org/10.1016/j.apgeochem.2012.05.008 ⇑ Corresponding author. Tel.: +52 646 1744601; fax: +52 646 1745303. E-mail address: carriquiry@uabc.edu.mx (J.D. Carriquiry). 1 Present address: UBIPRO, FES Iztacala, Universidad Nacional Autónoma de México, Av. de los Barrios 1, Los Reyes Iztacala, Tlalnepantla, México 54090, Mexico. Applied Geochemistry 27 (2012) 1579–1586 Contents lists available at SciVerse ScienceDirect Applied Geochemistry journal homepage: www.elsevier.com/locate/apgeochem