Oceans & marine

The potential of carbon sequestration by marine based plants such as mangroves, seagrass and algae, often referred to as blue carbon, and the importance of better understanding it, has clearly been recognised (Mcleod et al. 2011). The IPCC Special Report on the Ocean and Cryosphere in a Changing Climate (2019) concluded blue carbon can play an important role in both climate regulation and adaptation. The term algae groups together several kinds of marine photosynthetic organisms. These are often subdivided into very small microalgae like phytoplankton, and larger macroalgae like kelp and seaweed. Although there is still large uncertainty about the total amount of carbon sequestered by these marine organisms, a recent estimate by Duarte et al. (2022) indicated that all macroalgae took in as much CO2 as the Amazon rainforest.

The oceans are the largest carbon sink for atmospheric carbon, and have taken up over 30% of anthropogenic emissions. Carbon uptake mainly occurs directly through ocean-atmosphere interaction or through weathering processes. Due to this uptake of carbon the oceans turn more acidic overtime, and since the start of the industrial revolution oceans have become 30% more acidic. This has all sorts of effects, as it for example impacts marine biochemistry, and prevents certain organisms from successfully growing.

Fisheries contribute to global CO2 emissions by the extraction of fish, disturbance of coastal and oceanic blue carbon ecosystems, and the use of fossil fuels as their main energy source. Fishing vessels are moreover a major source of short-lived climate forcers like black carbon (McKuin and Campbell 2016), which can have a major effect in Arctic and Northern regions (see Black carbon reduction).

Oceans play an important role in global heat transfer and carbon storage processes. As global temperatures and atmospheric carbon levels rise, some have suggested artificially modifying the vertical movement of water to enhance these processes.