Sargassum: An Emerging Anthropocene Risk


GEO Blue Planet

[20200630] How do you deal with 9m tonnes of suffocating seaweed?


This Web Workspace supports the GEO Blue Planet Working Group on Sargassum.


Sargassum: An Emerging Anthropocene Risk

The recent transition from the Holocene into the Anthropocene has created a number of Anthropocene risks that pose severe challenges on all scales from local to global (Key et al., 2019). Many of these risks constitute global catastrophic risks (GCRs; Avin et al., 2018), including climate change, ocean warming and acidification, extinction and resource depletions. The ocean is experiencing large and rapid changes and it is of fundamental importance to better understand the spectrum of possible futures for the ocean.

Harmful sargassum growth episodes are increasing both in frequency and magnitude. The growth of sargassum is to a large extent dependent on the availability of nutrients (nitrogen and phosphorous), iron, carbon, and ocean water temperature (Olabarria et al., 2013). Modern global warming is increasing ocean heat contents with estimated rates of 0.5 to 1.0 W/m2 (Cheng et al., 2016). Recent carbon emissions have increased availability of carbon in the ocean. Land use changes including deforestation and industrialized agriculture have increased the flows of nutrients into the ocean. The increase of flows of African atmospheric dust as a consequence of modern climate change further adds nutrients and in particular iron to the ocean (Djakourè et al., 2017).

The explosive growth of sargassum is attributed to a combination of modern ocean warming and the influx of nutirents into the ocean, which both are the result of human activities in the anthropocene. Thus, the risk associated with the threat of sargassum is one of the emerging Anthropocene risks.

Sargassum Blooms

In 2011, an unprecedented influx of sargassum occured from the West African Coast to the Brazilian, Caribbean and Gulf of Mexico coastlines. Since then, the massive influx of sargassum has returned in all but one year, with devastating impacts on tourism on many Caribbean islands and along the coasts of the Gulf of Mexico. The so-called “Great Sargassum Belt” consists of dense mats of sargassum, and the area covered by these mats continues to grow exponentially (Wang et al., 2019). In 2018, the mats were covering a distance of 8.850 km, and in 2019 a similar bloom occured (see, for example, the article by Nicola Davis in The Guardian). The current development in May and June 2020 also indicates a large bloom.

The exponential growth of sargassum during the last decade has resulted in beaching events with severe impacts on public health, tourism, fisheries, coastal infrastructure, and other ocean-related activities in the impacted regions (see, for example, the article by Anna Turns in The Guardian). It is expected that these beaching events will increase in magnitude and frequency in the future particularly in the tropical and subtropical Atlantic.

Purpose

This web space aims to provide comprehensive information on sargassum and an assessment of the risks associated with the repeated blooms of sargassum. The risk assessment can inform risk governance and facilitate the development of interventions to adapt and mitigate the impacts of the blooms.

References

Avin, S., Wintle, B. C., Weitzd¨o;rfer, J., hEigeartaigh, S. S. O., Sutherland, W. J., Rees, M. J., 2018. Classifying global catastrophic risks, Futures, 102, 20-26, DOI 10.1016/j.futures.2018.02.001.

Cheng, L., Trenberth, K. E., Palmer, M. D., Zhu, J., and Abraham, J. P., 2016. Observed and simulated full-depth ocean heat-content changes for 1970–2005, Ocean Sci., 12, 925-935, doi:10.5194/os-12-925-2016.

Djakourè, S., Araujo, M., Hounsou-Gbo, A., Noriega, C. and Bourlès, B., 2017. On the potential causes of the recent Pelagic Sargassum blooms events in the tropical North Atlantic Ocean. Biogeosciences Discuss., DOI: 10.5194/bg-2017-346.

Keys, P. W., Galaz, V., Dyer, M., Matthews, N., Folke, C., Nystr¨o;m, M., Cornell, S. E., 2019. Anthropocene risk, Nature Sustainability, DOI 10.1038/s41893-019-0327-x.

Olabarria, C., Arenas, F., Viejo, R.M., Gestoso, I., Vaz‐Pinto, F., Incera, M., Rubal, M., Cacabelos, E., Veiga, P. and Sobrino, C., 2013. Response of macroalgal assemblages from rockpools to climate change: effects of persistent increase in temperature and CO2. Oikos, 122(7), pp.1065-1079.

Wang, M., Hu, C., Barnes, B. B., Mitchum, G., Lapointe, B., Montoya, J. P., 2019. The great Atlantic sargassum belt. Science, 365(6448), 83-87, doi 10.1126/science.aaw7912.


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