The potential of the marine bivalve mollusc Glossus humanus (L.) as a sclerochronological archive

Abstract

In order to assess its potential as a sclerochronological archive, we present statistical and geochemical analyses of internal growth increment series in shells of the heart cockle Glossus humanus (L.), a large marine bivalve. The investigated samples were collected from Loch Sunart and the Sound of Mull, Scotland, United Kingdom. High-resolution stable isotope (δ18O) analyses and radiocarbon (14C) determinations indicated that G. humanus forms annual growth lines. Examination of the growth increment series revealed that the maximum longevity of G. humanus in this region was 78 years. Radiocarbon dating and crossmatching techniques, derived from dendrochronology, were used to provide an estimation of the temporal distribution of the fossil G. humanus. Of the shells that contained >25 growth increments, seven were found to statistically crossmatch, including shells from two distinct sites 15 km apart. The calibrated 14C determinations independently confirmed the crossmatching of three G. humanus shells from the Sound of Mull with a separately constructed Glycymeris glycymeris chronology and a further three G. humanus shells from site 3, in the main basin of Loch Sunart, but indicate a significant difference (site 1) in the antiquity of the two G. humanus populations. Radiocarbon dating indicated that, despite their fragile nature, G. humanus shells remain preserved in near original condition for at least 700 years. Given the small amount of available shell material, it is unlikely that G. humanus will become a key species for the construction of long absolutely dated sclerochronologies. However, these data do indicate that the annually resolved G. humanus growth series could be used to supplement series from other long-lived bivalves and facilitate the construction of a robust multispecies sclerochronology spanning the last 1000 years.