Silicon-isotope composition of diatoms as an indicator of past oceanic change

• Main Authors: de La Rocha, Christina, Brzezinski, Mark A., Deniro, M.J., Shemesh, Aldo
• Other Authors: Laboratoire des Sciences de l'Environnement Marin (LEMAR) (LEMAR), Institut de Recherche pour le Développement (IRD)-Institut Français de Recherche pour l'Exploitation de la Mer (IFREMER)-Université de Brest (UBO)-Institut Universitaire Européen de la Mer (IUEM), Institut de Recherche pour le Développement (IRD)-Institut national des sciences de l'Univers (INSU - CNRS)-Université de Brest (UBO)-Centre National de la Recherche Scientifique (CNRS)-Institut de Recherche pour le Développement (IRD)-Institut national des sciences de l'Univers (INSU - CNRS)-Université de Brest (UBO)-Centre National de la Recherche Scientifique (CNRS)-Centre National de la Recherche Scientifique (CNRS), Department of Ecology, Evolution and Marine Biology Santa Barbara (EEMB), University of California Santa Barbara (UC Santa Barbara), University of California (UC)-University of California (UC), Department of Earth Science Santa Barbara (GEOL-UCSB), Department of Environmental Sciences and Energy Research Rehovot, Weizmann Institute of Science Rehovot, Israël
• Format: Article in Journal/Newspaper
• Language: English
• Published: HAL CCSD 1998
• Subjects: [SDU.STU.OC]Sciences of the Universe [physics]/Earth Sciences/Oceanography; Ross Sea; Southern Ocean; Antarc*; Antarctica
• Online Access: https://hal.univ-brest.fr/hal-00660848

International audience Silicon is essential for the growth of diatoms, a group of phytoplankton with opal (amorphous hydrated silica) shells. Diatoms largely control the cycling of silicon in the ocean and, conversely, diatom silica production rates can be limited by the availability of silicic acid. Diatoms are biogeochemically important in that they account for an estimated 75% of the primary production occurring in coastal and nutrient-replete waters1, rising to more than 90% during ice-edge blooms such as occur in the Ross Sea, off Antarctica. There are few means by which to reconstruct the history of diatom productivity and marine silicon cycling, and thus to explore the potential contribution of diatoms to past oceanic biogeochemistry or climate. Indices based on the accumulation of sedimentary opal are often biased by the winnowing and focusing of sediments and by opal dissolution. Normalization of opal accumulation records using particlereactive natural radionuclides may correct for sediment redistribution artefacts and the dissolution of opal within sediments, but not for opal dissolution before it arrives at the sea floor. Half of the opal produced in the euphotic zone may dissolve before sinking to a depth of 200m, constituting a potentially large bias to both normalized and uncorrected records of opal accumulation. Here we exploit the potential that variations in the ratio of 30Si to 28Si in sedimentary opal may provide information on past silicon cycling that is unbiased by opal dissolution. Our silicon stable-isotope measurements suggest that the percentage utilization of silicic acid by diatoms in the Southern Ocean during the last glacial period was strongly diminished relative to the present interglacial.