Glacial CO2 Cycles: A Composite Scenario

Abstract:

There are three main contributors to the glacial drawdown of atmospheric CO₂ content: starvation of the supply of carbon to the ocean-atmosphere reservoir, excess CO₂ storage in the deep sea, and surface-ocean cooling. In this talk, I explore a scenario in which all three play significant roles. Key to this scenario is the assumption that deep ocean storage is related to the extent of nutrient stratification of the deep Atlantic. The stronger this stratification, the larger the storage of respiration CO₂. Further, it is my contention that the link between Milankovitch insolation cycles and climate is reorganizations of the ocean’s thermohaline circulation leading to changes in the deep ocean’s CO₂ storage. If this is the case, the deep Atlantic d¹³C record kept in benthic foraminifera shells tells us that deep ocean CO₂ storage follows Northern Hemisphere summer insolation cycles and thus lacks the downward ramp so prominent in the records of sea level, benthic ¹⁸O and CO₂. Rather, the ramp is created by the damping of planetary CO₂ emissions during glacial time intervals. As it is premature to present a specific scenario, I provide an example as to how these three contributors might be combined. As their magnitudes and shapes remain largely unconstrained, the intent of this exercise is to provoke creative thinking.