Impact of Lateglacial cold events on the northern Aegean region reconstructed from marine and terrestrial proxy data

Abstract

Marine palynomorph data paired with other indicators of sea-surface hydrography (planktic foraminiferal assemblages and oxygen isotopes) were used to decipher the impact of cold events on the northern Aegean region during the last glacial to interglacial transition. The data, which were derived from marine sediment cores GeoTü SL152 and GeoTü SL148, point to a strong impact of the Heinrich 1 and Younger Dryas cold events on surface-water conditions in the northern Aegean Sea. Shifts in marine palynomorph assemblages correlate with changes in terrestrial vegetation and climate (i.e. precipitation and temperature reconstructions based on pollen assemblages) in the northern borderlands of the Aegean Sea. The climate responses of the Aegean region to Heinrich event 1 (H1, ca. 17.5 to ca. 15.7 cal ka BP) and Younger Dryas (ca. 12.6 to ca. 11.7 cal ka BP) events appear similar in magnitude (with mean annual temperatures between $6 and 108C and mean annual precipitation between $300 and $450 mm). However, the annual temperature decline during the H1 relative to the preceding already cold conditions was minor (<38C). The transition from the relatively warm and humid local equivalent of the Allerød interstadial to the Younger Dryas, on the other hand, witnessed an annual temperature decline of 68C and an annual precipitation decrease of 300 mm, the latter occurring abruptly within only ca. 150 a. The return to warmer conditions in the northern Aegean region after the Younger Dryas was completed at ca. 11.6 cal ka BP.

Contrasting patterns of climatic changes during the Holocene across the Italian Peninsula reconstructed from pollen data

“…Lake Ledro shows the opposite pattern, with cold temperatures before 6400-7000 cal yr BP, followed by an abrupt change towards warm summer conditions from 6400 cal yr BP to the present. This pattern of climate partitioning between the north and the south is similar to partitioning in the eastern Mediterranean, particularly in the northern and southern Aegean Sea Kotthoff et al, 2008Kotthoff et al, , 2011. The climate pattern observed in northern Italy from Lake Ledro (warm early to mid-Holocene followed by a summer cooling southern Aegean Sea based on three cores from the region.…”

“…8000, 6500 and 4200 cal yr BP and they correspond to strong shifts in the humidity index reconstructed from the Aegean cores. The earliest event seems to correspond with the regional expression of the 8.2 kyr event (Alley et al, 1997) in the Mediterranean region (Magny et al, 2003Kotthoff et al, 2008Kotthoff et al, , 2011Pross et al, 2009;Triantaphyllou et al, 2009b). This event is commonly explained through atmospheric circulation changes induced by freshwater pulses that produced a weakening of the thermohaline circulation in the North Atlantic.…”

Complexity of diatom response to Lateglacial and Holocene climate and environmental change in ancient, deep and oligotrophic Lake Ohrid (Macedonia and Albania)

“…If subject to winter lake ice cover, this lake would have been dimictic or monomictic rather than currently oligomictic. Low water temperature during the Younger Dryas in this lake is consistent with pollen-based air temperature reconstruction in Lake Maliq (Albania; Bordon et al, 2009), and SL152 (northern Aegean Sea; Kotthoff et al, 2011), with alkenoneand foram-inferred low sea surface temperature (SST) in MNB3 (northern Aegean Sea; Gogou et al, 2007;Geraga et al, 2010), and with the globally stacked proxy surface temperature record (Shakun et al, 2012). Intense wind action may have occurred during this cold period , in accordance with the observation that average wind speed in winter is higher than in summer today (Stanković, 1960).…”

A Late Glacial to Holocene record of environmental change from Lake Dojran (Macedonia, Greece)

“…Emeis et al, 2000). However, a separation in two phases such as indicated by Co1260 is not evident in other terrestrial records from Greece or in marine pollen records from the Aegean Sea and the Sea of Marmara (Rossignol-Strick, 1993;Digerfeldt et al, 2000;Lawson et al, 2004Lawson et al, , 2005Kotthoff et al, 2008aKotthoff et al, , 2011Valsecchi et al, 2012). At least the particular dry phase described from the northern Aegean region around 11 800 cal yr BP (Kotthoff et al, 2008a corresponds with the low OM content and low TOC/TN ratios in Co1260 between 11 800 and 11 600 cal yr BP.…”

“…Yin and Lan, 1995;Wang et al, 2002). This could have limited the productivity in the lake center although temperatures increased rapidly in the Mediterranean region during the early Holocene (Allen et al, 1999;Bordon et al, 2009;Kotthoff et al, 2011). Despite more humid conditions as…”