Lake sediments from Store Koldewey, Northeast Greenland, as archive of Late Pleistocene and Holocene climatic and environmental changes

A 2.9 m long sedimentary record was studied from a small lake, here referred to as Duck Lake, located at 76°25'N, 18°45'W on Store Koldewey, an elongated island off the coast of Northeast Greenland. The sediments were investigated for their geophysical and biogeochemical characteristics, and for their fossil chironomid assemblages. Organic matter began to accumulate in the lake at 9.1 cal. kyr BP, which provides a minimum age for the deglaciation of the basin. Although the early to mid-Holocene is known as a thermal maximum in East Greenland, organic matter accumulation in the lake remained low during the early Holocene, likely due to late plant immigration and lack of nutrient availability. Organic matter accumulation increased during the middle and late Holocene, when temperatures in East Greenland gradually decreased. Enhanced soil formation probably led to higher nutrient availability and increased production in the lake. Chironomids are abundant throughout the record after 9.1 cal. kyr BP and seem to react sensitively to changes in temperature and nutrient availability. It is concluded that relative temperature reconstructions based on biogeochemical data have to be regarded critically, particularly in the period shortly after deglaciation when nutrient availability was low. Chironomids may be a suitable tool for climatic reconstructions even in those high arctic environments. However, a better understanding of the ecology of chironomids under these extreme conditions is needed.     

Early Holocene history of the southwestern Baltic Sea: the Ancylus Lake stage

One of the most discussed stages in the history of the Baltic Sea is the Ancylus Lake phase. This paper presents detailed information from the Darss Sill threshold area as well as the adjacent basins, i.e. the Mecklenburg Bay and Arkona Basin located in the southwesternmost Baltic. The threshold area was transgressed at the Baltic Ice Lake maximum phase and during the following regression about 10.3 ka BP a river valley was incised in the Darss Sill to a level of 23-24 m below present sea level (b.s.l.). Preboreal sediments in the study area show lowstand basin deposition in the Arkona Basin and the existence of a local lake in Mecklenburg Bay. The lowstand system is followed by the Ancylus Lake transgression that reached a maximum level of 19 m b.s.l. Thus, at the maximum level the water depth was about 5 m over the threshold, and the shore level fall during the Ancylus Lake regression must be in the same range. The Darss Sill area is the key area for drainage of the Ancylus Lake, and if the previously suggested regression of 8-10 m in southeastern Sweden is to be achieved, isostatic rebound must also play a role. The existence of the so-called Dana River in the Darss Sill area cannot be supported by our investigations. We observed no signs of progressive erosion of the Darss Sill area in the Early Holocene, and there are no prograding systems in Mecklenburg Bay that can be related to the Ancylus Lake regression. On the contrary, local lakes developed in Mecklenburg Bay and in the Darss Sill threshold area. In the Darss Sill area, marl was deposited in a lake in the valley that developed after the final drainage of the Baltic Ice Lake. Studies of diatoms and macrofossils, combined with seismic interpretation and radiocarbon dating, provide detailed information about the chronology and the relative shore level of these lake phases as well as about environmental conditions in the lakes.     

Altimeter Signal-to-Noise for Deep Ocean Processes in Operational Systems

The ocean signal for this study is the sea surface height due to the slowly varying (greater than 5-day) ocean processes, which are predominantly the deep ocean mesoscale. These processes are the focus of present assimilation systems for monitoring and predicting ocean circulation due to ocean fronts and eddies and the associated environmental changes that impact real time activities in areas with depths greater than about 200 m. By this definition, signal-to-noise may be estimated directly from altimeter data sets through a crossover point analysis. The RMS variability in crossover differences is due to instrument noise, errors in environmental corrections to the satellite observation, and short time period oceanic variations. The signal-to-noise ratio indicates that shallow areas are typically not well observed due to the high frequency fluctuations. Many deep ocean areas also contain significant high frequency variability such as the subpolar latitudes, which have large atmospheric pressure systems moving through, and these in turn generate large errors in the inverse barometer correction. Understanding the spatial variations of signal to noise is a necessary prerequisite for correct assimilation of the data into operational systems.     

Early Holocene drowned lagoonal deposits from the Kattegat, southern Scandinavia

Shallow seismic profiling indicated the presence of a drowned lagoon-barrier system formed during the transgression of the southern Kattegat, and investigations of core material have confirmed this. Studies of plant and animal macrofossils show that the lagoonal sediments contain a mixture of marine, brackish, lacustrine, telmatic and terrestrial taxa, and analyses of foraminifers indicate brackish-water conditions. Low oxygen isotope values obtained on shells of marine molluscs also point to lowered salinity. The lagoonal sediments are situated at depths between 24 and 35 m below present sea level. They are dated to between c. 10.5 cal. ka BP and c. 9.5 cal. ka BP, and reflect a period characterized by a moderate relative sea level rise. The lagoonal sediments are underlain by lateglacial glaciomarine clay and silt, which are separated from the Holocene deposits by an unconformity. The earliest Holocene sediments consist of littoral sand with gravel, stones and shells; these sediments were formed during the transgression of the area before the barrier island-lagoon system was developed. The lagoonal sediments are overlain by mud, which contains animal remains that indicate increasing water depths.     

Pilgrimstad revisited – a multi‐proxy reconstruction of Early/Middle Weichselian climate and environment at a key site in central Sweden

Wohlfarth, B., Alexanderson, H., Ampel, L., Bennike, O., Engels, S., Johnsen, T., Lundqvist, J. & Reimer, P. 2010: Pilgrimstad revisited – a multi‐proxy reconstruction of Early/Middle Weichselian climate and environment at a key site in central Sweden. Boreas, 10.1111/j.1502‐3885.2010.00192.x. ISSN 0300‐9483. The site Pilgrimstad in central Sweden has often been cited as a key locality for discussions of ice‐free/ice‐covered intervals during the Early and Middle Weichselian. Multi‐proxy investigations of a recently excavated section at Pilgrimstad now provide a revised picture of the climatic and environmental development between ～80 and 36 ka ago. The combination of sedimentology, geochemistry, OSL and ¹⁴C dating, and macrofossil, siliceous microfossil and chironomid analyses shows: (i) a lower succession of glaciofluvial/fluvial, lacustrine and glaciolacustrine sediments; (ii) an upper lacustrine sediment sequence; and (iii) Last Glacial Maximum till cover. Microfossils in the upper lacustrine sediments are initially characteristic for oligo‐ to mesotrophic lakes, and macrofossils indicate arctic/sub‐arctic environments and mean July temperatures >8 °C. These conditions were, however, followed by a return to a low‐nutrient lake and a cold and dry climate. The sequence contains several hiatuses, as shown by the often sharp contacts between individual units, which suggests that ice‐free intervals alternated with possible ice advances during certain parts of the Early and Middle Weichselian.     

Occurrence and distribution of king eiders Somateria spectabilis and common eiders S. mollissima at Disko, West Greenland

King eiders and common eiders were recorded at Disko Island, West Greenland, in the period 1989-1993. Both species occur year-round in the area, although in low numbers during the period of extensive ice-cover January-April. In May and the first half of June, large numbers of king and common eiders on spring migration stage along the western coast of Disko. In the autumn (August-October) an estimated 15,400-20.100 king eiders undergo prcbasic moult in the area, with the highest concentrations in the fjords and bays of western Disko and along the coast of southeast Disko. This estimate indicates that a recent population decline may have taken place. Only two female common eiders with ducklings were recorded during the study period. In the period July-September an estimated 3,200–4,800 male common eiders undergo prcbasic moult in the area, mainly at the archipelago of Kitsissut and in the outer fjords and bays of western Disko Island.     

Quaternary marine stratigraphy and geochronology in central West Greenland

A new stratigraphic framework is proposed for the Quaternary of a portion of central West Greenland, based primarily on faunal and geochronologic studies of shallow shelf deposits. Twenty-four occurrences of pre-Holocene deposits were already known in West Greenland and data from 18 new sites are presented, together with new information on some of the previously described localities. Four pre-Holocene marine events are described. The interglacial Ivnaarssuit and Nordre Laksebugt marine events are considered to be Middle Pleistocene in age. The interstadial Laksebugt marine event is considered to be late Middle Pleistocene, whereas the Svartenhuk marine event is correlated with the last interglacial. For the last glacial period an extensive ice shelf is proposed west of Disko. The oldest postglacial deposits are dated at 10,470 ± 130 ¹⁴C-years BP.     

Revision of the early Holocene lake sediment based chronology and event stratigraphy on Hochstetter Forland, NE Greenland

The previously established and often debated lake sediment based chronology and event stratigraphy from Hochstetter Forland, NE Greenland, has been re-examined. These new studies show that the last deglaciation of the coastal area is several thousand years younger than previously described. The main reason behind the difference is the fact that the older chronology was based on ¹⁴C datings of bulk sediment samples, which are now shown to contain enough coal fragments to produce erroneous ages. The re-examination was performed on sediments from two lakes located within the Nanok moraine system: one is situated at or slightly above the marine limit around 65 m. the other at 21–22 m a.s.l. The combined stratigraphy from the two lakes shows that the area was deglaciated before 9000 BP, after which followed deposition of glaciomarine sediments, fining upwards. The first vegetation seems to have been dominated by grasses, Lycopodium and Polypodiaceae. At c . 8000 BP the limnic production increased significantly and a pioneer vegetation characterized the area. At this time the 'Artemisia' grains appear. A short but distinct climatic cooling occurs at c . 7500 BP causing a significant drop in lake productivity and possibly also producing coarser sediments in the (glacio)marine environment. About 200 years later the lake productivity again increased, very rapidly, and the marine sediments became finer and more rich in molluscs, as a response to the beginning of the climatic optimum. Because of the time-lag between climate and vegetation response it took another 300 years before Betulci nana immigrated, at the same time as the 'Artemisia' grains disappeared, and another several hundred years before a real dwarf-shrub vegetation developed in these parts of Hochstetter Forland. Before the lower lake was isolated from the sea at c . 6000 BP, coarse wave-washed sediments, followed by a typical isolation sequence, were deposited in it.