Interannual variability of SST the Norwegian sea near the Lofoten Islands in 1998-2020 according to satellite monitoring during the cod spawning period

INTERANNUAL VARIABILITY OF SST THE NORWEGIAN SEA NEAR THE LOFOTEN ISLANDS IN 1998-2020 ACCORDING TO SATELLITE MONITORING

DURING THE COD SPAWNING PERIOD

 

G.P. Vanyushin and T.V. Bulatova

 

Russian Federal Research Institute of Fisheries and Oceanography (VNIRO), Moscow, Russia

e-mail: ladimon@mail.ru

 

Abstract

For fishing purposes, satellite monitoring of SST is used to study the influence of temperature conditions in water areas important for the development of aquatic organisms on the formation of their biological productivity. One of such water areas is the Lofoten Islands zone in the Norwegian Sea. This area (as a reference zone) is known as the main spawning region of one of the main fishing objects - the north-eastern Arctic cod. A digital massif of infrared data from NOAA satellites is used to monitor temperature conditions. Verification of satellite data was carried out by using quasi-synchronous measurements of water temperature from ships, buoys and shore stations. Matrices created on the basis of weekly SST maps for the period 1998-2020 were used to assess the temperature situation in this water area when analyzing the interannual variability of SST. Calculations of the average monthly and long-term average values of SST and SST anomalies were made, the dynamics of SST was evaluated.

The results of the analysis showed that in general, in 1998-2020, there was a positive trend of SST growth in the Lofoten Islands area. In the period from 1998 to 2001, the average annual indicators of SST, gradually decreasing, reached a minimum (6.91 °C) in 2001, but then up to 2006 (8.29 °C) showed high growth rates. In the period 2006-2020, the temperature situation in the area of the Lofoten Islands somewhat stabilized, the average annual SST values fluctuated from 7.85 °C (2008) to 8.55 ° C (2017). After the maximum reached in 2017, there was a slight decline in SST (to 8.05 °C). The comparative assessment of SST indicators with climatic data is especially relevant for the period of the main spawning of the north-eastern Arctic cod, which takes place on March-April. The obtained results showed that in 1998-2020, the SST in the period March-April was on average higher than the climatic one. Negative anomalies of SST were noted only in 2001 (-0.26°C). In general, the analysis of the dynamics of the long-term course of seasonal average values of SST in the period March-April 1998-2020 showed the presence of a trend for an increase in seasonal average anomalies of SST in area near the Lofoten Islands. A decrease in the values of SST anomalies (from 0.86 °C to -0.26 ° C) was noted only for the period 1998-2001. After 2001 began an increase of temperature anomalies which reached a maximum in 2015 (2.04 °C). Since this year, a certain decrease in the values of SST anomalies has been observed in the studied water area, which continues to the present.

Keywords: satellite monitoring, sea surface temperature (SST), the Lofoten Islands, the North-East Atlantic (NEA) cod, spawning area, comparative analysis.