A severe centennial-scale drought in midcontinental North America 4200 years ago and apparent global linkages

Abstract

We present evidence from a variety of physical and biological proxies for a severe drought that affected the mid-continent of North America between 4.1 and 4.3 ka. Rapid climate changes associated with the event had large and widespread ecological effects, including dune reactivation, forest fires and long-term changes in forest composition, highlighting a clear ecological vulnerability to similar future changes. Drought is also documented in the Middle East and portions of Africa and Asia, where it was similar in timing, duration and magnitude to that recorded in the central North American records. Some regions at high latitudes, including northern Europe and Siberia, experienced cooler and/or wetter conditions. Widespread mid-latitude and subtropical drought, associated with increased moisture at some high latitudes, has been linked in the instrumental record to an unusually steep sea surface temperature (SST) gradient between the tropical eastern and western Pacific Ocean (La Ninia) and increased warmth in other equatorial oceans. Similar SST patterns may have occurred at 4.2 ka, possibly associated with external forcing or amplification of these spatial modes by variations in solar irradiance or volcanism. However, changes in SST distribution bracketing the 4.2 ka event are poorly known in most regions and data are insufficient to estimate magnitude of changes in solar and volcanic forcing at this time. Further research is needed to delineate geographical patterns of moisture changes, ecological responses, possible forcing mechanisms and climatology of this severe climatic event.

Paired oxygen isotope records reveal modern North American atmospheric dynamics during the Holocene

“…We suggest that the inversely correlated component of isotopic change in the western and eastern sites may reflect long-term variability of the mean state of PNA through the Holocene based on the documented association of anti-phase precipitation isotopic variation in these regions with PNA. During the MH, relatively low d 18 ARTICLE across North America [19][20][21] , and corresponds temporally with the 4.2-3.9 kyr before present (BP) abrupt climate event documented globally 22 . Our result is supported by independent proxy evidence from a range of sites across the continent.…”

Holocene palaeohydrological changes in the northern Mediterranean borderlands as reflected by the lake-level record of lake ledro, northeastern Italy

“…orbitally-driven induced changes in summer insolation. However, the abrupt rise in lake levels around 4500 cal yr BP points to the crucial impact of the climatic oscillation around 4500-4000 cal yr BP (Marchant and Hooghiemstra, 2004;Booth et al, 2005;Magny et al, 2009b;Giraudi et al, 2011) in the northwestern Mediterranean area. In the case of Lake Ledro, the marked rise in lake level around 4500 cal yr BP may have been accentuated by human impact due to early and middle Bronze age settlements.…”

Ecology and the ratchet of events: Climate variability, niche dimensions, and species distributions

“…Recent paleoclimate studies indicate that low-frequency climate trends have been punctuated by significant fluctuations (29,30) and rapid transitions between climate states (31)(32)(33). For example, toward the end of the orbitally controlled early-Holocene warm period, between ca.…”