376
Chemical Oceanography, 4th Edition
some can use dissolved or particulate organic P. Most species can grow at NO 3
– and PO 4
3–
levels 29 times the maximum values in the oceans. The minimum level of PO 4
3– needed
is about 0.3 μM but may vary with different species. This does not occur in the oceans
since N is exhausted before P falls to a critical level. Heavy blooms in enclosed areas can
be caused by excess amounts of NO 3
– and PO 4
3– from sewage or fertilizer runoff. SiO 2 is
needed for the growth of diatoms; the minimum levels needed are about 1.8 μM (which
may occur in subtropical waters). Trace metals (Fe, Mn, Mo, Zn, Cu, Co, V) are required for
the healthy growth of phytoplankton. These metals are needed for proteins and enzymes,
for example:
Ferrodoxin (Fe protein)
Enzymes (Mn, Mo, Cu, Zn, Co)
Phytoplankton can assimilate chelated forms of many elements. EDTA (ethylenediamine
N,N,N,N′ tetraacetic acid) is frequently added to cultures to permit nontoxic forms of metals to be available without the risk of the precipitation of hydroxides. Recent work has
indicated that shortages of Fe may limit the production of plankton in waters that have
high levels of nutrients (N, P, and Si), for example, the North Pacific and Southern Ocean
waters. The input of Fe from atmospheric sources could control the primary production in
these regions. This is discussed further in the chapter.
9.1.6.5 Organic Factors
Phytoplankton growth will not take place unless minute amounts of specific organics are
available. Some organics, however, also inhibit the growth of algae. Vitamin B 12 and B 1
(thiamine) are growth promoters. Ascorbic acid and cysteine may also be needed. Bacteria
may produce some of these compounds. A shortage of vitamin B 12 appears to limit the rates
of photosynthesis by stopping cell division, causing a loss of pigmentation and cell size.
9.1.7 growth and Distribution of Phytoplankton in the Sea
The rates of plankton growth are similar to bacteria that have been extensively studied.
An idealized growth curve is given in Figure 9.6. This simple growth curve does not occur
in the oceans because of physical and chemical factors as well as biological (grazing) and
hydrographic (horizontal and vertical water movement) factors. Discussion of the various
phases follows.
1. Lag phase: This delay of growth is thought to be due to a lack of balance in the
enzymatic reactions in the cell caused by growth promoters.
2. Exponential phase: This is the linear exponential growth phase, where the number of cells (N) increases according to
ln(N/ N 0 ) = k t
(9.12)
where N 0 is the initial number of cells, and k is related to the nature of the organism and conditions of growth. The half- time of growth t 1/2 = ln 2/k. In a culture,
the value of k = 0.1 to 1.0 h –1 , while in the sea, k = 0.09 to 0.015. This gives an average t 1/2 = 8 to 46 h at sea.
Chemical Oceanography, 4th Edition
some can use dissolved or particulate organic P. Most species can grow at NO 3
– and PO 4
3–
levels 29 times the maximum values in the oceans. The minimum level of PO 4
3– needed
is about 0.3 μM but may vary with different species. This does not occur in the oceans
since N is exhausted before P falls to a critical level. Heavy blooms in enclosed areas can
be caused by excess amounts of NO 3
– and PO 4
3– from sewage or fertilizer runoff. SiO 2 is
needed for the growth of diatoms; the minimum levels needed are about 1.8 μM (which
may occur in subtropical waters). Trace metals (Fe, Mn, Mo, Zn, Cu, Co, V) are required for
the healthy growth of phytoplankton. These metals are needed for proteins and enzymes,
for example:
Ferrodoxin (Fe protein)
Enzymes (Mn, Mo, Cu, Zn, Co)
Phytoplankton can assimilate chelated forms of many elements. EDTA (ethylenediamine
N,N,N,N′ tetraacetic acid) is frequently added to cultures to permit nontoxic forms of metals to be available without the risk of the precipitation of hydroxides. Recent work has
indicated that shortages of Fe may limit the production of plankton in waters that have
high levels of nutrients (N, P, and Si), for example, the North Pacific and Southern Ocean
waters. The input of Fe from atmospheric sources could control the primary production in
these regions. This is discussed further in the chapter.
9.1.6.5 Organic Factors
Phytoplankton growth will not take place unless minute amounts of specific organics are
available. Some organics, however, also inhibit the growth of algae. Vitamin B 12 and B 1
(thiamine) are growth promoters. Ascorbic acid and cysteine may also be needed. Bacteria
may produce some of these compounds. A shortage of vitamin B 12 appears to limit the rates
of photosynthesis by stopping cell division, causing a loss of pigmentation and cell size.
9.1.7 growth and Distribution of Phytoplankton in the Sea
The rates of plankton growth are similar to bacteria that have been extensively studied.
An idealized growth curve is given in Figure 9.6. This simple growth curve does not occur
in the oceans because of physical and chemical factors as well as biological (grazing) and
hydrographic (horizontal and vertical water movement) factors. Discussion of the various
phases follows.
1. Lag phase: This delay of growth is thought to be due to a lack of balance in the
enzymatic reactions in the cell caused by growth promoters.
2. Exponential phase: This is the linear exponential growth phase, where the number of cells (N) increases according to
ln(N/ N 0 ) = k t
(9.12)
where N 0 is the initial number of cells, and k is related to the nature of the organism and conditions of growth. The half- time of growth t 1/2 = ln 2/k. In a culture,
the value of k = 0.1 to 1.0 h –1 , while in the sea, k = 0.09 to 0.015. This gives an average t 1/2 = 8 to 46 h at sea.