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North Atlantic forcing of moisture delivery to Europe throughout the Holocene.

ABSTRACT: Century-to-millennial scale fluctuations in precipitation and temperature are an established feature of European Holocene climates. Changes in moisture delivery are driven by complex interactions between ocean moisture sources and atmospheric circulation modes, making it difficult to resolve the drivers behind millennial scale variability in European precipitation. Here, we present two overlapping decadal resolution speleothem oxygen isotope (δ(18)O) records from a cave on the Atlantic coastline of northern Iberia, covering the period 12.1-0 ka. Speleothem δ(18)O reveals nine quasi-cyclical events of relatively wet-to-dry climatic conditions during the Holocene. Dynamic Harmonic Regression modelling indicates that changes in precipitation occurred with a ~1500 year frequency during the late Holocene and at a shorter length during the early Holocene. The timing of these cycles coincides with changes in North Atlantic Ocean conditions, indicating a connectivity between ocean conditions and Holocene moisture delivery. Early Holocene climate is potentially dominated by freshwater outburst events, whilst ~1500 year cycles in the late Holocene are more likely driven by changes internal to the ocean system. This is the first continental record of its type that clearly demonstrates millennial scale connectivity between the pulse of the ocean and precipitation over Europe through the entirety of the Holocene.

SUBMITTER: Smith AC

PROVIDER: S-EPMC4842961 | biostudies-literature |

REPOSITORIES: biostudies-literature

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Project description:The forcing mechanisms responsible for centennial to millennial variability of mid-latitude storminess are still poorly understood. On decadal scales, the present-day geographic variability of North-Atlantic storminess responds to latitudinal shifts of the North-Atlantic westerly wind-belt under the prime control of the North-Atlantic Oscillation (NAO). An equivalent mechanism operating at centennial to millennial time scales during the Holocene is still to be ascertained, especially owing to the lack of high-resolution and continuous records of past-storminess extending far enough in time. Here we present a reconstruction of past storminess activity based on a high-resolution record of wind-blown sand retrieved from a near-coastal wetland. Our record extends back to ca. 10,000 B.P. and allows to continuously document fluctuations in the frequency of Holocene storm-force winds at our study-site at a mean high temporal resolution of 40 years. Large similarities between our record and palaeo-oceanographic records of Holocene climate changes in the North-Atlantic suggest that our past-storminess record reproduces a signal of significance for the North-Eastern Atlantic realm. We find that Holocene North-Atlantic storminess is dominated by robust millennial (≈2,500-year) to centennial (≈400 and 200-year) periodicities. These changes in storminess were accompanied by changes in the precipitation regimes over northern Europe, evidencing large-scale shifts in the latitudinal positions of the Atlantic westerlies akin to present-day NAO patterns. We propose that these shifts originate from changes in the position and extent of the Azores high-pressure system and Polar vortex, as supported by climate model simulations. Finally, we demonstrate that enhanced zonal storminess activity over the North-Atlantic was the driver of centennial-scale changes in North-Atlantic oceanic circulation, while ocean dynamics most likely influenced back the atmospheric circulation at millennial time-scales. This may vouch for the instrumental role played by North-Atlantic storminess in triggering abrupt climate change at centennial scales during the Holocene.

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North Atlantic forcing of moisture delivery to Europe throughout the Holocene.

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