Ice Duration Research Articles

Re-assessing abundance of Southern Hudson Bay polar bears by aerial survey: effects of climate change at the southern edge of the range

The Southern Hudson Bay polar bear (Ursus maritimus Phipps, 1774) subpopulation is considered stable, but conflicting evidence lends uncertainty to that designation. Capture–recapture studies conducted in 1984–1986 and 2003–2005 and an aerial survey conducted in 2011/2012 suggested that abundance was likely unchanged since the mid-1980s. However, body condition and body size declined since then, and duration of sea ice decreased by about 30 days. Due to the conflicting information on subpopulation status and ongoing changes in sea ice, we conducted another aerial survey in 2016 to determine whether abundance had changed. We collected data via mark–recapture distance sampling and double-observer protocols. Results suggest that abundance declined 17% from 943 bears (95% CI: 658–1350) in 2011/2012 to 780 (95% CI: 590–1029) in 2016. The proportion of yearlings declined from 12% of the population in 2011 to 5% in 2016, whereas the proportion of cubs remained similar (16% in 2011 vs. 19% in 2016) suggesting low survival of the 2015 cohort. In a warming Arctic, duration of sea ice is predicted to continue to decline in Hudson Bay affecting all ice-dependent wildlife; therefore, further monitoring of this subpopulation is warranted. We recommend a conservative approach to harvest management and repeating the aerial survey in 2021.

The past and future of global river ice

More than one-third of Earth’s landmass is drained by rivers that seasonally freeze over. Ice transforms the hydrologic1,2, ecologic3,4, climatic5 and socio-economic6–8 functions of river corridors. Although river ice extent has been shown to be declining in many regions of the world1, the seasonality, historical change and predicted future changes in river ice extent and duration have not yet been quantified globally. Previous studies of river ice, which suggested that declines in extent and duration could be attributed to warming temperatures9,10, were based on data from sparse locations. Furthermore, existing projections of future ice extent are based solely on the location of the 0-°C isotherm11. Here, using satellite observations, we show that the global extent of river ice is declining, and we project a mean decrease in seasonal ice duration of 6.10 ± 0.08 days per 1-°C increase in global mean surface air temperature. We tracked the extent of river ice using over 400,000 clear-sky Landsat images spanning 1984–2018 and observed a mean decline of 2.5 percentage points globally in the past three decades. To project future changes in river ice extent, we developed an observationally calibrated and validated model, based on temperature and season, which reduced the mean bias by 87 per cent compared with the 0-degree-Celsius isotherm approach. We applied this model to future climate projections for 2080–2100: compared with 2009–2029, the average river ice duration declines by 16.7 days under Representative Concentration Pathway (RCP) 8.5, whereas under RCP 4.5 it declines on average by 7.3 days. Our results show that, globally, river ice is measurably declining and will continue to decline linearly with projected increases in surface air temperature towards the end of this century. An analysis based on Landsat imagery shows that the extent of river ice has declined extensively over past decades and that this trend will continue under future global warming.

Reduced sea ice protection period increases storm exposure in Kivalina, Alaska

On Arctic coasts, erosion is limited by the presence of nearshore sea ice, which creates a protective barrier from storms. In Kivalina, an Alaskan Inupiaq Inuit community, decreasing seasonal sea ice extent and a lengthening of the open-water season may be resulting in fall storms that (1) generate higher, longer, and more destructive waves and (2) cause damage later in the year, resulting in increased flooding and erosion. We assess trends in the duration of nearshore sea ice and their relationship with storm occurrence over the period 1979–2015 in Kivalina. Analysis of passive microwave sea ice concentration data indicates that the open-water season has increased by 5.6 ± 1.2 days/decade over the last 37 years, with moderate evidence that it is extending further into the fall than into the spring. This is correlated with an increased reporting frequency of high-damage storms; 80% of reported storms since 1970 occurred in the last 15 years. Each high-damage storm event occurred during the open-water season for that year. Our findings support Kivalina villagers’ assertions that climate change increases storm exposure and associated damages from flooding and erosion.

The Impact of the NAO on the Delayed Break-Up Date of Lake Ice over the Southern Tibetan Plateau

ABSTRACTThe changing characteristics of lake ice phenology over the Tibetan Plateau (TP) are investigated using historical satellite retrieved datasets during 2002–15 in this study. The results indicate that the freezing process mainly starts in December, and the ice melting process generally occurs in April for most lakes. However, the changes in lake ice phenology have varied depending on the location in recent years, with delayed break-up dates and prolonged ice durations in the southern TP, but no consistent changes have occurred in the lakes in the northern TP. Further analysis presents a close connection between the variation in the lake ice break-up date/ice duration over the southern TP and the winter North Atlantic Oscillation (NAO). The positive NAO generally excites an anomalous wave activity that propagates southward from the North Atlantic to North Africa and, in turn, strengthens the African–Asian jet stream at its entrance. Because of the blocking effect of the TP, the enhanced westerly jet can be divided into two branches and the south branch flow can deepen the India–Myanmar trough, which further strengthens the anomalous cyclonic circulation and water vapor transport. Therefore, the increased water vapor transport from the northern Indian Ocean to the southern region of the TP can increase the snowfall over this region. The increased snow cover over the lake acts as an insulating layer and lowers the lake surface temperature in the following spring by means of snow–ice feedback activity, resulting in a delayed ice break-up date and the increased ice duration of the lakes over the southern TP in recent years.

Observational Study on the Supercooled Fog Droplet Spectrum Distribution and Icing Accumulation Mechanism in Lushan, Southeast China

A fog monitor, hotplate total precipitation sensor, weather identifier and visibility sensor, ultrasonic wind speed meter, an icing gradient observation frame, and an automated weather station were involved in the observations at the Lushan Meteorological Bureau of Jiangxi Province, China. In this study, for the icing process under a cold surge from 20–25 January 2016, the duration, frequency, and spectrum distribution of agglomerate fog were analyzed. The effects of rain, snow, and supercooled fog on icing growth were studied and the icing and meteorological conditions at two heights (10 m and 1.5 m) were compared. There were 218 agglomerate fogs in this icing process, of which agglomerate fogs with durations less than and greater than 10 min accounted for 91.3% and 8.7%, respectively. The average time interval was 10.3 min. The fog droplet number concentration for sizes 2–15 μm and 30–50 μm increased during rainfall, and that for 2–27 μm decreased during snowfall. Icing grew rapidly (1.3 mm h−1) in the freezing rain phase but slowly (0.1 mm h−1) during the dry snow phase. Intensive supercooled fog, lower temperatures and increased wind speed all favored icing growth during dry snow (0.5 mm h−1). There were significant differences in the thickness, duration, density, and growth mechanism of icing at the heights of 10 m and 1.5 m. Differences in temperature and wind speed between the two heights were the main reasons for the differences in icing conditions, which indicated that icing was strongly affected by height.

Physical, biogeochemical, and meteorological factors responsible for interannual changes in cyanobacterial community composition and biovolume over two decades in a eutrophic lake

This study used a 20-year dataset (1995–2014) to identify factors affecting cyanobacterial community composition (CCC) and abundance in a eutrophic lake. We hypothesized that differences in thermal structure, nutrients, and meteorology drive interannual variability in CCC and abundance. Cluster analysis differentiated dominant cyanobacteria into rare, low abundance, or sporadically occurring taxa. The bloom-forming genera were Microcystis and Aphanizomenon, accounting for ~ 70% of total cyanobacterial biovolume (BV) on average, whereas unusually high abundance of Planktothrix, Synechococcus, and Oscillatoria were clear outliers in three of the years. Variability in CCC was significantly correlated (P 0.3) with ice duration, Kjeldahl nitrogen (TKN), and spring nitrite + nitrate (NO2+3); ice duration and TKN were associated with the occurrence of primarily non-bloom-forming genera. Pairwise correlations tested linear, exponential, and polynomial correlates of absolute and relative total Cyanophyta, Microcystis, or Aphanizomenon BV. TKN, total nitrogen (TN) and phosphorus (TP), TN:TP ratio, Schmidt stability, and rainfall correlated with total Cyanophyta, Microcystis, and Aphanizomenon BV, whereas ice cover, NO2+3, and TKN correlated with relative Microcystis and Aphanizomenon BV. Despite increasing TN:TP ratio over two decades, cyanobacterial abundance had not changed significantly. These data suggest differing responses of cyanobacterial genera to important environmental factors over two decades.

Sensitivity study of a wind farm maintenance decision - A performance and revenue analysis

Commercial operation and maintenance of wind farms always involves trying to find the most cost-effective solution from various possible options. In this paper, a maintenance action within a Spanish wind farm was studied, whereby a blade replacement was required to prevent catastrophic failure. The conducted replacement was accompanied by an underperformance resolved in a later blade re-pitching. We analyse the decision taken in terms of the power performance and net present value from the cash flow resulting from the energy sales. The impact of the timing of the maintenance is discussed in various what-if scenarios. The sensitivity to environmental causes of underperformance is compared by varying the duration of blade icing and comparing the performance in different wind directions. Country dynamics and subsidy impacts are hypothetically evaluated for the prevailing electricity market conditions as if the turbine were operating in either Spain, Netherlands or the UK. The findings highlight the uncertainty in power performance and the importance of maintenance accuracy. It is shown that the decision-making of operators should not only consider the seasonality of the wind resource, but also the seasonality in electricity markets.

Linking Ross Sea Coastal Benthic Communities to Environmental Conditions: Documenting Baselines in a Spatially Variable and Changing World

Understanding the functionality of marine benthic ecosystems, and how they are influenced by their physical environment, is fundamental to realistically predicting effects of future environmental change. The Antarctic faces multiple environmental pressures associated with greenhouse gas emissions, emphasising the need for baseline information on biodiversity and the bio-physical processes that influence biodiversity. We describe a survey of shallow water benthic communities at eight Ross Sea locations with a range of environmental characteristics. Our analyses link coastal benthic community composition to seafloor habitat and sedimentary parameters and broader scale features, at locations encompassing considerable spatial extent and variation in environmental characteristics (e.g. seafloor habitat, sea ice conditions, hydrodynamic regime, light). Our aims were to: (i) document existing benthic communities, habitats and environmental conditions against which to assess future change, (ii) investigate the relationships between environmental and habitat characteristics and benthic community structure and function, and (iii) determine whether these relationships were dependent on spatial extent. A very high percentage (>95%) of the between-location variability in macro- or epifaunal community composition was explainable using multi-scale environmental variables. The explanatory power varied depending on the scale of influence of the environmental variables measured (fine and medium-scale habitat, broad scale), and with community type. However, the inclusion of parameters at all scales produced the most powerful model for both communities. Ice duration, ice thickness and snow cover were important broad scale variables identified that directly relate to climate change. Even when using only habitat-scale variables, extending the spatial scale of the study from three locations covering 32 km to eight locations covering ~340 km increased the degree of explanatory power from 18-32% to 64-78%. The increase in explanatory power with spatial extent lends weight to the possibility of using an indirect ‘space for time’ substitution approach for future predictions of the effects of change on these coastal marine ecosystems. Given the multiple and interacting drivers of change in Antarctic coastal ecosystems a multidisciplinary, long term, repeated observation approach will be vital to both improve and test predictions of how coastal communities will respond to environmental change.

Range extension of a boreal amphipod Gammarus oceanicus in the warming Arctic.

The recent (2008–2016) occurrence of a boreal intertidal amphipod Gammarus oceanicus along the Spitsbergen coast is compared with corresponding data from 1980 to 1994. We aimed to compare the pace of environmental changes in the area (ice retreat, temperature increase) with distribution change of G. oceanicus. Material for the study was collected from intertidal, at low water level from over 100 locations on Spitsbergen, the main island of Svalbard archipelago (expanding from 76 to 80°N). The west coast of the island has been exposed to a steady increase in sea surface and air temperature (2°C in 20 years), as well as a significant decrease in fast ice duration (from over 5 months to less than 1 per year). A total length of more than 3,600 km of the island's coastline has been recently impacted by warming. Of the two sibling Gammarus species that dwell in the Spitsbergen littoral, G. setosus, the local cold water species remains generally where it was observed about 20–30 years ago. By contrast, boreal G. oceanicus has expanded its distribution range by over 1,300 km along the west and north coasts of Spitsbergen and gained dominating position on the number of sites, where it was previously just an occasional species.

A Southwest Pacific Perspective on Long‐Term Global Trends in Pliocene‐Pleistocene Stable Isotope Records

AbstractContinuous stable isotope records from marine sediment cores spanning the Pliocene have been used to assess the oceans' response to major perturbations in the climate system as the oceans play an integral role in regulating the global distribution of heat and gases. The Early to mid‐Pliocene has previously been characterized as a time of relative warmth followed by Late Pliocene Southern Hemisphere cooling and bipolar glaciation at ~2.7 Ma. Previous studies have predominantly focused on the Atlantic and Equatorial Pacific Oceans. In this study, we extended the deep water benthic foraminifera stable isotope record from Ocean Drilling Program (ODP) Site 1123 in the southwest Pacific, back to the warm Early Pliocene. This is a high‐latitude site at the gateway where the abyssal waters enter the Pacific Ocean and provides information about the connection between the Southern Ocean and the Pacific. We identify a dichotomy between the deep southwest Pacific and South Atlantic δ13C records spanning the mid‐Pliocene and suggest that this is most likely the result of variations in the relative contributions of Northern versus Southern Hemisphere deep waters to the different basins. At 3.6 Ma, δ13C values start to decrease; this is interpreted to represent alteration in preformed values as a result of increased remineralization of carbon caused by a reduction in deep ocean ventilation in the Southern Ocean. This is likely the consequence of a greater extent and seasonal duration of sea ice in the Southern Ocean from Antarctic Ice Sheet expansion and cooling.

Changes in surface icing duration over north China during 1961–2015

Climate extremes are changing at mid–high latitudes due to the effects of climate change. We defined the duration of surface icing (ice formation on open water) in north China from 1961 to 2015, along with its annual start and end date, based on daily measurements by observers at 346 weather stations. A comprehensive analysis of the temporal and spatial variations in these data showed that the regional mean of annual surface icing duration has a high correlation coefficient of 0.97 with the number of frost days (calculated from the daily minimum temperature below 0 °C), with some discrepancies. As the start date trended later and the end date trended earlier in this region, the surface icing duration decreased by 2.6 days/decade from 1961 to 2015 and the slope became steeper by −4.8 days/decade during the most recent 25 years. These results contribute to a better understanding of changes in climatic extremes related to global climate change.

Indirect load case estimation for propeller-ice moments from shaft line torque measurements

In order to estimate the forces exerted on ship propellers during ice navigation, the rotational dynamics of the propulsion system need to be accurately modelled. The blade measurements of ice loads on the propellers of ships during ice navigation is challenged by the harsh operating environment. Shaft line measurements are therefore performed inboard, and the required propeller loads are subsequently estimated through the use of a dynamic model and the solution of an inverse problem. The inverse problem is mathematically ill-posed and requires the determination of the ice-induced load on the propeller blade from shaft line measurements. The present study investigated full-scale torsional responses on the shaft line of a polar supply and research vessel during navigation through sea ice on a 68-day voyage between Cape Town and Antarctica. The vessel spent almost 11 days in ice with observed concentrations above 90% and a maximum thickness of 3 m. The aim was to evaluate the extreme ice-induced moments on the shaft line and thereby determine how sparsely published operational loadings compare to the design loads of an ice-going vessel. Ice-induced moments on the propeller were obtained from operational measurements through three previously published approaches to solving the ill-conditioned inverse problem. The regularization methods used included truncated Singular Value Decomposition, truncated Generalized Singular Value Decomposition and Tikhonov regularization. The maximum ice-induced external moment was found to be 941.5 kNm, which was just within the maximum allowed ice-induced torque on the propeller. The duration of ice impacts on the propeller ranged from 25 to 228 ms. A secondary peak was evident in torsional responses obtained from propeller-ice impacts which is thought to be a shear stress wave that propagates and reflects back in the shaft line. From the inversely determined ice-induced loads, the number of impacts, the duration, the shape and the damping of water on the propeller was identifiable. The results obtained were physically reasonable, indicating that the current methods are suitable for obtaining ice-induced loading on the propeller from shaft line measurements.

Study of ice accretion feature and power characteristics of wind turbines at natural icing environment

Wide cold regions with high air density as well as wind speed are much beneficial for the wind energy exploitation. However, wind turbines in these regions always suffer a series of icing issues, especially the blade aerodynamics degradation and much production loss in winter. Therefore, the paper aims to study the ice accretion feature on blades and the effect of ice severity on the power performance of wind turbines at natural icing environment. The ice distribution on the blade is analyzed quantitatively in the image processing method, and it is found that the ice thickness on the blade increases rapidly from the root to the middle of the blade, and then slowly from the middle to the blade tip. In the icing duration period, both the pitch angle and rotor speed of the wind turbine fall remarkably at the same wind speed, and the pitch angle shows more sensitive to the blade icing for wind turbines with the traditional control strategy. Based on the statistical operating data of the 300 kW wind turbine in different icing cases, the rotor performance deteriorates more seriously as the ice thickness of the blade increases, which changes the original matching relation between the rotor and generator. In addition, the ice thickness of the leading edge at r/R = 0.95 shows great correlation with power loss in given icing cases, and this correlation still needs to be studied further at more icing events. The results can provide a reference for the operation performance of wind turbines in cold regions.

The environmental niche separation between charophytes and angiosperms in the northern Baltic Sea

Charophytes and angiosperms are the most important primary producers and habitat modifiers in shallow soft-bottom fresh and brackish water bodies. The sheltered bays of the low-salinity northern Baltic Sea provide unique habitats, where euryhaline macrophytes of both freshwater and marine origin can thrive. The regional cohabitation of several species, with generally similar biological traits, raises questions about the mechanisms underlying the coexistence. Generally, sympatric populations rely on niche separation to reduce competition pressure that, in turn, facilitates long-term coexistence. A large benthos biomass data-set, covering the whole extent of the Estonian sea area, the northern Baltic Sea, together with a set of 13 environmental variables (bathymetrical, hydrodynamical, chemical, biological) was used to test the potential niche separation between regionally coexisting charophytes and angiosperms. A constrained correspondence analysis indicated both the grouping of some species and a distinct niche separation of others. The niche centers of angiosperms Zostera marina, Zannichellia palustris, and Potamogeton perfoliatus diverged most strongly from all the other species, while those of Chara connivens and Myriophyllum spicatum nearly coincided. Depth, salinity, and duration of ice were the most influential environmental gradients that discerned the environmental niches of the species. Comparison of the breadths of the environmental niche spaces, occupied by the studied species, showed highly species-specific results. Within the studied species, Z. palustris and Z. marina had the lowest niche specialization, and C. connivens had the highest specialization. Altogether, among the angiosperms the variability of the environmental niche breadth was higher compared to the charophytes.

Impact of icing severity on corona performance of glaze ice-covered conductor

This paper presents the results of laboratory experiments carried out on an ac-energized stranded conductor subjected to simulated glaze icing, which were conducted in a corona cage located in an artificial climate chamber. With the increase of icing duration, the grow of icing severity of conductors lead to the corona onset voltage fell from 54.8 to 41.9 kV, correspondingly, the surface irregularity of stranded conductor decreased from 0.41 to 0.31. Through the ultraviolet photon frame and ultraviolet photon curve, corona development process of glaze ice-covered conductor were divided into three stages, that is, burst corona mode, comprehensive corona mode and glow mode. The impact of icing severity on the corona loss and audible noise was investigated. With regard to corona loss, it is in proportion to icing severity at a given surface gradient, whereas no obvious impact was observed with audible noise could be established. In addition, corona performance in comparison with rain condition was also studied, the corona loss of glaze ice-covered conductor was higher than that of rain, instead the audible noise of glaze ice-covered conductor was lower than that of rain after a certain surface gradient. The presented results could provide references to the design of ac overhead transmission lines crossing cold regions.

Behavior of satellite-tracked Antarctic minke whales (Balaenoptera bonaerensis) in relation to environmental factors around the western Antarctic Peninsula

Background The Antarctic minke whale (Balaenoptera bonaerensis) is a relatively small baleen whale species and is well suited to life in the Antarctic pack ice. Information on their individual movement and distribution patterns is largely unknown due to their association with sea ice habitat where direct observations are limited. The primary objectives of this study are (1) to use satellite telemetry to quantify the movement patterns, distribution, and presumed foraging areas of Antarctic minke whales and (2) to assess the environmental conditions that are associated with areas used by minke whales along the western Antarctic Peninsula.ResultsIndividual movement patterns from three Antarctic minke whales fitted with ARGOS-linked transmitters were analyzed with respect to environmental conditions. Behavioral states were identified using the Multi-Scale Straightness Index. Satellite telemetry revealed disparate behavioral patterns between these three individuals. Generalized additive model analysis demonstrated environmental variables, particularly sea ice, bathymetry, and sea surface temperature, are the best predictors of presumed foraging areas.ConclusionsSatellite telemetry from three individuals revealed Antarctic minke whale summer foraging spaces are highly individualized but can generally be associated with pack ice habitat over the continental shelf. The coupled relationship between minke whales, krill, and sea ice suggests that these whales may be sensitive to changes in sea ice concentration, extent, and duration, making them particularly vulnerable to climate change.

Ice duration drives winter nitrate accumulation in north temperate lakes

AbstractThe duration of winter ice cover on lakes varies substantially with climate variability, and has decreased over the last several decades in many temperate lakes. However, little is known of how changes in seasonal ice cover may affect biogeochemical processes under ice. We examined winter nitrogen (N) dynamics under ice using a 30+ yr dataset from five oligotrophic/mesotrophic north temperate lakes to determine how changes in inorganic N species varied with ice duration. Nitrate accumulated during winter and was strongly related to the number of days since ice‐on. Exogenous inputs accounted for less than 3% of nitrate accumulation in four of the five lakes, suggesting a paramount role of nitrification in regulating N transformation and the timing of chemical conditions under ice. Winter nitrate accumulation rates ranged from 0.15 μg N L−1 d−1 to 2.7 μg N L−1 d−1 (0.011–0.19 μM d−1), and the mean for intermediate depths was 0.94 μg N L−1 d−1 (0.067 μM d−1). Given that winters with shorter ice duration (< 120 d) have become more frequent in these lakes since the late 1990s, peak winter nitrate concentrations and cumulative nitrate production under ice may be declining. As ice extent and duration change, the physical and chemical conditions supporting life will shift. This research suggests we may expect changes in the form and amount of inorganic N, and altered dissolved nitrogen : phosphorus ratios, in lakes during winters with shorter ice duration.

Lake ice phenology of Nam Co, Central Tibetan Plateau, China, derived from multiple MODIS data products

Abstract Lake ice phenology, including freeze-up and break-up dates, is a sensitive indicator of climate change. However, uniformly created lake ice phenology records are still required on the Tibetan Plateau (TP) for a more accurate analysis of climate change. In this study, we present a new automated method to extend the interpretation of existing in-situ lake ice records, using multiple MODIS data products. Our results showed strong agreement with the in-situ data at Nam Co (Co means lake in Tibetan language) on the central TP. The multiple MODIS based method is therefore well-suited to the detection of lake ice phenology. The result showed that in 2000–2015, the mean lake ice duration (ID) in the middle of Nam Co was ~ 87 d; the freeze-up start (FUS) date delayed 0.58 d/yr and the break-up start (BUS) date delayed 0.09 d/yr, giving a total decrease in ID at the rate of 0.49 d/yr. We suggest the delayed freeze-up dates became more marked in response to climate warming. Changes in lake ice coverage in Nam Co are affected by a number of local and regional climatic factors, such as air temperature and wind speed.

Evaluating species-specific changes in hydrologic regimes: an iterative approach for salmonids in the Greater Yellowstone Area (USA)

Despite the importance of hydrologic regimes to the phenology, demography, and abundance of fishes such as salmonids, there have been surprisingly few syntheses that holistically assess regional, species-specific trends in hydrologic regimes within a framework of climate change. Here, we consider hydrologic regimes within the Greater Yellowstone Area in the Rocky Mountains of western North America to evaluate changes in hydrologic metrics anticipated to affect salmonids, a group of fishes with high regional ecological and socioeconomic value. Our analyses assessed trends across different sites and time periods (1930–, 1950–, and 1970–2015) as means to evaluate spatial and temporal shifts. Consistent patterns emerged from our analyses indicating substantial shifts to (1) earlier peak discharge events; (2) reductions of summer minimum streamflows; (3) declines in the duration of river ice; and (4) decreases in total volume of water. We found accelerated trends in hydrologic change for the 1970–2015 period, with an average peak discharge 7.5 days earlier, 27.5% decline in summer minimum streamflows, and a 15.6% decline in the annual total volume of water (1 October–September 30) across sites. We did observe considerable variability in magnitude of change across sites, suggesting different levels of vulnerability to a changing climate. Our analyses provide an iterative means for assessing climate predictions and an important step in identifying the climate resilience of landscapes.

Seasonal geomorphic processes and rates of sand movement at Mount Baldy dune in Indiana, USA

Abstract Winds are very strong, frequent, and have high energy (annual DP ∼800 VU) along the southern shores of Lake Michigan, allowing the coexistence of fixed and active dunes. Six years (2007–13) of monitoring Mount Baldy in the Indiana Dunes National Lakeshore reveals that this is the most active coastal dune in the Great Lakes region. This paper documents aeolian processes and changes in the dune’s morphology that occur temporarily, following storms, or seasonally, due to weather (climate) variations. Most of the sand transport in this area takes place during strong storms with gale force (>17.5 m/s) winds, which occur in the autumn and winter months. A single storm, such as the October 28–31, 2013 event, can contribute 25% of the annual sand transport and dune movement inland. In its most active year (June 1, 2011 through May 31, 2012), Mount Baldy moved inland on average 4.34 m, with a maximum of 6.52 m along the blowout’s axis (155° azimuth). During this particularly active season, there were six storms with sustained gale force winds, winter air temperatures were warmer than average, and shelf ice on Lake Michigan lasted only one day. The dune is least active during the summer season, when the winds are weakest. The late fall and winter winds are the strongest. But in a typical year, most of the dune’s advance inland takes place during the spring thaw when sand is released from over-steepened and lumpy slip face, allowing it to avalanche to the toe of the slip face. However, with a warming air temperatures, a reduction in the duration of winter shelf ice, and rising Lake Michigan levels, the annual rates of sand transport and dune movement may increase. The recent Mount Baldy management strategy, which includes planting vegetation and installing wind barriers on the dune’s stoss side in an effort to fix the dune and stop its further movement inland, may potentially cause the destruction of the mobile sand, open dune habitat, resulting in the extinction of rare plants, insects, lizards, birds, and mammals.