Reconciling down core anticorrelation of diatom carbon and nitrogen isotopic ratios from the Southern Ocean

• Published in: Paleoceanography
• Main Authors: Crosta, Xavier, Shemesh, A.
• Other Authors: Environnements et Paléoenvironnements OCéaniques (EPOC), Observatoire aquitain des sciences de l'univers (OASU), Université Sciences et Technologies - Bordeaux 1 (UB)-Institut national des sciences de l'Univers (INSU - CNRS)-Centre National de la Recherche Scientifique (CNRS)-Université Sciences et Technologies - Bordeaux 1 (UB)-Institut national des sciences de l'Univers (INSU - CNRS)-Centre National de la Recherche Scientifique (CNRS)-École Pratique des Hautes Études (EPHE), Université Paris sciences et lettres (PSL)-Université Paris sciences et lettres (PSL)-Centre National de la Recherche Scientifique (CNRS), Department of Earth and Planetary Sciences Rehovot, Weizmann Institute of Science Rehovot, Israël
• Format: Article in Journal/Newspaper
• Language: English
• Published: HAL CCSD 2002
• Subjects: paleoceanography; geochemistry; diatoms; Southern Ocean; [SDU.OCEAN]Sciences of the Universe [physics]/Ocean; Atmosphere; [SDU.STU.OC]Sciences of the Universe [physics]/Earth Sciences/Oceanography; [SDU.STU.CL]Sciences of the Universe [physics]/Earth Sciences/Climatology; Antarctic; Antarctic Ocean; Indian; The Antarctic; Antarc*; Sea ice
• Online Access: https://hal.science/hal-02105706; https://hal.science/hal-02105706/document; https://hal.science/hal-02105706/file/Crosta_Paleocean2002.pdf; https://doi.org/10.1029/2000PA000565

International audience Oceanic nutrient cycling in the Southern Ocean is supposed to have an important impact on glacial-interglacial atmospheric CO 2 changes and global climate. In order to characterize such nutrient cycling over the last two climatic cycles we investigated carbon and nitrogen isotopic ratios of diatom-bound organic matter (d 13 C diat and d 15 N diat , respectively) in two cores retrieved form the Atlantic and Indian sectors of the Antarctic Ocean. The two cores show the same isotopic patterns. The d 13 C diat values are depleted during glacial periods and enriched during interglacial periods, indicating lower productivity during cold times. The d 15 N diat values are enriched during glacial periods and depleted during interglacial periods, arguing for greater nitrate utilization during cold times. Taken at face value, this apparent contradiction leads to opposite conclusions on the role of the Southern Ocean biological pump on the atmospheric CO 2 changes. However, the two sets of data can be reconciled by a ''sea ice plus mixing rate scenario'' that calls upon a balance between the effect of cutting off gas transfer at the ocean-atmosphere boundary and the effect of reducing vertical transport of nutrients through the pycnocline.