Disentangling the Evidence of Milankovitch Forcing From Tree-Ring and Sedimentary Records

Abstract

Tree-ring records constitute excellent high-resolution data and provide valuable information for climate science and paleoclimatology. Tree-ring reconstructions of past temperature variations agree to show evidence for annual-to-centennial anomalies in past climate and place the industrial-era warming in the context of the late Holocene climate patterns and regimes. Despite their wide use in paleoclimate research, however, tree rings have also been deemed unsuitable as low-frequency indicators of past climate. The arising debate concerns whether the millennia-long tree-ring records show signals of orbital forcing due to the Milankovitch cycles. Here, we produce a summer-temperature reconstruction from tree-ring chronology running through mid- and late-Holocene times (since 5486 BCE) comprising minimum blue channel light intensity (BI). The BI reconstruction correlates with existing and new tree-ring chronologies built from maximum latewood density (MXD) and, unlike the MXD data, shows temperature trends on Milankovitch scales comparable to various types of sedimentary proxy across the circumpolar Arctic. Our results demonstrate an unrevealed potential of novel, unconventional tree-ring variables to contribute to geoscience and climate research by their capability to provide paleoclimate estimates from inter-annual scales up to those relevant to orbital forcing.

Depositional history of peatland pines (Pinus sylvestrisL.) in NW Enontekiö, Finnish Lapland: implications for Middle Holocene drought and temperature fluctuations

“…Generally, these indications appear to link the occurrence of the peatland pines at the Pousuj€ arven suo site, and the subsequent southward retreat of the pine tree line, to the orbital forcing due to Milankovitch cycles (Berger 1978(Berger , 1988. In this respect, the findings concur with previous palaeobotanical works demonstrating an association between the high-latitude summer-temperature cooling due to the decreasing insolation and the retreat of pine and other arboreal species from high altitude and latitude sites in Fennoscandia through the Middle and Late Holocene (Kullman 1992(Kullman , 1995Selsing 1996;Eronen et al 1999b;Sepp€ a & Birks 2002;Helama et al 2004Helama et al , 2022. Such temperature-mediated association may not be similarly evident at lower latitudes.…”

“…1999b; Seppä & Birks 2002; Helama et al . 2004, 2022). Such temperature‐mediated association may not be similarly evident at lower latitudes.…”

“…Much less attention has been paid to retrieving subfossil remains of peatland pines from high-latitude sites in northern Fennoscandia. In fact, in this region, dendrochronological research has focused particularly on subfossil pine remains unearthed from lake sites, which have produced large collections of tree-ring dated subfossil pinewood samples (Eronen et al 1999a(Eronen et al , b, 2002Grudd et al 2002;Helama et al 2008Helama et al , 2022. Such trees typically grew on thick organogenic riparian substrate, a peat belt bordering the lakeshore, after which the downed boles have been preserved in anoxic sedimentary environment of small Arctic lakes (Eronen et al 1999a;Helama et al 2010b).…”

“…2002; Helama et al . 2008, 2022). Such trees typically grew on thick organogenic riparian substrate, a peat belt bordering the lakeshore, after which the downed boles have been preserved in anoxic sedimentary environment of small Arctic lakes (Eronen et al .…”