Ocean-arcs as a hidden cooling mechanism during the early Paleozoic

Andrew Merdith, Maëlis ARNOULD , Lucy McGee, Alexandre Janin, Simon Williams, Stefan Loehr, Morgan L. Blades , Benjamin Mills

The late Cambrian to end Ordovician is marked by a long-term climatic cooling, culminating with the short lived (<2 Ma) Hirnantian icehouse, before recovering to warmer climates. Increased silicate weathering during the Laurentian Taconic orogeny, driven by the accretion of ocean island arcs and obduction of ophiolites, has been invoked as a causal mechanism to help explain cooling. However, prior to their accretion or obduction through arc-continent collision, these will have occurred as a series of mafic–intermediate volcanic islands. At the present-day, oceanic island arcs located in equatorial regions contribute the highest silicate weathering flux globally. We demonstrate that the abundance and evolution of low latitude ocean arcs in the late Cambrian and Ordovician can help account for gradual cooling over this time. We extract estimates of ocean arc lengths from a full-plate reconstruction and, using constraints from the present day, parameterise their potential contribution to the silicate weathering cycle within an Earth System model (SCION). We show that ocean arc weathering induces a minimum cooling of 1–2°C, and up to 5–7°C in our preferred scenario and helps reconcile model strontium and osmium isotope records with geochemical proxy data. We conclude that the prevalence of ocean-arcs and associated delivery of mafic weathering material was an important contributor to silicate weathering at this time and could be an overlooked CO2 drawdown mechanism throughout Earth history.