Rolf Zale

A late Holocene lake sediment sequence from Livingston Island, South Shetland Islands, with palaeoclimatic implications

Analysis of a 1.5 m thick sediment sequence from Midge Lake, Byers Peninsula, Livingston Island, shows that the lake and its catchment have undergone significant changes during the last 4000 years. Radiocarbon dating (AMS), sediment lithology, and microfossil analyses indicate that the lake was deglaciated over 4000 14 C years ago. Distinct peaks in accumulation rates of sediment, Pediastrum algae, pollen and spores, as well as changes in the diatom assemblage, suggest significant environmental changes between ca 3200 and 2700 y BP. These changes are interpreted as reflecting a milder and more humid, maritime climate. The increased humidity can explain independent observations of glacier growth during this period. The combined data also indicate that between ca 1500 and 500 y BP the area might have experienced more continental conditions with slightly colder and drier climate than today. Since the 14 C dates from the Midge Lake sediments are regarded as reliable and the sediment sequence is rich in tephra layers this sediment sequence will be critical for a forthcoming tephra chronology of the region.

Late Holocene tephrochronology of the northern Antarctic Peninsula

Abstract Andesitic and basaltic andesitic tephra layers are abundant in Holocene deposits from the Antarctic Peninsula. Visually discernible tephra horizons occur in three lakes on Livingston Island. Tephra in two other lakes and in a moss bank on Elephant Island, with very low ash concentrations, were detected magnetically. Deception Island is the most likely volcanic source for the tephra. With direct 14C dating, age/depth curves, and cross-correlations at least 14 tephra horizons dating to between ca. 4700 and 250 yr B.P. were identified and now form the basis for a preliminary regional tephrochronology that will be a valuable dating tool for investigating the Holocene climatic history of Antarctica.

Lake Sediment Cores from the Antarctic Peninsula and Surrounding Islands

ABSTRACTSediment cores from two lakes on the Antarctic Peninsula, Hidden Lake on James Ross Island and Lake Boeckella in Hope Bay, are described, analysed and dated with regard to climatic changes during the Holocene. It was found that lichenometry, using Rhizocarpon geograficum, can be used locally to separate moraines of different age. Minimum datings of the deglaciation were found to be 8680 B. P. in Hope Bay and 3900 B. P. in the Hidden Lake area. A cold period, culminating around 5000 B. P., can be dated in the sediment from Lake Boeckella. A slightly lower content of organic material in the lakes around 2100 B. P. might be caused by a slightly colder climate at that time. Evidence of a very distinct climatic deterioration around 800 B. P. can be found in the sediment from Hidden Lake. Weaker traces of a colder climate can be found in Lake Boeckella around 500 B. P.

Holocene development of the fauna of Lake Boeckella, northern Antarctic Peninsula

The origins of the freshwater fauna that inhabits Antarctic lakes are poorly known. The species present today could be relict species that have survived Quaternary glaciations on the continent, or Holocene migrants from more temperate regions. One approach to investigating these questions is to study faunal microfossils in lake sediment. This approach was applied to a 293 cm sediment core from Lake Boeckella, located at the northern tip of the Antarctic Peninsula. The microfossils indicated that most of the metazoan species that occur in the lake today have been present since soon after the lake’s formation c. 5.5 ka ago. In particular, the centropagid copepod Boeckella poppei (Mrázek) has been present throughout the lake’s history, suggesting a local source for this species. The development of biodiversity in the lake with time was in general more consistent with local (Antarctic) rather than distant (South American) sources, though an alternative explanation is that dispersal to Antarctica was more efficient in the mid-Holocene. Evidence of dispersal from extra-continental sites comes from the scattered occurrence throughout the core of Eubosmina chilensis (Daday), a South American species that does not reach the Antarctic or the sub-Antarctic islands at present, and which failed to establish a permanent population in the lake.

Deglaciation and shoreline displacement on Alexandra Land, Franz Josef Land

14C datings of driftwood from raised beaches on the island Alexandra Land, Franz Josef Land, Russia, indicate deglaciation by 6800 14C years BP. The age of a diamicton containing small shell fragments, found beneath a beach ridge formed c. 5000 BP, has been dated to 8265 ?90 t4C years BP (age after sea correction 7755 BP), suggesting that Alexandra Land was at least partly deglaciated by that time. The deposit containing shell fragments has been interpreted as a till which, if the interpretation is correct, indicates that a glacial advance occurred sometime between 7800 and 6800 BP. The highest shoreline, 23.5 m a.s.l., was formed either during a rapid deglaciation of the island or during a transgression. A shoreline displacement curve has been constructed for Alexandra Land. The rate of shore displacement since 6800 BP is calculated to 0.3 m/100 years. No pumice was found on Alexandra Land. Lunar Ice Cap on Alexandra Land was smaller than it is at present when the highest shoreline was formed, 6800 BP. The ice cap is believed to now be close to its Midto Late Holocene maximum, as almost all fluctuations of the Lunar Ice Cap since the deglaciation seem to have been within the present day glacier margin. A climatic deterioration c. 2000 BP is indicated by the formation of an ice/snow dammed lake. Evidence of former glacier movement directions, such as striae and chattermarks, were not found on Alexandra Land. However, the large scale bedrock topography and the orientation of elongated bedrock basins seem to indicate ice flow in a southeast to northwest direction.

Estimating species colonization dates using DNA in lake sediment

Detection of DNA in lake sediments holds promise as a tool to study processes like extinction, colonization, adaptation and evolutionary divergence. However, low concentrations make sediment DNA di ...