Glacial/interglacial changes in sediment rain rate in the SW Indian sector of subantarctic waters as recorded by $^{230}$Th, $^{231}$Pa, U, and $\delta^{15}$N

• Published in: Paleoceanography
• Main Authors: Francois, Roger, Bacon, Michael, Altabet, Mark, Labeyrie, Laurent
• Other Authors: Woods Hole Oceanographic Institution (WHOI), Centre des Faibles Radioactivités, Commissariat à l'énergie atomique et aux énergies alternatives (CEA)-Centre National de la Recherche Scientifique (CNRS)
• Format: Article in Journal/Newspaper
• Language: English
• Published: HAL CCSD 1993
• Subjects: [SDU.OCEAN]Sciences of the Universe [physics]/Ocean; Atmosphere; [SDU.ENVI]Sciences of the Universe [physics]/Continental interfaces; environment; Southern Ocean
• Online Access: https://hal.science/hal-03584506; https://hal.science/hal-03584506/document; https://hal.science/hal-03584506/file/Paleoceanography%20-%20October%201993%20-%20Francois%20-%20Glacial%20interglacial%20changes%20in%20sediment%20rain%20rate%20in%20the%20SW%20Indian%20Sector%20of.pdf; https://doi.org/10.1029/93PA00784

International audience High-resolution records of opal, carbonate, and torrigenous fluxes have been obtained from a highsedimentation rate core (MD84-527: 43'50'S; 51'19'E; 3269 m) by normalization to $^{230}$Th. This method estimates paleofluxes to the seafloor on a point-by-point basis and distinguishes changes in sediment accumulation due to variations in vertical rain rates from those due to changes in syndepositional sediment redistribution by bottom currents. We also measured sediment $\delta^{15}$N to evaluate the changes in nitrate utilization in the overlying surface waters associated with paleoflux variations. Our results show that opal accumulation rates on the seafloor during the Holocene and stage 3, based on $^{14}$C dating, were respectively tenfold and fivefold higher than the vertical rain rates, At this particular location, changes in opal accumulation on the seafloor appear to be mainly controlled by sediment redistribution by bottom currants rather than variations in opal fluxes from the overlying water column. Correction for syndeposifional sediment redistribution and the improved time resolution that can be achieved by normalization to $^{230}$Th disclose important variations in opal rain rates. We found relatively high but variable opal paleofiux during stage 3, with two maxima centered at 36 and 30 kyr B.P., low opal paleofiux during stage 2 and deglaciafion and a pronounced maximum during the early Holocene, We interpret this record as reflecting variations in opal production rates associated with climateinduced latitudinal migration of the southern ocean frontal system. Sediments deposited during periods of high opal paleofiux also have high authigenic U concentrations, suggesting more reducing conditions in the sediment, and high Pa-231/Th-230 ratios, suggesting increased scavenging from the water colunto. Sediment $\delta^{15}$N is circa 1.5 per mil higher during isotopic stage 2 and deglaciation. The low opal rain rates recorded during that period appear to have been associated ...