Ice streaming and ice-sheet re-advances in SE Scotland and NE England: new evidence from multibeam...

Abstracts / Quaternary International 279-280 (2012) 462–565468

(although this is equivocal). d 18O values show a complex transition intothe Last Interglacial with fluctuating lake levels. In one core only, thesefluctuations coincide with an increase in pistachio. Both cores show thesame trend in the d 18O values within the Interglacial. As with the Holo-cene, the oak forest dominates during a period of gradually increasingd 18O values. The current chronology is not robust enough yet to establishrates of change. However, the hydroclimatic evolution of the Last Inter-glacial resembles that of the Holocene; the vegetation succession does not.Higher resolution work is needed to establish why the discrepancy exists.

PALAEOFIRE RECORDS FROM NORTHERN LUZON, PHILIPPINES

Janelle Stevenson. Australian National University, AustraliaE-mail address: janelle.stevenson@anu.edu.au

Three palaeoecological records from three distinct settings in northernLuzon reveal changes in the regions fire history from the mid-Holocenethrough tothepresent. Two lowlandsites record significant shifts inburningat around 4,500 yrs BP and fromaround 2,000 to 1,500 yrs BP. It is difficult todetermine whether human activity can be attributed to these phases of fireactivity due to scarce archaeological data for the region. Regional climaticdata however suggests aweakeningof theAsianMonsoon from7,000 yrs BPto around 1,000 yrs BP,with several periods ofweakening embeddedwithinthis time frame, themost pronounced being a 500 yr period centred around4,400 yrs BP and overlapping with the increased charcoal accumulation,general vegetation change and lower lake levels.While themost recent pastis missing from one if these lowland sites, the other shows no significantshift in burning for the last 200 yrs. In contrast a third site from the CentralCordillera at 2,400m asl records a fairly steady input of charcoal for the last4,000 years, with the last 200 yrs marked by a dramatic increase in fireactivity. This change is likely to be a result of human activities, in particularmining and land-use intensification since WWII.

A PRELIMINARY LATE PLEISTOCENE POLLEN RECORD FROMVIENTIANE, LAOS PDR

Janelle Stevenson. Australian National University, AustraliaE-mail address: janelle.stevenson@anu.edu.au

A swamp once connected to the Mekong River and within the city ofVientiane has continuous record that dates to beyond 50,000 yrs. Thecharcoal record shows significant fire activity at around 40 ka and between30-25 ka, with fire activity by contrast subdued since 19 ka. Palynologicalanalyses are still in progress, but there are have been significant vegetationchanges since 19 ka.

QUANTITATIVE INTER-ANNUAL AND DECADAL JUNE-JULY-AUGUSTTEMPERATURE VARIABILITY (570 BC - AD 120; IRON AGE - ROMANPERIOD) RECONSTRUCTED FROM THE VARVED SEDIMENTS OF LAKESILVAPLANA, SWITZERLAND

Monique Stewar. University of Bern/OCCR, SwitzerlandE-mail address: monique.stewart@giub.unibe.cht

Annually resolved June-July-August (JJA) temperatures were reconstructedusing biogenic Silica (bSi) and chironomids preserved in the varved sedi-ments of Lake Silvaplana, Switzerland (Type II regression - Standard MajorAxis calibration-in-time; 570 BC to AD 120 þ/� 150 years). These temper-atures were partitioned into awarmer (+0.3 �C; ca. 570 BC – 351 BC), cooler(�0.2 �C; ca. 350 BC – 16 BC) and moderate period (+0.1 �C; ca. 15 BC – AD120) relative to the reconstruction average (10.9 �C; reference AD 1950 –

2000 ¼ 9.8 �C) with 30 year (climatology) moving averages and relateddetrended standard deviations (Mean-Variability Change MVC), movinglinear trends and change points. Warm and variable JJA temperatures wereinferredat the Late IronAge -RomanPeriod transition (approximately50BCto AD 100 in this region) and a cold anomaly at ca. 470 BC (Early - Late IronAge). Overall, inter-annual and decadal temperature variability in 570 BC –

AD 120 exceeded the last millennium whereas multi-decadal and lowerfrequency temperature variability were comparable. Reconstructed JJAtemperatures from570 BC –AD 120were then used to verify current trendsand European climate model outputs for the 21st century which suggestincreased inter-annual summer temperature variability and extremes in

a generally warmer climate (heteroscedasticity; hotspot of variability).Specifically, MVC plots for JJA temperatures from 570 BC – AD 120 werecompared to MVC plots of instrumental and reconstructed temperatures(from the same sediment core and proxies but a different study) from AD1177 to AD 2000. Reconstructed JJA temperatures from 570 BC – AD 120showed that inter-annual JJA temperature variability increased rapidlyabove a threshold of w 10 �C mean JJA temperature. This increase acceler-ated with continued warming up to >11.5 �C. Finally, it was found that theRoman Period serves as an analogue for warmer 21st century JJA tempera-tures in the Alps.

ICE STREAMING AND ICE-SHEET RE-ADVANCES IN SE SCOTLAND ANDNE ENGLAND: NEW EVIDENCE FROM MULTIBEAM BATHYMETRY DATA

Heather Stewart. British Geological Survey, United KingdomE-mail address: hast@bgs.ac.uk

Multibeam bathymetry datasets have been combined with high-resolutiondigital surface models (NEXTMap) to reveal strong onshore-offshoreevidence of palaeo-ice streaming in the catchments of the Forth and theTweed, and offshore NE England. Long suspected to terminate offshore, theflow path and dimensions of the Forth and Tweed palaeo-ice streams cannow be reconstructed with some certainty using these new data. Theglacial landsystem is extremely well preserved on the sea bed with nosignificant burial by modern sediments. The multibeam bathymetry datareveal a surprising number of moraines and streamlined bedforms, ofvarying dimensions; along with meltwater channels, tunnel valleys, rogenmoraines and possible eskers. Seismic records from the region confirm theerosional and depositional architecture of these glacial features. The wholepattern of features, covering around 10,000 km2, has been mapped indetail and charts a fast-flowing corridor of the last British Ice Sheet fromthe Scottish Central Lowlands and Firth of Forth east and southeast into theNorth Sea Basin. Of particular note are numerous highly elongate bed-forms, with elongation ratios of more than 10:1, strongly suggestive of icestreaming; and two broad arcuate morainic belts offshore NE Englandmarking frontal positions of the ice sheet during retreat. Spatial relation-ships between the moraine belts and superimposed streamlined bedformsindicate considerable re-advances of the ice margin in this area, possibly ata late stage during ice-sheet deglaciation.

SOOT AS EVIDENCE FOR WIDESPREAD FIRES AT THE YOUNGER DRYASONSET (YDB, 12.9 KA)

Adrienne Stich. DePaul University, United StatesE-mail address: shiftingmirage@gmail.com

Evidence continues to grow in support of a major extraterrestrial (ET)impact as a trigger for the late Pleistocene megafaunal extinction in NorthAmerica at the onset of the Younger Dryas (YDB, 12.9 ka). Sediment at thebase of a C-rich, dark layer is marked by peaks in magnetic microspherules,Ir, nanodiamonds, and other materials consistent with an ET event (Fire-stone, 2007; Kennett, 2008). This layer also exhibits spikes in charcoal, Cspherules, glass-like C, and PAHs indicative of continent-wide burning,coeval with evidence for a major abrupt increase in burning in Greenland(Mayewski, 1993; Legrand, 1997). Synchronous, widespread soot in highabundances is a marker for extensive, impact-related fires. Soot analysisallowed us to test the possibility that the explosion of an impactor trig-gered combustion of biomass or fossil C, as hypothesized for the Creta-ceous-Paleogene (K-P, 65 Ma) (Wolbach, 1985; Belcher et al., 2009).Previous analyses of samples from N. America and Europe, yielded YDBsoot (�10%) at two sites in N. America: Murray Springs, AZ (20 ppm) andBlackville, SC (2000 ppm) (Wolbach, 2007). We now report results fromanalysis of six more sites: Arlington Canyon and nearby Arlington Springs,CA; Bull Creek, OK; Hall's Cave, TX; Murray Springs (new sampling); andLommel, Belgium. Soot concentrations spike in the YDB layer at four ofthese sites: 2000 ppm at Arlington Canyon, CA; 500 ppm at Bull Creek;2000 ppm at Hall's Cave, TX; and 6000 ppm at Murray Springs, 30x higherthan previously observed there. Significant YDB soot at five locations up to3500 km apart across North America, combined with other wildfireevidence, suggests widespread burning and aeolian transport of sootacross North America w12.9 ka ago. These results support an impactsufficient to ignite continental-scale fires.