Upwelling rates in the ocean involving carbon and nitrogen

[cgarr017]

This is a 3 part question that i have attempted to answer. I'm pretty sure I'm on the right track but i think i made 1 or 2 small mistakes along the way. the question states:
The average depth of the ocean is 3.8km and the ocean surface area is 360x10^12 m^2. The average upwelling rate of deep water into the surface ocean is 4 m/yr.
a) about how long would it take to upwell the entire volume of the ocean?
b)assume that the average nitrogen content of deep water is 40 micro molarity or 40x10^-6 moles per liter. What is the flux of nitrogen to the surface ocean due to upwelling(express your answer as moles N m^-2 yr^-1)?
c) At a C:N molar ratio of 106:16 what is the productivity of the surface ocean(expressed as moles C m^-2 yr^-1) sustained by nitrogen upwelling. Re-calculate this productivity flux as a global(whole ocean) rate of upwelled N-driven primary productivity, expressed in units of gigatons C/yr.

MY ATTEMPT AT AN ANSWER:
a) 3800m/4m/yr=950 yrs
b) 40 x10^-6 moles per liter;
upwelling rate of 4m/yr=400 cm/yr;
therefore 400cm rises 1cm^2/yr;
360x10^12 m^2 x 3.8km=1.368x10^18 m^3;
3.6x10^18 cm^2 x 400 cm= 1,440x10^18cm^3/yr;
1 liter=1,000 cm^3;
1,440x10^15 L/yr x 40x10^-6 moles/L;
=5.76x10^13 moles N/yr
(i think that's right but it needs to be expressed as moles N m^-2 yr^-1. would i just divide 5.76x10^13 by the surface area of 360x10^12m^2?)
c) 5.76x10^13 moles N/yr at a C:N ratio of 106:16=3.82x10^14 moles C/yr;
3.82e14/360e12m^2= 1.061 moles C/m^2/yr?;
1.061 moles C/m^2/yr= 12.73 g C/m^2/yr;
Gigaton= 1e15 g;
1.273e-14 Gt C/m^2/yr x surface area(360e12m^2)= 4.5828 Gt C/yr

Is this correct?

 

[cgarr017]

bump
anybody...?