Andrew

You calculation is way of the mark.

Iron does not cause growth of Fish directly, it only causes growth of 
phytoplankton. 

These are consumed by zooplankton and small fish and these by bigger fish.

The Phytoplankton to Fish ratio for the large fish that people prefer to 
eat is about 100 : 1.

So the Iron required may be at least 100,000 tons.

Actually it would be more since all the fish that grow in the oceans cannot 
be caught.

This should be dosed in the area where the fish is caught, since the 
nutrients are being removed from that area and the phytoplankton would be 
consumed by the fish in that area.

We are already fertilizing the oceans with N P K.

All the sewage we are releasing contains N and P.
Average per person is 5 g of N and 0.5 g of P per day.
This is about 12 million tons per year of N and 1.2 million tons of P.

About 100 million tons of Urea and 30 million tons of Phosphate fertilizer 
is used by farmers, a lot of this runs off into rivers and finally into the 
ocean.

Sewage and Fertilizer is causing eutrophication and dead zones in coastal 
waters and is resulting in decline in fisheries.

It is not just oceans that are iron deficient, even people suffer from it. 

http://www.who.int/water_sanitation_health/diseases/anemia/en/
Scope of the problem

"Nine out of ten anaemia sufferers live in developing countries, about 2 
billion people suffer from anaemia and an even larger number of people 
present iron deficiency (WHO, 2000). Anaemia may contribute to up to 20% of 
maternal deaths."
About 2 Billion people are anemic, i.e., suffer from acute iron deficiency.

Human feces and urine does not contain much Iron.
That is why there is an imbalance in water - our urine contains N and P but 
not Iron.

http://en.wikipedia.org/wiki/Anemia
The body can absorb up to 6 mg iron daily from the gastrointestinal tract. 

For 7 Billion people that is about 42 tons per day, 15,330 tons per year.
For the 2 Billion suffering from anemia it is about 4,380 tons per year.

Total Iron Ore mined is about 2,800 million tons.
Total Iron on Earth is about 20,000,000,000,000 billion tons ( 20 x 10 ^ 24 
kg )

Of course, since we are not able to cure the 2 billion people of anemia, 
expecting to solve the iron deficiency problem in oceans is perhaps 
expecting too much.

Keith Henson

Fertilizing the oceans to restore fisheries is NOT prohibited, that is why 
the Haida Salmon Restoration Project is perfectly legal. They are on the 
right path, I hope more people do similar projects.

Deep sea fishing fleets go out with empty holds and return with the holds 
full of fish.
They can easily carry Iron for fertilization and empty these in the fishing 
areas, before they start to fish.

Regards

Bhaskar

On Sunday, 22 June 2014 14:58:31 UTC+5:30, andrewjlockley wrote:
>
> Approx 100MT annual catch 
> Approx 1 part in 100000 is iron 
> Therefore need to replace 1000t iron pa into ocean ecosystems. But iron 
> isn't a limiting nutrient everywhere, so perhaps far less. 
>
> Should boats be tipping NPK fertiliser over the side, too? Far larger 
> volumes are required. 
>
> Marine reserves are likely a better way to protect ecosystems. 
>
> A
> On 22 Jun 2014 10:18, "Keith Henson" <hkeith...@gmail.com <javascript:>> 
> wrote:
>
>> It's a shame this business got mixed up with geoengineering because it
>> is something that should be done on it's own merits.
>>
>> Humans fish the seas.  As a result they remove vast amounts of
>> elements from the materials circulating in the ocean biosphere.  We
>> are going to fish, and remove elements, particularly iron, from the
>> sea. We damn well should put it back.
>>
>> When a ship comes in with a load of fish and an estimated amount of
>> iron in the fish, the next trip out they should be required to take an
>> equivalent amount of iron out with them.  Or buy credits from someone
>> who does this as a business.
>>
>> It's not like it would be a significant cost burden on fishermen.  And
>> if it has positive effects on the catch, they should be overjoyed to
>> do it.
>>
>> Any minor effects it has on CO2 is just a fortunate happenstance.
>>
>> Keith Henson
>>
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