- Email: [email protected]
Palaeofire records from Northern Luzon, Philippines
468
Abstracts / Quaternary International 279-280 (2012) 462–565
(although this is equivocal). d 18O values show a complex transition into the Last Interglacial with fluctuating lake levels. In one core only, these fluctuations coincide with an increase in pistachio. Both cores show the same trend in the d 18O values within the Interglacial. As with the Holocene, the oak forest dominates during a period of gradually increasing d 18O values. The current chronology is not robust enough yet to establish rates of change. However, the hydroclimatic evolution of the Last Interglacial resembles that of the Holocene; the vegetation succession does not. Higher resolution work is needed to establish why the discrepancy exists.
a generally warmer climate (heteroscedasticity; hotspot of variability). Specifically, MVC plots for JJA temperatures from 570 BC – AD 120 were compared to MVC plots of instrumental and reconstructed temperatures (from the same sediment core and proxies but a different study) from AD 1177 to AD 2000. Reconstructed JJA temperatures from 570 BC – AD 120 showed that inter-annual JJA temperature variability increased rapidly above a threshold of w 10 C mean JJA temperature. This increase accelerated with continued warming up to >11.5 C. Finally, it was found that the Roman Period serves as an analogue for warmer 21st century JJA temperatures in the Alps.
PALAEOFIRE RECORDS FROM NORTHERN LUZON, PHILIPPINES ICE STREAMING AND ICE-SHEET RE-ADVANCES IN SE SCOTLAND AND NE ENGLAND: NEW EVIDENCE FROM MULTIBEAM BATHYMETRY DATA
Janelle Stevenson. Australian National University, Australia E-mail address: [email protected]
Three palaeoecological records from three distinct settings in northern Luzon reveal changes in the regions fire history from the mid-Holocene through to the present. Two lowland sites record significant shifts in burning at around 4,500 yrs BP and from around 2,000 to 1,500 yrs BP. It is difficult to determine whether human activity can be attributed to these phases of fire activity due to scarce archaeological data for the region. Regional climatic data however suggests a weakening of the Asian Monsoon from 7,000 yrs BP to around 1,000 yrs BP, with several periods of weakening embedded within this time frame, the most pronounced being a 500 yr period centred around 4,400 yrs BP and overlapping with the increased charcoal accumulation, general vegetation change and lower lake levels. While the most recent past is missing from one if these lowland sites, the other shows no significant shift in burning for the last 200 yrs. In contrast a third site from the Central Cordillera at 2,400 m asl records a fairly steady input of charcoal for the last 4,000 years, with the last 200 yrs marked by a dramatic increase in fire activity. This change is likely to be a result of human activities, in particular mining and land-use intensification since WWII. A PRELIMINARY LATE VIENTIANE, LAOS PDR
PLEISTOCENE
POLLEN
RECORD
FROM
Janelle Stevenson. Australian National University, Australia E-mail address: [email protected]
A swamp once connected to the Mekong River and within the city of Vientiane has continuous record that dates to beyond 50,000 yrs. The charcoal record shows significant fire activity at around 40 ka and between 30-25 ka, with fire activity by contrast subdued since 19 ka. Palynological analyses are still in progress, but there are have been significant vegetation changes since 19 ka. QUANTITATIVE INTER-ANNUAL AND DECADAL JUNE-JULY-AUGUST TEMPERATURE VARIABILITY (570 BC - AD 120; IRON AGE - ROMAN PERIOD) RECONSTRUCTED FROM THE VARVED SEDIMENTS OF LAKE SILVAPLANA, SWITZERLAND Monique Stewar. University of Bern/OCCR, Switzerland E-mail address: [email protected]
Annually resolved June-July-August (JJA) temperatures were reconstructed using biogenic Silica (bSi) and chironomids preserved in the varved sediments of Lake Silvaplana, Switzerland (Type II regression - Standard Major Axis calibration-in-time; 570 BC to AD 120 þ/ 150 years). These temperatures were partitioned into a warmer (+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 – AD 120) relative to the reconstruction average (10.9 C; reference AD 1950 – 2000 ¼ 9.8 C) with 30 year (climatology) moving averages and related detrended standard deviations (Mean-Variability Change MVC), moving linear trends and change points. Warm and variable JJA temperatures were inferred at the Late Iron Age - Roman Period transition (approximately 50 BC to AD 100 in this region) and a cold anomaly at ca. 470 BC (Early - Late Iron Age). Overall, inter-annual and decadal temperature variability in 570 BC – AD 120 exceeded the last millennium whereas multi-decadal and lower frequency temperature variability were comparable. Reconstructed JJA temperatures from 570 BC – AD 120 were then used to verify current trends and European climate model outputs for the 21st century which suggest increased inter-annual summer temperature variability and extremes in
Heather Stewart. British Geological Survey, United Kingdom E-mail address: [email protected]
Multibeam bathymetry datasets have been combined with high-resolution digital surface models (NEXTMap) to reveal strong onshore-offshore evidence of palaeo-ice streaming in the catchments of the Forth and the Tweed, and offshore NE England. Long suspected to terminate offshore, the flow path and dimensions of the Forth and Tweed palaeo-ice streams can now be reconstructed with some certainty using these new data. The glacial landsystem is extremely well preserved on the sea bed with no significant burial by modern sediments. The multibeam bathymetry data reveal a surprising number of moraines and streamlined bedforms, of varying dimensions; along with meltwater channels, tunnel valleys, rogen moraines and possible eskers. Seismic records from the region confirm the erosional and depositional architecture of these glacial features. The whole pattern of features, covering around 10,000 km2, has been mapped in detail and charts a fast-flowing corridor of the last British Ice Sheet from the Scottish Central Lowlands and Firth of Forth east and southeast into the North Sea Basin. Of particular note are numerous highly elongate bedforms, with elongation ratios of more than 10:1, strongly suggestive of ice streaming; and two broad arcuate morainic belts offshore NE England marking frontal positions of the ice sheet during retreat. Spatial relationships between the moraine belts and superimposed streamlined bedforms indicate considerable re-advances of the ice margin in this area, possibly at a late stage during ice-sheet deglaciation. SOOT AS EVIDENCE FOR WIDESPREAD FIRES AT THE YOUNGER DRYAS ONSET (YDB, 12.9 KA) Adrienne Stich. DePaul University, United States E-mail address: [email protected]
Evidence continues to grow in support of a major extraterrestrial (ET) impact as a trigger for the late Pleistocene megafaunal extinction in North America at the onset of the Younger Dryas (YDB, 12.9 ka). Sediment at the base of a C-rich, dark layer is marked by peaks in magnetic microspherules, Ir, nanodiamonds, and other materials consistent with an ET event (Firestone, 2007; Kennett, 2008). This layer also exhibits spikes in charcoal, C spherules, 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 high abundances is a marker for extensive, impact-related fires. Soot analysis allowed us to test the possibility that the explosion of an impactor triggered combustion of biomass or fossil C, as hypothesized for the Cretaceous-Paleogene (K-P, 65 Ma) (Wolbach, 1985; Belcher et al., 2009). Previous analyses of samples from N. America and Europe, yielded YDB soot (10%) at two sites in N. America: Murray Springs, AZ (20 ppm) and Blackville, SC (2000 ppm) (Wolbach, 2007). We now report results from analysis of six more sites: Arlington Canyon and nearby Arlington Springs, CA; Bull Creek, OK; Hall's Cave, TX; Murray Springs (new sampling); and Lommel, Belgium. Soot concentrations spike in the YDB layer at four of these 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 higher than previously observed there. Significant YDB soot at five locations up to 3500 km apart across North America, combined with other wildfire evidence, suggests widespread burning and aeolian transport of soot across North America w12.9 ka ago. These results support an impact sufficient to ignite continental-scale fires.
Abstracts / Quaternary International 279-280 (2012) 462–565
(although this is equivocal). d 18O values show a complex transition into the Last Interglacial with fluctuating lake levels. In one core only, these fluctuations coincide with an increase in pistachio. Both cores show the same trend in the d 18O values within the Interglacial. As with the Holocene, the oak forest dominates during a period of gradually increasing d 18O values. The current chronology is not robust enough yet to establish rates of change. However, the hydroclimatic evolution of the Last Interglacial resembles that of the Holocene; the vegetation succession does not. Higher resolution work is needed to establish why the discrepancy exists.
a generally warmer climate (heteroscedasticity; hotspot of variability). Specifically, MVC plots for JJA temperatures from 570 BC – AD 120 were compared to MVC plots of instrumental and reconstructed temperatures (from the same sediment core and proxies but a different study) from AD 1177 to AD 2000. Reconstructed JJA temperatures from 570 BC – AD 120 showed that inter-annual JJA temperature variability increased rapidly above a threshold of w 10 C mean JJA temperature. This increase accelerated with continued warming up to >11.5 C. Finally, it was found that the Roman Period serves as an analogue for warmer 21st century JJA temperatures in the Alps.
PALAEOFIRE RECORDS FROM NORTHERN LUZON, PHILIPPINES ICE STREAMING AND ICE-SHEET RE-ADVANCES IN SE SCOTLAND AND NE ENGLAND: NEW EVIDENCE FROM MULTIBEAM BATHYMETRY DATA
Janelle Stevenson. Australian National University, Australia E-mail address: [email protected]
Three palaeoecological records from three distinct settings in northern Luzon reveal changes in the regions fire history from the mid-Holocene through to the present. Two lowland sites record significant shifts in burning at around 4,500 yrs BP and from around 2,000 to 1,500 yrs BP. It is difficult to determine whether human activity can be attributed to these phases of fire activity due to scarce archaeological data for the region. Regional climatic data however suggests a weakening of the Asian Monsoon from 7,000 yrs BP to around 1,000 yrs BP, with several periods of weakening embedded within this time frame, the most pronounced being a 500 yr period centred around 4,400 yrs BP and overlapping with the increased charcoal accumulation, general vegetation change and lower lake levels. While the most recent past is missing from one if these lowland sites, the other shows no significant shift in burning for the last 200 yrs. In contrast a third site from the Central Cordillera at 2,400 m asl records a fairly steady input of charcoal for the last 4,000 years, with the last 200 yrs marked by a dramatic increase in fire activity. This change is likely to be a result of human activities, in particular mining and land-use intensification since WWII. A PRELIMINARY LATE VIENTIANE, LAOS PDR
PLEISTOCENE
POLLEN
RECORD
FROM
Janelle Stevenson. Australian National University, Australia E-mail address: [email protected]
A swamp once connected to the Mekong River and within the city of Vientiane has continuous record that dates to beyond 50,000 yrs. The charcoal record shows significant fire activity at around 40 ka and between 30-25 ka, with fire activity by contrast subdued since 19 ka. Palynological analyses are still in progress, but there are have been significant vegetation changes since 19 ka. QUANTITATIVE INTER-ANNUAL AND DECADAL JUNE-JULY-AUGUST TEMPERATURE VARIABILITY (570 BC - AD 120; IRON AGE - ROMAN PERIOD) RECONSTRUCTED FROM THE VARVED SEDIMENTS OF LAKE SILVAPLANA, SWITZERLAND Monique Stewar. University of Bern/OCCR, Switzerland E-mail address: [email protected]
Annually resolved June-July-August (JJA) temperatures were reconstructed using biogenic Silica (bSi) and chironomids preserved in the varved sediments of Lake Silvaplana, Switzerland (Type II regression - Standard Major Axis calibration-in-time; 570 BC to AD 120 þ/ 150 years). These temperatures were partitioned into a warmer (+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 – AD 120) relative to the reconstruction average (10.9 C; reference AD 1950 – 2000 ¼ 9.8 C) with 30 year (climatology) moving averages and related detrended standard deviations (Mean-Variability Change MVC), moving linear trends and change points. Warm and variable JJA temperatures were inferred at the Late Iron Age - Roman Period transition (approximately 50 BC to AD 100 in this region) and a cold anomaly at ca. 470 BC (Early - Late Iron Age). Overall, inter-annual and decadal temperature variability in 570 BC – AD 120 exceeded the last millennium whereas multi-decadal and lower frequency temperature variability were comparable. Reconstructed JJA temperatures from 570 BC – AD 120 were then used to verify current trends and European climate model outputs for the 21st century which suggest increased inter-annual summer temperature variability and extremes in
Heather Stewart. British Geological Survey, United Kingdom E-mail address: [email protected]
Multibeam bathymetry datasets have been combined with high-resolution digital surface models (NEXTMap) to reveal strong onshore-offshore evidence of palaeo-ice streaming in the catchments of the Forth and the Tweed, and offshore NE England. Long suspected to terminate offshore, the flow path and dimensions of the Forth and Tweed palaeo-ice streams can now be reconstructed with some certainty using these new data. The glacial landsystem is extremely well preserved on the sea bed with no significant burial by modern sediments. The multibeam bathymetry data reveal a surprising number of moraines and streamlined bedforms, of varying dimensions; along with meltwater channels, tunnel valleys, rogen moraines and possible eskers. Seismic records from the region confirm the erosional and depositional architecture of these glacial features. The whole pattern of features, covering around 10,000 km2, has been mapped in detail and charts a fast-flowing corridor of the last British Ice Sheet from the Scottish Central Lowlands and Firth of Forth east and southeast into the North Sea Basin. Of particular note are numerous highly elongate bedforms, with elongation ratios of more than 10:1, strongly suggestive of ice streaming; and two broad arcuate morainic belts offshore NE England marking frontal positions of the ice sheet during retreat. Spatial relationships between the moraine belts and superimposed streamlined bedforms indicate considerable re-advances of the ice margin in this area, possibly at a late stage during ice-sheet deglaciation. SOOT AS EVIDENCE FOR WIDESPREAD FIRES AT THE YOUNGER DRYAS ONSET (YDB, 12.9 KA) Adrienne Stich. DePaul University, United States E-mail address: [email protected]
Evidence continues to grow in support of a major extraterrestrial (ET) impact as a trigger for the late Pleistocene megafaunal extinction in North America at the onset of the Younger Dryas (YDB, 12.9 ka). Sediment at the base of a C-rich, dark layer is marked by peaks in magnetic microspherules, Ir, nanodiamonds, and other materials consistent with an ET event (Firestone, 2007; Kennett, 2008). This layer also exhibits spikes in charcoal, C spherules, 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 high abundances is a marker for extensive, impact-related fires. Soot analysis allowed us to test the possibility that the explosion of an impactor triggered combustion of biomass or fossil C, as hypothesized for the Cretaceous-Paleogene (K-P, 65 Ma) (Wolbach, 1985; Belcher et al., 2009). Previous analyses of samples from N. America and Europe, yielded YDB soot (10%) at two sites in N. America: Murray Springs, AZ (20 ppm) and Blackville, SC (2000 ppm) (Wolbach, 2007). We now report results from analysis of six more sites: Arlington Canyon and nearby Arlington Springs, CA; Bull Creek, OK; Hall's Cave, TX; Murray Springs (new sampling); and Lommel, Belgium. Soot concentrations spike in the YDB layer at four of these 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 higher than previously observed there. Significant YDB soot at five locations up to 3500 km apart across North America, combined with other wildfire evidence, suggests widespread burning and aeolian transport of soot across North America w12.9 ka ago. These results support an impact sufficient to ignite continental-scale fires.