Mid-Holocene Iberian hydroclimate variability and paleoenvironmental change: molecular and isotopic insights from Praia Rei Cortico, Portugal

At Praia Rei Cortico (PRC), coastal Portugal, we analyzed compound-specific isotopes of plant wax-derived n-alkanes in combination with molecular distribution proxies and C/N ratios to reconstruct hydrologic and environmental change in a mid-Holocene wetland. During this relatively brief segment of the Holocene (6.6-5.4k cal a BP), substantial shifts in the stable hydrogen isotope composition of terrestrially sourced C(29)n-alkanes (delta Dn-C29) record significant multi-decadal changes in precipitation origin and storm trajectory. Wetland formation at PRC occurred during a humid interval (6.6-6.5kcalaBP) with a dominantly tropical precipitation source, likely the result of a persistent negative phase of the North Atlantic Oscillation, which permitted the establishment and dominance of Sphagnum moss. A subsequent decrease in precipitation significantly reduced Sphagnum abundance at PRC, which is evidenced by decreased sedimentary C/N ratios and reduced mid-chain n-alkane abundances. From 5.9 to 5.4k cal a BP, relatively low delta Dn-C29 values coincide with sand invasion along the Iberian coast and cooling in the North Atlantic. Strong correspondence between Dn-C29 values and the occurrence of ice-rafted debris recorded in deep sea sediment cores during this period illustrate a marked North Atlantic control on the trajectory of mid-latitude storms and precipitation regimes in Iberia. (C) 2017 John Wiley & Sons, Ltd.