In the last 20 years a summer following a warm winter usually was also warm.
Besides, a change of the wind conditions was observed. In summer, repeatability of
the northern and eastern winds increased along with the simultaneous decrease of
the western ones. This phenomenon limited the transformed river water flowing
into the shelf central area and promoted their propagation to the south.
The listed climatic changes induced the ones in the phytoplankton community
structure and development. As a result, its species diversity and abundance
increased, and the development phases changed. The winter bloom was observed
more often.
10.2.2.1 Variability of Hydrobiological Parameters in NWBS
Inter-annual seasonal variability anomalies of the chlorophyll a concentration are
presented on Fig. 10.9, where the winter and spring values are pooled together for
areas affected by riverine discharge (northern and western) and the central area
extending up to 32
30
0 E and affected by fresh water influx from time to time. The
anomaly is defined as deviation of seasonal values from the average long-term,
normalized by the standard deviation.
It was found earlier that regional meteorological conditions and the volume of
riverine discharge might affect the water transparency and the concentration of
1
2
Fig. 10.8 Distribution pattern of C Chl (a, b) and a g (c, d) on the section along the western shore of
the sea winter (a, 1), (c, 1), spring (a, 2), (c, 2), summer (b, 1), (d, 1), and autumn (b, 2), (d, 2)
periods
170
A.S. Kukushkin