Oasis in the Sargasso Sea

upwelling_eddy.gifWood’s Hole researchers in the Eddies Dynamics, Mixing, Export, and Species composition (EDDIES) project confirmed that ocean productivity is enhanced by upwelling eddies in the oligotropic Sargasso Sea. The slowly swirling water masses were teeming with diatoms in concentrations 10,000 to 100,000 times the norm, among the highest ever observed in the Sargasso Sea. They compare these features to “oases in the desert”.

The researchers employed a combination of remote sensing, video plankton recorders, ocean drifters, tracers and traditional measurements of water properties and current speeds during six months of ship-based work in the summers of 2004 and 2005.

This type of information is important to our understanding of highly migratory seabirds, mammals, and fish. The satellite tracked animals seem to ‘home in’ on these features for extended periods of time.

NASA’s Earth Observatory hosts the story here
Image from Ocean Atlas page on air-sea interactions

7 Replies to “Oasis in the Sargasso Sea”

  1. Fantastic finding, although my first question is: just how persistent are these, and at what scale? As someone who works with highly migratory species (HMS) of fishes, it strikes me that either a) these are persistent — or regular! — features that could be homed in upon yearly, for example, for HMS spawning, or b) that the presence or absence of these features at unpredictable temporal/spatial scales might play a role in variable yearly recruitment patterns for HMS juveniles as they move from the eastern to western North Atlantic.

    Certainly food for thought… thanks for the post!

  2. I haven’t seen interannual maps of the eddy field in this study, but eddies can be persistent in space and time. Haida eddies off BC last 2 years and more, but they are infrequent. Gulf of Mexico loop current eddies have been identified as nursery habitat for billfish. The eddies are unpredictable, but you’re almost always likely to find one in the Gulf somewhere.

    This intersection between satellite oceanography and marine biology is the hottest thing happening today, in my opinion. Deep Sea Research II has an entire issue dedicated to these and other “hotspots” in the North Pacific.


  3. It has been suggested (I’ve heard this somewhere or read it, can’t remember where – I really need to get organized and start writing down such things) that birds can smell DMSO (a by-product of bacteria metabolism – a lot of food – a lot of bacteria – a lot of DMSO) far away. I can easily imagine how this could be a queue for birds to seek eddies.

  4. Sorry for the delay, but I was (and still am) virusstruck (ACDC anyone? :) ), which effectively grounded me to the bed.

    Anyway, I couldn’t sleep until I solved the DMS(O) mystery. I quote from Nybakken and Bertness’ Marine Biology: An ecological approach:

    “As noted previously, we now know from satellite tracking of certain albatrosses that these birds regularly travel immense distances to forage for food for their chicks. The knowledge has raised the question of how the albatrosses, and related procellariiform seabirds such as petrels and shearwaters, find their patchily distributed food sources – mainly krill, quid and fish – in a vast and featureless ocean. The first clue to the answer is that these birds possess an anatomically elaborate sense of smell, which, in contrast, is poorly developed in most birds. Included in this mechanism is an elaborate olfactory epithelium housed within a tubular-shaped nose, as well as large olfactory bulbs in the brain that rely information to higher centers. Because of the tubular nature of the nostrils, these birds are also called “tube-nosed” seabirds.
    Nevitt (1999) has demonstrated that at least some of these birds respond quickly to the presence of the gas dimethyl sulfide (DMS) in the air. It is known that when krill feed upon phytoplankton, their prey release dimethyl sulfide, which can persist for hours or even days. The presence of krill in turn tends to attract their predators, which may in turn be preyed upon by the birds and other predators. Since krill occur in patches whose location is unpredictable in the vast reaches of the oceans, a mechanism that would allow them to be detected from large distances would make foraging more certain and less wasteful of energy.”

    Levitt, G. 1999. Foraging by seabirds on an olfactory landscape. Americ. Sci. 87:46-53.

  5. I am the person who is studying DMS and seabirds so please feel free to contact me with any questions.

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