What is the salinity of the water?
The salinity of seawater varies quite a bit from the surface to the bottom. If you look at the website for the research vessel were are working from (http://thompson.ocean.washington.edu/) and click on the area that is called scientific data you will see that there is a lot of data posted there. Open a file called 17406001-2.PDF in the area called CTD data plots. You will see a graph of salinity, temperature and fluorescence as it changes with depth. The green line shows a plot of salinity and you can see that the water is fresher (less saline) near the surface and has it highest salinity near the bottom.
