HR: 1340h
AN: PP43A-0618    [Abstracts]
TI: Medieval Warmth, Little Ice Age Cooling, and 20th Century Warming Reconstructed from Icelandic Lake Sediments
AU: * Geirsdottir, A
EM: age@hi.is
AF: Earth Science Institute, Dept Geosciences University of Iceland, Reykjavik, 101 Iceland
AU: Miller, G
EM: gmiller@colorado.edu
AF: INSTAAR & GeolSci, University of Colorado, Boulder, CO 80309-0450 United States
AU: Wooller, M
EM: ffmjw@uaff.edu
AF: Alaska Stable Isotope Facility, Water and Env Rsch Center Inst. Marine Sciences University of Alaska, Faribanks, AL 99775 United States
AU: Wang, Y
EM: ffyw@uaf.edu
AF: Alaska Stable Isotope Facility, Water and Env Rsch Center Inst. Marine Sciences University of Alaska, Faribanks, AL 99775 United States
AB: Historical records from Iceland provide one of the most compelling lines of evidence for North Atlantic warmth and reduced sea ice during Medieval times, colder summers and expanded sea ice during the Little Ice Age, followed by ameliorated conditions during the 20th century. Icelandic terrestrial records, particularly those derived from lake sediments, tend instead to be over-printed by the ancillary effects associated with colonization, especially by soil erosion that resulted from deforestation and overgrazing. Here we present data for the past 2000 years from Haukadalsvatn, a large (3.3 km2), deep (42 m) lake set in a large catchment (172 km2), resulting in high sedimentation rates that exceed 1.5 m ka-1 in the central basin. Much of the catchment is at high elevation, and was probably never forested, reducing the anthropogenic signature. Two cores recovered with the GLAD200 Hydraulic Piston Corer in 2003 capture the entire sediment fill, consisting of 30 m of sediment; the upper 16 m are lacustrine, the lower 14 m are marine. The lacustrine sediments are finely laminated and interspersed with diagnostic tephra that provide additional age control. The last 2000 years is represented by the uppermost 4.5 m of sediment. Total organic carbon has been measured in continuous 1-cm-samples, providing a continuous record at ca. 3-year resolution. Studies of modern terrestrial and aquatic vegetation document a large difference in their d13C, with terrestrial vegetation typically 8 per mil lighter. The d13C of total organic carbon from Haukadalsvatn sediment indicates that carbon stored in the lake sediments is dominated by terrestrial carbon sources. However, intervals of low total carbon concentrations are also periods of relatively heavy d13C, suggesting that they represent intervals of reduced terrestrial erosion with a stronger contribution from aquatic sources. Overall, the interval from 2000 to 900 BP is characterized by relatively low rates of soil erosion, and slow rates of change. Sharp increases in soil erosion begin about 900 BP, and intensify after 600 BP, ending late in the 19th century, broadly coincident with the Little Ice Age. This period of landscape instability is punctuated by about a century of landscape stability about 400 BP. This pattern broadly follows the historical record of sea ice variability off the coast of Iceland.
DE: 1045 Low-temperature geochemistry
SC: Paleoceanography and Paleoclimatology [PP]
MN: 2004 AGU Fall Meeting