Danni M. Pearce*1, Simon J. Carr2 and Sven Lukas2

*1 d.pearce@worc.ac.uk University of Worcester, Institute for Science and the Environment, Henwick Grove, Worcester, WR2 6AJ, U.K. 2 Queen Mary, University of London, Department of Geography, Mile End Road, Mile End, London, E1 4NS, U.K.

• Mapping followed a morphostratigraphic approach which permits reconstruction of the likely ice-mass

geometry and palaeo-ELAs to be calculated.

• Palaeo-precipitation and temperature totals are derived using established techniques and compared

to those gained from empirical modern temperature measurements.

Figure 1. Location map of the English Lake District .

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Fagurhólsmýri Off-glacier Breiðamerkurjökull

This research was conducted whilst at QMUL and DMP

would like to gratefully acknowledge QMUL for funding this

research.

Thanks go to the advice and time from Jostein Bakke, Simon

Lewis, Des McDougall, Matthew Roberts, Finnur Palsson,

and all field assistants especially Heather Channon and Alex

Clarke.

Figure 2. Excerpt of geomorphological map in the study area showing landsystem contrasts used to delineate past glacier

extent and reconstructed glacier limits. Numbers correspond to geomorphological features described in (Pearce, 2010).

The regional versus glacier influenced data (Fig.5) has established a 2°C to 2.5°C difference in

temperature purely due to the cooling effect of a glacierised surface, referred herein as the:

‘Cooling Effect’.

Figure 5. Mean daily temperature for on glacier, off-ice and regional from AWS stations, Fagurhólsmýri, Off-glacier and

Breiðamerkurjökull Iceland.

Clear morphostratigraphic relationships between landform assemblages (Figure 2) enabled

individual outlets to be identified and correlated across c. 100 km2 forming a coeval plateau icefield

covering an area of c. 33 km2. Using the AABR method and BR = 1.9 the mean study area

ELA = 532 m.

Revised

southern sector

of plateau

icefield

Northern sector of

plateau icefield

(McDougall, 2001)

Figure 3. Glacier reconstruction for Widdygill according

to Wilson (2002). Topographic contours and ice-surface

contours at 50 m intervals.

Including previously

reconstructed limits,

(c. 55 km2) the total area of

plateau ice covering the

Lake District to c. 88 km2.

N

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Wilson (2002) inferred a valley glacier situated just beyond

the icefield in Widdygill Foot (see red box).

The accumulation zone of the valley glacier is situated in the

ablation zone of the icefield, unrepresentative of modern ice

masses.

Observed thick sediment blankets and moraines above the

valley head suggest the ice-mass was coeval with the

icefield.

Integrating this value to the reconstructed

Lake District icefield, lowers Pa and T3 at

the icefield ELA to a scenario that is more

in line with sub-fossil records; colder and

drier (see Table 1) .

At the ELA 532 m:

T3 from: 4.9°C ± 0.5°C

To between: 1.8°C and 3.3°C

Pa reduced from: 2179 ± 295 mm a-1

To between: 1207 and 1720 mm a-1

Bracketed precipitation at sea-level:

From: 1398 and 1835 mm a-1

To: 895 and 1276 mm a-1

Breiðamerkurjökull

Fagurhólsmýri

Off-ice

Figure 4. Iceland and location of Automatic Weather Stations on

Breiðamerkurjökull and foreland. The color of location corresponds to

the data in Figure 5.

Key

To establish whether glaciation in the south-west central

Lake District (Fig 1.) was connected to the previously

reconstructed YD plateau icefield and determine the

effect of a glacierised surface on air temperatures and its

use as a calibration for palaeo-climatic calculations.

Palaeo-climate

A large number of sites remain unmapped in the central Lake District, England, precluding

characterisation of the style and extent of former Younger Dryas (YD) c. 12.9-11.7 cal. ka BP))

ice masses during this key period.

Additionally, environmental changes have been documented using both proxy-based records

and model simulations but a disparity still exists between model simulations and climate

reconstructions using glaciers as proxies. Palaeo-ecological data and modelling data denote a

broadly cold and dry climate during the YD, but glacier-based reconstructions consistently

produce a warm and wet scenario at the glacier ELA, affecting the validity of the models.

It is proposed that the lack of agreement between these is in part due to methodological

shortfalls, e.g. the failure to include the cooling effect of glacierised surfaces on reconstructed

air temperatures. Using empirical data from automatic weather stations around Vatnajökull,

Iceland, we investigate this effect.

It is important to note this data set is

short-term and likely to reflect current

weather, temperature differences and

maybe very different at other locations

and in fact across the ablation

season. A longer dataset is required

and under different climates.

This can only serve as an initial

empirical recording .

Glacier derived palaeo-precipitation (standard approach): Previous glacier-based YD climate reconstructions for Scotland suggest equal or increased

precipitation at sea-level than at present. In part, this is a consequence of employing the Ohmura et al., (1992) regression equation as the dataset obscures the

local climate signal but it is also presumed representative of climatic conditions during the YD.

Discrepancy exists between the Scottish reconstructions and the c. 54% decrease in Pa for the Lake District. At present, the area experiences a pronounced

orographic effect and it is difficult to envisage YD precipitation not influenced by relief. However, it is suggested here that the climate operating around the western

sea-board was extreme enough to significantly reduce/shut down any orographic effect during the stadial, thus accounting for the difference between present values

and YD.

Glacier ‘cooling effect’ approach: The disparities between the sub-fossil record and glacier based reconstructions could partly be a result of the geological

proxies used to reconstruct former ice masses i.e. geomorphology. However, although the precipitation-temperature relationship is complex, a simple explanation

may, in part, be attributable to the influence on air-temperatures exerted by a glacierised surface, which is presently unaccounted for in palaeo-climatic calculations.

The data presented suggests only c. 38% of present precipitation totals were received during the Younger Dryas. Therefore, caution is required when using proxies

un-affected by the cooling of a glacieriesd surface (i.e. synoptic) to derive local glacier-climates.

Method of

calculation

ELA

(m)

T3 at

0m

altitude

T3 at

ELA

Pa at ELA Pa at 0m

altitude

Pa at

Lorton Vale

Pa at 0m

altitude

present day

Pa at ELA

present day

% of present day

Pa at 0m compared

to YD

(°C) (°C) (mm/a-1 ) (mm a-1 ) (mm a-1 ) (mm a-1 ) (mm a-1 )

Standard

approach

532 8 4.6 ±

0.5

2179 ± 295 1398 - 1835 3553 3392 4574 41 - 54

‘Cooling Effect’ 532 5.5 to 6 1.8 - 3.3 1207 - 1720 895 - 1276 3553 3392 1207 - 1720 26 - 38

Table 1. Comparison of Pa and T3 values established using standard techniques and those derived from the ‘cooling effect’

calibration.