Light and Nutrients in the Indian Ocean
87
grouped as a frequency distribution, using 0.00, 0.05, 0.10 ,ug-at 1- 1 as the class midpoints, for various depth intervals throughout the water column. The mean (~"l, variance
(S2), standard deviation (s) and standard error of estimate (s/ yn, where n is the number
of observations) are given in Table 2 through 5, for each area and depth level selected.
a) Observations during the SW Monsoon Period, 1963
Data for the Arabian Sea sections at 20° N, 15° Nand 9° N were obtained in August
and early September. This also includes the stations in the region of the Gulf of Aden
and around Socotra and Cape Guardafui. Equatorial sections were sampled in September,
and most of the southern areas were visited in October. It may be assumed that this
distribution represents monsoon and post-monsoon conditions and particularly reflects
the seasonal upwelling near Cape Guardafui, as already discussed in a preceding section.
aa) Total Organic Phosphorus
Results of the statistical treatment of the frequency distribution for the data on total
organic phosphorus are given in Table 2. The total water column was sampled and the
data divided into 1000 m increments. Since the first 1000 m segment includes so
many more sampling depths than the others, it is more nearly equivalent to all the depth
levels below 1000 m, which is the right-hand column given for each set of data in Table 2.
Accessory regions are those locations in which enough data were grouped together in a
close geographical area that it justified separate statistical treatment from that of the
latitudinal sections. Also, south of the Equator the western end of some sections was
separated from the easterly, mid-ocean part of the section. The pattern of distribution
for the calculated mean concentrations in ,ug-at 1- 1 at each depth interval has been plotted
in Fig. 15.
High mean values of total organic phosphorus (from 0.12 to 0.185 .ug-at 1- 1 ) are
found in the sudace to 1000 m depth segment. Almost all other depths of all sections
show little significant concentrations of organic phosphorus. Most values in the deeper
parts of the water column are 0.03 .ug-at 1- 1 or less. The effects of upwelling along the
Arabian coast and near Socotra can be seen in the high surface levels north of the Equator.
Slight enrichment in organic phosphorus at the deeper depths of the Arabian Sea presumably results from the surface productivity associated with upwelling conditions (YENTSCH,
1965, redrawn in MCGILL and LAWSON, 1966). There is a slight enrichment noted at
25° S in the section across the Mozambique Channel. With that exception, however, all
distributions for mean organic phosphorus concentration show a trend to higher values
north of the Equator than south. There is no equatorial peak in organic phosphorus,
as was seen in an similar data treatment for the Atlantic Ocean, based in IGY data
(MCGILL, 1963). This difference presumably is due to the special effects of the monsoon
circulation.
f3f3) Particulate and Dissolved Organic Phosphorus
For the surface to 200-m depth level, particulate phosphorus was determined by filtration for all water samples. The statistical data on particulate, dissolved and total organic
phosphorus at these surface levels is presented in Table 3. Mean concentrations are
plotted in Fig. 16. A separation of total organic phosphorus in the photic zone (0 - 200 m)
87
grouped as a frequency distribution, using 0.00, 0.05, 0.10 ,ug-at 1- 1 as the class midpoints, for various depth intervals throughout the water column. The mean (~"l, variance
(S2), standard deviation (s) and standard error of estimate (s/ yn, where n is the number
of observations) are given in Table 2 through 5, for each area and depth level selected.
a) Observations during the SW Monsoon Period, 1963
Data for the Arabian Sea sections at 20° N, 15° Nand 9° N were obtained in August
and early September. This also includes the stations in the region of the Gulf of Aden
and around Socotra and Cape Guardafui. Equatorial sections were sampled in September,
and most of the southern areas were visited in October. It may be assumed that this
distribution represents monsoon and post-monsoon conditions and particularly reflects
the seasonal upwelling near Cape Guardafui, as already discussed in a preceding section.
aa) Total Organic Phosphorus
Results of the statistical treatment of the frequency distribution for the data on total
organic phosphorus are given in Table 2. The total water column was sampled and the
data divided into 1000 m increments. Since the first 1000 m segment includes so
many more sampling depths than the others, it is more nearly equivalent to all the depth
levels below 1000 m, which is the right-hand column given for each set of data in Table 2.
Accessory regions are those locations in which enough data were grouped together in a
close geographical area that it justified separate statistical treatment from that of the
latitudinal sections. Also, south of the Equator the western end of some sections was
separated from the easterly, mid-ocean part of the section. The pattern of distribution
for the calculated mean concentrations in ,ug-at 1- 1 at each depth interval has been plotted
in Fig. 15.
High mean values of total organic phosphorus (from 0.12 to 0.185 .ug-at 1- 1 ) are
found in the sudace to 1000 m depth segment. Almost all other depths of all sections
show little significant concentrations of organic phosphorus. Most values in the deeper
parts of the water column are 0.03 .ug-at 1- 1 or less. The effects of upwelling along the
Arabian coast and near Socotra can be seen in the high surface levels north of the Equator.
Slight enrichment in organic phosphorus at the deeper depths of the Arabian Sea presumably results from the surface productivity associated with upwelling conditions (YENTSCH,
1965, redrawn in MCGILL and LAWSON, 1966). There is a slight enrichment noted at
25° S in the section across the Mozambique Channel. With that exception, however, all
distributions for mean organic phosphorus concentration show a trend to higher values
north of the Equator than south. There is no equatorial peak in organic phosphorus,
as was seen in an similar data treatment for the Atlantic Ocean, based in IGY data
(MCGILL, 1963). This difference presumably is due to the special effects of the monsoon
circulation.
f3f3) Particulate and Dissolved Organic Phosphorus
For the surface to 200-m depth level, particulate phosphorus was determined by filtration for all water samples. The statistical data on particulate, dissolved and total organic
phosphorus at these surface levels is presented in Table 3. Mean concentrations are
plotted in Fig. 16. A separation of total organic phosphorus in the photic zone (0 - 200 m)