The influence of land position, land size and albedo on Mesoarchaean climate

Climate change potentially played a pivotal role in the Mesoarchaean gold mega-event, when microbial fixation bound huge amounts of gold in 2.9 Ga siliciclastic sediments. Remnants of this are still preserved in the Witwatersrand gold province (Kaapvaal Craton), where the auriferous 2.90–2.79 Ga Central Rand Group is distinguished from the essentially barren 2.95–2.91 Ga West Rand Group, despite similar sedimentology. This has been explained by intense chemical weathering in Central Rand Group times having facilitated gold leaching from the Archaean hinterland. In this study we investigated the principal drivers behind the suspected climate shift at around 2.9 Ga by performing 124 simulations using Planet Simulator, an Earth system model of intermediate complexity. We assessed the effects of varying land distribution (land concentrated at the equator, at the poles, and dispersed across various latitudes), land surface area, atmospheric CO₂-equivalent concentrations, and surface albedo. In addition to the expected strong dependence of global mean temperature on atmospheric greenhouse gas concentration, our results reveal reduced temperature variability at higher atm. CO₂-equivalents. Increasing land area generally leads to cooling, except at low CO 2 -equivalent concentrations (3–5%) and low albedo (<0.2). When land exceeds ~13% of total Earth's surface, it starts to have a pronounced climatic effect. Among the various spatial land positions, land distribution across different latitudes shows the highest climate sensitivity. The postulated 2.9 Ga climatic shift may be linked to emergence of extensive low-albedo (<0.2) surfaces (e.g., mafic/ultramafic rocks) and/or drift of the Kaapvaal Craton to middle or lower latitudes. • Sensitivity study of Archaean climate drivers was conducted using Planet Simulator. • At >13% land cover, climate shifts from atmospheric- to surface-driven. • Continental growth, esp. at mid-latitudes, can alter global temperature by up to 20 °C. • Increase of dark surface (α < 0.2) led to global warming, possibly aiding gold formation.