Nitrogen isotopic evidence for deglacial changes in nutrient supply in the eastern equatorial Pacific

• Published in: Paleoceanography
• Main Authors: Robinson, R., Martinez, P., Pena, L., Cacho, I.
• 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)
• Format: Article in Journal/Newspaper
• Language: English
• Published: HAL CCSD 2009
• Subjects: [SDU]Sciences of the Universe [physics]; Pacific; Southern Ocean
• Online Access: https://hal-insu.archives-ouvertes.fr/insu-03523359; https://hal-insu.archives-ouvertes.fr/insu-03523359/document; https://hal-insu.archives-ouvertes.fr/insu-03523359/file/Paleoceanography%20-%202009%20-%20Robinson%20-%20Nitrogen%20isotopic%20evidence%20for%20deglacial%20changes%20in%20nutrient%20supply%20in%20the%20eastern.pdf; https://doi.org/10.1029/2008PA001702

International audience The Eastern Equatorial Pacific (EEP) is a high nutrient-low chlorophyll region of the ocean. Downcore nitrogen isotope records from the EEP have been previously interpreted as a direct reflection of changes in nutrient consumption. However, the observed changes in sedimentary d 15 N since the last glacial maximum have no coherent relationship with export productivity or an inferred variation in the iron-to-nitrate ratio of the surface waters. Rather, downcore N isotope records in the EEP strongly resemble changes in the extent of water column denitrification as recorded in nearby sedimentary d 15 N records along the western margin of the Americas. This similarity is attributed to the overprinting of the N isotopic composition of nitrate in the EEP through the advection of nitrate westward from the margins in the subsurface. A local nitrogen isotope record of changes in the degree of nutrient consumption is extracted from the bulk sedimentary record by subtracting two different sedimentary d 15 N records of denitrification changes from two new EEP d 15 N records (TR163-22 and ODP Site 1240). The denitrification records used are from 1) the Central American margin (ODP Site 1242) and 2) the South American margin (GeoB7139-2). The degree of consumption in the surface waters declines rapidly from elevated values during the last glacial maximum to a pair of minima around 15 and 11-13 ka, and finally it increases into the Holocene. The derived EEP nitrogen isotope record indicates that the regional peak in export productivity occurred when the supply of nutrients exceeded the apparently high demand. The influx of nutrients during the deglaciation is attributed to the resumption of intense overturning in the Southern Ocean and the release of sequestered CO 2 and nutrient-rich, O 2 poor waters from the deep ocean. This has important implications for understanding the glacial-interglacial scale variation in intermediate water suboxia and water column denitrification.