noaa-ocean-8455 Southern Ocean Diatom-bound Nitrogen Isotope Data Robinson, R.S.; Sigman, D.M. Southern Ocean Diatom-bound Nitrogen Isotope Data 2008-07-01 NCDC-Paleoclimatology ONLINE Files Pending https://www.ncdc.noaa.gov/paleo/study/8455 Investigator R.S. Robinson Investigator D.M. Sigman earth science paleoclimate paleocean nitrogen isotopes geoscientificInformation cal yr BP cal yr BP Complete -63.11 -53.88 -169.98 -4.93 -2677 -2677 Ocean Southern Ocean NBP9802-06PC>LATITUDE -61.88>LONGITUDE -169.98 Ocean Atlantic Ocean South Atlantic Ocean RC13-259>LATITUDE -53.88>LONGITUDE -4.93 Ocean Southern Ocean NBP9802-05GC>LATITUDE -63.11>LONGITUDE -169.74 None Please cite original publication, online resource, dataset and publication DOIs (where available), and date accessed when using downloaded data. If there is no publication information, please cite investigator, title, online resource, and date accessed. The appearance of external links associated with a dataset does not constitute endorsement by the Department of Commerce/National Oceanic and Atmospheric Administration of external Web sites or the information, products or services contained therein. For other than authorized activities, the Department of Commerce/NOAA does not exercise any editorial control over the information you may find at these locations. These links are provided consistent with the stated purpose of this Department of Commerce/NOAA Web site. English DOC/NOAA/NESDIS/NCEI National Centers for Environmental Information, NESDIS, NOAA, U.S. Department of Commerce https://www.ncdc.noaa.gov/data-access/paleoclimatology-data DATA Center Contact Bruce Bauer bruce.a.bauer@noaa.gov paleo@noaa.gov 303-497-6280 303-497-6513

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Boulder CO 80305-3328 USA online ASCII Robinson, R.S. and D.M. Sigman. 2008. Nitrogen isotopic evidence for a poleward decrease in surface nitrate within the ice age Antarctic. Quaternary Science Reviews, 27(9-10), 1076-1090.

Surface sediment diatom-bound ŋ15N along a latitudinal transect of 170°W shows a previously unobserved increase to the South of the Antarctic Polar Front. The southward ŋ15N increase is best explained by the combination of two changes toward the South, a decrease in the isotope effect of nitrate assimilation (ŋ) and an increase in the degree of nitrate consumption, both associated with shoaling of the mixed layer into the seasonal ice zone (SIZ). New downcore records show high amplitude changes in diatom-bound ŋ15N during the last ice age, with intervals of higher ŋ15N, including the last glacial maximum, the transition between marine isotope stages 5 and 4, and marine isotope stage 6, while other intervals are similar in ŋ15N to interglacial sediments. Variation in the range of 0-3ŋ, as seen in previously published records, may be entirely due to changes in ŋ. However, the observed magnitude of the change of 4-10ŋ in the three new records and the locations of these records relative to the modern meridional gradient in mixed layer depth appear to require increased nitrate consumption to explain the high-ŋ15N intervals. The new sites are near the modern Southern Antarctic Circumpolar Current Front (SACCF), and one of the sites has been shown to be associated with sporadic summer sea ice during the LGM. As with other Antarctic sites, the available proxy data suggest that they were characterized by lower export production. Based on these and other observations, we propose that the weak southward nitrate decrease in the modern Antarctic surface was a fully developed ŋnutrient frontŋ in the glacial Antarctic, associated with the SACCF. Both modern ocean and paleoceanographic work is needed to test this hypothesis, which would have major implications for atmospheric CO2.

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