Impact of global cooling on Early Cretaceous high pCO2 world during the Weissert Event

Abstract

The Weissert Event ~133 million years ago marked a profound global cooling that punctuated the Early Cretaceous greenhouse. We present modelling, high-resolution bulk organic carbon isotopes and chronostratigraphically calibrated sea surface temperature (SSTs) based on an organic paleothermometer (the TEX86 proxy), which capture the Weissert Event in the semi-enclosed Weddell Sea basin, offshore Antarctica (paleolatitude ~54 °S; paleowater depth ~500 meters). We document a ~3–4 °C drop in SST coinciding with the Weissert cold end, and converge the Weddell Sea data, climate simulations and available worldwide multi-proxy based temperature data towards one unifying solution providing a best-fit between all lines of evidence. The outcome confirms a 3.0 °C ( ±1.7 °C) global mean surface cooling across the Weissert Event, which translates into a ~40% drop in atmospheric pCO2 over a period of ~700 thousand years. Consistent with geologic evidence, this pCO2 drop favoured the potential build-up of local polar ice.

Bottom water redox dynamics during the Early Cretaceous Weissert Event in ODP Hole 692B (Weddell Sea, Antarctica) reconstructed from the benthic foraminiferal assemblages

“…The new calcareous nannofossil biostratigraphy of ODP Hole 692B allowed a revision of the age assignment by Mutterlose and Wise (1990) for the stratigraphic interval comprised between 93 mbsf and 53.53 mbsf, initially interpreted to be Valanginian-Hauterivian. The revised calcareous nannofossil biostratigraphy applies the chronostratigraphic framework of the Berriasian -Barremian interval reported in Cavalheiro et al (2021). Calcareous nannofossil assemblages (Supplementary Fig S1, Table S1) contain relatively diverse and moderate to well-preserved specimens.…”

“…This finding is consistent with the recent revision of the LO of M. speetonensis, placed in the late Valanginian, close to the topmost part of the Weissert Event (Möller et al, 2015) . The LO of M. speetonenesi marks the base of Zone BC5 and the NC3/NC4 zonal boundary is tentatively placed between 82 mbsf and 83 mbsf just above the CIE of the Weissert Event following the inter-calibration of Tubodiscus verenae (absent in ODP Hole 692B) concerning the chemo-and magneto-stratigraphy (see Cavalheiro et al, 2021 for further discussion).…”

“…A total of 143 samples, including a published data set (Cavalheiro et al, 2021), were analyzed for bulk organic stable carbon isotope ratios (δ 13 Corg) by Europa Scientific Elemental Analyser -Isotope Ratio Mass Spectrometry (EA -IRMS). Analysis was carried out at Iso-Analytical, Crewe Cheshire (UK).…”

“…For that, we used a revised chronostratigraphic framework based on calcareous nannofossil biostratigraphy. (Cavalheiro et al, 2021). The primary aims of this study are the identification of: 1) quantitative changes in benthic foraminiferal assemblages to derive oxygen and organic-matter fluxes to the seafloor; 2) the paleobathymetric setting; 3) the paleoecological preferences of benthic foraminifera; and thus, paleoenvironmental changes in bottom water conditions before, during and after the Weissert Event.…”

Clumped isotope evidence for Early Jurassic extreme polar warmth and high climate sensitivity

“…47 data are from the following: Keating-Bitonti et al, 2011;Douglas et al, 2014;Petersen et al, 2016b, a;Evans et al, 2018;Wierzbowski et al, 2018;Meyer et al, 2018;Vickers et al, 2019Vickers et al, , 2020Vickers et al, , 2021Brigaud et al, 2020;Fernandez et al, 2021;de Winter et al, 2021. TEX H 86 paleothermometry data are from the following: Jenkyns et al, 2012;Lunt et al, 2012;Douglas et al, 2014;Frieling et al, 2014;O'Brien et al, 2017;Robinson et al, 2017;Cramwinckel et al, 2018;O'Connor et al, 2019;Ruebsam et al, 2020;Cavalheiro et al, 2021 ternal moulds (Suan et al, 2011). Interestingly, protobranch bivalves, to which Dacryomya belongs, are not well adapted to salinities lower than 20 ‰ (Zardus, 2002).…”