Reconstructing volcanic ash input to the Pacific Ocean: how does it link to Cenozoic climate?

Volcanic ash is known to influence a range of biogeochemical processes once deposited in the oceans, with explosive volcanism inputting large amounts of highly reactive and nutrient-rich material to the oceans every year. This material can stimulate increases in primary productivity, with ash alleviating nutrient limitations. This may eventually lead to enhanced carbon burial at the seafloor, with evidence from deep time suggesting this process may play a role in episodes of global cooling. As a result, reconstructing the amount of volcanic ash entering the oceans is important for understanding the role explosive volcanic activity has on global climates. However, extant records of changing volcanic intensity are either limited to regional studies of small numbers of volcanoes or are based on imperfect methods such as visible tephra layer counting.

In this work, we use the output of a model-derived dataset of sediment provenance from the Pacific Ocean, which provides estimates of changing volcanic material input for 67 sites. We use these data, and an inverse weighting approach, to reconstruct changing levels of volcanic ash input for the Cenozoic Period (66 million years ago to present). With around 75% of all active volcanoes located in the Pacific Ring of Fire, this record likely represents the majority of all volcanic ash through the Cenozoic, and so we compare it to known climate change through the period. We see increases in volcanic ash input around 35 million years ago and 10 million years ago, which can be linked to eruptions from the Sierra Madre Occidental, and Izu Bonin Arc, respectively. The first uptick occurs at the same time as the Eocene-Oligocene transition, an episode of global climate cooling, whilst the second covers the descent into the Pleistocene glaciations. These findings hint at the climatic impact of ash input, one which has major implications for the development of the Earth system.