USAP-DC

ABSTRACT
Intellectual Merit:
The high concentration of the major nutrients nitrate and phosphate is a fundamental characteristic of the Antarctic Zone in the Southern Ocean and is central to its role in global ocean fertility and the global carbon cycle. The isotopic composition of diatom-bound organic nitrogen is one of the best hopes for reconstructing the nutrient status of polar surface waters over glacial cycles, which in turn may hold the explanation for the decline in atmospheric carbon dioxide during ice ages. The PIs propose to generate detailed diatom-bound nitrogen isotope (δ15Ndb) records from high sedimentation rate cores from the Kerguelen Plateau. Because the cores were collected at relatively shallow seafloor depths, they have adequate planktonic and benthic foraminifera to develop accurate age models. The resulting data could be compared with climate records from Antarctic ice cores and other archives to investigate climate-related changes, including the major steps into and out of ice ages and the millennial-scale events that occur during ice ages and at their ends. The records generated in this project will provide a critical test of hypotheses for the cause of lower ice age CO2.

Broader impacts:
This study will contribute to the goal of understanding ice ages and past CO2 changes, which both have broad implications for future climate. Undergraduates will undertake summer internships, with the possibility of extending their work into junior year projects and senior theses. In addition, the PI will lead modules for two Princeton programs for middle school teachers and will host a teacher for a six-week summer research project.

Person	Role
Sigman, Daniel	Investigator and contact

Antarctic Earth Sciences

Award # 1401489

USAP-1401489_1

None in the Database

Repository	Title (link)	Format(s)	Status
PANGAEA	Diatom-bound nitrogen isotope and opal flux records over the Holocene period in Southern Ocean sediment cores MD12-3396, MD11-3353 and PS75/072-4.	None	exists
PANGAEA	Diatom-bound N isotope records over the last two glacial cycles in sediment core PS75/072-4.	None	exists
CLIVAR	GOSHIP section IO8S and P18S	None	exist
Publication	Deep-sea coral evidence for lower Southern Ocean surface nitrate concentrations during the last ice age	None	exists

1. Studer, Anja S., et al. "Antarctic Zone nutrient conditions during the last two glacial cycles." Paleoceanography 30.7 (2015): 845-862. (doi:10.1002/2014PA002745)
2. Studer, Anja S., et al. "Increased nutrient supply to the Southern Ocean during the Holocene and its implications for the pre-industrial atmospheric CO 2 rise." Nature geoscience 11.10 (2018): 756. (doi:10.1038/s41561-018-0191-8)
3. Wang, Xingchen Tony, et al. "Deep-sea coral evidence for lower Southern Ocean surface nitrate concentrations during the last ice age." Proceedings of the National Academy of Sciences 114.13 (2017): 3352-3357. (doi:10.1073/pnas.1615718114)
4. Fripiat, François, et al. "The isotope effect of nitrate assimilation in the Antarctic Zone: Improved estimates and paleoceanographic implications." Geochimica et Cosmochimica Acta 247 (2019): 261-279. (doi:10.1016/j.gca.2018.12.003)
5. Kemeny P C, Kast E R, Hain M P, et al. A seasonal model of nitrogen isotopes in the ice age Antarctic Zone: Support for weakening of the Southern Ocean upper overturning cell[J]. Paleoceanography and Paleoclimatology, 2018, 33(12): 1453-1471. (doi:10.1029/2018PA003478)
6. Smart, S. M., Fawcett, S. E., Ren, H., Schiebel, R., Tompkins, E. M., Martínez‐García, A., … Sigman, D. M. (2020). The Nitrogen Isotopic Composition of Tissue and Shell‐Bound Organic Matter of Planktic Foraminifera in Southern Ocean Surface Waters. Geochemistry, Geophysics, Geosystems, 21(2). (doi:10.1029/2019gc008440)
7. Studer, A. S., Sigman, D. M., Martínez-García, A., Benz, V., Winckler, G., Kuhn, G., … Haug, G. H. (2015). Antarctic Zone nutrient conditions during the last two glacial cycles. Paleoceanography, 30(7), 845–862. (doi:10.1002/2014pa002745)
8. Kemeny, P. C., Kast, E. R., Hain, M. P., Fawcett, S. E., Fripiat, F., Studer, A. S., … Sigman, D. M. (2018). A Seasonal Model of Nitrogen Isotopes in the Ice Age Antarctic Zone: Support for Weakening of the Southern Ocean Upper Overturning Cell. Paleoceanography and Paleoclimatology, 33(12), 1453–1471. (doi:10.1029/2018pa003478)
9. Kemeny, P. C., Weigand, M. A., Zhang, R., Carter, B. R., Karsh, K. L., Fawcett, S. E., & Sigman, D. M. (2016). Enzyme-level interconversion of nitrate and nitrite in the fall mixed layer of the Antarctic Ocean. Global Biogeochemical Cycles, 30(7), 1069–1085. (doi:10.1002/2015gb005350)
10. Ren, H., Studer, A. S., Serno, S., Sigman, D. M., Winckler, G., Anderson, R. F., … Haug, G. H. (2015). Glacial-to-interglacial changes in nitrate supply and consumption in the subarctic North Pacific from microfossil-bound N isotopes at two trophic levels. Paleoceanography, 30(9), 1217–1232. (doi:10.1002/2014pa002765)
11. Ren, H., Sigman, D. M., Martínez-García, A., Anderson, R. F., Chen, M.-T., Ravelo, A. C., … Haug, G. H. (2017). Impact of glacial/interglacial sea level change on the ocean nitrogen cycle. Proceedings of the National Academy of Sciences, 114(33), E6759–E6766. (doi:10.1073/pnas.1701315114)
12. Hasenfratz, A. P., Jaccard, S. L., Martínez-García, A., Sigman, D. M., Hodell, D. A., Vance, D., … Haug, G. H. (2019). The residence time of Southern Ocean surface waters and the 100,000-year ice age cycle. Science, 363(6431), 1080–1084. (doi:10.1126/science.aat7067)
13. Smart, S. M., Fawcett, S. E., Thomalla, S. J., Weigand, M. A., Reason, C. J. C., & Sigman, D. M. (2015). Isotopic evidence for nitrification in the Antarctic winter mixed layer. Global Biogeochemical Cycles, 29(4), 427–445. (doi:10.1002/2014gb005013)
14. Fripiat, F., Sigman, D. M., Massé, G., & Tison, J. (2015). High turnover rates indicated by changes in the fixed N forms and their stable isotopes in Antarctic landfast sea ice. Journal of Geophysical Research: Oceans, 120(4), 3079–3097. (doi:10.1002/2014jc010583)
15. Sigman, D. (2020). Bulk suspended PON d15N from several cruises conducted in the Southern Ocean south of Africa from 2012-2019. Biological and Chemical Oceanography Data Management Office. (doi:10.1575/1912/bco-dmo.805324.1)
16. Sigman, D. (2020). Size-fractionated zooplankton d15N from net tows on R/V S.A. Agulhas II cruises VOY016 and VOY019 in the Southern Ocean south of Africa during 2015-2016. Biological and Chemical Oceanography Data Management Office. (doi:10.1575/1912/bco-dmo.805737.1)