Climatic influence on peatland formation and lateral expansion in sub‐arctic Fennoscandia     

JAN WECKSTRÖM  HEIKKI SEPPÄ  ATTE KORHOLA 《Boreas: An International Journal of Quaternary Research》2010,39(4):761-769

Weckström, J., Seppä, H. & Korhola, A. 2010: Climatic influence on peatland formation and lateral expansion in sub‐arctic Fennoscandia. Boreas, Vol. 39, pp. 761–769. 10.1111/j.1502‐3885.2010.00168.x. ISSN 0300‐9843. The initiation and lateral expansion patterns of five small sub‐arctic peatlands in the Fennoscandian tree‐line region were studied by 21 accelerator mass spectrometry (AMS) ¹⁴C‐dated basal‐peat samples representing three to six dates per site. The radiocarbon dates were converted to calendar years and are based on the median probability. When combined with earlier basal‐peat dates from the region, four distinctive periods can be observed in the cumulative record of the dates. The early Holocene, from c. 10 000 to 8000 cal. yr BP, was characterized by the fast initiation and rapid expansion of peatlands, whereas at 8000–4000 cal. yr BP lateral expansion was modest. The most intensive period of peatland expansion occurred at the beginning of the late Holocene at c. 4000 to 3000 cal. yr BP, after which it slowed down towards the present. All these periods are in rough agreement with the main Holocene climatic periods in the area, namely the relatively warm and moist early Holocene, the warm and dry Holocene thermal maximum (HTM) at 8000–4000 cal. yr BP, and the start of the cooler and moister trend (neoglacial cooling) from c. 4000 cal. yr BP to the present, indicating a broad‐scale climatic control on the lateral growth of sub‐arctic peatlands in Fennoscandia. In order to study the lateral expansion of peatlands and to evaluate their Holocene succession patterns, more studies based on multiple dates from the same peatland are needed.  相似文献   

The Litorina transgression in the Helsinki region, southern Finland: new evidence from coastal mire deposits     

ATTE KORHOLA 《Boreas: An International Journal of Quaternary Research》1995,24(2):173-182

Sediment profiles were obtained, from the basal sections of two mire basins located above the highest Litorina shore in the Helsinki region, for pollen, diatom and Cladocera analyses and radiocarbon dating with the aim of exploring the relative sea-level changes during the Litorina stage of the Baltic Sea. Both profiles provided indications of 'long-distance effects' of the Litorina transgression around 7500–6100 BP, in the form of eutrophication, inundation, increased Pediastrum abundances, declined chydorid diversity and the presence of saline water diatoms. The results support the idea that sea level rose during the Litorina stage in the Helsinki region and suggest that this transgressive event had considerable effects on natural conditions in the coastal ecosystems. The findings contradict earlier accounts of a shore level stillstand during the Littorina stage in the Helsinki district.  相似文献   

Holocene development and early extreme acidification in a small hilltop lake in southern Finland   总被引：2，自引：0，他引：2  

ATTE A. KORHOLA  MATTI J. TIKKANEN 《Boreas: An International Journal of Quaternary Research》1991,20(4):333-356

The Holocene development of Pieni Majaslampi, a small hilltop lake which is exceptionally old for the conditions prevailing in southern Finland, is studied here by sedimentological and biostratigraphical methods. The lake is naturally acidic, with a pH of 4.5, and has been so since at least 8500 C¹⁴ BP, as determined from inferred-pH techniques based on contemporary diatom-pH relationships. The lake was found to have been subjected to extremely pronounced acidification during its early developmental stages, the pH having dropped from 5.8 to 4.7 between c. 10,000 and 8500 BP. Predicted pH values ranged from 4.5 to 5.1 over the remainder of its 8500-year history. Low pH values of 4.5-4.7 were found at the end of the Boreal Chronozone and in the Subboreal Chronozone and higher pH values of 4.7-5.1 in the Atlantic and Subatlantic chronozones. This pattern is believed to reflect changes in macroclimate, particularly humidity. The rapid early acidification was shown in the cladoceran succession by the replacement of Bosmina longirostris by Bosmina (Eubosmina) longispina and by an increased number of species such as alonella nana and Alonella excisa. considerable shifts in diatom species composition and abundance were observed during the most recent times, but distributions indicate that all the abundant taxa most frequently occur under acidic conditions, suggesting that other factors in addition to pH may be responsible for the shifts.  相似文献   

Three-dimensional reconstruction of carbon accumulation and CH4 emission during nine millennia in a raised mire     

ATTE KORHOLA  JUKKA ALM  KIMMO TOLONEN  JUKKA TURUNEN  H GNE JUNGNER 《第四纪科学杂志》1996,11(2):161-165

A three-dimensional model, based on numerous vertical and horizontal ¹⁴C datings and GIS simulation from a concentrically domed mire in southern Finland, demonstrates considerable variation in actual (net) rate of carbon accumulation (ARCA) through time. Lateral growth between 9000 and 3000 yr ago accounts for only 25% of the total carbon sequestration, whereas bog formation after ombrotrophication is responsible for the remaining 75%. On the other hand, the most rapid increase in landscape CH₄ flux occurred between 4500 and 3000 yr ago, the period of the fastest horizontal growth. In addition to autecological factors, a climatic shift towards cooler and wetter conditions is a plausible mechanism for maintaining accelerated carbon accumulation.  相似文献