Meteorological validation of chironomids as a paleotemperature proxy using varved lake sediments

Abstract

In order to improve the reliability of climate models in their projections for the future, spatially and temporally detailed paleoclimate proxy data are needed. In this study, we examined annually laminated sediments from Lake Nurmijärvi (Finland) for their fossil Chironomidae assemblages over a time period with available meteorological observational data (since 1830s). In doing so, we correlated chironomid-based inferences of summer air temperatures against instrumentally measured values using two different reconstruction approaches, namely, calibration-in-space (CiS, multilake training set) and calibration-in-time (CiT, calibration of time series data against meteorological data). The results showed that the principal variability in fossil chironomid assemblages in the sediment core corresponded to the measured air temperatures. In addition, the temperatures reconstructed using CiS ( R = 0.38, p = 0.014) and CiT ( R = 0.51, p = 0.001) correlated significantly with the meteorological data; however, the CiS approach showed higher variability and larger differences against the instrumentally measured values. A significant lag of on average 4–8 years was also found in the chironomid response to observed temperature change that is, nevertheless, much shorter time span than with some other paleoclimate proxies. The results verify the usability and sensitivity of chironomids as a paleoclimate proxy in the Nurmijärvi varved sediment record with the potential value of an exceptionally well-resolved downcore record of the Holocene climate change in the future. The CiT approach can potentially provide accurate paleotemperature estimates at the late-Holocene scale, but the CiS approach may be more useful at longer timescales if the community compositions change significantly from those occurring during the calibration period of the CiT.

Characterization of the Medieval Climate Anomaly, Little Ice Age and recent warming in northern Lapland

“…The chironomid-based mean July air temperature (T Jul ) reconstruction used the regional expanded Fennoscandian calibration model (weighted-averaging partial least squares) combining several data sets (Nyman et al, 2005;Luoto, 2009;Luoto et al, 2014. The model has been downcore validated against meteorological data (instrumental measurements) using varved lake sediments by Luoto and Ojala (2016) and applied in its current form by Rantala et al (2016b). The temperature gradient in the training set varies from 7.9 to 17.6 ∘ C. The two-component model includes 180 lakes and 129 taxa having an r 2 jack of 0.86, a root-mean-squared error of prediction (RMSEP) Figure 1.…”

Review and test of reproducibility of subdecadal resolution palaeoenvironmental reconstructions from microfossil assemblages

“…Chironomids would seem to fall far short of these ideals, with the larvae taking months, or even years, to mature (Tokeshi, 1995). reconstruct August air temperature because this variable explains the most variance in a Canadian calibration set (Larocque et al, 2006); several other papers reconstruct July air temperature (Lang et al, 2017;Larocque and Hall, 2003;Luoto and Ojala, 2016). While it is widely believed (Eggermont and Heiri, 2011) that summer air temperature is a key variable affecting chironomid assemblages, there is no particular reason to suspect July or August temperatures to be uniquely important.…”

“…With a few exceptions (Kamenik et al, 2009;Larocque-Tobler et al, 2011a, 2011bLuoto and Ojala, 2016), transfer-function models for quantitative palaeoclimate reconstructions are calibrated on a spatial calibration set of sites with paired microfossil and climatological normals that span a wide climatic range (Birks et al, 2010). Over a spatial calibration set, the correlation between air temperature in different months can be expected to be high.…”

“…Kamenik et al (2009) introduced calibration-in-time to microfossil data, using it to reconstruct April-November temperatures from the pollen stratigraphy from Mauntschas Mire, Switzerland. Subsequently, calibration-in-time models have been used to reconstruct summer temperatures from chironomid stratigraphies (Larocque-Tobler et al, 2011a, 2011bLuoto and Ojala, 2016).…”

“…Chrysophyte stomatocysts have also been used to reconstruct summer calcium concentrations (Hernández-Almeida et al, 2015b), which might reflect summer mixing and so were correlated with summer wind. High-resolution chironomid head capsule stratigraphies have been used to reconstruct summer air (e.g., Larocque et al, 2009a;Luoto and Ojala, 2016;Zhang et al, 2017a) and water (Medeiros et al, 2012) temperature. Highresolution pollen records have been used to reconstruct summer air temperature (Kamenik et al, 2009).…”