Trace-metal isotope 'fingerprints' of past solid Earth-ocean interactions

Abstract

Reconstructing the solid Earth processes that impact global carbon cycling is central to a full understanding of atmospheric pCO 2 and climate evolution, both in the geological past and into the long-term future. Changes in trace-metal concentrations and isotopic compositions in ocean sediments can be read as a record of fluctuations of the solid Earth-ocean interactions we would like to better understand, because these processes often perturb metal as well as carbon cycles. However, multiple processes can affect the same trace-metal or isotope system, creating ambiguity in proxy interpretations. Taking a multi-proxy approach can help resolve this. We present an Earth system model-based systematic analysis of effects of changing weathering, sedimentation, and magmatism in multiple proxy systems (Sr, Li, Os, Ca, δ 13 C), which are critical proxy systems for unravelling the sources and sinks of carbon through time. Although different solid-Earth processes yield similar responses in individual proxy systems, each solid Earth process leaves a distinct multi-proxy geochemical 'fingerprint' in the rock record. Importantly, these fingerprints are time-dependent, often yielding more distinct responses transiently than in steady state. Finally, we show how climate and weathering feedbacks can further modulate and overprint a simpler transient response, impacting both the amplitude and timing of metal isotope excursions. Our study highlights the importance of multi-proxy approaches to studying solid Earth-ocean interactions in the geologic record and demonstrates both the benefits of fully integrating analyses of carbon and metal cycle proxy dynamics as well as the use of numerical models in disentangling coeval drivers and feedbacks.