An enhanced carbon sink of ~2PgC/yr was observed following the Mount Pinatubo eruption. In this study we used a biogeochemical model (CASA) linked to an atmospheric tracer model (MATCH) with interannually varying transport, to predict the atmospheric CO2 response to various hypotheses for the enhanced sink. By comparing the modeled CO2 growth rate, and seasonal minimum with observation we found that global Net Primary Production could not have increased following the eruption. The enhanced sink is explained by several land and ocean sink mechanisms acting in concert.