Evidence for a rapid release of carbon at the Paleocene-Eocene thermal maximum

Abstract

The Paleocene/Eocene thermal maximum (PETM) and associated carbon isotope excursion (CIE) are often touted as the best geologic analog for the current anthropogenic rise in pCO 2. However, a causal mechanism for the PETM CIE remains unidentified because of large uncertainties in the duration of the CIE's onset. Here, we report on a sequence of rhythmic sedimentary couplets comprising the Paleocene/Eocene Marlboro Clay (Salisbury Embayment). C-depleted carbon to the ocean-atmosphere system in a geologically short interval of time (1-3). Proposed mechanisms include the destabilization of the global methane reservoir by a thermal trigger (2, 4) or physical disturbance (5), production of thermogenic CH 4 and CO 2 during the emplacement of a large igneous province (6, 7), wildfires burning peatlands (8), desiccation of a large epicontinental sea (9), decomposition of terrestrial permafrost (10), and bolide impact (11,12). The only consensus is that a precise chronology providing rates for the onset of the CIE is essential to distinguish among these mechanisms. Efforts to establish such a chronology have relied on average sedimentation rates based on integrated magneto-and biostratigraphic constraints (1), identifying cycles in deep sea cores and assigning an orbital periodicity (13,14), or measuring the concentration of extraterrestrial 3 He and applying an estimated flux to establish sedimentation rates (15,16). The lack of a precise timescale for the δ 13 C excursion precludes further advances in identification of the source(s) of the light carbon and calculation of the release rates and magnitudes. Until these are better quantified, the relevance of the CIE as an analog for the Anthropocene remains speculative.Deep sea bulk carbonate records show that the CIE began with an abrupt initial δ 13 C decrease of ∼1‰ followed by a more gradual decrease of similar magnitude (17). Bulk carbonate δ implications for the size of the carbon release necessary to produce the CIE. This uncertainty highlights the dire need for a precise chronometer for the onset of the carbon isotope excursion.Here, we present high-resolution bulk stable isotope and % CaCO 3 records from the northern Salisbury Embayment [35°N paleolatitude (18)] on the Atlantic coastal plain, using the Millville (ODP 174X) and newly recovered Wilson Lake B cores. Both of these cores contain the upper Paleocene-lower Eocene Marlboro Clay unit that has been correlated to deep sea CIE sections using carbon isotope and biostratigraphy (19,20). These cores have two unique features that distinguish them as outstanding temporal archives for the onset of the CIE: (i) expanded sections of the Marlboro Clay in both the Wilson Lake B (15.5 m) and Millville (12.6 m) cores and (ii) distinct and rhythmic bedding of silty clays through the entire section containing the δ 13 C excursion. The δ 13 C excursions in the Wilson Lake B and Millville cores have amplitudes of −6‰ and −4.5‰, respectively (Fig. S1), with ∼3.5‰ of the decrease representing the virtually instantaneous initia...

Drilling disturbance and constraints on the onset of the Paleocene–Eocene boundary carbon isotope excursion in New Jersey

“…Significant new evidence relating to the pattern and timing of the CIE onset was presented by Wright and Schaller (2013) from a drill site at Millville, New Jersey (Ocean Drilling Program (ODP) Leg 174X; Sugarman et al, 2005). Their data show one of the clearest and best-resolved onsets yet published (reproduced here as Fig.…”

“…1) with a run of intermediate bulk sediment δ 13 C values showing a somewhat stepped appearance, including intervals of little change or possibly even reversals in the trend. Critically, Wright and Schaller (2013) described the Marlboro clay formation at Millville and the nearby Wilson Lake B core (as yet unpublished, but a re-drill of a Wilson Lake core studied at high resolution by Gibson et al, 1993, Sluijs et al, 2007a, and Stassen et al, 2012b as "characterized by rhythmic couplets of silty kaolinitic clay distinguished by 1 to 2 mm layers of swelling smectite clays and micaceous silt, recurring every 1-3 cm through the entirety of the unit". They referred to similar layers in the same formation in the nearby Ancora core (ODP Leg 174X; Harris et al, 2010), the South Dover Bridge core (Maryland, Self-Trail et al, 2012), and an exposure at Medford, the latter without citation.…”

“…Wright and Schaller (2013) argued for this partly on the sedimentology (especially the rhythmicity of the layering), and partly on the basis of a high-resolution bulk oxygen isotope record through two sections (approximately 25 and 10 cm, respectively) of the Wilson Lake B core. These sections were claimed to show cyclic variability in δ 18 O values, with maxima corresponding to the thin smectitic layers.…”

Anthropogenic carbon release rate unprecedented during the past 66 million years

“…1). However, currently only one section, from Millville, NJ, has cm-resolution bulk isotope records (foraminiferal isotopes at lower resolution) 22 , potentially offering the highest fidelity recording of the onset 23,24 (Fig. 2).…”

Two massive, rapid releases of carbon during the onset of the Palaeocene–Eocene thermal maximum

“…Several proposed models do not satisfy these constraints, either because the triggering mechanism is unique (for example, bolide impacts 21 ), or because they release carbon at relatively low rates (for example, seaway desiccation 22 , permafrost oxidation 23 ). Recent evidence for extremely rapid PETM C release that has been suggested to support an impact trigger for the event 3 is derived from a short marine-margin record, which may truncate evidence for the POE. Our data indicate two, ∼10 3 -year-long C release events at the PETM onset and are thus inconsistent with bolide impact as the sole PETM C release mechanism.…”