Additional co-authors: TJ Heaton, AG Hogg, KA Hughen, KF Kaiser, B Kromer, SW Manning, RW Reimer, DA Richards, JR Southon, S Talamo, CSM Turney, J van der Plicht, CE Weyhenmeyer

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IntCal13 and Marine13 radiocarbon age calibration curves 0-50,000 years cal BP

[1] We present a 53-Myr stack (the “LR04” stack) of benthic δ18O records from 57 globally distributed sites aligned by an automated graphic correlation algorithm This is the first benthic δ18O stack composed of more than three records to extend beyond 850 ka, and we use its improved signal quality to identify 24 new marine isotope stages in the early Pliocene We also present a new LR04 age model for the Pliocene-Pleistocene derived from tuning the δ18O stack to a simple ice model based on 21 June insolation at 65°N Stacked sedimentation rates provide additional age model constraints to prevent overtuning Despite a conservative tuning strategy, the LR04 benthic stack exhibits significant coherency with insolation in the obliquity band throughout the entire 53 Myr and in the precession band for more than half of the record The LR04 stack contains significantly more variance in benthic δ18O than previously published stacks of the late Pleistocene as the result of higher-resolution records, a better alignment technique, and a greater percentage of records from the Atlantic Finally, the relative phases of the stack's 41- and 23-kyr components suggest that the precession component of δ18O from 27–16 Ma is primarily a deep-water temperature signal and that the phase of δ18O precession response changed suddenly at 16 Ma

/pdf/a-pliocene-pleistocene-stack-of-57-globally-distributed-n5iphe7mt2.pdf

A Pliocene-Pleistocene stack of 57 globally distributed benthic δ18O records

Atmospheric carbon dioxide concentration is expected to exceed 500 parts per million and global temperatures to rise by at least 2 degrees C by 2050 to 2100, values that significantly exceed those of at least the past 420,000 years during which most extant marine organisms evolved. Under conditions expected in the 21st century, global warming and ocean acidification will compromise carbonate accretion, with corals becoming increasingly rare on reef systems. The result will be less diverse reef communities and carbonate reef structures that fail to be maintained. Climate change also exacerbates local stresses from declining water quality and overexploitation of key species, driving reefs increasingly toward the tipping point for functional collapse. This review presents future scenarios for coral reefs that predict increasingly serious consequences for reef-associated fisheries, tourism, coastal protection, and people. As the International Year of the Reef 2008 begins, scaled-up management intervention and decisive action on global emissions are required if the loss of coral-dominated ecosystems is to be avoided.

/pdf/coral-reefs-under-rapid-climate-change-and-ocean-398ioolbkj.pdf

Coral Reefs Under Rapid Climate Change and Ocean Acidification

Radiocarbon (14C) ages cannot provide absolutely dated chronologies for archaeological or paleoenvironmental studies directly but must be converted to calendar age equivalents using a calibration curve compensating for fluctuations in atmospheric 14C concentration. Although calibration curves are constructed from independently dated archives, they invariably require revision as new data become available and our understanding of the Earth system improves. In this volume the international 14C calibration curves for both the Northern and Southern Hemispheres, as well as for the ocean surface layer, have been updated to include a wealth of new data and extended to 55,000 cal BP. Based on tree rings, IntCal20 now extends as a fully atmospheric record to ca. 13,900 cal BP. For the older part of the timescale, IntCal20 comprises statistically integrated evidence from floating tree-ring chronologies, lacustrine and marine sediments, speleothems, and corals. We utilized improved evaluation of the timescales and location variable 14C offsets from the atmosphere (reservoir age, dead carbon fraction) for each dataset. New statistical methods have refined the structure of the calibration curves while maintaining a robust treatment of uncertainties in the 14C ages, the calendar ages and other corrections. The inclusion of modeled marine reservoir ages derived from a three-dimensional ocean circulation model has allowed us to apply more appropriate reservoir corrections to the marine 14C data rather than the previous use of constant regional offsets from the atmosphere. Here we provide an overview of the new and revised datasets and the associated methods used for the construction of the IntCal20 curve and explore potential regional offsets for tree-ring data. We discuss the main differences with respect to the previous calibration curve, IntCal13, and some of the implications for archaeology and geosciences ranging from the recent past to the time of the extinction of the Neanderthals.

https://dspace.stir.ac.uk/bitstream/1893/30981/1/intcal20_northern_hemisphere_radiocarbon_age_calibration_curve_055_cal_kbp.pdf

The IntCal20 Northern Hemisphere Radiocarbon Age Calibration Curve (0-55 cal kBP)

We used 5704 14C, 10Be, and 3He ages that span the interval from 10,000 to 50,000 years ago (10 to 50 ka) to constrain the timing of the Last Glacial Maximum (LGM) in terms of global ice-sheet and mountain-glacier extent. Growth of the ice sheets to their maximum positions occurred between 33.0 and 26.5 ka in response to climate forcing from decreases in northern summer insolation, tropical Pacific sea surface temperatures, and atmospheric CO2. Nearly all ice sheets were at their LGM positions from 26.5 ka to 19 to 20 ka, corresponding to minima in these forcings. The onset of Northern Hemisphere deglaciation 19 to 20 ka was induced by an increase in northern summer insolation, providing the source for an abrupt rise in sea level. The onset of deglaciation of the West Antarctic Ice Sheet occurred between 14 and 15 ka, consistent with evidence that this was the primary source for an abrupt rise in sea level ~14.5 ka.

https://science.sciencemag.org/content/sci/325/5941/710.full.pdf

The Last Glacial Maximum.

Climate dependent contrast in surface mass balance in East Antarctica over the past 216 kyr

/pdf/dating-and-synchronizing-paleoclimatic-records-over-thelast-4ecldmpn9d.pdf

Dating and synchronizing paleoclimatic records over thelast interglacial

Les forages polaires fournissent des archives exceptionnelles des conditions climatiques et environnementales passees. Produire une datation robuste des carottes de glace ainsi qu’une estimation de l’incertitude associee est essentiel pour interpreter les enregistrements climatiques et environnementaux qu’elles contiennent. Cependant, c’est une tâche complexe car elle implique d’utiliser differentes methodes. Dans cet article, nous presentons IceChrono1, un modele probabiliste qui combine differentes sources d’information chronologique pour produire une datation commune et optimale pour plusieurs carottes de glace, ainsi qu’une estimation de l’incertitude associee. IceChrono1 est base sur l’inference de trois quantites : le taux d’accumulation de neige en surface, la profondeur de piegeage de l’air et la fonction d’amincissement. IceChrono1 integre de multiples informations chronologiques : un scenario modelise du processus de sedimentation (accumulation de la neige, densification de la neige en glace et piegeage de l’air, ecoulement de la glace), des horizons bien dates pour contraindre l’âge de la glace ou l’âge de l’air, des intervalles de profondeur definis sur la glace ou via des mesures sur l’air piege dont la duree est connue, des observations du delta profondeur (le decalage en profondeur entre des evenements synchrones enregistres dans la glace et dans l’air) et finalement des liens stratigraphiques reliant des marqueurs identifies dans la glace, dans l’air piege ou dans les deux a la fois entre les carottes de glace. L’inference est formulee comme un probleme d’optimisation aux moindres carres, impliquant que toutes les densites de probabilites sont supposees gaussiennes. Elle est resolue numeriquement en utilisant l’algorithme de Levenberg-Marquardt (supposant ainsi que le modele est presque lineaire au voisinage de la solution) et une evaluation numerique du Jacobien du modele. IceChrono1 est librement disponible sous la licence libre GPL v3 (General Public License v3).

/pdf/icechrono1-un-modele-probabiliste-pour-calculer-une-3c6gjg808t.pdf

Icechrono1 : un modèle probabiliste pour calculer une chronologie commune et optimale pour plusieurs carottes de glace

The presence of ice as old as 1.5 Ma is very likely southwest of Dome C, where a bedrock relief high makes the ice thin enough to prevent basal melting. Three-dimensional ice flow modelling is required to ensure that the basal ice is old enough above the bedrock, and that the age resolution of the ice archive is sufficient. A 3D ice flow simulation is led to calculate selection criteria that together locate patches of ice with likely old, well-resolved, undisturbed and datable ice. These patches on the flanks of the bed relief are a balance trade-off between risks of basal melting and sufficient age resolution. The trajectories of the ice particles towards these sites are short and the ice flows over a smoothly undulating bed. Several precise locations of potential 1.5 Ma-old ice are proposed, to nourish the collective thinking on the precise location of a future drill site.

/pdf/brief-communication-oldest-ice-patches-diagnosed37-km-37ifhz6kbv.pdf

Frédéric Parrenin

Papers

Climate dependent contrast in surface mass balance in East Antarctica over the past 216 kyr

Dating and synchronizing paleoclimatic records over thelast interglacial

Icechrono1 : un modèle probabiliste pour calculer une chronologie commune et optimale pour plusieurs carottes de glace

Brief communication: "Oldest Ice" patches diagnosed37 km southwest of Dome C, East Antarctica

On the availability of old meteoric ice in the vicinity of Dome B, East Antarctica