Sampling in the open ocean. – Using a 50 cm diameter opening zooplankton net, to

Question

Sampling in the open ocean. – Using a 50 cm diameter opening zooplankton net, towed at 2 knots for 5 minutes, you capture and count 7350 copepods that are, on average, each 1 mm long. Assuming that copepods are confined to the upper 200 meters of the ocean and that your sample is representative of the global ocean. If you lined up all the copepods in the ocean end to end, how many copepod light years are there in the global ocean? Show your conversions going from your zooplankton tow to light years. Assume a mean global ocean area of 361,900,000 km2. A light year is measure of distance, not of time.

Explanation / Answer

Diameter of net= 50 cm or 0.5m

Area of net= 3.14*(0,5)2

= 0.785 m2

Area of ocean= 361,900,000 km2

or 3.619*1014 m2

Number of nets to cover upper 1mm of the whole ocean

= 3.619*1014 m2/ 0.785 m2

= 4.61*1014

Number of nets to cover 200 m(200,000mm)

= 4.61*1014 * 200,000

= 9.22*1019

Length of plankton

= 9,22*1019 *7350*1 mm

=6.78*1020m

= 7167 light years

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