Figure 1. The bottom of Lake Superior is below sea level! To measure certain parameters and to collect water from hundreds of meters below the surface, scientists can deploy this “CTD rosette.” The gray vertical tubes are water sampling bottles that can be closed at chosen depths so that water from that location is brought back on board. Below the gray tubes is a package of instruments that measures such things as temperature, salinity, oxygen, and other parameters, giving LLO scientists a “vertical profile” of lake conditions. Photo credit: Blue Heron crew.