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Massive Sargassum Seaweed Bloom is Choking The Caribbean — Climate Change a Likely Culprit
19
August, 2015
According
to Carribean leaders, it’s a disaster that will take at least
100,000 people and 120 million dollars to clean up.
And disaster may not be the best word to describe it — for an
enormous Caribbean beach and water choking bloom of sargassum algae
may be a new abnormal ocean condition. Yet one more dangerous upshot
of a warming world.
(Great,
sulfur-stinking mats of sargassum algae are now choking the beaches
and near-shore waters of the Caribbean. In some places the mats are
10 feet deep. These great piles of seaweed can foul beaches, kill off
native species, and result in ocean dead zones when they rob waters
of nutrients and then die off — pulling life-giving oxygen out of
the water by decomposition. Image source: Mission
Blue.)
*
* * * *
A
Legend of the Ancient Mariners
The
story, in this case, begins with an enormous mat of algae called the
Sargasso Sea. This vast collection of organisms has at its foundation
two forms of algae that produce inter-connected floating masses of
seaweed. The mats collect and link together in an Atlantic Ocean Gyre
— forming a vast region off the United States Coast.
Ancient
sailors crossing the Atlantic during the dawn of North American
colonization often passed through the Sargasso Sea. It tended to be a
notable feature of their travels as the floating mats were sometimes
dense enough to halt the progress of vessels.
(An
1891 map proved by NOAA shows the regions of low and high
concentration sargassum seaweed in the North Atlantic and Caribbean.
Image source: NOAA
— Teachers at Sea.)
For
hundreds of years the enormous collection remained a mystery. But by
the 20th Century researchers had found that the seaweed was
transported by the Gulf Stream from the Gulf of Mexico and Carribean
into an area just south of Bermuda. There it bloomed as it fed on
nutrient-laden run-off spreading outward from the large estuaries of
the North American Continent. The sargassum then efficiently recycled
these nutrients to support a vital community of hundreds of sea
creatures and birds.
The
Sargassum algae that make up the Sargasso Sea are not only native to
this region. It ranges the tropical and subtropical zones of the
Atlantic — blooming wherever there is warmth and nutrients to
support it. Lately, there have been signs that biodiversity in the
Sargasso Sea is falling. Recent research expeditions are noting fewer
and fewer of the species traditionally supported by the sargassum
mats. It’s a potential sign of failing ocean health. One that is,
perhaps, linked to the massive accumulation of sargassum in the
Carribean during recent years.
(Big
changes in the Sargasso Sea. MBARI expedition finds lower
biodiversity in the sargassum mats. Video source: MBARI/Youtube.)
Ocean
Sargassum Fertilization in a Warming World
Due
to its highly efficient use of nutrients, pelagic sargassum thrives
in warm, well-fertilized waters. And lately, as the Earth has warmed,
run-off into the Atlantic Ocean habitats of the sargassum has
increased. Added
heat in the atmosphere has resulted in greater instances of heavy
downpours.
These downpours increase erosion — flushing more nutrients into
streams and rivers.
In
addition, fertilizer-based farming industry leaves soil laden with
phosphates and nitrogen. So the heavier downpours are now raining
over lands that are artificially loaded with nutrient. Adding to the
fertilizer flush is a constant rain of nitrogen particle fallout from
an immense and global burning of fossil fuels over the world’s
waters — a third new source of nutrient that wasn’t there for the
sargassum to access before. Finally, an added warmth in the surface
waters due to greenhouse gasses forcing the world to heat up by 1
degree Celsius over the past 135 years creates a yet more ideal
environment for the sargassum to grow and bloom.
Reports
now indicate that much of the seaweed choking off the Caribbean’s
beaches and waters is issuing from a region east of the Amazon River
outflow. These reports hint that deforestation, a resulting increase
in erosion of Amazon Rainforest soils, and the rise of industrialized
farming in Brazil may also be playing a role in the current epic
bloom.Finally,
there is growing evidence that the Gulf Stream current — a
transporter of sargassum out of the Carribean and Gulf of Mexico may
be slowing down as thermo-haline circulation weakens.
All these factors — the warming waters, the increased nutrient
loading of the surface waters, and the reduction of sargassum
transport due to Gulf Stream slowing — combined hint at a sargassum
seaweed train wreck whose epicenter is the Caribbean Sea.
Caribbean
Beaches, Ocean Life Under Threat
Over
recent years, it’s thought that these factors combined to help
generate a massive bloom of sargassum in the Caribbean. As early as
Fall of 2014 reports had been trickling in of 3-4 foot thick mats
collecting along Caribbean coastlines and piling up on beaches. By
August of 2015 the mats have grown to as dense as 10 feet thick. Now
vast swaths of beaches are covered in the sulfur-stink of this great
pile of dying biomass.
Typically
sargassum is a vital part of the life-giving system of the Atlantic
Ocean. Numerous species of fish, including tuna and jacks, rely on
the food provided by the prolific algae. Birds, turtles, and scores
of invertebrates also rely on the algae in one way or another. But
when the algae becomes too prolific it turns from boon into curse.
Sea turtle nests become fouled with the stuff. New hatchlings often
are unable to clamber through the dense piles to reach the sea. The
dense tangles reduce the mobility of larger animals including sharks,
rays, and adult turtles. And when the piles become too thick large
sections of the sargassum are cut off from light and nutrients. The
result is that the large masses can contain oxygen deprived zones
where the dead matter decays. These
little pockets host hydrogen sulfide and other sulfur producing
bacteria —
further toxifying the waters and resulting in the now prevalent
reports of a ‘rotten eggs’ smell near the sargassum piles.
(“From
the surface, it looks bad. But could you imagine if you were a fish?”
Dave Eliot goes underwater to take a look at these climate-change
enhanced algae blooms. Video source:YouTube.)
For
Caribbean Island nations, who rely so much on their pristine beaches
and ocean habitats as a source of economic stability, the amazing
accumulation of sargassum is a disaster. Today Sir
Hilary Beckles of the University of the West Indies called on the
international community for aid saying:
“Herein is an endemic and systemic threat to the resilience and development of these nations and therefore we must have an international response to this… What you are looking at is maybe US$120 million . . . and probably we would have to deploy over 100,000 people to carry out a similar strategy across the Caribbean space to make our beaches available to those who wish to use them for their multiple purposes… We must show our children enjoying our beaches and give visitors the assurance that the weed is not killing us and that life goes on. We must let people know that we in the Caribbean are not sitting on our hands but trying to find solutions to the threat presented by the Sargassum weed.”
But,
as with so many of the disasters cropping up these days — simply
reacting to the symptoms (be it sargassum, or drought, or flood, or
mass migration, or sea level rise, or wildfires, or species
endangerment, or a thousand other issues related to human fossil fuel
emissions and a great heating of the atmosphere and oceans) does not
address the root cause. And for that you need a rapid cessation of
fossil fuel burning.
Links:
Hat
tip to Andy in San Diego
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