Findes Bølling i Bølling Sø? - nye undersøgelser af en klassisk lokalitet

Danmark har været et foregangsland indenfor kvartærgeologi. Den første oversigt – globalt set – over skovens udvikling efter sidste istid blev således publiceret af naturforskeren Japetus Stenstrup allerede i 1842. Den første påvisning af en varmeperiode under overgangen fra sidste istid til den nuværende mellemistid, i senglacialtiden, skyldes Hartz og Milters, efter arbejde i lergrave syd for Allerød i Nordsjælland for godt 100 år siden

The palaeoenvironment of the 'Antrea Net Find'

The 'Antrea Net Find', found in 1914 in Korpilahti in the Karelian Isthmus , is one of the most important archaeological discoveries in Finland. For a long time, it was the oldest dated net find in Europe. New sediment samples were taken from the assumed find spot in 1998. The original net material and the new sediment sequence around the find spot were re-investigated using modern physical and palaeoecological techniques, They included AMS radiocarbon dates from the net material and the sediment above the find, as well as lithostratigraphical and isotope analyses from the surrounding sediment sequence. Also the material of the net cord was investigated. The palaeoenvironment of the Korpilahti area around the time of the event was reconstructed using modern biostratigraphical diatom and pollen methods. The 'Antrea Net Find' was recovered from the uppermost part of silty clay gyttja. The AMS radiocarbon date of the net yielded an age of 9 140±135 BP. The net cord has been made of willow bast. The dates from the silty gyttja sediment above the find level yielded the ages 9095±90 and 8965±85 BP. Stable isotope data indicate a rapid change in the sediment c. 9000 BP (8250 calBC). The radiocarbon dates with the diatom stratigraphy typical for the Ancylus Lake stage from Korpilahti suggest that the artefacts sank at the time of the maximum of the Ancylus transgression between 9200 and 9100 BP (8400 and 8300 calBC). At this time, the environment was characterized by forests dominated by pine, which had been present for hundreds of years, and thus the bark of old trees was readily available for the bark floats

Effect of Temperature on the Size of Sedimentary Remains of Littoral Chydorids

The body size of aquatic invertebrates is, to a great extent, dependent on ambient temperature, but size distributions are also determined by other factors like food supply and predation. The effect of temperature on organisms is formulated in the temperature–size hypothesis, which predicts a smaller body size with increasing temperature. In this study, the effect of temperature on the subfossil remains of three littoral Cladocera (Alona affnis, A. quadrangularis, and Chydorus cf. sphaericus) was investigated. Exoskeletal remains of these species can be found in large numbers in lacustrine sediments and over a wide north–south range in Europe. The total length of both headshield and postabdomen for A. affinis and A. quadrangularis and carapace length for C. cf. sphaericus were measured to observe their response to changes in latitude and temperature. A different response to ambient temperature in the growth of body parts was observed. The size of the headshields of both Alona species and of the carapace of Chydorus was significantly larger in colder regions as opposed to warm ones. It turned out that the postabdomen was not a good predictor of ambient temperature. While the sizes of all remains increased with latitude, the sizes of the Alona remains was smaller in the mountain lakes of the Southern Carpathians than in other cold lakes, in this case in Finland, a fact indicative of the importance of other factors on size distribution. This study demonstrates that a morphological response to climate is present in littoral cladocerans, and, therefore, changes in the length of headshield and carapace may be used as a proxy for climate changes in paleolimnological records

Sexual reproduction of chydorids (Anomopoda, Chydoridae) as indicator of climate in recent sediments of Lake Aitajärvi, northern Finnish Lapland

The pres ent work is a part of the de vel op ment of a method which uses the rela tive pro por tions of asexu ally and sexually re pro duc ing chy do rid fe males to re con struct the length of the open- water sea son. Sur face sedi ments (5 cm) of Lake Ai tajärvi, north ern Fin nish Lap land, were ex am ined for mod ern and re cent pro por tions of chy do rid cla do ceran ephip pia in sub arc tic cli mate near the pine limit. The to tal chy do rid ephip pium pro por tions (TCE) were stead ily 9.5–9.7% in the Ai tajärvi sedi ment but de clined to 8.4% in the up per most sam ple. The re sult was com pared with the sur face sedi ment TCE from four lakes in south ern Fin land where it var ied be tween 3–6%. It was also com pared with the TCE from two lakes in north ern most Fin nish Lap land above the treeline in very se vere cli mate, where it was 26–30%. These very high val ues sug gest that there might be a thresh old in cli mate con di tions be tween Ai tajärvi and the two north ern most lakes that al ters the re pro duc tion of chy do rids to wards an even more im por tant role of sex ual repro duc tion

Subfossil shell margins and tail spines of Daphnia in Finnish lake sediments - is Daphnia underrepresented in cladocera analysis?

One of the short com ings of the analy sis of sub fos sil Cla do cera (wa ter flee) re mains is that pres er va tion of re mains is se lec tive. Of Daph nia spp. which are very com mon in zoo plank ton as sem blages of lakes, usu ally only postab domi nal claws and ephip pia are found. In the pres ent pa per I de scribe Daph nia shell mar gins and some tail spines from the Holo cene sedi ments of a lake in south ern Fin land where the mar gins were much more abun dant than the postab dominal claws, in di cat ing that postab domi nal claws may be un der rep re sented. Daph nia claws, shell mar gins and tail spines were found also in sur face sam ples of 17 Fin nish lakes and thus the abun dance of tail spines could be com pared with that of postab domi nal claws. The re sults showed that in most cases the tail spines are more abun dant than postab domi - nal claws and may give a closer es ti mate of the true abun dance of Daph nia. How ever, in some lakes claws were clearly more fre quent than tail spines. Ap par ently, there are dif fer ences in pres er va tion of dif fer ent types of Daph nia re mains be tween lakes, pos si bly con nected with wa ter chem is try. Over all, the re sults in di cate that proba bly Daph nia re mains are al ways un der rep re sented in lake sedi ments

Findings of Alona protzi Hartwig 1900 (Branchiopoda: Anomopoda. Chydoridae) in Finland

Alona protzi is a rare spe cies of Cla do cera, oc cur ring in lake lit to ral through out Europe. How ever, lit tle is known about this ani mal, and so far it has not been in cluded in pro vi sional lists of spe cies found in Fin land. In this short re port we pres ent our find ings of Alona protzi, both re cent and sub fos sil ma te rial, as well as one pre vi ous, un pub lished finding site of the spe cies in Fin land. We found three sub fos sil shells of this spe cies in the bot tom sedi ments of two lakes. In a third lake we found in tact ani mals, an ephip pial fe male and a male, while sam pling stony bot tom of lake lit to ral

First records of Alona werestschagini sinev in Finland - subfossil remains from subarctic lakes

Sub fos sil re mains of a new spe cies of Cla do cera (wa ter fleas) of the fam ily Chy do ri dae in Fin land, Alona wer estschagini Si nev, were found in the sedi ments of four lakes above the treeline in north ern most Fin nish Lap land. The remains were found in sur face sedi ments of three lakes and in early Holo cene sedi ments of one lake where the spe cies was a pio neer which soon dis ap peared. The re mains of A. wer est schagini, ex cept the male postab do men, closely re sem ble Alona gut tata. In Eura sia A. wer est schagini has a wide but patchy dis tri bu tion in cold cli mates, sug gest ing that it is a post gla cial rel ict adapted to cold cli mate and oligo trophic lakes. Re cently it has been found also in Nor way and Kola Pen in sula. The early Holo cene finds in di cate that the spe cies spread to north ern most Fin land af ter the re treat of the Scan di na vian Ice Sheet. Since the spe cies has been found in lakes in very se vere con di tions it may be used as a palaeo lim no logi cal in di ca tor in sedi ment stud ies