So, I got defeated by life again and my post is late. But it’s
here! This week I mostly spent my time writing and getting well, so there’s not
any exciting travel news to report on. Life is going to return to a normal pace
for a little while, which maybe will be interesting for those of you
non-researchers who want to know what a scientist does day-to-day. For the
moment I’ve decided to declare this Phytoplankton Friday. (Yes, I know it’s no
longer Friday, but the alliteration doesn’t work with Saturday.)
When we were sailing on Lake Erie, it was very obvious that
the eastern part of the lake had little to no problems with nuisance
phytoplankton blooms: the water was very clear. However, in the western part of
the lake, the water had a distinctive greenish tinge to it from all the
phytoplankton floating around. While phytoplankton blooms can be harmful in
some contexts, mostly phytoplankton are important engines of the planet. I
remember when I used to teach for Introductory Oceanography at the University
of Michigan, the students were always very excited to get to the section on
biological oceanography. And then they were incredibly disappointed that we
talked mostly about plankton, and not about whales, dolphins, and fish. The
truth is though, that there would be no whales, dolphins, or fish without
plankton.
A little bit of explanation: Plankton are organisms that
float in a body of water and cannot swim against a current. Phytoplankton are
photosynthetic, or plant-like, plankton. They comprise two main groups,
cyanobacteria and single-celled algae. Phytoplankton are the base of the aquatic
food chain. These tiny organisms are responsible for nearly half of the world’s
primary productivity, or the organic matter that phytoplankton produce after
meeting their basic energy needs. In other words, they fix almost as much
organic matter as all the trees, grasses, and other land plants combined! This
also means that about half of the oxygen that you breathe was produced by
phytoplankton. In fact, cyanobacteria are responsible for the oxygenation of
the atmosphere some 2.4 billion years ago. Today, satellites are giving us
wonderful information about the spatial and seasonal variation in phytoplankton
primary production. Here is the southern hemisphere during austral (southern)
summer:
You can explore on your own and make your own globes at http://oceancolor.gsfc.nasa.gov/cgi/biosphere_globes.pl
.
Phytoplankton are so productive and numerous that—contrary
to popular belief that the oil we burn was once dinosaurs—their remains created
the oil that drives the modern world. Their skeletons also can form large
limestone deposits, like the White Cliffs of Dover.
 |
| White Cliffs of Dover (Wikimedia Commons) |
During my Ph.D., I became interested in a group of phytoplankton
known as diatoms. Most diatoms are marine, although they are also found in
freshwater. Diatoms are distinctive because they build elaborate, beautiful skeletons
out of amorphous hydrated silica, leading to the description of their living in
“little glass houses.” (Glass is also made from silica.)
 |
| Diatoms can either be pennate (top) or centric (bottom). (Wikimedia Commons) |
Diatoms first came to
prominence during the Mesozoic Era,
and have become increasingly dominant in the global ecosystem since then. Diatoms
do well in nutrient-rich environments, such as coastal and upwelling areas, where
they are able to outcompete other phytoplankton. Today they are responsible for
around 40% of total marine primary productivity and around 50% of all the
carbon exported to the ocean’s interior. And although there is much talk about
the carbon dioxide levels in the atmosphere, note that the deep ocean is a much bigger carbon reservoir than the
atmosphere.
 |
| Image from http://earthobservatory.nasa.gov/Features/CarbonCycle/ |
Next time, Part 2:
metals and phytoplankton.
