Blue Frontiers: Kelp Forests to Increase Carbon Sequestration

Building off our previous Scorcher on mangroves [1], this segment dives deeper into the possibilities of blue carbon by discussing the potential for kelp forests to be leveraged as a climate mitigation strategy. Amidst evolving blue carbon discussions, kelp is now adding to the arsenal of innovative natural climate solutions gaining recognition.

Kelp forests are large carbon sinks, in part due to their impressively fast growth rate. Under ideal conditions, kelp can grow up to 18 inches per day [2], creating towering canopies of underwater forests that support a variety of marine species. Belonging to genus Macrocystis, kelp is classified as a macroalgae, typically found in cool and relatively shallow waters. Since kelp is an algae, it does not have a plant-like root system, but instead collects nutrients directly from the water column and through photosynthesis [3].

The premise supporting kelp as a blue carbon solution is centered around permanence and scalability. As kelp grows, it continuously releases organic material, which is either deposited in marine sediments, consumed by aquatic life, or transported to shore. Primary production of kelp releases particulate organic carbon (POC) and dissolved organic carbon (DOC) with an estimated 90% of that sequestered carbon eventually reaching the deep sea [4]. If kelp biomass sinks to the ocean floor (naturally or intentionally), the carbon stored in macroalgal detritus is thought to be permanently sequestered due to the extremely low risk of reversal from deep-ocean disturbances [5]. In this case, carbon burial into sea floor sediments means that it is likely to remain there for centuries, if not millennia. Based on this finding, some reports estimate that ramping up kelp production through rehabilitation and afforestation activities could durably sequester between 1-5 billion tons of carbon dioxide per year [6], with approximately 18 million square miles considered ecologically viable for seaweed production (including kelp and other species) [7]. Depictions of kelp cultivation have also included the use of offshore line systems [6] to provide added flexibility for project location and deployment. While metrics like these are useful for considering the potential scope of new project types, we caution against adopting plantation style approaches that prioritize kelp over broader ecosystem health. Since the ocean is a major contributor to the global carbon cycle, increasing kelp cultivation suggests an intriguing opportunity for large-scale and cost-effective carbon sequestration, but one that should also be evaluated carefully.

From a carbon accounting perspective, there remain many challenges to overcome, and scientists are still uncertain about the ecological effects of drastically scaling up macroalgae deposition in marine environments [8]. To address these and other knowledge gaps, initiatives such as the Kelp Forest Foundation are working to develop a new voluntary carbon protocol for kelp cultivation projects to quantify and validate the carbon sequestration impact [9]. As we continue to follow the research and development of blue carbon innovation there appears to be mounting evidence that the oceans can, and will, emerge as a worthwhile arena for future carbon project development.

News + Resources
[1] Scorcher – Mangrove Forests Make Waves for Blue Carbon Markets
[2] NOAA – What is a kelp forest?
[3] Oceana – Giant Kelp
[4] Nature – Substantial role of macroalgae in marine carbon sequestration
[5] Kelp Blue – CO2 Removal
[6] Energy Futures Initiative – Expanding the Options for Carbon Dioxide Removal in Coastal and Ocean Environments
[7] Current Biology – Blue Growth Potential to Mitigate Climate Change through Seaweed Offsetting
[8] MIT – Companies hoping to grow carbon-sucking kelp may be rushing ahead of the science
[9] Kelp Forest Foundation – Blue Carbon Methodology