Back of the envelop calculations for global carbon cycle and oceans

1. What is the volume of water is the worldπs oceans? How much does that volume of water weigh?

Oceans cover ~70% of the earthπs surface. Average depth of the worldπs oceans is ~4000m. Surface area of earth is 5 x 10¹⁴m².

Answer = 1.4 x 10¹⁸m³.

2. It is estimated that erosion lowers the heights of continents by about 6 cm every 1000 years. Given the information about, figure out how many cubic meters of soil and dirt wash away each year.

Answer = 10¹⁰m³ per year.

3. If all this material was being dumped directly into the oceans, how long would it take the worldπs oceans to fill with dirt and rocks?

Answer ~140 million years.

4. Given the following concentrations of trace elements in sea water, assuming what flux of exchange between deep oceans and surface oceans, and assuming what flux of photosynthetic rates, how long would it take to deplete the oceans of nutrients if nutrients were taken up by photosynthetic organisms and stored in that form.

5. 10% of the nutrients taken up by phytoplankton are not mineralized in the euphotic zone but instead sink into the deep ocean. Given the estimates of the amount of excess anthropomorphic CO₂ going into the atmosphere each year, how rapidly would phytoplankton have to live and die to have an impact on atmospheric CO₂ levels?