Marine Snow- Teacher’s Notes
Introduction
Marine snow is organic material, including dead animals, plants and fecal matter
and inorganic particles such as sand and soot that floats down to the seabed just
as leaves and decaying material fall on to a forest floor. It is referred to as marine
snow because it looks like white fluffy bits, it was first noticed by the explorer
William Beebe as he observed it from his bathysphere.
The relevance of marine
snow
The continuous falling of
these small particles from
the sunlit photic zone to
the deep aphotic zone
provides a source of food
plus carbon and nitrogen
for scavenging animals
that live in the deep sea.
It is the major determinant
of abundance and activity
of large and small deepsea animals.
The process
The consumption of the organic material begins almost straight away; it is
consumed by microbes, zooplankton and other filter feeding animals, especially
in the first 1000m of its journey. As the marine snow falls the particles aggregate
together and increase in size, they are held in place by sticky nets of mucus
made by plankton. The oceanic currents determine the speed of the particles
descent, but it is generally slow, perhaps 10 to a few 100m per day. They travel
sideways (imagine a balloon dropped from a height) and often land several miles
away from where they started. The amount of marine snow falling varies with the
seasons; during the spring phytoplankton blooms the productivity is greater. It
also varies between ocean basins.
Ooze
The small percentage of material not consumed in the shallower waters becomes
incorporated into the muddy “ooze” blanketing the seafloor, where it is further
decomposed through biological activity. About three-quarters of the deep ocean
floor is covered in this thick, smooth ooze. The ooze collects as much as six
meters (20 feet) every million years. On average it is ~300m (950 feet) thick but
can be up to nearly 10 km (6.2 miles). At areas of young crust, for example near
a spreading ridge, the amount of sediment is less than at older parts of the
oceanic crust.
Microfossils and foraminifera in the
sediments
Sediment also comprises of millions of
tiny microfossils such as diatoms,
radiolarians and foraminifera. These
are the remains of creatures that had
skeletons made of carbonate or silica.
Their sensitivity to environmental
change,
wide
distribution
and
abundance of shells make them a
valuable tool for understanding past
climatic events especially as the
benthic (bottom) foraminifera record is
more than 550 million years old.
Because of the length of time a
foraminifera
species
exists
is
geologically brief (around 5-15 million years), the shells are also very useful for
determining the age of sediments in which they occur.
Upwelling
In some ocean basins there is a strong upwelling current which brings the
nutrients from the bottom sediments up through the water column to the
phytoplankton in the photic zone. Here they feed on the carbon and nitrogen,
completing the cycle of matter and flow of energy in the open ocean food chain.
Basic food chain
Nutrients - Phytoplankton – Zooplankton – Invertebrates - Vertebrates.
Sediments and drilling on the JOIDES Resolution
The sediments are also important to the geologists and drillers on-board the JR.
If there is a good depth of sediment then it is much easier to drill a hole into the
seabed than if there isn’t. This is because the drillers need to be able to stabilize
the drilling equipment
before they begin to
make a hole.