The Ocean During the Last Glacial Maximum (LGM) and Early Deglaciation Constrained by Isotopes

MUGLIA, JUAN; MIX, ALAN; SCHMITTNER, ANDREAS

Miami

Congreso; 2018 International AMOC Science Meeting; 2018

Circulation changes have been suggested to play an important role in atmospheric CO2 changes during the Last Glacial Maximum (LGM) and the following deglaciation. However, quantitative, transient reconstructions of the ocean through the last deglaciation constrained by proxies remain scarce. Here we simulate the glacial and post-glacial ocean using a coupled physical-biogeochemical, global, three-dimensional, model constrained simultaneously by δ13C, radiocarbon, and δ15N to explore the effects of AMOC differences and Southern Ocean iron fertilization on the distributions of these isotopes. We find that a weak (6-9 Sv or about half of today´s) and shallow AMOC best reproduces the sediment isotope data from the LGM. Increasing the atmospheric soluble iron flux in the model´s Southern Ocean intensifies export production, carbon storage, and further improves agreement with LGM δ13C and δ15N reconstructions. This ocean state leads to a drawdown of atmosheric CO2 by ~80ppm. We use this state to initialize simulations of the early deglaciation, covering the time period from the LGM to the end of Heinrich Stadial I. The simulations are compared with a compilation of benthic δ13C data in order to constrain changes in AMOC and water mass structure, and asses the relative importance of different processes in the variations of that isotope, ocean carbon storage, and atmospheric CO2.