Revised Postglacial Sea-Level Rise and Meltwater Pulses from Barbados

Paul Blanchon,Alexis Medina-Valmaseda,Fiona D Hibbert

doi:10.5334/oq.87

Paul Blanchon, Alexis Medina-Valmaseda + Show 1 more

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https://doi.org/10.5334/oq.87

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Abstract

Reconstructions of postglacial sea-level rise have provided key insight into the rapid disintegration of ice-sheets and the discharge of large meltwater pulses during the last deglaciation. The most complete reconstruction is from Barbados where thick, backstepping sequences of the reef-crest coral <em>Acropora palmata</em> have been recovered in cores from the insular shelf and slope off the Island’s south coast. Differences in the depth, timing, and magnitude of meltwater pulses between the Barbados reconstruction and other reefal records, however, has led to significant uncertainty in their origin, and the consequent timing of ice-sheet collapse. Here we re-analyse the published sedimentary, stratigraphic, and chronological data from Barbados, and find evidence for <em>ex-situ</em> data which indicates that reefal sequences contain coral clasts generated during hurricanes. By adjusting for biases caused by these ex-situ data, we provide a revised sea-level reconstruction which shows that MWP-1b was an 8–11 m rise from –53 m in ~250 years starting at 11.3 ka, which is 5 m smaller, and 150 years younger than previous estimates. It also shows that the onset of MWP-1a cannot be determined at Barbados because the downslope core sequences are not reef-crest deposits due to their association with deeper coral assemblages and lack of depositional relief. The end of this meltwater pulse can however be determined from the upslope reef, and occurred at a similar time and depth to that documented from Tahiti.

Highlights

Postglacial reconstructions of sea level (SL) derived from submerged sequences of drowned coral-reefs have provided key insight into the timing and nature of ice-loss during the last glacial termination (Fairbanks 1989; Bard et al 1990; Blanchon and Shaw 1995; Bard et al 2010; Deschamps et al 2012; Abdul et al 2016)
Coral ages in Acropora palmata (Ap) units above and below these gaps indicated that the first pulse, Meltwater Pulses (MWP)-1a, was a 19 m jump from –93 m in 450 years starting at 14.1 ka, and the second, MWP-1b, was a 14 m jump from –56 m in 300 years starting at 11.4 ka (Bard et al 1990; Peltier and Fairbanks 2006)
Our re-analysis of the published stratigraphy and facies data in Ap sequences from the Barbados cores shows that stratigraphically inverted ages are common in all Ap units dated at a sub-metre resolution, these ages have a vertical and horizontal spread that is inconsistent with those of in-situ assemblages, and Ap units in cores from the slope have no depositional relief and are associated with deeper coral assemblages

Summary

Introduction

Postglacial reconstructions of sea level (SL) derived from submerged sequences of drowned coral-reefs have provided key insight into the timing and nature of ice-loss during the last glacial termination (Fairbanks 1989; Bard et al 1990; Blanchon and Shaw 1995; Bard et al 2010; Deschamps et al 2012; Abdul et al 2016). Using only the age-depth data from these corals, and correcting them for tectonic uplift, he reconstructed SL rise during the last deglaciation and identified two “exceedingly rapid” rise events separated by a period of reduced melting. He suggested that the rapid-rises corresponded to intense pulses of seasonal melt-water discharge during the disintegration of Northern Hemisphere ice-sheets, and termed them Meltwater Pulses (MWP). Subsequent drilling and further sampling of the existing cores has recently supported the timing and magnitude of MWP-1b on Barbados (Abdul et al 2016)

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