Stagnation period

Stagnation Periods lengths of time during which little atmospheric mixing occurs... 

This value can be taken as the initial concentrations for both CE and CH for the second stagnation period. We leave it to the reader to check that at the end of the second stagnation period the concentrations are ... 

The behavior of the model is graphically summarized in the figure below. At first sight it seems to be paradoxical that during the second stagnation period CE drops below its steady-state CE. In fact, this happens because CE is coupled to CH which, in turn, remains below during the whole stagnation period. 

During the stagnation period, the following NTA concentrations are found in Greifensee ... 

Figure 15.6. Photosynthesis and respiration, (a) A well-balanced ecosystem may be characterized by a stationary state between photosynthetic production, P (rate of production of organic material) and heterotrophic respiration, R (rate of destruction of organic matter). Photosynthetic functions and respiratory functions may become vertically segregated in a lake or in the sea. In the surface waters the nutrients become exhausted by photosynthesis, (b) The subsequent destruction (respiration) of organism-produced particles after settling leads to enrichment of the deeper water layers with these nutrient elements and a depletion of dissolved oxygen. The relative compositional constancy of the aquatic biomass and the uptake (P) and release (R) of nutritional elements in relatively constant proportions (see equation 3) are responsible for a co-variance of carbon, nitrate, and phosphate in lakes (during stagnation period) and in the ocean an increase in the concentration of these elements is accompanied by a decrease in dissolved oxygen, (c, d) The constant proportions AC/AN/AP/AO2 typically observed in these waters are caused by the stoichiometry of the P-R processes.

Figure 15.10. Simplified scheme of typical transformation of phosphorus in a stratified lake. One milligram of phosphoms introduced into a lake during the stagnation period may lead to the synthesis of 100 mg algae (dry mass), which upon mineralization cause an oxygen consumption in the hypolimnion of 140 mg Oj from the organic P mineralized in the hypolimnion 0.6 mg are assumed to accumulate during the stagnation period, while 0.2 mg are assumed to be adsorbed [e.g., on iron(lll) oxide] and transferred into the sediments another 0,2 mg reaches the surface waters as phosphate by eddy diffusion.

Values for the whole period 1988-1990. h Values for the stagnation periods only (April-September). 

Matthaus, W., Nausch, G., Lass, H. U., Nagel, K., Siegel, H., 1999. The Baltic Sea in 1998— characteristic features of the current stagnation period, nutrient conditions in the surface layer and exceptionally high deep water temperatures. Deutsche Hydrographische Zeitschrift, 51, 67-84. 

The significant deepwater renewals and stagnation periods have been studied by Nehring (1981) in central Baltic deepwaters for the period 1952-1979. Regional and temporal variations in characteristics of stagnation periods have been investigated by Matthaus (1986) based on the data observed between 1952 and 1985. 

The Institute of Marine Research and later the Baltic Sea Research Institute in War-nemiinde were laigely involved in investigations of the analysis of specific inflows of highly saline water and the study of the water renewals in the central Baltic, as well as on the stagnation periods following these events in the central Baltic deep water. 

Francke and Nehring (1986) dealt with the moderate MBIs in November 1982 (Qg =13) and January 1983 (096=12), the latest inflows before the beginning of the longest stagnation period observed in the central Baltic so far. 

The Gotland Basin deep water does not show regular seasonal variations (cf. Matthaus, 1977, 1978), and the effects of MBls can be clearly identified. Three marked stagnation periods occurred during the past century—from 1922 to 1933-1934,1952-1961, and 1977-1992 identified by means of salinity (cf. Fig. 10.12). 

The strongMBI in December 1975/January 1976 (No. 15 in Table 10.2) was the beginning of the most significant stagnation period observed so far, lasting for 16 years in the Eastern Gotland Basin. The salinity decreased to the lowest values on record in the central Baltic deepwater, that is, from 13 psu in April 1977 to about 11 psu in January 1993 in the 200 m... 

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