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

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)

The 5.2 ka climate event: Evidence from stable isotope and multi-proxy palaeoecological peatland records in Ireland

AbstractEvidence for a major climate event at 5.2 ka has been reported globally and is associated with considerable societal disruption, but is poorly characterised in northwest Europe. This event forms part of a broader period of re-organisation in the Earth's ocean-atmosphere circulation system between 6 and 5 ka. This study tests the nature and timing of the event in northwest Europe, a region highly sensitive to change in meridional overturning circulation and mid-latitude westerly airflow. Here we report three high-resolution Irish multi-proxy records obtained from ombrotrophic peatlands that have robust chronological frameworks. We identify the 5.2 ka event by a sustained decrease in δ18Ocellulose at all three sites, with additional and parallel changes in δ13Ccellulose and palaeoecological (testate amoebae, plant macrofossil and humification) data from two sites in northern Ireland. Data from Sluggan Moss demonstrate a particularly coherent shift towards wetter conditions. These data support the hypothesis that the event was caused by a prolonged period of positive North Atlantic Oscillation conditions, resulting in pervasive cyclonic weather patterns across northwest Europe, increasing precipitation over Ireland

The ‘4.2 kyr event’ in the British Isles: evidence for an abrupt climate event in the North Atlantic?

Palaeoenvironmental and archaeological data from several regions around the world show evidence of a multi-centennial climatic event occurring approximately 4.2 cal. kyr BP. Abrupt climate change events (ACCs) in the early-Holocene were dominated by meltwater pulse events associated with the final stages of deglaciation, a mechanism unlikely to have driven subsequent ACCs in the mid- and late-Holocene. A study of the ‘4.2 kyr event’ therefore provides an opportunity to study ACCs in the context of comparable environmental conditions to those of the modern day, thus providing valuable lessons for the future. Whilst the climatic change and/or impact of the 4.2 kyr event is clear in certain regions (such as southwest Asia), more work must be done to disentangle the timing and magnitude of change at this time in other regions, including northwest Europe. A more comprehensive reconstruction of the event’s spatial and temporal variability will help determine the likely drivers of this event. Here we present the results of a multi-proxy examination of a peat sequence from Sluggan Moss, Northern Ireland. A range of palaeohydrological proxy analyses have been undertaken, including: humification, plant macrofossil and testate amoebae analyses. Furthermore, stable isotopic analysis (13C and 18O) of Sphagnum ?-cellulose presents an opportunity to examine changes in atmospheric circulation across the 4.2 kyr event. The chronological resolution on the sequence is exceptionally high, providing an excellent opportunity to determine the synchroneity of the climatic signal across the North Atlantic region around 4.2 cal. kyr BP

Efstadalsvatn � a multi-proxy study of a Holocene lacustrine sequence from NW Iceland

Multi-proxy data, both lithostratigraphic and biostratigraphic, are presented from Efstadalsvatn, a lake in NW Iceland. The sequence covers the period 10,000 to 3500 14C yr B.P. The biostratgraphic data include the first Icelandic chironomid-based reconstruction of Holocene mean July air temperatures, using a Norwegian training set in the absence of modern Icelandic data. The results show that deglaciation and ecosystem development probably began before 10,000 14C yr B.P. and that July temperatures were around 48C at ca. 9500 14C yr B.P.14 Temperatures then rose to ca. 88C at the time of the deposition of the Saksunarvatn tephra (9100 14C yr B.P.), reaching ca. 108C by 8500 14C yr B.P., high enough for the growth of tree birch, although successful birch colonisation did not take place until 6750 14C yr B.P. There is some evidence for cooling immediately preceding 9100 14C yr B.P. There is little firm biostratigraphic evidence for the 8200 cal. B.P. event, although this may be due to a relatively low resolution pollen sampling interval, but there are changes at this time in the total carbon (TC) and mass susceptibility (MS) data. Optimal temperatures and relative vegetation stability may have occurred between 8000�6100 14C yr B.P. but the chironomid assemblages indicate higher temperatures after 5000 14C yr B.P. This latter interpretation may, however, reflect delayed colonisation of thermophilous taxa and requires further investigation. There is evidence in the lithostratigraphy for greater local terrestrial instability after 6100 14C yr B.P. but it seems unlikely that this led to the redevelopment of ice in the catchment. The biostratigraphic records appear to show a degree of resistence to climate forcing throughout the early and middle Holocene. The new chironomid-based temperature reconstruction needs to be refined by further studies in Iceland, particularly the development of an Icelandic training set, but has already demonstrated the problems of paleoclimatic interpretations based on pollen and/or macrofossil evidence alone

Was there a ‘4.2 kyr event’ in Great Britain and Ireland? Evidence from the peatland record

Palaeoenvironmental and archaeological data from several regions of the world show evidence of a multi-centennial climatic event c. 4200 cal yr BP. Owing to the absence of continental ice-sheets, studies of this mid-Holocene event provide an opportunity to examine abrupt climatic change within an environmental context comparable to that of the modern day. Whilst the climatic change and/or impact of the event is clear in certain regions, such as western Asia, more work must be done to disentangle the timing and magnitude of changes in other regions, including northern Europe. A more comprehensive reconstruction of the event’s spatial and temporal variability will help determine the likely drivers of the event. Presented here are the results of a temporally-focussed, high-resolution and multi-proxy (testate amoebae, plant macrofossil, peat humification and stable isotopic analyses) examination of peat sequences from northern Ireland, with radiocarbon chronologies supplemented by the region’s excellent tephrochronolog

Regional climate change from peat stratigraphy for the mid- to late Holocene in central Ireland

At the millennial scale bog surface wetness (BSW) records show a clear Holocene climate event stratigraphy,with major phases comparable with other regional climate proxies such as chironomid inferredtemperature records. Moving towards the centennial scale, however, and towards the limits of chronologicalcertainty within the records, regional differences are apparent which likely reflect the moreheterogeneous precipitation patterns which occur on shorter timescales. The BSW data presented in thispaper are reconstructed from testate amoebae assemblages from central Ireland and are compared withother regional records. The results suggest that this region is in phase with the North of Ireland in termsof timings and durations of climate change, but the comparisons are less clear with a stacked and tunedrecord from Northern Britain that shows an apparent offset compared to the Irish records. This mayreflect variations in past regional precipitation or be a function of the tuning and stacking process. Thebroad phases of comparison between the Irish records, and the extension of the central Irish record backto 6000 cal BP, allow comparisons with low frequency temperature reconstructions from chironomids,which also show a broad level of correlation, with cooler temperatures relating to wetter BSW atcentennial to millennial timescales

A sediment-based multiproxy palaeoecological approach to the environmental archaeology of lake dwellings (crannogs), Central Ireland

A multiproxy study of Ballywillin Crannog, Lough Kinale, central Ireland is presented. The methodology used reveals the wealth of information that a multiproxy approach can contribute in lake settlement studies. Plant macrofossils, pollen and spores, diatoms, chironomids and Coleoptera from a lake core are used to reconstruct local and regional vegetation change and lake history to establish the age and function of the crannog. The palaeoecological evidence suggests that Ballywillin Crannog was constructed around AD620, with its most intensive period of occupation after AD1150. Cereals and a range of gathered fruits and nuts were brought onto and cooked on the crannog, and cereal grains were possibly stored there