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

When dating marine samples with 14 C, the reservoir-age effect is usually assumed to be constant, although atmospheric 14 C 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 5 global ocean circulation model forced by transient atmospheric ∆ 14 C 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 ∼30% reduced Atlantic meridonal overturning circulation leads to increased reservoir ages by up to ∼500 years in high latitudes. Temporal variations are proportional to the absolute value of the reservoir age; regions with large 10 reservoir age also show large variation. Temporal variations range between ∼300 years in parts of the subtropics and ∼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.