Did Archean mantle plume events stimulate or limit marine productivity?

English Abstract:

Iron Formations are a hallmark of Archean chemical sedimentation, yet the impact of associated mantle plume events on biological productivity in the oceans is poorly understood. Iron Formations typically have low organic carbon content, but are commonly stratigraphically associated with organic matter-rich shales. Low organic carbon contents in iron formations have been explained by oxidative remineralization of organic matter in presence of co-precipitated iron oxyhydroxides. To understand the impact of mantle plume events on biological productivity in the Archean oceans, it is critical to know what in general controlled organic productivity and burial in the Archean oceans and how high they were.

We approach this question from the perspective of biogeochemical carbon cycle under largely anoxic surface conditions typical for the Archean. Since organic carbon from older sediments would not be oxidized during continental weathering, carbon isotope mass balance requires that carbonate carbon released from older sedimentary successions during continental weathering would also not be utilized for biomass production. As a result, Archean organic productivity and burial were limited and processed only juvenile, mantle-derived carbon. The limitation was likely imposed by a smaller flux of nutrients delivered from the continents under anoxic surface conditions. Mantle plume events that led to deposition of iron formations could have also resulted in a higher flux of nutrients to seawater via submarine hydrothermal processes and acidic weathering conditions, induced by a higher volcanic flux of CO₂ and SO₂ to the atmosphere. We thus suggest that on a geological timescale mantle plume events could have led to enhanced marine productivity, which might explain associated, short-lived oxidation events before the GOE.