During the later part of the last century there was rapid development of the study and understanding of the changing environments of the last 2 million years. This came to provide a firm background ...for todays knowledge of the significance and importance of climatic change. Interdisciplinary research has been a prominent, if not essential, contributor to the successes achieved. In illustration of this connection, this volume describes here such developments in the University of Cambridge. In 1948 the University established a Subdepartment of Quaternary Research, with teaching and research activities covering geological, biological and archaeological topics. An interdisciplinary approach was an essential ingredient, and the research covered both terrestrial and marine spheres. The book traces the history of Quaternary research in Britain and Ireland, particularly the continental influences which stimulated research and indeed led to the establishment of the Subdepartment.The early years of the Subdepartment were an exceptionally exciting time for Quaternary researchers. This period saw the development of radiocarbon dating and of marine geochemical studies, together with the improvement of interpretation of palaeobotanical data, and the consequent incorporation of a vast accession of new information relating to these subjects. Stratigraphy, the binding topic of Quaternary research, became much better understood: first, in the terrestrial sphere with the formulation of divisions of the Quaternary based on accepted geological principles and providing a measure of the passage of time to students of the several disciplines involved, including landscape history, ecosystem history and archaeology, and secondly in the marine sphere a formulation of units defined by isotope studies.The organisation of the Subdepartment and the problems of developing
interdisciplinary science are considered. An important aspect is the variety of staff and students involved in interdisciplinary research and teaching. In order to give a complete an account as possible of the activities of the Subdepartment, a listing of staff and students and their interests is compiled, which I think is necessary to give a rounded view of the Subdepartment as a whole.Research topics and their development are considered one-by-one, and the numbers of publications in each sphere are summarised over the life of the Subdepartment, giving a clear view of how research developed over the period of 45 years. These activities were brought to an end in 1994, with the dissolution of the Subdepartment, which is described, together with a discussion of achievements and the voicing of some reflections.In a final part, I take a wider view of the history of Quaternary research, with aspects of geology and biology considered, together with notes on the Quaternary community, research support and journals.
The North American Ice Sheet Complex (NAISC; consisting of the Laurentide, Cordilleran and Innuitian ice sheets) was the largest ice mass to repeatedly grow and decay in the Northern Hemisphere ...during the Quaternary. Understanding its pattern of retreat following the Last Glacial Maximum is critical for studying many facets of the Late Quaternary, including ice sheet behaviour, the evolution of Holocene landscapes, sea level, atmospheric circulation, and the peopling of the Americas. Currently, the most up-to-date and authoritative margin chronology for the entire ice sheet complex is featured in two publications (Geological Survey of Canada Open File 1574 Dyke et al., 2003; ‘Quaternary Glaciations – Extent and Chronology, Part II’ Dyke, 2004). These often-cited datasets track ice margin recession in 36 time slices spanning 18 ka to 1 ka (all ages in uncalibrated radiocarbon years) using a combination of geomorphology, stratigraphy and radiocarbon dating. However, by virtue of being over 15 years old, the ice margin chronology requires updating to reflect new work and important revisions. This paper updates the aforementioned 36 ice margin maps to reflect new data from regional studies. We also update the original radiocarbon dataset from the 2003/2004 papers with 1541 new ages to reflect work up to and including 2018. A major revision is made to the 18 ka ice margin, where Banks and Eglinton islands (once considered to be glacial refugia) are now shown to be fully glaciated. Our updated 18 ka ice sheet increased in areal extent from 17.81 to 18.37 million km2, which is an increase of 3.1% in spatial coverage of the NAISC at that time. Elsewhere, we also summarize, region-by-region, significant changes to the deglaciation sequence. This paper integrates new information provided by regional experts and radiocarbon data into the deglaciation sequence while maintaining consistency with the original ice margin positions of Dyke et al. (2003) and Dyke (2004) where new information is lacking; this is a pragmatic solution to satisfy the needs of a Quaternary research community that requires up-to-date knowledge of the pattern of ice margin recession of what was once the world’s largest ice mass. The 36 updated isochrones are available in PDF and shapefile format, together with a spreadsheet of the expanded radiocarbon dataset (n = 5195 ages) and estimates of uncertainty for each interval.
•Updated deglaciation sequence using regional studies/expertise and radiocarbon data.•Region-by-region overview of significant ice margin changes from 18 ka to 1 ka.•New 18 ka 14C (∼21.7 ka cal.) ice sheet is 3.1% larger than previous estimates.•36 updated isochrones (PDFs/shapefiles) and radiocarbon dataset (n = 5195 ages).•Ice margins of Dyke et al. (2003) retained where new information is lacking.
Polymeric materials containing quaternary ammonium and/or phosphonium salts have been extensively studied and applied to a variety of antimicrobial-relevant areas. With various architectures, ...polymeric quaternary ammonium/phosphonium salts were prepared using different approaches, exhibiting different antimicrobial activities and potential applications. This review focuses on the state of the art of antimicrobial polymers with quaternary ammonium/phosphonium salts. In particular, it discusses the structure and synthesis method, mechanisms of antimicrobial action, and the comparison of antimicrobial performance between these two kinds of polymers.
Continental-scale estimates of vegetation cover, including land-surface properties and biogeographic trends, reflect the response of plant species to climate change over the past millennia. These ...estimates can help assess the effectiveness of simulations of climate change using forward and inverse modelling approaches. With the advent of transient and contiguous time-slice palaeoclimate simulations, vegetation datasets with similar temporal qualities are desirable. We collated fossil pollen records for the period 21,000–0 cal yr BP (kyr cal BP; calibrated ages) for Europe and Asia north of 40°N, using extant databases and new data; we filtered records for adequate dating and sorted the nomenclature to conform to a consistent yet extensive taxon list. From this database we extracted pollen spectra representing 1000-year time-slices from 21 kyr cal BP to present and used the biomization approach to define the most likely vegetation biome represented. Biomes were mapped for the 22 time slices, and key plant functional types (PFTs, the constituents of the biomes) were tracked though time. An error matrix and index of topographic complexity clearly showed that the accuracy of pollen-based biome assignments (when compared with modern vegetation) was negatively correlated with topographic complexity, but modern vegetation was nevertheless effectively mapped by the pollen, despite moderate levels of misclassification for most biomes. The pattern at 21 ka is of herb-dominated biomes across the whole region. From the onset of deglaciation (17–18 kyr cal BP), some sites in Europe record forest biomes, particularly the south, and the proportion of forest biomes gradually increases with time through 14 kyr cal BP. During the same period, forest biomes and steppe or tundra biomes are intermixed across the central Asian mountains, and forest biomes occur in coastal Pacific areas. These forest biome occurrences, plus a record of dated plant macrofossils, indicate that some tree populations existed in southern and Eastern Europe and central and far-eastern Eurasia. PFT composition of the herbaceous biomes emphasises the significant contribution of diverse forbs to treeless vegetation, a feature often obscured in pollen records. An increase in moisture ca. 14 kyr cal BP is suggested by a shift to woody biomes and an increase in sites recording initialization and development of lakes and peat deposits, particularly in the European portion of the region. Deforestation of Western Europe, presumably related to agricultural expansion, is clearly visible in the most recent two millennia.
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•Pollen biomes for 1000-yr time slices from 21 to 0 ka BP are mapped for Eurasia.•Tundra and steppe biomes dominated 21–14 ka BP, but forest biomes were also present.•From 14 ka BP woody biomes expanded and wetland indicators became more prominent.•Extensive taxon list underlines importance of forbs in glacial-age non-woody biomes.•The grass-forb tundra biome maps European agricultural land in recent millennia.
Quaternary ammonium compounds (QACs) represent one of the most effective classes of disinfectant agents in dental materials and resin nanocomposites. This reviews aims to give a wide overview on the ...research in the field of antibacterial QACs in dental materials and nanocomposites.
An introduction to dental materials components as well as the microorganisms and methods of evaluation for the antimicrobial assays are presented. Then, the properties and synthesis route of QACs, as monomer and filler, are shown. Finally, antimicrobial monomers and fillers, specifically those contain quaternary ammonium salts (QASs), in dental materials are reviewed.
QACs have been used as monomer and micro/nanofiller in restorative dentistry. They possess one or more methacrylate functional groups to participate in polymerization reactions. QACs with multiple methacrylate groups can also be used as crosslinking agents. Furthermore, QACs with chain length from ∼12 to 16 have higher antimicrobial activity in cured dental resins. In general, increasing the chain length leads to a threshold value (critical point) and then it causes decrease in the antimicrobial activity.
The current state of the art of dental materials and resin nanocomposites includes a wide variety of antimicrobial materials. Among them, QACs presents low cytotoxicity and excellent long-term antimicrobial activity without leaching out over time.
The concept of Quaternary average conditions has gained popularity over the past few decades, especially with studies of long-term landscape evolution. In this paper, we critically assess this ...concept by analyzing the marine isotope record (LR04 δ18O stack) relative to the Quaternary. This shows that the frequency and amplitude of climate glacial-interglacial cycles are not constant throughout the Quaternary, with a clear change during the Middle Pleistocene Transition (MPT), and that many minor oscillations exist within each cycle. For this reason, the identification of pre- and post-MPT most-frequent and, cumulatively, longest-lasting (rather than average) conditions is recommended. The most-frequent pre-MPT δ18O value of 3.725 ± 0.025‰ last occurred during 11.31–11.47 ka, while the most-frequent post-MPT δ18O value of 4.475 ± 0.025‰ last occurred during 14.81–15.04 ka. However, many other δ18O values were almost as frequent throughout the Quaternary and we present geomorphological reasons as to why it is unlikely that the present-day landscape reflects Quaternary average or, indeed, most-frequent conditions. Collectively, our results indicate that extreme caution should be taken when attempting to infer long-term landscape evolution processes (including the buzzsaw hypothesis) based on average Quaternary conditions.
The new sea-level database for Britain and Ireland contains >2100 data points from 86 regions and records relative sea-level (RSL) changes over the last 20 ka and across elevations ranging from ∼+40 ...to −55 m. It reveals radically different patterns of RSL as we move from regions near the centre of the Celtic ice sheet at the last glacial maximum to regions near and beyond the ice limits. Validated sea-level index points and limiting data show good agreement with the broad patterns of RSL change predicted by current glacial isostatic adjustment (GIA) models. The index points show no consistent pattern of synchronous coastal advance and retreat across different regions, ∼100–500 km scale, indicating that within-estuary processes, rather than decimetre- and centennial-scale oscillations in sea level, produce major controls on the temporal pattern of horizontal shifts in coastal sedimentary environments.
Comparisons between the database and GIA model predictions for multiple regions provide potentially powerful constraints on various characteristics of global GIA models, including the magnitude of MWP1A, the final deglaciation of the Laurentide ice sheet and the continued melting of Antarctica after 7 ka BP.
•New sea-level database for Britain and Ireland with >2100 data points from 86 regions.•Records of relative sea-level (RSL) changes over the last 20 ka across elevations ranging from ∼+40 to −55 m.•RSL data show good agreement with the broad patterns of RSL change predicted by glacial isostatic adjustment (GIA) models.•No clear evidence across regions, ∼100-500 km scale, of decimetre- and centennial-scale oscillations in sea level.•Constrains features of global GIA models, including MWP1A, final deglaciation of Laurentia, Antarctic melting post 7 ka BP.
The Eurasian ice sheet complex (EISC) was the third largest ice mass during the Last Glacial Maximum with a span of over 4500 km and responsible for around 20 m of eustatic sea-level lowering. Whilst ...recent terrestrial and marine empirical insights have improved understanding of the chronology, pattern and rates of retreat of this vast ice sheet, a concerted attempt to model the deglaciation of the EISC honouring these new constraints is conspicuously lacking. Here, we apply a first-order, thermomechanical ice sheet model, validated against a diverse suite of empirical data, to investigate the retreat of the EISC after 23 ka BP, directly extending the work of Patton et al. (2016) who modelled the build-up to its maximum extent. Retreat of the ice sheet complex was highly asynchronous, reflecting contrasting regional sensitivities to climate forcing, oceanic influence, and internal dynamics. Most rapid retreat was experienced across the Barents Sea sector after 17.8 ka BP when this marine-based ice sheet disintegrated at a rate of ∼670 gigatonnes per year (Gt a−1) through enhanced calving and interior dynamic thinning, driven by oceanic/atmospheric warming and exacerbated by eustatic sea-level rise. From 14.9 to 12.9 ka BP the EISC lost on average 750 Gt a−1, peaking at rates >3000 Gt a−1, roughly equally partitioned between surface melt and dynamic losses, and potentially contributing up to 2.5 m to global sea-level rise during Meltwater Pulse 1A. Independent glacio-isostatic modelling constrained by an extensive inventory of relative sea-level change corroborates our ice sheet loading history of the Barents Sea sector. Subglacial conditions were predominately temperate during deglaciation, with over 6000 subglacial lakes predicted along with an extensive subglacial drainage network. Moreover, the maximum EISC and its isostatic footprint had a profound impact on the proglacial hydrological network, forming the Fleuve Manche mega-catchment which had an area of ∼2.5 × 106 km2 and drained the present day Vistula, Elbe, Rhine and Thames rivers through the Seine Estuary. During the Bølling/Allerød oscillation after c. 14.6 ka BP, two major proglacial lakes formed in the Baltic and White seas, buffering meltwater pulses from eastern Fennoscandia through to the Younger Dryas when these massive proglacial freshwater lakes flooded into the North Atlantic Ocean. Deglaciation temporarily abated during the Younger Dryas stadial at 12.9 ka BP, when remnant ice across Svalbard, Franz Josef Land, Novaya Zemlya, Fennoscandia and Scotland experienced a short-lived but dynamic re-advance. The final stage of deglaciation converged on present day ice cover around the Scandes mountains and the Barents Sea by 8.7 ka BP, although the phase-lagged isostatic recovery still continues today.
•A new model reconstruction for the EISC deglaciation (23-8 ka BP) is presented.•Ice loading across the High Arctic is tested independently against RSL observations.•The potential locations of >6000 subglacial lakes during the LGM are identified.•The proglacial Fleuve Manche mega-catchment extended >2.5 × 106 km2 across Eurasia.•The EISC contribution to global sea level rise during Meltwater Pulse 1A was ∼2.5 m.
The rapid emergence of antibiotic-resistant bacterial “superbugs” with concomitant treatment failure and high mortality rates presents a severe threat to global health. The superbug risk is further ...exacerbated by chronic infections generated from antibiotic-resistant biofilms that render them refractory to available treatments. We hypothesized that efficient antimicrobial agents could be generated through careful engineering of hydrophobic and cationic domains in a synthetic semirigid polymer scaffold, mirroring and amplifying attributes of antimicrobial peptides. We report the creation of polymeric nanoparticles with highly efficient antimicrobial properties. These nanoparticles eradicate biofilms with low toxicity to mammalian cells and feature unprecedented therapeutic indices against red blood cells. Most notably, bacterial resistance toward these nanoparticles was not observed after 20 serial passages, in stark contrast to clinically relevant antibiotics where significant resistance occurred after only a few passages.
The COVID-19 pandemic has led to significantly increased human exposure to the widely used disinfectants quaternary ammonium compounds (QACs). Xenobiotic metabolism serves a critical role in the ...clearance of environmental molecules, yet limited data are available on the routes of QAC metabolism or metabolite levels in humans. To address this gap and to advance QAC biomonitoring capabilities, we analyzed 19 commonly used QACs and their phase I metabolites by liquid chromatography–ion mobility–tandem mass spectrometry (LC–IM–MS/MS). In vitro generation of QAC metabolites by human liver microsomes produced a series of oxidized metabolites, with metabolism generally occurring on the alkyl chain group, as supported by MS/MS fragmentation. Discernible trends were observed in the gas-phase IM behavior of QAC metabolites, which, despite their increased mass, displayed smaller collision cross-section (CCS) values than those of their respective parent compounds. We then constructed a multidimensional reference SQLite database consisting of m/z, CCS, retention time (rt), and MS/MS spectra for 19 parent QACs and 81 QAC metabolites. Using this database, we confidently identified 13 parent QACs and 35 metabolites in de-identified human fecal samples. This is the first study to integrate in vitro metabolite biosynthesis with LC–IM–MS/MS for the simultaneous monitoring of parent QACs and their metabolites in humans.
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