Spatial and temporal distribution of Holocene temperature maxima in the northern Nordic seas: interplay of Atlantic-, Arctic- and polar water masses

Abstract

Subsurface and bottom water temperatures on the western shelf of Svalbard at 79°N are reconstructed in order to investigate the relative influence of warm Atlantic water, cold Arctic/polar water and meltwater during the Holocene. The study is based on sediment core NP05-21GC, which has been investigated for the distribution of planktic foraminiferal species, oxygen and carbon isotopes measured in benthic and planktic foraminifera and subsurface and bottom water temperatures calculated from transfer functions. The data are compared to several other records from the western margin of Svalbard. The results indicate that until 9600 years BP the water column west of Svalbard was stratified by a pycnocline situated at a water depth of c. 100 m on the shelf and at c. 30 m on the slope. The water mass above the pycnocline consisted of cold Arctic/polar water and meltwater, whereas the water mass below the pycnocline consisted of warm Atlantic water. After 9600 the supply of Arctic/polar water and meltwater diminished weakening the pycnocline and from 9000 to 6000 years BP warm Atlantic water occupied the entire water column. The upper and deeper water masses experienced different Holocene temperature maxima. In the Atlantic water the temperature maximum occurred during the early Holocene 11,500–8200 years BP, only interrupted by the cold Pre-Boreal Oscillation c. 11,300–10,800 years BP. The maximum was followed by a gradual temperature decrease until c. 5000 years BP. In the upper water masses the temperature maximum occurred from c. 9000–6000 years BP. The timing of the maximum here is influenced by the decreasing supply of cold Arctic/polar water versus the increasing dominance of Atlantic water. The temperatures of both the surface and bottom water decreased to a minimum from c. 5000–2000 years BP. During the last 2000 years conditions have been increasingly unstable although with slightly increasing subsurface temperatures.