Millennial-scale glacial meltwater pulses and their effect on the spatiotemporal benthic δ18O variability

Ratios of oxygen isotope values obtained from foraminiferal calcite are one of the most established paleoceanographic proxies. They are used in the context of estimating variations in ice volume, ocean temperature, and salinity and provide a means to date marine sediment cores across different ocean basins. Our study addresses the question how the delta O-18 of the deglacial meltwater signal propagates into the interior ocean, when large-scale millennial-scale reorganizations of the Atlantic Meridional Overturning Circulation ( AMOC) are present. Analyzing a series of idealized tracer-injection experiments conducted with an earth system model, we find that a substantial weakening of the AMOC leads to a massive delay in the export of the glacioeustatic oxygen isotope signal into the deep ocean, whereas the Atlantic-Pacific lag in benthic oxygen isotope signals is not increased. Furthermore, it is shown that an AMOC cessation causes a decoupling of delta O-18 propagation time and water mass age, in particular in the deep Pacific. Our results lend further support to the notion that benthic oxygen isotope records obtained from stacks are not a useful global chronostratigraphic tool during periods of millennial-scale global ocean circulation changes. The regionally varying delay effect of the deglacial sea level signal studied here adds onto existing uncertainties in the interpretation and decomposition of benthic oxygen isotope in terms of sea level, temperature, and hydrographic variations.