K Adamson

Paradoxical cold conditions during the medieval climate anomaly in the Western Arctic

In the Northern Hemisphere, most mountain glaciers experienced their largest extent in the last millennium during the Little Ice Age (1450 to 1850 CE, LIA), a period marked by colder hemispheric temperatures than the Medieval Climate Anomaly (950 to 1250 CE, MCA), a period which coincided with glacier retreat. Here, we present a new moraine chronology based on 36Cl surface exposure dating from Lyngmarksbræen glacier, West Greenland. Consistent with other glaciers in the western Arctic, Lyngmarksbræen glacier experienced several advances during the last millennium, the first one at the end of the MCA, in ~1200 CE, was of similar amplitude to two other advances during the LIA. In the absence of any significant changes in accumulation records from South Greenland ice cores, we attribute this expansion to multi-decadal summer cooling likely driven by volcanic and/or solar forcing, and associated regional sea-ice feedbacks. Such regional multi-decadal cold conditions at the end of the MCA are neither resolved in temperature reconstructions from other parts of the Northern Hemisphere, nor captured in last millennium climate simulations.

Middle Pleistocene glaciation, alluvial fan development and sea-level changes in the Bay of Kotor, Montenegro

Abstract A coarse-grained alluvial fan at Lipci in the Bay of Kotor, western Montenegro, was deposited in the Middle Pleistocene by a high-energy, steep gradient proglacial stream draining an outlet glacier on the Orjen massif. The fan apex is currently about 50 m above sea-level, but the majority (c. 60%) of this landform now lies offshore. Field mapping, sedimentological analysis and uranium-series dating were combined with a marine bathymetric survey and seismic profiling to explore the morphology and history of the entire fan complex. The Lipci fan was deposited on the margin of a large polje downstream of moraines that formed during the Middle Pleistocene (Marine Isotope Stage 12). The sea-level may have been more than 120 m lower than present during the glacial stages of the Middle Pleistocene. The sediments on the terrestrial portion of the fan are strongly cemented by secondary calcite and the oldest uranium-series ages show that the fan was deposited before 320 ka. These ages are consistent with a larger uranium-series dataset (n=39) from other glacial and glacio-fluvial formations surrounding Mount Orjen. Seismic profiling of the submerged portion of the fan in the Bay of Kotor shows well-preserved palaeochannels with inset terraces. The Lipci fan is unusual because even its distal segments are well preserved after exposure to multiple post-Marine Isotope Stage 12 regression–transgression cycles. This is probably due to the strong cementation of the fan sediments and its sheltered location in the Bay of Kotor.

Glacial crushing of limestone and the production of carbonate-rich silts in a Pleistocene glaciofluvial system: a potential source of loess in Southern Europe

Abstract This paper explores the modification of limestone bedrock and fine‐grained sediment within the Pleistocene glacial and proglacial environments of the rjen massif in western Montenegro. We have characterised the fine‐grained components of till and outwash using lithological and particle size data. Two main types of fine‐grained outwash sediment have been recognised and each is associated with a distinctive meltwater route. Fine‐grained sediments deposited downstream of bedrock gorges (type 1 meltwater route) typically display a bimodal particle size distribution, where the carbonate silt fraction (10–60 μm) has been depleted and non‐carbonate silts become dominant. This probably reflects both physical sorting and corrosion of the fine‐grained limestone sediment within the proglacial fluvial environment. The 10–60 μm component matches the particle size characteristics of typical loess. Fine‐grained outwash deposits from directly in front of the former ice margin (type 2 meltwater route) show unimodal particle size distributions which more closely resemble the grain size characteristics of the glacial till, but they also show evidence of silt depletion. We argue that the fine‐grained sediment exported from glaciated limestone catchments during the cold stages of the Pleistocene formed an important source of the carbonate‐rich loess in this region.