Ice Meltwater Research Articles

Winter transport of subsurface warm water toward the Arctic Chukchi Borderland

Winter subsurface transport of the Pacific-origin warm water toward the Arctic Chukchi Borderland located west of the Canada Basin was investigated by mooring measurements and modeling analyses. In mid-winter or spring of 2011–2014, subsurface warming signals under sea ice were detected by the multi-year bottom-tethered mooring data in the Chukchi Abyssal Plain (CAP) of the western Chukchi Borderland. Lateral advection of shelf-origin ocean heat is a key process for the subsurface warming. To address the detailed pathways and processes of subsurface warm water transport, which have not been deeply explored, an interannual experiment for 2001–2014 was performed using a pan-Arctic sea ice-ocean model configured in a high-resolution framework. The horizontal grid size was set to approximately 5km so that narrow intense currents along complex sharp topography could be resolved. The model result captured the similar seasonality of subsurface temperature in the CAP region and produced interannual variability in the ocean heat content associated with the shelf-origin water distribution around the Chukchi Borderland. In addition to the Barrow Canyon throughflow, westward jets along the steep flank of the Chukchi shelf break constituted a primary pathway for the subsurface warm water transport toward the Chukchi Borderland in the model experiment. Since the simulated shelf break jet was much faster than main streams of the Beaufort Gyre, its role in ocean heat transport should be considered separately. Whereas ocean heat in the Chukchi shelf break region was partly lost via wind-driven turbulent mixing into upper halocline depths of approximately 20m, a substantial amount of the subsurface warm water remained even after mid-winter. The highly stratified condition due to anomalous sea ice meltwater assisted the winter heat transport.

Dynamics of Soil Moisture and Salt Content After Infiltration of Saline Ice Meltwater in Saline-Sodic Soil Columns

Saline ice meltwater can be used for irrigation and leaching of salts in salt-affected soil regions. A laboratory experiment was conducted using soil columns to investigate the redistribution of soil moisture, salt and sodium adsorption ratio (SAR) in saline-sodic soil under the infiltration of saline ice meltwater. Soils were treated using saline water of three irrigation volumes (1 600, 2 400 and 3 200 mL) at four salinity levels. These four salinity levels included salt free (0 g L−1), low salinity level (1.4 g L−1), moderate salinity level (2.7 g L−1) and high salinity level (4.1 g L−1). The prepared saline water was frozen into ice, and then the ice was put on the surface of soil columns. After 96 h, the infiltration rate and soil moisture content of saline ice treatments were greater than those of salt-free ice treatments, increasing with the increase of ice salinity. Infiltration of saline ice meltwater increased soil moisture content in the upper layers for all treatments. Both salt contents and SAR values in the upper soil layers decreased in all saline ice treatments and were lower than those in salt-free ice treatment. However, this trend was reversed in the deeper (below 20cm) soil layers. The highest desalting rate and lowest SAR were observed in high-salinity treatment under three irrigation volumes in the 0–15 cm soil layer, especially under irrigation volume of 2 400 mL. These results indicate that saline ice (0–20cm) meltwater irrigation is beneficial to saline-sodic soil reclamation, and the best improvement effect would be achieved when using high-salinity ice under optimal irrigation volume.

Glacial landforms of northwest Saskatchewan

ABSTRACTA comprehensive map of glacial landforms is presented for the area of northwest Saskatchewan, Canada. Remote sensing of 1-arc (∼30 m resolution) Shuttle Radar Topography Mission digital elevation models over an area of approximately 15,000 km2 were used as the primary data source for landform identification. A total of 16,856 landforms were identified pertaining to Quaternary glacial and postglacial activity. Ten landform types were mapped: ice flow parallel lineations (flutings, drumlins, mega-scale glacial lineations, and crag-and-tail ridges), moraines (major and minor), ice-thrust ridges, crevasse-fill ridges, meltwater landforms (major and minor meltwater channels and eskers), palaeo-shorelines and dunes. Collectively, these landforms constitute a glacial and postglacial landform record, which exhibits a more complex pattern than previously recognised, with evidence of multiple cross cutting ice flow directions. This geomorphological mapping of the regional landform record provides the prerequisite for future reconstructions of the glacial dynamics and chronology of northwest Saskatchewan.

Evaluation of the net CO2 uptake in the Canada Basin in the summer of 2008

The third Chinese National Arctic Research Expedition (CHINARE) was conducted in the summer of 2008. During the survey, the surface seawater partial pressure of CO2 (ρCO2) was measured, and sea water samples were collected for CO2 measurement in the Canada Basin. The distribution of ρCO2 in the Canada Basin was determined, the influencing factors were addressed, and the air-sea CO2 flux in the Canada Basin was evaluated. The Canada Basin was divided into three regions: the ice-free zone (south of 77°N), the partially ice-covered zone (77°–80°N), and the heavily ice-covered zone (north of 80°N). In the ice-free zone, ρCO2 was high (320 to 368 μatm, 1 μatm=0.101 325 Pa), primarily due to rapid equilibration with atmospheric CO2 over a short time. In the partially ice-covered zone, the surface ρCO2 was relatively low (250 to 270 μatm) due to ice-edge blooms and icemelt water dilution. In the heavily ice-covered zone, the seawater ρCO2 varied between 270 and 300 μatm due to biological CO2 removal, the transportation of low ρCO2 water northward, and heavy ice cover. The surface seawater ρCO2 during the survey was undersaturated with respect to the atmosphere in the Canada Basin, and it was a net sink for atmospheric CO2. The summertime net CO2 uptake of the ice-free zone, the partially ice-covered zone and the heavily ice-covered zone was (4.14±1.08), (1.79±0.19), and (0.57±0.03) Tg/a (calculated by carbon, 1 Tg=1012 g), respectively. Overall, the net CO2 sink of the Canada Basin in the summer of 2008 was (6.5±1.3) Tg/a, which accounted for 4%–10% of the Arctic Ocean CO2 sink.

Hydrologic Controls and Water Vulnerabilities in the Naryn River Basin, Kyrgyzstan: A Socio-Hydro Case Study of Water Stressors in Central Asia

Water vulnerabilities in Central Asia are affected by a complex combination of climate-sensitive water sources, trans-boundary political tensions, infrastructure deficiencies and a lack of water management organization from community to federal levels. This study aims to clarify the drivers of water stress across the 440 km Naryn River basin, headwater stem to the Syr Darya and the disappearing North Aral Sea. We use a combination of human and physical geography approaches to understand the meltwater-controlled hydrology of the system (using hydrochemical mixing models) as well as the human-water experience (via community surveys). Surveys indicate that current water stress is primarily a function of water management and access issues resulting from the clunky transition from Soviet era large-scale agriculture to post-Soviet small-plot farming. Snow and ice meltwaters play a dominant role in the surface and ground water supplies to downstream communities across the study’s 4220 m elevation gradient, so future increases to water stress due to changes in volume and timing of water supply is likely given frozen waters’ high sensitivities to warming temperatures. The combined influence of social, political and climate-induced pressures on water supplies in the Naryn basin suggest the need for proactive planning and adaptation strategies, and warrant concern for similar melt-sourced Central Asian watersheds.

Estimating sea level rise for Vietnam East Sea

Sea level rise for Vietnam East Sea in the 21st century was determined under both RCP 4.5 and RCP 8.5 scenarios. Changes in sea level of the Vietnam East Sea due to dynamic and thermosteric processes was estimated using results of different Atmosphere - Ocean General Circulation Model (AOGCMs) under the prescribed method in the IPCC’s Fifth Assessment Report (AR5). Changes in sea level due to ice melting and land water storage was determined using a transfer function for global water balance based on the contribution of each sea level rise contributing component for different regions. Changes in sea level as a result of the vertical motion of the Earth’s crust due to changes in the Earth’s cryosphere was determined using the ICE5G models. The results showed that for the RCP 8.5 scenario, by the end of the 21st century, the average sea level rise is 76 cm, with estimated values varying between 52 cm and 106 cm at the 5% and 95% confidence intervals, respectively. For the RCP 4.5 scenario, the average sea level rise is 52 cm, with values of 33 cm and 75 cm at the 5% and 95% confidence interval, respectively. The sea level rise scenario determined for the Vietnam East Sea is slightly higher in comparison with the globally estimated results in AR5.

Spring phytoplankton communities of the Labrador Sea (2005–2014): pigment signatures, photophysiology and elemental ratios

Abstract. The Labrador Sea is an ideal region to study the biogeographical, physiological, and biogeochemical implications of phytoplankton community composition due to sharp transitions between distinct water masses across its shelves and central basin. We have investigated the multi-year (2005–2014) distributions of late spring and early summer (May to June) phytoplankton communities in the various hydrographic settings of the Labrador Sea. Our analysis is based on pigment markers (using CHEMTAX analysis), and photophysiological and biogeochemical characteristics associated with each phytoplankton community. Diatoms were the most abundant group, blooming first in shallow mixed layers of haline-stratified Arctic shelf waters. Along with diatoms, chlorophytes co-dominated at the western end of the section (particularly in the polar waters of the Labrador Current (LC)), whilst Phaeocystis co-dominated in the east (modified polar waters of the West Greenland Current (WGC)). Pre-bloom conditions occurred in deeper mixed layers of the central Labrador Sea in May, where a mixed assemblage of flagellates (dinoflagellates, prasinophytes, prymnesiophytes, particularly coccolithophores, and chrysophytes/pelagophytes) occurred in low-chlorophyll areas, succeeding to blooms of diatoms and dinoflagellates in thermally stratified Atlantic waters in June. Light-saturated photosynthetic rates and saturation irradiance levels were highest at stations where diatoms were the dominant phytoplankton group ( > 70 % of total chlorophyll a), as opposed to stations where flagellates were more abundant (from 40 up to 70 % of total chlorophyll a). Phytoplankton communities from the WGC (Phaeocystis and diatoms) had lower light-limited photosynthetic rates, with little evidence of photoinhibition, indicating greater tolerance to a high light environment. By contrast, communities from the central Labrador Sea (dinoflagellates and diatoms), which bloomed later in the season (June), appeared to be more sensitive to high light levels. Ratios of accessory pigments (AP) to total chlorophyll a (TChl a) varied according to phytoplankton community composition, with polar phytoplankton (cold-water related) having lower AP : TChl a. Polar waters (LC and WGC) also had higher and more variable particulate organic carbon (POC) to particulate organic nitrogen (PON) ratios, suggesting the influence of detritus from freshwater input, derived from riverine, glacial, and/or sea ice meltwater. Long-term observational shifts in phytoplankton communities were not assessed in this study due to the short temporal frame (May to June) of the data. Nevertheless, these results add to our current understanding of phytoplankton group distribution, as well as an evaluation of the biogeochemical role (in terms of C : N ratios) of spring phytoplankton communities in the Labrador Sea, which will assist our understanding of potential long-term responses of phytoplankton communities in high-latitude oceans to a changing climate.

Composition of freshwater in the spring of 2014 on the southern Labrador shelf and slope

The Labrador Current is an important conduit of freshwater from the Arctic to the interior North Atlantic subpolar gyre. Here we investigate the spatial variability of the freshwater sources over the southern Labrador shelf and slope during May–June 2014. Using measurements of seawater properties such as temperature, salinity, nutrients, and oxygen isotopic composition, we estimate the respective contributions of saline water of Atlantic and Pacific origins, of brines released during sea ice formation, and of freshwater from sea ice melt and meteoric water origins. On the southern Labrador shelf, we find a large brine signal and Pacific water influence indicating a large contribution of water from the Canadian Arctic. The brine signal implies that more than 4 m of sea ice formed upstream, either in the Arctic or in Baffin Bay and the northern Labrador Sea. Over the midshelf and slope at 52°N, we find a stronger influence of slope water from the West Greenland Current with a smaller contribution of Pacific water and no brine signal. Thus, there is advection of water from the slope region to the midshelf between 55°N and 52°N. Very freshwater with high meteoric content is found close to the coast in June 2014. Observations from 1995 and 2008 suggest a higher fraction of brine and Pacific water on the shelf compared to that observed in 2014.

Glacier Melting, Disaster and Awareness Programme

Large ice formations, like glaciers and the polar ice caps, naturally melt back a bit each summer. But, in the winter, snows, made primarily from evaporated seawater, are generally sufficient to balance out the melting. Recently, though, persistently higher temperatures caused by global warming have led to greaterthan- average summer melting as well as diminished snowfall due to later winters and earlier springs. This imbalance results in a significant net gain in runoff versus evaporation for the ocean, causing sea levels to rise. Satellite measurements tell us that over the past century, the Global Mean Sea Level (GMSL) has risen by 4 to 8 inches (10 to 20 centimeters). However, the annual rate of rise over the past 20 years has been 0.13 inches (3.2 millimeters) a year, roughly twice the average speed of the preceding 80 years. As with glaciers and the ice caps, increased heat is causing the massive ice sheets, that cover Greenland and Antarctica to melt at an accelerated pace. Scientists also believe ice-melt water from above and seawater from below is seeping beneath Greenland's and West Antarctica's ice sheets, effectively lubricating ice streams and causing them to move more quickly into the sea. Moreover, higher sea temperatures are causing the massive ice shelves that extend out from Antarctica to melt from below, weaken, and break off. When sea levels rise rapidly, as they have been doing, even a small increase can have devastating effect on coastal habitats. As seawater reaches farther inland, it can cause destructive erosion, flooding of wetlands, contamination of aquifers and agricultural soils, and lost habitat for fish, birds, and plants. When large storms hit land, higher sea levels mean bigger, more powerful storm surges that can strip away everything in their path. In addition, hundreds of millions of people live in areas that will become increasingly vulnerable to flooding. Higher sea levels would force them to abandon their homes and relocate. Low-lying islands could be submerged completely. Thus, it needs launching of serious awareness programme through print media, electronic media to curb the glacier melting by reducing heavy consumption of hydrocarbon and focus on zero pollution researches to develop energy production alternatives.

A unique “icy seep” aquatic habitat in the high Teton Range: Potential refuge for biological assemblages imperiled by climate change

Alpine streams are threatened as meltwater sources diminish. We established baseline monitoring efforts of alpine streams in the Teton Range during 2015 by describing biotic and abiotic conditions of surface glacier and snowmelt streams. Our results indicated a third alpine stream type, icy seeps. Icy seeps are fed by subterranean ice melt, extremely cold but stable water temperature (summer mean <2°C), moderately high streambed stability (Pfankuch Index ~18-25), and relatively high specific conductivity (>50 μS cm-1). In 2016, we documented several icy seeps in the Teton massif, and our data suggest that they have the potential to serve as climate refugia for organisms and processes associated with extremely cold meltwater, due to the subterranean ice sources being more insulated from atmospheric conditions than surface glaciers and snowpack. Our 2016 work focused on locating icy seeps and documenting physical conditions, invertebrates, diatoms, and microbes in these alpine streams. We are processing the biological data, but microbial assemblages in icy seeps are similar to those found in streams fed by dwindling surface glacier ice. We are preparing to submit a paper about the microbial patterns, including how they compare to alpine streams representing comparable hydrological sources in Glacier National Park.
 
 Featured photo by Nicole Y-C on Unsplash. https://unsplash.com/photos/9XixVlnUCbk

Closing the sea level budget on a regional scale: Trends and variability on the Northwestern European continental shelf

Long‐term trends and decadal variability of sea level in the North Sea and along the Norwegian coast have been studied over the period 1958–2014. We model the spatially nonuniform sea level and solid earth response to large‐scale ice melt and terrestrial water storage changes. GPS observations, corrected for the solid earth deformation, are used to estimate vertical land motion. We find a clear correlation between sea level in the North Sea and along the Norwegian coast and open ocean steric variability in the Bay of Biscay and west of Portugal, which is consistent with the presence of wind‐driven coastally trapped waves. The observed nodal cycle is consistent with tidal equilibrium. We are able to explain the observed sea level trend over the period 1958–2014 well within the standard error of the sum of all contributing processes, as well as the large majority of the observed decadal sea level variability.

Bio-availability of iron derived from subarctic first-year sea ice

Sea ice contains high concentrations of iron (Fe), and melting of sea ice is one of the possible processes that supplies Fe to surface waters (e.g., Lannuzel et al., 2007). To assess the biological availability (bio-availability) of Fe in sea ice, a shipboard bottle incubation experiment (Exp. I) was conducted with surface water from the western subarctic North Pacific and Fe derived from sea ice collected from the Sea of Okhotsk, as compared to Fe derived from inorganic Fe (FeCl3). Addition of FeCl3 solution stimulated the growth of phytoplankton relative to a control treatment. Addition of sea ice meltwater enhanced the particulate labile Fe (>0.22μm) by 112nM and 0.26nM of dissolved Fe (<0.22μm) in the incubated seawater and allowed the phytoplankton to grow, especially large (>10μm) phytoplankton, at their maximum growth rate in the incubated seawater. In contrast, addition of desferrioxamine B (DFB) plus sea ice meltwater, in which the strong ligand DFB reduced the bio-availability of Fe, significantly depressed the growth of the large and small (0.8–10μm) phytoplankton relative to the control. These results clearly demonstrated that Fe stored in the sea ice stimulates growth of the phytoplankton. We carried out another shipboard bottle incubation experiment (Exp. II) to determine the relationship between concentrations of Fe and phytoplankton growth rates by adding FeCl3 solution at a series of concentrations to the seawater. The results indicated that the amount of dissolved Fe that the incubation bottles received from addition of the sea ice meltwater in Exp. I was insufficient to saturate the growth rate of the large phytoplankton. Therefore, the maximum growth rate achieved by the large phytoplankton can be accounted for by the use of the particulate labile Fe released from the sea ice meltwater. These results indicate that Fe stored in sea ice (mainly in particulate form) is bio-available and can contribute to phytoplankton growth when it is released into surface waters in the spring.

Dynamic simulations of the late MIS 3 transgressions in the East China Sea and southern Yellow Sea, China

Abundant evidences of higher sea levels from Jiangsu and Fujian coasts have proved a marine transgression event during 30–40 ka BP, suggesting that there was a stage with high sea level and a warm climate when ice sheets shrank in the Northern Hemisphere. The duration of 30–40 ka BP spanned a period in the late Marine Isotope Stage 3 (MIS 3) and was in nature an interstadial epoch during the Last Glacial period of the Quaternary. Different from the glacial period with a cold climate, this marine transgression considered as a penultimate higher sea level during the Quaternary remains a puzzle that why the evidence is contrary to the Quaternary glacial theory. It is important to understand sea level rise for these areas sensitively responding to the global changes in the future. To recognize the key issues on sea level changes, the eustatic sea level (H S) was defined as the glaciation-climateforced sea levels, and the relative sea level change (H R) was defined as that a sea level record was preserved in sediment that experienced multiple secondary actions of land and sea effects. On the basis as defined above, we constructed multi-level models of climate-driven glacio-eustatic changes and land-sea systems. By integrating data sets from eight borehole cores and prescribing the boundary conditions, we simulated the changes of H S and H R in the East China Sea and southern Yellow Sea areas in the late MIS 3. The marine transgression strata from the borehole core data was identified at ca. 30 m below present sea level as a result of the collective influence of ice melting water, neotectonic subsidence, sediment compaction and terrestrial sediment filling since ca. 35 ka ago, whereas the simulated relative sea-levels turned out to be–26.3––29.9 m a.s.l. The small error involved in the simulation results of ±(2.5–4.5) m demonstrated the credibility of the results. Our results indicated that sea level change in the late MIS 3 was dominated by glacial effects, in which the eustatic sea-level was between–19.2––22.1 m a.s.l. The study sheds light on the nature of sea-level changes along the east coast of China in the late MIS 3 and contributes to understanding the characteristics of marine transgression under the effects of multiple complex land-sea interactions.

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.

Spatial variation of stable isotopes in different waters during melt season in the Laohugou Glacial Catchment, Shule River basin

To evaluate isotopic tracers at natural abundances by providing basic isotope data of the hydrological investigations and assessing the impacts of different factors on the water cycle, a total of 197 water samples were collected from the Laohugou Glacial catchment in the Shule River basin northwestern China during the 2013 ablation seasons and analyzed their H- and O-isotope composition. The results showed that the isotopic composition of precipitation in the Qilianshan Station in the Laohugou Glacial catchment was remarkable variability. Correspondingly, a higher slope of δ18O-δD diagram, with an average of 8.74, is obtained based on the precipitation samples collected on the Glacier No.12, mainly attributed to the lower temperature on the glacier surface. Because of percolation and elution, the isotopic composition at the bottom of the firn is nearly steady. The δ18O /altitude gradients for precipitation and melt water were -0.37‰/100 m and -0.34‰/100 m, respectively. Exposed to the air and influenced by strong ablation and evaporation, the isotopic values and the δ18O vs δD diagram of the glacial surface ice show no altitudinal effect, indicating that glacier ice has the similar origins with the firn. The variation of isotopic composition in the melt water,varying from -10.7‰ to -16.9‰ (δ18O) and from -61.1‰ to -122.1‰ (δD) indicates the recharging of snowmelt and glacial ice melt water produced at different altitudes. With a mean value of -13.3‰ for δ18O and -89.7‰ for δD, the isotopic composition of the stream water is much closer to the melt water, indicating that stream water is mainly recharged by the ablation water. Our results of the stable isotopic compositions in natural water in the Laohugou Glacial catchment indicate the fractionations and the smoothing fluctuations of the stable isotopes during evaporation, infiltration and mixture.

A new algorithm for discriminating water sources from space: A case study for the southern Beaufort Sea using MODIS ocean color and SMOS salinity data

Abstract Identification of surface water sources in the Arctic Ocean is a key factor to better understand physical and biogeochemical processes. It is however restricted both geographically and temporally when using field observations. In this proof-of-concept study, we propose a new algorithm for discriminating surface water sources using satellite remote sensing data alone. The algorithm uses salinity and the light absorption coefficient of colored dissolved organic matter at 443 nm [aCDOM(443), m− 1] derived from SMOS/MIRAS and Aqua/MODIS satellite sensors, respectively, to identify the fraction of three end-members (i.e., seawater, ice melt water, and river water including precipitation) through the mass balance equations. An uncertainty analysis showed that fractions of river water can be derived reasonably, with caution of fractions for ice melt water and seawater. Application of this algorithm may lead to the discrimination of water sources in the surface layer of the Arctic Ocean in various environments where seawater, ice melt water, and river water are intermingled, which might be useful to improve our understanding of physical and biogeochemical processes related to each water source.

Study on the facilities and procedures for meltwater erosion of thawed soil

High erosion rate of seasonal thawed soils by snow- and ice-melting runoff in the high altitude and latitude cold regions has great impacts on ecological systems, industries, agriculture and various manmade infrastructures as well as people's lives. The facilities and procedures are of great importance for the studies on simulating erosion processes of melt-frozen soil. This study focuses on the method and facility for simulating the thawing process of frozen soil. The facility includes soil freezing system, melt-water supply system and experimental flume system for thawed soil erosion. The soil freezing system provides enough space to freeze soil columns in flumes. The water supply system deliveries snow- or ice-melting water flow of constant-rate at 0°C. The soil flumes of 200 or 300cm long, 10cm wide and 12cm high are designed to be assemble and convenient for soil freezing before they are thawed in one-dimensional manner from top to bottom. The one-dimensional thawing process is realized as follows. The frozen soil flume is put on ice boxes and thermally insulated with heat-insulating materials all around to prevent frozen soil from being thawed from sidewalls and bottom. The soil thaws with this system shows that it can meet the requirements of simulating the process of soil thawing from top to bottom. The thawed soil flumes are connected from end to end to form rills of 6–8m long to run the erosion experiments under different designed hydraulic condition. The equipment provides facility, method and operation process for simulating one-dimensional soil thawing to serve research on the effect of thawed soil depth on erosion process.

Changing distributions of sea ice melt and meteoric water west of the Antarctic Peninsula

The Western Antarctic Peninsula has recently undergone rapid climatic warming, with associated decreases in sea ice extent and duration, and increases in precipitation and glacial discharge to the ocean. These shifts in the freshwater budget can have significant consequences on the functioning of the regional ecosystem, feedbacks on regional climate, and sea-level rise. Here we use shelf-wide oxygen isotope data from cruises in four consecutive Januaries (2011–2014) to distinguish the freshwater input from sea ice melt separately from that due to meteoric sources (precipitation plus glacial discharge). Sea ice melt distributions varied from minima in 2011 of around 0 % up to maxima in 2014 of around 4–5%. Meteoric water contribution to the marine environment is typically elevated inshore, due to local glacial discharge and orographic effects on precipitation, but this enhanced contribution was largely absent in January 2013 due to anomalously low precipitation in the last quarter of 2012. Both sea ice melt and meteoric water changes are seen to be strongly influenced by changes in regional wind forcing associated with the Southern Annular Mode and the El Niño–Southern Oscillation phenomenon, which also impact on net sea ice motion as inferred from the isotope data. A near-coastal time series of isotope data collected from Rothera Research Station reproduces well the temporal pattern of changes in sea ice melt, but less well the meteoric water changes, due to local glacial inputs and precipitation effects.

Water mass characteristics and their temporal changes in a biological hotspot in the southern Chukchi Sea

Abstract. We analysed mooring and ship-based hydrographic and biogeochemical data obtained from a Hope Valley biological hotspot in the southern Chukchi Sea. The moorings were deployed from 16 July 2012 to 19 July 2014, and data were captured during spring and autumn blooms with high chlorophyll a concentrations. Turbidity increased and dissolved oxygen decreased in the bottom water at the mooring site before the autumn bloom, suggesting an accumulation of particulate organic matter and its decomposition (nutrient regeneration) at the bottom. This event may have been a trigger for the autumn bloom at this site. The bloom was maintained for 1 month in 2012 and for 2 months in 2013. The maintenance mechanism for the autumn bloom was also studied by hydrographic and biogeochemical surveys in late summer to autumn 2012 and 2013. Nutrient-rich water from the Bering Sea supplied nutrients to Hope Valley, although a reduction in nutrients occurred in 2012 by the influence of lower-nutrient water that would have remained on the Chukchi Sea shelf. In addition, nutrient regeneration at the bottom of Hope Valley could have increased nutrient concentrations and explained 60 % of its nutrient content in the bottom water in the autumn of 2012. The high nutrient content with the dome-like structure of the bottom water may have maintained the high primary productivity via the vertical nutrient supply from the bottom water, which was likely caused by wind-induced mixing during the autumn bloom. Primary productivity was 0.3 g C m−2 d−1 in September 2012 and 1.6 g C m−2 d−1 in September 2013. The lower productivity in 2012 was related to strong stratification caused by the high fraction of surface sea ice meltwater.

Effects of icing degree on ice growth characteristics and flashover performance of 220 kV composite insulators

Icing degree is one of the important factors influencing insulator's icing flashover performance. But there may be differences between the effects of icing degree under non-energized and energized icing conditions. For this purpose, the comparative tests of non-energized and energized glaze ice accumulation are conducted on 2 types of typical 220kV composite insulators under different icing degrees in this paper. Combining with the numerical calculation of electric field distribution, the monitoring of leakage current, the measurement of the ice-melting water conductivity and the observation of flashover arc paths, the influences of icing degree on ice growth characteristics and flashover voltages of composite insulators are deeply analyzed. Results indicate that with the increase of icing degree, all relevant ice parameters gradually increase but their regularities are related to the shed configuration and the position of sheds as well as whether the ice deposits on non-energized or energized insulators. These variations lead to differences of the quantity and length of icicle air gaps and the conductivity of the water film on the ice surface, and then affect the flashover arc path and icing flashover voltage. The icing flashover voltages of energized ice-covered insulators are higher than that under non-energized condition and their difference becomes larger with the increase of icing degree while the effect of shed configuration on the icing flashover performance gradually becomes less apparent when the icing becomes heavier.