Dust-borne soluble iron delivery to the Last Glacial Maximum oceans: Source inheritance versus atmospheric processing

COSENTINO, N. J.; HAMILTON, D. S.; LAMBERT, F.; RIQUELME, F.; ZHU, J.; ALBANI, SAMUEL; MAHOWALD, N. M.

Roma

Congreso; XXI INQUA Congress; 2023

INQUA

During the last 800,000 years, atmospheric CO2 concentration during glacial periods was between 25 and 45% smaller than during interglacial periods. Roughly one fourth of this difference is estimated to be due to a dust-induced stronger biological pump, mostly in the iron-limited southern oceans and northern Pacific, during dustier glacials. How was dust-borne soluble iron delivered to the glacial oceans? In the present-day climate, dust-borne iron at emission is mostly insoluble and solubilized through proton- and organic ligand-promoted atmospheric processing. However, this may not have been the case during glacials. First, drier glacials may have implied less chemical weathering of continental dust sources, thereby raising source-inherited iron solubility. Second, present-day anthropogenic gas emissions acidify the atmosphere and enhance the solubility of dust-borne iron during atmospheric transport, an effect which was absent during glacials. We thus hypothesize that during glacials dust-borne soluble iron inputs to iron-limited oceans were more strongly controlled by source-inherited iron solubility, and less so by atmospheric processing, compared to the present. To test this hypothesis, we will perform a set of Last Glacial Maximum (LGM, 21 ka BP) and pre-industrial (1850 AD) simulations using the Community Earth System Model 2, with coupled atmospheric and land components and with an atmospheric iron processing module. Dust emission rates will be tuned against a compilation of LGM and present-day dust deposition flux observations, and sensitivity analyses will be performed on two parameters: source-inherited iron solubility of dust and the intensity of atmospheric processing. Results will be discussed in the session.