Earth and Planetary Science Letters 381 (2013) 104–115 Contents lists available at ScienceDirect Earth and Planetary Science Letters www.elsevier.com/locate/epsl Eocene seasonality and seawater alkaline earth reconstruction using shallow-dwelling large benthic foraminifera David Evans a,∗ , Wolfgang Müller a , Shai Oron b,c , Willem Renema d a Department of Earth Sciences, Royal Holloway University of London, Egham, TW20 0EX, UK b Department of Geological and Environmental Sciences, Ben-Gurion University of the Negev, Beer-Sheva, Israel c The Interuniversity Institute for Marine Sciences (IUI), Eilat, Israel d Naturalis Biodiversity Center, Leiden, The Netherlands article info abstract Article history: Received 10 January 2013 Received in revised form 31 July 2013 Accepted 15 August 2013 Available online xxxx Editor: G. Henderson Keywords: large benthic foraminifera LA-ICPMS Mg/Ca Eocene seasonality Nummulites Operculina deep-time Intra-test variability in Mg/Ca and other (trace) elements within large benthic foraminifera (LBF) of the family Nummulitidae have been investigated using laser-ablation inductively-coupled plasma mass spectrometry (LA-ICPMS). These foraminifera have a longevity and size facilitating seasonal proxy retrieval and a depth distribution similar to ‘surface-dwelling’ planktic foraminifera. Coupled with their abundance in climatically important periods such as the Paleogene, this means that this family of foraminifera are an important but under-utilised source of palaeoclimatic information. We have calibrated the relationship between Mg/Ca and temperature in modern Operculina ammonoides and observe a ∼ 2% increase in Mg/Ca ◦ C −1 . O. ammonoides is the nearest living relative of the abundant Eocene genus Nummulites, enabling us to reconstruct mid-Eocene tropical sea surface temperature seasonality by applying our calibration to fossil Nummulites djokdjokartae from Java. Our results indicate a 5–6 ◦ C annual temperature range, implying greater than modern seasonality in the mid-Eocene (Bartonian). This is consistent with seasonal surface ocean cooling facilitated by enhanced Eocene tropical cyclone-induced upper ocean mixing, as suggested by recent modelling results. Analyses of fossil N. djokdjokartae and Operculina sp. from the same stratigraphic interval demonstrate that environmental controls on proxy distribution coefficients are the same for these two genera, within error. Using previously published test–seawater alkaline earth metal distribution coefficients derived from an LBF of the same family (Raitzsch et al., 2010) and inorganic calcite, with appropriate correction systematics for secular Mg/Ca sw variation (Evans and Müller, 2012), we use our fossil data to produce a more accurate foraminifera-based Mg/Ca sw reconstruction and an estimate of seawater Sr/Ca. We demonstrate that mid-Eocene Mg/Ca sw was  2 mol mol −1 , which is in contrast to the model most commonly used to correct deep-time Mg/Ca data from foraminifera, but in agreement with most other Paleogene proxy and model data. This indicates that Mg/Ca sw has undergone a substantial (3–4×) rise over the last ∼ 40 Ma.  2013 Elsevier B.V. All rights reserved. 1. Introduction The trace element chemistry of foraminifera tests is increasingly being used as a palaeoceanic reconstruction tool. Many potential proxies linking test chemistry to palaeoenvironmental information have been developed (see e.g. Katz et al., 2010), which are most commonly applied in the fossil record to either planktic or deep benthic foraminifera (where deep is used here to distinguish these foraminifera from the shallow-dwelling large benthic species un- der consideration in this study) (e.g. Tripati et al., 2011; Bohaty et al., 2012; Lear et al., 2000). The abundance of foraminifera in sediment cores, along with the widespread distribution of some species (Fraile et al., 2008) has resulted in this group of organisms * Corresponding author. E-mail address: david.evans.2007@rhul.ac.uk (D. Evans). becoming one of the key sources of palaeoceanic proxy informa- tion available (Pearson, 2012). A disadvantage with the use of planktic foraminifera for palaeo- ceanic reconstruction is that they are relatively short lived, min- eralising over days or weeks (Anderson and Faber, 1984), thus providing a short temporal record of changes in (e.g.) sea surface temperature (SST) (but see Wit et al., 2010). This may be further complicated by migration through the water column during the lifespan of some foraminifera (Eggins et al., 2003) or seasonal bias in biomineralisation (e.g. Jonkers et al., 2010). Seasonality is in- creasingly being recognised as a key component of climate change (Hollis et al., 2012; Denton et al., 2005; Crowley et al., 1986), al- though there are a limited amount of studies that have attempted to reconstruct seasonality from periods such as the Paleogene, po- tentially one of the most important time intervals with respect to similarity to predicted future pCO 2 (Zachos et al., 2008). Much of 0012-821X/$ – see front matter  2013 Elsevier B.V. All rights reserved. http://dx.doi.org/10.1016/j.epsl.2013.08.035