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

• Main Author: Jessen, Catherine
• Format: Doctoral or Postdoctoral Thesis
• Language: English
• Published: Quaternary Sciences, Department of Geology, Lund University 2006
• Subjects: Geology; marklära; geomorfologi; climatology; klimatologi; rapid climate change; Holocene climate; atmospheric CO2 concentrations; geochemical proxy indicators; Paleobotanik; palynology; palynologi; fylogeni; geomorphology; fysisk geografi; Geologi; physical geography; kartografi; pedology; cartography; phylogeny; Palaeobotany; stomatal frequency; lake sediments; Faroe Islands; Saksunarvatn; ice core; North Atlantic
• Online Access: https://lup.lub.lu.se/record/546226; https://portal.research.lu.se/files/4516214/3159884.pdf

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 ...