Subaerial volcanism is a potentially major contributor to oceanic iron and manganese cycles

Jack Longman,Morgan T Jones,Martin R Palmer,Thomas M Gernon,Hayley R Manners

doi:10.1038/s43247-022-00389-7

Abstract

Surface ocean availability of the micronutrients iron and manganese influences primary productivity and carbon cycling in the ocean. Volcanic ash is rich in iron and manganese, but the global supply of these nutrients to the oceans via ash deposition is poorly constrained. Here, we use marine sediment-hosted ash composition data from ten volcanic regions, and subaerial volcanic eruption volumes, to estimate global ash-driven nutrient fluxes. Using Monte Carlo simulations, we estimate average fluxes of dissolved Iron and Manganese from volcanic sources to be between 50 and 500 (median 180) and 0.6 and 3.2 (median 1.3) Gmol yr−1, respectively. Much of the element release occurs during early diagenesis, indicating ash-rich shelf sediments are likely important suppliers of aqueous iron and manganese. Estimated ash-driven fluxes are of similar magnitude to aeolian inputs. We suggest that subaerial volcanism is an important, but underappreciated, source of these micronutrients to the global ocean.

Highlights

Surface ocean availability of the micronutrients iron and manganese influences primary productivity and carbon cycling in the ocean
We compare the composition of fresh ash from 10 active volcanic regions globally (Fig. 1) with the composition of ash recovered from marine sediments of various ages (Supplementary Fig. 1), to estimate the loss of Fe and Mn over a longer timescale than permitted in experimental studies
The longer timescale approach is analogous to studies of dissolved and colloidal Fe released from shelf sediments during long-term diagenesis, which is known to be an important source of Fe to surface waters where it can stimulate phytoplankton growth[26]

Summary

Introduction

Surface ocean availability of the micronutrients iron and manganese influences primary productivity and carbon cycling in the ocean. Our simulations suggest a likely net flux from ash diagenesis of 0.6–3.2 Gmol Mn yr−1, (Fig. 3), with the median value from the ‘medium’ scenario of 1.3 Gmol Mn yr−1 comparable with both dissolved fluvial flux and atmospheric deposition, but smaller than the hydrothermal Mn flux (Table 1) and particulate fluvial flux[40].

Results

Conclusion