Supplemental Material: Enhanced precipitation in the Gulf of Mexico during the Eocene–Oligocene transition driven by interhemispherical temperature asymmetry

Table S1: Leaf wax isotopic records in the Gulf of Mexico; Table S2: Reconstructions of mean annual precipitation based on leaf wax carbon isotopic records; Table S3: Sea surface temperature reconstructions; Table S4: Leaf wax isotopic records of modern trees.

Supplemental Material: Enhanced precipitation in the Gulf of Mexico during the Eocene–Oligocene transition driven by interhemispherical temperature asymmetry

Table S1: Leaf wax isotopic records in the Gulf of Mexico; Table S2: Reconstructions of mean annual precipitation based on leaf wax carbon isotopic records; Table S3: Sea surface temperature reconstructions; Table S4: Leaf wax isotopic records of modern trees.

Long-term Aptian marine osmium isotopic record of Ontong Java Nui activity

The early to mid-Aptian was punctuated by episodic phases of organic-carbon burial in various oceanographic settings, which are possibly related to massive volcanism associated with the emplacement of the Ontong Java, Manihiki, and Hikurangi oceanic plateaus in the southwestern Pacific Ocean, inferred to have formed a single plateau called Ontong Java Nui. Sedimentary osmium (Os) isotopic compositions are one of the best proxies for determining the timing of voluminous submarine volcanic episodes. However, available Os isotopic records during the age are limited to a narrow interval in the earliest Aptian, which is insufficient for the reconstruction of long-term hydrothermal activity. We document the early to mid-Aptian Os isotopic record using pelagic Tethyan sediments deposited in the Poggio le Guaine (Umbria-Marche Basin, Italy) to precisely constrain the timing of massive volcanic episodes and to assess their impact on the marine environment. Our new Os isotopic data reveal three shifts to unradiogenic values, two of which correspond to black shale horizons in the lower to mid-Aptian, namely the Wezel (herein named) and Fallot Levels. These Os isotopic excursions are ascribed to massive inputs of unradiogenic Os to the ocean through hydrothermal activity. Combining the new Os isotopic record with published data from the lowermost Aptian organic-rich interval in the Gorgo a Cerbara section of the Umbria-Marche Basin, it can be inferred that Ontong Java Nui volcanic eruptions persisted for ~5 m.y. during the early to mid-Aptian.

Magnetostratigraphic evidence for post-depositional distortion of osmium isotopic records in pelagic clay: implications for mineral flux estimates

<p>Deep-sea sediment sometimes lacks biostratigraphic or radiometric age constraints. Chemical stratigraphy and magnetostratigraphy is useful for dating it. Oxic pelagic clay contains Fe-Mn oxyhydroxides that can retain seawater <sup>187</sup>Os/<sup>188</sup>Os values, and its age can be estimated by fitting the isotopic ratios to the seawater <sup>187</sup>Os/<sup>188</sup>Os curve. On the other hand, the stability of Fe-Mn oxyhydroxides is sensitive to redox change, and it is not clear whether the original <sup>187</sup>Os/<sup>188</sup>Os values are always preserved in sediments. However, due to the lack of independent age constraints, the reliability of <sup>187</sup>Os/<sup>188</sup>Os ages of pelagic clay have never been tested. Magnetostratigraphy is often unsuccessful for pelagic clay older than a few Ma, which has been attributed to diagenesis. Here we report multiple polarity reversals in ca. 35 Ma pelagic clay around Minamitorishima Island, which is inconsistent with a <sup>187</sup>Os/<sup>188</sup>Os age model. In a ~5 m thick interval, previous studies correlated <sup>187</sup>Os/<sup>188</sup>Os data to a brief (<1 million years) isotopic excursion in the late Eocene. Paleomagnetic measurements revealed at least 12 polarity zones in the interval, indicating a >2.9 – 6.9 million years duration. Quartz and feldspars content showed that while the paleomagnetic chronology gives reasonable eolian flux estimates, the <sup>187</sup>Os/<sup>188</sup>Os chronology leads unrealistically high values. These results suggest that the low <sup>187</sup>Os/<sup>188</sup>Os signal has diffused from an original thin layer to the current ~5 m interval, causing an underestimate of the deposition duration. The preservation of the polarity patterns indicates that a mechanical mixing such as bioturbation cannot be the main process for the diffusion, so diagenetic re-distribution of Fe-Mn oxyhydroxides and associated Os may be responsible. The paleomagnetic chronology presented here also demands reconsiderations of the timing, accumulation rate, and origins of the high content of rare-earth elements and yttrium in pelagic clay around Minamitorishima Island. It is also indicated that old oxic pelagic clay can be a faithful paleomagnetic recorder, and success of magnetostratigraphy depends on sedimentation rate and polarity length rather than diagenesis.</p><p>Usui, Y., Yamazaki, T. <em>Earth Planets Space</em> <strong>73, </strong>2 (2021). https://doi.org/10.1186/s40623-020-01338-4</p>

How Can Climate Models Be Used in Paleoelevation Reconstructions?

Paleoelevation reconstructions derived from proxy data such as stable oxygen isotope records in terrestrial archives have been determined for Cenozoic mountain ranges around the world. Recent studies have highlighted that a variety of paleoclimate processes can contribute to the isotopic composition of a measured precipitation (δ18Op) signal used in elevation reconstructions. These processes can include: regional, global, and topographic variations in paleotemperature; environmental conditions of an air mass before orographic ascent; evapotranspiration; water vapor recycling; and changes in the vapor source. In some cases, these processes can overprint the elevation signal sought in proxy data and preclude robust elevation reconstructions. Recent advances in isotope tracking climate models allow us to estimate paleoclimate changes during orogen development and associated changes in paleo δ18Op due to both climate and topographic changes. These models account for adiabatic and non-adiabatic temperature changes, relative humidity variations, changing continental evapotranspiration, vapor recycling, vapor source changes, etc. Modeling strategies using high-resolution isotopes-enabled General Circulation Models (iGCMs) together with time-specific boundary conditions and variable topography provide a powerful tool for enhancing elevation reconstructions from δ18Op proxy data. In this review, we discuss the principles, benefits and caveats of using iGCMs for interpreting isotopic records from natural archives for paleoelevation reconstructions. We also highlight future challenges for the application of iGCMs to paleoaltimetry proxy data that open up new avenues for research on tectonic-climate interactions.

Late Pleistocene palaeoecology and phylogeography of woolly rhinoceroses

The woolly rhinoceros (Coelodonta antiquitatis) was a cold-adapted herbivore, widely distributed from western Europe to north-east Siberia during the Late Pleistocene. Previous studies associate the extinction of the species ~14,000 years before present to climatic and vegetational changes, and suggest that later survival of populations in north-east Siberia may relate to the later persistence of open vegetation in that region. Here, we analyzed carbon (δ13C) and nitrogen (δ15N) stable isotopes and mitochondrial DNA sequences to elucidate the evolutionary ecology of the species. Our dataset comprised 286 woolly rhinoceros isotopic records, including 192 unpublished records, from across the species range, dating from >58,600 14C years to ~14,000 years before present. Crucially, we present the first 71 isotopic records available to date of the 15,000 years preceding woolly rhinoceros extinction. The data reveal ecological flexibility and geographical variation in woolly rhinoceros stable isotope compositions through time. In north-east Siberia, we detected δ15N stability through time. This could reflect long-term environmental stability, and might have enabled the later survival of the species in the region. To further investigate the palaeoecology of woolly rhinoceroses, we compared their isotopic compositions with that of other contemporary herbivores. This analysis suggests possible niche partitioning between woolly rhinoceros and both horse (Equus spp.) and woolly mammoth (Mammuthus primigenius), and isotopic similarities between woolly rhinoceros and both musk ox (Ovibos moschatus) and saiga (Saiga tatarica) at different points in time. To provide phylogeographical context to the isotopic data, we analyzed 61 published mitochondrial control region sequences. The data show a lack of geographic structuring; we found three haplogroups with overlapping distributions, all of which show a signal of expansion during the Last Glacial Maximum. Furthermore, our genetic findings support the notion that environmental stability in Siberia had an impact on the paleoecology of woolly rhinoceroses in the region. Our study highlights the utility of combining stable isotopic records with ancient DNA to advance our knowledge of the evolutionary ecology of past populations and extinct species.

Magnetostratigraphic evidence for post-depositional distortion of osmium isotopic records in pelagic clay and its implications for mineral flux estimates

Chemical stratigraphy is useful for dating deep-sea sediments, which sometimes lack radiometric or biostratigraphic constraints. Oxic pelagic clay contains Fe–Mn oxyhydroxides that can retain seawater 187Os/188Os values, and its age can be estimated by fitting the isotopic ratios to the seawater 187Os/188Os curve. On the other hand, the stability of Fe–Mn oxyhydroxides is sensitive to redox change, and it is not clear whether the original 187Os/188Os values are always preserved in sediments. However, due to the lack of independent age constraints, the reliability of 187Os/188Os ages of pelagic clay has never been tested. Here we report inconsistency between magnetostratigraphic and 187Os/188Os ages in pelagic clay around Minamitorishima Island. In a ~ 5-m-thick interval, previous studies correlated 187Os/188Os data to a brief (< 1 million years) isotopic excursion in the late Eocene. Paleomagnetic measurements revealed at least 12 polarity zones in the interval, indicating a > 2.9–6.9 million years duration. Quartz and feldspars content showed that while the paleomagnetic chronology gives reasonable eolian flux estimates, the 187Os/188Os chronology leads to unrealistically high values. These results suggest that the low 187Os/188Os signal has diffused from an original thin layer to the current ~ 5-m interval, causing an underestimate of the deposition duration. The preservation of the polarity patterns indicates that a mechanical mixing such as bioturbation cannot be the main process for the diffusion, so diagenetic redistribution of Fe–Mn oxyhydroxides and associated Os may be responsible. The paleomagnetic chronology presented here also demands reconsiderations of the timing, accumulation rate, and origins of the high content of rare-earth elements and yttrium in pelagic clay around Minamitorishima Island.