The Annual Cycle of Phytoplankton Primary Production and Hydrography in the Disko Bugt area, West Greenland

About this book

The distribution and size of phytoplankton production and biomass in relation to physical and chemical parameters in the upper 50 m at Godhavn and in Kangikerdlak in the inner part of Disko Fjord was investigated through 2 1/2 years (1973)-75). Some data from other parts of Disko Bugt are presented in The Annual Cycle of Phytoplankton Primary Production and Hydrography in the Disko Bugt area, West Greenland.

In both locations the hydrography alternates between an unstable winter situation with isothermal (±1.75°C) and isohaline (33.5-34.0‰) conditions throughout, and a highly stable summer situation when dilution and heating, especially of the upper 20-30 m, raise the temperature at the surface to 9.9°C and at 50 m to 3.8°C at Godhavn, and to 12°C and 3.5°C respectively in Kangikerdlak. Salinities drop correspondingly to 30.6‰ in Kangikerdlak.

The 1% depth for green light is greatly reduced beneath ice and snow. During the ice free period of Godhavn it varies from 12 m during the spring phytoplankton bloom to more than 60 m from Oct. through the winter. In Kangikerdlak the 1% depth reaches only 40 m in winter, and outflowing turbid fresh water creates 1% depths of as little as 4-5 m in June-Aug. At Godhavn NO₃-N reaches highs of 10.05 µgat/liter and 10.15 µgat/liter at 0 and 50 m respectively in winter, whereas during the summer, depletion to less than 0.01 µgat/liter occurs in the upper 40 m and to 1.0 µgat/liter at 50 m. PO₄-P is similarly reduced from 0.8 µgat/liter and 1.1 µgat/liter to less than 0.01 µgat/liter in the upper 20 m and to 0.21 µgat/liter at 50 m. In Kangikerdlak depletion of NO₃-N is similar to conditions at Godhavn, whereas PO₄-P reaches a low of 0.1 µgat/liter only, while in mid summer it reaches 1.88 µgat/liter at the surface, giving an N:P ration which is below 0.1 in the upper 5 m only.

At Godhavn primary production is about 90 gC · m^-2 · yr^–1 (75-104 g) with a maximum of about 5.5 gC · m^-3 · yr^-1 at 5-10 m, whereas in Kangikerdlak production was concentrated near the surface with about 6.0 gC · m^-3 · yr^-1 at 5-10 m, whereas in kangikerdlak production was concentrated near the surface with about 6.0 gC · m^-3 · yr^-1 and a total of 35 gC · m^-2 · yr^-1 at most. Production at Jacobshavn off the glacier fjord is probably greater than at Godhavn, whereas at Christianshåb and Egedesminde it is definitely lower.

Phytoplankters larger than 56 µ contribute about 50% of annual and up to 90% of daily production. Due to thee great stability, production usually extends no deeper than compensation depth, and most of the chlorophyll is usually in the nutrient rich water below this depth, where it sinks, is consumed, or degrades into phaeopigment. P/B is highest where there is least chlorophyll. Light reduces production in the upper 5-10 m, and inhibition may extend to 30 m. Correlations between production, P/B or P/B/light and nutrients reveal possible saturation values of 0.08-0.78 µgat NO₃-N/liter and 0.17-0.22 µgat PO₄-P/liter. PO₄-P seems to be the limiting nutrient in some cases, although NO₃-N is most quickly and thoroughly depleted.

Dark fixation at Godhavn is about 24 gC · m^-2 · yr^-1, and at Kangikerdlak about 15 gC · m^-2 · yr^-1. 55-60% of dark fixation is presumed to be biotic and 16-64% is associated with particulate matter larger than 56 µ.

Although oxygen is never at a minimum in Disko Bugt, saturation as well as absolute O₂ values and pH show profiles in the bay that clearly reflect the high degree of stratification compared to waters south of the bay.

Contents

Abstract
Introduction
Materials and methods
Hydrography of the upper 50-90 m off Godhavn
Hydrography of the upper 50 m in Kangikerdlak
Primary production by phytoplankton in the upper 50 m in Kangikerdlak
Hydrography in other parts of the Disko Bugt area
Other primary production measurements in Disko Bugt
Primary production and nutrients inshore and offshore at Godhavn
References

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