Continental Ice Sheets Research Articles

The penultimate deglaciation: protocol for PMIP4 transient numerical simulations between 140 and 127 ka, version 1.0

Abstract. The penultimate deglaciation (PDG, ~ 138–128 thousand years before present, hereafter ka) is the transition from the penultimate glacial maximum to the Last Interglacial (LIG, ~ 129–116 ka). The LIG stands out as one of the warmest interglacials of the last 800 ka, with high-latitude temperature warmer than today and global sea level likely higher by at least 6 meters. Considering the transient nature of the Earth system, the LIG climate and ice-sheets evolution were certainly influenced by the changes occurring during the penultimate deglaciation. It is thus important to investigate, with coupled Atmosphere-Ocean General Circulation Models (AOGCMs), the climate and environmental response to the large changes in boundary conditions (i.e. orbital configuration, atmospheric greenhouse gas concentrations, ice-sheet geometry, and associated meltwater fluxes) occurring during the penultimate deglaciation. A deglaciation working group has recently been set up as part of the Paleoclimate Modelling Intercomparison Project (PMIP) phase 4, with a protocol to perform transient simulations of the last deglaciation (19–11 ka; although the protocol covers 26–0 ka). Similar to the last deglaciation, the disintegration of continental ice-sheets during the penultimate deglaciation led to significant changes in the oceanic circulation during Heinrich Stadial 11 (~ 136–129 ka). However, the two deglaciations bear significant differences in magnitude and temporal evolution of climate and environmental changes. Here, as part of the PAGES-PMIP working group on Quaternary Interglacials, we propose a protocol to perform transient simulations of the penultimate deglaciation under the auspices of PMIP4. This design includes time-varying changes in orbital forcing, greenhouse gas concentrations, continental ice-sheets as well as freshwater input from the disintegration of continental ice-sheets. This experiment is designed for AOGCMs to assess the coupled response of the climate system to all forcings. Additional sensitivity experiments are proposed to evaluate the response to each forcing. Finally, a selection of paleo records representing different parts of the climate system is presented, providing an appropriate benchmark for upcoming model-data comparisons across the penultimate deglaciation.

Origin of the Redwater River Drainage Basin Determined by Topographic Map Interpretation: Eastern Montana, USA

Topographic and geologic map interpretation strongly suggests the eastern Montana Redwater River valley eroded headward across large southeast-oriented ice-marginal melt water floods. The north-oriented Redwater River heads in an area to the south of recognized continental glaciation and flows into the recognized glaciated region before joining the east-oriented Missouri River. Detailed topographic maps show the eastern drainage divide is asymmetric with steeper slopes on the Redwater River side and is crossed by shallow dry valleys linking northwest-oriented Redwater River tributaries with southeast-oriented streams that flow as barbed tributaries to the northeast-oriented Yellowstone River. The western drainage divide is also crossed by shallow dry valleys linking northwest-oriented drainage routes to north-oriented Missouri River tributaries with southeast-oriented and barbed tributaries to the northeast- and north-oriented Redwater River. Alluvium from upstream Yellowstone River source areas found within the Redwater River drainage basin suggests the Redwater River and much longer Yellowstone River valleys eroded headward from a continental ice sheet margin as headward erosion of the larger Yellowstone River valley across the southeast-oriented flood flow was supplemented by northeast- and north-oriented flow moving at the present day Redwater-Yellowstone River drainage divide elevation.

Quaternary evolution of the Ploučnice River system (Bohemian Massif) based on fluvial deposits dated with optically stimulated luminescence and in situ produced cosmogenic nuclides

The Ploučnice River system, located in the central Bohemian Massif, is draining an area almost not covered by continental ice sheets but instead archiving the fluvial deposits. The fluvial style changes from a high-energy braided to a long-bend meandering river in the upper terrace levels (36 to 29 m above present floodplain). The middle terrace levels (22 to 14 m above present floodplain) indicate a fluvial style changing from a high- to medium-energy braided river. In the lower terrace levels (13 to 5 m above present floodplain), the terrace deposits indicate high-energy braided to long-bend meandering river environments. To provide greater details on the timing of fluvial terrace formation, this study applied 26Al and 10Be isochron burial and optically stimulated luminescence (OSL) dating methods to terraces of the Ploučnice River system. Terrace fluvial infills are dated with isochron burial dating in relative altitude 34, 29, and 14 m above present floodplain (apf); whereas terrace accumulations in relative altitude 19, 12, and 6 m apf are dated with OSL. Because of differences in age results between the two dating methods, we propose two different evolution models: the first is based on isochron burial and OSL dating, and the second model is on OSL dating results only. The time span represented by the river terraces remains unclear and varies from Eburonian to Weichselian (1680 to 56 ka) or from Saalian to Weichselian (138 to 56 ka) with the estimation of the highest terrace (248 ka) respectively. The former river evolution model is based on tectonic activity at least since 1000 ka. Morphotectonic analysis recognized new lineaments of which the general direction corresponds with the main direction of the Ohře fault zone (NE- to ENE-striking) and Lužice fault zone (NW-striking). Based on dated terrace ages of 1153 ± 123 ka at 14 m apf and 138 ± 21 ka at 19 m above present floodplain, we propose a normal fault being active from at least 1153 ka. The second river evolution model assumes possible remobilization of clasts analyzed by isochron burial dating before their final deposition. From three OSL ages we calculated a mean incision rate and estimated an age of upper terrace levels at 34 m apf to be 248 ± 38 ka (Saalian age). As remobilization of clasts in high-energy fluvial and glaciofluvial environments is very likely, age determination is challenging. Nevertheless, we interpret the terrace record in the Ploučnice River system as a product of Quaternary climatic changes influenced by tectonic processes.

Upper Sun River Drainage Basin Origin Determined by Topographic Map Interpretation Techniques: Lewis and Clark and Teton Counties, Montana, USA

A new and fundamentally different regional geomorphology paradigm in which massive south- and southeast-oriented meltwater floods flowed across the entire Missouri River drainage basin is tested by interpreting detailed topographic maps of the Montana upper Sun River drainage basin region by trying to explain origins of previously unexplained or poorly explained erosional landforms located upstream from Sun River Canyon (which cuts across Montana’s north-to-south oriented Sawtooth Range). Mountain passes, through valleys, and other drainage divide low points along what are today high mountain ridges, including the North American east-west continental divide, are interpreted to be evidence of drainage routes that once crossed the region. These drainage divide crossings suggest that prior to erosion of present-day upper Sun River drainage basin valleys, massive floods moved in south directions across what are today the north-oriented Middle and South Fork Flathead River drainage basins into today’s upper Sun River drainage basin area and carved a complex of diverging and converging channels into what was probably a low relief surface now represented by the crests of the region’s highest mountain ridges. Further, the map evidence shows how a diverging complex of south- and southeast-oriented upstream Sun River drainage basin flood flow channels changed flow direction to cross the Sawtooth Range in a northeast direction before converging on the Montana plains at a location downstream from Sun River Canyon. The observed upper Sun River drainage basin area topographic map evidence is consistent with the new geomorphology paradigm predictions, in which massive south-oriented meltwater floods flowing across the rising rim of a continental ice sheet created deep “hole” (created by deep ice sheet erosion and ice sheet weight caused crustal warping) are diverted to flow in northeast and north directions into and across deep “hole” space being opened up by ice sheet melting.

Use of Topographic Map Evidence to Test a Recently Proposed Regional Geomorphology Paradigm: Wind River-Sweetwater River Drainage Divide Area, Central Wyoming, USA

Topographic map evidence from the Wyoming Wind River-Sweetwater River drainage divide area is used to test a recently proposed regional geomorphology paradigm defined by massive south- and southeast-oriented continental ice sheet melt water floods that flowed across the entire Missouri River drainage basin. The new paradigm forces recognition of an ice sheet created and occupied deep “hole” and is fundamentally different from the commonly accepted paradigm in which a pre-glacial north- and northeast-oriented slope would have prevented continental ice sheet melt water from reaching or crossing the Wind River-Sweetwater River drainage divide. Divide crossings (or low points) are identified as places where water once flowed across the drainage divide. Map evidence is interpreted first from the accepted paradigm perspective and second from the new paradigm perspective to determine the simplest explanation. Both paradigm perspectives suggest south-oriented water crossed the drainage divide, although accepted paradigm interpretations do not satisfactorily explain the large number of observed divide crossings and are complicated by the need to bury the Owl Creek and Bridger Mountains to explain why the Wind River now flows in a north direction through Wind River Canyon. New paradigm interpretations explain the large number of divide crossings as diverging and converging channel evidence (as in flood-formed anastomosing channel complexes), Owl Creek and Bridger Mountain uplift to have occurred as south-oriented floodwaters carved Wind River Canyon, and a major flood flow reversal (caused by ice sheet related crustal warping and the opening up of deep “hole” space by ice sheet melting) as being responsible for the Wind River abrupt turn to the north. While this test only addresses topographic map evidence, Occam’s Razor suggests the new paradigm offers what in science should be the preferred Wind River-Sweetwater River drainage divide origin interpretations.

Use of Stream and Dismembered Stream Valleys Now Crossing Wyoming’s Northern Laramie Mountains to Test a Recently Proposed Regional Geomorphology Paradigm, USA

Detailed topographic maps show multiple stream valleys and what are probably dismembered stream valleys that extend completely across Wyoming’s northern Laramie Mountains. Several of the most obvious valleys are described with valley origins first explained (or attempted to be explained) from the commonly accepted regional geomorphology paradigm (accepted paradigm) perspective and second from a recently proposed regional geomorphology paradigm (new paradigm) perspective in an effort to determine which of the two paradigms provides the simplest explanations. Accepted paradigm explanations require at least some of the valley erosion to have occurred prior to deposition of Oligocene and Miocene sediments that once covered the northern Laramie Mountains (with some of the exhumed valleys now containing sediment cover remnants). In contrast the fundamentally different new paradigm requires immense south-oriented continental ice sheet melt water floods to have crossed the region as ice sheet related crustal warping raised the region and the Laramie Mountains (and implies sediments now partially filling some of the valleys are probably flood deposited materials). The new paradigm provides simpler explanations for the origins of the valleys now extending completely across the northern Laramie Mountains and also for their related barbed tributaries, truncated side valleys, and drainage route U-turns than the accepted paradigm, although the new paradigm also leads to a fundamentally different middle and late Cenozoic regional geologic history than is currently recognized. One paradigm cannot be used to judge a different paradigm, but the paradigms can be compared based on their ability to explain evidence and Occam’s Razor can determine which of the two paradigms provides the simplest explanations. New paradigm explanations for northern Laramie Mountains valley origins investigated here require fewer assumptions than the accepted paradigm explanations suggesting the new paradigm merits serious future consideration.

Detrital zircon age and provenance constraints on late Paleozoic ice-sheet growth and dynamics in Western and Central Australia

U–Pb dating and Hf-isotope provenance analysis of detrital zircons from the glaciogenic lower Permian Grant Group of the Canning Basin indicate sources principally from basement terranes in central Australia, with subordinate components from terranes to the south and north. Integrating these data with field outcrop and subsurface evidence for ice sheets, including glacial valleys and striated pavements along the southern and northern margins of the basin, suggests that continental ice sheets extended over several Precambrian upland areas of western and central Australia during the late Paleozoic ice age (LPIA). The youngest zircons constrain the maximum age for contemporaneous ice sheet development to the late Carboniferous (Kasimovian), whereas palynology provides a minimum age of early Permian (Asselian–Sakmarian). Considering the palynological age of the Grant Group within the context of regional and global climate proxies, the main phase of continental ice sheet growth was possibly in the Ghzelian–Asselian. The presence of ice sheets older than Kasimovian in western and central Australia remains difficult to prove given a regional gap in deposition possibly covering the mid-Bashkirian to early Ghzelian within the main depocentres and even larger along basin margins, and the poor evidence for older Carboniferous glacial facies. There is also no evidence for extensive glacial facies younger than mid-Sakmarian in this region as opposed to eastern Australia where the youngest regional glacial phase was Guadalupian.

Chemical weathering across the western foreland of the Greenland Ice Sheet

Proglacial streams deliver melt water and chemical weathering products, including nutrients and radiogenic isotopes, from continental ice sheets to the ocean. Weathering products are also delivered to the ocean in non-glacial streams that form following ice sheet retreat and are disconnected from ice sheet meltwater by hydrologic divides. If weathering reactions differ in non-glacial and proglacial stream catchments, the streams could deliver different types and magnitudes of solutes to the ocean, depending on relative discharge volumes. Unlike proglacial streams, however, little is known of non-glacial stream solute compositions or discharge. Here we show specific discharges are similar from a proglacial stream draining the Greenland Ice Sheet (GrIS) with several streams disconnected from the ice sheet. We also evaluate weathering reactions across a 170-km transect in western Greenland that contains one proglacial stream draining the GrIS, and two coastal (ice distal) and three inland (ice proximal) areas with non-glacial streams. Non-glacial streams exhibit solute compositions and offsets between dissolved and bedload Sr isotope ratios that indicate weathering increases toward the coast with exposure age and precipitation. Major element mass balance calculations show weathering reactions shift from predominately carbonic acid weathering of carbonate minerals inland near the ice sheet to predominately sulfuric acid weathering of carbonate minerals near the coast. Strontium concentrations and isotopic ratios of the proglacial stream reflect mixing of at least two subglacial sources and minor in-stream weathering that consumes CO2. About 5 times less CO2 is consumed per liter in the proglacial than inland non-glacial streams; however, arid conditions inland suggest limited discharge from the ungauged inland streams leads to less total CO2 weathering than proglacial stream. One coastal area consumes less CO2 per liter than the proglacial stream and another coastal area exhibits net CO2 production. These results indicate estimates for glacial foreland solute fluxes and CO2 weathering consumption and production should include estimates from both non-glacial and proglacial streams. Understanding weathering fluxes from these two types of streams will be important for evaluations of past ice sheet retreat and predictions of future solute and CO2 fluxes associated with continued ice sheet retreat.

INDIAN INLAND WATER AND PARTS OF ANTARCTIC ICE SHEET ELEVATION AND ICE SHEET VELOCITY MONITORING USING ALTIMETRY AND SAR BASED DATASETS

Abstract. The monitoring of inland water and continental ice sheets is very important from water management and global climate related studies. The current study utilizes the SGDR data from Saral-Altika during 2013–2017 to estimate and monitor water level in 24 major reservoirs of India. The R2 value for majority of reservoirs was more than 0.99 and RMSE error value also was less than 0.40 m. In addition, wide rivers of India such as Mahanadi River, was also monitored using Altika data covering part of Mahanadi River from Khairmal to Naraj gauging sites during 2013–2016 time period. One dimensional hydro-dynamic (1D-HD) model was setup for this part of river to generate river Discharge at virtual gauge. The part of Antarctic ice sheet South of Indian research station Maitri, East Antarctica, was studied for ice sheet elevation changes using ground based stake network as well as space based altimeter/LIDAR datasets during 2003–2017 time period. 2003–2009 time was used for getting elevation changes using Icesat-1 level 2 altimetry product, and Geophysical Data Record (GDR) data from Altika was used with slope correction from 2013–2016 time period. An extensive network of ground based stake networks were used for validating the derived elevation changes. The ice sheet and glacier line of site velocity was estimated using Sentinel-1 based InSAR data with 6 to 12 day time interval data sets for year 2016 and 2017. The derived glacier velocity was comparable with optical image (Landsat-8) based glacier velocity for same year and also with historical Radarsat-1 based glacier velocity results.

Eutrophication histories of three contrasting lakes in a naturally nutrient-rich boreal watercourse

The Iisalmi Route watercourse in central-eastern Finland contains a number of highly eutrophic lakes. Despite substantial impacts from anthropogenic activity, the region appears to be naturally eutrophic because of its geological setting. A passive continental ice sheet deposited fine-grained basal till that contributes to the naturally eutrophic status of the lakes. Detailed paleolimnological studies in the Iisalmi Route are few. Therefore, we studied the eutrophication histories of three contrasting Iisalmi Route lakes: (1) small headwater Lake Saarisjarvi, (2) larger, but very shallow headwater Lake Nalantojarvi, and (3) large central basin, Lake Porovesi. We compared the suitability of three diatom-total phosphorus transfer functions for application to fossil samples. A local transfer function, specifically targeted to the Iisalmi Route, was the most suitable for the headwater lakes. In contrast, two regional transfer functions, which have larger geographical coverage, performed equally well for the large central basin. All three lakes proved to have been naturally eutrophic for thousands of years. Highest natural variability occurred in the longest core, from shallow headwater Lake Nalantojarvi. This variability reflects the dynamic development of the basin and its catchment after deglaciation. Diatom assemblage changes in cores from Lakes Saarisjarvi and Porovesi suggest cultural eutrophication, most likely after the region was colonized in the sixteenth century, followed by salinization in more recent times. Our study deepens understanding of naturally eutrophic boreal lakes that are located on fine-grained tills and their sensitivity to natural and anthropogenic forcing. Our results also highlight the importance of selecting appropriate transfer functions and realistic restoration targets when dealing with naturally eutrophic lakes.

Paleoceanography and ice sheet variability offshore Wilkes Land, Antarctica – Part 3: Insights from Oligocene–Miocene TEX<sub>86</sub>-based sea surface temperature reconstructions

Abstract. The volume of the Antarctic continental ice sheet(s) varied substantially during the Oligocene and Miocene (∼34–5 Ma) from smaller to substantially larger than today, both on million-year and on orbital timescales. However, reproduction through physical modeling of a dynamic response of the ice sheets to climate forcing remains problematic, suggesting the existence of complex feedback mechanisms between the cryosphere, ocean, and atmosphere systems. There is therefore an urgent need to improve the models for better predictions of these systems, including resulting potential future sea level change. To assess the interactions between the cryosphere, ocean, and atmosphere, knowledge of ancient sea surface conditions close to the Antarctic margin is essential. Here, we present a new TEX86-based sea surface water paleotemperature record measured on Oligocene sediments from Integrated Ocean Drilling Program (IODP) Site U1356, offshore Wilkes Land, East Antarctica. The new data are presented along with previously published Miocene temperatures from the same site. Together the data cover the interval between ∼34 and ∼11 Ma and encompasses two hiatuses. This record allows us to accurately reconstruct the magnitude of sea surface temperature (SST) variability and trends on both million-year and glacial–interglacial timescales. On average, TEX86 values indicate SSTs ranging between 10 and 21 ∘C during the Oligocene and Miocene, which is on the upper end of the few existing reconstructions from other high-latitude Southern Ocean sites. SST maxima occur around 30.5, 25, and 17 Ma. Our record suggests generally warm to temperate ocean offshore Wilkes Land. Based on lithological alternations detected in the sedimentary record, which are assigned to glacial–interglacial deposits, a SST variability of 1.5–3.1 ∘C at glacial–interglacial timescales can be established. This variability is slightly larger than that of deep-sea temperatures recorded in Mg ∕ Ca data. Our reconstructed Oligocene temperature variability has implications for Oligocene ice volume estimates based on benthic δ18O records. If the long-term and orbital-scale SST variability at Site U1356 mirrors that of the nearby region of deep-water formation, we argue that a substantial portion of the variability and trends contained in long-term δ18O records can be explained by variability in Southern high-latitude temperature and that the Antarctic ice volume may have been less dynamic than previously thought. Importantly, our temperature record suggests that Oligocene–Miocene Antarctic ice sheets were generally of smaller size compared to today.

Geomorphic History of the Beaver Creek Drainage Basin as Determined from Topographic Map Evidence: Eastern Montana and Western North Dakota, USA

The Beaver Creek drainage basin is located along the North Dakota-Montana border slightly to the south of a recognized continental ice sheet margin and immediately to the east of the deep northeast-oriented Yellowstone River valley with Beaver Creek flowing in a north and northeast direction to join the north-oriented Little Missouri River. The Beaver Creek drainage basin originates on an escarpment-surrounded upland and its erosional history was determined by analyzing detailed topographic maps aided by previously made field observations that showed coarse-grained and distinctive alluvium had been transported in an east direction across the Beaver Creek drainage basin and across what is now the deep Little Missouri River valley to sediments making up southwest North Dakota high points containing both the distinctive alluvium and Oligocene age fossils. Drainage divides surrounding the Beaver Creek drainage basin show numerous divide crossings (or notches) linking northwest-oriented Yellowstone River tributary valleys with east-oriented Beaver Creek tributary valleys and west- or northwest-oriented Beaver Creek tributary valleys with southeast- or east-oriented Little Missouri River tributary valleys and suggest the Beaver Creek valley eroded headward across a large-scale flood formed anastomosing channel complex. Buttes located just to the east of the Beaver Creek-Little Missouri River drainage divide suggest the east-oriented water removed as much as 150 meters, or more, of Beaver Creek drainage basin bedrock, and even greater amounts of bedrock from regions to the south of the Beaver Creek drainage basin. Topographic map evidence and routes traveled by the distinctive alluvium suggest a continental ice sheet blocked a large and high-level northeast-oriented river and diverted at least some of the water along the ice sheet margin with the east-oriented floodwaters being captured in a progressive sequence by headward erosion of the Little Missouri River, Beaver Creek, and Yellowstone River valleys (in that order).

Modelled subglacial floods and tunnel valleys control the life cycle of transitory ice streams

Abstract. Ice streams are corridors of fast-flowing ice that control mass transfers from continental ice sheets to oceans. Their flow speeds are known to accelerate and decelerate, their activity can switch on and off, and even their locations can shift entirely. Our analogue physical experiments reveal that a life cycle incorporating evolving subglacial meltwater routing and bed erosion can govern this complex transitory behaviour. The modelled ice streams switch on and accelerate when subglacial water pockets drain as marginal outburst floods (basal decoupling). Then they decelerate when the lubricating water drainage system spontaneously organizes itself into channels that create tunnel valleys (partial basal recoupling). The ice streams surge or jump in location when these water drainage systems maintain low discharge but they ultimately switch off when tunnel valleys have expanded to develop efficient drainage systems. Beyond reconciling previously disconnected observations of modern and ancient ice streams into a single life cycle, the modelling suggests that tunnel valley development may be crucial in stabilizing portions of ice sheets during periods of climate change.

Late Mississippian glacio-eustasy recorded in the eastern Paleo-Tethys Ocean (South China)

Long-lived and extensive glaciation during the Carboniferous and early Permian has been the focus of many studies over the past decade revealing systematic changes in sea level and climatic conditions. The nature of the inception of Carboniferous glaciation, however, remains poorly resolved with uncertainty regarding the timing and dynamics of buildup of continental ice sheets. Here we present detailed sedimentary facies and depositional cycles from Upper Mississippian shallow-water platform and contemporaneous carbonate slope successions from the eastern Paleo-Tethys Ocean region (South China) to reveal systematic variations that provide insight into the sedimentary response to the onset of Carboniferous glaciation. Based on detailed sedimentological logging and facies analysis, four upper Visean cycles and four Serpukhovian cycles were identified from the carbonate platform Yashui section, bounded by either subaerial surfaces or zones, or transgressive surfaces. The cycle tops roughly correspond to intervals rich in normally graded bioclastic wacke- to packstones and with distinct rises (~1‰) in conodont δ18OPO4 in the carbonate slope Naqing section. In particular, the four Serpukhovian cycles correlate well to depositional cycles defined in the Lower Yangtze Platform succession of South China and in the cyclothemic successions in the Donets Basin, Ukraine, suggesting a glacio-eustatic control, most likely caused by repeated advance and retreat of Gondwana glaciation during the onset but prior to widespread glaciation across the mid-Carboniferous boundary.

Late Santonian-early Campanian lake-level fluctuations in the Songliao Basin, NE China and their relationship to coeval eustatic changes

In contrast to glacio-eustasy, which is mainly controlled by the waxing and waning of continental ice sheets during icehouse climate stages, the concept of aquifer or limno-eustasy suggests that the effects of groundwater storage and release may have been the main driver of short-term (10s kyr to a few Myr) sea-level changes in the Cretaceous ice-free world. Presumably climate-controlled hydrological cycling could change the water volumes of continental reservoirs and oceans by transporting water between continents and oceans, resulting in out-of-phase relation between lake and sea levels.In the present study, we present lake-level fluctuations in Members 1 and 2 of the Nenjiang Formation (late Santonian-early Campanian) in the Songliao Basin that are indicated by basin-scale correlations of Fischer Plots based on natural gamma-ray logging data. Meanwhile, the Al/K ratios of the SK1 core indicate that changes in precipitation forced lake-level fluctuations in the basin. Compared to global sea-level changes, lake-level fluctuations show an out-of-phase relation with sea-level variations in the lacustrine phase of the basin, suggesting that climate-driven water transport between continents and oceans controlled short-term sea-level changes in the late Santonian-early Campanian. During the phase of marine-lake connectivity (basal Nenjiang Member 1), although the marine regression-driven decrease in lake-level corresponds to salinity stratification and strongly reducing water conditions, increasing precipitation in the basin implies that the hydrological cycle transported more water from the oceans toward continents. Based on the results we suggest that limno-eustasy controlled water levels in the Songliao basin in the late Santonian-early Campanian.

Antarctic Surface Ice Velocity Retrieval from MODIS-Based Mosaic of Antarctica (MOA)

The velocity of ice flow in the Antarctic is a crucial factor to determine ice discharge and thus future sea level rise. Feature tracking has been widely used in optical and radar imagery with fine resolution to retrieve flow parameters, although the primitive result may be contaminated by noise. In this paper, we present a series of modified post-processing steps, such as SNR thresholding by residual, complex Butterworth filters, and triple standard deviation truncation, to improve the performance of primitive results, and apply it to MODIS-based Mosaic of Antarctica (MOA) datasets. The final velocity field result displays the general flow pattern of the peripheral Antarctic. Seventy-eight out of 97 streamlines starting from seed points are smooth and continuous. The RMSE with 178 manually selected tie points is within 60 m·a−1. The systematic comparison with Making Earth System Data Records for Use in Research Environments (MEaSUREs) datasets in seven drainages shows that the results regarding high magnitude and large-scale ice shelf are highly reliable; absolute mean and median difference are less than 18 m·a−1, while the result of localized drainage suffered from too much tracking error. The relative differences from manually selected and random points are controlled within 8% when speed is beyond 500 m·a−1, but bias and uncertainty are pronounced when speed is lower than that. The result through our accuracy control strategy highlights that coarse remote-sensed images such as Moderate Resolution Imaging Spectrophotometer (MODIS) can still offer the capability for comprehensive and long-term continental ice sheet surface velocity mapping.

Development of small lakes in Estonia: paleolimnological studies

In this paper we give an brief overview of the paleolimnological studies revealing the development of Estonian lakes and their surrounding landscapes during the Holocene. The paper is mostly focused on the studies carried out in the Institute of Ecology (IoE) at Tallinn University. Development of lakes and their ecological environment can be roughly divided into two major periods: natural stage from emergence of lakes after withdrawal of continental ice sheet to signs of first anthropogenic impacts and the period where the human activity has clearly influenced the lake and its environment.

Arctic warming induced by the Laurentide Ice Sheet topography

Abstract. It is well known that ice sheet–climate feedbacks are essential for realistically simulating the spatiotemporal evolution of continental ice sheets over glacial–interglacial cycles. However, many of these feedbacks are dependent on the ice sheet thickness, which is poorly constrained by proxy data records. For example, height estimates of the Laurentide Ice Sheet (LIS) topography at the Last Glacial Maximum (LGM; ∼ 21 000 years ago) vary by more than 1 km among different ice sheet reconstructions. In order to better constrain the LIS elevation it is therefore important to understand how the mean climate is influenced by elevation discrepancies of this magnitude. Here we use an atmospheric circulation model coupled to a slab-ocean model to analyze the LGM surface temperature response to a broad range of LIS elevations (from 0 to over 4 km). We find that raising the LIS topography induces a widespread surface warming in the Arctic region, amounting to approximately 1.5 ∘C per km of elevation increase, or about 6.5 ∘C for the highest LIS. The warming is attributed to an increased poleward energy flux by atmospheric stationary waves, amplified by surface albedo and water vapor feedbacks, which account for about two-thirds of the total temperature response. These results suggest a strong feedback between continental-scale ice sheets and the Arctic temperatures that may help constrain LIS elevation estimates for the LGM and explain differences in ice distribution between the LGM and earlier glacial periods.

Simulated precipitation changes in Central Asia since the Last Glacial Maximum

The availability of freshwater has been and remains a crucial concern in westerlies-dominated arid Central Asia. Understanding precipitation changes in this area and the underlying mechanisms, therefore, is of great importance. This study explores precipitation changes in Central Asia (35°–50° N and 50°–70° E) since the Last Glacial Maximum (LGM) and their control factors using results from the “Simulation of Transient Climate Evolution over the last 21,000 years”. Transient simulations reveal that a wet climate occurred during the LGM, the Bølling-Allerød warm period, and the middle Holocene, and a dry climate occurred during Heinrich event 1, the Younger Dryas, and the early Holocene in this area. Model results are in good agreement with proxy records since the last deglaciation. These changes were mainly controlled by Earth's orbital parameters, meltwater discharges into the oceans and continental ice sheets. The contribution of GHG concentrations to precipitation changes was minor. External forcing factors influenced the precipitation mainly through affecting the water vapor input from the North Atlantic and Mediterranean Sea, and vertical motions of the atmosphere over Central Asia. The North Atlantic Oscillation was an important atmospheric bridge connecting the external forcings to precipitation changes in Central Asia. There were complex relationships between precipitation changes in Central Asia and East Asia since the LGM due to the differences of the dominating factors.

Anisotropic radial basis function methods for continental size ice sheet simulations

In this paper we develop and implement anisotropic radial basis function methods for simulating the dynamics of ice sheets and glaciers. We test the methods on two problems: the well-known benchmark ISMIP-HOM B that corresponds to a glacier size ice and a synthetic ice sheet whose geometry is inspired by the EISMINT benchmark that corresponds to a continental size ice sheet. We illustrate the advantages of the radial basis function methods over a standard finite element method. We also show how the use of anisotropic radial basis functions allows for accurate simulation of the velocities on a large ice sheet, which was not possible with standard isotropic radial basis function methods due to a small ratio between the typical thickness and length of an ice sheet. Additionally, we implement a partition of unity method in order to improve the computational efficiency of the radial basis function methods.