Modeling variations of marine reservoir ages during the last 45 000 years

When dating marine samples with C-14, the reservoir-age effect is usually assumed to be constant, although atmospheric C-14 production rate and ocean circulation changes cause temporal and spatial reservoir-age variations. These lead to dating errors, which can limit the interpretation of cause and effect in paleoclimate data. We used a global ocean circulation model forced by transient atmospheric Delta C-14 variations to calculate reservoir ages for the last 45 000 years for a present day-like and a last glacial maximum-like ocean circulation. A similar to 30% reduced Atlantic meridonal overturning circulation leads to increased reservoir ages by up to similar to 500 years in high latitudes. Temporal variations are proportional to the absolute value of the reservoir age; regions with large reservoir age also show large variation. Temporal variations range between similar to 300 years in parts of the subtropics and similar to 1000 years in the Southern Ocean. For tropical regions, which are generally assumed to have nearly stable reservoir ages, the model suggests variations of several hundred years.