Phosphate nutrient ocean

It required about three billion years for all the oceans of Earth to become saturated with phosphates for the first time. Until then oceans acted as a giant sink for phosphorus, holding it in solution too dilute to be of much use as a nutrient to life forms. When Earth s oceans became saturated, any new dissolved phosphates entering the seas caused precipitation of exactly the same amount of phosphate someplace else. This action became faster and faster until today there is a complete replacement of phosphate in oceans every 4.9 x 10 years, a very short time on a geological time scale. This estimate is based upon the estimate of McKelvey et al. that 2x10 tons of phosphorus are delivered to the seas each year, and Horn and Adams estimate of the phosphorus in the seas. " ... 

Over 20% of the world s open ocean surface waters are replete in light and major nutrients (nitrate, phosphate, and silicate), yet chlorophyll and productivity values remain low. These so-called "high-nitrate low-chlorophyll" or HNLC regimes (Chisholm and Morel, 1991) include the sub-arctic North Pacific (Martin and Fitzwater, 1988 Martin et al, 1989 Miller et al, 1991), the equatorial Pacific (Murray et al, 1994 Fitzwater et al, 1996) and the southern Ocean (Martin et al.,... 

Fig. 14-6 Profiles of potential temperature and phosphate at 21 29 N, 122 15 W in the Pacific Ocean and a schematic representation of the oceanic processes controlling the P distribution. The dominant processes shown are (1) upwelling of nutrient-rich waters, (2) biological productivity and the sinking of biogenic particles, (3) regeneration of P by the decomposition of organic matter within the water column and surface sediments, (4) decomposition of particles below the main thermocline, (5) slow exchange between surface and deep waters, and (6) incorporation of P into the bottom sediments.

Horizontal distributions of (a) 02(mLyL), (b) percent saturation of 02(%), (c) phosphate ( j,mol/L), (d) nitrate ( ji,mol/L), and (e) silicate ( ji,mol/L) at 4000 m depth in the worid s major ocean basins. The horizontal distribution of AOU was presented In Figure 8.2. Source After Conkright, M. E., et al. (2002). World Ocean Atlas 2001, Volume 4 Nutrients, NOAA Atlas NESDIS 52, U.S. Government Printing Office (See companion website for color version.)... 

Nitrogen pollution has received far more attention than that of phosphorus for two reasons. First, it has been considered as the nutrient-limiting primary production in estuaries and coastal waters. Second, its loading into the coastal zone has been far greater than that of phosphorus (Figure 24.21). It is also more efficiently exported into the ocean due in part to formation of iron phosphate minerals in anoxic estuarine sediments. 

Primary production in the ocean is controlled by major nutrients, such as nitrate and phosphate, but also by certain trace metals. Dissolved iron was hypothesized (over 50 years ago) to be a key nutrient limiting primary production rates in the sea. However, credible data for the concentration of dissolved iron in seawater have only become available in the last 8 years. Iron is present in surface seawater at concentrations less than 0.5 nanomole per kilogram. These low concentrations of dissolved iron suggest that it is, in fact, a nutrient that can limit primary production in the ocean (Martin et al., 1989). The role of iron in limiting productivity of the ocean can be resolved only when measurements of dissolved iron at concentrations below 1 nanomole per kilogram become routine. There is evidence that other trace metals could also control phytoplankton growth. 

Fig. 9. Dissolved inorganic carbon, salinity, phosphate, nitrate, and temperature in surface ocean waters, during the 1982-83 El Nino, at the same longitude as in Fig. 7. Note that the high values for CO2 and nutrients south from the equator have disappeared while the water temperature has become warmer as warm waters from the Western Pacific flooded over the region. Measurements by C. D. Keeling, R. F. Weiss and others.

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