370
Chemical Oceanography, 4th Edition
per unit time per unit volume (mg C m –3 h –1 ) or under unit surface area (g C m –2 day –1 ). The
primary production is normally determined from measurements performed at depths of
100, 10, and 1 m.
P = (1/5)(2P 100 + 2P 10 + P 1 )(D/2) N K
(9.7)
where D is the depth at which light is 1% of surface, N is the number of hours to sunset,
and K is the fudge factor (1.0 in the tropics).
The new production is defined as the primary production associated with newly available nitrogen (NO 2
–
, NO 3
–
, NH 3 ). The new production plus the regenerative production
(the primary production associated with recycled nitrogen) is equal to the total primary production.
P T = P NEW + P REG
(9.8)
These definitions are based on the systems being in steady state. The ratio of the new production to the total production is called the f ratio:
f = P NEW / P T
(9.9)
The f ratio is useful in describing the fraction of organic nitrogen and carbon exported
from the surface waters of the oceans into the deep ocean. The oxidation of these organic
compounds returns NO 3
– and CO 2 to the deep waters. It also represents the capacity of the
system to sustain secondary and higher levels of production.
9.1.2 Standing Crop or biomass
The biomass is concentrated by centrifugation or filtration, and the cells are counted by
eye, with a Coulter counter, or by analyzing a chemical component of the cell. The concentration of chlorophyll- a, determined by spectroscopic and fluorometric methods, is often
used as an indicator of the levels of biomass. The rate of consumption of micronutrient elements is also used to obtain integrated values of primary productivity over fairly lengthy
periods. Since NO 3
– and PO 4
3– can be regenerated and recycled several times a year, these
values will tend to be minimal levels.
A number of methods have been used to determine the primary productivity (see
Table 9.2). A brief discussion of the most popular methods used to determine primary
production are given in the next two sections.
9.1.3 The O 2 liberation Method of Measuring Primary Productivity
A series of 300-ml glass- stoppered bottles are filled with seawater collected using clean
techniques (Teflon- lined bottles on Kevlar line). The bottles are suspended at various
depths throughout the photic zone or in a water bath under various light levels. Dark or
“light- tight” bottles filled with the same seawater are suspended at the same depths. After
3 to 8 h, the water is analyzed for O 2 . The increase of O 2 in the light bottles is a measure of
the net photosynthesis. The gross productivity is obtained from the difference in the O 2 in
the light and dark bottles (the loss of O 2 from respiration). Some problems with the method
are as follows:
Chemical Oceanography, 4th Edition
per unit time per unit volume (mg C m –3 h –1 ) or under unit surface area (g C m –2 day –1 ). The
primary production is normally determined from measurements performed at depths of
100, 10, and 1 m.
P = (1/5)(2P 100 + 2P 10 + P 1 )(D/2) N K
(9.7)
where D is the depth at which light is 1% of surface, N is the number of hours to sunset,
and K is the fudge factor (1.0 in the tropics).
The new production is defined as the primary production associated with newly available nitrogen (NO 2
–
, NO 3
–
, NH 3 ). The new production plus the regenerative production
(the primary production associated with recycled nitrogen) is equal to the total primary production.
P T = P NEW + P REG
(9.8)
These definitions are based on the systems being in steady state. The ratio of the new production to the total production is called the f ratio:
f = P NEW / P T
(9.9)
The f ratio is useful in describing the fraction of organic nitrogen and carbon exported
from the surface waters of the oceans into the deep ocean. The oxidation of these organic
compounds returns NO 3
– and CO 2 to the deep waters. It also represents the capacity of the
system to sustain secondary and higher levels of production.
9.1.2 Standing Crop or biomass
The biomass is concentrated by centrifugation or filtration, and the cells are counted by
eye, with a Coulter counter, or by analyzing a chemical component of the cell. The concentration of chlorophyll- a, determined by spectroscopic and fluorometric methods, is often
used as an indicator of the levels of biomass. The rate of consumption of micronutrient elements is also used to obtain integrated values of primary productivity over fairly lengthy
periods. Since NO 3
– and PO 4
3– can be regenerated and recycled several times a year, these
values will tend to be minimal levels.
A number of methods have been used to determine the primary productivity (see
Table 9.2). A brief discussion of the most popular methods used to determine primary
production are given in the next two sections.
9.1.3 The O 2 liberation Method of Measuring Primary Productivity
A series of 300-ml glass- stoppered bottles are filled with seawater collected using clean
techniques (Teflon- lined bottles on Kevlar line). The bottles are suspended at various
depths throughout the photic zone or in a water bath under various light levels. Dark or
“light- tight” bottles filled with the same seawater are suspended at the same depths. After
3 to 8 h, the water is analyzed for O 2 . The increase of O 2 in the light bottles is a measure of
the net photosynthesis. The gross productivity is obtained from the difference in the O 2 in
the light and dark bottles (the loss of O 2 from respiration). Some problems with the method
are as follows: