Geology Reference
In-Depth Information
to the air, there is a flow into the ocean via the solubility pump; if some of the gas is
removed from the air, it flows out from the ocean, until, in both cases, equilibrium is
reached.
The biological pump is itself divided in two—the 'biological organic pump' and the
'biological carbonate pump', already known to us as Gaia's great chalk journey. Let us
now take up the story of a carbon atom as it experiences a journey through the biological
organic pump. After being exhaled by a microbe in the soil, our carbon atom finds itself
wafting in the air over the ocean, linked with two oxygen brothers in a molecule of car-
bon dioxide. Suddenly a wave catches it, and our carbon dioxide molecule is dissolved
in the clear ocean water. A passing alga, photosynthesising in the bright sun, absorbs it,
and soon the dextrous metabolism of the cell links our carbon atom to a multitude of
other atoms in the long chain of a vast sugar molecule. Now our carbon atom floats in
the lovely translucent greenness of the alga's body, waiting for oxygen to break open the
sugar molecule, releasing its embodied solar energy. But before this happens, the alga is
devoured by a tiny amoeba-like predator known as a radiolarian, which extends its en-
gulfing pseudopods through tiny gaps in its exquisite silica shell. Many other predators
roam the surface waters— small fish, tiny free-floating shrimp-like carnivores (the cope-
pods), and jellyfish raking the water with their long stinging tentacles for their sugarrich
prey. The radiolarian is itself eaten by a copepod, which digests much of the carbon that
was in our alga's body, but the particular sugar molecule in which our carbon atom hap-
pens to find itself evades this fate, and is excreted into the water in a faecal pellet along
with the remains of several other algae. As the heavy faecal pellet sinks down towards
the depths of the ocean, translucent green is slowly replaced by dark green, then by deep
blue and eventually by pitch blackness as our carbon atom reaches the abyss. During this
long downwards journey a host of creatures devour most of the faecal pellets, releasing
carbon dioxide into the sea. But the faecal pellet that has transported our carbon atom
into the depths is one of the few that survives, and it settles at last on a layer of soft mud
on the seabed. Even here, there are creatures that eat and digest faecal pellets, but our
carbon atom avoids this fate, and is gradually covered in silt and sand washed in by a
river draining the nearby continent. It is now one of the tiny proportion of carbon atoms
to have reached the deep sediments from the surface ocean via the biological organic
pump. Only 1% of the organic matter in the sinking mass of faecal pellets arrives on the
sea floor, and of this only 0.1% is buried in the sediments.
Phosphorus and nitrogen from the surface waters are also transported to the ocean
depths by the biological pump, greatly affecting the chemistry and ecology of the sur-
face ocean, and, as we shall later discover, the oxygen content of the atmosphere. Or-
ganic carbon from the land in the form of tiny fragments of undigested leaf and wood
also makes its way into the ocean sediments, transported by the great rivers of the world.
