Response of the Great Barrier Reef to sea level and environmental changes over the past 30,000 yearsCitation for published version:

Traditional approaches to age‐depth modeling typically assume no uncertainty for the depth value of dated intervals. However, such an assumption may not be fully valid in the case of poor coring recovery or significant sediment deformation, as well as in the case of a large subsampling interval. In consideration of these issues, we present a new age‐depth modeling routine, Undatable, which includes uncertainty in both age and depth. Undatable uses Bayesian radiocarbon (14C) calibration software (MatCal) and a deterministic approach with a positive sediment accumulation rate assumed a priori which, combined with efficient programming practices, allows for the rapid production (in a matter of seconds in many cases) of age‐depth models for multiple types of geological archives. Undatable has so far been successfully applied to coral archives, as well as sediment archives from estuarine, lacustrine, and deep‐sea environments. Through the inclusion of a bootstrapping option, the software performs particularly well in the case of a large scatter in age‐depth constraints by expanding the uncertainty envelope of the age‐depth model. Unlike other deterministic models, increasing the density of age‐depth constraints results in increased precision in Undatable, even at centennial scale, thus emulating the results of probabilistic models. In addition to the code itself, we also provide an interactive graphical user interface (GUI) that allows users to experiment with multiple age‐depth model settings to investigate the sensitivity of a given data set to multiple parameters.

The matcal function provides radiocarbon (14 C) age calibration in Matlab using the Bayesian highest posterior density (HPD). The function produces a probability distribution function (PDF) of calibrated ages, as well as 1 sigma (68.27%) and 2 sigma (95.45%) probability calibrated age credible intervals, calculated using HPD. Publication ready calibration plots are also produced, with the option to save to disk. Calibration output can be in either Cal BP or BCE/CE (BC/AD), and a reservoir age can be specified if necessary. The user can choose from a number of calibration curves, including the latest version of IntCal.

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2016-12-23T18:47:23

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The Late Pliocene epoch is a potential analogue for future climate in a warming world. Here we reconstruct Plio-Pleistocene East Antarctic Ice Sheet (EAIS) variability using cosmogenic nuclide exposure ages and model simulations to better understand ice sheet behaviour under such warm conditions. New and previously published exposure ages indicate interior-thickening during the Pliocene. An ice sheet model with mid-Pliocene boundary conditions also results in interior thickening and suggests that both the Wilkes Subglacial and Aurora Basins largely melted, offsetting increased ice volume. Considering contributions from West Antarctica and Greenland, this is consistent with the most recent IPCC AR5 estimate, which indicates that the Pliocene sea level likely did not exceed +20 m on Milankovitch timescales. The inception of colder climate since ∼3 Myr has increased the sea ice cover and inhibited active moisture transport to Antarctica, resulting in reduced ice sheet thickness, at least in coastal areas.

Stable global temperatures of the last 10-15 years have been a topic of considerable discussion. A new proxy extension of the global temperature record enables better placement of this feature in a longer historical perspective. The fixed-grid composite covers the interval 1801-1984, with an extension to 1782, and anchors the global temperature record in the last major cold interval of the Little Ice Age, when carbon dioxide concentration was at preanthropogenic levels. Except for greater and longer cooling (approximately twice the length of Pinatubo) associated with the Tambora eruption, the proxy agrees with the most widely cited previous assessment of global temperature over this interval, lending more confidence to a centennial extension of the global temperature record. The proxy correlation is as high as 0.83 for the interval 1907-1984 (df = 8, p = 0.001), with the 21st century 1.0 ∘ C ± 0.2 ∘ C warmer than the nonvolcanic base state. This remarkable linearity requires a clear theoretical understanding as to how an exceedingly complex system can, on the global average, behave in such a simple way. Removal of the linear radiatively forced component from the global temperature record yields an estimate of natural variability for the last 230 years and indicates no unusual natural variability during the recent 10-15 years. Based on the estimate of unforced variability over the last 170 years, there is about a 40% chance of continued "natural cooling" over the next few years, with about a 10% chance of cooling persisting into the next decade.