Marine Animal-Sediment Interactions Under Global Change - Biogeochemical Consequences in the 21st Century

Benthic animals profoundly control the cycling and storage of carbon and other elements in marine systems, particularly in coastal sediments. Recent climate change has altered the distribution and abundance of many seafloor taxa and modified the vertical exchange of materials between ocean and sediment layers. Here, we examine how global change could alter animal-mediated biogeochemical cycling in ocean sediments, which represent Earth's largest interactive landscape for organic carbon storage. The fossil record shows repeated major responses from the benthos during mass extinctions and global carbon perturbations, including reduced diversity, dominance of simple trace fossils, decreased burrow size and bioturbation intensity, and non-random extinction. The broad dispersal capacity of many extant benthic species facilitates poleward shifts corresponding to their environmental niche as overlying water warms. Evidence suggests that locally persistent populations will likely respond to environmental shifts through genetic adaptation rather than via phenotypic plasticity. Regional and global ocean models largely ignore changes in benthic biological activity and their feedbacks on sedimentary biogeochemical processes, insufficiently integrating animal ecology and biogeochemistry. The emergence of bioturbation, ventilation and seafloor-habitat maps, and progress in our mechanistic understanding of organism-sediment interactions enable incorporation of potential effects of climate change on benthic macrofaunal mediation of elemental cycles into regional and global ocean biogeochemical models.