Abstract
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 (≈2,200-year) to centennial (≈450, 300 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 millennial and 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.
Highlights
The forcing mechanisms responsible for centennial to millennial variability of mid-latitude storminess are still poorly understood
In opposition to the steady increase of Aeolian Sand Influxes (ASI) observed throughout unit II, which we link to the mid-Holocene transgression, we argue that the gradual decrease in ASI shown for unit IV may be the expression of an intense westward progradation undergone by the exposed coastline after 4,300 cal
Our results further corroborate the hypothesis that North Atlantic westerlies and storm-tracks underwent millennial to centennial shifts in their latitudinal position during the Holocene
Summary
OPEN Holocene centennial to millennial shifts in North-Atlantic storminess and ocean dynamics. LOVECLIM simulations support our hypothesis that Holocene periods of high storminess activity over Northern Europe were associated with a stronger and more northward-located Azores high-pressure centre and with a strengthened polar vortex, in a configuration resembling present-day positive NAO-situations (Fig. 4D) Between these two strong centres of action, a narrow corridor most likely funnelled the Atlantic Westerly Jet and associated cyclonic perturbations, driving storm-tracks towards northern Europe (Fig. 4D). This would have fostered large SST differences between the eastern and western part of this area, in line with the hypothesis that SST differences in the Nordic Seas relates to NAO variability[58] and, maybe more importantly, to North-eastern Atlantic storminess activity All in all, these results support the proposition recently made that persistent positive NAO-like situations and associated enhanced North Atlantic storminess during the Holocene may have been instrumental in amplifying or even triggering abrupt pluri-centennial cold events by strengthening the SPG and causing a freshening of the North Atlantic inflow and, in turn, the slowdown of the Atlantic Meridional Overturning Circulation[5,6]. Our results are in favour of the IRD-events in the North Atlantic to be (at least partially) the result of strengthened and northward-located westerlies and storm-tracks in the North Atlantic during NAO-like situations that would have enhanced the SPG and helped spreading Ice-Rafted Debris over the North- western Atlantic
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