Comparison of Quaternary interglacial periods in the Iceland Sea

Five Quaternary interglacial periods are represented in core 57-7 from the Iceland Sea. Analysis of coccolith and planktonic foraminiferal assemblages from the interglacial periods (Oxygen Isotope Stages 1, 5, 7, 9 and 11) shows both similarities and differences in the assemblages. The differences indicate that the palaeoenvironment was not identical in the five interglacial periods. Oxygen Isotope Substage 5e reflects the warmest period, with the greatest inflow of warm Atlantic water. During this interval the Arctic Front apparently had a more westerly position than it has today. Substages 5a and 5c were periods when Arctic water masses dominated, as at the present day. In Oxygen Isotope Stages 7 and 9 inflow of Atlantic water was limited. Oxygen Isotope Stage 11 reflects a period of great productivity, but the region was still dominated by Arctic water masses. The position of the Arctic Front was possibly close to that of today, but not at the extreme western position it had in Oxygen Isotope Substage 5e.     

Sedimentology and stratigraphy in the cave Hamnsundhelleren,western Norway

The stratigraphy in Hamnsundhelleren is as follows. A basal weathered rock bed of unknown age is followed by laminated clay deposited under stadial conditions and correlated with palaeomagnetism to the Laschamp excursion (43–47 000 yr BP). Angular blocks, bones and clay above this are ¹⁴C dated to the Ålesund Interstadial (28–38 000 yr BP). Another stadial laminated clay following the Ålesund Interstadial includes a palaeomagnetic excursion correlated with Lake Mungo (28 000 yr BP). The newly discovered Hamnsund Interstadial above this consists of frost-weathered clay and scattered angular blocks. It is ¹⁴C dated to 24 500 yr BP on bones mixed into the Ålesund Interstadial. The Hamnsund Interstadial is succeeded by another stadial laminated clay and then a Late-glacial–Holocene mixture of bones and blocks. In Hamnsundhelleren and other similar caves four successive phases of sedimentary environments for each ice-free–ice-covered cycle have been identified: (i) ice-free phase (deposition of bones and frost-weathered blocks); (ii) subaerial ice-dammed lake phase (sand or silt deposited in a lateral glacial lake); (iii) subglacial ice-dammed lake phase (cave closed by ice, deposition of till, debris flows and laminated clay); (d) ice-plugged phase (cave is plugged by frozen lake water and/or glacial ice, no deposition).     

Stable isotopes in a stalagmite from NW Sweden document environmental changes over the past 4000 years

Sundqvist, H. S., Holmgren, K., Moberg, A., Spötl, C. & Mangini, A. 2009: Stable isotopes in a stalagmite from NW Sweden document environmental changes over the past 4000 years. Boreas, 10.1111/j.1502‐3885.2009.00099.x. ISSN 0300‐9483. This study of a 4000‐year‐old stalagmite from Korallgrottan in northwestern Sweden highlights the potentials and challenges when using stable isotopes in stalagmites as climate proxies, as well as the fact that the relationship between climate and proxy may change through time. Both the oxygen and the carbon isotopes display an overall trend of enrichment together with decreasing growth rates over the time period covered by the stalagmite, which is considered a generally cooling period according to current palaeoclimate understanding. The stable isotope records show enriched isotopic values during the, for Scandinavia, comparatively cold period AD 1300–1700 and depleted values during the warmer period AD 800–1000. The indication of a negative relationship between measured δ¹⁸O and surface temperature concurs with earlier reported stalagmite records from regions with a seasonal snow cover and is further supported by the fact that the stalagmite δ¹⁸O record shows general similarities with both regional and hemispheric temperature reconstructions available for the past 500 and 2000 years, respectively. Compared with a stable isotope record of lacustrine carbonates from northern Sweden, however, shifting correlations over time between the two records indicate that a local hydrological change may have taken place at Korallgrottan, or at the lake, compared with around 1000 years ago. The earlier part of the stalagmite δ¹⁸O might thus be influenced, to some extent, by another process than the later part, which means that a negative relationship between δ¹⁸O and surface temperature might not hold for the entire 4000‐year‐old record.     

New data from the Holsteinian interglacial site Öje, central Sweden

The stratigraphy at Öje, central Sweden, has been reinvestigated. Till-covered organic sediments were encountered in two out of three excavations, while in one excavation only till occurred. One sediment succession was analysed for pollen and macrofossils. The vegetation represented by both pollen and macrofossil flora indicates a correlation with (the latter) part of the Holsteinian Interglacial, also in accordance with the predominantly acidophilous diatom flora.     

How Sessile are Sea Anemones? A Review of Free-living Forms in the Actiniaria Cnidaria: Anthozoa

Abstract. There is scattered information in the literature that sea anemones are not always sedentary but instead may temporarily or permanently live loosely attached, detached or even pelagically. This is the first attempt to summarize and assess these observations and their probable ecological significance for the life cycles of the respective species. According to current knowledge there are no truly pelagic species of sea anemones; thus, the 'Minyadidae' sensu C arlgren , 1949 have to be abolished as a taxonomic group. Instead, there are indications that there are phases and stages within the life course of many anemone species which are liable to lead a free life in response to abiotic and biotic environmental factors. Juvenile, post-metamorphic stages seem to be of major significance in these respects and may be subjected to long distance dispersal. It is speculated that some of these free-living stages may represent morphologically and/or ecologically different stages between larvae and adults. The newly discovered lifestyle of 'straying predator' is described from sublittoral habitats off South Africa.     

Early Weichselian interstadial sediments at Härnösand, Sweden

The till-covered organic sediments at Härnösand have been resampled and reinvestigated with respect to their micro- and macrofossil content. The sediments were deposited in a shallow freshwater basin with a sandy substratum and probably under oligotrophic conditions. The regional vegetation consisted of a shrub or herb tundra, later changing into an open Betula forest with scattered Picea and Larix . In the lake, submerged plants such as Potamogeton filiformis and Isoëtes lacustris grew, together with Carex . On the shores the vegetation consisted of Betula nana , occasional Betula trees, Salix and Selaginella selaginoides . The beetle fauna suggests an average July temperature of 10–11°C. The flora indicates limited leaching and, thus, deposition during a relatively long and warm interstadial is suggested. The Härnösand sediments are subsequently correlated with the Brörup Interstadial.     

PALAEOCLIMATOLOGICAL SURVEY OF STALAGMITES FROM COASTAL AREAS IN TANZANIA

ABSTRACT. The aim of this study was to assess the potential of Tanzanian stalagmites as palaeoclimatic archives. Twelve stalagmites were collected in cave systems in the coastal areas. U-series dating, combined with published ¹⁴C-data, shows that one of the stalagmites was precipitated during the latter half of the latest glacial, between approximately 39 and 27 ka. Stable isotope analysis results indicate millennial-scale fluctuations in atmospheric CO₂ level during that time; and these fluctuations show a pattern very similar to that of the δ¹⁸O variations in the GRIP and Byrd ice-cores. The other stalagmites analysed turned out to be too porous and/or contained too much detritus to allow for reliable U-series dating. Due to low uranium content, the precision of the dating results is generally also poor. Samples from the five most compact and clean specimens yielded ages from c. 105 ka to c. 17 ka, though sometimes with an inverse age stratigraphy, indicating that the stalagmite precipitates were partly not compact enough to prevent post-depositional uranium leakage.