Variations in the biological pump throughout 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 (POC), is a fundamental process for fixing atmospheric carbon dioxide in the oceans, transferring carbon away from the atmosphere to the deep ocean, and maintaining the CO2 level of the atmosphere. The level of carbon sequestration caused by the biological pump has varied throughout the last 50 million years, from particularly weak during the warm Eocene period to much stronger during the Holocene. However, persistently warm climates from the more recent past, e.g., the Miocene Climate Optimum (MCO; 17 to 13.8 Ma – million years ago), also affected the biological sequestration of carbon. A series of scientific ocean drill sites from the equatorial Pacific exhibit very low percentages of sedimentary POC from the period prior to 14 Ma but show higher and much more variable POC percentages from the period afterwards. Although lower absolute productivity may have contributed to more limited POC burial during the MCO, higher relative POC degradation also occurred. Ratios of POC to other productivity indicators indicate a greater relative loss of POC. Temperature records suggest that higher levels of POC degradation occurred in the upper water column and that global cooling strengthened the biological pump but led to more burial variability. Similar records of low POC levels during the MCO can be found in the North Pacific, suggesting that this was a global – rather than regional – change. A weakened biological pump during warm climate intervals helps to sustain periods of global warmth.