[Coral-List] Sargassum Season and Dust

[tomascik at novuscom.net]

Sargassum may be the Canary in the coal mine signaling a possible regime
shift in the Atlantic equatorial upwelling system, as well as the
upwelling system off the west coast of Africa.

 The following  quote from the Abstract should concern everyone:

 "The bloom of 2011 might be a result of Amazon River discharge in
 previous years, but recent increases and interannual variability after
 2011 appear to be driven by upwelling off West Africa during boreal
 winter and by Amazon River discharge during spring and summer,
 indicating a possible regime shift and raising the possibility that
 recurrent blooms in the tropical Atlantic and Caribbean Sea may become
 the new norm."


 Tom

>
> Thanks for the brief review, Gene,
>
>
> The Sahara dust hypothesis is an intriguing one, both in terms of iron
> enrichment resulting in widespread Caribbean nutrification, and as a
> potential source of pathogens. My colleagues and I have included dust in
> some recent synthesis papers related to Caribbean reef ecosystem function
> (see below).
>
>
> But as I communicated to Gene a few months back, I'm having doubts about
> dust.
>
>
> Recent trips to the Red Sea reveal highly oligotrophic reef systems that
> are dumped on regularly by desert dust. Check out this video of the reefs
> off Egypt:
>
>
>
> https://youtu.be/DKGlOfa1clw<https://nam05.safelinks.protection.outlook.com/?url=https%3A%2F%2Fyoutu.be%2FDKGlOfa1clw&data=01%7C01%7Cpawlikj%40uncw.edu%7C816e7d31de284894298608d6f3e70234%7C2213678197534c75af2868a078871ebf%7C1&sdata=dUMUvCZL9B0AAc%2BiBBQJh4VKunl1oqkiQmTfVq5WRM0%3D&reserved=0>
>
>
>
> In the water column above Red Sea reefs, there was visible trichodesmium,
> near daily accumulations of dust on the boat deck, but on the reefs, no
> seaweeds, sponges, or coral disease.
>
> What is different is that there are no river inputs to the Red Sea, and a
> LOT of freshwater coming into the Caribbean from the Amazon (driven N by
> surface currents), Orinoco, Magdelena, and Mississippi (see the vicious
> circle hypothesis paper, below). We've also found that the sponges on the
> Saudi side of the Red Sea are starving as you move offshore along a
> gradient of decreasing DOC, something we don't see in the Caribbean, where
> levels of labile DOC seem to be higher, probably because of all the
> seaweed.
>
>
> In short, I think river inputs (and DOC) are much more important than dust
> in explaining the difference between Caribbean reefs and those in other
> parts of the tropics.
>
>
> Any thoughts from the oceanographers at KAUST?
>
>
> Regards,
>
>
> Joe
>