Millennial-scale glacial meltwater pulses and their effect on the spatio-temporal 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, salinity and provide a means to date marine sediment cores across different ocean basins. Our study addresses the question how the δ¹⁸O 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 δ¹⁸O 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.

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