Richard Kirby proposed a citizen science project in which people measure the namesake "depth" corresponding to these instruments. For 10 points each:
[10h] Name these scientific instruments, one type of which consists of a solid white circle with a 30-centimeter radius.
ANSWER: Secchi ("SEK-ee") disks [prompt on partial answers]
[10m] While the black-and-white Secchi disk is usually used in freshwater, the solid white Secchi disk is mostly used to determine the transparency of this type of water, whose salinity is typically about 3.5 percent.
ANSWER: seawater [or ocean water; prompt on saltwater; prompt on brine]
[10e] Kirby's Secchi disk study uses measurements of water transparency to determine the distribution of these organisms. Diatoms are a subtype of these primary producers, which produce about half the world's oxygen.
ANSWER: phytoplankton [prompt on plankton]
<Joseph Krol , Science - Earth - liquid/gas>