Synoptic climatology of the formation of algal blooms in the South Caspian

Document Type : Research Article

Authors

• Abdolazim Ghanghermeh
• Gholamreza Roshan

Golestan University

10.22067/geo.v1i2.16449

Abstract

Introduction
One of the important events that usually occur in seas and large water bodies’ concurrent with the change of season is the growth and species increase of Phytoplankton. In the natural environment, this event does not result in imbalances of water ecosystems. However, pollution caused by human activities results in excessive growth and reproduction of Phytoplankton and other opportunist species. A certain species, cyan bacteria, which in dense populations (100 to 1000 numbers in a millilitre), is dangerous to water bodies and the cause of Algal blossoming or blooms. Algal blooms result in a decrease in water quality through the formation of a thick putrid foam-like layer on the surface of the water. This layer prevents sunlight from penetrating the water, and decreases oxygen availability. In this way, it has a negative effect on the biological and ecological structure of the aquatic ecosystems. The species that forms this layer may thus directly harm the creatures that live in this water column, and in some instances, result in their death. As the formation of Algal blooms depends on the physical and biochemical conditions of the water body together with the conditions of the water and air (sunlight, water temperature, wind speed, etc.), the Caspian sea is of interest considering both its special physical and chemical features and human interference. The Caspian Sea ecosystem is constantly changing,, and in recent years, numerous Algal blooms in the Caspian Sea have been observed. For this reason, this study has aimed to evaluate climatic patterns simultaneous with Algal blooms. The goal of this study is to identify climatic patterns simultaneous with Algal blooms in the southern Caspian, for the months of August and September 2005. By so doing, the results aim to provide the initial stage of prediction of the timing and occurrence of Algal Bloom events in the Caspian Sea.
Material and Methods
The study region for this research is the southern area of the Caspian Sea, in which one of the most exceptional Algal blooms, occurred in August and September 2005 (Figure no. 1). The data used in this research include 1000 HPA and 500 HPA air pressure, 10- meter meridian (V-wind) and zonal (U-wind) winds, at 10m altitude, the air temperature at 2m altitude, surface temperature and Chlorophyll A. The range of patterns in air pressure from the Greenwich meridian to 80˚ E longitude, patterns of the wind and air temperature for the region of the Caspian Sea and its neighbouring areas from 40° to 60° E and 35˚ to 50˚N are also used. These data were obtained from NOAA website in Netcdf format and converted to text format (ASCII) there were then converted into time and place matrixes for the above mentioned two months. Finally, temporal series plots were produced for each, variable and were Composited for the analysis. For this study, wind fields less than 4.8 meter per second, and air temperature exceeding 25˚C were evaluated. It is noteworthy that the research method in this research generally includes circulation to environment method.
Results and Discussion
The findings of this research demonstrate that, at the time of the formation of Algal blooms in the southern Caspian Sea; the map pattern of air pressure presents an anticyclone system. The duration and source of this anticyclone is located over the Atlantic Ocean, in the high-pressure regions of the Azores high. This pattern is clear up to the level of 850 HPA. In the 500 HPA level, a relatively weak atmospheric ridge is observed. As a result of this anticyclone circulation, the wind rotates clockwise over the region. The direction of wind which is mostly over the southern Caspian has the lowest speed from northeast to the southwest. Perpendicular streams of the air demonstrate a weak decrease in speed in the regions of the southwest of the Caspian. This pattern in the perpendicular surface is stretched on the north-south axis of the Caspian Sea up to 500 HPA level. During this period, the surface temperature, air temperature and Chlorophyll have specific conditions.
Conclusion
Considering that Algal blooms are formed when the physical and biochemical conditions of water in the southern Caspian are prepared, and when there are appropriate climatic conditions, occurrence in other regions of the Caspian Sea is possible. The occurrence of the Algal blooms of the months of August and September 2005, especially in the southern Caspian, demonstrates climatic conditions required for its occurrence. These include the occurrence of an anticyclone circulation, accompanied by a long period of relatively high stability. Furthermore, the hot period of the year causes the increase in the temperature of the surface of the water of the Caspian Sea (Figure 2), clearly demonstrated by the results of the investigation of the air temperature. Wind speed is considerably low in stable atmospheric conditions, and these results in instability and imbalance of the sea surface. Therefore, the conditions of the combination of the surface and deep waters reach their minimum. Although the combination of the upper layer of water is essential for bringing the necessary nutrients to the surface, the wind threshold can bring about these conditions more easily. While we took wind as our presupposition, by considering the synoptic winds with the wind threshold of 4.8 meter per second, it should be noted that this matter needs further investigation in order to be confirmed.

Keywords

• Synoptic climatology
• Algal blooms
• South Caspian
• Pattern of the peripheral circulation
• Ridge

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