Abrupt and consistent responses of aquatic and terrestrial ecosystems to the 8200 cal. yr cold event: a lacustrine record from Lake Arapisto, Finland

Abstract

A 8400-7700 yr cal. BP section of the sediments of a small lake in southern Finland was studied by high-resolution pollen and cladoceran analyses to examine the response of terrestrial and aquatic ecosystems to the 8200 cal. yr BP cold event. Furthermore, a pollen-based T ann reconstruction and proportions of chydorid ephippia were used to determine changes in temperature and in the length of openwater season during the event. The pollen data, with abrupt decreases of the early-flowering Alnus, Corylus and Ulmus at c. 8350 cal. yr BP, may partly reflect vegetation dynamics but possibly also decreased pollen productivity and reproduction caused by cold winters and springs. The reconstructed T ann indicated a rapid temperature fall and a subsequent recovery. Proportions of chydorid ephippia suggested a considerable reduction in the length of open-water season at the beginning of the event, followed by periodically shorter open-water seasons. In the aquatic ecosystem only one species, the dominant planktonic cladoceran Bosmina longirostris, responded by decreasing dramatically and almost became extinct during the coldest period. However, we were unable to reconstruct the causative link between the inferred climate change and its decrease. The response of both aquatic and terrestrial proxies at c. 8350 cal. yr BP was consistent, indicating an abrupt start of the event and also an abrupt end at c. 8100 cal. yr BP.

Younger Dryas Cladocera assemblages from two valley mires in central Poland and their potential significance for climate reconstructions

“…These species were often found to be pioneer taxa, i.e., early immigrants following the retreat of the ice (Szeroczyńska, 1998a). Additionally, in a cold climate, a higher proportion of chydorid ephippia is expected in lake sediments, because when the open-water season is shorter, the relative duration of the asexual reproduction period is limited, compared to that of the sexual reproduction period (Sarmaja-Korjonen & Seppä, 2007).…”

“…Dominik Pawłowski of Cladocera ephippia, based on changes in reproduction and usually dependent on the length of the open-water season, is a very useful technique for reconstructing climate trends (Sarmaja-Korjonen, 2003;Sarmaja-Korjonen & Seppä, 2007;Nevalainen et al, 2011).…”

Evidence for higher-than-average air temperatures after the 8.2 ka event provided by a Central European δ18O record

“…changes in the relative contribution of Atlantic and Mediterranean air masses), could have influenced the d 18 O precip signal. In general, it must be considered that Atlantic air masses reaching the Alps are isotopically more depleted compared to those originating from the Mediterranean because of the longer transport pathway and the more depleted source water (Kaiser et al, 2002 O ostracods data is very similar (1.5e2.0 C) to that inferred from pollen-based MAAT reconstructions in the North Atlantic realm (Feurdean et al, 2008;Sarmaja-Korjonen and Sepp€ a, 2007;Veski et al, 2004 (von Grafenstein et al, 1999a).…”

“…Nevertheless, an important argument against a significant influence of local precipitation seasonality changes on the Mondsee d 18 O ostracods record is again the above-mentioned striking similarity of the amplitude of the calculated MAAT drop (~1.5e2.0 C) with independent, pollen-based MAAT reconstructions (Feurdean et al, 2008;Sarmaja-Korjonen and Sepp€ a, 2007;Veski et al, 2004). Interestingly, a period of higher-than-average MAATs directly after the 8.2 ka event that would be similar to our interpretation of the Mondsee d 18 O ostracods data has never been particularly emphasized elsewhere although numerous proxy records from the North Atlantic realm provide unequivocal evidence for the 8.2 ka BP cooling.…”

Subfossil chydorid (Cladocera, Chydoridae) ephippia as paleoenvironmental proxies: evidence from boreal and subarctic lakes in Finland

“…The converse holds, in a cold climate under which the relative length of parthenogenetic reproduction is limited because of a short open-water season, and therefore the relative share of ephippia in sediments is higher. For paleoclimatological purposes, ephippium analysis has been utilized in the reinvestigation of the late-glacial Bølling Sø site in Denmark (Bennike et al, 2004), a study of the 8.2 ka cold event of southern Finland (Sarmaja-Korjonen & Seppä, 2007), detecting the ''Little Ice Age'' (LIA) in southern Finland (Luoto et al, 2008, and characterizing Holocene climate trends (Nevalainen et al, in press). In these studies, the TCE value was evidently higher during the known cold climate phases when compared to ''normal'' or warm periods.…”