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 (C_org), 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 C_org % in the period prior to 14 Ma but higher and much more variable C_org % afterward. Although lower absolute productivity may have contributed to the lower C_org burial at the MCO, higher relative C_org degradation also occurred. Ratios of C_org to other productivity indicators indicate higher relative loss of C_org. Temperature records imply that the higher C_org 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 C_org 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.