Week 4
24 July 2006

Searching for the Elusive Element Using Biological Oceanography

Part II
Science Spotlight - Kristen Buck

Biological Oceanography

Kristen Buck, PhD candidate at the University of California, Santa Cruz, is conducting research on how dissolved metals, such as iron (Fe) and copper (Cu) bind to organic molecules. When these metals are bound to organic molecules, they stay in solution and their availability of biological processes is affected.

Question: What is a molecule? Organic molecules do not necessarily come from organic farms. What are they?

Dissolved Fe and Cu exist in many forms or “species.” Finding out which of these species are present in ocean water is important because only some species are available for biological processes such as photosynthesis.

Kristen measures the distribution of dissolved Fe and Cu in the various species. What she has found is that most of the Fe and Cu in ocean waters is the kind that is bound to organic molecules. In the case of the Fe, that means the iron is soluble and available for biological processes. On the contrary, the Cu bound to organic molecules is not bioavailable. Measuring the distribution of Cu between organic and inorganic species can tell scientists what role copper is playing in the environment. Is it a nutrient (at low inorganic copper concentrations)? Or is it a toxicant (at higher inorganic copper concentrations)?

Question: Select two minerals that are necessary in a person’s diet.  What is the recommended daily nutrient level? At what level does this mineral become toxic?

Kristen describes some of her work with incubations;

Organic molecules play an important role in Fe solubility. Fe is more soluble in the presence of organic molecules that bind Fe. We do not know exactly which organic molecules exist in these waters, but we have some idea about which ones they might be. In order to analyze the role of some of these ligands (organic molecules that can bind something, in this case Fe) that make Fe soluble, I conducted an incubation experiment. I collected water from the surface waters over the shelf of King George Island.

Question: Find King George Island at 63 degrees 00’ South and 60 degrees 00’W.

At this shelf, there are lots of particles suspended in the water from the mixing of the shelf sediments up into the water column. Since Fe comes from the continents (approximately 4% of the continental crust is iron), we know there will be Fe on these particles.

Question: What else is a component of the continental crust? (Name at least 2)

Once the Fe was in the bottles, I added (57)Fe to some of the bottles, and I also added (57)Fe with different ligands to other bottles. (57)Fe is a non-radioactive stable isotope (variation of an element). It is a natural element found only in small quantities. (57)Fe is useful because although it does not occur in significant amounts naturally, it is a type of iron and will go through all the processes or cycles of Fe. Therefore, it can be used to trace the processes (or cycling) of Fe. From this work, I can determine how fast Fe cycles between the dissolved and particle phases. I can also see how different kinds of ligands  affect the solubility of Fe. Again, since iron is such an important component in the ocean, we want to learn all we can about its characteristics.