Question

# Ekman transport and biological productivity. The average upwelling velocity was determined to be 0.3 m/day between

1°S and 1°N and 150°W and 140°W in the Equatorial Pacific. The nitrate concentration is 15 mmoles NO3/m3 in the upwelled water and 5 mmoles NO3/m3 in the surface waters between 1°N and 1°S. The mixed layer is 50 m deep. Assume the current velocity and nitrate concentration in the surface waters at 150 ̊W equal those at 140 ̊W and that there are 100 km per degree of longitude and latitude.

a.Draw a picture of the situation and label the inflows and outflows. What direction will water motion be across the 1 ̊S and 1 ̊N edges of the box

b.Calculate the current velocity (m/s) in the mixed layer at 1°N, assuming the surface current speeds are equal at 1°S and 1°N.

c.What is the residence time (days) of the water in the mixed layer?

d.Calculate the rate of biological export of nitrogen (mmoles N/m2/day) assuming the NO3budget is at steady-state.

e.Estimate the rate biological rate of export of carbon (mmoles C/m2/d). What assumption did you make?