Mean cover and frequencies of vascular plant species during three decades around Abisko Scientific Research Station

Plant species distributions are expected to shift and diversity is expected to decline as a result of global climate change, particularly in the Arctic where climate warming is amplified. We have recorded the changes in richness and abundance of vascular plants at Abisko, sub-Arctic Sweden, by re-sampling five studies consisting of seven datasets; one in the mountain birch forest and six at open sites. The oldest study was initiated in 1977-1979 and the latest in 1992. Total species number increased at all sites except for the birch forest site where richness decreased. We found no general pattern in how composition of vascular plants has changed over time. Three species, Calamagrostis lapponica, Carex vaginata and Salix reticulata, showed an overall increase in cover/frequency, while two Equisetum taxa decreased. Instead, we showed that the magnitude and direction of changes in species richness and composition differ among sites.

Zooplankton and chlorophyll in upper water layers within research polygons in the Atlantic Ocean, June-September 2001

During Cruise 46 of R/V Akademik Mstislav Keldysh (from June to September 2001), vertical distributions of Radiolaria (Acantharia - Bac and Euradiolaria - Beur), mesozooplankton (from 0.2 to 3.0 mm size, Bm), and chlorophyll a (Cchl) in the epipelagic zone of the North Atlantic were studied. To examine the above-listed characteristics, samples were taken by Niskin 30 l bottles from 12-16 depth levels within the upper 100 to 200 m layer in the subarctic (48°11'N, 16°06'W) and subtropical (27°31'N, 75°51'W) waters, as well as in the transitional zone (41°44'N, 49°57'W). The latter proved to be characterized by the highest values of all averaged parameters examined by us within the upper 100 m layer (Bm - 365mg/m**3, Bac - 140 mg/m**3, Beur - 0.37 mg/m**3, and Cchl - 0.32 mg/m**3). For subarctic and subtropical waters corresponding characteristics were as follows: Bm - 123 and 53 mg/m**3, Bac - 0 and 0.06 mg/m**3, Beur - 0.17 and 0.19 mg/m**3, and Cchl - 0.27 and 0.05 mg/m**3, respectively. Percentage of Acantharia in total biomass of Radiolaria and zooplankton ranged from 0 to 39%, whereas that of Euradiolaria varied from 0.01 to 0.36%. Depth levels with maximum abundance of Acantharia were located above maxima of zooplankton and chlorophyll a or coincided with them. As for Euradiolaria, vertical profiles of their biomass were more diverse as compared with Acantharia. The latter group preferred more illuminated depth levels for its maximum development (10-100% of surface irradiance, E0) with respect to Euradiolaria (1-60% of E0). Possible reasons for this difference are discussed.