Monday, November 3, 2008

Coring never boring

One of our many science objectives is to examine the diversity (in other words, the number of different types) of small organisms on the sea floor in Explorers Cove, and to monitor changes in diversity over time. One way to accomplish this goal is for scuba divers to take sediment cores and bring these small samples to the surface for analysis. It is important that the divers take the cores haphazardly so that sampling bias is reduced -- in other words, sampling should be as random as possible so that the results are statistically sound. You can see a video of a diver taking sediment cores here; please also see the "skittle core" activity for K-12 students, developed in conjunction with a highly dedicated group of teachers that we work with.

Once the core reaches the surface, a scientist will slice it into sections that are one centimeter in thickness. Each section is then sieved, and the organisms within each slice are poured into storage bottles, which are refrigerated to keep the critters inside healthy. Back in the lab shack, the organisms in each sample are identified and counted. Simple statistical methods allow us to estimate the total population of a given organism at each dive site (we call these sites "sampling stations"). 

Doing this year-after-year allows us to plot changes in population over time. Shown here is Claire selecting a "good" core for analysis. (The best cores have perfectly clear water above the sediment, which indicates that minimal disturbance was caused by the coring process.) She is then seen cutting the core into 1-cm slices using a thin piece of metal, and then placing each slice into a sieve (in this case, she uses a 1-mm mesh size), and anything smaller than 1-mm diameter is washed away. The "sieve residue" is then seen being transferred to a storage bottle. Coring is one of my favorite things to do in Antarctica...

No comments:

Post a Comment