Deep ocean water phosphorus

An extreme iron fertilization scenario modeled by Sarmiento and Orr (1991) relies on the sustained depletion of phosphorus in Southern Ocean surface waters by continuous iron addition. The three-dimensional, multi-layered model predicts a global increase of export production and the possibility of anoxia in deep oceanic waters. Specifically, the results indicate a POC export increase of 6-30 GtCy-1, i.e., a doubling of export production, after 100 years of fertilization. In addition, anoxia is predicted for certain parts of the southwest Indian Ocean. Considering the enormous scale of this hypothesized fertilization operation (0.6Mt utilizable Fey-1 Sarmiento Orr, 1991) and the low spatial resolution of the model, the exercise provides limited insights into more realistic iron fertilization scenarios. 

The difference in carbonate ion concentration between NADW and the rest of the deep ocean is related to the difference in PO4 concentration. NADW has only about half the concentration of PO4 as does, for example, deep water in equatorial Pacific. This is important because, for each mole of phosphorus released during respiration, 120 mol of CO2 are also produced. This excess CO2 reacts with ion to form two HCOJ... 

Ketchum B. H., Corwin N., and Keen D. J. (1955) The significance of organic phosphorus determinations in ocean waters. Deep-Sea Res. 2, 172-181. 

Implications of these results are that phosphorus removed from the surface waters as biological flux is 30-65 times more hkely to come from upwelling than from rivers (1.3-3.0 x 10 /4.6 x 10 ), indicating that ocean circulation is far more important in regulating biological productivity than river inflow. Also, only 1 in 30-65 atoms of P that rains to the deep ocean is actually buried the rest are degraded in the deep and recycled back to surface waters. This results in a residence time for phosphorus with respect to burial of 30 000-65 000 y 30-65 times the ocean circulation rate. 

The moles X/moles P in average plankton is given by a, and b is the surface water concentration in phosphorus free water (water stripped of nutrients). In the case of P itself, the surface ocean concentration is close to zero, while the deep Pacific has a concentration of 2.5 fm. For N, the N/P ratio of plankton is 16 and the surface water concentration is Ojuu. The predicted deep sea nitrate is 40 m. The ratio of (deep)Z(surface) is greater than 10. For calcium, the Ca/P of plankton = 36 and the surface water content is 10 000yUM. The predicted deep ocean concentration... 

The problem is to calculate the steady-state concentration of dissolved phosphate in the five oceanic reservoirs, assuming that 95 percent of all the phosphate carried into each surface reservoir is consumed by plankton and carried downward in particulate form into the underlying deep reservoir (Figure 3-2). The remaining 5 percent of the incoming phosphate is carried out of the surface reservoir still in solution. Nearly all of the phosphorus carried into the deep sea in particles is restored to dissolved form by consumer organisms. A small fraction—equal to 1 percent of the original flux of dissolved phosphate into the surface reservoir—escapes dissolution and is removed from the ocean into seafloor sediments. This permanent removal of phosphorus is balanced by a flux of dissolved phosphate in river water, with a concentration of 10 3 mole P/m3. 

The committee recommends the development of a seawater-based reference material containing the nutrient elements nitrogen (as N03), phosphorus (as P04) and silicon (as Si(OH)4) at concentrations similar to those in oceanic deep waters (40 pM for N03, 3 pM for P04, and 150 pM for Si(OH)4) and certified for these constituents. 

Figure 8.2 Regression of total (dissolved and particulate) nitrogen and phosphorus from estuaries, surface films, and oceanic surface (< 50 m) and deep waters. (Modified from Downing, 1997.)...

In addition to this net export of nutrients, the Eastern Mediterranean is the largest body of water in the world in which the primary productivity is phosphorus limited (Krom etal., 1991). The deep waters of the eastern basin have a nitrate/phosphate ratio of 25-28 1 compared to 22 1 in the Western Mediterranean and 15-17 1 found generally in the world s oceans. These... 

---