Glacial-Interglacial Changes in Atlantic Ocean Circulation and Carbon Processes Inferred from Benthic Foraminiferal ????13C

• Main Author: Bengtson, Shannon
• Format: Doctoral or Postdoctoral Thesis
• Language: unknown
• Published: UNSW Sydney 2021
• Subjects: North Atlantic Deep Water; Paleoceanography; δ13C; Antarctic; Antarc*; NADW; North Atlantic
• Online Access: https://dx.doi.org/10.26190/unsworks/22711; http://hdl.handle.net/1959.4/71091

Benthic foraminiferal δ13C is a climate proxy which can be used to infer past changes in ocean circulation and carbon processes. However, the interpretation of this proxy can be challenging due to the multitude of factors that can influence benthic δ13C. In this thesis, I compile benthic foraminiferal δ13C data from different time periods within the past 150 thousand years (kyr) and use this proxy to make inferences about carbon processes and the extent of North Atlantic Deep Water (NADW). I start by presenting two statistical models to reconstruct the extent of NADW and Antarctic Bottom Water (AABW) based on benthic foraminiferal δ13C. I test these statistical models using the output of two isotope-enabled climate models, the UVic ESCM and LOVECLIM, both integrated under Last Glacial Maximum (LGM) and Holocene boundary conditions. I find that the statistical models can reliably reconstruct the simulated NADW and AABW δ13C features when fed with randomly sampled climate model output (‘pseudoproxies’). This methodology is then applied to benthic δ13C data in the remainder of the thesis. I develop a new compilation of δ13C data for the last interglacial period (LIG) and compare it to the Holocene. I find that the mean global oceanic δ13C LIG-Holocene anomaly is approximately -0.2 ‰, most likely the result of weathering-burial imbalances. Reconstructions of Atlantic Ocean δ13C distribution using the compiled data suggest that the depth and meridional extents of NADW and AABW were similar during the LIG and the Holocene. I then extend my analysis to include δ13C data from the Penultimate Glacial Maximum (PGM) and the Penultimate Deglaciation (PDG) and compare these to the LGM and the Last Deglaciation (LDG), respectively. I find that the mean Atlantic Ocean PGM-LGM δ13C anomaly is about the same as the LIG-Holocene anomaly, which may suggest that some important changes in weathering and burial fluxes occur between the LIG and the LGM. My reconstruction suggests a similarly shallow NADW during both glacial periods. I then compare the evolution of δ13C over the PDG and the LDG by aligning the deglaciations based on boreal summer insolation maximum at 65o N. The data suggest a deepening of NADW during the early phase of the deglaciation that occurred earlier and more gradually during the PDG than the LDG. The data also show changes in δ13C associated with a resumption of AMOC following Heinrich Stadial 11 and 1.