A CONTINUOUS MULTI-MILLENNIAL RECORD OF SURFICIAL BIVALVE MOLLUSK SHELLS FROM THE SÃO PAULO BIGHT, BRAZILIAN SHELF

To fully evaluate the potential of using surficial shell accumulations for paleoenvironmental studies, an extensive time series of individually dated specimens of the infaunal bivalve mollusk Semele casali was assembled using amino acid racemization [AAR] ratios (n=275) calibrated against radiocarbon dates (n=32). The shells were collected from surface sediments at multiple sites across a sediment-starved shelf in the shallow sub-tropical São Paulo Bight marine province (São Paulo State, Brazil). The resulting ¹⁴C-calibrated AAR time series, one of the largest AAR datasets compiled to date, ranges from modern to 10,348 cal years, is strongly right skewed, and represent a remarkably complete time-series (73.8% of the Holocene record is represented at 250 year bins and 90.9% at 500 year bins). Extensive time-averaging observed across all sites without little variation between bathymetric gradients indicates long survival of carbonate shells at sediment surfaces where the net sedimentation rate is low. Benthic organisms collected from active depositional surfaces can provide multi-millennial time series of biomineral records and serve as a major source of geochemical proxy data for reconstructing environmental and climatic trends throughout the Holocene at centennial resolution. Surface sediments can represent time-rich shell accumulations that record the entire Holocene, and not just the present.