North American continental margin records of the Paleocene‐Eocene thermal maximum: Implications for global carbon and hydrological cycling

Abstract

The impacts of the Paleocene‐Eocene thermal maximum (PETM) (∼55 Ma), one of the most rapid and extreme warming events in Earth history, are well characterized in open marine and terrestrial environments but are less so on continental margins, a major carbon sink. Here, we present stable isotope, carbonate content, organic matter content, and C:N ratio records through the PETM from new outcrop sections in California and from cores previously drilled on the New Jersey margin. Foraminifer δ18O data suggest that midlatitude shelves warmed by a similar magnitude as the open ocean (5°C–8°C), while the carbon isotope excursion (CIE), recorded both in carbonate and organic matter δ13C records, is slightly larger (3.3–4.5‰) than documented in open ocean records. Sediment accumulation rates increase dramatically during the CIE in marked contrast to the open ocean sites. In parallel, mass accumulation rates of both organic and inorganic carbon also increased by an order of magnitude. The estimated total mass of accumulated carbon in excess of pre‐CIE rates suggests that continental margins, at least along North America, became carbon sinks during the CIE, mainly because of weathering feedbacks and rising sea level. This result is significant because it implies that the negative feedback role of carbon burial on continental margins was greater than previously recognized.

Eustatic variations during the Paleocene‐Eocene greenhouse world

“…In continental margin sections in California, United States, a decrease in grain size across the onset of the PETM is consistent with sea level rise [John et al, 2008]. In northern Egypt, ostracode assemblages show increased abundances of upper bathyal and outer neritic taxa from the upper Paleocene to lower Eocene consistent with a $20 m rise in sea level [Speijer and Morsi, 2002] (Figure 9).…”

“…Question marks indicate sequences of which precise dating is uncertain, and gray crosses indicate hiatuses. Study 1, this study; study 2 after Powell et al [1996] and Bujak and Brinkhuis [1998]; study 3, after Payne et al [2005]; study 4, after Iakovleva et al [2001]; study 5, after John et al [2008]; study 6, after Speijer and Morsi [2002]; and study 7, after Crouch and Brinkhuis [2005]. LST (2) , Lowstand Systems Tract Type 2.…”

“…Symbols filled with stripes indicate marginal marine sites for which published information has indicated an increase in terrigenous sediment supply (TS) during the PETM or other hyperthermals. Increase in terrigenous sediment supply for Bass River and Wilson Lake is from Sluijs et al [2007b] and John et al [2008]. Numbers refer to the following sites: site 1, Lomonosov Ridge, Arctic Ocean (SL, TS ); site 2, Doel, North Sea (SL [Steurbaut et al, 2003]); site 3, Basque Region, Bay of Biscay (SL, TS Pujalte and Schmitz, 2006]); site 4, Forada, Central Northern Tethys (TS [Giusberti et al, 2007]); site 5, Turgay Straight (SL [Iakovleva et al, 2001]); site 6, Lodo Formation, California (SL [John et al, 2008]); site 7, Gebel Duwi, Central Southern Tethys (SL [Speijer and Morsi, 2002]); site 8, Tawanui, Southwestern Pacific (TS [Crouch et al, 2003b], SL [Crouch and Brinkhuis, 2005]); and site 9, Clarence River Valley, Southwestern Pacific (TS PETM [Hollis et al, 2005], TS other presumed hyperthermals [Nicolo et al, 2007]).…”

“…Still, the brief Chron C25n ($0.5 Ma; ) appears expanded relative to the very long and condensed interval between the onset of C24n and the CIE ($1.3 Ma) ( Figure 3). The CIE has been identified between 357.3 and $347 mbs from d 13 C records on multiple carbon bearing phases [Cramer et al, 1999;Sluijs et al, 2007b;John et al, 2008]. At Wilson Lake (Figure 4), the CIE has been identified between $110.0 and $96 mbs from d 13 C records on multiple carbon bearing phases Zachos et al, 2006;Sluijs et al, 2007b].…”

“…Assuming sedimentation rates of between 1 and 10 cm/ka, the transgression initiated $20-200 ka before the CIE and continued for $10 ka after the onset of the CIE. Importantly, the coastline migrated farther away from the site during the PETM, even though sediment supply to the New Jersey Shelf increased tremendously [Sluijs et al, 2007b;John et al, 2008].…”