Abstract
Soils – constituting the largest terrestrial carbon pool - are vulnerable to climatic warming. Currently existing uncertainties regarding carbon fluxes within terrestrial systems can be addressed by studies of past carbon cycle dynamics and related climate change recorded in sedimentary successions. Here we show an example from the Early Jurassic (early Toarcian, c. 183 mya) marginal-marine strata from Poland, tracking the hinterland response to climatic changes through a super-greenhouse event. In contrast to anoxia-related enhanced carbon storage in coeval open marine environments, Total Organic Carbon (TOC) concentrations in the Polish successions are substantially reduced during this event. Increasing temperature favoured fungal-mediated decomposition of plant litter – specifically of normally resistant woody tissues. The associated injection of oxidized organic matter into the atmosphere corresponds to abrupt changes in standing vegetation and may have contributed significantly to the amplified greenhouse climate on Earth. The characteristic Toarcian signature of multiple warm pulses coinciding with rapidly decreasing carbon isotope ratios may in part be the result of a radical reduction of the terrestrial carbon pool as a response to climate change.
Highlights
The terrestrial carbon pool and carbon cycle are characterized by complex, non-linear behaviour[1,2,3,4] and is hard to model robustly[5]
Total Organic Carbon (TOC) content and carbon isotope ratios (Supplementary Table 1; Fig. 2) in the strata coeval to T-OAE are strongly depleted despite growing proximity of the coastal vegetation zone
The frequency of fungal spores, which is correlated with negative C isotope peaks and enhanced cuticular plant litter sequestration, pointing to climate-driven enhanced decomposition of wood and rapid destruction of terrestrial carbon pool, which in turn may have played an important role in the aggravation of the Jurassic greenhouse disaster
Summary
The terrestrial carbon pool and carbon cycle are characterized by complex, non-linear behaviour[1,2,3,4] and is hard to model robustly[5]. Based on carbon isotope stratigraphy, using fossil wood and recording the series of stratigraphically abrupt 5 CIE steps characteristic of the T-OAE, the Ciechocinek Formation strata were correlated to marine strata from England[16,18,26]. These CIEs are most prominently visible in the expanded records of Mechowo, Gorzow Wielkopolski and Brody-Lubienia (Fig. 2). During the T-OAE humid conditions (with perennially high humidity and rapid weathering) and enhanced hydrological cycle resulted in enhanced erosion associated with more sandy facies[23] (Fig. 2) and in elevated kaolinite content[27]
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