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Limnological responses to late Holocene permafrost dynamics at the Stordalen mire, Abisko, northern Sweden

Nilsson, Anders (2006) In Dissertations in Geology at Lund University
Department of Geology
Abstract
A composite sediment sequence, consisting of a Russian core and an overlapping freeze core, comprising
the uppermost meter of the sediment record, was retrieved from Lake Inre Abborrtjärn in the Torneträsk
valley in Lappland, northern Sweden. The core was subsampled for analysis of organic matter content,
inorganic carbon content and analysis of the sediment composition using a technique known as structural
analysis, resulting in a high-resolution data set spanning the last 2000 years. The chronology of the sediment
sequence is based on radiocarbon dating and 210Pb dating of the uppermost sediments.
The aims of the study were to evaluate possible connections between sediment stratigraphic changes and
variations in permafrost in the... (More)
A composite sediment sequence, consisting of a Russian core and an overlapping freeze core, comprising
the uppermost meter of the sediment record, was retrieved from Lake Inre Abborrtjärn in the Torneträsk
valley in Lappland, northern Sweden. The core was subsampled for analysis of organic matter content,
inorganic carbon content and analysis of the sediment composition using a technique known as structural
analysis, resulting in a high-resolution data set spanning the last 2000 years. The chronology of the sediment
sequence is based on radiocarbon dating and 210Pb dating of the uppermost sediments.
The aims of the study were to evaluate possible connections between sediment stratigraphic changes and
variations in permafrost in the adjacent mire complex at Stordalen, with a main focus on variations in the
presence of calcareous laminations in the sediments and their coupling to water chemistry (pH and alkalinity)
of the lake. Since both Lake Inre Abborrtjärn and the Stordalen mire are situated in an area with
abundant carbonate-rich bedrock exposures, the impacts of modern catchment hydrology as well as the
influence on pH exerted by ombrotrophic mires and fens were assessed based on a water chemical survey.
The stratigraphic records were also compared to meteorological data from the Abisko Scientific Research
Station and temperature reconstructions from the Torneträsk area and the Northern Hemisphere
beyond the short instrumental records.
The study shows that the calcareous laminations originate from calcium carbonate precipitation by
Characean algae (Chara sp.) as a result of photosynthesis during the summer months. The precipitation
of calcium carbonate is dependent on lake-water pH and thus related to variations in the chemical composition
of catchment runoff. From c. 1240 AD an expansion of ombrotrophic peat and permafrost aggradation
at the Stordalen mire lowered the pH of the lake-water as a result of increased inflow of humic
waters and DOC. Two periods of permafrost expansion were recognized in the sediment record, the first
period at c. 1240-1425 AD and the second at c. 1550-1850 AD, with a period of climatic amelioration in
between when the influence of ombrotrophic peat on lake-water pH decreased. From c. 1850 AD and
onwards the permafrost gradually started to disintegrate with an acceleration during the last decades.
Thus, changes in lake-water chemistry as recorded in sediment sequences may provide detailed information
on past variations in permafrost occurrences in subarctic settings. (Less)
Abstract (Swedish)
En sedimentsekvens bestående av en ryssborrkärna och en överlappande frysborrkärna, omfattande den
översta metern lagerföljden har provtagits från sjön Inre Abborrtjärn i Torneträskdalen, Lappland, norra
Sverige. Kärnan provtogs för analys av organiskt material och karbonater samt sedimentens sammansättning
med hjälp av strukturanalys. Detta resulterade i ett högupplöst dataset som spänner över de senaste
2000 åren. Kronologin för sedimentsekvensen baseras på blydatering (210Pb) i toppen och två 14Cdateringar
längre ner i sekvensen.
Målsättningen med denna studie var att utvärdera möjliga kopplingar mellan förändringar i sedimentstratigrafin
och variationer i permafrostutbredning i den intilliggande torvmarken vid Stordalen.... (More)
En sedimentsekvens bestående av en ryssborrkärna och en överlappande frysborrkärna, omfattande den
översta metern lagerföljden har provtagits från sjön Inre Abborrtjärn i Torneträskdalen, Lappland, norra
Sverige. Kärnan provtogs för analys av organiskt material och karbonater samt sedimentens sammansättning
med hjälp av strukturanalys. Detta resulterade i ett högupplöst dataset som spänner över de senaste
2000 åren. Kronologin för sedimentsekvensen baseras på blydatering (210Pb) i toppen och två 14Cdateringar
längre ner i sekvensen.
Målsättningen med denna studie var att utvärdera möjliga kopplingar mellan förändringar i sedimentstratigrafin
och variationer i permafrostutbredning i den intilliggande torvmarken vid Stordalen. Variationer
i förekomsten av kalklamineringar i sedimentsekvensen avspeglar sjöns vattenkemi (alkalinitet och pH)
beroende på inflöde av vatten från olika delar av avrinningsområdet. Eftersom både Inre Abborrtjärn och
torvmarken vid Stordalen ligger i ett område med kalkrik berggrund har påverkan på sjövattnets alkalinitet
utvärderats mot bakgrund av en hydrokemisk kartläggning av området. De stratigrafiska resultaten har
jämförts med meteorologiska mätserier från Abisko Naturvetenskapliga Station och temperaturrekonstruktioner
baserade på oberoende data, dels för Torneträskdalen specifikt och dels för hela norra halvklotet.
Studien påvisar att kalklamineringarna uppkommer vid kalkutfällning till följd av bottenlevande kransalgers
(Chara sp.) fotosyntes under sommarmånaderna. Utfällningen av kalk är beroende av pH vilket i sin
tur kan relateras till variationer i alkalinitet i sjöns tillflöden. Efter ca 1240 AD expanderade de ombrotrofa
torvmarkerna beroende på ökad förekomst av permafrost i myrmarken, vilket resulterade i ökat inflöde
av relativt surt humöst vatten med löst organiskt kol till sjön. Två perioder av permafrostexpansion
avspeglas i sedimentsekvensen, den första ca 1240-1425 AD och den andra ca 1560-1930 AD. Däremellan
rådde troligtvis ett mildare klimat, då permafrostens inverkan på sjöns alkalinitet minskade. Från ca
1930 AD och fram till idag har utbredningen av permafrost gradvis minskat, med en ökad nedbrytningshastighet
under de senaste årtiondena.
Sedimentstratigrafiska förändringar till följd av variationer i vattenkemi i små torvmarkssjöar kan ge detaljerad
information om permafrostdynamik i sub-arktiska miljöer. (Less)
Please use this url to cite or link to this publication:
author
Nilsson, Anders
supervisor
organization
alternative title
Limnologiska effekter av sen-Holocen permafrostdynamik i en torvmark vid Stordalen, Abisko, norra Sverige
year
type
H1 - Master's Degree (One Year)
subject
keywords
geography, geology, limnological responses, late Holocene, permafrost dynamics, Stordalen mire, Abisko, northern Sweden
publication/series
Dissertations in Geology at Lund University
report number
194
funder
Swedish Research Council
language
English
id
2338818
date added to LUP
2012-02-06 11:14:27
date last changed
2012-02-06 11:14:27
@misc{2338818,
  abstract     = {A composite sediment sequence, consisting of a Russian core and an overlapping freeze core, comprising
the uppermost meter of the sediment record, was retrieved from Lake Inre Abborrtjärn in the Torneträsk
valley in Lappland, northern Sweden. The core was subsampled for analysis of organic matter content,
inorganic carbon content and analysis of the sediment composition using a technique known as structural
analysis, resulting in a high-resolution data set spanning the last 2000 years. The chronology of the sediment
sequence is based on radiocarbon dating and 210Pb dating of the uppermost sediments.
The aims of the study were to evaluate possible connections between sediment stratigraphic changes and
variations in permafrost in the adjacent mire complex at Stordalen, with a main focus on variations in the
presence of calcareous laminations in the sediments and their coupling to water chemistry (pH and alkalinity)
of the lake. Since both Lake Inre Abborrtjärn and the Stordalen mire are situated in an area with
abundant carbonate-rich bedrock exposures, the impacts of modern catchment hydrology as well as the
influence on pH exerted by ombrotrophic mires and fens were assessed based on a water chemical survey.
The stratigraphic records were also compared to meteorological data from the Abisko Scientific Research
Station and temperature reconstructions from the Torneträsk area and the Northern Hemisphere
beyond the short instrumental records.
The study shows that the calcareous laminations originate from calcium carbonate precipitation by
Characean algae (Chara sp.) as a result of photosynthesis during the summer months. The precipitation
of calcium carbonate is dependent on lake-water pH and thus related to variations in the chemical composition
of catchment runoff. From c. 1240 AD an expansion of ombrotrophic peat and permafrost aggradation
at the Stordalen mire lowered the pH of the lake-water as a result of increased inflow of humic
waters and DOC. Two periods of permafrost expansion were recognized in the sediment record, the first
period at c. 1240-1425 AD and the second at c. 1550-1850 AD, with a period of climatic amelioration in
between when the influence of ombrotrophic peat on lake-water pH decreased. From c. 1850 AD and
onwards the permafrost gradually started to disintegrate with an acceleration during the last decades.
Thus, changes in lake-water chemistry as recorded in sediment sequences may provide detailed information
on past variations in permafrost occurrences in subarctic settings.},
  author       = {Nilsson, Anders},
  keyword      = {geography,geology,limnological responses,late Holocene,permafrost dynamics,Stordalen mire,Abisko,northern Sweden},
  language     = {eng},
  note         = {Student Paper},
  series       = {Dissertations in Geology at Lund University},
  title        = {Limnological responses to late Holocene permafrost dynamics at the Stordalen mire, Abisko, northern Sweden},
  year         = {2006},
}