标题：Do Diatom, Chironomid, and Pollen Records Consistently Infer Holocene July Air Temperature? A Comparison Using Sediment Cores from Four Alpine Lakes in Northern Sweden
其他标题：Do Diatom, Chironomid, and Pollen Records Consistently Infer Holocene July Air Temperature? A Comparison Using Sediment Cores from Four Alpine Lakes in Northern Sweden
摘要：The aim of this study is to assess the performance of diatom, chironomid, and pollen transfer functions for inferences of July air temperature during the Holocene using sediments from four alpine lakes in an area with low human impact in northern Sweden. The study demonstrates that diatom, chironomid, and pollen assemblages in the sediment cores contain climate information so that present-day temperature at each lake can be inferred with reasonable confidence for most proxies. Most proxy records from the sites consistently infer a long-term decreasing trend in July air temperature from ca. 6000 cal yr BP until the present. However, there are also large variations in the temporal patterns of the inferred temperatures during some periods, especially before 7000 cal yr BP, when there are also nonsynchronous changes in loss-on-ignition in the four lakes. This variability indicates that local conditions in the catchments (influence of snowfields, soil-forming processes) had a large impact on the organism assemblages in the early Holocene. Long-distance transport of pollen into high alpine lakes makes temperature inferences from pollen transfer functions unreliable. Due to the uncertainties of the methods, predictive errors of the transfer functions, and variability caused by local catchment/lake characteristics, only long-term trends in climate can be inferred. High-resolution studies using diatoms, chironomids, and pollen for climate reconstruction are probably not meaningful during periods with small changes in climate (<1°C). Future research should concentrate on low-resolution, multiproxy, and multilake studies to further understand the relationship between the proxies and climate.
