Wildfire activity enhanced during phases of maximum orbital eccentricity and precessional forcing in the Early Jurassic

Teuntje P Hollaar,Sarah J Baker,Jean-François Deconinck,Micha Ruhl,Stephen P Hesselbo,Claire M Belcher,Luke Mander

doi:10.1038/s43247-021-00307-3

Abstract

Fire regimes are changing due to both anthropogenic climatic drivers and vegetation management challenges, making it difficult to determine how climate alone might influence wildfire activity. Earth has been subject to natural-background climate variability throughout its past due to variations in Earth’s orbital parameters (Milkankovitch cycles), which provides an opportunity to assess climate-only driven variations in wildfire. Here we present a 350,000 yr long record of fossil charcoal from mid-latitude (~35°N) Jurassic sedimentary rocks. These results are coupled to estimates of variations in the hydrological cycle using clay mineral, palynofacies and elemental analyses, and lithological and biogeochemical signatures. We show that fire activity strongly increased during extreme seasonal contrast (monsoonal climate), which has been linked to maximal precessional forcing (boreal summer in perihelion) (21,000 yr cycles), and we hypothesize that long eccentricity modulation further enhances precession-forced fire activity.

Highlights

Fire regimes are changing due to both anthropogenic climatic drivers and vegetation management challenges, making it difficult to determine how climate alone might influence wildfire activity
We present a high-resolution and astronchronologically tuned record of wildfire activity that focuses on an interval of the Mochras succession that most clearly shows the expression of precession and eccentricity[43,45,46] (Fig. 1), and which allows us to examine the link between wildfire and climatic shifts
We present counts of 46,204 macrocharcoal particles (>125 μm) and counted projections of >15 million microcharcoal particles (

Summary

Introduction

Fire regimes are changing due to both anthropogenic climatic drivers and vegetation management challenges, making it difficult to determine how climate alone might influence wildfire activity. It is difficult to disentangle natural wildfire climatedrivers from anthropogenic influences on ignitions[3], humandriven shifts in distribution of vegetation types across the landscape[4], or fuel management practices[5] This makes the study of palaeofire of utility in disentangling the role of land management practices[4,5] from climate change alone in driving variations in wildfire activity. Milankovitch theory describes how Earth’s orbital motions of precession, obliquity and eccentricity determine the seasonal and latitudinal distribution of insolation received on Earth and, to a smaller extent, the net received solar radiation[9,10] These orbital processes cause variations in average regional and global temperatures and ice sheet growth (e.g. forcing the Pleistocene glacial cycles), seasonality, monsoonal strength, and associated storm activity[11,12,13]. Hao et al.[33] found variations in fire activity, evidenced by both charcoal and soot deposition over a single precessional cycle preserved in Holocene aged sediments of Quighai Lake in China

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