Halocarbon Emission Estimates from Prospective Expansions in Seaweed Mariculture

Seaweed farming has been proposed as a natural climate solution with the potential to draw down carbon dioxide and as such, it is receiving growing attention. With numerous plans to upscale current production for a diverse range of applications, the seaweed industry is expected to significantly expand over the next decades.

Seaweeds emit natural short-lived halocarbons (SLH), such as bromoform (CHBr3), dibromomethane (CH2Br2), and methyl iodide (CH3I). These trace gases and their products have complex direct and indirect effects in the atmosphere, for example, with regards to radiative forcing, ozone depletion, and oxidative capacity. Based on the assumption that expanding seaweed aquaculture will lead to increasing SLH emissions, our future goal is to investigate the interplay of resulting impacts on the climate system.

In this study we create SHL emission scenarios by combining present-state emission rates with future-projected seaweed distributions. We distinguish between anthropogenic and natural sources, and partition the natural source strengths from macroalgae versus phytoplankton. This way we can derive SHL emissions based on only the assumed elevated proportion from seaweeds. In the future, we plan to utilize these datasets to initialize and force a fully-coupled Earth system model. We will implement a parameterization that uses the prescribed ocean concentrations and prognostically adjusts SHL sea-air fluxes according to key environmental variables. Ultimately, these experiments will contribute to a better understanding of the combined effect of climate change and expanding seaweed aquaculture.

This project is part of Blue Carbon Canada—a collaborative research initiative that aims to assess the potential for Canada’s coastal systems to serve as natural climate solutions.