Eutrophication and Deoxygenation Forcing of Marginal Marine Organic Carbon Burial During the PETM

Abstract

The Paleocene‐Eocene Thermal Maximum (PETM) is recognized globally by a negative excursion in stable carbon isotope ratios (δ13C) in sedimentary records, termed the carbon isotope excursion (CIE). Based on the CIE, the cause, duration, and mechanisms of recovery of the event have been assessed. Here, we focus on the role of increased organic carbon burial on continental margins as a key driver of CO2 drawdown and global exogenic δ13C during the recovery phase. Using new and previously published sediment proxy data, we show evidence for widespread enhanced primary production, low oxygen waters, and high organic carbon (Corg) burial in marginal and restricted environments throughout the δ13C excursion. With a new biogeochemical box model for deep and marginal environments, we show that increased phosphorus availability and water column stratification on continental margins can explain the increased Corg burial during the PETM. Deoxygenation and recycling of phosphorus relative to Corg were relatively mild, compared to modern day anoxic marine systems. Our model reproduces the conditions reconstructed by field data, resulting in a burial of 6,000 Pg across the PETM, in excess of late Paleocene burial, and ∼3,300 Pg C for the critical first 40 kyr of the recovery, primarily located on continental margins. This value is consistent with prior data and model estimates (∼2,000–3,000 Pg C). To reproduce global exogenic δ13C patterns, this Corg burial implies an injection of 5,000–10,000 Pg C during the first ∼100–150 kyr of the PETM, depending on the source's δ13C (−11‰ to −55‰).

Deoxygenation and organic carbon sequestration in the Tethyan realm associated with the middle Eocene climatic optimum

“…The mechanism(s) responsible for subsequent climatic recovery, in the aftermath of the middle Eocene climatic optimum, presumably through atmospheric CO 2 drawdown (Bijl et al, 2010;Sluijs et al, 2013;Henehan et al, 2020), remain(s) similarly enigmatic. Remarkably, the termination of the middle Eocene climatic optimum occurred on a time scale similar to that seen at the Paleocene-Eocene thermal maximum, for which silicate weathering and organic carbon burial were likely important (Ravizza et al, 2001;Pogge von Strandmann, 2021;Papadomanolaki et al, 2022). Osmium isotope compositions of marine sediments and carbon cycle simulations coupled to CO 2 reconstructions (Caves et al, 2016) indicate a weakened silicate weathering feedback during the middle Eocene compared to, e.g., the Neogene and Paleocene.…”

Spatial and Temporal Patterns in Petrogenic Organic Carbon Mobilization During the Paleocene‐Eocene Thermal Maximum

“…The TOC values and LSR were acquired for each location from published studies (Table 1). C org records from ODP Site 1172 (Papadomanolaki et al., 2022) and TDP Site 14 (Aze et al., 2014) were linearly interpolated to match the depths of the biomarker data, using R Package Astrochron (Meyers, 2014). LSR estimates were obtained (where possible) for three key time intervals: (i) pre‐PETM (Paleocene); (ii) the “core” (onset and body of the CIE) of the PETM; (iii) and the recovery of the PETM (see Text S1 in Supporting Information ).…”

Tracing North Atlantic volcanism and seaway connectivity across the Paleocene–Eocene Thermal Maximum (PETM)

“…The PETM led to a global increase in continental weathering and erosion (Pogge von Strandmann et al, 2021;Pujalte et al, 2015;Ravizza et al, 2001) and widespread enhanced 160 marine organic carbon burial (John et al, 2008;Kaya et al, 2022;Papadomanolaki et al, 2022), which both act as negative feedbacks to increased atmospheric CO2 levels. The emplacement of flood basalt lavas and widespread ash deposits would have significantly enhanced the availability of fresh reactive silicate material at the surface (Dessert et al, 2003).…”

“…Modelling estimates based on inverted pH proxy data arrived at far greater degassing volumes (>10,000 Gt C), which would require less 12 C-enriched sources to match the CIE (Gutjahr et al, 2017). Yet, this high-volume carbon release scenario might be at odds with the extremely enhanced organic carbon burial rates for the PETM, a carbon sink would rapidly drive exogenic δ 13 C to positive values if not balanced 80 by a heavily 12 C-enriched source (Kaya et al, 2022;Papadomanolaki et al, 2022). These studies suggest that the carbon source is both 12 C-enriched and voluminous, complicating interpretations of the CIE purely on grounds of the source δ 13 C signature.…”