My recent research has focused on the Holocene shore displacement in parts of central Sweden, with one research area in Ångermanland and eastern Jämtland and another in Gästrikland. I have constructed a general shore displacement curve for the Holocene in west-central Gästrikland (Berglund 2005, Fig 1) and I am in the process of adjusting this curve for middle Holocene (7.5-5 ka BP) and the earliest ice-free time (11-9 ka BP). My method has been 14C dating of the isolation of lake basins at different elevations along with altitude determinations of these basins. The isolation is the moment when a lake is formed by the emergence of its threshold over sea level, an effect of the strong glacio-isostatic uplift. The isolation is normally easily seen in a sediment core as a change from grey minerogenic sediment to brown, more organic sediment (Fig 2).
The shore displacement, i.e. sea level fall, was initially rapid (8-10 m/100 yrs after deglaciation at 11 ka) but slowed soon, partly as an effect of the Ancylus lake damming (c. 10.8-10 ka). Between 9.5 and 7.5 ka BP the shore displacement was around 2 m/100 yrs. During mid-Holocene there are some minor irregularities (phases of slower or more rapid regression), probably mainly due to slowing isostatic uplift while global sea level still rose (until c. 6 ka BP) and both these factors being slightly irregular. It is possible that regional climate may have played some part too, with high-water phases in the Baltic related to stronger westerly air circulation. After 5.5 ka BP there seems to have been a regular regression at a pace of a little less than 1 m/100 yrs.
The results are applicable within the region but with decreasing precision the farther away you move from Gästrikland, because of the fact that isostatic uplift differs between areas.
Fig 1. Shore displacement in Gästrikland during the Holocene. Error margins are probably around ±150 years in time, ±1 m in altitude. Dashed sections considered uncertain, with larger error margins. Vertical line indicates time of deglaciation, c. 11000 cal yrs BP. From Berglund (2005).
I have also worked with pollen analysis to determine the forest succession and composition, and indirectly to get information about environment (climate and openness of the landscape). My results indicate that birch and pine forests existed in newly deglaciated areas already after 3-4 centuries. For the early Holocene, geographical factors such as available land area, substrate and exposure probably were greater obstacles to forest establishment than climate. The Mid-Holocene vegetation in Gästrikland includes linden, elm and hazel in considerable proportions along with pine, birch and alder.
Fig 2. Sediment cores from Lake Skessen, S of Hofors, Gästrikland. The transition from grey to brown sediment reflects the change from open sea or bay to lake (i.e. the isolation of the basin). Photo M. Berglund 2009.
Dept. of Natural Sciences, Engineering and Mathematics
SE-871 88 Härnösand, Sweden
Telephone +46 611 86279
Position: lecturer (universitetslektor) Physical Geography, Mid Sweden University