Can glacial–interglacial cycles impact microbially mediated early marine burial diagenesis?

Sediments are the interface between the “fast” and “slow” carbon cycle. However, the transition of carbon from the fast-cycling reservoirs into the slow-cycling lithospheric reservoir is not a straightforward one. Dissolution and precipitation of calcium carbonate, as well as the remineralization of organic matter take place at the entrance to the world’s largest carbon storage. Under the umbrella of “early marine burial diagenesis” (EMBD), these processes control mass fluxes of carbon and other elements, potentially releasing or sealing large amounts of carbon to or from the ocean. Despite its significance for carbon cycling and retrieving information on Earth system evolution from carbonate successions, EMBD itself has never been observed in situ since currently available methods allow sampling or measuring only of either lithified or unlithified material, destroying or severely altering the remaining sample. This technical bottleneck also limits our understanding of the interplay between climatic and EMBD processes. Here we summarize the knowns and unknowns of EMBD in the context of carbon cycling by synthesizing evidence from the rock record, sedimentological observations, and geochemical models. We aim to evaluate the extent to which lithification patterns could reflect external environmental forcing versus internal, self-organized processes. We further present a modelling approach estimating the impact of glacial–interglacial cycles on the depth of subsurface redox processes with implications on auto- vs. allocyclicity of EMBD.