Ocean circulation may have undergone reductions and reinvigorations in the past closely tied to regional climate changes. Measurements of 231Pa/230Th ratios in a sediment core from the Bermuda Rise have been interpreted as evidence that the Atlantic Meridional Overturning Circulation (AMOC) was weakened or completely eliminated during a period of catastrophic iceberg discharges (Heinrich-Event 1, H1). Here we present new data from the Bermuda Rise that show further 231Pa/230Th peaks during Heinrich-2 (H2) and Heinrich-3 (H3). Additionally, a tight correlation between diatom abundances (biogenic silica) and 231Pa/230Th is discovered in this core. Our results redirect the interpretation of 231Pa/230Th from the Bermuda Rise as a proxy for ocean circulation towards a proxy that reacts highly sensitive to changes of particle composition and water mass properties.

Sediment depth is given in mcd. AGE (ka) is an improvement of an astronomical tuned timescale [Grützner et al., 2002, doi:10.1016/S0025-3227(02)00320-1], now based on high resolution CaCO3 data derived from XRF core scanning. The carbonate record for ODP Site 1063 shows a high similarity to the CaCO3 content in the nearby piston core GPC 5 [Keigwin and Jones, 1994, doi:10.1029/94JC00525]. Correlation of CaCO3 was used to transfer the radiocarbon-based age model of GPC 5 to ODP Site 1063. The 21 radiocarbon dates reported by Keigwin and Jones [1994] for the last 36 kyr have been converted to calendar ages as described by Fairbanks et al. [2005, doi:10.1016/j.quascirev.2005.04.007]. This data sets extends the study by McManus et al. 2004 (doi:10.1038/nature02494) from the nearby core GGC5 back to 35 ka, covering H2 and H3.

Supplement to: Lippold, Jörg; Gruetzner, Jens; Winter, Diane M; Lahaye, Yann; Mangini, Augusto; Christl, Marcus (2009): Does sedimentary 231Pa/230Th from the Bermuda Rise monitor past Atlantic Meridional Overtuning Circulation? Geophysical Research Letters, 36, L12601