Reconstructing Holocene conditions under the McMurdo Ice Shelf using Antarctic barnacle shells

• Published in: Earth and Planetary Science Letters
• Main Authors: Burgess, SN, Henderson, G, Hall, B
• Format: Article in Journal/Newspaper
• Language: English
• Published: 2016
• Subjects: Antarctic; McMurdo Ice Shelf; McMurdo Sound; Ross Sea; The Antarctic; Antarc*; Ice Shelf; Ice Shelves
• Online Access: https://doi.org/10.1016/j.epsl.2010.08.015; https://ora.ox.ac.uk/objects/uuid:ee492a20-1c4b-4093-b47e-51da9be71513

This study evaluates the potential of barnacles for paleoceanographic reconstruction and, in particular, of the Antarctic species Bathylasma corolliforme to reconstruct past conditions under ice shelves. Like other barnacle species, this Antarctic barnacle secretes a robust low-Mg calcite shell with distinct growth increments on the external surface indicating growth over a number of years (30-50 in samples studied here). The Bathylasma samples used in this study grew in the Ross Sea and became entrained at the grounding line of a coastal ice shelf in McMurdo Sound, offering potential as an archive of changing conditions in this difficult to access environment under the McMurdo ice shelf. Nine barnacle shells were subsampled at high resolution (60μm) for δ18O and δ13C analysis. These samples were dated with 14C and U-Th techniques, although the later did not yield useful age information due to open-system behaviour of barnacle calcite. Measured δ18O values indicate that Bathylasma calcifies close to equilibrium with ambient seawater. One older sample (≈200ka) has similar δ18O and δ13C values as the eight Holocene samples, suggesting that barnacle calcite is not prone to significant diagenesis in this setting. Apparent isotope equilibrium and lack of diagenesis make barnacles a promising archive for reconstruction of past ocean conditions. Cycles of δ18O observed within each sample sometimes correlate with the external growth ridges, but not always, and have amplitudes of typically 0.6%. This magnitude of variation suggests shell growth during a significant portion of the year, although it remains unclear whether growth continues throughout the year. However, the prominent growth bands suggest at least a signficant seasonal slowing in growth rate. Variations in barnacle δ18O within each plate and between plates are too large to be caused by temperature, and instead reflect changes in δ18O of the seawater, allowing some assessment of seawater salinity under the ice shelf. Salinities are lowered by addition of ...