Deglacial patterns of South Pacific overturning inferred from 231Pa and 230Th.

The millennial-scale variability of the Atlantic Meridional Overturning Circulation (AMOC) is well documented for the last glacial termination and beyond. Despite its importance for the climate system, the evolution of the South Pacific overturning circulation (SPOC) is by far less well understood. A recently published study highlights the potential applicability of the 231Pa/230Th-proxy in the Pacific. Here, we present five sedimentary down-core profiles of 231Pa/230Th-ratios measured on a depth transect from the Pacific sector of the Southern Ocean to test this hypothesis using downcore records. Our data are consistent with an increase in SPOC as early as 20 ka that peaked during Heinrich Stadial 1. The timing indicates that the SPOC did not simply react to AMOC changes via the bipolar seesaw but were triggered via Southern Hemisphere processes.

Improved Separation of Pa from Th and U in Marine Sediments with TK400 Resin.

Protactinium-231 is a radionuclide of broad interest in paleoceanography and paleoclimatology. This study describes an improved method for the purification and separation of Pa from marine sediment samples using the new TK400 resin by TrisKem International. The focus lies on the improvement of the separation of the abundant 232Th from the Pa fraction of the sample, which would reduce the peak tailing from 232Th on masses 231 and 233 during ICP-MS measurement. Furthermore, the reusability of TK400 has been tested. For this purpose, the conventional method using Dowex AG1X8 for the separation and purification of Pa has been compared to methods using the TK400 resin. A combination of a Dowex AG1X8 prior to a TK400 column has shown most convincing results. Based on our results we suggest a new efficient procedural method of analyzing 231Pa from marine sediment samples using TK400. Chemical Pa yields for a Dowex-TK400 combination are highest compared to the Dowex only method. Furthermore, the 232Th/231Pa ratio of the Pa-fractions has been reduced by 1 order of magnitude compared to conventional methods with Dowex AG1X8. Additionally, the reusability of TK400 resin up to nine times has been proven. The usage of TK400 is only limited in the presence of samples with a high matrix load (e.g., Fe). Therefore, matrix from sediment samples needs to be removed (here using Dowex resin) before samples are loaded onto TK400. We also report a series of concentration measurements from standard reference materials (UREM-11, NIST 2702), which have been used for 233Pa calibration.