High resolution Lateglacial and early-Holocene summer air temperature records from Scotland inferred from chironomid assemblages

Stephen J Brooks,Ian P Matthews,Hilary H Birks,H.John B Birks

doi:10.1016/j.quascirev.2012.03.007

Abstract

Lateglacial and early-Holocene mean July air temperatures have been reconstructed, using a chironomid-based inference model, from lake-sediment sequences from Abernethy Forest, in the eastern Highlands of Scotland, and Loch Ashik, on the Isle of Skye in north-west Scotland. Chronology for Abernethy Forest was derived from radiocarbon dates of terrestrial plant macrofossils deposited in the lake sediments. Chronology for Loch Ashik was derived from tephra layers of known ages, the first age-depth model of this kind. Chironomid-inferred temperatures peak early in the Lateglacial Interstadial and then gradually decline by about 1 °C to the beginning of the Younger Dryas (YD). At Abernethy Forest, the Lateglacial Interstadial is punctuated by three centennial-scale cold oscillations which appear to be synchronous with the Greenland Interstadial events GI-1d, when temperatures at Abernethy fell by 5.9 °C, GI-1c, when temperatures fell by 2.3 °C, and GI-1b, when temperatures fell by 2.8 °C. At Loch Ashik only the oscillation correlated with GI-1d is clearly defined, when temperatures fell by 3.8 °C. The start of the YD is clearly marked at both sites when temperatures fell by 5.5 °C at Abernethy Forest and 2.8 °C at Loch Ashik. A warming trend is apparent during the late-YD at Abernethy Forest but at Loch Ashik late-YD temperatures became very cold, possibly influenced by its close proximity to the Skye ice-field. The rapidly rising temperatures at the YD – Holocene transition occur about 300 years earlier at both sites than changes in sediment lithology and loss-on-ignition. The temperature trends at both sites are broadly similar, although between-site differences may result from the influence of local factors. Similar climate trends are found at other sites in the northern British Isles. However, the British summer temperature records differ in detail from trends in the oxygen-isotope records from the Greenland ice-cores and from other chironomid-inferred temperature records available from Scandinavia, north-west Europe and central Europe, which suggest important differences in the influence of climatic forcing at regional scales.

Highlights

Climatic changes during the last glacialeinterglacial transition (LGIT) between approximately 16e8 ka BP are of considerable interest to climate scientists because they provide insights into atmosphere-ocean-terrestrial climate linkages during a period of rapid, high amplitude climate change
We provide high temporal resolution chironomid-inferred mean July air temperature records for Loch Ashik and Abernethy Forest and compare them against other high resolution temperature records from Britain, mainland north-west Europe and Greenland to determine regional and local trends
This model is generally well-constrained through the first part of the Lateglacial Interstadial where the uncertainties are comparable or better than the counting errors produced for NGRIP (Lowe et al, 2008)

Summary

Introduction

Climatic changes during the last glacialeinterglacial transition (LGIT) between approximately 16e8 ka BP are of considerable interest to climate scientists because they provide insights into atmosphere-ocean-terrestrial climate linkages during a period of rapid, high amplitude climate change. The only published Lateglacial to early-Holocene chironomid-inferred temperature records from Britain and Ireland are from Whitrig Bog, south-east Scotland (Brooks and Birks, 2001), Lough Nadourcan, western Ireland (Watson et al, 2010), Fiddaun in western Ireland (van Asch et al, 2012), and five sites in the English Lake District (Bedford et al, 2004; Lang et al, 2010) These records show general similarities between each other and with the ice-core records but there are differences in detail, which may reflect regional climatic differences or may be related to the low precision of the chronological data available to anchor and correlate each record temporally. More high resolution records with wellfounded, independently derived, chronologies are required to quantify the magnitude, timing and rate of climate change in the British Isles during LGIT and establish the extent of regional and local differences in these trends and in other records across Europe

Methods

Results

Discussion

Conclusion