Atlantic meridional overturning circulation variability since the last glaciation: Insights from a novel multiproxy approach

• Main Author: Valley, Shannon Gabrielle
• Other Authors: Lynch-Stieglitz, Jean, Cobb, Kim, Ito, Takamitsu, Bracco, Annalisa, Marchitto, Thomas M., Earth and Atmospheric Sciences
• Format: Doctoral or Postdoctoral Thesis
• Language: English
• Published: Georgia Institute of Technology 2021
• Subjects: Atlantic Meridional Overturning Circulation; Last Glacial Maximum; Fuller; Ice Sheet
• Online Access: http://hdl.handle.net/1853/64066

Atlantic Meridional Overturning Circulation (AMOC) transports warm surface water northward across the equator, carrying heat from the Southern to the Northern Hemisphere. AMOC plays a central role in the global redistribution of heat and precipitation during both abrupt and longer-term climate shifts. Over the next century, AMOC is projected to weaken due to greenhouse gas warming, though projecting the variability of its future behavior is dependent on a better understanding of how AMOC changes are forced, including the evolving states of its constituent water masses. To address this, I analyzed several water mass tracer records from Florida Straits intermediate water- a water mass that forms part of AMOC’s upper branch. To investigate AMOC variability during the Younger Dryas (YD) and Heinrich Stadial 1 (HS1)- climatological periods associated with ice sheet melt- I generated a new, high-resolution record of benthic seawater Cd (Cdw) from a Florida Straits sediment core at 546 m water depth. This record provides additional evidence for lower Cdw relative to modern during both the YD and HS1. Lower Cdw values are interpreted as AMOC weakening, reflecting a decreased northward transport of southern-sourced higher nutrient intermediate waters by the surface return flow of AMOC. Comparison of this new Cdw record with previously published neodymium isotope and δ18O records from the same core shows synchronous transitions, further illustrating the connection between Cdw levels and AMOC strength in the Florida Straits. An increase in Cdw near 16 ka bolsters existing evidence for a resumption of upper branch AMOC strength approximately midway through Heinrich Stadial 1. The Cdw record was extended to ∼35,000 yr before present, including all of Marine Isotope Stages (MIS) 2 and part of MIS 3, and temperature and oxygen isotopic composition of seawater were also reconstructed from the same core in order to provide a fuller picture of water mass properties and circulation at this location. During the Last Glacial Maximum ...