Marine Reservoir Age Variability Over the Last Deglaciation: Implications for Marine Carbon Cycling and Prospects for Regional Radiocarbon Calibrations

Marine radiocarbon dates, corrected for ocean-atmosphere reservoir age offsets (R-ages), are widely used to constrain marine chronologies. R-ages also represent the surface boundary condition that links the ocean interior radiocarbon distribution (i.e., radiocarbon ventilation ages) to the ocean's large-scale overturning circulation. Understanding how R-ages have varied over time is therefore essential both for accurate dating and for investigations into past ocean circulation/carbon cycle interactions. A number or recent studies have shed light on surface reservoir age changes over the last deglaciation; however, a clear picture of global/regional spatiotemporal patterns of variability has yet to emerge. Here we combine new and existing reservoir age estimates to show coherent but distinct regional reservoir age trends in the subpolar North Atlantic and Southern Ocean. It can be further shown that similar but lower amplitude changes occurred at midlatitudes in each hemisphere. An apparent link between regional patterns of reservoir age variability and the thermal bipolar seesaw suggests a causal link with changes in ocean circulation, mixed-layer depth, and/or sea ice dynamics. A further link to atmospheric CO2 is also apparent and underlines a potentially dominant role for changes in the ocean's disequilibrium carbon pool, rather than changes in ocean transport, in deglacial CO2 change. The existence of significant R-age variability over the last deglaciation poses a problem for marine radiocarbon age calibrations. However, its apparent regional consistency also raises the prospect of developing region-specific marine calibration curves for radiocarbon-dating purposes.