Late-Holocene climate variability and ecosystem responses in Alaska inferred from high-resolution multiproxy sediment analyses at Grizzly Lake. (15th October 2015)

• Record Type: Journal Article
• Authors: Tinner, Willy; Beer, Ruth; Bigler, Christian; Clegg, Benjamin F.; Jones, Richard T.; Kaltenrieder, Petra; van Raden, Ulrike J.; Gilli, Adrian; Hu, Feng Sheng
• Is Part Of: Quaternary science reviews. Volume 126(2015)
• Page Start: 41
• Page End: 56
• Publication Date: 2015-10-15
• Subjects: Paleoecology -- Vegetation -- Boreal -- Fire -- Erosion -- Climate change -- 2800 event -- 2.8 ka event; Geology, Stratigraphic -- Quaternary -- Periodicals; Stratigraphie -- Quaternaire -- Périodiques; 551.79
• DOI: 10.1016/j.quascirev.2015.08.019
• Languages: English
• ISSNs: 0277-3791

Abstract

Abstract: The late-Holocene shift from Picea glauca (white spruce) to Picea mariana (black spruce) forests marked the establishment of modern boreal forests in Alaska. To understand the patterns and drivers of this vegetational change and the associated late-Holocene environmental dynamics, we analyzed radiocarbon-dated sediments from Grizzly Lake for chironomids, diatoms, pollen, macrofossils, charcoal, element composition, particle size, and magnetic properties for the period 4100–1800 cal BP. Chironomid assemblages reveal two episodes of decreased July temperature, at ca. 3300–3150 (ca −1 °C) and 2900–2550 cal BP (ca −2 °C). These episodes coincided with climate change elsewhere in the Northern Hemisphere, atmospheric reorganization, and low solar activity. Diatom-inferred lake levels dropped by ca. 5 m at 3200 cal BP, suggesting dry conditions during the period 3200–1800 cal BP. P. glauca declined and P. mariana expanded at ca. 3200 cal BP; this vegetational change was linked to diatom-inferred low lake levels and thus decreased moisture availability. Forest cover declined at 3300–3100, 2800–2500 and 2300–2100 cal BP and soil erosion as inferred from increased values of Al, K, Si, Ti, and Ca intensified, when solar irradiance was low. Plant taxa adapted to disturbance and cold climate (e.g. Alnus viridis, shrub Betula, Epilobium ) expanded during these periods of reduced forest cover. This open vegetation type was associated with high fire activity that peaked at 2800 cal BP, when climatic conditions were particularly cold and dry. Forest recovery lagged behind subsequent climate warming (≤+3 °C) by ca. 75–225 years. Our multiproxy data set suggests that P. glauca was dominant under warm-moist climatic conditions, whereas P. mariana prevailed under cold-dry and warm-dry conditions. This pattern implies that climatic warming, as anticipated for this century, may promote P. glauca expansions, if moisture availability will be sufficiently high, while P. mariana may expand under dry conditions, possibly exacerbating climate impacts on the fire regime. Highlights: We analyze radiocarbon-dated sediments from Grizzly Lake, Alaska. High-resolution chironomid, diatom, pollen, macrofossil, charcoal, element composition, particle size, and magnetic analyses track environmental dynamics 4100–1800 cal BP. Forests declined, tundra expanded and soil erosion increased at 3200, 2800–2500 and 2250 cal BP., when temperatures and/or solar irradiance were low. Forests re-established in response to climate warming (<+3 °C at rates of 0.5–2°/century) within 75–225 years. The Late Holocene decline of Picea glauca and the expansion of Picea mariana were primarily caused by declining moisture availability.