Dynamics of sediment flux to a bathyal continental margin section through the Paleocene–Eocene Thermal Maximum

Abstract

The response of the Earth system to greenhousegas-driven warming is of critical importance for the future trajectory of our planetary environment. Hyperthermal events -past climate transients with global-scale warming significantly above background climate variability -can provide insights into the nature and magnitude of these responses. The largest hyperthermal of the Cenozoic was the Paleocene-Eocene Thermal Maximum (PETM ∼ 56 Ma). Here we present new high-resolution bulk sediment stable isotope and major element data for the classic PETM section at Zumaia, Spain. With these data we provide a new detailed stratigraphic correlation to other key deep-ocean and terrestrial PETM reference sections. With this new correlation and age model we are able to demonstrate that detrital sediment accumulation rates within the Zumaia continental margin section increased more than 4-fold during the PETM, representing a radical change in regional hydrology that drove dramatic increases in terrestrial-to-marine sediment flux. Most remarkable is that detrital accumulation rates remain high throughout the body of the PETM, and even reach peak val-ues during the recovery phase of the characteristic PETM carbon isotope excursion (CIE). Using a series of Earth system model inversions, driven by the new Zumaia carbon isotope record, we demonstrate that the silicate weathering feedback alone is insufficient to recover the PETM CIE, and that active organic carbon burial is required to match the observed dynamics of the CIE. Further, we demonstrate that the period of maximum organic carbon sequestration coincides with the peak in detrital accumulation rates observed at Zumaia. Based on these results, we hypothesise that orbitalscale variations in subtropical hydro-climates, and their subsequent impact on sediment dynamics, may contribute to the rapid climate and CIE recovery from peak-PETM conditions.

Large Igneous Province thermogenic greenhouse gas flux could have initiated Paleocene-Eocene Thermal Maximum climate change

“…During PETM initiation, release of 0.3–1.1 PgC yr –1 of carbon as greenhouse gases to the ocean–atmosphere system 4–6 drove 4–5 °C of global warming 7 over a short period (<20,000 years) 5,8–10 . Although the North Atlantic Igneous Province (NAIP) LIP and the PETM are closely coincident in time 11–13 , the rate and duration of NAIP carbon emissions have not yet been reconciled with the <20 kyr onset of PETM climate change 8,9,14,15 .…”

Negative carbon isotope excursions: an interpretive framework

“…We employ an inverse modeling technique to produce nCIEs wherein the isotopic signature of the surface ocean dissolved inorganic carbon pool (δ 13 C DIC) is forced to follow a prescribed δ 13 C evolution, while an internal algorithm determines how much atmospheric CO 2 input with a specified isotopic signature is necessary to match this profile (Cui et al 2011, Cui et al 2013, Kirtland Turner and Ridgwell 2013, Dunkley Jones et al 2018. We choose to force surface DIC δ 13 C rather than atmospheric CO 2 δ 13 C because the former is a closer approximation to data from marine carbonates.…”

“…carbon release over longer timescales that approach the residence time of carbon in the exchangeable reservoir, it becomes crucial to account for feedbacks such as carbonate compensation and rock weathering. More recently, modeling approaches have been utilized that explicitly consider the timing of a nCIE derived from sedimentary age models (Cui et al 2011, Cui et al 2013, Gutjahr et al 2017, Dunkley Jones et al 2018 in calculating the mass of carbon required to generate a particular nCIE.…”

Constraints on the onset duration of the Paleocene–Eocene Thermal Maximum

“…The Bighorn Basin orbital chronology is broadly consistent with onset duration estimates based on an age model that assumed dynamic sedimentation as a function of the depositional environment [ 49 ]. Similarly, independent cyclostratigraphy on a shallow marine section from the paleo-Tethys at Zumaia demonstrated that the majority of the PETM CIE occurred within approximately 5 kyr with the remainder occurring over a single precession cycle [ 50 ]. By contrast, tuning using Fe counts across a PETM section from Spitsbergen in the Svalbard Archipelago suggested the onset of the PETM CIE in bulk marine organic carbon occurred gradually over a full precession cycle [ 51 ].…”

“…My focus is particularly on the onset duration of the PETM, so I focus on just the duration over which carbon is emitted in these scenarios (approx. 70 kyr maximum) and exclude the representation of enhanced removal of 13 C-depleted carbon that could account for the relatively rapid recovery in δ 13 C following the body of the CIE [ 9 , 50 , 63 ]. I add one further PETM carbon input scenario for comparison to the existing published scenarios (dark blue lines in figure 4 ): this combines short onset duration (3 kyr) for the input of isotopically depleted carbon (δ 13 C = −35‰) with an extended interval (70 kyr) of elevated rates of volcanic outgassing (δ 13 C = −6‰).…”