Changes in bioavailable dust-borne iron (Fe) supply to the iron-limited Southern Ocean may influence climate by modulating phytoplankton growth and CO2 fixation into organic matter that is exported to the deep ocean. The chemical form (speciation) of Fe impacts its bioavailability, and glacial weathering produces highly labile and bioavailable Fe minerals in modern dust sources. However, the speciation of dust-borne Fe reaching the iron-limited Southern Ocean on glacial–interglacial timescales is unknown, and its impact on the bioavailable iron supply over geologic time has not been quantified. Here we use X-ray absorption spectroscopy on subantarctic South Atlantic and South Pacific marine sediments to reconstruct dust-borne Fe speciation over the last glacial cycle, and determine the impact of glacial activity and glaciogenic dust sources on bioavailable Fe supply. We show that the Fe(II) content, as a percentage of total dust-borne Fe, increases from ~5 to 10% in interglacial periods to ~25 to 45% in glacial periods. Consequently, the highly bioavailable Fe(II) flux increases by a factor of ~15 to 20 in glacial periods compared with the current interglacial, whereas the total Fe flux increases only by a factor of ~3 to 5. The change in Fe speciation is dominated by primary Fe(II) silicates characteristic of glaciogenic dust. Furthermore, our results suggest that glacial physical weathering increases the proportion of highly bioavailable Fe(II) in dust that reaches the subantarctic Southern Ocean in glacial periods, which represents a positive feedback between glacial activity and cold glacial temperatures.
Shoenfelt, Elizabeth M., et al. "Highly bioavailable dust-borne iron delivered to the Southern Ocean during glacial periods." Proceedings of the National Academy of Sciences of the United States of America, vol. 115, no. 44, Oct. 2018. https://doi.org/10.1073/pnas.1809755115
Shoenfelt, Elizabeth M., Winckler, Gisela, Lamy, Frank, Anderson, Robert F., & Bostick, Benjamin C. (2018). Highly bioavailable dust-borne iron delivered to the Southern Ocean during glacial periods. Proceedings of the National Academy of Sciences of the United States of America, 115(44). https://doi.org/10.1073/pnas.1809755115
Shoenfelt, Elizabeth M., Winckler, Gisela, Lamy, Frank, et al., "Highly bioavailable dust-borne iron delivered to the Southern Ocean during glacial periods," Proceedings of the National Academy of Sciences of the United States of America 115, no. 44 (2018), https://doi.org/10.1073/pnas.1809755115
@article{osti_1483093,
author = {Shoenfelt, Elizabeth M. and Winckler, Gisela and Lamy, Frank and Anderson, Robert F. and Bostick, Benjamin C.},
title = {Highly bioavailable dust-borne iron delivered to the Southern Ocean during glacial periods},
annote = {Changes in bioavailable dust-borne iron (Fe) supply to the iron-limited Southern Ocean may influence climate by modulating phytoplankton growth and CO2 fixation into organic matter that is exported to the deep ocean. The chemical form (speciation) of Fe impacts its bioavailability, and glacial weathering produces highly labile and bioavailable Fe minerals in modern dust sources. However, the speciation of dust-borne Fe reaching the iron-limited Southern Ocean on glacial–interglacial timescales is unknown, and its impact on the bioavailable iron supply over geologic time has not been quantified. Here we use X-ray absorption spectroscopy on subantarctic South Atlantic and South Pacific marine sediments to reconstruct dust-borne Fe speciation over the last glacial cycle, and determine the impact of glacial activity and glaciogenic dust sources on bioavailable Fe supply. We show that the Fe(II) content, as a percentage of total dust-borne Fe, increases from ~5 to 10% in interglacial periods to ~25 to 45% in glacial periods. Consequently, the highly bioavailable Fe(II) flux increases by a factor of ~15 to 20 in glacial periods compared with the current interglacial, whereas the total Fe flux increases only by a factor of ~3 to 5. The change in Fe speciation is dominated by primary Fe(II) silicates characteristic of glaciogenic dust. Furthermore, our results suggest that glacial physical weathering increases the proportion of highly bioavailable Fe(II) in dust that reaches the subantarctic Southern Ocean in glacial periods, which represents a positive feedback between glacial activity and cold glacial temperatures.},
doi = {10.1073/pnas.1809755115},
url = {https://www.osti.gov/biblio/1483093},
journal = {Proceedings of the National Academy of Sciences of the United States of America},
issn = {ISSN 0027-8424},
number = {44},
volume = {115},
place = {United States},
publisher = {National Academy of Sciences},
year = {2018},
month = {10}}
Argonne National Laboratory (ANL), Argonne, IL (United States)
Sponsoring Organization:
National Inst. of Environmental Health Sciences; National Science Foundation; USDOE Office of Science (SC), Basic Energy Sciences (BES) (SC-22). Scientific User Facilities Division
Grant/Contract Number:
AC02-06CH11357; AC02-76SF00515
OSTI ID:
1483093
Journal Information:
Proceedings of the National Academy of Sciences of the United States of America, Journal Name: Proceedings of the National Academy of Sciences of the United States of America Journal Issue: 44 Vol. 115; ISSN 0027-8424
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