Seasonal temperature variability of the Neoglacial (3300–2500 BP) and Roman Warm Period (2500–1600 BP) reconstructed from oxygen isotope ratios of limpet shells (Patella vulgata), Northwest Scotland Ting Wang a, ⁎, Donna Surge a , Steven Mithen b a Department of Geological Sciences, University of North Carolina at Chapel Hill, Mitchell Hall, Campus Box # 3315, Chapel Hill, NC 27599, USA b School of Archaeology, University of Reading, Whiteknights, PO Box 220, Reading RG6 6AF, UK abstract article info Article history: Received 7 July 2011 Received in revised form 20 December 2011 Accepted 22 December 2011 Available online 31 December 2011 Keywords: Oxygen isotope Patella vulgata Neoglacial Roman Warm Period Northwest Scotland Subboreal/Subatlantic transition Seasonal sea-surface temperature variability for the Neoglacial (3300–2500 BP) and Roman Warm Period (RWP; 2500–1600 BP), which correspond to the Bronze and Iron Ages, respectively, was estimated using ox- ygen isotope ratios obtained from high-resolution samples micromilled from radiocarbon-dated, archaeolog- ical limpet (Patella vulgata) shells. The coldest winter months recorded in Neoglacial shells averaged 6.6 ± 0.3 °C, and the warmest summer months averaged 14.7 ± 0.4 °C. One Neoglacial shell captured a year with- out a summer, which may have resulted from a dust veil from a volcanic eruption in the Katla volcanic system in Iceland. RWP shells record average winter and summer monthly temperatures of 6.3 ± 0.1 °C and 13.3 ± 0.3 °C, respectively. These results capture a cooling transition from the Neoglacial to RWP, which is further supported by earlier studies of pine history in Scotland, pollen type analyses in northeast Scotland, and Eu- ropean glacial events. The cooling transition observed at the boundary between the Neoglacial and RWP in our study also agrees with the abrupt climate deterioration at 2800–2700 BP (also referred to as the Subbor- eal/Subatlantic transition) and therefore may have been driven by decreased solar radiation and weakened North Atlantic Oscillation conditions. © 2011 Elsevier B.V. All rights reserved. 1. Introduction Pre-industrial climate reconstructions during the mid to late Holo- cene provide the necessary information for understanding natural variation in the climate system prior to anthropogenic changes in the atmosphere, hydrosphere, and land use. Moreover, paleoclimate reconstructions that use archaeological sources contribute to our un- derstanding of human–climate relationships (Surge and Walker, 2005; Walker and Surge, 2006; Hallmann et al., 2009; Hufthammer et al., 2010; Jones et al., 2010; Patterson et al., 2010; Andrus, 2011; Helama and Hood, 2011; Wang et al., 2011), particularly in regions that are sensitive to climate change. These paleoclimate records can be compared to proxies of possible climate forcings (e.g., solar activ- ity, the North Atlantic Oscillation, Atlantic Meridional Overturning Circulation) and to predictions made by regional climate models (Shindell et al., 2001; Renssen et al., 2006; Swindles et al., 2007; Mann et al., 2009, and many others). Linking paleoclimate records with proxies of climate forcings is particularly important for the North Atlantic sector because the North Atlantic plays a critical role in heat transport and climate change at regional and global scales. The majority of Holocene climate proxies provide decadal, annual, or single season (mostly summer and the growing season) resolution. Few studies provide the high resolution necessary to reconstruct seasonal-scale variability. Regional climate models demonstrate the need for such high-resolution, seasonality studies. Numerical (ideal- ized multi-level primitive equation) and sensitivity (ECBilt-CLIO) model experiments show that small changes in the coupled atmo- spheric–oceanographic climate system influence regional mid- latitude seasonality in the North Atlantic sector (Lee and Kim, 2003; van der Schrier et al., 2007). Therefore, climate archives capable of capturing seasonal-scale resolution can provide the data necessary to gain insights into the mechanisms controlling seasonal variability at mid-latitudes in the North Atlantic. High-resolution time series of oxygen isotope ratios (δ 18 O) in mollusc shells have been widely used in paleoclimate and paleoeco- logical studies (Jones and Allmon, 1995; Schöne et al., 2005a, 2005b; Surge and Walker, 2005, 2006; Goewert and Surge, 2008, and many others). Their fast growth makes them ideal candidates to capture seasonal variability. Archaeological middens found along the northwest coast of Scotland contain abundant limpet (Patella vul- gata) shells, providing a rich source of seasonal climate records and information on human subsistence strategies. Isotopic studies of Pa- tella shells have shown that these shells are useful for reconstructing sea-surface temperature (SST) and inferring climate change Palaeogeography, Palaeoclimatology, Palaeoecology 317–318 (2012) 104–113 ⁎ Corresponding author. Tel.: + 1 919 843 1994; fax: + 1 919 966 4519. E-mail addresses: twang@email.unc.edu, twang@live.unc.edu (T. Wang), donna64@unc.edu (D. Surge), s.j.mithen@reading.ac.uk (S. Mithen). 0031-0182/$ – see front matter © 2011 Elsevier B.V. All rights reserved. doi:10.1016/j.palaeo.2011.12.016 Contents lists available at SciVerse ScienceDirect Palaeogeography, Palaeoclimatology, Palaeoecology journal homepage: www.elsevier.com/locate/palaeo