THE PRODUCTION O F M A R I N E P L A N K T O N
159
(2) in temperate and subpolar waters rates arc! about 70-120 g C/m2. A t
high latitudes very high rates may hold for E,hort periods (even up to
5 g C/m2/day) but the flowering period is short.
(3) Antarctic production - approximately 100 g C/m2/year except for
especially rich zones (e.g. South Georgia).
(4) Arctic - very low production in true Arctic - perhaps < 1 g C/
m2/year in Polar Sea.
Apart from very shallow, highly productive inshore areas, continental
shelf waters do not exceed offshore regions at the same latitude very
greatly. The timing of the phytoplankton cycle may be strongly
affected, and the crop per unit volume is far higher.
Both Anderson (1964) and Teixeira (1963) suggest that productivity
and standing crop are both much higher in inshore waters than offshore
in temperate and tropical regions respectively. Ketchum et al. (1958)
point out that tropical oceanic waters may sometimes show high rates
of production, but in general the net photosynthetic production in
tropical oceanic waters is low; nutrient impotrerishment of the surface
layers and the lack of effective vertical mixing probably causes the
phytoplankton to be in less “healthy” cordition, so reducing the
effective production over the year. Yentsch and Vaccaro (1958) point
out that nitrogen deficiency causes a reduction in chlorophyll, and may
also lead to temporaiy disbalance in the chlorophyl1:carotenoid ratio.
Steele (1962) and Steele and Baird (1962) have demonstrated that the
chlorophyl1:carbon ratio is influenced by nutrient level, thus in turn
affecting productivity.
A factor in the total production of a column of sea water is not only
the depth of the euphotic zone but also the precise distribution of the
algal cells. I n earlier considerations of critical depth it was assumed that
the algae were regularly distributed throughout the photosynthetic
zone so that production rate decreased logaritl-.mically from the surface
(cf. Fig. 6). We know little of the precise distribution of phytoplankton
throughout the euphotic zone at high latitudes; the photosynthetic
zone is relatively thin and continual wave action may give a reasonably
equal distribution, though the recent study by ‘Burkholder and Sieburth
(1 961) for Antarctic waters suggested that the maximum chlorophyll
concentration occurred at the surface. Halldal (1953) observed a fairly
even distribution of phytoplankton in Norwegian Sea waters with a
deep mixed layer, but in July, August and September when stratification was obvious, the majority of the aigae were massed in the upper
25m. In tropical waters, surface inhibition of photoeynthesis has been
clearly demonstrated, and a maximum of phytoplankton is frequently
found at some depth in the photosynthetic zone (e.g. Menzel and Ryther,
159
(2) in temperate and subpolar waters rates arc! about 70-120 g C/m2. A t
high latitudes very high rates may hold for E,hort periods (even up to
5 g C/m2/day) but the flowering period is short.
(3) Antarctic production - approximately 100 g C/m2/year except for
especially rich zones (e.g. South Georgia).
(4) Arctic - very low production in true Arctic - perhaps < 1 g C/
m2/year in Polar Sea.
Apart from very shallow, highly productive inshore areas, continental
shelf waters do not exceed offshore regions at the same latitude very
greatly. The timing of the phytoplankton cycle may be strongly
affected, and the crop per unit volume is far higher.
Both Anderson (1964) and Teixeira (1963) suggest that productivity
and standing crop are both much higher in inshore waters than offshore
in temperate and tropical regions respectively. Ketchum et al. (1958)
point out that tropical oceanic waters may sometimes show high rates
of production, but in general the net photosynthetic production in
tropical oceanic waters is low; nutrient impotrerishment of the surface
layers and the lack of effective vertical mixing probably causes the
phytoplankton to be in less “healthy” cordition, so reducing the
effective production over the year. Yentsch and Vaccaro (1958) point
out that nitrogen deficiency causes a reduction in chlorophyll, and may
also lead to temporaiy disbalance in the chlorophyl1:carotenoid ratio.
Steele (1962) and Steele and Baird (1962) have demonstrated that the
chlorophyl1:carbon ratio is influenced by nutrient level, thus in turn
affecting productivity.
A factor in the total production of a column of sea water is not only
the depth of the euphotic zone but also the precise distribution of the
algal cells. I n earlier considerations of critical depth it was assumed that
the algae were regularly distributed throughout the photosynthetic
zone so that production rate decreased logaritl-.mically from the surface
(cf. Fig. 6). We know little of the precise distribution of phytoplankton
throughout the euphotic zone at high latitudes; the photosynthetic
zone is relatively thin and continual wave action may give a reasonably
equal distribution, though the recent study by ‘Burkholder and Sieburth
(1 961) for Antarctic waters suggested that the maximum chlorophyll
concentration occurred at the surface. Halldal (1953) observed a fairly
even distribution of phytoplankton in Norwegian Sea waters with a
deep mixed layer, but in July, August and September when stratification was obvious, the majority of the aigae were massed in the upper
25m. In tropical waters, surface inhibition of photoeynthesis has been
clearly demonstrated, and a maximum of phytoplankton is frequently
found at some depth in the photosynthetic zone (e.g. Menzel and Ryther,