Posts Tagged ‘Trichodesmium’

Salinity Processes in the Upper Ocean Regional Study (SPURS): Life in the Sargasso Sea

September 24th, 2012 by Maria-Jose Viñas

By Eric Lindstrom

John snags a flying fish in mid flight.

There are not many places in the open ocean that get their own special name as a “sea.” Most seas are what we call marginal seas – offshoots of the major ocean basins.

The Sargasso Sea, as a vast track of the western subtropical North Atlantic Ocean is known, has a special characteristic – something noted by Portuguese sailors for centuries and even visible from space. It is the home waters of Sargassum, a genus of brown macroalgae (seaweed) that inhabit the open ocean. The sea is named after the seaweed and it seems that small clumps are nearly always within sight of the ship (we have yet to see giant mats of the stuff in the SPURS region). Anyway, the Sargasso Sea is special because of a plant. Well, it is more complicated than that!

A patch of Sargassum at the surface (Photo: Julian Shanze.)

Sargassum, up close.

Closeup of Sargassum.

In my opinion, the really cool thing about Sargassum is that each clump can be a teeming ecosystem by itself. Several varieties of fish (e.g. Sargassum fish and flying fish), crabs , and nudibranchs live in close association with the weed. Each clump is a complex island of life floating free at the surface of the deep ocean. When you are out here in the vast emptiness of the open ocean, it is just hard to imagine how this intricate web of life came to be, survived, and actually thrives. Every time I am in the Sargasso Sea, it seems such a wonder.

A flying fish.

Barnacles on French glider recovered by Knorr.

We had spectacular sunset last night and I was reminded of the old adage: “Red sky at night, sailor’s delight. Red sky in morning, sailor’s warning.” Here we are still in proximity to Hurricane Nadine and is this saying true, or is it just an old wives’ tale? Like the answer to most questions, there is a web site for that. In fact I think it may be true for us; we are well south of the hurricane weather and forecasts have good weather for in days ahead.

Sunset sen from the Knorr.

An interesting sidebar to today’s blog topic is another kind of life we have found in great abundance at our SPUR study location. It was a mystery for a few days – we were seeing lots of floating microscopic reddish dusty particles. Some said it looked a little like sawdust (but where are the trees?), and some wondered whether it was floating dust from the Sahara. Well, thank goodness for the Web again. I discovered that it’s a bloom of an important nitrogen-fixing bacterium (Trichodesmium) also known as “sea sawdust.” It certainly reinforces the idea that a key to identification is a good description!

Trichodesmium in a bucket of sea water.

A Trichodesmium bloom in the Pacific Ocean seen from space.

Trichodesmium, it turns out, just loves these sea conditions – just as much as SPURS oceanographers love the North Atlantic salinity maximum!

Notes from the Field