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

Abstract

At Praia Rei Cortiço (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 (δD n ‐C29 ) record significant multi‐decadal changes in precipitation origin and storm trajectory. Wetland formation at PRC occurred during a humid interval (6.6–6.5k cal a BP ) 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 δD n ‐C29 values coincide with sand invasion along the Iberian coast and cooling in the North Atlantic. Strong correspondence between δD n ‐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.

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