Dynamics of Marine Ecosystems
December 9th, 2013
Silica in the Southern Ocean
The ocean is teeming with a near incomprehensible variety of life that can thrive in a number of environments in many different ways. The basis for any ecosystem starts with the smallest of organisms that rely on nutrients being brought to them from the ocean. One of the important nutrients that organism rely on is silica. Certain organisms use silica to live and while that may not seem like much, silica’s role in the ocean, especially in the Southern Ocean, has a global impact. Silica in the Southern Ocean has immediate effects on the ecosystems that reside there and overtime, affects the ecosystems of the oceans that interact with it.
To understand the concentrations of silica in the Southern Ocean it is best to understand exactly what silica is composed of and where it comes from. Silica is made up of Silicon dioxide (SiO2) but can undergo hydration to become Silicic Acid (H4SiO4), both of which are prevalent in the Southern Ocean. Silica can be supplied to the ocean through a number of different ways. The sources that provide the largest influx of silica in order of most to least are through rivers and estuaries, volcanic and hydrothermal activity, glacial melting, and being eroded from basaltic rock on the seafloor. River influx of silica is by far the largest contributor to the ocean by almost two times the amount of volcanic and hydrothermal activity and these processes have been going on for millions and millions of years. Most of the silica in the ocean is located at the ocean floor as sedimentary layers and this is always increasing because any influx of silica from the surface or higher depths would result in sedimentary increase a majority of the time. This result of silica influxes is normal in the Southern Ocean but to a much larger degree than anywhere else, hence the largest silica sink in the world is the sediments of the Southern Ocean. The Southern Ocean holds between fifty and seventy five percent of the ocean’s silica, but even with these staggering high numbers, it holds less than one percent of the oceans organic carbon. This composition of silica and organic carbon is significantly different than any other ocean floor and this proved to be quite a mystery for scientists for some time. Part of the answer lies in the biology of the organisms that utilize silica to survive in the ocean and the rest of the answer lies in the chemical composition of the Southern Ocean.
Planktonic organisms that utilize silica most efficiently and commonly are diatoms, which play a large role in primary production in all the world’s oceans. Diatoms are some of the most plentiful phytoplankton on the planet and utilize silica to build their cell walls. Once these organisms die, there siliceous structure sinks down to the bottom through the biological pump. Silica from a deceased diatom will break down and dissolve, which can allow for...