Salinity levels have an immediate effect on the surrounding ecology, since many aquatic creatures can survive only in either marine, brackish, or fresh environments. It's just as important for sailors (of any era), who need a fresh water supply to survive.

To measure the salinity gradient, our students collect water samples at regular intervals. On the Half Moon, we collect surface water samples the old-fashioned way: by simply heaving a tethered canvas bucket overboard and hauling it back on board.