A community-based geological reconstruction of Antarctic Ice Sheet deglaciation since the Last Glacial Maximum

A robust understanding of Antarctic Ice Sheet deglacial history since the Last Glacial Maximum is important in order to constrain ice sheet and glacial-isostatic adjustment models, and to explore the forcing mechanisms responsible for ice sheet retreat. Such understanding can be derived from a broad range of geological and glaciological datasets and recent decades have seen an upsurge in such data gathering around the continent and Sub-Antarctic islands. Here, we report a new synthesis of those datasets, based on an accompanying series of reviews of the geological data, organised by sector. We present a series of timeslice maps for 20ka, 15ka, 10ka and 5ka, including grounding line position and ice sheet thickness changes, along with a clear assessment of levels of confidence. The reconstruction shows that the Antarctic Ice sheet did not everywhere reach the continental shelf edge at its maximum, that initial retreat was asynchronous, and that the spatial pattern of deglaciation was highly variable, particularly on the inner shelf. The deglacial reconstruction is consistent with a moderate overall excess ice volume and with a relatively small Antarctic contribution to meltwater pulse 1a. We discuss key areas of uncertainty both around the continent and by time interval, and we highlight potential priorit. © 2014 The Authors

Comparison of the GC content of the cultivation-only sequences with the overall values.

a<p>Sequences from cultivation that were not picked up by pyrosequencing.</p

Bar chart illustrating the number of OTUs picked up from one or more samples for the forward dataset.

<p>The number of OTUs is log₂ transformed. Blue bars, total sequences (pyrosequences plus cultivated sequences); red bars, pyrosequences only; green bars, cultivation sequences only.</p

Overview of the distribution of the phyla per sample for the forward sequencing dataset.

<p>Circle area is a log₂ transformation of the number of sequences ([log₂(N)*5/PI], with N the number of sequences in that phylum). Color intensity reflects the number of OTUs per phylum (total OTUs/total sequences), with a darker hue indicating a higher relative richness. The first two columns show the total number of sequences and diversity of each phylum for pyrosequencing and cultivation separately. The phyla are ordered according to decreasing total number of sequences. The yellow to red scale shows pyrosequencing data, the blue-purple scale the cultivation data.</p

Appendix E. Results of the variation partitioning analyses.

Results of the variation partitioning analyses

Appendix F. Figures showing the response of local diatom richness to the available chemical, morphological, and historical variables.

Figures showing the response of local diatom richness to the available chemical, morphological, and historical variables

Appendix D. A figure showing the interhemispheric asymmetry in local intercalibrated genus richness in 1855 freshwater lakes.

A figure showing the interhemispheric asymmetry in local intercalibrated genus richness in 1855 freshwater lakes

Appendix B. The diatom genera encountered in this study.

The diatom genera encountered in this study

Appendix A. References to the source data used to construct the intercalibrated diatom data set.

References to the source data used to construct the intercalibrated diatom data set