Cold Climatic Periods Research Articles

A major midlatitude hurricane in the Little Ice Age

Abstract. An unusually severe hurricane (Louisbourg Storm) struck Nova Scotia, Canada, in 1757. Historic records describing storm conditions as well as damage to ships and coastal fortifications indicate an intensity beyond any modern (post-1851) Atlantic cyclones striking the same region, yet this storm struck during a cold climate period known as the Little Ice Age (LIA). Its track and timing coincided with a British naval blockade of a French fleet at Fortress Louisbourg during the Seven Years' War (1756–1763). This provides a unique opportunity to explore growing scientific evidence of heightened storminess in the North Atlantic despite a colder climate expected to suppress hurricane intensification but which research is increasingly showing to have supported North Atlantic storms of exceptional strength. Weather attributes extracted from the logs of naval vessels scattered by the Louisbourg Storm provided multiple hourly observations recorded at different locations. Wave height and wind force estimates at ship locations were compared to extreme storm surge heights calculated for Louisbourg Harbour and a shipwreck site south of Fortress Louisbourg. Comparing these metrics to those of modern analogues that crossed the same bathymetry reflects landfall intensity consistent with a powerful major hurricane. Historical records show this storm originated as a tropical cyclone at the height of hurricane season and intensified into the northern midlatitudes along the Gulf Stream. Its intensity at landfall is consistent with established seasonal climatological models where highly baroclinic westerlies driven by autumn continental cooling encounter intensifying north-tracking tropical cyclones fuelled by sea surface temperatures that peak in autumn. Stronger seasonal contrasts from earlier and colder continental westerlies in the Little Ice Age (LIA) may have triggered explosive extratropical transition from a large hurricane resulting in a more severe strike. It suggests that tropical cyclones lasting days to weeks and the conditions that generate them are likely masked by cooler historic mean annual to multi-decadal LIA climate reconstructions.

Temporal and spatial comparisons of ocean quahog (Arctica islandica) growth and lifespan on the mid-Atlantic continental shelf during inshore transgressions of their range from the Neoglacial through the twentieth century

Arctica islandica provide long-term records of climate change on the U.S. northeast continental shelf transgressing and regressing across the shelf numerous times synchronously with cold and warm climatic periods. The availability of A. islandica in the death assemblage over a wide geographic and temporal range makes this species well suited for documenting both spatial and temporal influences of climate change in the Mid-Atlantic through the correlation of growth rates in response to changing water conditions. This study focuses on comparing regional growth of subfossil ocean quahogs obtained offshore of the Delmarva Peninsula (Delmarva), and living during the cold periods since the Holocene Climate Optimum, with living A. islandica from offshore New Jersey, offshore Long Island, and Georges Bank. These populations exhibited different growth rates, with subfossil individuals from Delmarva death assemblages, representing previous Holocene cold periods, having growth rates as greater than or equal the growth rates of living individuals. Moreover, the growth rates for subfossil A. islandica from Delmarva that were alive from 1740 to 1940 were more rapid than contemporaneous individuals of the same age alive today. Higher growth rates for A. islandica from off Delmarva suggest that conditions supported near maximum growth during the cold periods after the Holocene Climate Optimum, possibly due to increased food supply in water shallower than that inhabited today. Unlike many bivalves, evidence for range recession of A. islandica as bottom water temperatures warm is found first in juvenile abundance, suggesting that recruitment ceases long before the population's demise: range recession in this species is a 100+ year process determined by the survivorship of the oldest and largest individuals. This study is the largest spatial and temporal growth comparison of A. islandica ever recorded and the first record of the process by which this species' inshore range regresses as temperatures rise.

Петромагнитные данные изменения природной среды голоцена в бассейне озера Чистое (Северное Приохотье)

The results of a comprehensive study of Lake Chistoye basin sediments are presented. Magnetic and mineralogical characteristics of various granulometric fractions of deluvial deposits, modern surface bottom sediments, and core materials have been studied. The relationship between the petromagnetic parameters of deluvium and lake sediments is shown. The composition of magnetic minerals has been determined. The dependence of magnetic characteristics on the granulometric composition of sediments has been established. Scalar magnetic parameters in core sediments show wide-amplitude variations reflecting frequent changes in sedimentation conditions. Sediments with high values of MS, Js, Jrs might have been formed in the periods of cold climate, with intensive flow of detritus material into the basin.

Chemical weathering in the Himalayan system in response to the evolution of the Indian summer monsoon since 37 ka

Based on clay mineralogy, siliciclastic grain sizes and geochemical records from deep-sea sediments in the central Bay of Bengal (BoB), the evolutionary history of the Indian summer monsoon and associated weathering process in the Himalayan system since 37 ka were reconstructed. Clay minerals and ThLa elements indicate a mixture of sediments originating from the Ganges-Brahmaputra (G-B) Rivers, Indo-Burman ranges/Irrawaddy River and Godavari-Krishna (G-K) Rivers. The ThLa quantitative reconstruction revealed that sediment supply from the G-B Rivers was reduced during a series of millennial-scale cold climate events (i.e., Younger Dryas and Heinrich Events) and the Last Glacial Maximum. By removing the control of sea-level factors on the percentage of clay minerals in the sediments, we suggests that the marked decrease in the illite chemistry index and the increase in the (illite+chlorite)/smectite ratio during cold climate periods reflect enhanced physical weathering and weakened chemical weathering in the Himalayan system. Comparing the contribution from the G-B Rivers and the sedimentation rates in different regions of the BoB, it was inferred that the sediments of the G-B Rivers were mostly deposited in the upper and middle Bengal Fan. During the Holocene, the Active Channel played a crucial role in delivering sediments from the G-B Rivers to the lower Bengal Fan. The decreased chemical index of alteration (CIA) and increased K₂O/TiO₂ ratio indicated the weakening of the Indian summer monsoon. At that moment, the Himalayan system was involved in cold climatic conditions accompanied by glacial extension, which led to enhanced physical weathering and increased sediment contributions from the highlands.

Climatic and environmental changes in the Baidunzi wetland, Northwest China, over the last 800 years inferred from glycerol dialkyl glycerol tetraethers

To help understand the temperature and moisture variations in the semiarid and semi-humid regions of China that lie a transitional zone between the Westerlies and the East Asian monsoon, reconstruction of the regional climatic changes over the last millennium is useful. However, high-resolution time-series data related to the histories of climatic changes in these areas are limited. Therefore, this multiproxy analysis of a sediment core from the Baidunzi wetland, northwest China, was conducted using grain size, total organic carbon, glycerol dialkyl glycerol tetraethers (GDGTs), and molecular biomarkers. The results show that GDGTs can reliably reconstruct paleoclimate changes recorded in sediments in salt marsh environments. The climate and environment history of the past 800 years can be divided into the three stages: the end of the dry Medieval Warm Period (MWP) (1278–1366 CE), a humid Little Ice Age (LIA) (1366–1896 CE), and the humid Current Warm Period (CWP) (1896–1999 CE). The Baidunzi setting during the end of the MWP was a warm and dry wetland with high salinity, low water levels, and emersed aquatic plants, and the depositional environment transitioned from fluvial facies to shore lake facies. In contrast, the local climate during the LIA was cold and humid, and the era was characterized by the appearance of vascular flora and two short-term flooding events, that caused a rise in water levels. The lowest temperatures and highest salinities of the period were correlated, which was likely caused by seasonal freeze-thaw cycles. During the CWP, the local climate was warm and humid, with a higher water level than during the LIA, and emersed plants again developed in shallow lagoon facies. Generally, salinity was positively correlated with temperature, except for freezing and thawing salinization resulting from episodes of extremely low temperatures. The warm–dry to cold–humid climate changes of the area were like those of arid Central Asia, which indicates that the Baidunzi region was affected mainly by the Westerlies and was impacted by southward intrusions of that system. The area was also affected by the North Atlantic Oscillation and experienced diminished evaporation during periods of cold climate.

Jovian Planets and Lunar Nodal Cycles in the Earth’s Climate Variability

This study utilizes time-series data devised to measure solar irradiation, sea surface temperatures, and temperatures in the lower atmosphere to gain a better understanding of how gravitational effects from the moon and Jovian planets (Jupiter, Saturn, Uranus, and Neptune) influence solar activity and climatic conditions on Earth. Then, standard statistical methods are used to determine the degree of correlation among these time series and construct a Jovian gravitational model. The study reveals a direct relationship between JSUN perihelion coincidences and TSI amplitude variations in cycles up to 4,450 years. The forced solar accumulation of heat in oceans introduces a new phase relation between solar forced cycles and new climate variation. Earth’s axis nutation cycles have coincidences with lunar nodal tide cycles and lunar forced sea surface temperature cycle periods up to 446 years. Earth’s temperature variation shows coincidence with constructive and destructive interference between lunar-forced and accumulated solar-forced temperature variations in oceans. Upcoming events have a computed modern temperature maximum in 2025 and a deep minimum in 2070. Interference between solar-forced temperature cycles of 333,2142, and 4,450 years and a lunar-forced temperature cycle of 445 years indicates that “The Little Ice Age” covers a total period of 820 years from 1330 to 2150 A.D. and an upcoming temporary cold climate period from 2070 to 2150.

Age, origin and palaeoclimatic implications of peri- and paraglacial boulder-dominated landforms in Rondane, South Norway

Boulder-dominated landforms of periglacial, paraglacial and related origin constitute a valuable, but often unexplored source of palaeoclimatic and morphodynamic information. The timing of landform development initiation and its subsequent stabilization can be linked to past climatic conditions offering the potential to reconstruct cold climatic periods. In this study, Schmidt-hammer exposure-age dating (SHD) was applied to a variety of boulder-dominated landforms (sorted stripes, blockfield, rock-slope failure, paraglacial alluvial fan) in Rondane, eastern South Norway for the first time. On the basis of old and young control points a regional SHD calibration curve was established and successively utilized for the calculation of surface exposure ages for individual landforms. The chronological investigation of development and stabilization of the respective landforms permitted an assessment of Holocene climate variability in Rondane and its impact on overall landform evolution. Our obtained SHD age estimates ranged from 11.44 ± 1.22 ka (ST-D2) to 4.09 ± 1.51 ka (AF1) showing their inactive and relict character. Most surface exposure ages for sorted stripes clustered between 9.88 ± 1.35 ka and 9.25 ± 1.21 ka, hence indicating stabilization during the late stage of the Erdalen Event or shortly thereafter. It is inferred that the blockfield formed prior to the Last Glacial Maximum, was protected by cold-based ice throughout glaciation and shortly reactivated during the Erdalen Event only to subsequently becoming inactive. The surface exposure age of a rock-slope failure (7.58 ± 0.73 ka) falls into the early phase of the Holocene Thermal Maximum (HTM, ~8.0–5.0 ka). This indicates permafrost degradation and/or increasing hydrological pressure negatively influencing slope stability. The paraglacial alluvial fan with its four subsites yielded ages between 8.73 ± 1.63 ka and 4.09 ± 1.51 ka. The old exposure ages point to fan aggradation following regional deglaciation due to paraglacial processes, whereas the younger ages can be explained by increasing precipitation during the onset neoglaciation at ~4.0 ka. Our results underline the importance of meltwater for the activation of periglacial landforms in a continental climate and indicate that the Erdalen Event and immediately following onset of the HTM had major impact on landscape evolution in Rondane. Our obtained surface exposure ages from boulder-dominated landforms in Rondane give important insights into the local palaeoclimatic variability during the Holocene.

PERICLIMv1.0: a model deriving palaeo-air temperatures from thaw depth in past permafrost regions

Abstract. Periglacial features, such as various kinds of patterned ground, cryoturbations, frost wedges, solifluction structures, and blockfields, are among the most common relics of cold climate periods, which repetitively occurred throughout the Quaternary. As such, they are widespread archives of past environmental conditions. Climate controls on the development of most periglacial features, however, remain poorly known, and thus empirical palaeo-climate reconstructions based on them have limited validity. This study presents and evaluates a simple new inverse modelling scheme called PERICLIMv1.0 (PERIglacial CLIMate) that derives palaeo-air temperature characteristics related to the palaeo-active-layer thickness, which can be recognized using many relict periglacial features found in past permafrost regions. The evaluation against modern temperature records showed that the model reproduces air temperature characteristics with average errors ≤1.3 ∘C. The past mean annual air temperature modelled experimentally for two sites in the Czech Republic hosting relict cryoturbation structures was between -7.0±1.9 and -3.2±1.5 ∘C, which is well in line with earlier reconstructions utilizing various palaeo-archives. These initial results are promising and suggest that the model could become a useful tool for reconstructing Quaternary palaeo-environments across vast areas of mid-latitudes and low latitudes where relict periglacial assemblages frequently occur, but their full potential remains to be exploited.

Formation of Ti-rich bauxite from alkali basalt in continental margin carbonates, Payas region, SE Turkey: implications for sea level change in the Upper Cretaceous

The Payas region bauxite deposits occur as a sandwiched layer that is a few kilometers long and an average of 10 m thick between the lower and upper Cretaceous carbonates of the Arabian Platform. The bauxites occur as 2 types, comprising blanket and pocket, are chemically and texturally homogeneous, and have a thrust structure with ophiolitic mélange formations. The bauxite varies in color, from reddish-brown to grayish-green to black, and has a massive, patchy, and very rare oolitic-pisolitic texture. The bauxite mainly consists of diaspore, hematite, rutile, anatase, rare kaolinite, boehmite, and pyrite minerals.The prismatic and lath-shaped euhedral rutile within the bauxites indicated in situ formation of the bauxites from Ti-rich basaltic pyroclastics. The chondrite-normalized rare earth element pattern of the bauxite was similar to the basalt pattern and had a very weak Eu anomaly (0.9). There are 2 groups of elements have been enriched in the Payas region bauxite: the first group contains TiO2 (9.67wt%), Cr (752 ppm), V (617 ppm) and Ni (72 ppm), and the second group comprises Zr (993 ppm), Nb (86 ppm) and Sn (7 ppm). These 2 groups of element enrichment indicated that the parental material of bauxite had an alkali basalt character. The carbon and oxygen isotope stratigraphy throughout the carbonate section from the bottom to the top indicated that the climate was warm during bauxitization (mean δ18OVPDB: -6.15‰) and relatively cold after bauxite deposition (mean δ18OVPDB: -4.71‰). A marine regression during the warm climate could have been related to the uplifting of the coastal zone, which was linked to the vertical fault movements of the normal faults. A rapid transgression after bauxite formation during the cold climate period can be explained by subsidence of the continental margin, which was associated with episodic ophiolitic nappe loading during the closure of the Neotethyan Ocean in the region.

Validation of a Predictive Fire Risk Indication Model using Cloud-based Weather Data Services

Abstract The high and dense representation of wooden homes in Norway, combined with periods of dry and cold climate during the winter season resulting in very dry indoor conditions, have historically resulted in severe fires. Thus, it is important to have an accurate estimate of the current and near future fire risk to take proper planning precautions. Cloud computing services providing access to weather data in the form of measurements and forecasts combined with recent developments in fire risk modelling may enable smart and fine-grained fire risk predication services. The main contribution of this study is implementation and experimental validation of a predictive fire risk indication model, which exploits cloud-provided measurements from weather stations and weather forecasts to predict the current and future fire risk for wooden homes at a given geographical location. The basic idea of the model is to estimate the indoor climate using measured and forecasted outdoor climate for computing indoor wooden fuel moisture content and an estimated time to flashover as indication of the fire risk. The model implementation was integrated into a micro-service based software system and experimentally validated during one winter at selected geographical locations, relying on weather data provided by the RESTful API of the Norwegian Meteorological Institute. Additionally, weather data from several historical fires were considered to relate our predictions to known fire incidents. Our evaluation demonstrates the ability to provide trustworthy and accurate fire risk indications using a combination of weather data measurements and forecast data. Furthermore, our cloud-and micro-service based software system implementation is efficient with respect to data storage and computation time.

"Domesticated Landscapes of Li Gonglin: A View from the Anthropocene," by De-nin Lee

Reviewed by: "Domesticated Landscapes of Li Gonglin: A View from the Anthropocene," by De-nin Lee Foong Ping De-nin Lee, "Domesticated Landscapes of Li Gonglin: A View from the Anthropocene," JSYS 45 (2015): 139–74. If the grand peaks, valleys, and waterfalls of paradigmatic Song dynasty landscapes entreat viewers to appreciate high-minded retreat alongside travelers and recluses, what constitutes their "domestication"? Paintings that show knowledge of terrain and technology, that picture efficient agriculture and engineered waterways. Taking up perspectives from eco-art history and criticism, Lee takes special notice of motifs like rice fields, mulberry groves, newly-planted trees, and fish-stocked ponds, urging us to examine them as signs of anthropogenic change. Li Gonglin 李公麟, an artist of great range and invention, is not often studied as a landscapist. Lee conceives of a unique picture in his oeuvre from an eco-critical perspective. "The Lodge of Establishing Virtue" is one of the two opening scenes in Li's portrait of his estate, Mountain Villa (Shanzhuang tu 山莊圖), which stands out from the following sections, and indeed from the Song visual record of works by named artists. The scene was conceptualized in a manner outside of the landscape painter's typical brushwork-orientated repertoire. Robert Harrist underlined Li's use of mapmaking and printmaking conventions when discussing Mountain Villa's transformation of wilderness into a garden-estate. Pan Anyi's study of Li's Buddhist beliefs considered the painting in relation to a paradise. But nature is not only a pure muse for eremites. Some images imply ecological ruptures and the material impact of meeting human needs. Lee calls attention to our assumptions about landscape images—long informed by art, historical, philosophical, and literary discourse—as fundamentally representing a harmonious relationship between humans and nature. Her stated aim is to inflect images of leisure, such as Li Gonglin's, with implied labor. Within the cultural constant of seeking revelations of heavenly approval or disapproval in nature, the symbolism of cosmic harmony in landscapes was particularly useful for imperial purposes. Those picturing advanced technology also rendered power and legitimacy visible, pointing to capable and benevolent rule. Liu Heping has demonstrated the implications of paintings of mills and hydrological engineering. Pang Huiping's study of snow scenes has shown how this subject's meanings needed redirection at court during an actual period of cold climate. Domesticated landscapes counter notions of the pristine wilderness and the ideals that it entails, seeing instead evidence of environmental change and the parties responsible for it. Water-powered [End Page 232] machines redirected natural watercourses; harvesting timber to build dams and dykes for flood prevention fed cycles of erosion. Thus images of land-ownership represent limitations upon the land's ability to generate wealth and impositions upon ecology. With this lens, Lee understands a picture of tree cultivation as a possible reference to windbreaking fengshui forests that prevented erosion and filtered water. From this perspective, various parts of the productive ecology of a working estate might delineate amongst cultivated, soon-to-be cultivated, and uncultivated landscapes, and between the symbolic and mundane features and purposes of Li's estate. Of course, no single lens precludes any other. In an unexpected cross-disciplinary, cross-temporal move, Lee finds purchase in Xie Lingyun's 謝靈運 poems, where the estate is a site of spatial operations and "habituated practices" that problematize conventional oppositions of rustic and urban. Li Gonglin offers "visual cognates" of Xie's panoptic gaze. Li Gonglin's painting is indeed self-reflexive and complex in its juxtaposition of multiple visual conventions. The image itself calls for a correspondingly intersectional interpretive strategy, as Lee's essay proposes. [End Page 233] Foong Ping Seattle Art Museum Copyright © 2021 Society for Song, Yuan, and Conquest Dynasties Studies

Late Pleistocene and Early Holocene aeolian deposits of Tasmania and their climatic implications

AbstractLate Pleistocene and Early Holocene aeolian deposits in Tasmania are extensive in the present subhumid climate zone but also occur in areas receiving >1000 mm of rain annually. Thermoluminescence, optically stimulated luminescence, and radiocarbon ages indicate that most of the deposits formed during periods of cold climate. Some dunes are remnants of longitudinal desert dunes sourced from now-inundated continental shelves which were previously semi-arid. Others formed near source, often in the form of lunettes east of seasonally-dry lagoons in the previously semi-arid Midlands and southeast of Tasmania, or as accumulations close to floodplains of major rivers, or as sandsheets in exposed areas. Burning of vegetation by the Aboriginal population after 40 ka is likely to have influenced sediment supply. A key site for determining climate variability in southern Tasmania is Maynes Junction which records three periods of aeolian deposition (at ca. 90, 32 and 20 ka), interspersed with periods of hillslope instability. Whether wind speeds were higher than at present during the last glacial period is uncertain, but shells in the Mary Ann Bay sandsheet near Hobart and particle size analysis of the Ainslie dunes in northeast Tasmania suggest stronger winds during the last glacial period than at present.

Revisiting the Role of Convective Deep Water Formation in Northern Baltic Sea Bottom Water Renewal

AbstractDeep water renewal and ventilation of the Baltic Sea is commonly considered to occur solely via saltwater inflows from the North Sea. However, recent analysis of geophysical and sediment proxy data suggests convective deep water formation during wintertime as a second process that has contributed to the ventilation of the northern and central Baltic Sea bottom waters during cold climate periods. Here, we investigate the role of deep water formation in the northern Baltic Sea in a regional ocean circulation model. Selecting the particularly cold winter 1986/1987 as a reference period, we perform sensitivity experiments in which the atmospheric temperature forcing is changed and/or localized brine rejection on subgrid scales is accounted for through a parameterization. We study the sinking and circulation of water masses via passive tracers introduced into the model. Generally, our model results support the established view that convective deep water formation does not play a major role in Baltic Sea deep water renewal. While a reduction of air temperatures does not qualitatively change the sinking and circulation of water masses in our experiments, brine rejection could potentially lead to localized deep water formation. However, the impact is too weak to possibly change the large‐scale deep water exchange between the Baltic proper and the northern Baltic sub‐basins. Although being in line with established knowledge, through consideration of the model limitations, our results provide insights on how and under which circumstances convective deep water formation could potentially have occurred during cold climate periods.

Interdecadal Variability of the Black Sea Cold Intermediate Layer and Its Causes

The long-term variability of the Black Sea intermediate layer temperature is analyzed using an updated database for the period from 1951 to 2017. The existence of interdecadal temperature variations in the vicinity of the cold intermediate layer (CIL) with a period of ~50 years and the amplitude to 0.7°C is confirmed. It is shown that the CIL cooling/warming is accompanied by its upward/downward displacement. The analysis of temperature fields in the surface and subsurface layers constructed from data averaged over different decades revealed that the cold and warm climate periods are characterized by changes in the ratio between the intensity of the two main CIL sources: winter convection in the open sea and subduction of cold water from the northwestern shelf. A dramatic sea surface temperature rise during the recent 20 years led to the fact that currently observed temperature minima in the upper 100-m layer considerably exceeded the minima registered during the period of the previous quasiperiodic temperature rise in the mid-20th century.

The Middle Pleistocene fluvial sequence at Uichteritz, central Germany: Chronological framework, paleoenvironmental history and early human presence during MIS 11

The site of Uichteritz (Saxony-Anhalt, Germany) is a Quaternary gravel quarry hosting several Middle-Pleistocene fluvial units of the Saale River. This fluvial archive contains detailed information on (1) the timing of Middle Pleistocene fluvial aggradation and erosion periods in the region, (2) the driving forces for those alternations, as well as (3) early human presence indicated by the presence of Lower Paleolithic stone artefacts. Here we establish a luminescence-based numerical chronology at Uichteritz. Additionally, geophysical, sedimentological and micromorphological analyses were applied to obtain information on depositional and post-depositional processes of the fluvial sequence.Our results point to several fluvial aggradation periods between ca. 420 and 180 ka. A first fluvial unit was deposited during the late Elsterian period, followed by formation of a Luvisol during MIS 11 and its fluvial reworking at the transition from MIS 11 to MIS 10 and/or during early MIS 10. These MIS 10/11 deposits, with an age of about 400 ka, also contain reworked Lower Paleolithic stone artefacts that document the initial appearance of humans in northwestern central Europe during MIS 11. After a period of fluvial incision during MIS 10, which was accompanied by a change in the course of the Saale River, several stacked fluvial sequences of the Saalian Main Terrace (SMT) formed between MIS 8 and MIS 6, mainly during cold climatic periods. Our age estimates confirm the correlation of the Elsterian ice advances with MIS 12, and the Saalian ice advances with later MIS 6.

Methanol and ethanol concentrations in a Greenland ice core

The first methanol and ethanol concentrations in a Greenland ice core are reported for 14 annual samples ranging from 1686 to 1947 AD. Concentrations ranged from 83 nM to 1666 nM and 16 nM–424 nM for methanol and ethanol, respectively. Low median methanol and ethanol concentrations from 1686 to 1745 result primarily from natural emissions during a cold climate period. These concentrations provide a baseline alcohol level in deposition before impacts from various sources (e.g. naturally recovering plant populations, anthropogenic sources, and changing atmospheric oxidation chemistry) increased alcohol concentrations in the atmosphere. Concentrations of both alcohols increased after 1745 possibly due to increased biogenic and anthropogenic sources. Because both of these alcohols react with hydroxyl radicals, this increase has important implications for changing atmospheric oxidation chemistry. Samples were also analyzed for various other ice core components (e.g. aldehydes, anions, H+, DOC) to investigate possible correlation with alcohol concentrations. These ice core data are significant because they can be used to determine the extent temporal trends in alcohol concentrations were due to changes in atmospheric chemistry and varying source type and magnitude.

Riverine influence in Sr isotope ratio of mollusk shells and relationship with foraminiferal assemblages in a Late Quaternary succession of the Po River Delta (Northern Italy)

The freshwater influence in the 87Sr/86Sr ratio of mollusk shells were analyzed within a Late Quaternary subsurface succession of the Po River Delta (core 187-S1). Sr isotope ratios of the Po and others rivers' (Brenta, Adige and Reno) waters, discharging in the Adriatic Sea, at about 30 km North and South of the Po Delta, show a domi¬nant contribution in the core area of fluvial water with isotope ratios remarkably lower than seawater values. Core 187-S1 consists of continental deposits formed during cold-climate periods, with intercalated two paralic to shallow-marine intervals indicative of warm-climate conditions and attributed to the last interglacial (Eemian) and to the Holocene period. Foraminiferal assemblages of these intervals reveal a comparable transgressive-re¬gressive palaeoenvironmental evolution and great variation in river discharge, with highest influence of freshwater observed in the Hol¬ocene prodelta.The new Sr isotope ratios from marine and deltaic mollusks are commonly comparable with those of seawater and are not influenced by freshwater dilution, also in beach ridge samples, deposited at very shallow water depth. Excluding two anomalous ratios from the trans¬gressive part of the Holocene succession, deviation from marine val¬ues toward lower ratios (consistent with remarkable influx of river water) are observed in samples with foraminiferal assemblages indic-ative of inner prodelta and great proximity of the river mouth. This work shows that combining foraminiferal micropalaeon¬tology and Sr isotope data of freshwater draining the analyzed are¬as, it is possible to recognize conditions (i.e. deltaic settings greatly influenced by fluvial water with low 87Sr/86Sr ratio) that hamper the application of the Sr isotope ratios as dating tool for shallow marine fossils.

A low-δ18O intrusive breccia from Koegel Fontein, South Africa: Remobilisation of basement that was hydrothermally altered during global glaciation?

The Cretaceous Koegel Fontein igneous complex is situated on the west coast of South Africa, and has a high proportion of rocks with abnormally low δ18O values. The rocks with the lowest δ18O values (−5.2‰) belong to intrusive matrix-supported breccia pipes and dykes, containing a variety of clast types. The breccia rocks range in SiO2 from 44 to 68wt% and their whole-rock δ18O values vary between −5.2‰ and +1.8‰. The major and trace element composition of the breccia rocks is consistent with them containing variable proportions of clasts of Cretaceous intrusive rocks and basement gneiss and the matrix being fluidized material derived from the same source as the clasts. Based on the nature of the clasts contained in the breccia, it was emplaced just prior to intrusion of the main Rietpoort Granite at 134Ma. All components of the breccia have low δ18O value and, at least in the case of the gneiss clasts, this predates incorporation in the fluidized material.Although the early Cretaceous appears to have been a period of cold climate, it is unlikely that the δ18O values of ambient precipitation (~−10‰) would have been low enough to have generated the required 18O-depletion. The basement gneiss was probably ~2–3km below the Cretaceous surface, minimizing the possibility of interaction with isotopically unmodified meteoric water, and there is no evidence for foundered blocks of cover rocks in the breccia. There is, therefore, no evidence for downwards movement of material. We favour a model where basement gneiss interacted with extremely 18O-depleted fluid during crustal reworking at ~547Ma, a time of global glaciation. Low-δ18O metamorphic fluids produced by dehydration melting of 18O-depleted gneiss became trapped and, as the fluid pressure increased, failure of the seal resulted in explosive upwards movement of fluidized breccia. Migration was along pre-existing dykes, incorporating fragments of these dykes, as well as the country rock gneiss.

Discovery of bacteriopheophytin-a in lacustrine deposits from Lake Zigetang on the central Tibetan Plateau and its paleoenvironmental significance

Lake Zigetang is located on the central Tibetan Plateau (TP) and represents a rare but typical meromictic lake in China. The lake’s stable meromixis sustains microflora communities, and changes in these communities are relatively independent of climate. Therefore, these communities can be used as paleoclimate proxies. In this paper, the stratification properties and their relationships with the microflora of Lake Zigetang were analyzed. We found that water depth and climate conditions were two important factors for maintaining meromixis in Lake Zigetang. Generally, stratification was enhanced during warm periods, while temperature differences between the mixolimnion and monimolimnion were decreased during cold periods. The presence of anoxygenic phototrophic bacteria (APB) was demonstrated by the discovery of bacteriopheophytin-a (Bph-a) in the sediments. This bacterial community is mainly concentrated at the bottom of the chemocline and the top of the monimolimnion, where it forms a thin APB layer. Moreover, total APB productivity is mainly affected by the light intensity penetrating to the APB layer, which exponentially increases as the thermocline becomes shallow. Therefore, high Bph-a values in the lake corresponded to a shallow thermocline and warm periods, low Bph-a values corresponded to cold periods, and zero changes indicated that the water was completely mixed and reflected an extreme cold climate or low lake level period. Thus, Bph-a can be used as a climate proxy to reconstruct the history of lake stratification and climate changes.

Reconstructing Last Glacial Maximum and Younger Dryas paleolandscapes through subsurface paleosol stratigraphy: An example from the Po coastal plain, Italy

Paleosols are commonly used to reconstruct ancient landscapes and past environmental conditions. Through identification and subsurface mapping of two pedogenically modified surfaces formed at the onset of the Last Glacial Maximum (LGM) and during the Younger Dryas (YD) cold event, respectively, and based on their lateral correlation with coeval channel-belt sand bodies, we assessed the geomorphic processes affecting the Po coastal plain during the Late Pleistocene (30–11.5calky BP). The 3D-reconstruction of the LGM and YD paleosurfaces provides insight into the paleolandscapes that developed in the Po alluvial plain at the transitions between warm and cold climate periods. The LGM paleosol records a stratigraphic hiatus of approximately 5kyr (29–24calky BP), whereas the development of the YD paleosol was associated with a climatic episode of significantly shorter duration. Both paleosols, dissected by Apennine rivers flowing from the south, dip towards the north-east, where they are replaced by fluvial channel belts fed by the Po River. The LGM channel-belt sand body reflects the protracted lateral migration of the Po River at the onset of the glacial maximum. It is wider (>24km) and thicker (~15m) of the fluvial sand body formed during the YD. The northern margin of LGM Po channel-belt deposits was not encountered in the study area. In contrast, a spatially restricted paleosol, identified in the north at the same elevation as the southern plateau, may represent local expression of the Alpine interfluve during the YD event. This study highlights how 3D-mapping of regionally extensive, weakly developed paleosols can be used to assess the geomorphic response of an alluvial system to rapid climate change.