Indications for periodicities can be found in many Holocene paleoclimate proxies from the North Atlantic region and for the last years the focus has been on records that have cyclicities of short time, millennial to centennial timescale. In addition to the well known 11 and 200 years solar cycles the “1500 years cycle” is found at several sites in the North Atlantic. The 1500 year cycle has either been related to small solar variations (Bond et al, 2001) or changes in oceanic circulation (Biancha and McCave, 1999, Chapman and Shackleton, 2000, Debret et al, 2007). The North Atlantic Oscillation is a pressure difference between the Icelandic Low and Azores High that shows periodicities that have been related to the 11 year sunspots cycle and the 80-90 year Gleissberg cycle which represents amplitude changes of the 11 year cycle (Shindell et al, 2001). Analyzes of climate cycles of a short timescale gives the opportunity to discriminate between natural oscillations and anthropogenic effects on climate and can be helpful for modeling future climate change. In order to obtain a better picture of the spatial pattern of centennial and higher frequency climate variability, a high-resolution lake sediment core from Lake Haukadalsvatn in northwestern Iceland that contains paleoclimatic proxy data back 10,000 years is used. Cycles similar to the above-mentioned cycles can be found in the proxies from Lake Haukadalsvatn, such as the 1500, 200 and 80-90 years cycles.

Haukadalsvatn (3.3 km2, max depth 42 m) is a glacier-eroded lake at the head of Hvammsfjörður, western Iceland, with the largest part of the catchments (172 km2) above 500 m a.s.l. This location results in high sedimentation rates that exceed 1.5 m/ka in the central basin. In summer 2003, two long sediment cores were recovered from the deepest basin, using the DOSECC GLAD-200 core rig. The cores captured the entire 30-m-thick sediment fill; the lower 14 m consists of rapidly deposited ice-proximal to ice-distal deglacial marine sediment, the upper 16 m are lacustrine. The chronology of the sediment is based on tephra layers and ²¹⁰Pb and ¹³⁷Cs analysis in the upper part.

The total organic carbon (TOC) has been measured every cm for the last 10200 years and biogenic silica (BiSiO2) every 5-10 cm in the sediment core from Lake Haukadalsvatn. Due to the high sedimentation rate at the lake the two proxies afford time series of extremely high resolution. The TOC and BiSiO2 record co-vary most of the time and are thought to reflect the biogenic productivity in the lake that is controlled by summer temperature. For the last 1400 years and at several colder times over the Holocene the proxies are in antiphase. We interpret this to reflect increasing flux of terrestrial carbon into the water during cold intervals. The terrestrial carbon is related to extended soil erosion due to landscape instability during cold times and the impact of the settlement.

By splitting the time series in two parts, 1400-8000 years BP and 0-1400 years BP, according to the change in the total organic carbon, several peaks can be identified by spectral analysis (Welch method and Hanning windowing in the sptool in MatLab was used). In the spectrum for the TOC record from 1400-8000 years BP there are identifications of ~1500, 80-90 and 40 years peaks. In the BiSiO2 record the only significant peak is a ~1100 year’s peak that corresponds well with the 1500 year peak in the TOC record, with difference related to resolution difference. Both the TOC record and the BiSiO2 record show strong 200 year variations for the last ~800 years according to wavelets analysis.