A chironomid-based reconstruction of summer temperatures in NW Iceland since AD 1650

Abstract

Few studies currently exist that aim to validate a proxy chironomid-temperature reconstruction with instrumental temperature measurements. We used a reconstruction from a chironomid percentage abundance data set to produce quantitative summer temperature estimates since AD 1650 for NW Iceland through a transfer function approach, and validated the record against instrumental temperature measurements from Stykkishólmur in western Iceland. The core was dated through Pb-210, Cs-137 and tephra analyses (Hekla 1693) which produced a well-constrained dating model across the whole study period. Little catchment disturbance, as shown through geochemical (Itrax) and loss-on-ignition data, throughout the period further reinforce the premise that the chironomids were responding to temperature and not other catchment or within-lake variables. Particularly cold phases were identified between AD 1683-1710, AD 1765-1780 and AD 1890-1917, with relative drops in summer temperatures in the order of 1.5-2°C. The timing of these cold phases agree well with other evidence of cooler temperatures, notably increased extent of Little Ice Age (LIA) glaciers. Our evidence suggests that the magnitude of summer temperature cooling (1.5-2°C) was enough to force LIA Icelandic glaciers into their maximum Holocene extent, which is in accordance with previous modelling experiments for an Icelandic ice cap (Langjökull).

Reconstruction of past methane availability in an Arctic Alaska wetland indicates climate influenced methane release during the past ~12,000 years

“…5 Stratigraphy of common midge taxa from the LQ-West core 12,000 years. Paratanytarsus is often associated with macrophytes (Langdon et al 2011), whereas Corynocera ambigua is more enigmatic, occurring in cold oligotrophic lakes (Brooks et al 2007) and midthermal-range lakes (*11°C) (Barley et al 2006). The main change in fauna occurred at *10,000 cal year BP when the relative dominance of Paratanytarsus switched to an increased abundance of Corynocera ambigua, and coincided with the switch from organicrich peat to gyttja.…”

“…temperature, hydrology, and habitat) that occurred at this location during the Holocene. We used changes in the assemblages of chironomids preserved in the sediment core as a proxy of past temperature (Langdon et al 2011). We also used changes in the past oxygen isotope values (d 18 O) of lake water inferred from the d 18 O of chironomid head capsules preserved in the sediments as a proxy for hydrologic change Verbruggen et al 2010b;Wooller et al 2004Wooller et al , 2008 and plant macrofossils coupled with sediment characteristics (lithological description and elemental composition) as proxies for local habitat change Jones and Yu 2010).…”

Comparison between chironomid-inferred mean-August temperature from varved Lake Żabińskie (Poland) and instrumental data since 1896 AD

“…The method has been recently criticized due to divergences in reconstructions from Scandinavia (Velle et al, 2010(Velle et al, , 2012 but, when transfer functions are used following well-established rules (Juggins, 2013), they can provide accurate reconstructions . However, it is agreed amongst the chironomists that the technique can be sometimes limited due to other parameters such as anoxia (Quinlan et al, 1998), lake depth (Korhola et al, 2000), nutrients (Lotter et al, 1998) or macrophytes (Langdon et al, 2011) affecting the chironomid assemblages at some time in the past thus masking the temperature signal. Therefore, a "validation" of the technique should be provided before a long-term reconstruction is attempted.…”

Identifying cryptotephra units using correlated rapid, nondestructive methods: VSWIR spectroscopy, X‐ray fluorescence, and magnetic susceptibility

“…XRF core scanning has been used to identify tephra in lake cores with some success [ Moreno et al ., ; Langdon et al ., ; Kylander et al ., ] though ITRAX can have difficulty in the analytical detection of lighter elements (such as Si) [ Kylander et al ., ]. Nevertheless, Kylander et al .…”