Variations in the Biological Pump through the Miocene: Evidence from organic carbon burial in Pacific Ocean sediments

Abstract. The biological pump, defined as the marine biological production and sedimentation of particulate organic carbon (Corg), is a fundamental process to fix atmospheric carbon dioxide in the oceans, transfer carbon away from the atmosphere to the deep ocean, and maintain the CO2 level of the atmosphere. The level of carbon sequestration by the biological pump has varied throughout the last 50 million years, from particularly weak in the warm Eocene to much stronger in the Holocene. However, persistently warm climates in the more recent past, e.g., the Miocene Climate Optimum (MCO; 17 million years ago [Ma] to 13.8 Ma) also have affected the biological sequestration of carbon. A series of scientific ocean drill sites from the equatorial Pacific contain very low sedimentary Corg % in the period prior to 14 Ma but higher and much more variable Corg % afterward. Although lower absolute productivity may have contributed to the lower Corg burial at the MCO, higher relative Corg degradation also occurred. Ratios of Corg to other productivity indicators indicate higher relative loss of Corg. Temperature records imply that the higher Corg degradation occurred in the upper water column, and global cooling strengthened the biological pump but led to more variability in burial. Similar records of low Corg at the MCO can be found in the North Pacific, which suggest this was a global—rather than regional—change. A weakened biological pump during warm climate intervals helps to sustain periods of global warmth.