The role of environmental factors in the long-term evolution of the marine biological pump

The biological pump—the transfer of atmospheric carbon dioxide to the ocean interior and marine sediments as organic carbon—plays a critical role in regulating the long-term carbon cycle, atmospheric composition and climate. Despite its centrality in the Earth system, the response of the biological pump to biotic innovation and climatic fluctuations through most stages of Earth’s history has been largely conjectural. Here we use a mechanistic model of the biological carbon pump to revisit the factors controlling the transfer efficiency of carbon from surface waters to the ocean interior and marine sediments. We demonstrate that a shift from bacterioplankton-dominated to more eukaryote-rich ecosystems is unlikely to have considerably impacted the efficiency of Earth’s biological pump. In contrast, the evolution of large zooplankton capable of vertical movement in the water column would have enhanced carbon transfer into the ocean interior. However, the impact of zooplankton on the biological carbon pump is still relatively minor when compared with environmental drivers. In particular, increased ocean temperatures and greater atmospheric oxygen abundance lead to notable decreases in global organic carbon transfer efficiency. Taken together, our results call into question causative links between algal diversification and planetary oxygenation and suggest that climate perturbations in Earth’s history have played an important and underappreciated role in driving both carbon sequestration in the ocean interior and Earth surface oxygenation.