The emission of volatile halocarbons by seaweeds and their response towards environmental changes

Abstract

Volatile halocarbons can deplete the protective stratospheric ozone layer contributing to global climate change and may even affect local climate through aerosol production. These compounds are produced through anthropogenic and biogenic processes. Biogenic halocarbons may be produced as defence compounds, anti-oxidants, or by-products of metabolic processes. These compounds include very short-lived halocarbons (VSLH) e.g. bromoform (CHBr3), dibromomethane (CH2Br2), methyl iodide (CH3I), diiodomethane (CH2I2). Efforts to quantify the biogenic sources of these compounds, especially those of marine origin e.g. seaweeds, phytoplankton and seagrass meadows, are often complicated by inherent biological variability as well as spatial and temporal changes in emissions. The contribution of the coastal region and the oceans to the stratospheric load of halocarbons has been widely debated. This highlights the need to understand the factors affecting the release of these compounds from marine sources for which data for modelling purposes are generally lacking. Seaweeds are important sources of biogenic halocarbons subjected to changing environmental conditions. Huge uncertainties in the prediction of current and future global halocarbon pool exist due to the lack of spatial and temporal data input from coastal and oceanic sources. Therefore, investigating the effect of changing environmental conditions on the emission of VSLH by the seaweeds could help towards better estimations of halocarbon emissions. This is especially important in light of global changes in both climate and the environment, the expansion of seaweed cultivation industry, and the interactions between halocarbon emission and their environment. In this paper we review current knowledge of seaweed halocarbon emissions, how environmental factors affect these emissions, and identify gaps in understanding. Our aim is to direct much needed research to improve understanding of the contribution of marine biogenic sources of halocarbons and their impact on the environment.

Environmental effects of stratospheric ozone depletion, UV radiation, and interactions with climate change: UNEP Environmental Effects Assessment Panel, Update 2020

“…Atmospheric concentrations of anthropogenic halogen-containing very short-lived substances (VSLSs) have been increasing [ 407 ] and biogenic VSLSs are predicted to increase due to climate change [ 407 , 408 ]. For example, emissions of CHBr 3 from the ocean are projected to increase by 31% during 2010–2100 under a scenario of high emissions of GHGs [ 407 ].…”

New Aspects of Uptake and Metabolism of Non-organic and Organic Iodine Compounds—The Role of Vanadium and Plant-Derived Thyroid Hormone Analogs in Lettuce

“…The issue has been, to a limited extent, described in preliminary research by Smoleń et al (2020). This situation is different for marine algae, as these plants actively take up I, accumulate it in their tissues, and carry out methylation (Leblanc et al, 2006;Keng et al, 2020). The methylation process (I volatilization) has also been described for selected terrestrial plant species (Attieh et al, 2000;Nagatoshi and Nakamura, 2007;Itoh et al, 2009).…”

“…The functions of S-adenosyl-l-methionine (SAM)-dependent halide methyltransferase (HMT) or SAM-dependent halide/thiol methyltransferase (HTMT), enzymes responsible for I volatilization to CH 3 I or CH 2 I 2 , are subject to a complex control mechanism and are typical of a number of marine algae species (Keng et al, 2020) and terrestrial plants (Attieh et al, 2000;Nagatoshi and Nakamura, 2007;Itoh et al, 2009;Landini et al, 2012). These enzymes are not specific for I as a substrate but can also participate in the methylation of other group-17 elements (halogens) from the periodic table.…”

A Pathway to Carbon Neutral Agriculture in Denmark

“…Naturally, red seaweeds are strong oceanic emitters of bromoform, although the range of emission estimates is large. One study estimated emissions to the stratosphere at the rate of 29.1 to 274.2 micrograms per gram dry weight per day for red seaweeds (Keng et al 2020). If we assume that on average each ton of seaweed needs 30 days to grow in the ocean, the 46.2 million tons seaweed per year requested for cattle will release 40.3 to 379.9 gigagrams (Gg) bromoform annually to the stratosphere.…”