| 1. |
- Berglund, Mikael
(författare)
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Early Holocene in Gästrikland, east central Sweden : shore displacement and pattern of isostatic recovery
- 2012
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Ingår i: Boreas. - : Wiley-Blackwell. - 0300-9483 .- 1502-3885. ; 41:2, s. 263-276
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Tidskriftsartikel (refereegranskat)abstract
- In Gästrikland in central Sweden, deglaciation took place c. 11 000 cal. a BP. In the present study the shore displacement during the earliest ice-free period is investigated by the 14C dating of sediment from isolated lake basins. The shore displacement in Gästrikland includes an initial phase (∼500 years) of rapid regression, followed by a slowing of the relative sea level (RSL) fall to a rate similar to that of the remaining Holocene c. 9250 cal. a BP. The Ancylus Lake stage of the Baltic Sea belongs to the analysed interval. The RSL curve and glacial unloading history are used to separate and quantify elements of isostatic uplift. The postglacial uplift is ∼260 m, of which ∼45 m forms a rapid initial rise, which can be treated as qualitatively separate from the later, slower rise. There is considerable glacial unloading just prior to the deglaciation, but calculations suggest that only a small part of this relates directly to the rapid early Holocene rebound: most unloading is transferred either to uplift immediately prior to the deglaciation or to subsequent Holocene or future uplift. The isostatic rise in Gästrikland occurring between the end of the Younger Dryas stadial and the deglaciation, c. 11 500–11 000 cal. a BP, is estimated to be 100–110 m. Observations and estimations are incompatible with a Weichselian maximum ice thickness much smaller that 3000 m. The lack of glacial unloading during the Younger Dryas has a measurable impact on the Holocene isostatic rebound in Gästrikland, reducing it by an estimated 20–25 m.
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| 2. |
- Berglund, Mikael
(författare)
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The highest postglacial shore levels and glacio-isostatic uplift pattern in northern Sweden
- 2012
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Ingår i: Geografiska Annaler. Series A, Physical Geography. - : Swedish Society for Anthropology and Geography. - 0435-3676 .- 1468-0459. ; 94:3, s. 321-337
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Tidskriftsartikel (refereegranskat)abstract
- The detailed clay varve chronology and an extensive knowledge of the highest postglacial shore level elevation (HS) in northern Sweden, along the Bothnian western coast, provides opportunities for determining the pattern of isostatic rise and centre of uplift from the early Holocene. The shore level of c. 10 100 cal yr bp (10 ka) for this area is determined by subtracting, from the metachronous HS elevations, the fall in relative sea level between local deglaciation time and the chosen reference time. The area of highest uplift since 10 ka is situated somewhat north of the location with the world-record HS (Skuleberget in Angermanland), but south of the area with most rapid current rise. Wave erosion marks in the studied area are seen to be more consistent indicators of HS than glaciofluvial delta levels. The gradients of shore marks at 10 ka are generally small within the investigation area. The regional 10 ka shore level pattern shows considerable irregularity compared to the current uplift. Central Sweden and western Finland show 10 ka gradients that indicate isostatic response to late (1310 ka bp) glacial unloading. Indications of a secondary uplift centre west of the present investigation area are reported in previous work; this also suggests rapid isostatic response to unloading. Finally, the possibility of identifying errors in the varve-dated deglaciation chronology via the 10 ka shore level pattern is illustrated.
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| 3. |
- Berglund, Mikael
(författare)
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Time-transgressive early Holocene vegetational succession following shore displacement: a case study from central Sweden
- 2008
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Ingår i: Boreas. - : Wiley. - 0300-9483 .- 1502-3885. ; 37:1, s. 87-101
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Tidskriftsartikel (refereegranskat)abstract
- Deglaciation took place in eastern Jamtland and Angermanland in central Sweden c. 10 500 - 10 200 cal. yr BP. In the present study, vegetation development and shore displacement during the earliest ice-free period are investigated by C-14 dating of sediment from six isolated lake basins and by pollen analysis. A brief but distinct peak in Hippophae "occurs in all pollen diagrams coincident with basin isolation, followed by up to 500 years ( varying locally) by an Alnus rise. The Alnus curve does not display a synchronous rise in the area. Its expansion below the highest shore level is time-transgressive and controlled mainly by the timing of basin isolation. The relationship between regional Alnus expansion and changes in hydrology and climate is discussed. The pollen diagrams show Pinus predominance with Corylus to the east ( more coastal areas) and Betula predominance ( though less pronounced) to the west during the period 10 200 - 9000 cal. yr BP. However, comparisons between sites suggest marked variability in the forest development. Shore displacement in easternmost Jamtland c. 10 300 - 9000 cal. yr BP is equal to or slightly more rapid than that of SE Angermanland, contrary to the present pattern of isostatic recovery. A rapid shore level regression c. 10 300 - 10 000 cal. yr BP may be related to drainage of the Ancylus Lake.
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| 4. |
- Berglund, Mikael
(författare)
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Litorina Sea shore displacement and pollen analytical indications of forest succession during the Mid-Holocene in Gästrikland, east central Sweden
- 2010
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Ingår i: GFF. - Stockholm : Taylor & Francis. - 1103-5897 .- 2000-0863. ; 132:3, s. 213-226
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Tidskriftsartikel (refereegranskat)abstract
- This paper deals with the mid-Holocene shore level history and vegetation development in Gästrikland, east-central Sweden. This is investigated using sediment and microfossil records and 14C datings. The time span covered is c. 8000-5000 cal yr BP. Vegetation history during this time includes an increase in Tilia pollen 6500-6300 cal yr BP and a decrease in Ulmus and Corylus c. 5500 cal yr BP. The former change coincides with a sharp drop in relative sea level (RSL) of some 5 m; this RSL drop can be correlated to the regression from the L3 transgression of the Litorina Sea, identified in other areas around the Baltic Sea. The possible connections between RSL and climate (in particular changes on a maritime-continental continuum), as indicated by new pollen data and other records, are investigated. The new material shows, in comparison to other pollen records from southern and central Scandinavia, unusually high percentages of Tilia, Ulmus and Corylus pollen, but less Quercus. The change in pollen spectra around 5500 cal yr BP can be correlated to the northern European “elm decline”. A regional cooling is recorded in widespread data for this time, but observations suggest that other factors must be considered here, including disease and change in the physical landscape due to the ongoing land uplift.
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| 5. |
- Berglund, Mikael
(författare)
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Holocene shore displacement and chronology in Ångermanland, eastern Sweden, the Scandinavian glacio-isostatic uplift centre
- 2004
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Ingår i: Boreas. - Oslo : Taylor & Francis. - 0300-9483 .- 1502-3885. ; 33, s. 48-60
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Tidskriftsartikel (refereegranskat)abstract
- The shore displacement during the Holocene in southeastern Ångermanland, Sweden, has been investigated by means of radiocarbon-dating of isolation intervals in sediment cores from a total of nine new basins. Results from earlier investigations have been used in complement. There is a forced regression in the area from c. 9300 BP (c. 10500 cal. yr BP) until c. 8000 BP (c. 9000 cal. yr BP), on averagec. 8 m/100 years, after which there is a gradually slowing regression of c. 2.5–1.0 m/100 years up to the present time. The most rapid regression occurs during the later phase of the Ancylus Lake stage, 9500–9000 cal. yr BP. There is no evidence of halts in the regression. Crustal uplift in the area since deglaciation is c. 310 m. The deglaciation of southeastern Ångermanland took place c. 9300 BP (c. 10500 cal. yr BP); this is c. 900 years earlier than the age given by clay varve dating. The shore displacement curve provides a means of estimating the difference between the clay varve time scale and calibrated radiocarbon dates, by comparison with varve-dated altitudes of alluvial deltas of the River Ångermanalven. From c. 2500 to c. 8000 cal. BP there is a deficit in clay varves of some 300 years; further back in time this discrepancy increases significantly. The main explanation for the discrepancy is most likely lacking varves in the time-span 8500–10200 cal. yr BP, located along the upper reaches of River Ångermanalven below the highest shore level.
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| 6. |
- Berglund, Mikael
(författare)
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The Holocene shore displacement of Gästrikland, eastern Sweden : A contribution to the knowledge of Scandinavian glacio-isostatic uplift
- 2005
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Ingår i: Journal of Quaternary Science. - : Wiley. - 0267-8179 .- 1099-1417. ; 20:6, s. 519-531
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Tidskriftsartikel (refereegranskat)abstract
- The shore displacement in Gästrikland, east-central Sweden, has been investigated by means of AMS radiocarbon dating of sediment cores from isolated basins. Twenty dates from 11 sites are presented. Pollen and diatom analyses, and archive material from the Geological Survey of Sweden, have been used to identify isolation intervals in the cores and as chronological support to the 14C dates. An important pollen stratigraphical time-marker is a distinct mid-Holocene increase in Tilia. For the mid-Holocene, pollen stratigraphy is used rather than the 14C dates for the age determination. The deglaciation of Gästrikland, according to the new 14C dates, took place ca. 11 000 cal. yr BP (ca. 9500 14C yr BP). Through the Holocene the shore displacement is regressive. The regression was initially rapid (on average ca. 3.5 m per 100 yr 11 000-7500 cal. yr BP, probably much more rapid at the earliest stage), then slowed down considerably and was from ca. 5000 cal. yr BP (probably already from 7000 cal. yr BP) relatively constant, ca. 0.8-0.9 m per 100 yr. There are important differences between the shore level curve from Gästrikland and curves from other areas, indicating some irregularities in the regional glacio-isostatic rebound.
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