Regulation of last glacial-interglacial atmospheric CO2 by sea iron solubility in an Earth system model

OPAZO, N.; LAMBERT, FABRICE; RIDGWELL, A.; COSENTINO, NICOLÁS J.

Chicago

Congreso; AGU Fall Meeting 2022; 2022

AGU

Ice and sediment cores provide important information about the natural variability of atmospheric carbon dioxide (CO2), which has ranged between 180 and 280 ppm during glacial and interglacial periods, respectively. Recent studies have shown that the biological pump in the oceans is responsible for at least a quarter of this difference. One main factor responsible for the variation in CO2 concentration is iron supply to the surface ocean. As a result, an increase in wind-borne dust fluxes during cold periods, such as the Last Glacial Maximum (LGM), between 26-19 ka before present (BP), promotes significant biogeochemical activity by altering primary production and affecting the export and sequestration of carbon. Although the entire ocean is concerned, in certain areas, such as the high-nutrient, low-chlorophyll oceans, phytoplankton production is more sensitive to the availability of iron. However, both the deposition of dust and the solubilization of iron transported by dust particles are not homogeneous between basins, affecting the biological uptake of CO2. Here, we used the carbon-centric Earth system model of intermediate complexity cGENIE to quantify the effect of iron solubility on the biological pump under different Earth's conditions. We worked with LGM and Holocene (12-8 ka BP) surface dust flux reconstructions based on empirical data and CMIP5 model simulations. Since the present-day and past solubility of iron are not well constrained, a sensitivity analyses on this parameter was carried out both globally and for specific ocean basins to establish the main zones and conditions linked to the drawdown of CO2.