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8
Micronutrients in the Oceans
8.1 Introduction
Marine phytoplankton require certain trace elements for growth. These nutrients are used
until they become limiting and further growth is inhibited. A crude way of assessing
the availability and need of marine plants for various elements can be made by examining the composition of phytoplankton compared to the concentration in average seawater.
Such a comparison is shown in Table 8.1. The most important micronutrients are nitrogen
and phosphorus. Some organisms (diatoms) have siliceous frustules and require silica.
Although other elements such as Fe, Mn, Cu, Zn, Co, and Mo are also essential for growth,
it is generally thought that growth is not inhibited or limited by the concentration of these
metals. An exception for certain waters may be Fe and Mn. In addition, certain organic
compounds, such as vitamins, are necessary for growth. This chapter discusses the major
micronutrients P, N, and Si.
8.2 Phosphorus in Seawater
Phosphorus occurs in seawater in dissolved and particulate forms. In surface waters, dissolved and particulate organic phosphates occur due to the decomposition of plants. These
dissolved organic phosphorus compounds make up a significant but variable portion of dissolved P in surface waters. Although the compounds have not all been identified, they are
undoubtedly related to the decomposition and excretion products of marine organisms.
Sugar phosphates, phospholipids, phosphonucleotides, and their hydrolyzed products
occur. Phosphate esters (O–P bonds) and more stable aminophosphonic acids (C–P bonds)
may also make up a considerable portion of the organic- phosphorus compounds. At present, the details of the cycling of these compounds in surface waters are largely unknown.
Dissolved inorganic phosphorus exists entirely as the ionized products of H 3 PO 4 .
H 3 PO 4 → H + + H 2 PO 4
–
(8.1)
H 2 PO 4
– → H + + HPO 4
2–
(8.2)
HPO 4
2– → H + + PO 4
3–
(8.3)
8
Micronutrients in the Oceans
8.1 Introduction
Marine phytoplankton require certain trace elements for growth. These nutrients are used
until they become limiting and further growth is inhibited. A crude way of assessing
the availability and need of marine plants for various elements can be made by examining the composition of phytoplankton compared to the concentration in average seawater.
Such a comparison is shown in Table 8.1. The most important micronutrients are nitrogen
and phosphorus. Some organisms (diatoms) have siliceous frustules and require silica.
Although other elements such as Fe, Mn, Cu, Zn, Co, and Mo are also essential for growth,
it is generally thought that growth is not inhibited or limited by the concentration of these
metals. An exception for certain waters may be Fe and Mn. In addition, certain organic
compounds, such as vitamins, are necessary for growth. This chapter discusses the major
micronutrients P, N, and Si.
8.2 Phosphorus in Seawater
Phosphorus occurs in seawater in dissolved and particulate forms. In surface waters, dissolved and particulate organic phosphates occur due to the decomposition of plants. These
dissolved organic phosphorus compounds make up a significant but variable portion of dissolved P in surface waters. Although the compounds have not all been identified, they are
undoubtedly related to the decomposition and excretion products of marine organisms.
Sugar phosphates, phospholipids, phosphonucleotides, and their hydrolyzed products
occur. Phosphate esters (O–P bonds) and more stable aminophosphonic acids (C–P bonds)
may also make up a considerable portion of the organic- phosphorus compounds. At present, the details of the cycling of these compounds in surface waters are largely unknown.
Dissolved inorganic phosphorus exists entirely as the ionized products of H 3 PO 4 .
H 3 PO 4 → H + + H 2 PO 4
–
(8.1)
H 2 PO 4
– → H + + HPO 4
2–
(8.2)
HPO 4
2– → H + + PO 4
3–
(8.3)