INTRA-OCEANIC SUBDUCTION ZONES AND THEIR IMPACT ON PALEOCLIMATE

Subduction plays a crucial role in transferring materials between the Earth’s interior and its surface, exerting significant influences on long-term climate through carbon storage and emissions. Plate tectonic-related carbon fluxes over time can be estimated through various calculations, such as tracking global subduction lengths and slab fluxes, all of which hinge on kinematic analyses of global plate reconstruction models and in particular their reconstruction of past subduction. However, due to the continual recycling and loss of oceanic plates into the mantle, ancient intra-oceanic subduction zones (i.e. subduction of an oceanic plate underneath another oceanic plate) may be absent or poorly-constrained in global plate motion models.

In this study, we estimate global subduction lengths and slab fluxes from "TOMOPAC", a new plate reconstruction model that includes deep mantle constraints to recreate intra-oceanic subduction in the Pacific-Panthalassa region. We link TOMOPAC and its identified intra-oceanic subduction zones using K-means clustering across a set of global P- and S-wave tomographic models. We then compare TOMOPAC to a commonly used global plate model to estimate carbon fluxes and the implications for ancient climates (Matthews et al., 2016). Incorporating intra-oceanic subduction through TOMOPAC increases the overall length of subduction zones between 50-85 Ma and 117-190 Ma. This increase is particularly noticeable in the northern Pacific area, which in TOMOPAC is populated by a complicated network of smaller, younger plates instead of a single large plate. We calculate the amount of subducted crustal carbon implied by TOMOPAC using the carbon content found in the top layer of the oceanic crust and seafloor sediments. Our findings will help to further explore the role of intra-oceanic subduction zones in the carbon cycle.