Ice Duration Research Articles

Barrier breach recovery in a lacustrine environment: Role of sediment supply and shoreline development

Barrier breaching in response to high water levels and storm activity is common in the Laurentian Great Lakes of North America. Lacustrine breach recovery depends on the availability and transport of sediment from both alongshore and offshore sources and interannual variations in water levels. The recovery of two barrier breaches along the east coast of Point Pelee foreland, located on the north shore of Lake Erie, was monitored during a period of record high-water levels between 2016 and 2022. Despite both breaches developing during the same period, the southern breach (East Beach, EB) started to recover and close despite increasing water levels, while the northern breach (Hillman Marsh, HM) did not recover even as water levels fell below pre-breach levels. The opposing responses and hysteresis curves of the breaches are associated with differences in the availability of sediment from adjacent shorelines due to varying degrees of human impacts at each site. The increased sediment supply from more natural and diffusive shorelines adjacent to EB allowed for breach recovery, whereas a limited sediment supply from the highly fortified shoreline at HM prohibited breach recovery. If barrier recovery or reformation further landward is not possible, sensitive marsh habitat critical to migratory birds will be exposed to increasing wave energy, particularly as the extent and duration of lake ice decreases with climate change.

A Fully Coupled Thermo-Hydro-Mechanical-Chemical Model for Methane Hydrate Bearing Sediments Considering the Effect of Ice

The ice generation is one of the challenges facing the methane hydrate depressurization, which, however, has not been fully addressed by existing numerical models for hydrate-bearing sediments (HBS). In this study, we develop a high-fidelity, fully coupled thermo-hydro-mechanical-chemical numerical model that incorporates the effect of ice. The model, developed using COMSOL, takes into account water–ice phase change, thermally induced cryogenic suction and constitutive relation in HBS. It is verified well against the temperature, pressure and cumulative gas production of Masuda’s experiment. The model is then employed to investigate multiphysical responses and gas/water production when ice generation is induced by setting a low outlet pressure. The results reveal that ice forms near the outlet boundary of the specimen center, leading to a reduction in intrinsic permeability and fluid velocity and an increase in the bulk modulus of ice-HBS. This enhanced bulk modulus results in higher porosity under axial load. Although the exothermic effect of ice generation promotes the hydrate dissociation, the effect on cumulative gas production is negligible after the ice melts. A negative correlation between ice saturation and water production rate is observed, indicating that a higher gas–water ratio can be achieved by adjusting the ice duration during hydrate production. The developed coupled model proves to be crucial for understanding the effect of ice on hydrate exploitation.

Gas hydrate dissociation by depressurization along with ice occurrence and sand migration

The extraction efficiency and safety of hydrate reservoirs are important for the industrialization of hydrate energy production. In this connection, various depressurization schemes with different amplitudes, rates and modes have been tried in field production tests. In this work, production profiles of laboratory-scale hydrate-bearing sediments were simulated through different depressurization schemes at a constant ambient temperature of 275.45 K. The results show that there are the freezing - melting behavior (FMB) and isothermal stage in the system with the depressurization amplitude (ΔP) range of 1.27–2.67 MPa, but not in the system with a ΔP of 0.83 MPa. In addition, the lower final outlet pressure and the higher depressurization rate increase the ice content and the ice duration of the system. Based on this, the linear equation of beginning freezing time of system (each observation point) can be obtained by fitting. According to the maximum ice content of system (0.06–3.56 E−4m2) under deep depressurization mode, the function of ice content of the system with the ΔP and the production time can be obtained. Moreover, the effects of FMB and sand detaching behavior were analyzed on pore fluid migration. FMB can temporarily block 0–66.56% of the migration space of pore fluid (MSPF). It can be revealed that the pore water velocity of observation points in the absence of FMB increases first and then steadily declines over time. But the former stage due to FMB can be divided into a slight decrease/increase and a sharp increase. Meanwhile, it can be found from the sediment components that the behaviors of skeleton sand detaching and hydrate dissociation can expand the MSPF, with contribution percentages of 0–13.49% and 86.51–100%, respectively. Finally, the high depressurization rate can advance the peak of gas production and water production by 14–22 min and 13–17 min, respectively. The high ΔP can improve the production rate peaks of gas and water about 34–59% and 17.4–41%, respectively, and advance the peak of sand production by 19–60 min. The findings of this work clearly illustrate the importance of the depressurization scheme for the extraction of hydrate resources and provide a basis for the best production scheme.

Winter dynamics of abiotic and biotic parameters in eutrophic temperate lakes

Winter conditions in lakes of temperate climatic zones, especially the duration and thickness of ice and snow cover, are strongly influenced by climate changes. The aim of this study was to follow the dynamics of abiotic (organic carbon, total phosphorus, total nitrogen) and biotic (chlorophyll a, cyanobacteria, algae, nanoflagellates, ciliates, rotifers, crustaceans) parameters during two consecutive winters in three eutrophic lakes of different mixing regime (northeastern Poland). Our results showed that dissolved organic carbon was highly stable during both winters and practically did not differ among the studied lakes. Total phosphorus and chlorophyll a concentrations differed significantly between the dimictic and meromictic lakes. The concentrations of nutrients and chlorophyll a and the biomass of phytoplankton, protists, rotifers and crustaceans reached higher values in late winter than in early winter, depending on the lake type (morphometry, mixing regime) and the year of the study. The composition of phytoplankton and ciliates was more or less similar throughout the study in all lakes during both years, but the share of individual groups in the total biomass differed between early and late winter. A high cyanobacterial biomass in January under the ice in the meromictic lake was probably a legacy of the summer/autumn community. Small prostomatid ciliates were the most important group in late winter in the shallow lake. Cladocerans (Bosmina coregoni and B. longispina) were an important component of winter crustacean community on some occasions, especially in the shallow lake. Phosphorus was the major factor determining phytoplankton biomass. Heterotrophic nanoflagellates and rotifers were negatively related to ice cover, while ciliates were positively related to the water temperature. Our study demonstrated that the dynamics, abundance, and structure of the phytoplankton and zooplankton communities in eutrophic lakes changed from one winter to the next despite similar environmental conditions.

Uptake of sympagic organic carbon by the Barents Sea benthos linked to sea ice seasonality

On Arctic shelves, where primary production occurs in both the pelagic and sympagic (ice-associated) habitats, sympagic organic material (OM) can constitute a disproportionate fraction of benthic diets due to higher sinking rates and lower grazing pressure than pelagic OM. Less documented is how sympagic OM assimilation across feeding guilds varies seasonally and in relation to sea ice duation. We therefore investigated the relative abundance of sympagic vs pelagic OM in Barents Sea shelf megabenthos in the summer and winter of 2018 and 2019, from 10 stations where sea ice duration ranged from 0 to 245 days per year. We use highly branched isoprenoids, which are lipid biomarkers produced with distinct molecular structures by diatoms in sea ice and the water column, to determine the ratio of sympagic-to-pelagic OM assimilated by benthic organisms. From 114 samples of 25 taxa analysed, we found that the proportion of sympagic OM assimilated ranged from 0.4% to 95.8% and correlated strongly (r2 = 0.754) with the duration of sea ice cover. The effect of sea ice duration was more evident in fauna collected during summer than winter, indicating that sympagic signals are more evident in the summer than in the winter at higher latitudes. Our data show that sympagic production can supply a high fraction of carbon for Barents Sea benthos, although this is highly variable and likely dependent on availability and patchiness of sympagic OM deposition. These results are comparable to similar studies conducted on benthos in the Pacific Arctic and highlight the variable importance of sympagic OM in the seasonal ice zone of Arctic inflow shelves, which are the Arctic regions with highest rates of sea ice loss.

Under‐Ice Hydrography of the La Grande River Plume in Relation to a Ten‐Fold Increase in Wintertime Discharge

AbstractA large under‐ice plume forms because of the regulated winter discharge from the La Grande River hydroelectric complex (NE James Bay, Canada), which is among the largest winter discharges in the circumpolar north. In 2016–2017, field campaigns were completed to characterize the under‐ice plume's structure, extent, and short‐term dynamics related to tides, weather, and discharge. Amid concerns of the freshwater's impact on eelgrass, the lateral spreading of the under‐ice plume into inshore areas was also assessed. When discharges averaged 4,800 m3 s−1 throughout the January–March periods, the freshwater influence of La Grande River extended more than 100 km north along the James Bay coast, with the brackish (salinity <25) under‐ice plume more than three times larger than for a natural winter discharge of ∼460 m3 s−1. The core area of the under‐ice plume, defined as the area with a highly stratified water column and surface layer of salinity <5, extended 30–35 km north and >20 km south. It was stable throughout the January–March 2016–2017 periods and, despite 30% higher winter discharge, was not significantly larger compared to survey periods in 1984–1987. This stability appears to be due to coastal geometry and width of the landfast ice cover, under which the plume can spread with limited mixing. Inshore salinity was about 5–10 units lower in winter versus the open‐water period. The seasonal duration of reduced salinity at eelgrass habitats will depend on landfast ice duration as well as river discharge magnitude.

Lake Ice Will Be Less Safe for Recreation and Transportation Under Future Warming

AbstractMillions of lakes from around the world freeze during winter. These frozen surfaces provide essential ecosystem services that are vital to many northern communities. However, the availability of safe lake ice that is oftentimes required to support these services is under threat from climate change. Here we use a 100‐member ensemble of climate model simulations to investigate changes in the presence of safe lake ice for different recreation and provisioning activities across the Northern Hemisphere. Our projections suggest that the duration of safe ice for recreational purposes will shorten, on average, by 13, 17, and 24 days within a 1.5°C, 2°C, and 3°C warmer world (relative to 1900–1929), respectively. The projected change in the duration of safe ice will be greater in higher latitudes, but with the most densely populated lower‐latitude regions experiencing the greatest percent change. The use of lake ice to support critical transportation infrastructure will also be influenced by future warming through the loss of thicker ice this century. However, our projections suggest that the magnitude of change in the duration of safe ice will differ depending on the ice thickness requirements. For transportation that requires the thickest ice cover, the number of days with safe ice will decline by 90%, 95%, and 99% with 1.5°C, 2°C, and 3°C global warming, respectively. We highlight the need for the development and implementation of adaptation plans to address the imminent loss of critical wintertime transportation infrastructure across the Northern Hemisphere.

Summer ecosystem structure in mountain lakes linked to interannual variability of lake ice, snowpack, and landscape attributes

AbstractMountain lakes experience interannual variability in spring snowpack and ice cover that can lead to differences in physical, chemical, and biological properties in the succeeding summer. Lake studies that capture extreme years of snow and ice would be useful to understand and anticipate effects of climate change, but such data are rare for remote mountain lakes. Monitoring of lakes in Olympic, North Cascades, and Mount Rainier National Parks from 2007 to 2018 allowed us to examine limnological differences along interannual and elevation‐driven climate gradients that included unusually high (2011–2012) and 100‐yr record low (2015) snowpack years. Years with lower spring snowpack had earlier ice‐out. Across lakes, our analysis suggested an average of 0.075°C lake warming per day of lost ice duration (0.525°C per week), giving rise to other ecosystem changes linked to temperature such as lower dissolved oxygen, higher total dissolved N, higher chlorophyll, and higher abundance of cladoceran zooplankton. Conversely, in years with higher snowpack and a shorter ice‐free season, lakes were colder and clearer (1 m deeper Secchi depth for every 1 m May snow water equivalent), with more dilute ions as well as lower algal biomass and zooplankton abundance. These results add to evidence that changes in snowpack or ice‐out dates alter mountain lake ecology through multiple processes associated with hydrology, terrestrial‐aquatic connection, water temperature, productivity, ion composition, and plankton communities.

Biodiversity of coastal epibenthic macrofauna in Eastern Canadian Arctic: Baseline mapping for management and conservation

Arctic ecosystems are changing rapidly due to global warming, industrial development, and economic growth. However, the ecological consequences for these ecosystems are difficult to predict due to limited knowledge on species abundance, distribution, and biodiversity patterns. This study evaluated the diversity and assemblage composition of epibenthic macrofauna in shallow coastal areas from five Eastern Arctic locations with increasing economic and shipping activity. Benthic trawls (n=198) were conducted in nearshore coastal habitats of Anaktalak Bay (Labrador), Churchill (Manitoba), Deception Bay (Quebec), Iqaluit (Nunavut), and Milne Inlet (Nunavut), at depths between 3 and 30 m. Diversity and assemblage composition were compared at various taxonomic levels from phylum to species and correlations with broad oceanographic variables were investigated to identify potential drivers of biodiversity. The spatial variability of benthic assemblages was also assessed within each study location. A total of 297,417 macroinvertebrates was identified, belonging to 900 taxa. Abundance and taxonomic richness were highest in Anaktalak Bay. Shannon-Wiener diversity was higher in Anaktalak Bay, Iqaluit, and Milne Inlet than in Churchill and Deception Bay. Churchill showed the lowest diversity metrics among locations. No relationships were observed between diversity and depth, chlorophyll-a, particulate organic carbon, sea surface temperature, or sea ice duration. Assemblages differed among locations at all taxonomic levels, with the highest dissimilarities at the species level; however, dispersion of samples within-groups was significant, suggesting that factors other than locations (e.g., habitat type) influence assemblage composition. While Churchill, Deception Bay, and Iqaluit showed distinct local spatial patterns in diversity metrics and assemblage composition, no patterns were detected in Anaktalak Bay and Milne Inlet. This study represents one of the largest systematic assessments of coastal epibenthic biodiversity in the Canadian Arctic. It identifies patterns of biodiversity and assemblage composition and provides a baseline for studies of community change and the development of informed management and conservation strategies for Arctic coastal ecosystems.

Climate warming shortens ice durations and alters freeze and break-up patterns in Swedish water bodies

Abstract. Increasing air temperatures reduce the duration of ice cover on lakes and rivers, threatening to alter their water quality, ecology, biodiversity, and physical, economical and recreational function. Using a unique in situ record of freeze and break-up dates, including records dating back to the beginning of the 18th century, we analyze changes in ice duration (i.e., first freeze to last break-up), freeze and break-up patterns across Sweden. Results indicate a significant trend in shorter ice duration (62 %), later freeze (36 %) and earlier break-up (58 %) dates from 1913–2014. In the latter 3 decades (1985–2014), the mean observed ice durations have decreased by about 11 d in northern (above 60∘ N) and 28 d in southern Sweden relative to the earlier three decades. In the same period, the average freeze date occurred about 10 d later and break-up date about 17 d earlier in southern Sweden. The rate of change is roughly twice as large in southern Sweden as in the northern part. Sweden has experienced an increase in occurrence of years with an extremely short ice cover duration (i.e., less than 50 d), which occurred about 8 times more often in southern Sweden than previously observed. Our analysis indicates that even a 1 ∘C increase in air temperatures in southern (northern) Sweden results in a mean decrease of ice duration of 22.5 (±7.6) d. Given that warming is expected to continue across Sweden during the 21st century, we expect increasingly significant impacts on ice cover duration and hence, ecology, water quality, transportation, and recreational activities in the region.

Continuous Loss of Global Lake Ice Across Two Centuries Revealed by Satellite Observations and Numerical Modeling

AbstractLake ice loss has been detected worldwide due to recent climate warming, yet spatially and temporally detailed information on the changes in global ice phenology does not exist. Here, we build a global lake ice phenology database comprising three lake ice phenologies—freeze‐up, break‐up, and ice duration—for each year across two centuries (1900–2099). The timing of all three phenologies experienced mild but statistically significant warming trends in the 20th century; continued warming trends were detected in ∼60% of the lakes from 2001 to 2020. Under a high emissions scenario (RCP 8.5), future global median ice duration would be shortened by 49.9 days by the end of the 21st century; such change can be substantially reduced under lower emission scenarios. We revealed continuous loss of global lake ice during the observed period, our generated database provides critical baseline information to evaluate the consequences of historical and future lake ice changes.

Future warming accelerates lake variations in the Tibetan Plateau

AbstractMounting evidence suggests that lakes in the Tibetan Plateau (TP) have been exposed to the dangers of climate warming. However, rare studies have been devoted to quantitatively estimating the contribution of climate warming to changes in lake ice phenology and lake expansion. Our results reveal a warmer future will further shorten lake ice duration in the TP and aggravate lake expansion in the Inner TP (ITP). Based on the statistical model and CMIP6 multimodel ensemble mean, the projected lake ice duration loss in the TP was presented. Specifically, the rising temperature in the cold season at the middle of the 21st century will lead to the generation of 22 ice‐free days and 29 ice‐free days in the scenarios of SSP2‐4.5 and SSP5‐8.5, respectively. While at the end of the 21st century, the average lake ice duration will decrease by 35 and 71 days, respectively, and some individual models indicate that a few lakes will no longer freeze in the scenario of SSP5‐8.5. Moreover, the results retrieved from the lake mass balance model simulation indicate that the increased precipitation in the warm season will yield the total lake expansion of approximately 8,000 and 9,000 km2 from 2015 to 2050 in the scenarios of SSP2‐4.5 and SSP5‐8.5, respectively. But the simulations suggest that lake expansion in the future is insensitive to the glacier mass loss. This study presents evidence to illustrate that the future warming will greatly impact the lake evolution in the TP and benefits for understanding of the TP cryosphere response to climate warming.

Climate projections over the Great Lakes Region: using two-way coupling of a regional climate model with a 3-D lake model

Abstract. Warming trends in the Laurentian Great Lakes and surrounding areas have been observed in recent decades, and concerns continue to rise about the pace and pattern of future climate change over the world's largest freshwater system. To date, most regional climate models used for Great Lakes projections either neglected the lake-atmosphere interactions or are only coupled with a 1-D column lake model to represent the lake hydrodynamics. This study presents a Great Lakes climate change projection that has employed the two-way coupling of a regional climate model with a 3-D lake model (GLARM) to resolve 3-D hydrodynamics essential for large lakes. Using the three carefully selected Coupled Model Intercomparison Project Phase 5 (CMIP5) general circulation models (GCMs), we show that the GLARM ensemble average substantially reduces surface air temperature and precipitation biases of the driving GCM ensemble average in present-day climate simulations. The improvements are not only displayed from an atmospheric perspective but are also evident in the accurate simulations of lake temperature and ice coverage. We further present the GLARM projected climate change for the mid-21st century (2030–2049) and the late 21st century (2080–2099) in the Representative Concentration Pathway (RCP) 4.5 and RCP 8.5 scenarios. Under RCP 8.5, the Great Lakes basin is projected to warm by 1.3–2.1 ∘C by the mid-21st century and 4.1–5.0 ∘C by the end of the century relative to the early century (2000–2019). Moderate mitigation (RCP 4.5) reduces the mid-century warming to 0.8–1.8 ∘C and late-century warming to 1.8–2.7 ∘C. Annual precipitation in GLARM is projected to increase for the entire basin, varying from 0 % to 13 % during the mid-century and from 9 % to 32 % during the late century in different scenarios and simulations. The most significant increases are projected in spring and fall when current precipitation is highest and a minimal increase in winter when it is lowest. Lake surface temperatures (LSTs) are also projected to increase across the five lakes in all of the simulations, but with strong seasonal and spatial variability. The most significant LST increases occur in Lakes Superior and Ontario. The strongest warming is projected in spring that persists into the summer, resulting from earlier and more intense stratification in the future. In addition, diminishing winter stratification in the future suggests the transition from dimictic lakes to monomictic lakes by the end of the century. In contrast, a relatively smaller increase in LSTs during fall and winter is projected with heat transfer to the deep water due to the strong mixing and energy required for ice melting. Correspondingly, the highest monthly mean ice cover is projected to reduce to 3 %–15 % and 10 %–40 % across the lakes by the end of the century in RCP 8.5 and RCP 4.5, respectively. In the coastal regions, ice duration is projected to decrease by up to 60 d.

Diversity in Zooplankton and Sympagic Biota during a Period of Rapid Sea Ice Change in Terra Nova Bay, Ross Sea, Antarctica

Sea ice is a major driver of biological activity in the Southern Ocean. Its cycle of growth and decay determines life history traits; food web interactions; and populations of many small, ice-associated organisms. The regional ocean modelling system (ROMS) for sea ice in the western Ross Sea has highlighted two modes of sea ice duration: fast-melting years when water temperature warms quickly in early spring and sea ice melts out in mid-November, and slow-melting years when water temperature remains below 0 °C and sea ice persists through most of December. Ice-associated and pelagic biota in Terra Nova Bay, Ross Sea, were studied intensively over a 3-week period in November 1997 as part of the PIPEX (Pack-Ice Plankton Experiment) campaign. The sea ice environment in November 1997 exhibited features of a slow-melting year, and the ice cover measured 0.65 m in late November. Phytoplankton abundance and diversity increased in the second half of November, concomitant with warming air and water temperatures, melting sea ice and progressive deepening of a still weak pycnocline. Water column phytoplankton was dominated by planktonic species, both in abundance and diversity, although there was also some input from benthic species. Pelagic zooplankton were typical of a nearshore Antarctic system, with the cyclopoid copepod Oithona similis representing at least 90% of total abundance. There was an increase in numbers coinciding with the period of ice thinning. Conversely, ice-associated species such as the calanoid copepods Stephos longipes and Paralabidocera antarctica decreased over time and were found in low numbers once the water temperatures increased. Stratified sampling under the sea ice, to 20 m, revealed that P. antarctica was mainly found in close association with the under-ice surface, while S. longipes, O. similis, and the calanoid copepod Metridia gerlachei were dispersed more evenly.

Annual cycle of phytoplankton, protozoa and diatom species from Scotia Bay (South Orkney Islands, Antarctica): Community structure prior to, during and after an anomalously low sea ice year

Deepening the knowledge on Antarctic coastal plankton and its links with environmental conditions is essential to understand the role of these organisms in the carbon and energy flow, and to detect and predict impacts of climate change. This study addresses for the first time the seasonal succession (February 2016 to April 2017) of the phytoplanktonic and protozoan communities of Scotia Bay (Laurie Island, South Orkney Islands) and covers the period of the largest negative anomaly in Antarctic sea ice coverage in the last 40 years and the lowest sea ice duration in the bay since 2012. The density and biomass of diatoms, dinoflagellates, silicoflagellates, pigmented and non-pigmented nanoflagellates, and ciliates were assessed in relation with physico-chemical and meteorological variables. Prevailing groups were diatoms in spring-summer, and nanoflagellates (pigmented and non-pigmented) and ciliates in autumn–winter. A marked contrast was found between February 2016 and February 2017 in coincidence with a time shift in the sea ice breakout (December 2015 vs. October 2016): February 2016 was dominated by diatoms (∼250 µgC l−1), whereas the bulk of biomass in February 2017 was represented by dinoflagellates (∼9 µgC l−1) and preceded in January by a massive bloom of the diatoms Odontella weissflogii, Eucampia antarctica, Thalassiosira tumida and Chaetoceros socialis (90% of total diatom biomass: ∼687 µgC l−1). The bloom occurred in association with an event of intense wind followed by days of relative calm. The strong 2015/2016 El Niño and a positive SAM coincided with a late 2015 sea ice breakout and a short productive period in Scotia Bay (January-March 2016), while the early breakout in 2016 occurred during a negative SAM and lead to a more extensive productive period (October 2016-January 2017). Future studies should cover interannual scales in order to understand feedbacks in the structure of microbial communities and environmental forces acting in normal and atypical conditions.

Climate change and mercury in the Arctic: Biotic interactions

Global climate change has led to profound alterations of the Arctic environment and ecosystems, with potential secondary effects on mercury (Hg) within Arctic biota. This review presents the current scientific evidence for impacts of direct physical climate change and indirect ecosystem change on Hg exposure and accumulation in Arctic terrestrial, freshwater, and marine organisms. As the marine environment is elevated in Hg compared to the terrestrial environment, terrestrial herbivores that now exploit coastal/marine foods when terrestrial plants are iced over may be exposed to higher Hg concentrations. Conversely, certain populations of predators, including Arctic foxes and polar bears, have shown lower Hg concentrations related to reduced sea ice-based foraging and increased land-based foraging. How climate change influences Hg in Arctic freshwater fishes is not clear, but for lacustrine populations it may depend on lake-specific conditions, including interrelated alterations in lake ice duration, turbidity, food web length and energy sources (benthic to pelagic), and growth dilution. In several marine mammal and seabird species, tissue Hg concentrations have shown correlations with climate and weather variables, including climate oscillation indices and sea ice trends; these findings suggest that wind, precipitation, and cryosphere changes that alter Hg transport and deposition are impacting Hg concentrations in Arctic marine organisms. Ecological changes, including northward range shifts of sub-Arctic species and altered body condition, have also been shown to affect Hg levels in some populations of Arctic marine species. Given the limited number of populations and species studied to date, especially within Arctic terrestrial and freshwater systems, further research is needed on climate-driven processes influencing Hg concentrations in Arctic ecosystems and their net effects. Long-term pan-Arctic monitoring programs should consider ancillary datasets on climate, weather, organism ecology and physiology to improve interpretation of spatial variation and time trends of Hg in Arctic biota.

Thermodynamics analysis and ice behavior during the depressurization process of methane hydrate reservoir

As potential alternative energy sources, natural gas hydrate has attracted international attentions. In order to optimize its exploitation process, the thermodynamics characteristics during hydrate dissociation were investigated in this study. Eleven reservoirs with three ratios of gas amounts in gas and hydrate phases (2.1, 2.9 and 4.6) were employed, and four exhaust rates (2.3, 4.7, 7.1 and 8.8 ln/min) were conducted to pressurize the reservoirs to 2.0 MPa. Hydrates dissociated at a constant rate during the depressurization stage, and the dissociation rate increased with higher depressurization rate, while the effect is enhancing with the increase of gas space. The temperature decreased with the dropped pressure in a similar trend, affected by both depressurization rate and hydrate saturation. During constant-pressure stage, the hydrate-bearing reservoir temperature kept at approximately −2.5 °C until ice formation, making the temperature increase to −1.5 °C. Ice formation can nearly quintuple the instantaneous rate of hydrate dissociation, while no obvious changes in hydrate dissociation before and after the end of ice melting. In addition, the induction time and existence duration of ice obey good stepwise spatial and temporal sequences. These results are great significant for pressure controlling and efficiency optimization of later period of methane hydrate exploitation.

Evaluation of Satellite-Derived Estimates of Lake Ice Cover Timing on Linnévatnet, Kapp Linné, Svalbard Using In-Situ Data

Arctic lakes are sensitive to climate change, and the timing and duration of ice presence and absence (i.e., ice phenology) on the lake surface can be used as a climate indicator. In this study of Linnévatnet, one of the largest lakes on Svalbard, we compare inferences of lake ice duration from satellite data with continuously monitored lake water temperature and photographs from automatic cameras. Visible surface reflectance data from the moderate-resolution imaging spectroradiometer (MODIS) were used to observe the change in the lake-wide mean surface reflectance of Linnévatnet from 2003–2019, and smoothing splines were applied to the to determine the date of summer ice-off (also called “break-up end”—BUE). Similarly, BUE and fall ice-on (or “freeze-up end”—FUE) were determined from lake-wide mean time series of Sentinel-1 microwave backscatter from 2014–2019. Overall, the ice timing dates identified from the satellite observations agree well with the in-situ observations (RMSE values of approximately 2–7 days for BUE and FUE, depending on the method and in-situ dataset), lending confidence to the accuracy of remote sensing of lake ice phenology in remote Arctic regions. Our observations of Linnévatnet indicate that BUE dates do not have a significant trend, while FUE dates have been occurring approximately 1.5 days later per year during the study period. These results support an overall decrease in annual duration of lake ice cover in this part of Svalbard.

Simple Method to Extract Lake Ice Condition From Landsat Images

Ice plays key roles in regulating hydrological, ecological, biogeochemical, and socioeconomic functions of lakes. Long-term <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">in situ</i> lake ice phenological records indicate that lake ice is trending toward later freeze-up, earlier breakup, and a shorter ice duration. Parallel to study of lake ice using <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">in situ</i> records and process-based models, satellite remote sensing can expand our understanding of lake ice change over large spatial scales. However, most remote sensing studies have focused on large lakes or short periods of time, which may not robustly represent changes over multidecadal time periods or in the much more numerous small lakes. Here, we present a random forest model, Sensitive Lake Ice Detection (SLIDE), to accurately extract ice conditions from Landsat TM, ETM+, and OLI images. We trained the model using a manually labeled lake ice dataset (1089 labeled areas over 995 lakes globally). Our results show that our model achieves accurate classification between ice/snow and water (accuracy: 97.8%, kappa coefficient: 95.5%). Comparing Landsat-derived ice cover with <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">in situ</i> ice conditions, we show that our model produces less bias, lower RMSE, and higher kappa than does the Landsat snow/ice flag from the quality assessment band. This is especially true during the transitional period surrounding the ice on and off dates reported from <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">in situ</i> (mean bias −7.3% from our model, −17.3% from the Landsat quality band). Our results demonstrate the feasibility of mining the rich Landsat archive to study lake ice dynamics and of better flagging ice-affected lake observations.

The Importance of Spring Mixing in Evaluating Carbon Dioxide and Methane Flux From a Small North‐Temperate Lake in Wisconsin, United States

AbstractIn limnological studies of temperate lakes, most studies of carbon dioxide (CO2) and methane (CH4) emissions have focused on summer measurements of gas fluxes despite the importance of shoulder seasons to annual emissions. This is especially pertinent to dimictic, small lakes that maintain anoxic conditions and turnover quickly in the spring and fall. We examined CO2 and CH4 dynamics from January to October 2020 in a small humic lake in northern Wisconsin, United States through a combination of discrete sampling and high frequency buoy and eddy covariance data collection. Eddy covariance flux towers were installed on buoys at the center of the lake while it was still frozen to continually measure CO2 and CH4 across seasons. Despite evidence for only partial turnover during the spring, there was still a notable 19‐day pulse of CH4 emissions after lake ice melted with an average daytime flux rate of 8–30 nmol CH4 m−2 s−1. Our estimate of CH4 emissions during the spring pulse was 16 mmol CH4 m−2 compared to 22 mmol CH4 m−2 during the stratified period from June to August. We did not observe a linear accumulation of gases under‐ice in our sampling period during the late winter, suggesting the complexity of this dynamic period and the emphasis for direct measurements throughout the ice‐covered period. The results of our study help to better understand the magnitude and timing of greenhouse gas emissions in a region expected to experience warmer winters with decreased ice duration.