Shell chemistry of the boreal Campanian bivalve <i>Rastellum diluvianum</i> (Linnaeus, 1767) reveals temperature seasonality, growth rates and life cycle of an extinct Cretaceous oyster

Abstract

Abstract. The Campanian age (Late Cretaceous) is characterized by a warm greenhouse climate with limited land-ice volume. This makes this period an ideal target for studying climate dynamics during greenhouse periods, which are essential for predictions of future climate change due to anthropogenic greenhouse gas emissions. Well-preserved fossil shells from the Campanian (±78 Ma) high mid-latitude (50∘ N) coastal faunas of the Kristianstad Basin (southern Sweden) offer a unique snapshot of short-term climate and environmental variability, which complements existing long-term climate reconstructions. In this study, we apply a combination of high-resolution spatially resolved trace element analyses (micro-X-ray fluorescence – µXRF – and laser ablation inductively coupled plasma mass spectrometry – LA-ICP-MS), stable isotope analyses (IRMS) and growth modeling to study short-term (seasonal) variations recorded in the oyster species Rastellum diluvianum from the Ivö Klack locality. Geochemical records through 12 specimens shed light on the influence of specimen-specific and ontogenetic effects on the expression of seasonal variations in shell chemistry and allow disentangling vital effects from environmental influences in an effort to refine paleoseasonality reconstructions of Late Cretaceous greenhouse climates. Growth models based on stable oxygen isotope records yield information on the mode of life, circadian rhythm and reproductive cycle of these extinct oysters. This multi-proxy study reveals that mean annual temperatures in the Campanian higher mid-latitudes were 17 to 19 ∘C, with winter minima of ∼13 ∘C and summer maxima of 26 ∘C, assuming a Late Cretaceous seawater oxygen isotope composition of −1 ‰ VSMOW (Vienna standard mean ocean water). These results yield smaller latitudinal differences in temperature seasonality in the Campanian compared to today. Latitudinal temperature gradients were similar to the present, contrasting with previous notions of “equable climate” during the Late Cretaceous. Our results also demonstrate that species-specific differences and uncertainties in the composition of Late Cretaceous seawater prevent trace element proxies (Mg∕Ca, Sr∕Ca, Mg∕Li and Sr∕Li) from being used as reliable temperature proxies for fossil oyster shells. However, trace element profiles can serve as a quick tool for diagenesis screening and investigating seasonal growth patterns in ancient shells.

First absolute seasonal temperature estimates for greenhouse climate from clumped isotopes in bivalve shells

“…Trace element (e.g. Sr/Ca and Mn/Ca) patterns and ultrastructure preservation demonstrate excellent preservation of primary calcite 23,39 (Supplementary Methods).…”

“…The three distinct localities contain a rich (> 200 species), well preserved Campanian rocky shore fauna 24,34 and were all deposited at the peak of transgression of the latest early Campanian, as supported by the restriction of these deposits to the Belemnellocamax mammillatus belemnite biozone and Sr-isotope chemostratigraphy 23,34,38 . The tectonic quiescence of the region since the Late Cretaceous limited burial and promoted excellent shell preservation 24 .…”

“…For the δ 18 Oc compositions we applied an acid correction factor of 1.00871 17 and reported versus VPDB with a typical reproducibility below 0.08‰ (95% confidence level). Results were combined with δ 18 Oc data previously measured in the same shells 23,39 ( Supplementary Data 2) to improve the confidence of seasonal age models and the temporal resolution of SST and δ Osw reconstructions.…”

Optimizing sampling strategies in high-resolution paleoclimate records

“…Combining multiple strontium isotope analyses from the same stratigraphic unit can reduce the uncertainty on these composite ages (Korte and Ullmann, 2016;de Winter et al, 2020b), allowing the dating method to be combined with cyclostratigraphy to produce for orbital scale age models (see 5.4.2). In stratigraphy studies that use this dating method, the need arises to compromise between the resolution of the age model and the precision and accuracy of dating, analogous to the tradeoff that occurs when combining Δ47 analyses for paleoseasonality reconstructions outlined in this study.…”

First absolute seasonal temperature estimates for greenhouse climate from clumped isotopes in bivalve shells

“…Here we use clumped isotope analyses on microsampled (~100 µg) profiles through fossil bivalve shells to obtain, for the first time, absolute SST and δ 18 Osw seasonality reconstructions of a greenhouse climate. We apply this new method on well-preserved oyster (Rastellum diluvianum and Acutostrea incurva) and rudist (Biradiolites suecicus) shells from Campanian (78.1±0.3 Ma 26 ) coastal localities of the Kristianstad Basin in southern Sweden (46±3°N paleolatitude 27 ; see Fig. 1 and METHODS).…”