Deep-sea coral evidence for lower Southern Ocean surface nitrate concentrations during the last ice age

• Published in: Proceedings of the National Academy of Sciences
• Main Authors: Wang, Xingchen T., Sigman, Daniel M., Prokopenko, Maria, Adkins, Jess F., Robinson, Laura, Hines, Sophia K, Chai, Junyi, Martinez Garcia, alfredo, Chen, Tianyu, Haug, Gerald H.
• Format: Article in Journal/Newspaper
• Language: English
• Published: 2017
• Subjects: Southern Ocean; nutrient consumption; atmospheric CO2; ice ages; Antarc*; Antarctic
• Online Access: https://hdl.handle.net/1983/f33afe39-c1d6-4fd0-a2fa-ba5d0bb853c7; https://research-information.bris.ac.uk/en/publications/f33afe39-c1d6-4fd0-a2fa-ba5d0bb853c7; https://doi.org/10.1073/pnas.1615718114; https://research-information.bris.ac.uk/ws/files/104278719/Wang_2017_PNAS.pdf; http://www.scopus.com/inward/record.url?scp=85016408889&partnerID=8YFLogxK

The Southern Ocean regulates the ocean’s biological sequestration of CO 2 and is widely suspected to underlie much of the ice age decline in atmospheric CO 2 concentration, but the specific changes in the region are debated. While more complete drawdown of surface nutrients by phytoplankton during the ice ages is supported by some sediment core-based measurements, the use of different proxies in different regions has precluded a unified view of Southern Ocean biogeochemical change. Here, we report measurements of the 15 N/ 14 N of fossil-bound organic matter in the stony deep-sea coral Desmophyllum dianthus , a new tool for reconstructing surface ocean nutrient conditions. The central robust observation is of higher 15 N/ 14 N across the Southern Ocean during the Last Glacial Maximum (LGM), 18-25,000 years ago. These data suggest a reduced summer surface nitrate concentration in both the Antarctic and Subantarctic Zones during the LGM, with little surface nitrate transport between them. After the ice age, the increase in Antarctic surface nitrate occurred through the deglaciation and continued in the Holocene. The rise in Subantarctic surface nitrate appears to have had both early deglacial and late deglacial/Holocene components, preliminarily attributed to the end of Subantarctic iron fertilization and increasing nitrate input from the Antarctic, respectively.