http://www.sciencedirect.com/science/article/pii/S0921818120300151 The Oceanic Anoxic Event 2 (OAE2, ca. 94.6 Ma) is one of the major perturbations in the global carbon cycle 13 δ during the Phanerozoic. Stable carbon isotopes ( C) from marine and continental sedimentary environments document this carbon cycle perturbation with a pronounced (> 2‰) positive carbon isotope excursion (CIE). Although the OAE2 stratigraphic interval has been intensively studied in terms of paleoceanography and paleoclimatology, several climatic and carbon cycle aspects are not yet well-understood. In particular, cyclic 13 δ short-term Milankovitch-scale C variations within the OAE2 and their potential implications for the global 13 δ carbon cycle have been rarely addressed. Here, we present high-resolution (5 cm, ~2 kyr) C data spanning 13 δ the OAE2 from the Paris Basin Chalk (Poigny Craie-701 drill-core) to show high amplitude short-term C oscillations, superimposed on the major CIE. Time-series analysis indicates that short-term oscillations are 13 δ astronomically paced, with eccentricity cycles being the most prominent. Orbital forcing of C variations is further supported by time-series analysis of the English Chalk (Eastbourne section). We suggest that orbitally paced carbon cycle oscillations were amplified by considerable emission of greenhouse gases from volcanism that caused the overall CIE. Astronomical calibration of the whole OAE2 (the perturbation and recovery phases) from the Poigny record provides a duration equivalent to eight to eight and a half short eccentricity cycles. Cyclostratigraphic correlations among several OAE2 key records indicate the same duration of the whole CIE. However, duration of the interval from the onset of CIE till the Cenomanian-Turonian boundary (CTB) is significantly different from one basin to another. In particular, a difference of almost two short eccentricity cycles is highlighted between the Anglo-Paris and Western Interior basins. According to cyclostratigraphic W. devonense approach and correlations, the entry of was at least 200 kyr later in the Western Interior Basin Quadrum gartneri (WIB, USA) than in Europe. Key calcareous nannofossil biohorizons (e.g., ) are also stratigraphically upshifted in the WIB with respect to the European sections, hence concurring with the hypothesis of a younger CTB in the WIB. We ascribe such significant temporal offset to diachroneity of the CTB, which is likely the result of different, regional biotic responses to the global OAE2 paleoenvironmental perturbation.

Bowen, G.J., Fischer-Femal, B., Reichart, G.-J., Sluijs, A., Lear, C.H., 2020. Joint inversion of proxy system models to reconstruct paleoenvironmental time series from heterogeneous data. Climate of the Past 16, 65-78.

https://www.clim-past.net/16/65/2020/ Paleoclimatic and paleoenvironmental reconstructions are fundamentally uncertain because no proxy is a direct record of a single environmental variable of interest; all proxies are indirect and sensitive to multiple forcing factors. One productive approach to reducing proxy uncertainty is the integration of information from multiple proxy systems with complementary, overlapping sensitivity. Mostly, such analyses are conducted in an ad hoc fashion, either through qualitative comparison to assess the similarity of single-proxy reconstructions or through step-wise quantitative interpretations where one proxy is used to constrain a variable relevant to the interpretation of a second proxy. Here we propose the integration of multiple proxies via the joint inversion of proxy system and paleoenvironmental time series models in a Bayesian hierarchical framework. The 'Joint Proxy Inversion' (JPI) method provides a statistically robust approach to producing self -consistent interpretations of multi-proxy datasets, allowing full and simultaneous assessment of all proxy and model uncertainties to obtain quantitative estimates of past environmental conditions. Other benefits of the method include the ability to use independent information on climate and environmental systems to inform the interpretation of proxy data, to fully leverage information from unevenly and differently sampled proxy records, and to obtain refined estimates of proxy model parameters that are conditioned on paleo-archive data. 18 δ Application of JPI to the marine Mg∕Ca and O proxy systems at two distinct timescales demonstrates many of the key properties, benefits, and sensitivities of the method, and it produces new, statistically grounded reconstructions of Neogene ocean temperature and chemistry from previously published data. We suggest that JPI is a universally applicable method that can be implemented using proxy models of wide-ranging complexity to generate more robust, quantitative understanding of past climatic and environmental change.

Bowling, T.J., Johnson, B.C., Marchi, S., De Sanctis, M.C., Castillo-Rogez, J.C., Raymond, C.A., 2020. An endogenic origin of cerean organics. Earth and Planetary Science Letters 534, 116069.