The Ups and Downs of the Holocene: Exploring Relationships between Global CO2 and Climate Variability in the North Atlantic Region

Catherine Jessen

Research output: ThesisDoctoral Thesis (compilation)

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Abstract

This thesis aimed to examine the relationship between climate and atmospheric CO2 concentrations through rapid climate changes during the Holocene. Climate was reconstructed using high-resolution, radiocarbon dated, lake sediment geochemical proxies (magnetic susceptibility, loss-on-ignition, total carbon/nitrogen/sulphur determinations and biogenic silica), vegetational reconstruction (pollen analysis) and stomatal frequency based CO2 reconstructions. The stomatal frequency based reconstructions of CO2 provides decadal scale data, which complement ice core measurements. Lakes sediments from south-central Sweden were collected and the analyses were focussed on a c. 1,000 year period centred at c. 4,000 cal. yr BP when an abrupt change to a cooler/wetter climate had previously been recorded. Secondly, lake sediments from the Faroe Islands earlier than the Saksunarvatn tephra layer (dated to 10,240 cal. yr BP) were collected, as it is known that this period was subject to sudden large-scale climatic coolings. The Faroe Islands are also expected, and have been previously shown, to be sensitive to ocean driven climatic change. The results from south-central Sweden showed that the transition from the relatively warm/dry middle Holocene climate to the cooler/wetter late Holocene was characterized by two major, well defined steps (c. 4,450-4,350 and c. 4,000-3,800 cal. yr BP). At c. 4,000-3,500 cal. yr BP, forest composition demonstrated distinct changes and pollen productivity declined markedly. Stomatal frequency analysis of Quercus and Betula indicated a fairly rapid decrease in concentrations around 3,600 cal. yr BP but due to large uncertainties produced by low leaf concentrations, this decrease is considered tenuous. The early Holocene results from the Faroe Islands covering the time period 11,230 to 10,330 cal. yr BP, and reconstructing both winter and summer conditions, indicate a period of increased storminess and cooler winters at c. 11,150 cal. yr BP. This was followed by a period of stability in both seasons between c. 11,000 and 10,680 cal. yr BP, at which time a distinct increase in variability is suggested by the data. Notably, a mainly winter cooling occurred at c. 10,600 cal. yr BP and winter/summer coolings at 10,450 and 10,300 cal. yr BP. These events broadly correlate with ?18O inferred atmospheric temperatures over Greenland and the reoccurrence of meltwater outbursts into the North Atlantic Ocean. The concurrent reconstruction of CO2 was based on Salix herbacea leaves and indicates a distinct decrease in global concentrations at c. 11,050 cal. yr BP, a consistent and steady decline between c. 10,900 and 10,600 followed by increased variability. The onset of CO2 variability occurs 80 years after the recorded changes in climate. The CO2 trends show a similar pattern to the reconstructed climatic changes and indicate that the climate of the Northern Hemisphere was significantly impacting the global carbon cycle. Additionally, the CO2 reconstruction shows a remarkable similarity to proxy-inferred solar activity changes, which may suggest that CO2 responded rapidly to these changes via responses in climate.
Original languageEnglish
QualificationDoctor
Awarding Institution
  • Quaternary Sciences
Supervisors/Advisors
  • Rundgren, Mats, Supervisor
  • Björck, Svante, Supervisor
  • Snowball, Ian, Supervisor
Award date2006 Mar 3
Publisher
ISBN (Print)91-86746-70-7
Publication statusPublished - 2006

Bibliographical note

Defence details

Date: 2006-03-03
Time: 13:15
Place: Pangea, Geocentrum II, Department of Geology, Sölvegatan 12, Lund University.

External reviewer(s)

Name: Walker, Michael
Title: Professor
Affiliation: University of Wales, Lampeter, UK

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Subject classification (UKÄ)

  • Geology

Free keywords

  • marklära
  • geomorfologi
  • climatology
  • klimatologi
  • rapid climate change
  • Holocene climate
  • atmospheric CO2 concentrations
  • geochemical proxy indicators
  • Paleobotanik
  • palynology
  • Geology
  • palynologi
  • fylogeni
  • geomorphology
  • fysisk geografi
  • Geologi
  • physical geography
  • kartografi
  • pedology
  • cartography
  • phylogeny
  • Palaeobotany
  • stomatal frequency
  • lake sediments

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