Ice records provide new insights into climatic vulnerability of Central Asian forest and steppe communities

Abstract

Forest and steppe communities in the Altai region of Central Asia are threatened by changing climate and anthropogenic pressure. Specifically, increasing drought and grazing pressure may cause collapses of moisture-demanding plant communities, particularly forests. Knowledge about past vegetation and fire responses to climate and land use changes may help anticipating future ecosystem risks, given that it has the potential to disclose mechanisms and processes that govern ecosystem vulnerability. We present a unique paleoecological record from the highalpine Tsambagarav glacier in the Mongolian Altai that provides novel large-scale information on vegetation, fire and pollution with an exceptional temporal resolution. Our palynological record identifies several late-Holocene boreal forest expansions, contractions and subsequent recoveries. Maximum forest expansions occurred at 3000-2800 BC, 2400-2100 BC, and 1900-1800 BC. After 1800 BC mixed boreal forest communities irrecoverably declined. Fires reached a maximum at 1600 BC, 200 years after the final forest collapse. Our multiproxy data suggest that burning peaked in response to dead biomass accumulation resulting from forest diebacks. Vegetation and fire regimes partly decoupled from climate after 1700 AD, when atmospheric industrial pollution began, and land use intensified. We conclude that moisture availability was more important than temperature for past vegetation dynamics, in particular for forest loss and steppe expansion. The past Mongolian Altai evidence implies that in the future forests of the Russian Altai may collapse in response to reduced moisture availability.

Variation of Ice Nucleating Particles in the European Arctic Over the Last Centuries

“…Ice deposited more than 12,000 years ago under cool, wet climate conditions on Sajama, Bolivia, contained more recoverable bacteria than modern ice, deposited at the same location during a warmer, dryer period (Christner et al, 2000). Even 5,000-year-old pollen grains are well preserved in ice and do not show any indication of deterioration, when visually inspected under the microscope (Brugger et al, 2018). Polen et al (2016) postulate a shift of the freezing curves toward lower temperatures with increasing storage time and successive freeze/thaw cycles.…”

“…Approximately 85% of photochemical reactions occur in the top 10 cm of the snowpack (King & Simpson, 2001). Even 5,000-year-old pollen grains are well preserved in ice and do not show any indication of deterioration, when visually inspected under the microscope (Brugger et al, 2018). It is unclear if this is sufficient to change IN activity.…”

Pollen‐recorded bioclimatic variations of the last ~2000 years retrieved from Bayan Nuur in the western Mongolian Plateau

“…; Brugger et al . ). However, discrepancies amongst different data sets on the issues of heat–water combinations during the past two millennia still exist and two groups of scholars have dominated the debate.…”

“…Several recent investigations have focused on the climate changes during the past two millennia primarily based on tree-ring and ice-core data (e.g. D' Arrigo et al 2001;Myglan et al 2012;Pederson et al 2014;B€ untgen et al 2016;Brugger et al 2018). However, discrepancies amongst different data sets on the issues of heat-water combinations during the past two millennia still exist and two groups of scholars have dominated the debate.…”

Annual layer counting using pollen grains of the Grigoriev ice core from the Tien Shan Mountains, central Asia

“…There is abundant tree pollen in the Belukha ice core area because of the vast Siberian boreal forests expanding north of Belukha Glacier. The Tsambagarav ice core in the same Altai Mountains, however, showed less tree pollen and dominance of the Artemisia type (Brugger et al 2018a). Because the Tsambagarav Glacier is in the Mongolian Altai, southeast of the Belukha Glacier and distant from the boreal forest, the pollen assemblage is dominated by herb pollen rather than tree pollen.…”