Добірка наукової літератури з теми "Antarctica, Ice cores, Climate, Environment"

During the past decades, the investigation of various elements, species, and isotopes in the frozen atmospheric archives stored in the Greenland and Antarctic ice caps for several hundred thousand years has provided a wealth of fascinating information on past and recent changes in the atmospheric environment of our planet. After a brief description of the Antarctic and Greenland ice caps, we give an overview of the procedures that are used in the field for collecting snow and ice from the surface down to great depths. We discuss the techniques used to date and analyse the samples. The main results obtained to date are then presented, with special emphasis on the very recent. The analysis of the snow and ice layers deposited during the past few centuries, especially since the Industrial Revolution, has allowed us to assess clearly the impact human activity has had on the atmosphere, for important constituents such as heavy metals, sulfur and nitrogen compounds, greenhouse gases, carbon and organic compounds, and artificial radionuclides. The analysis of ancient ice up to several hundred thousand years old has provided unique insight on the past natural changes that affected our atmosphere during glacial–interglacial transitions, especially the temperature, greenhouse gases, soil- and sea-derived aerosols, and heavy metals.Key words: Greenland, Antarctica, ice, global pollution, climate change, heavy metals.

AbstractIce-covered lakes in Antarctica preserve records of regional hydroclimate and harbour extreme ecosystems that may serve as terrestrial analogues for exobiotic environments. Here, we examine the impacts of hydroclimate and landscape on the formation history of Lake Eggers, a small ice-sealed lake, located in the coastal polar desert of McMurdo Sound, Antarctica (78°S). Using ground penetrating radar surveys and three lake ice cores we characterize the ice morphology and chemistry. Lake ice geochemistry indicates that Lake Eggers is fed primarily from local snowmelt that accreted onto the lake surface during runoff events. Radiocarbon ages of ice-encased algae suggest basal ice formed at least 735 ± 20 calibrated years before present (1215 C.E.). Persisting through the Late Holocene, Lake Eggers alternated between periods of ice accumulation and sublimation driven by regional climate variability in the western Ross Sea. For example, particulate organic matter displayed varying δ15N ratios with depth, corresponding to sea ice fluctuations in the western Ross Sea during the Late Holocene. These results suggest a strong climatic control on the hydrologic regime shifts shaping ice formation at Lake Eggers.

AbstractThis study investigates the processes of ice-marginal sedimentation in Vestfold Hills, Antarctica. Most debris is released from the ice when basal and englacial debris bands become warped and reach the surface of the glacier and where the debris bands are exposed by ablation of the ice surface. Once released, the debris is redistributed in the ice-marginal area by depositional processes that are controlled by the availability of water. During the short summer, melt water from snow and ice saturates the newly released debris and causes sediment flows and other mass-movement deposits. Melt-out and sublimation tills form after the layer of debris on the moraines is consolidated and melting rates decrease. When the thickness of deposits on the surface of ice-cored moraines reaches or exceeds the depth of summer thawing, the ice core no longer melts and the moraines become semi-permanent features. The sediments and land forms of the ice-marginal area closely resemble those formed by sub-polar glaciers with a complex thermal regime and are unlike those that form at the margins of dry-based polar glaciers. Although glacier thermal regime is understood to be a major control on debris dispersal and processes of glacial sedimentation, the evidence from Vestfold Hills suggests that the primary control is the climate of the glacier terminus area.

ABSTRACTIce deposits from Greenland and Antarctic ice sheets have stored over long periods of time information about the climate and environment of our planet. Attention will be focused on the 2083 m Vostok Antarctic ice core which represents a unusually long record (160 000 ka) due to the low accumulation rate (∼2 g cm−2a−1) and the rather uniform conditions of ice flow. This ice core provides a unique opportunity to obtain several palaeo-data such as temperature, accumulation (precipitation), aerosol loading, CO2 and trace gases over a full glacial-interglacial climatic cycle.The Vostok temperature, deduced from the interpretation of the deuterium content, and the CO2 records show a large 100 ka signal with a change of the order of 10°C and 70 ppmv respectively. The two records are closely correlated and both display shorter periodicities characteristic of the earth orbital parameters. CH4 concentrations also show variations from about 0·35 to about 0·65 ppmv linked with the glacial-interglacial warming. These features suggest a fundamental link between the climatic system and the carbon cycle and stress the role of radiatively active gases in climatic changes.The accumulation (precipitation) record appears to be governed by temperature with values during the coldest stages reduced by a factor of 2 with respect to the present rate. Ice deposited during these coldest stage is also characterised by high concentration of marine and terrestrial aerosols; these peaks probably reflect strengthened sources and meridional transport during full glacial conditions, linked to higher wind speed, more extensive arid areas on surrounding continent and a greater exposure of continental shelves.

Abstract Polar snow pits or ice cores preserve valuable information derived from the atmosphere on past climate and environment changes. A 1.57-m snow-pit record from the coastal site (Styx Glacier) in eastern Antarctica covering the period from January 2011 to January 2015 was discussed and compared with meteorological variables. The dominant contribution of the deposition of sea-salt aerosols due to the proximity of the site to the ocean and processes of sea ice formation was revealed in the ionic concentrations. Consistent seasonal peaks in δ 18 O, δ D, MSA, , and indicate the strong enhancement of their source during warm periods, whereas the sea-salt ions (Na + , K + , Mg 2+ , Ca 2+ , Cl − , and ) exhibit a distinct distribution. Monthly mean δ 18 O positively correlates with the air temperature record from an automatic weather station (AWS) located in the main wind direction. Despite the shortness of the record, we suspect that the slight depletion of the isotopic composition and lowering of the snow accumulation could be related to the cooler air temperature with the decrease of open sea area. Consistency with previous studies and the positive correlation of sea-salt ions in the snow pit indicate the relatively good preservation of snow layers with noticeable climate and environmental signals [e.g., changes in sea ice extent (SIE) or sea surface temperature]. We report a new snow-pit record, which would be comparative and supportive to understand similar signals preserved in deeper ice cores in this location.

AbstractTo determine annual layers for reconstructing the past environment at annual resolution from ice cores, we employed snow-stake data back to 1972, tritium content, solid electrical conductivity measurements (ECM) and stratigraphic properties for the 73m ice core at the H72 site, east Dronning Maud Land, Antarctica. the average annual surface mass balance at H72 is 307 mma–1w.e. during the last 27 years from continuous accumulation data, 317 mma–1 w.e. according to the densification model and 311 mma–1 w.e. according to the average surface mass balance for 167 years based on annual-layer counting. the ECM age is closely coincident with tritium age, and corresponds with the snow-stake record back to AD 1972 from the surface to 15 m depth. the H72 ice core is dated as AD 1831by ECMat 73.16 mdepth.The time series of yearly surface mass balance at H72 shows an almost constant 311 mm a–1 w.e. for the last 167 years. the oxygen-isotope records indicate a significant trend to lower values, with negative gradient of 1.7% (100 years)–1.

Lake sediments in the Larsemann Hills contain a great diversity of biological and physical markers from which past environments can be inferred. In order to determine the timing of environmental changes it is essential to have accurate dating of sediments. We used radiometric (210Pb and 137Cs), radiocarbon (AMS 14C) and uranium series (238U) methods to date cores from eleven lakes. These were sampled on coastal to inland transects across the two main peninsulas, Broknes and Stornes, together with a single sample from the Bolingen Islands. Radiometric dating of recent sediments yielded 210Pb levels below acceptable detection limits. However, a relatively well-defined peak in 137Cs gave a date marker which corresponds to the fallout maximum from the atmospheric testing of atomic weapons in 1964/65. Radiocarbon (AMS 14C) measurements showed stratigraphical consistency in the age-depth sequences and undisturbed laminae in some cores provides evidence that the sediments have remained undisturbed by glacial action. In addition, freshwater surface sediments were found to be in near-equilibrium with modern 14CO2 and not influenced by radiocarbon contamination processes. This dating program, together with geomorphological records of ice flow directions and glacial sediments, indicates that parts of Broknes were ice-free throughout the Last Glacial Maximum and that some lakes have existed continuously since at least 44 ka bp. Attempts to date sediments older than 44 ka bp using 128U dating were inconclusive. However, supporting evidence for Broknes being ice-free is provided by an Optically Stimulated Luminescence date from a glaciofluvial deposit. In contrast, Stornes only became ice-free in the mid to late Holocene. This contrasting glacial history results from the Dålk Glacier which diverts ice around Broknes. Lakes on Broknes and some offshore islands therefore contain the oldest known lacustrine sediment records from eastern Antarctica, with the area providing an ice-free oasis and refuge for plants and animals throughout the Last Glacial Maximum. These sediments are therefore well placed to unravel a unique limnological sequence of environmental and climate changes in East Antarctica from the late Pleistocene to the present. This information may help better constrain models of current climate changes and ensure the adequate protection of these lakes and their catchments from the impacts of recent human occupation.

Abstract. A high-frequency and precise ultrasonic sounder was used to record precipitated/deposited snow and drift events over a 3 yr period (17 January 2005 to 4 January 2008) at the Eagle automatic weather station (AWS) site. Through a comparison of the meteorological data with snow pit chemical/isotopic dating results, the snowdrift process effect during snow accumulation was assessed. We believe that ice/firn cores are the most important proxies of climate and the environment because of their high resolution and their preservation of historical greenhouse gas levels, although their limitations and measurement uncertainties must be taken into account, due to the event-driven snow dominates the snow deposition. This study found a difference between two dating results of up to 12 months for a ~ 95 cm snow pit, where the annual snow accumulation rate is 30.3 cm. A weakness is also indicated when simulating the surface mass balance in Antarctica.

Archives of changes in the natural environments are gathered in various kinds of sediments,depending on the time in the history of the Earth. The Quaternary environmental variations are recorded from the ocean cores and the Greenland or Antarctic ice cores. High temporal resolution for shorter periods may be derived from annually laminated lacustrine sediments. A versatile archive for palaeogeographical reconstruction of the time of the Pleistocene–Holocene transition in the fluvial has been found at Koźmin Las site in the Uniwejów Basin of the middle Warta river valley. Well-preserved remains of pine subfossil forest as trunks and in situ stumps and accompanying organic deposits, of the late Alleröd and Younger Dryas age, have been subjected to multiproxy palaeoecological analysis and geological investigations. The sediments stored signals of a few short terrestrial events intrrupted by periodic floods. It has been concluded that the forest was destroyed by deteriorating hydrological conditions or a sudden catastrophic event, like a strong wind, in response to a global climatic change of the Pleistocene–Holocene transition. The Late Weichselian natural events recorded at the site point to a possible reaction of the fluvial system in a changing climate and environment. The knowledge about the past is essential to the creation of current ecosystem management strategies.

Antarctic ice cores have become a unique and powerful resource for studies of climate change. They contain information on past climate, on forcing factors such as greenhouse gas concentrations, and on numerous other environmental parameters. For recent centuries, sites with high snow accumulation are chosen. They have, for example, provided the only direct evidence that carbon dioxide concentrations have increased by over 30% over the last two centuries. They have provided key datasets for other greenhouse gases, and for other forcings such as solar and volcanic. Over longer timescales, the Vostok ice core has shown how greenhouse gas concentrations and climate have closely tracked one another over the last 400 000 years. Other cores have shown detailed spatial and temporal detail of climate transitions, including the Antarctic response during rapid climate events such as Dansgaard-Oeschger events. The new core from Dome C has extended the range of ice cores back beyond 800 000 years, and even older ice could be obtained in future projects.

Previous studies have shown significant warming through the 1990s in the West Antarctic Ice Sheet (WAIS); but the records used in those studies end in early 2000, preventing trend analysis into the latest decade. Fourteen new snowpits and firn cores were collected in 2010 and 2011, which have been combined with previous cores to extend the isotopic records over WAIS. Significance of these isotopic patterns across WAIS was determined and is used to re-evaluate the warming of the West Antarctic interior over recent decades. We find that isotopic records longer than 50 years are needed to assess climate trends due to decadal variability. When assessed over periods greater than 50 years, there is a statistically significant warming trend over central WAIS. However, the isotopes in the 2000s are anomalously low in the isotopic records, which challenge the recent suggestion that the warming trend is accelerating. We attribute the isotopic low over the most recent decade to the coupling effect of anomalously low temperatures over central WAIS and associated increase in sea ice in the adjacent seas. This work strongly indicates that decadal variability and likely climate trends are both driven, at least in part, by atmospheric variability in the tropics as well as at high latitudes.

Ce travail traite de la simulation numérique du climat des grandes calottes de glace, en particulier des calottes de l'Antarctique et du Groenland, toujours existantes, dans des conditions climatiques différentes, à l'aide de modèles de circulation générale de l'atmosphère (MCGA). Le MCGA à grille variable LMDz a été adapté aux spécificités du climat polaire et validé pour le climat actuel. L'approche d'une grille variable, qui permet d'utiliser le MCGA à haute résolution spatiale (autour de 100 km) sur la région d'intérêt à un coût numérique raisonnable, a été validée en analysant la dynamique atmosphérique au bord de la région ciblée à l'aide d'un schéma de suivi des cyclones individuels. Des simulations du climat du Dernier Maximum Glaciaire (DMG) ont été faites pour le Groenland et l'Antarctique et analysées en tenant compte des archives glaciaires disponibles. Une explication possible des différences entre les deux méthodes principales de reconstruction des paléotempératures - l'analyse des isotopes de l'eau et la mesure directe de la température de la glace dans le trou de forage - au centre du Groenland a pu être proposée. Cette explication est basée sur des changements de paramètres climatiques locaux. C'est la première fois que l'approche de grille variable a été utilisée dans un MCGA pour des simulations du climat polaire à l'échelle de quelques années. Les simulations paléoclimatiques faites avec LMDz sont à une résolution spatiale inégalée à ce jour. Finalement, le climat du DMG, simulé par plusieurs MCGA dans le cadre du projet international PMIP (Paleoclimate Modelling Intercomparison Programme), a été analysé, et des implications des résultats pour l'interprétation des enregistrements glaciaires ont été discutées.

La complexité du système climatique nécessite de recourir à une grande variété d'indicateurs pour reconstruire ses variations passées. A ce titre, les glaces polaires constituent un outil d'investigation privilégié compte tenu de la grande diversité d'informations qu'elles recèlent. Dans cette étude, nous nous intéressons plus particulièrement au forage antarctique côtier de DSS, sur le site du Law-Dome et aux indicateurs climatiques que constituent les teneurs isotopiques et la teneur en air de la glace. Le nombre d'analyses et la précision des mesures isotopiques requises pour l'étude d'un forage polaire demandent une adaptation et une mise en oeuvre spécifique des techniques classiques de spectrométrie de masse. Notre étude présente une technique nouvelle et originale d'injection des échantillons mise au point sur l'un des spectromètre de masse du laboratoire; elle a permis d'accroître sensiblement le rendement de l'appareil en conservant la précision expérimentale. Récemment de nouvelles études ont remis en cause l'interprétation quantitative classique des isotopes en termes de température. L'analyse de nouveaux échantillons de neige de surface sur la zone de l'Antarctique de l'Est nous permet de discuter la validité de la relation spatiale isotope/température et de proposer une estimation de l'erreur associée. L'utilisation de l'excès en deutérium et d'un modèle isotopique simple apportent une information supplémentaire sur l'origine des précipitations actuelles. Face aux interrogations sur l'impact des activités humaines sur le climat, il est essentiel de replacer les fluctuations récentes dans la cadre de la variabilité climatique naturelle. L'unique résolution temporelle offerte par le forage de DSS nous permet d'étudier en détail le climat des 4000 dernières années. L'analyse spectrale des enregistrements suggère l'existence de modes oscillatoires à rapprocher des phénomènes ENSO et/ou de l'onde circumpolaire antarctique. L'analyse de la teneur en air des échantillons de DSS nous apporte enfin une information sur les variations d'altitude probablement subies par le LawDome au cours de la dernière transition climatique.

Déposés en Antarctique de l'Est au cours des 4 derniers cycles climatiques, les aérosols volcaniques (5-50 )um) et continentaux (2-3 )um) de la carotte de Vostok constituent des traceurs de circulations atmosphériques passées. Pour reconstruire leurs trajectoires troposphériques, il est nécessaire d'identifier les sources (volcans ou régions désertiques) à l'origine des émissions des cendres et des poussières continentales. Pour cela, on compare les caractéristiques géochimiques des aérosols avec les caractéristiques des sources potentielles répertoriées. Ces analyses reposent sur les concentrations en éléments majeurs (obtenues par microsonde électronique), en éléments traces (ICPMS), et sur les compositions isotopiques en Strontium et Néodyme (TIMS). Nous avons dû adapter ces méthodes analytiques à la petite taille des aérosols et à leur très faible quantité. Les caractéristiques géochimiques des volcans sources potentiels (latitude>30oS, activité<-500 ka) sont basées sur une synthèse bibliographique. On montre que les cendres des horizons volcaniques analysés proviennent essentiellement de l'arc volcanique des îles Sandwichs (situé dans l'Atlantique Sud, à 5000 km), mais aussi d'Antarctique de l'Ouest et d'Amérique du Sud. De plus, certains horizons peuvent être utilisés comme marqueurs stratigraphiques pour dater (e.g. 141 ka) et corréler les carottes. Les caractéristiques isotopiques (Sr et Nd) des régions désertiques d'Afrique du Sud, d'Australie, du Sud de l'Amérique du Sud, d'Antarctique et de Nouvelle Zélande sont mesurées sur des échantillons prélevés in situ. On remarque qu'il est nécessaire d'utiliser, pour la comparaison avec les aérosols, la fraction granulométrique inférieure à 5 um. Il est ainsi montré que les poussières continentales déposées à Vostok au cours des 4 derniers cycles climatiques proviennent de la Patagonie en période interglaciaire (flux -1,5 mg/m2/an) comme en période glaciaire (flux -20 mg/m2/an). Une partie de cette augmentation de flux peut être expliquée par la présence de vastes épandages de particules détritiques fluvio-glaciaires qui recouvrent, en période glaciaire, la Patagonie et le plateau continental argentin émergé. L'ensemble des sources des aérosols volcaniques et continentaux est donc localisé, quelle que soit la période climatique, dans une région située du côté Atlantique de l'Antarctique, aux moyennes et hautes latitudes. Le transport des particules semble quant à lui être assuré par un courant d'ouest circumpolaire convergent versl'Antarctique. Ce travail montre donc que, à partir des aérosols volcaniques et continentaux, on peut obtenir des paléo-informations dynamiques qui, au travers des corrélations, des datations, ou des modèles de circulation atmosphérique globaux, seront utiles aux reconstitutions des climats du passé.

Present-day observations near Antarctica’s ice sheets suggest anthropogenic warming is affecting ocean circulation, with implications for further ice sheet melt, and changes to global thermohaline circulation. The mechanisms for ocean-ice sheet-sea ice changes are uncertain, and it is unclear how they will respond to warmer than present climates. Sediment records on the Antarctic continental margin provide evidence of significant changes with respect to productivity, ice sheet size and ocean circulation, on glacial to interglacial timescales. In this thesis, I describe the integrated response of the Adélie region of East Antarctica to past orbital forcing driven climate, including during the warmer than present Last Interglacial (Marine Isotope Stage 5e) to provide clues to its future response. I have studied five marine sediment cores from the continental shelf and slope of the Antarctic margin to understand the changes in regional oceanography, regional ice sheet size, seasonal sea ice and primary productivity to deduce the relationships between these components, during glacial cycles over the past >240 k yrs. I use an integrated approach employing sedimentological (grain size, structure, Ice Rafted Debris/ IRD), micropaleontological (diatom data) and geochemical (biogenic silica and X-ray fluorescence/ XRF data) proxies. First, in Chapter 3, I describe the last deglacial retreat of the ice sheet, from the outer continental shelf of the Mertz Trough in the Adélie region. Three facies are identified in core TAN1302-68 based on sedimentological, geochemical, and biogenic changes. Facies III comprises a pebble structure, with high coarse sand to granule count and a geochemically and texturally homogenous matrix, suggesting an ice sheet covered this site. Overlying is Facies IIa, a massive interval with IRD (~1mm sized dispersed grains) and slight changes in Fe and Fe/Ti. Above it is Facies IIb, a laminated interval with IRD, and significant sedimentological (comprising decrease in coarse sand to granule counts in comparison to III; and an increase in very fine to fine sand in the sediment matrix to 39%) and geochemical (Si/Al, Ba/Ti, Fe, Ti, Zr/Rb) changes. Facies IIa is suggestive of an ice shelf distal environment, while the rapid changes in Facies IIb, suggests an ice shelf calving zone. At the top is Facies I, a massively bedded, geochemically homogenous sediment, with a high very fine to fine sand fraction (39%) and increased biogenic silica, Si/Al, and Ba/Ti suggesting open ocean setting with higher productivity and active bottom currents. Based on radiocarbon dating and sedimentation rates of ~2.3 cm/k yr, the ice sheet retreated over this core site at <14 k yr, while ice shelf calving occurred between ~12-8 k yr, during which time, at ~10 k yr, stronger bottom currents developed on the shelf. I suggest the strong bottom current is likely the commencement of Dense Shelf Water formation in the Adélie region. Secondly, in Chapter 4, I describe bottom currents, ice sheet dynamics and productivity on the Adélie continental slope, from the MIS 7 interglacial to the Holocene. The data is based on four cores: two cores from 2,600 m (TAN1302-58; TAN1302-30) and two cores from 3,000 m depth (TAN1302-44; TAN1302-39), collected from the WEGA and G channels. I characterise four different facies, which form a pattern down core. Using visual logs, productivity data (Si/Al and Ba/Ti, and biogenic silica) and IRD counts I associate these facies with interglacial (Facies 1), glacial (Facies 2), deglacial (glacial retreat; Facies 2A) and glaciation (glacial advance; Facies 1A) climates. I suggest sediments in three cores are deposited by contour currents (thermohaline induced bottom currents), based on evidence of traction structures, gradation, and coarsening, and consistency of biogenic silica and IRD data. I relate these characteristics to records of Adélie Antarctic Bottom Water down slope flow, based upon changes in sediment matrix texture, related to the decrease in very fine to fine sand content down slope. Facies 1 suggests MIS 7, MIS 5e and Holocene interglacial environments are fairly similar, comprising strong bottom currents (very fine to fine sand up to 43%), active ice sheet retreat (IRD is 2-15 grains/g), and low to high productivity (biogenic silica is 4-22%). Facies 2 suggest MIS 4-2 and MIS 6 glacials featured a stable ice sheet (IRD is 2-4 grains/g), lower productivity (biogenic silica is 2-11%), and generally reduced bottom current strength (very fine to fine sand is 0-10%). However, MIS 6 contains multiple traction structures, while MIS 4-2 contains locally increased sand and biogenic silica, suggesting a different source of bottom current during MIS 6, and a locally greater velocity of bottom current occurred at times during MIS 4-2. Facies 1A, suggests MIS 5/4 glaciation comprised low to moderate productivity (4-11%), and locally strong bottom currents, as evidenced by increased sand fraction and traction structures on the upper slope. Facies 2A suggests MIS 2/1 and MIS 6/5 deglacial comprised low to moderate productivity (2-10%) and generally slower bottom currents. The features of the glaciation and deglacial facies suggest stable ice sheets at these times. The fourth core (TAN1302-39) is influenced by turbidity current and debris flow deposits, with some influence of contourite deposits especially at its base, where carbonate facies is found. Lastly, in Chapter 5, I describe diatom assemblages from core TAN1302-44, from the base of the WEGA channel, studying the section from MIS 6/5 deglacial (~140 k yr) to the Holocene. I find diatom assemblages vary on glacial to interglacial timescale, according to the facies described in Chapter 4, suggesting diatoms reflect glacial cycles, likely in relation to regional sea ice and oceanographic changes. Using Principal Component Analysis, I have identified three main assemblages. PC1 comprises open ocean and seasonal sea ice species (Thalassiosira antarctica, Thalassiosira lentiginosa, Actinocyclus actinochilus, Asteromphalus hyalinus, Thalassiosira sp 2, Eucampia antarctica, and Fragilariopsis kerguelensis). PC1 is associated with the interglacial facies and suggests seasonal sea ice paleoenvironments and nutrients are similar between MIS 5e and Holocene. However, the unusual abundance of Thalassiosira antarctica resting spore and Thalassiosira lentiginosa (up to 40-60%), suggests some reworking by bottom currents and dissolution has affected the preservation of this assemblage. PC 2 comprises sea ice and coastal species (Fragilariopsis obliquecostata, Rhizosolenia styliformis, Asteromphalus parvulus and Chaetoceros dichaeta). It is associated with the glacial facies, but also with glaciation and deglacial facies, suggesting MIS 4-2 glacial, MIS 6/5 and MIS 2/1 deglacial and MIS 5/4 glaciation (especially MIS4-2 glacial) exhibit increased length of sea ice season relative to interglacials, but not a permanent sea ice cover. The gradual increase of PC 2, in the glaciation and throughout the glacial facies, suggests the sea ice season length gradually builds up with cooling, and rapidly disintegrates with warming. Lastly, PC 3 comprises warmer water/nutrient rich species (Thalassiothrix antarctica, Chaetoceros bulbosum and Thalassiosira oestrupii), which is associated with the deglacial and glaciation facies, suggesting increased upwelling of a water mass, which I infer is the Circumpolar Deep Water. To my knowledge, this study is among a few to present evidence of glacial Antarctic Bottom Water production from the Adélie Land region of East Antarctica. Furthermore, I present the first integrated sedimentological and XRF/ geochemical data set describing the timing and initial rate of ice sheet retreat from the Antarctic margin, from the Mertz Trough. This is the first study to describe contourite traction structures within the Quaternary glacial facies comprising ripples, mud off shoots, flaser bedding, pebble lined laminae, from the Adélie region and the Antarctic margin, and among just a few studies to describe the diatom assemblages for the last glacial cycle from the Antarctic continental margin.

Antarctic climate changes have been reconstructed from ice and sediment cores and numerical models (which also predict future changes). Major ice sheets first appeared 34 million years ago (Ma) and fluctuated throughout the Oligocene, with an overall cooling trend. Ice volume more than doubled at the Oligocene-Miocene boundary. Fluctuating Miocene temperatures peaked at 17–14 Ma, followed by dramatic cooling. Cooling continued through the Pliocene and Pleistocene, with another major glacial expansion at 3–2 Ma. Several interacting drivers control Antarctic climate. On timescales of 10,000–100,000 years, insolation varies with orbital cycles, causing periodic climate variations. Opening of Southern Ocean gateways produced a circumpolar current that thermally isolated Antarctica. Declining atmospheric CO2 triggered Cenozoic glaciation. Antarctic glaciations affect global climate by lowering sea level, intensifying atmospheric circulation, and increasing planetary albedo. Ice sheets interact with ocean water, forming water masses that play a key role in global ocean circulation.

Antarctic climate changes have been reconstructed from ice and sediment cores and numerical models (which also predict future changes). Major ice sheets first appeared 34 million years ago (Ma) and fluctuated throughout the Oligocene, with an overall cooling trend. Ice volume more than doubled at the Oligocene-Miocene boundary. Fluctuating Miocene temperatures peaked at 17–14 Ma, followed by dramatic cooling. Cooling continued through the Pliocene and Pleistocene, with another major glacial expansion at 3–2 Ma. Several interacting drivers control Antarctic climate. On timescales of 10,000–100,000 years, insolation varies with orbital cycles, causing periodic climate variations. Opening of Southern Ocean gateways produced a circumpolar current that thermally isolated Antarctica. Declining atmospheric CO2 triggered Cenozoic glaciation. Antarctic glaciations affect global climate by lowering sea level, intensifying atmospheric circulation, and increasing planetary albedo. Ice sheets interact with ocean water, forming water masses that play a key role in global ocean circulation.

Climate change is happening all around us, and one of the telltale signs is melting glaciers. We hear about it almost daily, pieces of ice the size of continents breaking off of Antarctica or the polar arctic ice breaking up and disappearing more and more quickly opening up navigational routes once unavailable due to thick winter ice cover. Will melting ice and glaciers so far away change our lives? Meltdown takes us deep into the cryosphere, the Earth’s frozen environment and picks apart why glacier melt caused by climate change will alter (and already is altering) the way we live around the world. From rising seas that will destroy property and flood millions of acres of coastal lands, displacing hundreds of millions of people, to rising global temperatures due to reflectivity changes of the Earth because of decreased white glacier surface area, to colossal water supply changes from glacier runoff reduction, to deadly glacier tsunamis caused by the structural weakening of ice on high mountaintops that will take out entire communities living in glacier runoff basins, to escaping methane gas from thawing frozen permafrost grounds, and changing ocean temperatures that affect jet streams and ocean water currents around the planet, glacier melt is altering our global ecosystems in ways that will drastically change our everyday lives. Meltdown takes us into the little-known periglacial environment, a world of invisible subterranean glaciers in our coldest mountain ranges that will survive the initial impacts of climate change but that are also ultimately at risk due to a warming climate. By examining the dynamics of melting glaciers, Meltdown helps us grasp the impacts of a massive geological era shift occurring right before our eyes.

At longer timescales, the interaction among climate, ecosystems, and the abiotic components of the environment become increasingly important. These relationships are apparent in the three chapters in part IV. Fountain and Lyons (chapter 16), examining the McMurdo Dry Valleys (MCM) ecosystem in Antarctic, provide an excellent example of a case where past climatic variations truly dictate current ecosystem status. The relatively large climate variations at MCM have concentrated nutrients that could not have been attained without this climate variability. Fountain and Lyons infer climate change from geomorphic evidence of past glacier positions and lake level heights as well as more recent isotopic results from ice cores and temperature measurements from boreholes. They focus on evidence from the most recent 60,000 years. Monger (chapter 17) provides an analysis of millennial-scale climate and ecosystem variability at the Jornada LTER site in southern New Mexico. Monger notes the difficulty of untangling prehistoric climate/ecosystem interactions, where researchers must rely on indirect proxy indicators in lieu of measured data. Monger analyzes a number of proxy data sources, including paleolake levels, plant remnants preserved in packrat middens, fossil pollens, carbon isotope ratios in paleosols, and erosion rates. Although noting the danger of circular reasoning in using proxy data (i.e., ecosystem response used to infer information about climatic change, which is in turn inferred from ecosystem response) Monger uses these data to construct a cogent picture of climate change at the Jornada site (JRN) since the Last Glacial Maximum (LGM) about 18,000–20,000 years b.p. Using remains of beetles, Elias (chapter 18) constructs a temperature history of the Colorado Alpine since the LGM. These late Holocene insect records show a progression from warmer-than-modern to coolerthan- modern summers, and back to warm again. All the authors in this section provide examples to show that it is at century to millennial timescales that ecosystems form, are broken apart and imprinted by the past, and reformed in new configurations. The McMurdo Dry Valleys is the most poleward-terrestrial ecosystem where streams, lakes, and soil are interconnected. In this polar desert, the biotic system must adopt a strategy to survive the winter in isolation, and the disturbance and formation of the landscape has been primarily dictated by climate and associated abiotic processes. During the last glacial period, the Ross Ice shelf entered Taylor Valley, damming the valley and forming a 200-m-deep lake (23.8 kyrs).

Comparison of the average mean surface air temperature around the world during 1951–1978 with that for 2010–2019 shows that the bulk of the warming is around the North Atlantic/Arctic region in contrast to the Antarctic ice sheet. Obviously, the temperature change is not global. Since there is a substantial difference between solar heat absorption between the equator and the poles, heat must be moving to the North Pole by surface ocean currents and tropical cyclones. The cold, dry Arctic air coming from Siberia picks up heat and moisture from the open oceans, making the sea water denser so that the warm water sinks slowly down to c. 2000 m. A deep-water thermohaline flow (THC) transports the excess hot (c. 18°C) water south to Antarctica. It is replaced by a cold (c. 2°C) surface water from that area. The latter quickly cool western Europe and Siberia, and glaciers start to advance in Greenland within about 10 years. The THC flow decreases in Interglacials, causing the increased build-up of heat in the Northern Hemisphere (c. 60% currently stored in the Atlantic Ocean), and the ice cover in the Arctic Ocean thaws. Several such cycles may take place during a single major cold event.

The northern European loess belt (NELB) was created in cold climate conditions on the foreground of Pleistocene continental glaciations. Loess-paleosol sequences (LPS) in this region were strongly influenced by periglacial processes and environments. Three types of periglacial structures are especially useful to reconstruct the former periglacial environment: cryogenic wedges with primary mineral infilling, cryoturbation and gelifluction structures, and ice-wedge pseudomorphs. These structures often form well-distinguishable marker horizons within LPS. We assume that at least some of these horizons were formed as a result of sudden, short-term cooling followed by equally sudden warming of the climate, when ice wedges and permafrost were decay. Periglacial records in the LPS confirm the general instability of the last glacial climate. The main periglacial stages correlate well with cold events of the marine record. However, their correlation with Greenland ice cores requires further research using modern methods and techniques.

Elias argues (chapter 18, p. 370) that ecosystems are shaped by environmental changes that have occurred over thousands of years so that the century to millennial timescale is of particular significance because “it is on these timescales that ecosystems form, break apart, and reform in new configurations.” Within this context, the authors for the three chapters in part IV evaluate evidence for climate variability since the Last Glacial Maximum (LGM) to the present. They evaluate the biological responses to these longer term changes and highlight the importance of past climatic conditions on current ecosystem function. If we view, as Elias does, glacial climate as a filter through which ecosystems have passed, then variability since the LGM comprises a significant fraction of the biotic history that shaped current ecosystems. This is an overriding theme for this section. Fountain and Lyons (chapter 16), examining a dry valley ecosystem in Antarctica (MCM), evaluate various proxy records to establish the historic context of their landscape. They argue that this historical context is important for a full understanding of ecosystems and that it is especially important for the MCM ecosystem. Providing an excellent example of legacy, the effect of past imprints on current ecosystem function, they present evidence that past climatic variations truly dictate current ecosystem status. During the LGM, ice blocked the current Taylor Valley, forming a lake that contained phytoplankton and algal mats. Subsequent warming eliminated the blockage, drained the large lake, forming several smaller ones, and established the current landscape. The former large lake supplied nutrients to the soil and current lakes. Fountain and Lyons (p. 334) state that “the vital importance of climatic legacy in the dry valleys is due to its extreme environment, low biodiversity, and short food chains.” They also observe a “polar amplification,” whereby the sharp solid/liquid phase transition of water allows small changes in climate to produce relatively large variations in ecosystem response. The Jornada Long-Term Ecological Research site (JRN) is representative of the desert shrubland and desert grassland ecosystems of the southwestern United States. Monger (chapter 17) makes use of a range of biotic (packrat middens, fossil pollen), abiotic (chronological data on lake levels, position of alpine glaciers and rock glaciers) and soil-geomorphic evidence to create a working hypothesis of the bioclimatic changes during the last 20,000 years. There is a remarkable consistency in these proxy estimates given their diversity.

Linking river behaviour and drainage basin evolution to Quaternary environmental change, most notably the effects of climatic variability, tectonics, and human activity on runoff and sediment delivery, has a long history of research in the Mediterranean areas of Europe, North Africa, and the Near East. This field of research was initially stimulated by the (re)discovery at the beginning of the twentieth century of many Classical Period remains buried by river alluvium; perhaps the best known of which is the site of Olympia in western Greece (Huntington 1910). The widespread evidence for large-scale shifts in river channel positions and the rapid growth of deltas and coastal alluvial plains in historical times (Judson 1963; Raphael 1973; Kraft et al. 1980; and Chapter 13) also provided much impetus for this research. In addition, archaeological investigations carried out soon after the Second World War in Algeria (Gaucher 1947), Italy (Selli 1962), Libya (McBurney and Hey 1955) and Spain (Gigout 1959) resulted in the recovery of large numbers of Palaeolithic stone tools from Pleistocene fluvial deposits. These early examples of what has now become more widely known as ‘geoarchaeology’ (Davidson and Shackley 1976; Butzer 1977) or ‘alluvial archaeology’ (Macklin and Needham 1992) were, with their strong interdisciplinary focus, highly innovative and ahead of their time in the way they integrated archaeology, geomorphology, and geochronology. Building on this theme, the principal aim of this chapter is to consider how river systems in the Mediterranean region have responded to the environmental changes that took place during the Late Quaternary–a time interval corresponding approximately to the last 130,000 years. There are a number of reasons for choosing this period for reviewing river-environment interactions in the Mediterranean: 1. It encompasses the last glacial–interglacial cycle (c.130 to 10 ka) for which there is now abundant global evidence from polar ice cores, speleothem records, and lake and marine sediments, for both longand short-term changes in climate. These changes included massive reorganizations of the atmosphere-ocean-cryosphere systems—often over timescales of less than 100 years (Lowe and Walker 1997)—and they are clearly recorded in the Mediterranean region (see Allen et al. 1999 and Chapter 4).