2.3. Results and discussion

The mean monthly distributions of chlorophyll concentrations, the particle backscattering coefficient, and TSM concentration in 1998-2010 are presented on the color maps.

Chlorophyll concentration

In the Northern and Middle regions the relatively high values of chlorophyll concentration (mostly 0.3-0.5 mg/m3, in places more than 0.5 mg/m3) are observed in May caused by spring phytoplankton bloom. The spring bloom can be observed in places in June. In other months chlorophyll concentration in these regions is within 0.15-0.3 mg/m3 and even less.

Particle backscattering and TSM

The enhanced values of bbp in the Northern and Middle regions are also seen in May, but their highest values (>0.02 m-1) are observed in July-September. The latter is attributable to the coccolithophore bloom, and the evidence of that has been obtained in the Professor Schtokman cruise in August 2004 [18] and in the Akademik Mstislav Keldysh in August 2009 [19]. In accordance with the satellite data, the water samples were taken, and an intense coccolithophore bloom was found (the coccolithophoride concentration exceeded 106 cell/l and even 107cell/l) [[18]. The areas of increased values of bbp are partly controlled by surface seawater temperature [20].

As seen from the maps, the coccolithophore blooms have been observed in the Barents Sea since 1998, just from the beginning of SeaWiFS observations. Smith et al. [21], analyzing data from AVHRR visible channel, concluded that coccolithophore blooms unambiguously presented in the Barents Sea between 1989–1992 but probably absent in other pre-SeaWiFS years.

In the Southern region and the White Sea chlorophyll concentration is usually higher than 0.3 mg/m3, enhanced values of the particle backscattering are also observed there.

The mean monthly distributions of TSM are similar to the bbp distributions. One of the main features of the TSM spatial distribution in the Barents Sea is their high variability (mostly pronounced in July-September). Values of TSM are varied from more 1 mg/l near the Pechora River runoff and Cheshkaya Bay and in the central parts in August-September (during coccolithophore bloom) to less than 0.15-0.1 mg/l for the northern and eastern Barents which are typical for open ocean waters.

Seasonal variability in different regions

Variability of the monthly mean values of chlorophyll concentration, the particle backscattering coefficient, and TSM in different regions of the Barents Sea throughout 1998-2010 is shown in Fig.3, 4, 5. It is seen that the variations of chlorophyll concentration in the Northern and Middle regions are in phase with each other, whereas they are out of phase with the ones in the Southern Barents. There is significant correlation between the variations of Chl and bbp values observed both in the Northern and Southern regions. This correlation can be explained by the fact that changes of both of the characteristics (Chl and bbp) are connected with the same basic factors: the spring phytoplankton bloom in the Northern Barents and the river run-off in the Southern region. In the Southern Barents both chlorophyll concentration and particle backscattering rise sharply in May-June that corresponds to the Pechora flood-time. The enhanced values of Chl and bbp are held up to September because of the Pechora discharge is high throughout summer and autumn due to frequent rain freshets [22].

No significant correlation is found between the variations of Chl and bbp in the Middle and Southern regions suggesting that the processes in coastal zone affect weakly the bio-optical characteristics in the open Barents Sea.

Variability of the monthly mean values of TSM in different regions of the Barents Sea and in the White Sea throughout 1998-2010 is well pronounced; its mechanism is same as for the bbp .

The mean monthly distributions of sea surface temperature (SST) in 1998-2010 are also given on the color maps, and variability of their monthly means in different regions of the Barents Sea throughout 1998-2010 is shown in Fig.6. It is seen that the warmest water is observed in July-August in all regions; the highest mean values can exceed 30C in the Northern Barents, 80C in the Middle Barents, and 90C in the Southern Barents (Fig.6). The maximum values of SST can exceed in places in the Northern Barents, 100C in open part of the Middle Barents, and 120C in coastal zone of the Middle and the Southern Barents (see color maps).

Inter-annual variability

The seasonal (May-September) mean values with their standard deviations for chlorophyll concentration, the particle backscattering coefficient, TSM and SST in different regions of the Barents Sea in 1998-2010 are given in Table 1.

It is seen that the highest Chl values are observed in the Southern Barents (the average over 1998-2010 is equal to 0.36 mg/m-3), in the Northern and the Middle regions the seasonal averages are close to each other (the average 0.24 mg/m-3). The inter-annual variability of chlorophyll concentration in the studied regions in 1998-2010 is not pronounced: changes in the mean seasonal values are within 0.22-0.27 mg/m-3 in the Northern Barents, 0.23-0.26 in the Middle, 0.35-0.37 mg/m-3 in the Southern Barents.

Inter-annual variability of the particle backscattering coefficient and TSM is more pronounced: the TSM averages are changed within 0.32-0.44 mg/l in the Northern Barents, 0.36-0.49 mg/l in the Middle, 0.91-1.02 mg/l in the Southern Barents.

The mean values of bbp in the Northern and Middle regions (4.8 and 5.3·10-3m-1) are about twice the typical values of bbp in open ocean [23]. In the Southern region the mean values of bbp increase more than twice.