Diet can play a significant role in anomalous radiocarbon ages derived from bone and other tissues when the food web incorporates depleted 14C reservoirs, such as the marine environment. Dietary effects from a post-bomb carbon variation have also been found in modern invertebrates and populations of Rattus exulans (Beavan and Sparks 1998). We now present the effect on absolute percent modern (pMC) and the conventional radiocarbon age (CRA) of a modern aquatic/terrestrial food web in a volcanic zone of the North Island, New Zealand. At Lake Taupo, geothermal venting transfers 14C depleted carbon to lake waters, which aquatic plants fix into the food chain; depleted 14C is shown to then pass on to shellfish, waterfowl, and Norway rat (Rattus norvegicus). The geothermally induced 14C variations from modern atmospheric pMC and CRA can increase apparent 14C ages by >2000 years.