Reconstructing Modes of the Amoc Back to the Penultimate Glacial Maximum
Thursday, 18 December 2014: 10:35 AM
The variability of the Atlantic Meridional Overturning Circulation (AMOC) that has controlled heat-transport from low to high latitudes and ocean CO2 storage is still poorly constrained beyond the last glacial maximum. Here we reconstruct both the strength and direction of the AMOC from a highly resolved marine sedimentary record recovered from the northwestern Atlantic Ocean. Measurements of two independent chemical water mass tracers (231Pa/230Th and εNd), not affected by changes in the global carbon cycle, from the very same samples reveal strikingly similar responses of the AMOC to ice sheet retreat during the last two glacial Terminations. In contrast to the prevailing view attesting a shallower and weaker north Atlantic overturning to glacial climates, we show that a deep and vigorous overturning circulation mode persisted throughout most of the last glacial cycle. Critical deviations from this mode were restricted to times of maximum ice-sheet extent during glacial maxima, suggesting that AMOC stability was largely insensitive to millennial scale melt-water pulses and buoyancy forcing during warm and intermediate climate states.