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This study presents a long-term, multi-proxy reconstruction of the Asian southwest monsoon during the Tortonian to Piacenzian, based on a 4.78 Ma record from Coastal Makran, northwestern Gulf of Oman, southeast Iran. The integration of humidity proxies (clay minerals, Th/K, volume magnetic susceptibility, and grain size analysis), marine redox sensitivity (Th/U), total organic matter, carbonate content, [.sup.87]Sr/[.sup.86]Sr ratio, and spectral gamma-ray data conducted here provide valuable information that fill the existing gap in marine palaeoclimate records. The results show that a strong winter monsoon condition associated with relatively low precipitation and subsequently low physical and chemical weathering dominated the region during late Tortonian--late Messinian (7.65-5.83 Ma). However, a few episodes of intense physical and chemical weathering related to high precipitation are observed during this period (6.23-6.01 Ma), which is consistent with increased organic matter input from continental reservoirs to the oceans. In addition, the data indicate that from the latest Messinian (5.82-5.33 Ma) to Zanclean-Piacenzian (5.33-2.87 Ma), a strong summer monsoon accompanied by a relatively wetter condition and higher physical and chemical weathering resulted in a high detrital input into the basin. This higher weathering period is associated with the highest rate of Himalayan uplift, causing enhanced precipitation. Wavelet analysis of spectral gamma-ray data revealed notable periodicities at 750 Ka and 1.7 Ma, with significant periodicities centered around 5.75-6.03 Ma over the latest Messinian--Zanclean. Comparison with palaeoclimate records from other sites indicates a teleconnection with respect to precipitation, weathering, and productivity, especially during the Messinian--Zanclean transition. Resume : Nous presentons une reconstitution de longue duree reposant sur plusieurs variables substitutives de la mousson du Sud-Ouest asiatique, du Tortonien au Piacenzien, etablie a la lumiere d'un registre de 4,78 millions d'annees de la region cotiere de Makran du nord-ouest du golfe d'Oman (sud-est de l'Iran). L'integration de variables substitutives de l'humidite (mineraux argileux, Th/K, susceptibilite magnetique volumique et granulometrie), de la sensibilite a l'oxydoreduction marine (Th/U), des matieres organiques totales, du contenu en carbonate, du [.sup.87]Sr/[.sup.86]Sr et de donnees de spectrometrie gamma fournit de l'information importante qui comble une lacune existante dans les profils paleoclimatiques marins durant la periode etudiee dans cette region. Les resultats montrent que des conditions de forte mousson hivernale associees a des precipitations relativement faibles, suivies d'une faible alteration physique et chimique predominaient dans la region du Tortonien tardif au Messinien tardif (de 7,65 a 5,83 Ma). Quelques episodes d'alteration physique et chimique intense associee a de fortes precipitations sont toutefois observes durant cette periode (de 6,23 a 6,01 Ma), ce qui concorde avec un apport accru aux oceans de matiere organique provenant de reservoirs continentaux. En outre, les donnees indiquent que, du Messinien sommital (de 5,82 a 5,33 Ma) au Zancleen-Piacenzien (de 5,33 a 2,87 Ma), une forte mousson estivale etait accompagnee de conditions relativement humides et d'une plus forte alteration physique et chimique qui se sont traduites par un fort apport detritique dans le bassin. Cette periode d'alteration accrue est associee au taux le plus eleve de soulevement himalayen a l'origine des precipitations accrues. L'analyse par ondelettes de donnees de spectrometrie gamma revele des periodicites marquees a 750 Ka et 1,7 Ma, dont des periodicites significatives centrees autour de 5,75 a 6,03 Ma au Messinien sommital-Zancleen. La comparaison des resultats aux archives paleoclimatiques pour d'autres sites indique une teleconnexion des precipitations, de l'alteration et de la productivite, particulierement durant la transition du Messinien au Zancleen. [Traduit par la Redaction], Introduction The Asian monsoon, an atmospheric circulation pattern, governs the climatic conditions of the entire continent of Asia. It is comprised of the Indian Summer monsoon, East Asian monsoon, and [...]

Unknown basal characteristics limit our ability to simulate the subglacial hydrology of rapidly thinning contemporary ice sheets. Subglacial water is typically conceptualised as being routed through either distributed, inefficient, and high pressure systems, or channelised, efficient, and low-pressure systems, transitioning between the two as a function of discharge. Sediment-based landforms generated beneath Pleistocene ice sheets, together with detailed digital elevation models, offer a valuable means of parameterising and testing models of subglacial hydrology. However, previous work using geomorphology to inform modelling has concentrated on landforms relating to channelised drainage (e.g., eskers) while using inherently channelised models unable to capture transitions in drainage state. Landscapes relating to the distributed drainage system, and the hypothesised transitional zone of drainage between distributed and channelised drainage modes have therefore been largely ignored. To address this, we use the Glacier Drainage System model (GlaDS), a 2D finite element model capable of capturing the transition between distributed and channelised drainage, to explore the genesis of 'murtoos', a distinctive triangular landform found in murtoo fields throughout Finland and Sweden. Murtoos are hypothesised to form 40–60 km from the former Fennoscandian ice margin at the onset of channelised drainage where water pressure is at or exceeds ice overburden pressure. Concentrating within a specific ice lobe of the former Fennoscandian Ice Sheet and parameterised using digital elevation models with a simulated former ice surface geometry, we carried out a range of sensitivity testing to explore murtoo genesis and drainage transitions beneath the palaeo ice sheet. Our modelling supports many of the predictions for murtoo origin, including the location of water pressures equal to ice overburden, the onset of channelised drainage, and the predicted water depths in terrain surrounding murtoo fields. Modelled channels also closely match the general spacing, direction and complexity of eskers and mapped meltwater routes. Our results demonstrate that examining palaeo basal topography alongside subglacial hydrology model outputs holds promise for mutually beneficial analyses of palaeo and contemporary ice sheets to assess the controls of hydrology on ice dynamics and subglacial landform evolution. [ABSTRACT FROM AUTHOR]

Unknown basal characteristics limit our ability to simulate the subglacial hydrology of rapidly thinning contemporary ice sheets. Subglacial water is typically conceptualised as being routed through either distributed, inefficient, and high-pressure systems, or channelised, efficient, and low-pressure systems, transitioning between the two as a function of discharge. Sediment-based landforms generated beneath Pleistocene ice sheets, together with detailed digital elevation models, offer a valuable means of parameterising and testing models of subglacial hydrology. However, previous work using geomorphology to inform modelling has concentrated on landforms relating to channelised drainage (e.g., eskers) while using inherently channelised models unable to capture transitions in drainage state. Landscapes relating to the distributed drainage system, and the hypothesised transitional zone of drainage between distributed and channelised drainage modes have therefore been largely ignored. To address this, we use the Glacier Drainage System model (GlaDS), a 2D finite element model capable of capturing the transition between distributed and channelised drainage, to explore the genesis of 'murtoos', a distinctive triangular landform found in murtoo fields throughout Finland and Sweden. Murtoos are hypothesised to form 40-60 km from the former Fennoscandian ice margin at the onset of channelised drainage where water pressure is at or exceeds ice overburden pressure. Concentrating within a specific ice lobe of the former Fennoscandian Ice Sheet and parameterised using digital elevation models with a simulated former ice surface geometry, we carried out a range of sensitivity testing to explore murtoo genesis and drainage transitions beneath the palaeo ice sheet. Our modelling supports many of the predictions for murtoo origin, including the location of water pressures equal to ice overburden, the onset of channelised drainage, and the predicted water depths in terrain surrounding murtoo fields. Modelled channels also closely match the general spacing, direction and complexity of eskers and mapped meltwater routes. Our results demonstrate that examining palaeo basal topography alongside subglacial hydrology model outputs holds promise for mutually beneficial analyses of palaeo and contemporary ice sheets to assess the controls of hydrology on ice dynamics and subglacial landform evolution. [ABSTRACT FROM AUTHOR]

How environmental conditions influence current distributions of organisms at the local scale in sensitive High Arctic freshwaters is essential to understand in order to better comprehend the cascading consequences of the ongoing climate change. This knowledge is also important background data for paleolimnological assessments of long-term limnoecological changes and in describing the range of environmental variability. We sampled five limnologically different freshwater sites from the Fuglebergsletta marine terrace in Hornsund, southern Svalbard, for aquatic invertebrates. Invertebrate communities were tested against non-climatic environmental drivers as limnological and catchment variables. A clear separation in the communities between the sites was observed. The largest and deepest lake was characterized by a diverse Chironomidae community but Cladocera were absent. In a pond with marine influence, crustaceans, such as Ostracoda, Amphipoda, and calanoid Copepoda were the most abundant invertebrates. Two nutrient-rich ponds were dominated by a chironomid, Orthocladius consobrinus, whereas themost eutrophic pond was dominated by the cladoceran Daphnia pulex, suggesting decreasing diversity along with the trophic status. Overall, nutrient related variables appeared to have an important influence on the invertebrate community composition and diversity, the trophic state of the sites being linked with their exposure to geese guano. Other segregating variables included water color, presence/absence of fish, abundance of aquatic vegetation and lake depth. These results suggest that since most of these variables are climate-driven at a larger scale, the impacts of the ongoing climate change will have cumulative effects on aquatic ecosystems.

The sedimentary environment, sediment characteristics and age-depth models of sediment sequences from Arctic lakes Revvatnet and Svartvatnet, located near the Polish Polar Station in Hornsund, southern Svalbard (77°N), were studied with a view to establishing a basis for paleolimnological climate and environmental reconstructions. The results indicate that catchment-to-lake hydroclimatic processes probably affect the transportation, distribution and accumulation of sediments in different parts of lakes Revvatnet and Svartvatnet. Locations with continuous and essentially stable sedimentary environments were found in both lakes between water depths of 9 and 26 m. We used several different dating techniques, including 137Cs, 210Pb, AMS 14C, and paleomagnetic dating, to provide accurate and secured sediment chronologies. Arecovered sequence from the northern basin of Revvatnet spans more than one thousand years long with laminated stratigraphy in the upper part of the sediment. Based on AMS 14C dates, it is possible to suppose that Revvatnet basin was not occupied by a valley glacier during the Little Ice Age. The dates were supported by 137Cs chronologies, but not confirmed with other independent dating methods that extent beyond the last 50 years. A sedimentary sequence from the northern basin of Svartvatnet provides a potential archive for the study of climate and environmental change for the last ca. 5000 years. Based on the stratigraphy and a Bayesian age-depth model of AMS14C and paleosecular variation (PSV) dates, the recovered sediment sections represent a continuous and stable sedimentation for the latter half of the Holocene.