Southern Ocean Diatom-bound Nitrogen Isotope Data ----------------------------------------------------------------------- World Data Center for Paleoclimatology, Boulder and NOAA Paleoclimatology Program ----------------------------------------------------------------------- NOTE: PLEASE CITE ORIGINAL REFERENCE WHEN USING THIS DATA!!!!! NAME OF DATA SET: Southern Ocean Diatom-bound Nitrogen Isotope Data LAST UPDATE: 5/2009 (Original receipt by WDC Paleo) CONTRIBUTOR: Rebecca S. Robinson, University of Rhode Island IGBP PAGES/WDCA CONTRIBUTION SERIES NUMBER: 2009-052 WDC PALEO CONTRIBUTION SERIES CITATION: Robinson, R.S. and D.M. Sigman. 2009. Southern Ocean Diatom-bound Nitrogen Isotope Data. IGBP PAGES/World Data Center for Paleoclimatology Data Contribution Series # 2009-052. NOAA/NCDC Paleoclimatology Program, Boulder CO, USA. ORIGINAL REFERENCE: 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, Vol. 27, Issues 9-10, pp. 1076-1090, May 2008. doi:10.1016/j.quascirev.2008.02.005 ABSTRACT: Surface sediment diatom-bound d15N along a latitudinal transect of 170°W shows a previously unobserved increase to the South of the Antarctic Polar Front. The southward d15N increase is best explained by the combination of two changes toward the South, a decrease in the isotope effect of nitrate assimilation (E) 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 d15N during the last ice age, with intervals of higher d15N, 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 d15N to interglacial sediments. Variation in the range of 0-3 per mil, as seen in previously published records, may be entirely due to changes in E. However, the observed magnitude of the change of 4-10 per mil 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-d15N 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 "nutrient front" 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. ADDITIONAL REFERENCES: Brunelle, B.G., et al., 2007. Evidence from diatom-bound nitrogen isotopes for Subarctic Pacific stratification during the last ice age and a link to North Pacific denitrification changes. Paleoceanography 22. Robinson, R.S., B.G. Brunelle, and D.M. Sigman. 2004. Revisiting nutrient utilization in the glacial Antarctic: Evidence from a new method for diatom-bound N isotopic analysis. Paleoceanography, Vol. 19, PA3001, doi:10.1029/2003PA000996. GEOGRAPHIC REGION: Southern Ocean PERIOD OF RECORD: ~ 160 KYrBP - present FUNDING SOURCES: Princeton Environmental Institute Postdoctoral Fellowship Program, US National Science Foundation OPP Grant ANT-0453680 to D.M.S., DEB-0083566 to Simon Levin, and BP and Ford Motor Company through the Princeton Carbon Mitigation Initiative. DESCRIPTION: Diatom-bound N isotope data and depth interval for each sample from RC13-259 (Atlantic Sector), NBP9802-05GC (Pacific Sector), and NBP9802-06PC (Pacific Sector). Diatom-bound d15N was measured after a physical and chemical separation adapted from Robinson et al., 2004 and Brunelle et al., 2007. Core RC13-259: 53.88°S, 4.93° W Core NBP5GC: 63.11°S, 169.74° W Core NBP9802-06PC: 61.88°S, 169.98° W DATA: Core RC13-259: Column 1: Depth cm Column 2: d15N_diatom (per mil v. air) Depth d15N_diatom 10 10.78 20 11.76 30 11.23 40 9.53 40 10.08 50 8.77 60 9.44 70 8.87 80 8.23 90 8.01 100 8.65 110 7.26 122 8.65 130 9.67 130 9.59 141 11.29 141 10.2 152 10.52 161 9.97 170 10.78 180 7.76 190 7.52 200 6.88 210 7.04 220 7.48 230 7.69 240 10.35 240 11.68 250 7.77 261 7.67 270 7.16 281 8.86 291 9.43 301 8.22 310 9.88 310 8.89 321 6.7 321 7.43 341 12.31 341 11.48 360 9.01 370 12.87 370 12.08 380 13.79 380 13.88 390 15.32 390 14.7 401 10.66 410 9.77 422 6.35 431 6.3 440 6.61 451 7.87 463 7.03 470 7.65 480 7.82 490 6.53 500 5.72 511 7.36 521 9.29 531 9.36 541 8.01 550 10.97 561 12.28 571 12.49 581 7.29 591 11.67 601 13.78 Core NBP5GC: Column 1: Depth cm Column 2: d15N_diatom (per mil v. air) Depth d15N_diatom 1 7.3 5 7.1 5 7.1 9 5.3 13 5.2 17 5.1 17 5.3 21 5.2 21 5 25 5.3 29 6.1 29 6.2 35 6.6 35 6.2 39 6 39 6.4 43 7.9 46 7.93 46 10.45 51 10.4 51 10.8 60 7.91 60 7.33 64 5.95 64 4.93 70 6.28 70 6.43 74 6.84 Core NBP9802-06PC: Column 1: Depth cm Column 2: d15N_diatom (per mil v. air) Depth d15N_diatom 0 3.61 0 3.78 10 4.04 20 3.10 20 3.62 30 4.17 50 3.22 70 4.26 80 3.91 90 4.05 110 3.68 120 5.08 130 4.99 140 3.86 140 3.93 150 3.50 159 4.78 190 5.05 220 5.87 240 6.06 250 7.12 280 5.33 310 6.68 320 3.35 330 3.76 340 3.68 360 4.06 370 4.07 380 3.06 390 3.84 390 3.71 400 4.49 400 4.84 410 4.49 410 4.75 420 6.02 420 7.59 450 3.57 450 4.78 460 4.36 470 4.02 480 3.60 490 3.94 510 3.47 510 3.99 530 6.66 530 6.59 570 3.53 580 4.17 590 3.34 600 4.01 610 2.74 610 3.14 620 3.53