A full list of publications can be found in the NIGL Annual Reports. This section
highlights some of our high-impact papers as they go to press. A full list of NERC staff publications and outputs can be found in the NERC Open Research Archive (NORA)
New paper discussing the Anthropocene – July 2014
We consider whether the Anthropocene is recorded in the isotope geochemistry of the atmosphere, sediments, plants and ice cores, and the time frame during which any changes are recorded, presenting examples from the literature. Carbon and nitrogen isotope ratios have become more depleted since the 19th century, with the rate of change accelerating after ∼AD 1950, linked to increased emissions from fossil fuel consumption and increased production of fertiliser. Lead isotope ratios demonstrate human pollution histories several millennia into the past, while sulphur isotopes can be used to trace the sources of acid rain.
Radioisotopes have been detectable across the planet since the 1950s because of atmospheric nuclear bomb tests and can be used as a stratigraphic marker. We find there is isotopic evidence of widespread human impact on the global environment, but different isotopes have registered changes at different times and at different rates.
Stratigraphical Basis for the Anthropocene – June 2014
Humankind has pervasively influenced the Earth’s atmosphere, biosphere, geosphere, hydrosphere and cryosphere, arguably to the point of fashioning a new geological epoch, the Anthropocene. To constrain the Anthropocene as a potential formal unit within the Geological Time Scale, a spectrum of indicators of anthropogenically-induced environmental change is considered, and shown as stratigraphical signals that may be used to characterize an Anthropocene unit, and to recognize its base. This volume describes a range of evidence that may help to define this potential new time unit and details key signatures that could be used in its definition. These signatures include lithostratigraphical (novel deposits, minerals and
mineral magnetism), biostratigraphical (macro- and micro-palaeontological successions and human-induced trace fossils) and chemostratigraphical(organic, inorganic and radiogenic signatures in deposits, speleothems and ice and volcanic eruptions). We include, finally, the suggestion that humans have created a further sphere, the technosphere, that drives global change.
C.N. Waters, J.A. Zalasiewicz, M. Williams, M.A. Ellis and A.M. Snelling. 2014. A Stratigraphical Basis for the Anthropocene. Special Publication 395. http://nora.nerc.ac.uk/506924/.
International Journal of Earth Sciences – May 2014
Lake Ohrid (Macedonia/Albania) is the oldest extant lake in Europe and exhibits an outstanding degree of endemic biodiversity. Here, we provide new high-resolution stable isotope and geochemical data from a 10 m core (Co1262) through the Late Glacial to Holocene and discuss past climate and lake hydrology (TIC, δ13Ccalcite, δ18Ocalcite) as well as the terrestrial and aquatic vegetation response to climate (TOC, TOC/N, δ13Corganic, Rock Eval pyrolysis). The data identifies 3 main zones: (1) the Late Glacial–Holocene transition represented by low TIC and TOC contents, (2) the early to mid-Holocene characterised by high TOC and increasing TOC/N and (3) the Late Holocene–Present which shows a marked decrease in TIC and TOC. In general, an overall trend of increasing δ18Ocalcite from 9 ka to present suggests progressive aridification through the Holocene, consistent with previous records from Lake Ohrid and the wider Mediterranean region. Several proxies show commensurate excursions that imply the impact of
short-term climate oscillations, such as the 8.2 ka event and the Little Ice Age. This is the best-dated and highest resolution archive of past Late Glacial and Holoce climate from Lake Ohrid and confirms the overriding influence of the North Atlantic in the north-eastern Mediterranean. The data presented set the context for the International Continental scientific Drilling Program Scientific Collaboration On Past Speciation Conditions in Lake Ohrid project cores recovered in spring–summer 2013, potentially dating back into the Lower Pleistocene, and will act as a recent calibration to reconstruct climate and hydrology over the entire lake history.
Lacey, J.H., Francke, A., Leng, M.J., Vane, C.H., Wagner, B. 2014. A high–resolution Late Glacial to Holocene record of environmental change in the Mediterranean from Lake Ohrid (Macedonia/Albania). International Journal of Earth Sciences. DOI 10.1007/s00531-014-1033-6.
The oxygen isotope composition of diatom silica (δ18Odiatom) is increasingly being used to reconstruct climate from marine and lacustrine sedimentary archives. Although diatoms are assumed to precipitate their frustule in isotopic equilibrium with their surrounding water, it is unclear whether internal processes of a given species affect the fractionation of oxygen between the water and the diatom. We present δ18Odiatom data from two diatom size fractions (3–38 and >38μm) characterized by different species in a sediment core from Heart Lake, Alaska. Differences in δ18Odiatom between the two size fractions varies from 0 to 1.2‰, with a mean offset of 0.01‰ (n=20). Fourier transform infrared spectroscopy confirms our samples consist of pure biogenic silica (SiO2) and δ18Odiatom trends are not driven by contamination. The maximum offset is outside the range of error, but the mean is within analytical error of the
technique (±1.06‰), demonstrating no discernible species-dependent fractionation in δ18Odiatom. We conclude that lacustrine δ18Odiatom measurements offer a reliable and valuable method for reconstructing δ18Owater. Considering the presence of small offsets in our two records, we advise interpreting shifts in δ18Odiatom only where the magnitude of change is greater than the combined analytical error.
Bailey, Hannah L.; Henderson, Andrew C.G.; Sloane, Hilary J.; Snelling, Andrea; Leng, Melanie J.; Kaufman, Darrell S. 2014. The effect of species on lacustrine δ18Odiatom and its implications for palaeoenvironmental reconstructions. Journal of Quaternary Science, 29 (4). 393-400.
The Scientific Collaboration on Past Speciation Conditions in Lake Ohrid (SCOPSCO) project is an international research initiative to study the influence of major geological and environmental events on the biological evolution of lake taxa. SCOPSCO drilling campaigns were carried out in 2011 and 2013. In 2011 we used gravity and piston coring at one of the five proposed drill sites, and in 2013 we undertook deep drilling with the Deep Lake Drilling System (DLDS) of Drilling, Observation and Sampling of the Earth's Continental Crust (DOSECC). In April and May 2013, a total of 2100 m sediments were recovered from four drill sites with water depths ranging from 125 to 260 m. The maximum drill depth was 569 m below the lake floor in the centre of the lake. By retrieving overlapping sediment sequences, 95% of the sediment succession was recovered. Initial data from borehole logging, core logging and geochemical measurements indicate that the sediment
succession covers >1.2 million years (Ma) in a quasi-continuous sequence. These early findings suggest that the record from Lake Ohrid will substantially improve the knowledge of long-term environmental change and short-term geological events in the northeastern Mediterranean region, which forms the basis for improving understanding of the influence of major geological and environmental events on the biological evolution of endemic species.
Wagner, B., Wilke, T., Krastel, S., Zanchetta, G., Sulpizio, R., Reicherter, K., Leng, M., Grazhdani, A., Trajanovski, S., Francke A., Lindhorst, K., Cvetkoska, A., Reed, J.M., Zhang, X., Lacey, J.H., Wonik, T., Baumgarten, H., Vogel, H. 2014. The SCOPSCO drilling project recovers more than 1.2 million years of history from Lake Ohrid. Scientific Drilling, 17, 19-29.
The transboundary Lake Prespa (Albania/former Yugoslav Republic of Macedonia/Greece) has been recognized as a conservation priority wetland. The high biodiversity encountered in the catchment at present points to the refugial character of this mountainous region in the southwestern Balkans. A lake sediment core retrieved from a coring location in the northern part of the lake was investigated through sedimentological, geochemical, and palynological analyses. Based on tephrochronology, radiocarbon and electron spin resonance (ESR) dating, and cross correlation with other Northern Hemisphere records, the age model suggests that the basal part of core Co1215 reaches back to 92 ka cal BP. Here we present the responses of this mid-altitude site (849 m a.s.l.) to climate oscillations during this interval and assess its sensitivity to millennial-scale variability. Endogenic calcite precipitation occurred in marine isotope stages (MIS) 5 and 1 and is synchronous with periods of increased primary production (terrestrial and/or lacustrine). Periods of pronounced phytoplankton blooms (inferred from green algae and dinoflagellate concentrations) are recorded in MIS 5 and MIS 1 and
suggest that the trophic state and lake levels underwent substantial fluctuations. Three major phases of vegetation development are distinguished: the forested phases of MIS 5 and MIS 1 dominated by deciduous trees with higher temperatures and moisture availability, the open landscapes of MIS 3 with significant presence of temperate trees, and the pine-dominated open landscapes of MIS 4 and MIS 2 with lower temperatures and moisture availability. Our findings suggest significant changes in forest cover and landscape openness, as well as in the properties of the vegetation belts (composition and distribution) over the period examined. The study area most likely formed the upper limit of several drought-sensitive trees (temperate tree refugium) at these latitudes in the Mediterranean mountains.
Panagiotopoulos, K., Böhm, A., Leng, M.J., Wagner, B., Schäbitz, F. 2014. Climate variability over the last 92Ka in SW Balkans from analysis of sediments from Lake Prespa. Climate of the Past, 10, 643-660.
Two sets of well-preserved human footprints have been found in tufa sediments in the Cuatrociénegas Basin, NE Mexico, and here we present their U-series dates of 10.55 ± 0.03 ka and 7.24 ± 0.13 ka. The former are the oldest known footprints in Mexico, although their exact location is unknown, the latter form part of a trackway with eleven in situ human footprints. Oxygen (and to a lesser extent) carbon isotope data from the sediments suggest that the tufa with in situ footprints formed during a transition to a wetter (less arid) period, while pollen evidence indicates the basin floor presence of pecan (Carya) and willow (Salix sp.) before the onset of regional Chihuahuan Desert aridity.
These footprints confirm the presence of humans, possibly nomadic hunter–gatherer groups, which persisted until the 18th Century AD.
Feldstead, N.J., Gonzalez, S., Huddart, D., Noble, S.R., Hoffmann, D.L., Metcalfe, S.E., Leng, M.J., Albert, B.M., Pike, A.W.G., Gonzalez-Gonzalez, A., Jimenez-Lopez, J, C. 2014. Holocene-aged human footprints from the Cuatrocienegas Basin, NE Mexico. Journal of Archaeological Sciences, 42, 250-259.
Deep-water mudstones from ancient epicontinental settings are significant repositories for organic matter, but the detailed temporal variations of, and controls on, the abundance and type of organic matter (OM) is little studied. Using micro-petrographic and geochemical data from late Mississippian mudstones of the Widmerpool Gulf, UK, the processes that delivered fine-grained sediment to this basin during a glacioeustatic sea-level cycle are interpreted from detailed lithofacies analysis. Seven primary lithofacies are identified from core, which show specific and systematic variations in total organic carbon (TOC) content and bulk carbon isotope composition of organic material (δ13Corg). During sea-level highstands, thin-bedded carbonate-bearing mudstones are the dominant facies deposited, contain up to 6.6% TOC (average 4.6±1.3%), and have mean δ13Corg of &nda28.5±0.9‰. During phases of lower sea level, thin-bedded silt-bearing clay-rich mudstones with up to 4.1% TOC (average 2.3±0.8%; mean δ13Corg: –28.2±1.0‰) were interbedded with more organic-lean graded silt-bearing mudstones and sand-bearing silt-rich mudstones (average TOC: 1.7±0.6%) derived from turbidity currents. The latter (mean δ13Corg: –26.2±0.7‰) are closely linked to significant proportions of terrestrial plant material, while some rare plant debris- and sand-bearing mudstones produced from debris flows have more than 7.0% TOC and δ≥–26.0‰.
The δ13C values of wood fragments ranged from –27.1‰ to –24.0‰ and therefore the δ13Corg is interpreted as a function of the ratio of marine and terrestrial organic matter. More negative values in the carbonate-bearing and the clay-rich mudstones indicate marine planktonic algae whereas the least negative values reflect greater contribution of terrestrial plant material. The data suggest that the marine conditions prevailed and supported marine planktonic algae throughout different sea-level stages. Marine OM was delivered to the sea floor by continuous hemipelagic settling whereas terrestrial OM was delivered by sediment density flows. Variations in bioproductivity and dilution by siliciclastics influenced the burial rate of marine OM. Organic-rich mudstones preserved in these marine basins are potential hydrocarbon source rocks, especially as unconventional (shale gas) reservoirs. Detailed microtextural and compositional analysis coupled with rigorous geochemical parameters as used in this study are important for the understanding of the source-rock potential of basinal mudstones, and of fine-grained organic-rich sediments in general.
Konitzer, S.F., Davies, S.J., Stephensin, M.H., Leng, M.J. 2014. Depositional Controls On Mudstone Lithofacies In A Basinal Setting: Implications for the Delivery of Sedimentary Organic Matter. Journal of Sedimentary Research, 84, 198-214.
The 74 (75) ka Toba eruption in Sumatra, Indonesia, is considered to be one of the largest volcanic events during the Quaternary. Tephra from the Toba eruption has been found in many terrestrial and marine sedimentary deposits, and acidity peaks related to the eruption have been used to synchronize ice core records from Greenland and Antarctica. Seismic profiles and sedimentological data from Lake Prespa on the Balkan Peninsula, SE Europe, indicate a lake level lowstand at 73.6 ± 7.7 ka based on ESR dating of shells. Tephrostratigraphy, radiocarbon dating and tuning of the total organic carbon content with the NGRIP isotope record, corroborate that the lake level lowstand was a short-term event superimposed on the general cooling trend at the end of MIS 5, most likely at the onset of the Greenland Stadial GS-20. Acknowledging that tectonic events or karst
processes could have triggered this lake level lowstand, the chronological correspondence between the lowstand and the Toba eruption is intriguing. Therefore a Toba-driven short-term shift to aridity in the Balkan region, leading to lake level changes and triggering spatial expansion events in one of the lake's most abundant benthic species, the carino mussel Dreissena presbensis, cannot be excluded.
Citation: Wagner, B., Leng, M. J., Wilke, T., Böhm, A., Panagiotopoulos, K., Vogel, H., Lacey, J. H., Zanchetta, G., and Sulpizio, R.: Distinct lake level lowstand in Lake Prespa (SE Europe) at the time of the 74 (75) ka Toba eruption, Clim. Past, 10, 261-267, doi:10.5194/cp-10-261-2014, 2014.
Iron (Fe) oxidizing bacteria have the potential to produce morphologically unique structures that may be used as biosignatures in geological deposits. One particular example is Mariprofundus ferrooxydans, which produces extracellular twisted ribbon-like stalks consisting of ferrihydrite, co-located with organic and inorganic elements. It is currently thought that M. ferrooxydans excrete and co-precipitate polysaccharides and Fe simultaneously, however the cellular production of these polysaccharides has yet to be confirmed. Here, we report on a time series study that used scanning
transmission X-ray microscopy (STXM) and C 1s and Ca 2p near-edge X-ray adsorption fine structure (NEXAFS) spectroscopy to investigate production of polysaccharides over the growth cycle of M. ferrooxydans.
Sarah A. Bennett, Brandy M. Toner, Roman Barco and Katrina J. Edwards. 2014. Carbon adsorption by Fe oxyhydroxide stalks produced by a lithotrophic iron-oxidizing bacteria. Geobiology DOI:10.1111/gbi.12074
The Limfjord region of northern Jutland, Denmark, supports a rich archaeological record dating back to the Mesolithic, which documents long-term change in human practices and utilisation of marine resources since approximately 7500 BP. The presence and availability of marine resources in the Limfjord is sensitively regulated by environmental parameters such as salinity, sedimentary regime, nutrient status and primary productivity, but long-term changes in these parameters are currently poorly understood. In this study a multiproxy approach (including sedimentary parameters, diatoms, molluscs, foraminifera, sedimentary pigments, C and O stable isotopes and plant macrofossils) has been adopted to assess environmental change over the period ca 7500–1500 cal yrs BP at Kilen, a coastal fjord (before AD 1856) situated in the Western Limfjord. A diatom-based salinity transfer function based on a pan-Baltic training set has been applied to the fossil diatom dataset for quantitative assessment of salinity change over the study period. This study demonstrates that large-scale shifts in salinity are a common feature of the Limfjord's long-term history and are driven by the level of connection with the North Sea and the Skagerrak respectively,
which in turn is likely driven by the complex interplay between climate, sea-level change, current velocity and rates of erosion/sedimentary accretion. Three shifts in state at Kilen are identified over the study period: a deep, periodically stratified fjord with medium–high salinity (and high productivity) between ca 7500–5000 BP, followed by a gradual transition to a shallow benthic system with more oceanic conditions (i.e. higher salinity, lower productivity, slower sedimentary accumulation rate and poorer fossil preservation) after ca 5000 BP and no stratification after ca 4400 BP, and lastly, within this shallow phase, an abrupt shift to brackish conditions around 2000 BP. Environmental–societal interactions are discussed on the basis of the data presented in this study and current environmental hypotheses for cultural change are challenged.
Jonathan P. Lewis, David B. Ryves, Peter Rasmussen Karen L. Knudsen, Kaj S. Petersen, Jesper Olsen, Melanie J. Leng, Peter Kristensen, Suzanne McGowan, Bente Philippsen. 2013. Environmental change in the Limfjord, Denmark (ca 7500–1500 cal yrs BP): a multiproxy study. Quaternary Science Reviews, 78, 126–140.
The Mg/Ca, Sr/Ca, δ18O and δ13C compositions are given for well-preserved specimens of ten belemnite species/genera from three stratigraphic intervals. The data help assess the use of these proxies for palaeo-oceanography. Samples are from Dorset, UK (Pliensbachian; 5 species); Cambridgeshire, UK (Callovian; 1 species); and the Vocontian Basin, SE France (Valanginian; 4 genera). In none of these belemnite populations (at species or genera level) does Mg/Ca correlate with δ18O. Neither do values of δ18O correlate with Mg/Ca along a microsampled radial profile across a single specimen of
Cylindroteuthis puzosiana (Callovian). The use of Mg/Ca is therefore considered to be unreliable as a palaeo-temperature indicator for these belemnite species and genera.
Q. Li, J.M. McArthur, P. Doyle, N. Janssen, M.J. Leng, W. Müller, S. Reboulet. 2013. Evaluating Mg/Ca in belemnite calcite as a palaeo-proxy. Palaeogeography, Palaeoclimatology, Palaeoecology, 388, 98-108.
Proceedings of the National Academy of Sciences – July 2013
The spread of farming from western Asia to Europe had profound long-term social and ecological impacts, but identification of the specific nature of Neolithic land management practices and the dietary contribution of early crops has been problematic. Here, we present previously undescribed stable isotope determinations of charred cereals and pulses from 13 Neolithic sites across Europe (dating ca. 5900–2400 cal B.C.), which show that early farmers used livestock manure and water management to enhance crop yields. Intensive manuring inextricably linked plant cultivation and animal herding and contributed to the remarkable resilience of these combined practices across diverse climatic zones. Critically, our findings suggest that commonly
applied paleodietary interpretations of human and herbivore δ15N values have systematically underestimated the contribution of crop-derived protein to early farmer diets.
Amy Bogaard, Rebecca Fraser, Tim H. E. Heaton, Michael Wallace, Petra Vaiglova, Michael Charles, Glynis Jones, Richard P. Evershed, Amy K. Styring, Niels H. Andersen, Rose-Marie Arbogast, László Bartosiewicz, Armelle Gardeisen, Marie Kanstrup, Ursula Maier, Elena Marinova, Lazar Ninov, Marguerita Schäfer, and Elisabeth Stephan. 2013. Crop manuring and intensive land management by Europe’s first farmers. PNAS doi: 10.1073/pnas.1305918110.
Global and Planetary Change – July 2013
Long (multi-millennial), continuous lake pollen records have provided insights into terrestrial ecosystem responses to orbital- and sub-orbital-scale climate forcing. By comparison, the potential of diatoms and stable isotopes to provide additional insights into limnetic response over comparable timescales has not been explored to the same extent, particularly in the Mediterranean region, even though such proxies are known to respond sensitively and rapidly to environmental change. Here we present a 19,000-year multiproxy record of limnetic change in the Ioannina basin, NW Greece, spanning the penultimate interglacial–glacial transition and the early penultimate glacial (c. 189–170 ka BP). The diatom record, the first from this interval in Southern Europe, reveals that lake conditions changed in concert with muted millennial-scale climate oscillations thought to originate in the North Atlantic, demonstrating clearly the sensitivity of diatoms to sub-orbital climate variability. Diatom and isotope-inferred changes in lake conditions coincided with the MIS 7/6 transition, whilst the new δ18O record suggests
increased moisture availability in SE Europe during MIS 6.5, adding support for a Mediterranean-wide increase in precipitation. Comparison with pollen data from the same sequence demonstrates that lake and terrestrial ecosystems co-varied, with no delay in forest expansion in response to climate change during this interval. Substantial changes in lake conditions contrast with subdued changes in catchment vegetation during an 8000 year-long cold interval in the early penultimate glacial. This may reflect differences in limnetic and terrestrial thresholds of response to environmental change, and perhaps also the influence of site specific factors in modulating terrestrial ecosystem response.
Wilson, Graham, Frogley, M., Roucoux, K., Jones, T., Leng, M., Lawson, I. and Hughes, P. (2013) Limnetic and terrestrial responses to climate change during the onset of the penultimate glacial stage in NW Greece. Global and Planetary Change, 107. pp. 213-225.
Journal of Paleolimnology – May 2013
Isotope geochemistry is an essential part of environmental and climate change research and over the last few decades has contributed significantly to our understanding of a huge array of environmental problems, not least in palaeolimnology and limnogeology. Here we describe some of the recent developments in the use of stable isotopes in palaeo-lake research. These are: better preparation, analysis, and interpretation of biogenic silica oxygen and silicon isotopes; extraction and characterisation of specific compounds such as leaf waxes and algal lipids for isotope analysis; determining the excess of 13C-18O bonds in
clumped isotopes; and the measurement of multiple isotope ratios in chironomid chitin. These advances have exciting prospects and it will be interesting to see how these techniques develop further and consequently offer a real advancement in our science over the next decade.
Leng, M.J. and Henderson, A.C.G. 2013. Recent advances in isotopes as palaeolimnological proxies. Journal of Paleolimnology, 49, 481-496.
Encyclopedia of Quaternary Science, 2nd Edition – April 2013
The second revised edition of the Encyclopedia of Quaternary Science, provides both students and professionals with an up-to-date reference work on this important and highly varied area of research. There are lots of new articles, and many of the articles that appeared in the first edition have been updated to reflect advances in knowledge since 2006, when the original articles were written.
Leng, M.J., Barker, P.A., Swann, G.E.A., Snelling, A.M. 2013. δ18O Records. In: Elias, S.A. (ed). The Encyclopedia of Quaternary Science, vol. 1, pp.481-488. Amsterdam: Elsevier.
Paleoceanography – April 2013
The development of a permanent, stable ice sheet in East Antarctica happened during the middle Miocene, about 14 million years (Myr) ago. The middle Miocene therefore represents one of the distinct phases of rapid change in the transition from the “greenhouse” of the early Eocene to the “icehouse” of the present day. Carbonate carbon isotope records of the period immediately following the main stage of ice sheet development reveal a major perturbation in the carbon system, represented by the positive δ13C excursion known as carbon maximum 6 (“CM6”), which has traditionally been interpreted as reflecting increased burial of organic matter and atmospheric pCO2 drawdown. More recently, it has been suggested that the δ13C excursion records a negative feedback resulting from the reduction of silicate weathering and an increase in atmospheric pCO2.
Here we present high-resolution multi-proxy (alkenone carbon and foraminiferal boron isotope) records of atmospheric carbon dioxide and sea surface temperature across CM6. Similar to previously published records spanning this interval, our records document a world of generally low (~300 ppm) atmospheric pCO2 at a time generally accepted to be much warmer than today. Crucially, they also reveal a pCO2 decrease with associated cooling, which demonstrates that the carbon burial hypothesis for CM6 is feasible and could have acted as a positive feedback on global cooling.
Badger M, Lear C, Pancost R, Foster G, Bailey T, Leng M, Abels H. 2013. CO2 drawdown following the middle Miocene expansion of the Antarctic Ice Sheet. Paleoceanography 28, 42–53.
Over the past 50 years, warming of the Antarctic Peninsula has been accompanied by accelerating glacier mass loss and the retreat and collapse of ice shelves. A key driver of ice loss is summer melting; however, it is not usually possible to specifically reconstruct the summer conditions that are critical for determining ice melt in Antarctic. Here we reconstruct changes in ice-melt intensity and mean temperature on the northern Antarctic Peninsula since AD 1000 based on the identification of visible melt layers in the James Ross Island ice core and local mean annual temperature estimates from the deuterium content of the ice. During the past millennium, the coolest conditions and lowest melt occurred from about AD 1410 to 1460, when mean temperature was 1.6°C lower than that of 1981–2000. Since the late 1400s, there has been a nearly tenfold increase in melt intensity from 0.5 to 4.9%.
The warming has occurred in progressive phases since about AD 1460, but intensification of melt is nonlinear, and has largely occurred since the mid-twentieth century. Summer melting is now at a level that is unprecedented over the past 1,000 years. We conclude that ice on the Antarctic Peninsula is now particularly susceptible to rapid increases in melting and loss in response to relatively small increases in mean temperature.
Nerilie J. Abram, Robert Mulvaney, Eric W. Wolff, Jack Triest, Sepp Kipfstuhl, Luke D. Trusel, Françoise Vimeux, Louise Fleet & Carol Arrowsmith. 2013. Acceleration of snow melt in an Antarctic Peninsula ice core during the twentieth century. Nature Geoscience. Online.
The Antarctic Peninsula is one of the fastest-warming regions on Earth, but its palaeoenvironmental history south of 63° latitude is relatively poorly documented, relying principally on the marine geological record and short ice cores. In this paper, we present evidence of late-Quaternary environmental change from the Marguerite Bay region combining data from lake sediment records on Horseshoe Island and Pourquoi-Pas Island, and raised beaches at Horseshoe Island, Pourquoi-Pas Island and Calmette Bay. Lake sediments were radiocarbon dated and analysed using a combination of sedimentological, geochemical and microfossil methods. Raised beaches were surveyed and analysed for changes in clast composition, size and roundness. Results suggest a non-erosive glacial regime could have existed on Horseshoe Island from 35,780 (38,650–33,380) or 32,910 (34,630–31,370) cal yr BP onwards.
There is radiocarbon and macrofossil evidence for possible local deglaciation events at 28,830 (29,370–28,320) cal yr BP, immediately post-dating Antarctic Isotopic Maximum 4, and 21,110 (21,510–20,730 interpolated) cal yr BP coinciding with, or immediately post-dating, Antarctic Isotopic Maximum 2. The Holocene deglaciation of Horseshoe Island commenced from 10,610 (11,000–10,300) cal yr BP at the same time as the early Holocene temperature maximum recorded in Antarctic ice cores.
Late Quaternary environmental changes in Marguerite Bay, Antarctic Peninsula,inferred from lake sediments and raised beaches. (2013) Dominic A. Hodgson; Stephen J. Roberts; James A. Smith; Elie Verleyen; Mieke Sterken; Minke Labarqueb; Koen Sabbe; Wim Vyverman; Claire S. Allen; Melanie J. Leng; Charlotte Bryant. Quaternary Science Reviews 68: 216–236.
Journal of Climate “ The Freshwater System West of the Antarctic Peninsula ” – April 2013
Climate change west of the Antarctic Peninsula is the most rapid of anywhere in the Southern Hemisphere, with associated changes in the rates and distributions of freshwater inputs to the ocean. Here, results from the first comprehensive survey of oxygen isotopes in seawater in this region are used to quantify spatial patterns of meteoric water (glacial discharge and precipitation) separately from sea ice melt. High levels of meteoric water are found close to the coast, due to orographic effects on precipitation and strong glacial discharge. Concentrations decrease offshore, driving significant southward geostrophic flows (up to ~30 cm s−1).
These produce high meteoric water concentrations at the southern end of the sampling grid, where collapse of the Wilkins Ice Shelf may also have contributed. As the regional freshwater system evolves, the continuing isotope monitoring described here will elucidate the ongoing impacts on climate and the ecosystem.
Michael P. Meredith, Hugh J. Venables, and Andrew Clarke, Hugh W. Ducklow and Matthew Erickson, Melanie J. Leng, Jan T. M. Lenaerts and Michiel R. van den Broek. 2013. The Freshwater System West of the Antarctic Peninsula: Spatial and Temporal Changes. Journal of Climate, 26, p. 1669-1684.
Special issue of the journal “Quaternary Science Reviews: Isotopes and Lakes” edited by Prof Melanie Leng – March 2013
Isotope geochemistry is increasingly an essential part of environmental and climate change research and now routinely contributes to our understanding of many critical environmental problems, which span the whole of Earth system science and not least in palaeolimnology and limnogeology. The International Association of Limnogeology organises an international conference every four years. The fifth International Limnogeology Congress, ILIC V, was held in Konstanz, Germany, from August 31st - September 3rd, 2011. During this congress we identified several papers where isotope methodologies were used in a particularly novel way, or provided an ‘added value’ data set.
Many of these are brought together in this volume as a series of state-of-the-art papers dealing with various aspects of isotopes in lake sediment archives. These papers are themed under isotopes in contemporary processes, isotopes in diatom silica from lake sediments, isotopes in organic materials in lake sediments, and isotopes in carbonates from lake sediments. The journal editors of this volume are Prof Melanie J. Leng (British Geological Survey and University of Leicester), Prof Phillip A. Barker (Lancaster University) and Prof Antje Schwalb (Universität Braunschweig,Germany).
The Early Jurassic Epoch was a predominantly greenhouse phase of Earth history, but a comprehensive understanding of its climate dynamics is hampered by a lack of high resolution multi-proxy environmental records. Here we report a geologically brief (approximately several hundred thousand years) negative carbon isotope excursion in both marine and terrestrial materials, recognised for the first time for the Late Sinemurian Substage (Early Jurassic, ~194 Ma) of eastern England. The Late Sinemurian carbon isotope excursion,
which is termed the S-CIE, is accompanied by peaks in the abundance of various pollen grains...
Riding, J.B., Leng, M.J., Kender, S., Hasselbo, S.P., Feist-Burkhardt, S. 2013. Isotopic and palynological evidence for a new Early Jurassic environmental perturbation. Palaeogeography, Palaeoclimatology, Palaeoecology, 374, 16-27.
The current issue of Elements Magazine is entitled ‘100 years of Isotope Geochronology’ and is co-edited by Dr Dan Condon (NIGL) and includes a several papers co-authored by Dan Condon and Matt Horstwood.
Earth and Planetary Science Letters – January 2013
Understanding the response of the Antarctic ice sheets during the rapid climatic change that accompanied the last deglaciation has implications for establishing the susceptibility of these regions to future 21st Century warming. A unique diatom δ18O record derived from a high-resolution deglacial seasonally laminated core section off the west Antarctica Peninsula is presented. By extracting and analysing single species samples from individual laminae, season-specific isotope records were separately generated to show
changes in glacial discharge (comprised of both glacial and iceberg sourced meltwater) to the coastal margin during spring and summer months...
Swann, G.E.A., Pike, J., Snelling, A.M., Leng, M.J., Williams, M.C. 2013. Seasonally resolved diatom δ18O records from the West Antarctica Peneinsula over the last deglaciation. Earth and Planetary Science Letters, 364, 12-23.
This paper describes a multi-proxy palaeoecological investigation of lake sediments undertaken in conjunction with an archaeological survey of the Upper Sangro Valley in the Abruzzo National Park, Central Italy. The data show how cultural factors had a profound effect on this mountainous region which, in this case, outweighed the effects of climatic fluctuations which are known to have occurred locally and across the wider region. These findings have positive implications for the
conservation of top predators which require large wooded ranges.
Brown, A.G., Hatton, J., Selby, K.A., Leng, M.J., Christie, N. 2013. Multi-proxy study of Holocene environmental change and human activity in the Central Apennine Mountains, Italy. Journal of Quaternary Science, 28, 71-82.
The Antarctic Peninsula Ice Sheet is the most northerly of the Antarctic ice sheets and the most vulnerable to climate warming. In light of recent instrumental records of warming along the Antarctic Peninsula, there has been much debate about what has influenced rising temperatures along the west Antarctica Peninsula (WAP) during the Holocene, with terrestrial and oceanic proxies often suggesting different, sometimes opposing, mean conditions. Here, we present a Holocene glacial (terrestrial ice) melt water record derived from marine δ18Odiatom from Palmer Deep, west Antarctic Peninsula. Our results provide a unique opportunity to assess atmospheric versus oceanic influence on melting along the WAP. We demonstrate that since approximately 5.0 ka the increasing occurrence of La Niña, as recorded in the lower latitude Pacific, and increasing summer insolation at 60ºS have had a stronger influence on glacial melt water inflow to the WAP margin than oceanic processes driven by the southern westerly winds.
Pike, J., Swann, G.A.E., Leng, M.J., Snelling, A. 2013. Glacial discharge along the west Antarctic Penninsula during the Holocene. Nature Geoscience. Online.
The late Mesoproterozoic Sveconorwegian orogen in southwest Baltica is traditionally interpreted as the eastward continuation of the Grenville orogen in Canada, resulting from collision with Amazonia, forming a central part in the assembly of the Rodinia supercontinent. We challenge this conventional view based on results from recent work in southwest Norway demonstrating voluminous subduction–related magmatism in the period 1050–1020 Ma, followed by geographically restricted high–T/medium–P metamorphism between 1035 and 970 Ma, succeeded by ferroan magmatism over large parts of south Norway in the period 990–920 Ma.
This magmatic and metamorphic evolution may be better understood as reflecting a long–lived accretionary margin, undergoing periodic compression and extension, than continent–continent collision. This study has implications for Grenville–Sveconorwegian correlations, comparisons with modern continental margins, Rodinia reconstructions and how we recognize geodynamic settings in ancient orogens.
Slagstad, T., Roberts, N.M.W., Marker, M., Røhr, T., Schiellerup, H. 2013. A Non-Collisional, Accretionary Sveconorwegian Orogen. Terra Nova 25, 30-37.
Precambrian Research – January 2013
We present a study of the position, nature and geochronology of the eastern margin of the Tanzania Craton near Mpwapwa, which yields new constraints on Archaean to Neoproterozoic orogenesis of central Tanzania. The eastern margin of the Tanzania Craton is a ca. 1960 Ma top-to-the-NW ductile thrust zone. Orthogneisses of the eastern part of craton were dated by U–Pb zircon at ca. 2.7 Ga. High grade paragneisses to the east (Mpwapwa Group) are also Archaean (>ca. 2.6 Ga) and thus do not belong to the Usagaran belt, but to the “Western Granulite” of the East African Orogen. Charnockites in the south have been dated at 2701 ±
21 Ma and point to a third Archaean assemblage. A post-Usagaran granite dated at 1873 ± 31 Ma shows Neoproterozoic metamorphic zircon rims that grew during the East African orogenic event.
A sliver of southern tonalitic orthogneiss, entrained in the craton margin shear zone, is an igneous rock of probable early Palaeoproterozoic or Archaean age (>ca. 2300 Ma) with a strong metamorphic overprint at ca. 1960 Ma (zircon), confirmed by a metamorphic titanite age of ca. 1990 Ma, this is believed to date the initial phase of craton-margin shearing and juxtaposition of the Archaean crustal blocks.
Thomas, R.J., Roberts, N.M.W., Jacobs, J., Bushi, A.M., Horstwood, M.S.A., Mruma, A. 2013. Structural and geochronological constraints on the evolution of the eastern margin of the Tanzania Craton in the Mpwapwa area, central Tanzania. Precambrian Research 224, 671-689.