By Net Charoenpong
A couple of days ago, we traversed out
of the subtropical gyre of the South Indian Ocean, a large oceanographic
feature marked by very low productivity in the surface. This vast expanse of
the ocean's "desert" is caused by the lack of nutrients. The water there
is possibly one of the bluest blues I have ever seen. So, what are nutrients
and why are they so important in oceanography? Nutrients are compounds that
promote biological growth including nitrogen compounds (like nitrate, nitrite
and ammonium), phosphate and dissolved silica. Just like the grass in our
backyard, phytoplankton (plant-like drifters of the sea) need nutrients to grow
and carry out photosynthesis which converts carbon dioxide to organic molecules
and oxygen. Fun fact, half of the oxygen we breathe is produced from the
phytoplankton in the ocean. On this cruise, we measured the five nutrients
mentioned above.
Our nutrient (shortened to simply NUTS)
team (Susan Becker and John Ballard, from Scripps Institute of Oceanography)
work tirelessly to sample and analyze almost every bottle from every cast we
take. John showed me the autoanalyzer,
the work horse of the NUTS team, which is used to determine the concentrations
of these five nutrients. Essentially, the analyses are based on colorimetric
methods where you add different chemicals which react with different nutrients
to produce colors. The intensity of the colors produced will in turn tell us
how much nutrients are in the water.
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Why do we care about nutrients? John
explained, "nutrients not only are essential to living organisms, they are
also used as tracers for water masses."
The latter are what oceanographers described as the layers of different
parcels of water from different origin that stack up on top of one another due
to their density difference.
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