Little Change in Ice Age Water Mass Structure From Cape Basin Benthic Neodymium and Carbon Isotopes

• Published in: Paleoceanography and paleoclimatology 2021-11, Vol.36 (11), p.n/a
• Main Authors: Hines, Sophia K. V., Bolge, Louise, Goldstein, Steven L., Charles, Christopher D., Hall, Ian R., Hemming, Sidney R.
• Format: Article
• Language: English
• Subjects: Abyssal zone; Age composition; Benthos; Carbon capture and storage; Carbon dioxide; Carbon isotopes; Carbon sequestration; Circulation; Deep water; Ice ages; Interglacial periods; Isotope composition; Isotopes; Last Glacial Maximum; Neodymium; Neodymium isotopes; Ocean circulation; Oceans; Shoaling; Stratification; Water circulation; Water depth; Water masses
• ISSN: 2572-4517; 2572-4525
• DOI: 10.1029/2021PA004281

A common conception of the deep ocean during ice age episodes is that the upper circulation cell in the Atlantic was shoaled at the Last Glacial Maximum compared to today, and that this configuration facilitated enhanced carbon storage in the deep ocean, contributing to glacial CO2 draw‐down. Here, we test this notion in the far South Atlantic, investigating changes in glacial circulation structure using paired neodymium and benthic carbon isotope measurements from International Ocean Discovery Program Site U1479, at 2,615 m water depth in the Cape Basin. We infer changes in circulation structure across the last glacial cycle by aligning our site with other existing carbon and neodymium isotope records from the Cape Basin, examining vertical isotope gradients, while determining the relative timing of inferred circulation changes at different depths. We find that Site U1479 had the most negative neodymium isotopic composition across the last glacial cycle among the analyzed sites, indicating that this depth was most strongly influenced by North Atlantic Deep Water (NADW) in both interglacial and glacial intervals. This observation precludes a hypothesized dramatic shoaling of NADW above ∼2,000 m. Our evidence, however, indicates greater stratification between mid‐depth and abyssal sites throughout the last glacial cycle, conditions that developed in Marine Isotope Stage 5. These conditions still may have contributed to glacial carbon storage in the deep ocean, despite little change in the mid‐depth ocean structure. Key Points We present high‐resolution, co‐registered εNd, δ13C, and δ18O records from the last 160,000 years Compiled Cape Basin εNd data show maximum North Atlantic Deep Water (NADW) influence at 2,615 m across the last glacial cycle The data does not favor significant shoaling of the core depth of NADW during the Last Glacial Maximum, but there is enhanced deep stratification