The fast-acting "pulse" of Heinrich Stadial 3 in a mid-latitude boreal ecosystem

A 3800 year-long radiocarbon-dated and highly-resolved palaeoecological record from Lake Fimon(N-Italy) served to investigate the effects of potential teleconnections between North Atlantic andmid-to-low latitudes at the transition from Marine Isotope Stage (MIS) 3 to 2. Boreal ecosystemsdocumented in the Fimon record reacted in a sensitive way to millennial and sub-millennial scaleNorthern Hemisphere atmospheric circulation patterns. The high median time-resolution of58 years allows the identification of five abrupt event-boundaries (i.e., main forest expansionand decline excursions) synchronous with the sharp stadial/interstadial (GS/GI) transitions withindating uncertainties. During Heinrich Stadial 3 (HS 3) we reconstruct more open and dry conditions,compared to the other GS, with a dominant regional scale fire signal. Linkages between local firesand climate-driven fuel changes resulted in high-magnitude fire peaks close to GI/GS boundaries,even exacerbated by local peatland conditions. Finally, palaeoecological data from the HS 3 intervalunveiled an internal variability suggesting a peak between 30,425 and 29,772 cal BP (2sigma error)which matches more depleted delta18O values in alpine speleothems. We hypothesise that this signal,broadly resembling that of other mid-latitudes proxies, may be attributed to the southward shiftof the Northern Hemisphere storm tracks and the associated delayed iceberg discharge events asdocumented during other HS.