Ocean · Puzzle #1 · Wednesday, September 30

Ocean: the answers

Four questions, each with one true number. Here they are with their answers, how to reason each one out, and where the number comes from. Play today's Ocean.

1. 1. About how many Prochlorococcus cells, the ocean's tiniest photosynthesizing plankton, live in the world's oceans at any time?

   

   The answer: about 2.9 octillion (2.9 × 10^27) cells. Its close cousin Synechococcus, counted in the same study, numbers about 7 × 10^26 cells, roughly four times fewer.

   Napkin math: Sunlit seawater holds around 100,000 of them per milliliter, and the ocean's top 200 meters hold roughly 10^25 milliliters of water.

   Source: PNAS (Flombaum et al. 2013), Present and future global distributions of the marine Cyanobacteria Prochlorococcus and Synechococcus

2. 2. How tall is the Denmark Strait cataract, the giant underwater waterfall between Greenland and Iceland, in feet?

   

   The answer: approximately 11,500 feet. That is more than three times taller than the largest waterfall on land, which NOAA lists at 3,212 feet.

   Napkin math: Cold, dense water spills down a seafloor drop of about two miles, and a mile is 5,280 feet.

   Source: NOAA National Ocean Service, Where is Earth's Largest Waterfall?

3. 3. How many successful English Channel swims has the Channel Swimming Association recorded since 1875, as of 2026?

   

   The answer: 3,283 swims. The CSA was founded in 1927 to observe and authenticate Channel swims; its fastest solo swim on record is 7 hours 17 minutes, set in 1994.

   Napkin math: Only a few people managed it in the early decades, but modern seasons see dozens of crossings a year, so 150 years adds up to a few thousand.

   Source: Channel Swimming Association, Channel Swimming Association home page

4. 4. How many countries' national surfing federations belong to the International Surfing Association, as of 2026?

   

   The answer: 120 countries. The ISA, founded in 1964, is recognized by the International Olympic Committee as the world governing authority for surfing.

   1. 195countries in the world
   2. ×0.75of them with a coastline

   ≈146.25countries

   Source: International Surfing Association, About the ISA

All of puzzle #1 · The archive