Ice-free Zones Research Articles

Ornithogenic sedimentary profiles of n-alkanes and PAHs constrain breeding penguin population dynamics at Cape Bird, Ross Island, Antarctica, over the past 1,500 years

Ornithogenic sediment may contain important paleoecological information concerning past bird population dynamics. In this paper, we analyse the distribution of n-alkanes and polycyclic aromatic hydrocarbons (PAHs) in two sedimentary profiles collected from abandoned penguin colonies at Cape Bird, Ross Island, Antarctica. The geochronology of the sediment profiles was determined using 210Pb and AMS 14C dating techniques, and spans the past 1500 years. We observe low levels of n-alkanes (0.93–2.67 μg g−1) and PAHs (20.5–46.8 ng g−1) concentrations dominated by short-chain n-alkanes, low-molecular-weight and alkyl PAHs. Principal Component Analysis (PCA) shows that the PC 1 scores for n-alkanes and PAHs are significantly correlated with the input intensity of penguin guano and penguin bioelements. Using these proxies in combination with Generalized Additive Model (GAM), we reveal that breeding penguin population growth reaches a historical peak during the Medieval Climate Anomaly (MCA) prior to 1550 CE. This growth in population size corresponds to the extent of sea ice cover and the activity of the local atmospheric-ocean circulation. Warming induced by El Niño and the positive phase of the Southern Annular Mode, along with the expansion of ice-free zones and increased oceanic nutrient and food availability, are considered primary factors contributing to the growth of breeding penguin populations. Additionally, variations in sea ice extent and Amundsen Sea Low significantly influence penguin population dynamics. Our study suggests that n-alkanes and PAHs may be valuable organic proxies for reconstructing historical changes in breeding penguin populations, with the local sea ice extent and atmospheric-oceanic circulation exerting a major influence on Antarctic penguin population dynamics.

Impact of climate change on snowpack dynamics in coastal Central-Western Greenland

Snow patterns in ice-free areas of Greenland play important roles in ecosystems. Within a changing climate, a comprehensive understanding of the snow responses to climate change is of interest to anticipate forthcoming dynamics in these areas. In this study, we analyze the future snowpack evolution of a polar maritime Arctic location, Qeqertarsuaq (Disko Island, Central-Western Greenland). A physically-based snow model (FSM2) is validated and forced with CMIP6 projections for SSP2–4.5 and SSP5–8.5 greenhouse gasses emission scenarios, using two models: CanESM5 and MIROC6. The future snowpack evolution is assessed through four key seasonal (October to May) snow climate indicators: snow depth, snow days, snowfall fraction and ablation rate. Comparison against the observed air temperature for the reference climate period demonstrates superior accuracies for MIROC6 SSP2.4–5, with anomalies at 19 %, compared to CanESM5 SSP5.8–5 (25 %) and CanESM5 SSP2.4–5 (78 %). In terms of precipitation, CanESM5 SSP2.4–5 and SSP2.4–5 exhibit smaller anomalies against the observed data (5 %) in contrast to MIROC6 SSP2.4–5 (15 %) and MIROC6 SSP2.8–5 (17 %). Results demonstrate distinct snowpack responses to climate change depending on the model and emission scenario. For CanESM5, seasonal snow depth anomalies with respect to the reference period range from – 38 % (SSP2–4.5, 2040–2050 period) to – 74 % (SSP5–8.5, 2090–2100 period). MIROC6 projects lower snowpack reductions, with a decrease ranging from – 38 % (SSP2–4.5, 2040–2050 period) to – 57 % (SSP5–8.5, 2090–2100 period). Similar reductions are anticipated for snowfall and snow days. Changes in the snowpack evolution are primarily driven by positive trends in downwelling longwave radiation and air temperature. The projected increase in precipitation by the mid to late 21st century will lead to more frequent rain-on-snow events, intensifying snowpack melting. These findings help enhance the comprehension of future snow dynamics in the ice-free zones of Greenland, as well as the associated hydrological and ecological changes.

Unrecognized diversity and distribution of soil algae from Maritime Antarctica (Fildes Peninsula, King George Island).

Eukaryotic algae in the top few centimeters of fellfield soils of ice-free Maritime Antarctica have many important effects on their habitat, such as being significant drivers of organic matter input into the soils and reducing the impact of wind erosion by soil aggregate formation. To better understand the diversity and distribution of Antarctic terrestrial algae, we performed a pilot study on the surface soils of Meseta, an ice-free plateau mountain crest of Fildes Peninsula, King George Island, being hardly influenced by the marine realm and anthropogenic disturbances. It is openly exposed to microbial colonization from outside Antarctica and connected to the much harsher and dryer ice-free zones of the continental Antarctic. A temperate reference site under mild land use, SchF, was included to further test for the Meseta algae distribution in a contrasting environment. We employed a paired-end metabarcoding analysis based on amplicons of the highly variable nuclear-encoded ITS2 rDNA region, complemented by a clone library approach. It targeted the four algal classes, Chlorophyceae, Trebouxiophyceae, Ulvophyceae, and Xanthophyceae, representing key groups of cold-adapted soil algae. A surprisingly high diversity of 830 algal OTUs was revealed, assigned to 58 genera in the four targeted algal classes. Members of the green algal class Trebouxiophyceae predominated in the soil algae communities. The major part of the algal biodiversity, 86.1% of all algal OTUs, could not be identified at the species level due to insufficient representation in reference sequence databases. The classes Ulvophyceae and Xanthophyceae exhibited the most unknown species diversity. About 9% of the Meseta algae species diversity was shared with that of the temperate reference site in Germany. In the small portion of algal OTUs for which their distribution could be assessed, the entire ITS2 sequence identity with references shows that the soil algae likely have a wide distribution beyond the Polar regions. They probably originated from soil algae propagule banks in far southern regions, transported by aeolian transport over long distances. The dynamics and severity of environmental conditions at the soil surface, determined by high wind currents, and the soil algae's high adaptability to harsh environmental conditions may account for the high similarity of soil algal communities between the northern and southern parts of the Meseta.

A Comparison of Frequency Domain Electro-Magnetometry, Electrical Resistivity Tomography and Borehole Temperatures to Assess the Presence of Ice in a Rock Glacier

Alpine permafrost is currently warming, leading to changes such as active layer deepening and talik formation. Frequency domain electro-magnetometry (FDEM) measurements were tested as a simple and efficient method to investigate ground characteristics along two transects on the ice-rich Schafberg rock glacier in the Eastern Swiss Alps. The results were compared with electrical resistivity tomography (ERT) and ground temperature data acquired simultaneously in boreholes. FDEM provides information on the electrical properties of the ground, allowing to investigate ground-ice distribution. Our device allowed measurements to a depth of around 7 m. In ice-rich permafrost, FDEM can provide an approximation of the active layer thickness, and ice-free zones within the permafrost such as intra-permafrost taliks can be identified. This rapidly applicable geophysical method can be used to monitor ground ice distribution easily and efficiently, making it an ideal complement to borehole temperature data, which only provide point information and are costly to install and maintain. At the Schafberg site the three methods FDEM, electrical resistivity tomography and borehole temperature measurements provided similar results, with regard to active layer thickness and the presence of unfrozen zones within the ice-rich permafrost.

Wind Waves in the Arctic Seas: Envisat and AltiKa Data Analysis

Wind-generated waves in the Kara, Laptev, and East-Siberian Seas are investigated using altimeter data from Envisat RA-2 and SARAL-AltiKa. Only isolated ice-free zones had been selected for analysis. Wind seas can be treated as pure wind-generated waves without any contamination by ambient swell. Such zones were identified using ice concentration data from microwave radiometers. Altimeter data, both significant wave height (SWH) and wind speed, for these areas were further obtained for the period 2002–2012 using Envisat RA-2 measurements, and for 2013 using SARAL-AltiKa. Dependencies of dimensionless SWH and wavelength on dimensionless wave generation spatial scale are compared to known empirical dependencies for fetch-limited wind wave development. We further check sensitivity of Ka- and Ku-band and discuss new possibilities that AltiKa's higher resolution can open.

Influence of the physical environment on polar phytoplankton blooms: A case study in the Fram Strait

The Fram Strait is the main gateway for water, heat and sea-ice exchanges between the Arctic Ocean and the North Atlantic. The complex physical environment results in a highly variable primary production in space and time. Previous regional studies have defined key bottom-up (ice cover and stratification from melt water controlling the light availability, and wind mixing and water transport affecting the supply of nutrients) and top-down processes (heterotrophic grazing). In this study, in situ field data, remote sensing and modeling techniques were combined to investigate in detail the influence of melting sea-ice and ocean properties on the development of phytoplankton blooms in the Fram Strait region for the years 1998–2009. Satellite-retrieved chlorophyll-a concentrations from temporarily ice-free zones were validated with contextual field data. These were then integrated per month on a grid size of 20×20km, resulting in 10 grids/fields. Factors tested for their influence on spatial and temporal variation of chlorophyll-a were: sea-ice concentration from satellite and sea-ice thickness, ocean stratification, water temperature and salinity time-series simulated by the ice-ocean model NAOSIM. The time series analysis for those ten ice-free fields showed a regional separation according to different physical processes affecting phytoplankton distribution. At the marginal ice zone the melting sea-ice was promoting phytoplankton growth by stratifying the water column and potentially seeding phytoplankton communities. In this zone, the highest mean chlorophyll concentration averaged for the productive season (April–August) of 0.8mgC/m3 was observed. In the open ocean the phytoplankton variability was correlated highest to stratification formed by solar heating of the upper ocean layers. Coastal zone around Svalbard showed processes associated with the presence of coastal ice were rather suppressing than promoting the phytoplankton growth. During the twelve years of observations, chlorophyll concentrations significantly increased in the southern part of the Fram Strait, associated with an increase in sea surface temperature and a decrease in Svalbard coastal ice.

Impacts of climate, lake size, and supra- and sub-permafrost groundwater flow on lake-talik evolution, Yukon Flats, Alaska (USA)

In cold regions, hydrologic systems possess seasonal and perennial ice-free zones (taliks) within areas of permafrost that control and are enhanced by groundwater flow. Simulation of talik development that follows lake formation in watersheds modeled after those in the Yukon Flats of interior Alaska (USA) provides insight on the coupled interaction between groundwater flow and ice distribution. The SUTRA groundwater simulator with freeze–thaw physics is used to examine the effect of climate, lake size, and lake–groundwater relations on talik formation. Considering a range of these factors, simulated times for a through-going sub-lake talik to form through 90 m of permafrost range from ∼200 to > 1,000 years (vertical thaw rates < 0.1–0.5 m yr−1). Seasonal temperature cycles along lake margins impact supra-permafrost flow and late-stage cryologic processes. Warmer climate accelerates complete permafrost thaw and enhances seasonal flow within the supra-permafrost layer. Prior to open talik formation, sub-lake permafrost thaw is dominated by heat conduction. When hydraulic conditions induce upward or downward flow between the lake and sub-permafrost aquifer, thaw rates are greatly increased. The complexity of ground-ice and water-flow interplay, together with anticipated warming in the arctic, underscores the utility of coupled groundwater-energy transport models in evaluating hydrologic systems impacted by permafrost.

Soil bacterial community abundance and diversity in ice-free areas of Keller Peninsula, Antarctica

The Antarctic is the most untouched terrestrial region of the planet but the most vulnerable to global environmental changes. In this regard, the monitoring of terrestrial environments is fundamental for the evaluation of such changes. This exploratory study aimed to provide baseline information against which to monitor changes in the Antarctic soil microbiome caused by global environmental changes or human activities and to find patterns in microbial diversity and community composition in ice-free zones of Antarctica. To achieve this goal we applied a high-throughput pyrosequencing based analysis of amplified 16S rRNA genes from twelve soil samples from the most prominent plant communities and soil types collected in the Keller Peninsula, King George Island, Antarctica. Such approach provided the variability necessary to investigate important ecological aspects of overall patterns of bacterial distribution. Quantitative and qualitative bacterial diversity measures were calculated and combined with metadata describing the samples. Overall, the soil bacterial communities in ice-free areas of Keller Peninsula were dominated by a small number of phyla found in most soils, including agricultural ones. Despite the differences in soil properties or plant cover the best predictor for the microbial community structure was the pH gradient. Our results provide evidence of no correlation between bacterial community and plant cover in Antarctic ice free zones.

Observations of Humpback Whales, Megaptera novaeangliae, in the Beaufort Sea, Alaska

Humpback Whales, Megaptera novaeangliae, are found in all of the world’s oceans (Reeves and others 2002). Humpback Whales, however, have generally not been found in the Arctic Ocean with the exception of the Barents Sea where warmer waters from the North Atlantic Drift provide rich nutrients for food resources, and ice free zones in the summer (Zabavnikov and others 2005). In the North Pacific, Asian stocks of Humpback Whales summer in the eastern Bering Sea, with some individuals occasionally entering the Arctic Ocean via the Bering Strait and summering along the Siberian coast of the Chukchi Sea (Tomilin 1937; Sleptsov 1961; Johnson and Wolman 1984; Angliss and Allen 2008). Further penetration into the Arctic Ocean, especially into the Beaufort Sea, has probably been prevented by the whales’ natural avoidance of colder waters and associated polar pack ice (Chittleborough 1965; Dawbin 1966). We report on the 1st confirmed sighting of Humpback Whales for the Beaufort Sea, Alaska. During August 2007, FEX LP contracted Agvik Marine LLC to barge oil drilling equipment from Cape Simpson to West Dock (Prudhoe Bay), Alaska, as part of a demobilization of onshore drilling activities conducted the previous 2 winters. On 1 August 2007, at UTM 454911E, 7879755N (WGS84) (about 87 km east of Point Barrow), KAH observed a whale at about 250 m from the barge, and initially identified the individual as a Humpback Whale based on the unique characteristics of the dorsal fin and flukes, and characteristic arching back. Five minutes later the same whale (presumably) approached to within about 75 m of the barge where it was photographed (Fig. 1) and confirmed by BA, an experienced Inupiat hunter, to be a Humpback Whale. During this close encounter, the whale turned on its side revealing the characteristic long pectoral flipper. At this time KAH and the barge’s captain observed a calf with the adult whale. The adult was last seen about 3 min later about 175 m from the barge, slowly traveling to the east. No photographs were taken of the calf or the undersides of the adult’s flukes. At the time of the encounter, the sea state was a Beaufort 3 (large wavelets with occasional whitecaps), the wind was from the east at 10 knots (about 19 km/hr), and visibility was excellent. The barge, hampered by the loss of an outboard engine, was reduced to traveling at ,6 km/hr. Other than approaching the barge, the whales showed no undue reaction to the vessel. Although adult whales were sighted at 3 locations during an 8-min period, we could not positively ascertain whether more than 1 adult whale was present. We believe that we observed only a single cow/calf pair, although it was possible some of the sightings were of an additional Humpback Whale. Further, 2 Gray Whales (Eschrichtius robustus) were observed minutes before the 1st Humpback Whale sighting. While an extralimital sighting of a Humpback Whale in the Beaufort Sea is unusual in itself, the presence of a calf is particularly noteworthy. Based on limited understanding of whales in the North Pacific, it is possible that the whales we observed were part of the Western North Pacific stock that breeds in Asian waters, especially near the Mariana, Ryukyu, and Bonin islands, and summers in the Bering Sea; although the Central North Pacific stock, which breeds among the Hawaiian Islands (Angliss and Allen 2008), may also summer in portions of the Bering Sea. Regardless of origin (Asia or NORTHWESTERN NATURALIST 90:160–162 AUTUMN 2009 160 NORTHWESTERN NATURALIST 90(2)

Climatological mean and decadal change in surface ocean pCO2, and net sea–air CO2 flux over the global oceans

A climatological mean distribution for the surface water pCO2 over the global oceans in non-El Nino conditions has been constructed with spatial resolution of 4° (latitude) ×5° (longitude) for a reference year 2000 based upon about 3 million measurements of surface water pCO2 obtained from 1970 to 2007. The database used for this study is about 3 times larger than the 0.94 million used for our earlier paper [Takahashi et al., 2002. Global sea–air CO2 flux based on climatological surface ocean pCO2, and seasonal biological and temperature effects. Deep-Sea Res. II, 49, 1601–1622]. A time-trend analysis using deseasonalized surface water pCO2 data in portions of the North Atlantic, North and South Pacific and Southern Oceans (which cover about 27% of the global ocean areas) indicates that the surface water pCO2 over these oceanic areas has increased on average at a mean rate of 1.5 μatm y−1 with basin-specific rates varying between 1.2±0.5 and 2.1±0.4 μatm y−1. A global ocean database for a single reference year 2000 is assembled using this mean rate for correcting observations made in different years to the reference year. The observations made during El Nino periods in the equatorial Pacific and those made in coastal zones are excluded from the database. Seasonal changes in the surface water pCO2 and the sea-air pCO2 difference over four climatic zones in the Atlantic, Pacific, Indian and Southern Oceans are presented. Over the Southern Ocean seasonal ice zone, the seasonality is complex. Although it cannot be thoroughly documented due to the limited extent of observations, seasonal changes in pCO2 are approximated by using the data for under-ice waters during austral winter and those for the marginal ice and ice-free zones. The net air–sea CO2 flux is estimated using the sea–air pCO2 difference and the air–sea gas transfer rate that is parameterized as a function of (wind speed)2 with a scaling factor of 0.26. This is estimated by inverting the bomb 14C data using Ocean General Circulation models and the 1979–2005 NCEP-DOE AMIP-II Reanalysis (R-2) wind speed data. The equatorial Pacific (14°N–14°S) is the major source for atmospheric CO2, emitting about +0.48 Pg-C y−1, and the temperate oceans between 14° and 50° in the both hemispheres are the major sink zones with an uptake flux of −0.70 Pg-C y−1 for the northern and −1.05 Pg-C y−1 for the southern zone. The high-latitude North Atlantic, including the Nordic Seas and portion of the Arctic Sea, is the most intense CO2 sink area on the basis of per unit area, with a mean of −2.5 tons-C month−1 km−2. This is due to the combination of the low pCO2 in seawater and high gas exchange rates. In the ice-free zone of the Southern Ocean (50°–62°S), the mean annual flux is small (−0.06 Pg-C y−1) because of a cancellation of the summer uptake CO2 flux with the winter release of CO2 caused by deepwater upwelling. The annual mean for the contemporary net CO2 uptake flux over the global oceans is estimated to be −1.6±0.9 Pg-C y−1, which includes an undersampling correction to the direct estimate of −1.4±0.7 Pg-C y−1. Taking the pre-industrial steady-state ocean source of 0.4±0.2 Pg-C y−1 into account, the total ocean uptake flux including the anthropogenic CO2 is estimated to be −2.0±1.0 Pg-C y−1 in 2000.

Remote sensing estimates of glacier mass balances in the Himachal Pradesh (Western Himalaya, India)

Although they correspond to an important fraction of the total area of mountain glaciers (33,000 km 2 out of 546,000 km 2), Himalayan glaciers and their mass balance are poorly sampled. For example, between 1977 and 1999, the average area surveyed each year on the field was 6.8 km 2 only. No direct mass balance measurement is available after 1999. To contribute to fill this gap, we use remote sensing data to monitor glacier elevation changes and mass balances in the Spiti/Lahaul region (32.2°N, 77.6°E, Himachal Pradesh, Western Himalaya, India). Our measurements are obtained by comparing a 2004 digital elevation model (DEM) to the 2000 SRTM (Shuttle Radar Topographic Mission) topography. The 2004 DEM is derived from two SPOT5 satellite optical images without any ground control points. This is achieved thanks to the good on-board geolocation of SPOT5 scenes and using SRTM elevations as a reference on the ice free zones. Before comparison on glaciers, the two DEMs are analyzed on the stable areas surrounding the glaciers where no elevation change is expected. Two different biases are detected. A long wavelength bias affects the SPOT5 DEM and is correlated to an anomaly in the roll of the SPOT5 satellite. A bias is also observed as a function of altitude and is attributed to the SRTM dataset. Both biases are modeled and removed to permit unbiased comparison of the two DEM on the 915 km 2 ice-covered area digitized from an ASTER image. On most glaciers, a clear thinning is measured at low elevations, even on debris-covered tongues. Between 1999 and 2004, we obtain an overall specific mass balance of − 0.7 to − 0.85 m/a (water equivalent) depending on the density we use for the lost (or gained) material in the accumulation zone. This rate of ice loss is twice higher than the long-term (1977 to 1999) mass balance record for Himalaya indicating an increase in the pace of glacier wastage. To assess whether these ice losses are size-dependant, all glaciers were classified into three samples according to their areal extent. All three samples show ice loss, the loss being higher for glaciers larger than 30 km 2. In the case of the benchmark Chhota Shigri glacier, a good agreement is found between our satellite observations and the mass balances measured on the field during hydrological years 2002–2003 and 2003–2004. Future studies using a similar methodology could determine whether similar ice losses have occurred in other parts of the Himalaya and may allow evaluation of the contribution of this mountain range to ongoing sea level rise.

A modelling insight into the Icelandic Last Glacial Maximum ice sheet

A three-dimensional thermomechanical model is used to investigate the Last Glacial Maximum (LGM) Icelandic ice sheet and the climate responsible for it at ∼ 21 ka BP . A series of sensitivity experiments reveal that Iceland is susceptible to the onset large-scale glaciation with only a 3 °C cooling perturbation relative to recent (1961–1990) climate. A 5 °C cooling perturbation is enough to force an ice sheet to beyond the present day coastline in virtually all sectors. A suite of 15 experiments driven by a GRIP δ O 18 time-series for 15,000 years from a climatic optimum at 36 ka to 21 ka BP scaled with 5.0–15.0 °C maximum cooling perturbation are initiated in order to identify a best-fit LGM ice sheet configuration compatible with the available empirical evidence. The optimum LGM model isolated requires an annual cooling of 10.0–12.5 °C relative to the recent climatology with over 50% precipitation suppression across the north and yields an extensive offshore ice sheet with an area of 3.29 × 10 5 km 2 and a volume of 3.09 × 10 5 km 3 . Over-extension of ice extent across the northern shelf is addressed by the introduction of strong aridity across this region but otherwise the ice-sheet is well pinned to the continental shelf-break in remaining sectors which tends to decouple it from further climatic forcing. The optimum LGM ice-sheet has a substantial proportion of its base grounded below sea-level and is dominated by basal sliding which activates extensive zones of fast flow. This results in a highly dynamic, low aspect ice sheet with a mean ice thickness of 940 m and a plateau elevation of ∼ 2000 m breached by numerous nunataks and ice-free zones providing potential, but spatially limited and frigid, ecological refugia through the vicissitudes of the LGM.

Three-Dimensional Modeling of Potential and Electric-Field Distributions Along an EHV Ceramic Post Insulator Covered With Ice—Part I: Simulations of a Melting Period

The main objective of this paper is to determine the potential and electric-field distributions along a typical ceramic extremely-high-voltage post insulator covered with atmospheric ice during a melting period. Commercial software, Coulomb 3D, based on the boundary element method (BEM), was used for all of the three-dimensional modeling and simulations. It was demonstrated that the BEM is well suited for evaluating the effect of ice shedding on the potential and electric-field distributions along an ice-covered insulator during a melting period. The results obtained show that the length and number of ice free zones, also called air gaps, are the major parameters that affect the applied voltage distribution along an ice-covered insulator. The mean electric field per arcing distance, affected mainly by the air-gap lengths, can provide a good indication of the presence of partial arcing along the different air gaps.