Snow above, snow below

by Ivo Grigorov, EURO-BASIN Project Office

While waiting for the expedition to change over the scientific party before heading back out to sea, how about an imaginary journey. Imagine you had James Cameron`s DEEPSEA CHALLENGER submersible for a day, and you were descending down just below the FS Meteor in the Faroe-Shetland Channel. What would you see?


The expedition objectives are to better understand the role of winter convection on the dynamics of the microbial loop, the evolution of oncoming spring bloom and its accompanying zooplankton community. The interaction between the two not only underpins marine ecosystems (all the way to species that end up on our dinner plates), but ultimately the flux of carbon to the deep ocean.

No small objective! But while FS Meteor is being snowed upon, hundreds and thousands of meters below deck, a snow-like phenomenon also occurs. You doubt it? Step into the Deepsea Challenger for an imaginary dive.

By the time you have had time to settle in into the tight titanium sphere that keeps you alive, you have dived deeper than light penetrates. Even in spring, it is dark, but then it always is. The current drift is gentle, it really is the calm before a deep sea ‘blizzard’.

The ‘snowflakes’ are not of the familiar type. Most of them are the settling particulate remains of a stand off that takes place every spring.

The single-celled phytoplankton that bloom when winter convection is reduced by the onset of spring, are grazed by agile zooplankton armed with fierce mandibles ready to crush anything in their path.

But for the zooplankton, it is not a simple triumph. Although single-celled phytoplankton cannot outswim the fast zooplankton, their strength is in numbers. Despite their microscopic size, the phytoplankton can bloom in such high densities that long wisps gently swayed by the ocean currents can be seen even from space (see the expedition`s Chlorophyll a satellite images).

Deep-sea snowflakes: the elegant remnants of the blooming phytoplankton. The sinking shells of the single-celled algae bring with them organic matter, thus sequestering atmospheric CO2 to the bowels of the oceans. Images courtesy of http://www.sinia-planeta.com

Phytoplankton armour also includes spines, hooks and all-encompassing calcite, glass or organic shells. These are the architects-supreme of the nano-world. Their shell designs not only serve a protective purpose, but are also intricate and elegant, providing maximum functionality with minimum material – every architect’s dream.

Even when the body armour serves its purpose well, the phytoplankton blooms have a limited lifespan. Grazed phytoplankton, moults of the crustacean grazers themselves, faecal pellets of animals of all sizes, and dust swept off the continents by the wind also accompany the dead plankton to the bowels of the ocean. Together, these remnants are termed ‘marine snow’ and carry significant amounts of carbon away from contact with the atmosphere.

At depths of 4500 meter, the marine snow reduces the visibility to that of a snow blizzard.

Snow falls 4800 m below sea level! Fluff and mucus cover the seabed in a brief moment. Images courtesy of Richard Lampitt, NOCS

This phenomenon, however, is more than just a ‘strange but true’ fact. It is directly linked to the environment that FS Meteor (and the rest of us) experience above deck. How much ‘marine snow’ occurs and how much carbon it sequesters to the ocean depths depends on when and how the spring bloom is initiated, and how fast zooplankton wakes up from its winter diapause to graze upon it. In a nut shell, the key questions of the ‘Deep Convection’ expedition.

If deep-sea ‘blizzards’ continue to tickle your imagination, and James Cameron`s Deepsea Challenger is not at hand, no problem! Join us for the expedition`s secont leg, 7th April 2012.

Related News:
What did James Cameron see in the Mariana Trench?
National Geographic exclusive interview
, 5 April 2012

Additional resources:
Lesson Plans:
The water colunm: where do animals belong? (K3-5) by National Geographic link

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