Tropical warming and intermittent cooling during the Cenomanian/Turonian oceanic anoxic event 2: Sea surface temperature records from the equatorial Atlantic

Abstract

Oceanic anoxic event 2 (OAE‐2) occurring during the Cenomanian/Turonian (C/T) transition is evident from a globally recognized positive stable carbon isotopic excursion and is thought to represent one of the most extreme carbon cycle perturbations of the last 100 Myr. However, the impact of this major perturbation on and interaction with global climate remains unclear. Here we report new high‐resolution records of sea surface temperature (SST) based on TEX86 and δ18O of excellently preserved planktic foraminifera and stable organic carbon isotopes across the C/T transition from black shales located offshore Suriname/French Guiana (Demerara Rise, Ocean Drilling Program Leg 207 Site 1260) and offshore Senegal (Cape Verde Basin, Deep Sea Drilling Project Leg 41 Site 367). At Site 1260, where both SST proxy records can be determined, a good match between conservative SST estimates from TEX86 and δ18O is observed. We find that late Cenomanian SSTs in the equatorial Atlantic Ocean (≥33°C) were substantially warmer than today (∼27°–29°C) and that the onset of OAE‐2 coincided with a rapid shift to an even warmer (∼35°–36°C) regime. Within the early stages of the OAE a marked (∼4°C) cooling to temperatures lower than pre‐OAE conditions is observed. However, well before the termination of OAE‐2 the warm regime was reestablished and persisted into the Turonian. Our findings corroborate the view that the C/T transition represents the onset of the interval of peak Cretaceous warmth. More importantly, they are consistent with the hypotheses that mid‐Cretaceous warmth can be attributed to high levels of atmospheric carbon dioxide (CO2) and that major OAEs were capable of triggering global cooling through the negative feedback effect of organic carbon‐burial‐led CO2 sequestration. Evidently, however, the factors that gave rise to the observed shift to a warmer climate regime at the onset of OAE‐2 were sufficiently powerful that they were only briefly counterbalanced by the high rates of carbon burial attained during even the most extreme interval of organic carbon burial in the last 100 Myr.

Evidence for oxic conditions during oceanic anoxic event 2 in the northern Tethyan pelagic realm

“…Contrary to other places where a general warming is observed (Jenkyns et al, 1994;Norris et al, 2002;Wilson et al, 2002;Voigt et al, 2004;Forster et al, 2007;Sinninghe Damsté et al, 2010), at Chrummflueschlucht, the evolution of the d 18 O record suggests a change in the regional hydrological cycle related to a possible cooling and more contrasted climate or more arid period (Keller et al, 2008).…”

“…During OAE 2, a brief cooling episode is recognized based on southward migrations of boreal fauna (Jefferies, 1962;Jenkyns et al, 1994;Gale and Christensen, 1996), on oxygen-isotope records and TEX 86 data Wilson et al, 2002;Voigt et al, 2004;Forster et al, 2007;Sinninghe Damsté et al, 2010). At Chrummflueschlucht, the small plateau of higher oxygen-isotope values at the onset of OAE 2 (peak "a") may relate to this cooling episode.…”

“…Major climatic and paleoceanographic changes have been associated with this event (Jenkyns et al, 1994;Huber et al, 2002;Norris et al, 2002;Forster et al, 2007). The onset of OAE 2 is characterized by an important positive excursion in the d 13 C carbonate bulk-rock record of approximately 2.5& (Schlanger and Jenkyns, 1976;Jenkyns, 1980;Schlanger et al, 1987;Gale et al, 1993;Erbacher et al, 1996;Jarvis et al, 2006;Voigt et al, 2006).…”

Confounding effects of oxygen and temperature on the TEX 86 signature of marine Thaumarchaeota

“…Excursions in O 2 concentration are also associated with short historic periods of pronounced cooling (53,54,61). For example, the TEX 86 paleotemperature proxy suggests a cooling of up to 12°C during the Plenus Cold Event (PCE) of OAE-2 (54).…”

Planktonic foraminiferal turnover across the Cenomanian – Turonian boundary (OAE2) in the northeast of the Tethys realm, Kopet-Dagh Basin

“…However, many authors have described an ephemeral but significant decrease in sea surface temperatures at the onset of OAE2 in some CTB sections (Lamolda et al 1994;Forster et al 2007;Jarvis et al 2011;Kaiho et al 2014 among others). This cooling has been attributed to a drop in atmospheric pCO 2 (Symbol for the negative decadic logarithm of the CO 2 concentration) levels which in turn was caused by enhanced carbon sequestration by burial of organic matter (Hasegawa et al 2003;Forster et al 2007). This event was first recognized as an incursion of boreal fauna in the shelf seas of NW Europe (e.g., Jefferies 1962;Gale & Christensen 1996;Voigt et al 2004) and called the Plenus Cold Event.…”