Effects Of Meltwater Research Articles

Influence of Glacial Meltwater on Summer Biogeochemical Cycles in Scoresby Sund, East Greenland

Greenland fjords receive considerable amounts of glacial meltwater discharge from the Greenland Ice Sheet due to present climate warming. This impacts the hydrography via freshening of the fjord waters and biological processes due to altered nutrient input and the addition of silts. We present the first comprehensive analysis of the summer carbon cycle in the world's largest fjord system situated in southeastern Greenland. During a cruise onboard RV Maria S. Merian in summer 2016, we visited Scoresby Sund and its northernmost branch, Nordvestfjord. In addition to direct measurements of hydrography, biogeochemical parameters and sediment trap fluxes, we derived net community production (NCP) and full water column particulate organic carbon (POC) fluxes, and estimated carbon remineralization from vertical flux attenuation. While the narrow Nordvestfjord is influenced by subglacial and surface meltwater discharge, these meltwater effects on the outer fjord part of Scoresby Sund are weakened due to its enormous width. We found that subglacial and surface meltwater discharge to Nordvestfjord significantly limited NCP to 32 – 36 mmol C m-2 d-1 compared to the outer fjord part of Scoresby Sund (58 – 82 mmol C m-2 d-1) by inhibiting the resupply of nutrients to the surface and by shadowing of silts contained in the meltwater. The POC flux close to the glacier fronts was elevated due to silt-ballasting of settling particles that increases the sinking velocity and thereby reduces the time for remineralization processes within the water column. By contrast, the outer fjord part of Scoresby Sund showed stronger attenuation of particles due to horizontal advection and, hence, more intense remineralization within the water column. Our results imply that glacially influenced parts of Greenland's fjords can be considered as hotspots of carbon export to depth. In a warming climate, this export is likely to be enhanced during glacial melting. Additionally, entrainment of increasingly warmer Atlantic Water might support a higher productivity fjord systems. It therefore seems that future ice-free fjord systems with high input of glacial meltwater may become increasingly important for Arctic carbon sequestration.

Effects of glacier melting on the planktonic communities of two Antarctic coastal areas (Potter Cove and Hope Bay) in summer

Climate change has contributed to the regional retreat and melting of glaciers in the Antarctic Peninsula. This phenomenon is expected to affect the composition of plankton communities. The aim of this study is to analyze the influence of glacier melting on the composition and structure of phytoplankton and micro- and mesozooplankton assemblages in two coastal areas located in the northwest (Potter Cove) and in the northern end (Hope Bay) of the Antarctic Peninsula during summer 2013. We expect differences in plankton assemblages between PC and HB related to the fact that these areas are subjected to different climatic and environmental conditions and that the glacier meltwater is accumulated in lakes in HB whereas the meltwater directly reaches the adjacent sea at PC. However, plankton communities differed according to their proximity to the glaciers in both areas investigated, with a transition from herbivorous to microbial plankton food webs towards the glacier. The microbial food web was favored under the effects of glacier meltwater due to the stratification of the water column that favors the development of small eukaryotic algae. These are potential prey for ciliates and heterotrophic dinoflagellates which, in turn, favors the development of small omnivorous copepods. Further away from the glaciers, the herbivorous food web consists of large phytoplankton and a greater representation of herbivorous mesozooplankton organisms. It can be inferred from this study that increases in atmospheric temperatures may favor the development of microbial plankton food webs in the Antarctic coastal seas during summer due to increased glacier meltwater.

Change in future climate due to Antarctic meltwater.

Meltwater from the Antarctic Ice Sheet is projected to cause up to one metre of sea-level rise by 2100 under the highest greenhouse gas concentration trajectory (RCP8.5) considered by the Intergovernmental Panel on Climate Change (IPCC). However, the effects of meltwater from the ice sheets and ice shelves of Antarctica are not included in the widely used CMIP5 climate models, which introduces bias into IPCC climate projections. Here we assess a large ensemble simulation of the CMIP5 model 'GFDL ESM2M' that accounts for RCP8.5-projected Antarctic Ice Sheet meltwater. We find that, relative to the standard RCP8.5 scenario, accounting for meltwater delays the exceedance of the maximum global-mean atmospheric warming targets of 1.5 and 2 degrees Celsius by more than a decade, enhances drying of the Southern Hemisphere and reduces drying of the Northern Hemisphere, increases the formation of Antarctic sea ice (consistent with recent observations of increasing Antarctic sea-ice area) and warms the subsurface ocean around the Antarctic coast. Moreover, the meltwater-induced subsurface ocean warming could lead to further ice-sheet and ice-shelf melting through a positive feedback mechanism, highlighting the importance of including meltwater effects in simulations of future climate.

Climate change and its impact on water availability of large international rivers over the mainland Southeast Asia

AbstractChanges in climate and the resulting hydrologic variability are of great concern in international river basins. Based on observed station data, climate change and its impact on water availability in large international rivers across mainland Southeast Asia (MSA) were investigated by a combined method of trend detection and hydrologic budget balance analysis. This method can be applied easily to other studies to evaluate impacts of climate change on run‐off and water resources at the basin scale. Precipitation showed a decreasing trend in the MSA during 1960–2016, especially in the dry season. Decreasing precipitation and increasing evapotranspiration were the main reasons for severe droughts during recent years. Climate change was the main reason for run‐off changes over the MSA. The presence of dams in the upstream region was not enough to change the annual variability of natural run‐off in the Mekong River. Run‐off and precipitation changes showed significant variances in different basins and regions, and in different periods. The overall trend of precipitation and run‐off showed a periodicity of about 35 years. Nonprecipitation effects were also significant in some regions, including increasing irrigation water demand in the Red River and increasing glacial melt in the Brahmaputra River basin. Melt increased at least 75.2 × 108 m3/10a during 1960–2003, representing 1.2% of mean annual run‐off in the Brahmaputra River. The positive effect of glacial meltwater was almost equal to the negative effect of evapotranspiration on run‐off change in the Lancang River. Increasing evapotranspiration played a dominant effect on run‐off changes in the Yarlung Zangbo River basin during 1960–2010.

Along-slope variations in sediment lithofacies and depositional processes since the Last Glacial Maximum on the northeast Baffin margin, Canada

Twelve piston cores were used to characterize late Quaternary lithofacies, depositional processes and deglacial history along the Baffin Bay slope between Lancaster Sound and Home Bay. Core investigations show four distinct laterally correlatable lithofacies along the slope – basal and upper diamicton, laminated red brown mud, tan carbonate gravelly, sandy mud and bioturbated brown mud. Basal diamicton largely represents glacigenic debris flow deposits during a glacial advance from Baffin Island at ~25 cal ka. The distribution and character of laminated red brown mud suggests a lateral supply to Baffin Bay slope from ice-proximal meltwater plumes and turbidity currents sourced in glacial ice from both Baffin Bay shelf and Home Bay between 41.5 cal ka to ~14.2 cal ka. An upper diamicton records a lesser, localized glacial advance that ended at about 14.2 cal ka. Tan carbonate mud events represent ice-rafted, enhanced detrital carbonate delivery to the slope between ~25 cal ka and ~11 cal ka. A gradual thinning of these events, from northern to southern Baffin Bay, corroborates a northern Baffin Bay, Lancaster Sound or Nares Strait iceberg source. Proglacial facies seaward of Home Bay contain beds with slightly elevated detrital carbonate that may represent the distal edge of carbonate ice-rafted from Lancaster Sound. Baffin Bay is a type example of a polar glacial basin in which direct glacial supply predominates over the effects of glacial meltwater. As a result, axial supply from the large ice streams north of Baffin Bay (particularly Lancaster Sound) is dominant in the Baffin Bay basin and lateral supply from smaller ice streams on Baffin Island predominates on the NE Baffin Slope.

Snowmelt Water Alters the Regime of Runoff in the Arid Region of Northwest China

Seasonal snowmelt water from mountainous areas is critical for water supply in arid regions. Snowmelt profoundly affects the parameterization of the Budyko framework, which describes the long-term relationship between precipitation and runoff. This is true in Xinjiang, a representative arid region in Northwest China. However, the effects of snowmelt water on the water balance in this region remain unclear. Based on observed runoff data in 64 catchments of Xinjiang during 2000–2010, we analyzed the effects of meltwater in the local water balance both spatially and temporally through the Budyko curve and redundancy analysis (RDA) methods, and then investigated the influences of changing meltwater on runoff. Inclusion of snowmelt water into the item of the water availability significantly improved the performance of the Budyko equation for predicting runoff. The results of RDA showed that snowmelt water, potential evaporation (PET), and rainfall combined explained 66% of the spatial variations in runoff, while the individual effects of snowmelt water, PET, and rainfall were 19%, 13%, and 1%, respectively, with the interactions among the three variables being 16%. These results suggest that the accelerating changes of meltwater due to climate warming will significantly alter the regimes of runoff in these regions.

Climatic Effect of Antarctic Meltwater Overwhelmed by Concurrent Northern Hemispheric Melt

AbstractRecords indicate that 14,500 years ago, sea level rose by 12–22 m in under 340 years. However, the source of the sea level rise remains contentious, partly due to the competing climatic impact of different hemispheric contributions. Antarctic meltwater could indirectly strengthen the Atlantic Meridional Overturning Circulation (AMOC), causing northern warming, whereas Northern Hemisphere ice sheet meltwater has the opposite effect. This story has recently become more intriguing, due to increasing evidence for sea level contributions from both hemispheres. Using a coupled climate model with freshwater forcing, we demonstrate that the climatic influence of southern‐sourced meltwater is overridden by northern sources even when the Antarctic flux is double the North American contribution. This is because the Southern Ocean is quickly resalinized by Antarctic Circumpolar water. These results imply that the pattern of surface climate changes caused by ice sheet melting cannot be used to fingerprint the hemispheric source of the meltwater.

Exploring the Potential Impact of Greenland Meltwater on Stratification, Photosynthetically Active Radiation, and Primary Production in the Labrador Sea

AbstractIn July 2012, the surface of the Greenland Ice Sheet (GrIS) melted to an extent unprecedented over the last 100 years; we questioned the potential for such an extreme melt event to impact marine phytoplankton offshore. We hypothesized that stratification from meltwater could reduce light limitation for phytoplankton, and used a suite of numerical models to quantify the impact for 2003–2012. Because much of the 2012 meltwater discharged from southern Greenland, our study focused on the southwestern and southeastern coasts of Greenland, and the Labrador Sea. A 1‐D phytoplankton model used output from a Regional Ocean Modeling System (ROMS) coupled with a Regional Climate Model and a hydrological model of meltwater from runoff sources on the ice sheet, peripheral glaciers, and tundra. ROMS was run with and without meltwater to test the sensitivity of phytoplankton photosynthetic rates to the meltwater input. With meltwater, the pycnocline was shallower during late summer and early fall and thus light limitation on photosynthesis was reduced. Averaged over all years, added meltwater had the potential to increase gross primary production by 3–12% in the summer (July–August), and 13–60% in the fall (September–October). This meltwater effect was amplified when light was more limiting, and thus was greatest in the fall, under cloudier conditions, with higher self‐shading, and with more light‐sensitive phytoplankton groups. As the GrIS melt is projected to increase, late summer primary production in this region has the potential to increase as well, which could constitute an important biosphere response to high‐latitude climate change.

Assessing ecological effects of glacial meltwater on lakes fed by the Greenland Ice Sheet: The role of nutrient subsidies and turbidity

ABSTRACT Meltwater discharge from the Greenland Ice Sheet (GrIS) exports sediment, solutes, total phosphorus (TP), dissolved inorganic nitrogen (DIN), and other macro- and micronutrients to associated aquatic ecosystems. It remains unclear how this meltwater affects the ecology of glacially fed (GF) lakes. We assessed a suite of physical, chemical, and biological features of four GF lakes, and compared them to those of four nearby snow- and groundwater-fed (SF) lakes. We found that TP concentrations were six times higher in GF compared to SF lakes, but microbial extracellular enzyme activities and aluminum, iron, and phosphorus sediment fractions suggested that much of this TP in GF lakes is likely not biologically available. Turbidity was fifteen times higher in GF lakes, and DIN was twice as high than in SF lakes, but these nitrogen differences were not significant. While diatom species richness did not significantly differ between lake types, GF lakes had higher water column chlorophyll a (Chl a). Diatom species distributions across all lakes were strongly associated with turbidity, TP, and dissolved organic carbon (DOC). While cosmopolitan diatom taxa such as Discostella stelligera were found in both lake types, diatom communities differed across lake types. For instance, Fragilaria and Psammothidium species dominated GF lakes, while Achnanthes species and Lindavia ocellata were dominant in SF lakes. In addition to turbidity, the moderate amounts of DIN in GF lakes may play an important role in shaping diatom communities. This is supported by the high abundance in GF lakes of taxa such as Fragilaria tenera and D. stelligera, which reflect nitrogen enrichment in some lakes. Our results demonstrate how GrIS meltwaters alter the ecology of Arctic lakes, and contribute to the growing body of literature that reveals spatial variability in the effects of glacial meltwaters on lake ecosystems.

Investigating the Direct Meltwater Effect in Terrestrial Oxygen‐Isotope Paleoclimate Records Using an Isotope‐Enabled Earth System Model

AbstractVariations in terrestrial oxygen‐isotope reconstructions from ice cores and speleothems have been primarily attributed to climatic changes of surface air temperature, precipitation amount, or atmospheric circulation. Here we demonstrate with the fully coupled isotope‐enabled Community Earth System Model an additional process contributing to the oxygen‐isotope variations during glacial meltwater events. This process, termed “the direct meltwater effect,” involves propagating large amounts of isotopically depleted meltwater throughout the hydrological cycle and is independent of climatic changes. We find that the direct meltwater effect can make up 15–35% of the δ18O signals in precipitation over Greenland and eastern Brazil for large freshwater forcings (0.25–0.50 sverdrup (106 m3/s)). Model simulations further demonstrate that the direct meltwater effect increases with the magnitude and duration of the freshwater forcing and is sensitive to both the location and shape of the meltwater. These new modeling results have important implications for past climate interpretations of δ18O.

Response of snow hydrological processes to a changing climate during 1961 to 2016 in the headwater of Irtysh River Basin, Chinese Altai Mountains

With changing climatic conditions and snow cover regime, regional hydrological cycle for a snowy basin will change and further available surface water resources will be redistributed. Assessing snow meltwater effect on runoff is the key to water safety, under climate warming and fast social-economic developing status. In this study, stable isotopic technology was utilized to analyze the snow meltwater effect on regional hydrological processes, and to declare the response of snow hydrology to climate change and snow cover regime, together with longterm meteorological and hydrological observations, in the headwater of Irtysh River, Chinese Altai Mountains during 1961-2015. The average δ18O values of rainfall, snowfall, meltwater, groundwater and river water for 2014–2015 hydrological year were -10.9‰, -22.3‰, -21.7‰, -15.7‰ and -16.0‰, respectively. The results from stable isotopes, snow melting observation and remote sensing indicated that the meltwater effect on hydrological processes in Kayiertesi River Basin mainly occurred during snowmelt supplying period from April to June. The contribution of meltwater to runoff reached 58.1% during this period, but rainfall, meltwater and groundwater supplied 49.1%, 36.9% and 14.0% of water resource to annual runoff, respectively. With rising air temperature and increasing snowfall in cold season, the snow water equivalent (SWE) had an increasing trend but the snow cover duration declined by about one month including 13-day delay of the first day and 17-day advancement of the end day during 1961–2016. Increase in SWE provided more available water resource. However, variations in snow cover timing had resulted in redistribution of surface water resource, represented by an increase of discharge percentage in April and May, and a decline in June and July. This trend of snow hydrology will render a deficit of water resource in June and July when the water resource demand is high for agricultural irrigation and industrial manufacture.

Altitudinal effect of soil n-alkane δD values on the eastern Tibetan Plateau and their increasing isotopic fractionation with altitude

Stable isotope paleoaltimetry has provided unprecedented insights into the topographic histories of many of the world’s highest mountain ranges. However, on the Tibetan Plateau (TP), stable isotopes from paleosols generally yield much higher paleoaltitudes than those based on fossils. It is therefore essential when attempting to interpret accurately this region’s paleoaltitudes that the empirical calibrations of local stable isotopes and the relations between them are established. Additionally, it is vital that careful estimations be made when estimate how different isotopes sourced from different areas may have been influenced by different controls. We present here 29 hydrogen isotopic values for leaf wax-derived n -alkanes (i.e., δ Dwax values, and abundance-weighted average δ D values of C29 and C31) in surface soils, as well as the δ D values of soil water ( δ Dsw) samples (totaling 22) from Mount Longmen (LM), on the eastern TP (altitude ~0.8–4.0 km above sea level (asl), a region climatically affected by the East Asian Monsoon (EAM). We compared our results with published data from Mount Gongga (GG). In addition, 47 river water samples, 55 spring water samples, and the daily and monthly summer precipitation records (from May to October, 2015) from two precipitation observation stations were collected along the GG transect for δ D analysis. LM soil δ Dwax values showed regional differences and responded strongly to altitude, varying from ‒160‰ to ‒219‰, with an altitudinal lapse rate (ALR) of ‒18 ‰ km‒1 ( R 2=0.83; p n =29). These δ Dwax values appeared more enriched than those from the GG transect by ~40‰. We found that both the climate and moisture sources led to the differences observed in soil δ Dwax values between the LM and GG transects. We found that, as a general rule, e wax/rw, e wax/p and e wax/sw values (i.e., the isotopic fractionation of δ Dwax corresponding to δ Drw, δ Dp and δ Dsw) increased with increasing altitude along both the LM and GG transects (up to 34‰and 50‰, respectively). Basing its research on a comparative study of δ Dwax, δ Dp, δ Drw( δ Dspringw) and δ Dsw, this paper discusses the effects of moisture recycling, glacier-fed meltwater, relative humidity ( RH ), evapotranspiration ( ET ), vegetation cover, latitude, topography and/or other factors on e wax/p values. Clearly, if e wax-p values at higher altitudes are calculated using smaller e wax-p values from lower altitudes, the calculated paleowater δ Dp values are going to be more depleted than the actual δ D values, and any paleoaltitude would therefore be overestimated.

Englacial latent-heat transfer has limited influence on seaward ice flux in western Greenland

ABSTRACTSurface meltwater can refreeze within firn layers and crevasses to warm ice through latent-heat transfer on decadal to millennial timescales. Earlier work posited that the consequent softening of the ice might accelerate ice flow, potentially increasing ice-sheet mass loss. Here, we calculate the effect of meltwater refreezing on ice temperature and softness in the Pâkitsoq (near Swiss Camp) and Jakobshavn Isbræ regions of western Greenland using a numeric model and existing borehole measurements. We show that in the Jakobshavn catchment, meltwater percolation within the firn warms the ice at depth by 3–5°C. By contrast, meltwater refreezing in crevasses (cryo-hydrologic warming) at depths of ~300 m warms the ice in Pâkitsoq by up to 10°C, but this causes minimal increase in ice motion (<10 m a−1). Pâkitsoq is representative of western Greenland's land-terminating ice, where the slow movement of ice through a wide ablation zone provides ideal conditions for cryo-hydrologic warming to occur. We find that only ~37% of the western Greenland ice flux, however, travels through such areas. Overall, our findings suggest that cryo-hydrologic warming will likely have only a limited effect on the dynamic evolution of the Greenland ice sheet.

Transient climate simulations of the deglaciation 21–9 thousand years before present (version 1) – PMIP4 Core experiment design and boundary conditions

Abstract. The last deglaciation, which marked the transition between the last glacial and present interglacial periods, was punctuated by a series of rapid (centennial and decadal) climate changes. Numerical climate models are useful for investigating mechanisms that underpin the climate change events, especially now that some of the complex models can be run for multiple millennia. We have set up a Paleoclimate Modelling Intercomparison Project (PMIP) working group to coordinate efforts to run transient simulations of the last deglaciation, and to facilitate the dissemination of expertise between modellers and those engaged with reconstructing the climate of the last 21 000 years. Here, we present the design of a coordinated Core experiment over the period 21–9 thousand years before present (ka) with time-varying orbital forcing, greenhouse gases, ice sheets and other geographical changes. A choice of two ice sheet reconstructions is given, and we make recommendations for prescribing ice meltwater (or not) in the Core experiment. Additional focussed simulations will also be coordinated on an ad hoc basis by the working group, for example to investigate more thoroughly the effect of ice meltwater on climate system evolution, and to examine the uncertainty in other forcings. Some of these focussed simulations will target shorter durations around specific events in order to understand them in more detail and allow for the more computationally expensive models to take part.

Quantification of factors impacting seawater and calcite δ18O during Heinrich Stadials 1 and 4

AbstractWe perform idealized experiments of a Heinrich Stadial using an oxygen‐isotope‐enabled Earth System Climate Model. Our results compare relatively well with the planktic and benthic δ18O records of Heinrich Stadials 1 and 4. We find that changes in surface can be equally attributed to the “temperature effect” due to fractionation during calcification; the “circulation and climate effect” due to changes in circulation, precipitation, and evaporation; and the “meltwater effect” due to the addition and subsequent advection of depleted fresh water from continental ice sheets. In contrast, the meltwater effect and circulation and climate effect have only a small impact on benthic during the cessation of the Atlantic Meridional Overturning Circulation (AMOC). Significant temperature changes simulated in both the deep Atlantic and Pacific Oceans substantially influence benthic during that time. During the AMOC recovery, however, anomalously low surface waters are advected to the deep Atlantic, thus generating a large (∼0.5‰) decrease in the deep North Atlantic. This is in contrast to a hypothesis that links such depletion seen in Atlantic sediment cores during the last glacial stadials to deepwater formation caused by brine rejection and sea ice formation.

Effects of glacier meltwater on the algal sedimentary record of an alpine lake in the central US Rocky Mountains throughout the late Holocene

The effects of alpine glaciers on the hydrology, physical features, and biogeochemistry of lakes have been investigated over contemporary time scales. However, the influence of these factors on algal communities over longer time scales remains unclear, yet is critical to paleolimnological interpretation of environmental change in alpine regions. We examined sedimentary algal pigments and fossil diatom assemblages in two proximal lakes with equivalent local climates, one glacier-fed and one snow-fed, in the central Rocky Mountains (USA) to determine how glacier meltwater has altered algal records over the last 3,000 years. Differences between the records of the two lakes intensified during the Medieval Climate Anomaly and the Little Ice Age, with the glacier-fed lake exhibiting an overall increase in fossil algal pigment concentrations and greater diatom assemblage turnover. Starting 1,000 years ago, the glacier-fed lake in this study showed evidence of nitrogen enrichment from glacier meltwater, as indicated by increasing relative abundances of Asterionella formosa and, to a lesser extent, Fragilaria crotonensis. Since the Little Ice Age, diatom species richness declined in the glacier-fed lake, and further decreased following the 1950s, while assemblage turnover increased. These results demonstrate that glaciers can strongly alter the algal sedimentary record and should be considered when interpreting high-elevation lake records.

Variability of fronts, fresh water input and chlorophyll in the Indian Ocean sector of the Southern Ocean

The aim of this study was to understand the variability in the fronts and water masses, and the effect of melt water on the concentration of chlorophyll (Chl a) in the Indian Ocean sector of the Southern Ocean using hydrographic data collected during the austral summer (February 2010 and 2011). The Southern Subtropical Front (SSTF) and Northern Sub Antarctic Front (SAF1) were found to be further south at 57°30′E than at 47–48°E. This southward shift of the fronts was consistent with the southward meandering (c. 2°) of the Antarctic Circumpolar Current (ACC) core from the western section to the eastern section, which could have been caused by the bottom topography. The intrusion of water masses also differed between the western and eastern transects of the study region as a result of the meandering of the ACC core. Fresh water layer thickness relative to the winter water in 2011 was more compared to that during 2010. This could have been due to the larger amount of sea ice that was present in the winter of 2010, which subsequently melted, resulting in the advection of melt water from the south and west of the study region. In situ observations and satellite data detected a high Chl a concentration (c. 0.38 mg m−3) south of the Northern Polar Front (PF1) in 2011, which was caused by this melt water.

The sediment properties of glacial diamicts from the Jutulsessen area of Gjelsvikfjella, East Antarctica: A reflection of source materials and regional climate

The glacial diamicts deposited in the Jutulsessen area of Gjelsvikfjella, Dronning Maud Land, East Antarctica show the effects of localized meltwater channels and wind processes, as well as of the dominant glacial processes. These glacial sediments are characterized by poor sorting and a variable mean particle size, and the localized meltwater channels have removed silt- and clay-sized sediments, resulting in the relative enrichment of coarser sediments. The X-ray diffraction (XRD) patterns of clay minerals in samples collected across the study area show very similar characteristics. Biotite is the dominant mica mineral in the clay together with chlorite and K-feldspar. The presence of illite, and small amounts of smectite, demonstrates the limited extent of chemical weathering due to the cold and arid conditions. The samples from the glacial fan area contain mixed-layer clays, suggesting the effects of localized meltwater and limited chemical activity which has altered the crystal structure of biotite at lower topographic level. Scanning electron microscopy (SEM) analysis of surface microtextures from representative quartz grains suggest the dominance of glacial and glaciofluvial processes. The low rates of biogenic activity in this area are indicated by the low total organic carbon (TOC) content of the sediments.

The effects of high meltwater on the limnology of Lake Fryxell and Lake Hoare, Taylor Valley, Antarctica, as shown by dissolved gas, tritium and chlorofluorocarbons

AbstractSmall changes in the availability of liquid water can have profound effects on the water levels, aqueous chemistry and biogeochemical dynamics of the closed-basin, perennially ice-covered lakes of the McMurdo Dry Valleys, Antarctica. We have compiled the published and unpublished data on dissolved gas, tritium and chlorofluorocarbons (CFCs) for Lake Fryxell and Lake Hoare to determine the effects of a high meltwater year (2001–02 summer) on the lakes. The dissolved gas, tritium and CFC data indicate that the pulse of freshwater that flowed onto the surfaces of the lakes did not mix extensively with the upper water column. At the bottom of Lake Hoare, the measurable CFC and lower dissolved gas values suggest that the recent meltwater may have mixed with bottom waters. The probable mechanism for this transportation is weak density currents withc. 0.1–1.5% surface water being transported downwards in Lake Hoare. This deep water input, while not constant, may have a significant effect on the chemistry of the bottom waters in Lake Hoare over time. In Lake Fryxell, the tritium and CFC data indicate that the recent meltwater did not significantly affect the bottom water chemistry; therefore, weak density currents may not be present in Lake Fryxell.

Modelling Late Weichselian evolution of the Eurasian ice sheets forced by surface meltwater-enhanced basal sliding

AbstractWe simulated the Late Weichselian extent and dynamics of the Eurasian ice sheets using the shallow-ice approximation ice-sheet model SICOPOLIS. Our simulated Last Glacial Maximum ice-sheet extents closely resemble geomorphological reconstructions, and areas of modelled fast flow are consistent with the known locations of palaeo-ice streams. Motivated by documented velocity response to increased meltwater inputs on Greenland, we tested the sensitivity of the simulated ice sheet to the surface meltwater effect (SME) through a simple parameterization relating basal sliding to local surface melt rate and ice thickness. Model runs including the SME produce significantly reduced ice volume during deglaciation, with maximum ice surface velocities much greater than in similar runs that neglect the SME. We find that the simple treatment of the SME is not applicable across the whole ice sheet; however, our results highlight the importance of the SME for dynamic response to increased melting. The southwest sector of the Scandinavian ice sheet is most sensitive to the SME, with fast flow in the Baltic ice stream region shutting off by 15 ka BP when the SME is turned on, coincident with a retreat of the ice-margin position into the Gulf of Bothnia.