Palaeolimnological evidence for marked Holocene environmental changes on Signy Island, Antarctica

first_imgLake-sediment cores from Heywood and Sombre Lakes on Signy Island (South Orkney Islands), Antarctica, have yielded a conformable radiocarbon chronology for the Holocene and a high-resolution record of environmental change. The lakes share a common climate and geology but have distinct catchments. This provides an opportunity for using lake sediments to differentiate between local, within lake/catchment, events and those at a regional scale. Analyses of various biological and physical remains from the lakes suggest that both catchments have undergone considerable changes during the last 5700 years. Macrofossils (moss and crustacean remains) are more abundant in the late Holocene, being associated with a period of high sediment accumulation, which is related to diatom evidence for more nutrient-rich conditions at the sites. This is interpreted as a response to a Holocene‘climate optimum’ at c. 3800–1300 14C yr BP. The record is consistent with other lake, ice and ocean core studies, although the climate optimum appears to have persisted for a longer period at Signy Island.last_img read more

Astrobiological instrumentation for Mars – the only way is down

first_imgIn this paper, in this edition of the Journal commemorating the life and work of David Wynn-Williams, we consider approaches to the astrobiological investigation of Mars. We provide a brief account of the scientific rationale behind the approach presented here. In particular, we outline the capabilities of the Raman spectrometer for the detection of biomarkers. David Wynn-Williams was an active champion of this instrument who was keen to field-qualify a version in Antarctica with a view to flying a Raman instrument onboard a Mars-bound space mission. We examine a scenario for the deployment of such an instrument in conjunction with other instrumentation and argue that subsurface deployment of scientific instruments is essential if we are to succeed in detecting any evidence that may exist for former life on Mars. We outline a mission scenario – Vanguard – which represents a novel but low-risk, low-cost approach to Mars exploration that was conceived and developed jointly by one of the authors (Ellery) and the late David Wynn-Williams.last_img read more

Volcanic time-markers for Marine Isotopic Stages 6 and 5 in Southern Ocean sediments and Antarctic ice cores: implications for tephra correlations between palaeoclimatic records

first_imgThree megascopic and disseminated tephra layers (which we refer to as layers A, B, and C) occur in late Quaternary glaciomarine sediments deposited on the West Antarctic continental margin. The stratigraphical positions of the distal tephra layers in 28 of the 32 studied sediment cores suggest their deposition during latest Marine Isotopic Stage (MIS) 6 and MIS 5. One prominent tephra layer (layer B), which was deposited subsequent to the penultimate deglaciation (Termination II), is present in almost all of the cores. Geochemical analyses carried out on the glass shards of the layers reveal a uniform trachytic composition and indicate Marie Byrd Land (MBL), West Antarctica, as the common volcanic source. The geochemical composition of the marine tephra is compared to that of ash layers of similar age described from Mount Moulton and Mount Takahe in MBL and from ice cores drilled at Dome Fuji, Vostok and EPICA Dome C in East Antarctica. The three tephra layers in the marine sediments are chemically indistinguishable. Also five englacial ash layers from Mt. Moulton, which originated from highly explosive Plinian eruptions of the Mt. Berlin volcano in MBL between 142 and 92 ka ago, are chemically very similar, as are two tephra layers erupted from Mt. Takahe at ca 102 ka and ca 93 ka. Statistical analysis of the chemical composition of the glass shards indicates that the youngest tephra (layer A) in the marine cores matches the ash layer that erupted from Mt. Berlin at 92 ka, which was previously correlated with tephra layers in the EPICA Dome C and the Dome Fuji ice cores. A tephra erupted from Mt. Berlin at 136 ka seems to correspond to a tephra layer deposited at 1733 m in the EPICA Dome C ice core. Additionally, the oldest tephra (layer C) in the marine sediments resembles an ash layer deposited at Vostok around 142 ka, but statistical evidence for the validity of this correlation is inconclusive. Although our results underscore the potential of tephrostratigraphy for correlating terrestrial and marine palaeoclimate archives, our study also reveals limitations of this technique, which may result in the miscorrelation of tephra. Such pitfalls comprise failure to recognise the occurrence of various tephra layers in marine sediment cores, ‘swamping’ of records with chemically indistinguishable tephra from a single volcanic source, and exclusive use of ‘geochemical fingerprinting’ for correlating ash layers.last_img read more

Investigating vegetation-climate feedbacks during the early Eocene

first_imgEvidence suggests that the early Eocene was a time of extreme global warmth. However, there are discrepancies between the results of many previous modelling studies and the proxy data at high latitudes, with models struggling to simulate the shallow temperature gradients of this time period to the same extent as the proxies indicate. Vegetation–climate feedbacks play an important role in the present day, but are often neglected in these palaeoclimate modelling studies, and this may be a contributing factor to resolving the model–data discrepancy. Here we investigate these vegetation–climate feedbacks by carrying out simulations of the early Eocene climate at 2 × and 4 × pre-industrial atmospheric CO2 with fixed vegetation (homogeneous shrubs everywhere) and dynamic vegetation. The results show that the simulations with dynamic vegetation are warmer in the global annual mean than the simulations with fixed shrubs by 0.9 °C at 2 × and 1.8 °C at 4 ×. Consequently, the warming when CO2 is doubled from 2 × to 4 × is 1 °C higher (in the global annual mean) with dynamic vegetation than with fixed shrubs. This corresponds to an increase in climate sensitivity of 26%. This difference in warming is enhanced at high latitudes, with temperatures increasing by over 50% in some regions of Antarctica. In the Arctic, ice–albedo feedbacks are responsible for the majority of this warming. On a global scale, energy balance analysis shows that the enhanced warming with dynamic vegetation is mainly associated with an increase in atmospheric water vapour but changes in clouds also contribute to the temperature increase. It is likely that changes in surface albedo due to changes in vegetation cover resulted in an initial warming which triggered these water vapour feedbacks. In conclusion, dynamic vegetation goes some way to resolving the discrepancy, but our modelled temperatures cannot reach the same warmth as the data suggest in the Arctic. This suggests that there are additional mechanisms, not included in this modelling framework, behind the polar warmth or that the proxies have been misinterpreted.last_img read more

Variable crustal thickness beneath Thwaites Glacier revealed from airborne gravimetry, possible implications for geothermal heat flux in West Antarctica

first_imgThwaites Glacier has one of the largest glacial catchments in West Antarctica. The future stability of Thwaites Glacier’s catchment is of great concern, as this part of the West Antarctic Ice Sheet has recently been hypothesized to already be en route towards collapse. Although an oceanic trigger is thought to be responsible for current change at the grounding line of Thwaites Glacier, in order to determine the effects of this coastal change further in the interior of the West Antarctic Ice Sheet it is essential to also better constrain basal conditions that control the dynamics of fast glacial flow within the catchment itself. One major contributor to fast glacial flow is the presence of subglacial water, the production of which is a result of both glaciological shear heating and geothermal heat flux. The primary goal of our study is to investigate the crustal thickness beneath Thwaites Glacier, which is an important contributor to regional-scale geothermal heat flux patterns. Crustal structure is an indicator of past tectonic events and hence provides a geophysical proxy for the thermal status of the crust and mantle. Terrain-corrected Bouguer gravity disturbances are used here to estimate depths to the Moho and mid-crustal boundary. The thin continental crust we reveal beneath Thwaites Glacier supports the hypothesis that the West Antarctic Rift System underlies the region and is expressed topographically as the Byrd Subglacial Basin. This rifted crust is of similar thickness to that calculated from airborne gravity data beneath neighboring Pine Island Glacier, and is more extended than crust in the adjacent Siple Coast sector of the Ross Sea Embayment. A zone of thinner crust is also identified near the area’s subaerial volcanoes lending support to a recent interpretation predicting that this part of Marie Byrd Land is a major volcanic dome, likely within the West Antarctic Rift System itself. Near-zero Bouguer gravity disturbances for the subglacial highlands and subaerial volcanoes indicate the absence of supporting crustal roots, suggesting either (1) thermal support from a warm lithosphere or alternatively, and arguably less likely; (2) flexural support of the topography by a cool and rigid lithosphere, or (3) Pratt-like compensation. Although forward modeling of gravity data is non-unique in respect to these alternative possibilities, we prefer the hypothesis that Marie Byrd Land volcanoes are thermally-supported by warmer upper mantle. The presence of such inferred warm upper mantle also suggests regionally elevated geothermal heat flux in this sector of the West Antarctic Rift System and consequently the potential for enhanced meltwater production beneath parts of Thwaites Glacier itself. Our new crustal thickness estimates and geothermal heat flux inferences in the Thwaites Glacier region are significant both for studies of the structure of the broader West Antarctic Rift System and for assessments of geological influences on West Antarctic Ice Sheet dynamics and glacial isostatic adjustment models.last_img read more

The Response of Ice Sheets to Climate Variability

first_imgWest Antarctic Ice Sheet loss is a significant contributor to sea level rise. While the ice loss is thought to be triggered by fluctuations in oceanic heat at the ice shelf bases, ice sheet response to ocean variability remains poorly understood. Using a synchronously coupled ice-ocean model permitting grounding line migration, this study evaluates the response of an ice sheet to periodic variations in ocean forcing. Resulting oscillations in grounded ice volume amplitude is shown to grow as a nonlinear function of ocean forcing period. This implies that slower oscillations in climatic forcing are disproportionately important to ice sheets. The ice shelf residence time offers a critical time scale, above which the ice response amplitude is a linear function of ocean forcing period and below which it is quadratic. These results highlight the sensitivity of West Antarctic ice streams to perturbations in heat fluxes occurring at decadal time scales.last_img read more

Isotopic signatures of major methane sources in the coal seam gas fields and adjacent agricultural districts, Queensland, Australia [in review]

first_imgIn regions where there are multiple sources of methane (CH4) in close proximity, it can be difficult to apportion the CH4 measured in the atmosphere to the appropriate sources. In the Surat Basin, Queensland, Australia, coal seam gas (CSG) developments are surrounded by cattle feedlots, grazing cattle, piggeries, coal mines, urban centres and natural sources of CH4. The use of carbon (δ13C) and hydrogen (δD) stable isotopic composition of CH4 can identify, distinguish between and apportion specific emissions of CH4. However, in Australia there is a paucity of data on the various isotopic signatures of the different source types. This research examines whether dual isotopic signatures of CH4 can be used to discriminate between sources of CH4 in the Surat Basin. We also highlight the benefits of sampling at nighttime in warm to hot climate regions. During two campaigns in 2018 and 2019, a mobile CH4 monitoring system was used to detect CH4 plumes. Seventeen plumes immediately downwind from known CH4 sources were sampled and analysed for their CH4 mole fraction and δ13CCH4 and δDCH4 signatures. The isotopic signatures of the CH4 sources were determined using Miller–Tans plots. These new source signatures were then compared to values documented in reports and peer-reviewed journal articles. In the Surat Basin, CSG sources have δ13CCH4 signatures between −56.0 ‰ and −51.0 ‰ and δDCH4 signatures between −207.0 ‰ and −193.0 ‰. Emissions from an open-cut coal mine have δ13CCH4 and δDCH4 signatures of −60.3 ± 0.2 ‰ and −210.5 ± 0.5 ‰ respectively. Emissions from two ground seeps (abandoned coal exploration wells) have δ13CCH4 signatures of −60.7 ± 0.2 ‰ and −59.9 ± 0.9 ‰ and δDCH4 signatures of −191.2 ± 0.5 ‰ and −185.1 ± 0.9 ‰. A river seep had a δ13CCH4 signature of −61.1 ±  0.9 ‰ and a δDCH4 signature of −225.5± 1.4 ‰. Three dominant agricultural sources were analysed. The δ13CCH4 and δDCH4 signatures of a cattle feedlot are −63.0 ± 1.2 ‰ and −309.0 ± 1.0 ‰ respectively, grazing (pasture) cattle have δ13CCH4 and δDCH4 signatures of −59.9 ± 0.8 ‰ and −291.6 ± 2.4 ‰ respectively, and a piggery sampled had δ13CCH4 and δDCH4 signatures of −47.5 ± 0.2 ‰ and −300.3 ± 1.8 ‰ respectively, which reflects emissions from animal waste. An abattoir had δ13CCH4 and δDCH4 signatures of −44.3 ± 0.3 ‰ and −315.0 ± 1.3 ‰ respectively. A plume from a waste-water treatment plant had δ13CCH4 and δDCH4 signatures of −47.6 ± 0.2 ‰ and −177.5 ± 1.4 ‰ respectively.last_img read more

Softball crowd sings national anthem unaccompanied

first_imgMay 28, 2018 /Sports News – National Softball crowd sings national anthem unaccompanied Beau Lund FacebookTwitterLinkedInEmailABCNews.com(FRESNO, Calif.) — Patriotism rang out during a high school softball tournament in California last Friday.Before Clovis High School faced off against Buchanan High School during the Central Section softball championship on May 25, the announcer said the national anthem would not be played.Typically, when there are several games in a row, the anthem is only played before the first game.But the crowd were having none of that.After the announcement was made, witnesses said many people booed and decided to take matters into their own hands.People in the crowd can be seen standing and singing “The Star-Spangled Banner” on their own.According to the Fresno Bee, when the song was done, the crowd erupted in applause.The game went on as planned after the patriotic interlude.The Central Section event coordinator, Bob Kayajanian, told the Fresno Bee not playing the anthem was a mistake.“We got caught [off-guard],” Kayajanian told the Fresno Bee. “Both the teams turned to face the field and they all started singing the national anthem. They started to play some music and the people took that as the national anthem and they all started singing, which I think is obviously a wonderful thing to show off their patriotism.”Kayajanian said the anthem will be played at every game now.Copyright © 2018, ABC Radio. All rights reserved.center_img Written bylast_img read more

Michael Sanders Named D2football.com Player of the Week

first_img Tags: Adams State Grizzlies/Dixie State Football/Michael Sanders/Rocky Mountain Athletic Conference Brad James FacebookTwitterLinkedInEmailST. GEORGE, Utah-Late Wednesday night, Dixie State quarterback Michael Sanders was named as the d2football.com national offensive player of the week for his exploits last Saturday in a 52-45 win over Colorado School of Mines.Sanders, a senior out of Phoenix, earned his second Rocky Mountain Athletic Conference Player of the Week Monday for going 31-48 for 553 yards and five touchdown passes with no interceptions in the upset win over the Top 10 Orediggers.Sanders completed passes to nine different receivers in the ballgame, including scoring strikes to three different receivers.This award is the Trailblazers’ first national award of the season and their first since 2015.Dixie State concludes the 2018 season at Alamosa, Colo. against the Adams State Grizzlies Saturday at 1:00 pm. Written by November 8, 2018 /Sports News – Local Michael Sanders Named D2football.com Player of the Weeklast_img read more

SUU Football Announces Media Availability Times For Big Sky Conference Media Day

first_img FacebookTwitterLinkedInEmailCEDAR CITY, Utah-Sunday and Monday as the Big Sky Football media days for 2019 commence at Spokane, Wash., Southern Utah University’s athletic department has revealed media availability times Monday for head coach Demario Warren, senior offensive lineman Zach Larsen and senior tailback Jay Green Jr.The two-day event will see Warren interviewed at 10:40 am MDT with Larsen and Green to address the media at 1:22 pm MDT.The Thunderbirds’ season commences August 31 at Las Vegas against the UNLV Rebels. Brad James Tags: Big Sky Conference media day/Demario Warren/Jay Green Jr./Las Vegas/SUU Football/UNLV Rebels/Zach Larsen Written by July 11, 2019 /Sports News – Local SUU Football Announces Media Availability Times For Big Sky Conference Media Daylast_img read more