Abstract
Abstract. Close coupling of Iberian hydroclimate and North Atlantic sea surface temperature (SST) during recent glacial periods has been identified through the analysis of marine sediment and pollen grains co-deposited on the Portuguese continental margin. While offering precisely correlatable records, these time series have lacked a directly dated, site-specific record of continental Iberian climate spanning multiple glacial cycles as a point of comparison. Here we present a high-resolution, multi-proxy (growth dynamics and δ13C, δ18O, and δ234U values) composite stalagmite record of hydroclimate from two caves in western Portugal across the majority of the last two glacial cycles (∼220 ka). At orbital and millennial scales, stalagmite-based proxies for hydroclimate proxies covaried with SST, with elevated δ13C, δ18O, and δ234U values and/or growth hiatuses indicating reduced effective moisture coincident with periods of lowered SST during major ice-rafted debris events, in agreement with changes in palynological reconstructions of continental climate. While in many cases the Portuguese stalagmite record can be scaled to SST, in some intervals the magnitudes of stalagmite isotopic shifts, and possibly hydroclimate, appear to have been somewhat decoupled from SST.
Highlights
The Portuguese continental margin is an important location for understanding variations in paleoceanographic conditions over orbital and millennial scales (Hodell et al, 2013; Voelker and de Abreu, 2011)
234U–230Th dating of Buraca Gloriosa (BG) and Gruta do Casal da Lebre (GCL) stalagmites reveals growth across approximately three-quarters of the last 220 ka, with periods of deposition interrupted by numerous hiatuses of varying length, with the longest gaps from 160– 147, 97–87, 72–60, 41–36, 32–30, and 17–15 ka (Figs. 5 and 6; Fig. S3)
The marine isotope stage (MIS) 6–5e boundary recorded by stalagmite BG67 is marked by both a change in drip position and a sharp transition from dense, clear calcite to a white, fibrous form
Summary
The Portuguese continental margin is an important location for understanding variations in paleoceanographic conditions over orbital and millennial scales (Hodell et al, 2013; Voelker and de Abreu, 2011). Denniston et al.: A stalagmite test of North Atlantic SST droclimate – growth dynamics and δ13C, δ18O, and δ234U values – spanning the majority of the last and penultimate glacial cycles (∼ 220 ka) at two cave sites in western Portugal. These time series offer a rare site-specific continental record capable of examining the coherence of SST controls on Iberian climate and ecosystem dynamics across glacial and interglacial periods. The new record provides a continental perspective of hydroclimate dynamics linked to regional oceanographic conditions
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