D341: Porcupine Abyssal Plain cruise 2009


Cruise blog

Thursday 23 July 2009

Snow in the Sea By Jennifer Riley

I am interested in how particles of organic matter, produced by both the microscopic plants and animals in the surface ocean, sinks into the deep ocean. These particles are known as Marine Snow. Certain types of both the phytoplankton (plants) and zooplankton (animals) in the surface ocean produce shells made out of chalk (calcium carbonate) and silica.

Scientific theory suggests that the more inorganic minerals (chalk and silica) there are in sinking particles the faster they will descend into the deep ocean. However, there is currently little knowledge on what marine snow particles are made of, how they form or even how fast they sink from the surface ocean. On D341 I am using a piece of equipment called the Marine Snow Catcher to collect some of these sinking particles and then microscopically examine them.

The Marine Snow Catcher is lowered to a pre-determined depth in the water column, for my purposes 50m, and closed. This traps 100L of sample inside it, which after being brought back onboard the ship, is left to settle for 3 hours. All the particles sinking from the surface ocean that have become trapped inside the Marine Snow Catcher settle into the bottom chamber during this time. This chamber can then be isolated and the settled particles taken away for detailed analysis.

For every particle caught in the snow catcher a photograph is taken to document what it looks like, its dimensions are measured and then a sinking rate experiment in conducted to determine the speed at which they sink. The particles are then preserved to determine their composition back at home.


Deploying the marine snow catcher

Marine snow settling in the bottom chamber

Microscopic image of a radiolarian
with marine snow around it

Microscopic image of diffuse marine snow

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