Late Paleocene CO₂ drawdown, climatic cooling, and terrestrial denudation in the southwest Pacific

Late Paleocene deposition of an organic-rich sedimentary facies on the continental shelf and slope of New Zealand and eastern Australia has been linked to short-lived climatic cooling and terrestrial denudation following sea-level fall. Recent studies have confirmed that the organic matter in this facies, termed Waipawa organofacies, is primarily of terrestrial origin, with a minor marine component. It is also unusually enriched in δ13C. In this study we aim to determine the cause or causes of this enrichment. For Waipawa organofacies and its bounding facies in the Taylor White section, Hawkes Bay, paired palynofacies and δ13C analysis of density fractions indicate that the heaviest δ13C values are associated with degraded phytoclasts (woody plant matter) and that the 13C enrichment is partly due to lignin degradation. Compound specific δ13C analyses of samples from the Taylor White and mid-Waipara (Canterbury) sections confirms this relationship but also reveal a residual 13C enrichment of ~ 2.5 ‰ in higher plant biomarkers (n-alkanes and n-alkanoic acids) and 3–4 ‰ in the subordinate marine component, which we interpret as indicating a significant drawdown of atmospheric CO2. Refined age control for Waipawa organofacies indicates that deposition occurred between 59.2 and 58.4 Ma, which coincides with a Paleocene oxygen isotope maximum (POIM) and the onset of the Paleocene carbon isotope maximum (PCIM). This timing suggests that this depositional event was related to global cooling and carbon burial. This relationship is further supported by published TEX86-based sea surface temperatures that indicate a pronounced regional cooling during deposition. We suggest that reduced greenhouse gas emissions from volcanism and accelerated carbon burial related to several tectonic factors and positive feedbacks resulted in short-lived global cooling, growth of ephemeral ice sheets, and a global fall in sea level. Accompanying erosion and carbonate dissolution in deep sea sediment archives may have hidden the evidence of this "hypothermal" event until now.

The potential of Hudson Valley glacial floods to drive abrupt climate change

The periodic input of meltwater into the ocean from a retreating Laurentide Ice Sheet is often hypothesized to have weakened the Atlantic meridional overturning circulation (AMOC) and triggered several cold periods during the last deglaciation (21,000 to 8,000 years before present). Here, we use a numerical model to investigate whether the Intra-Allerød Cold Period was triggered by the drainage of Glacial Lake Iroquois, ~13,300 years ago. Performing a large suite of experiments with various combinations of single and successive, short (1 month) and long (1 year) duration flood events, we were unable to find any significant weakening of the AMOC. This result suggests that although the Hudson Valley floods occurred close to the beginning of the Intra-Allerød Cold Period, they were unlikely the sole cause. Our results have implications for re-evaluating the relationship of meltwater flood events (past and future) to periods of climatic cooling, particularly with regards to flood input location, volume, frequency, and duration.

Carbonate shelf development and early Paleozoic benthic diversity in Baltica: a hierarchical diversity partitioning approach using brachiopod data

The Ordovician–Silurian (~485–419 Ma) was a time of considerable evolutionary upheaval, encompassing both great evolutionary diversification and one of the first major mass extinctions. The Ordovician diversification coincided with global climatic cooling and paleocontinental collision, the ecological impacts of which were mediated by region-specific processes including substrate changes, biotic invasions, and tectonic movements. From the Sandbian–Katian (~453 Ma) onward, an extensive carbonate shelf developed in the eastern Baltic paleobasin in response to a tectonic shift to tropical latitudes and an increase in the abundance of calcareous macroorganisms. We quantify the contributions of environmental differentiation and temporal turnover to regional diversity through the Ordovician and Silurian, using brachiopod occurrences from the more shallow-water facies belts of the eastern Baltic paleobasin, an epicontinental sea on the Baltica paleocontinent. The results are consistent with carbonate shelf development as a driver of Ordovician regional diversification, both by enhancing broadscale differentiation between shallow- and deep-marine environments and by generating heterogeneous carbonate environments that allowed increasing numbers of brachiopod genera to coexist. However, temporal turnover also contributed significantly to apparent regional diversity, particularly in the Middle–Late Ordovician.

Did the Justinianic Plague Truly Reach Frankish Europe around 543 AD?

This article focuses on the episodes of bubonic plague recorded around 543 AD in Frankish Europe which on re-reading appear doubtful. Beginning in 541 and for two centuries, the Justinianic plague ravaged the Mediterranean area over several successive waves. The first mentions concern Egypt; the plague then spreads northward to Constantinople and almost concomitantly or shortly afterward moves westward until it reaches Western Europe. For this last region, the main source is Bishop Gregory of Tours, who in both his historical and his hagiographic writings, provides numerous data on the first outbreaks that raged in Frankish Europe, episodes to which he was a contemporary (even if for the first, he was still in early childhood). According to Gregory, around 543, bubonic plague ravaged several areas under Frankish rule. However, among others, intertextual, contextualized and chronological analyses strongly suggest that these events were in fact fictional. Gregory seems to have wanted to balance during epidemics of plague, the behavior of two bishops of Clermont that were totally opposed. In the episode of 571, when plague struck the episcopal city, the unworthy Bishop Cautinus, to escape disease, had fled the city in cowardice. In the other episode, through the intercession of Gregory's paternal uncle, the virtuous Gallus, the immediate predecessor of Cautinus and that of a saint specific of the paternal branch, the city, including the diocese, was spared from the plague. Other references to similar events in which, through saints, the plague is driven out, or territories are protected from it are also dated arbitrarily from this period. Furthermore, unlike the episode of 571, the plague of 543 is never considered a punishment for sin; moreover, no miraculous healing of plague patients is recorded. Contemporary texts from other authors of Frankish Europe, although they are rare, do not mention any epidemic around 543 - especially the Vita of Caesarius of Arles, written shortly after the death of this bishop (from 542 to 547-9) by several hagiographers - while two of Gregory’s texts, which are repeated almost verbatim, indicate that the province of Arles was the region most affected. This fact underscores the decisive contribution that hagiographic texts can make in the analysis of facts considered to be historical. Finally, the dramatic deteriorations in the health situation described in Gregory’s reports could have a background of truth and be the consequence of the climatic cooling observed from 536, likely due to volcanic eruptions, but did not involve the bubonic plague.

Palaeogenomic analysis of black rat (Rattus rattus) reveals multiple European introductions associated with human economic history

The distribution of the black rat (Rattus rattus) has been heavily influenced by its association with humans. The dispersal history of this non-native commensal rodent across Europe, however, remains poorly understood, and different introductions may have occurred during the Roman and medieval periods. Here, in order to reconstruct the population history of European black rats, we generated a de novo genome assembly of the black rat, 67 ancient black rat mitogenomes and 36 ancient nuclear genomes from sites spanning the 1st-17th centuries CE in Europe and North Africa. Analyses of mitochondrial DNA confirm that black rats were introduced into the Mediterranean and Europe from Southwest Asia. Genomic analyses of the ancient rats reveal a population turnover in temperate Europe between the 6th and 10th centuries CE, coincident with an archaeologically attested decline in the black rat population. The near disappearance and re-emergence of black rats in Europe may have been the result of the breakdown of the Roman Empire, the First Plague Pandemic, and/or post-Roman climatic cooling.

Post-LGM evolution of the Dora Baltea glacial system and paleoclimatic implications in the Western Italian Alps

<p>Alpine glaciers repeatedly advanced and retreated from the high Alps to the forelands during the Quaternary and most recently reached their maximum extent and thickness during the Last Glacial Maximum (LGM, 26.5-19.0 ka ago)<sup> [1]</sup>. After the LGM, glaciers abandoned the Alpine foreland and retreated within the internal valleys. However, post-LGM withdrawal was not continuous but interrupted by stages of ice stasis or re-advance (stadials<sup> [2]</sup>), related to episodes of temporary climatic cooling. Glacial landforms and deposits associated to post-LGM ice stadials have been recognised across the Alps <sup>[2]</sup>. Our study contributes to this line of research by quantitatively reconstructing the age and configuration of several ice stages from the LGM to the Holocene, within the Dora Baltea (DB) catchment (SW Alps, Italy).</p><p>Following a detailed geomorphological mapping of glacial landforms and deposits, sixteen erratic boulders and two glacially-polished bedrocks were sampled along the DB valley for <em>in-situ</em><sup><em> </em>10</sup>Be surface-exposure dating, and five samples for luminescence dating were collected from fluvio-lacustrine and fluvio-glacial deposits. The obtained chronologies, combined with recalculated <sup>10</sup>Be surface-exposure ages from previous works in the study area <sup>[1, 3, 4, 5]</sup>, constrain seven post-LGM ice stages in the DB valley. The first three retreat stages occurred between the end of the LGM and the early Lateglacial, probably with rapid ice decay. The following three stages correspond to the well-known Gschnitz, Daun and Egesen Alpine Lateglacial stadials <sup>[2]</sup>, while we also identified a late-Holocene ice re-advance in the upstream DB catchment.</p><p>Paleo-ice configurations of each stage (including the LGM) were obtained with a semi-automatic ArcGIS routine (similar approach to GlaRe ArcGIS toolbox <sup>[6]</sup>), based on the areal interpolation of 2D ice surface profiles generated through Profiler v.2 <sup>[7]</sup>. Glacier equilibrium-line altitudes (ELAs) were computed for the eight 3D ice surface reconstructions <sup>[8]</sup>, with the aim of deriving potential paleoclimatic implications of the different reconstructed ice stages in comparison to other paleoclimatic proxies.</p><p> </p><p><strong>References</strong></p><p><sup>[1] </sup>Wirsig, C. et al., 2016, Quaternary Science Reviews.</p><p><sup>[2] </sup>Ivy-ochs, S., 2015, Cuadernos de Investigación Geográfica.</p><p><sup>[3] </sup>Gianotti, F. et al., 2015, Alpine and Mediterranean Quaternary.</p><p><sup>[4] </sup>Deline, P. et al., 2015, Quaternary Science Reviews.</p><p><sup>[5] </sup>Le Roy, M., 2012. Université Grenoble Alpes.</p><p><sup>[6] </sup>Pellitero, R. et al., 2016, Computers and Geosciences.</p><p><sup>[7] </sup>Benn, D., Hulton, N., 2010, Quaternary Science Reviews.</p><p><sup>[8] </sup>Pellitero, R. et al., 2015, Computers and Geosciences.</p>