Evidence for fire in the Pliocene Arctic in response to amplified temperature

Abstract

The mid-Pliocene is a valuable time interval for investigating equilibrium climate at current atmospheric CO 2 concentrations because atmospheric CO 2 concentrations are thought to have been comparable to the current day and yet the climate and distribution of ecosystems were quite different. One intriguing, but not fully understood, feature of the early to mid-Pliocene climate is the amplified Arctic temperature response and its impact on Arctic ecosystems. Only the most recent models appear to correctly estimate the degree of warming in the Pliocene Arctic and validation of the currently proposed feedbacks is limited by scarce terrestrial records of climate and environment. Here we reconstruct the summer temperature and fire regime from a subfossil fenpeat deposit on west-central Ellesmere Island, Canada, that has been chronologically constrained using cosmogenic nuclide burial dating to 3.9 + 1.5/ − 0.5 Ma.The estimate for average mean summer temperature is 15.4 ± 0.8 • C using specific bacterial membrane lipids, i.e., branched glycerol dialkyl glycerol tetraethers. This is above the proposed threshold that predicts a substantial increase in wildfire in the modern high latitudes. Macro-charcoal was present in all samples from this Pliocene section with notably higher charcoal concentration in the upper part of the sequence. This change in charcoal was synchronous with a change in vegetation that included an increase in abundance of fire-promoting Pinus and Picea. Paleo-vegetation reconstructions are consistent with warm summer temperatures, relatively low summer precipitation and an incidence of fire comparable to fire-adapted boreal forests of North America and central Siberia.To our knowledge, this site provides the northernmost evidence of fire during the Pliocene. It suggests that ecosystem productivity was greater than in the present day, providing fuel for wildfires, and that the climate was conducive to the ignition of fire during this period. The results reveal that interactions between paleo-vegetation and paleoclimate were mediated by fire in the High Arctic during the Pliocene, even though CO 2 concentrations were similar to modern values.Published by Copernicus Publications on behalf of the European Geosciences Union.

Evolution of woodcutting behaviour in Early Pliocene beaver driven by consumption of woody plants

“…Peat mosses can grow partially or fully submerged in water. Given that mid-Pliocene atmospheric CO 2 concentration levels were similar to modern (~ 400 ppm) 15,65,66 , moss exposed to the atmosphere would preferentially have used the abundant 12 CO 2 , resulting in low δ 13 C. Alternatively, low δ 13 C in peat mosses can also indicate an underwater growing environment rich in 13 C-depleted respired CO 2 from surrounding plants 62 .…”

“…The thickest peat deposit within this sequence, which yielded material for this study, sits 380 m above present day sea-level overlooking Strathcona Fiord. Most recent terrestrial cosmogenic nuclide burial dating of sands above this peat layer have yielded a date of 3.9 + 1.5/− 0.5 Ma 15 , placing the minimum age of peat formation during the late Early Pliocene (late Zanclean). This peat unit is characterized by an abundance of beaver-cut sticks 10,11 and has yielded a wide array of beautifully preserved plant macrofossils, invertebrates, and vertebrate fossil remains (Fig.…”

“…Late Early Pliocene mean global temperature was 2-3 °C above modern 28 and high latitude regions experienced amplified warming. Pliocene Arctic mean annual temperature was near freezing, which is ~ 15-22 °C warmer than present day, and tree line was ~ 2000 km further north 15,24,[29][30][31][32][33] . Summer temperatures at the Beaver Pond site reached 20 °C, while winter temperatures were more moderate than present day, with a low of ~ -12 °C 24 .…”

Contributions of aerosol‐cloud interactions to mid‐Piacenzian seasonally sea ice‐free Arctic Ocean

“…The dominancy of either effect can lead to a net warming (Shi & Liu, ) or cooling effect (Sagoo & Storelvmo, ) in response to increasing dust emission. With warm, moist, and forested Northern high latitudes, the emission and formation of greenhouse gases of methane, tropospheric ozone, and nitrous oxide are expected to increase (Unger & Yue, ), yet the enhanced biogenic emissions of aerosol precursors and emergence of frequent boreal forest fire (Fletcher et al, ) may create a constant flux of aerosols into the troposphere and hence promote cloud formation, and reflection of sunlight (Tunved et al, ). The net effect of these biogeochemical feedbacks is unknown and remains one of the most uncertain aspects of simulating past and future climate change at high latitudes.…”

The Environment at Lake El’gygytgyn Area (Northeastern Russian Arctic) Prior to and After the Meteorite Impact at 3.58 Ma

“…Early Pliocene pollen and macrofossil records from central and northern Yukon and Alaska exhibit that mixed boreal forests with pine, fir, larch, spruce, birch, alder, larch, and Douglas fir dominated the local vegetation there (e.g., Schweger et al, 2011 and references therein). In the Canadian Arctic (Ellesmere Island), an early Pliocene record from Strathcona Fjord shows that forest with larch, spruce, pine, birch and alder dominated nowadays treeless area (Fletcher et al, 2019).…”