Snow Pit Research Articles

Isotopic analysis of snow from Dome C indicates changes in the source of atmospheric lead over the last fifty years in East Antarctica

Lead (Pb) concentration and Pb isotope ratios have been determined in 109 snow pit samples collected at Dome C, on the East Antarctic Plateau, corresponding to the period 1971–2017. The Pb concentration was 8.2 ± 1.0 pg g−1 (mean ± 95%-confidence interval), with a decreasing trend from the early 1990s (the median Pb concentration halved from 9.0 pg g−1 in 1970–1980 to 4.4 pg g−1 in 2010–2017). The 206Pb/207Pb and 208Pb/207Pb ratios were 2.419 ± 0.003 and 1.158 ± 0.003 (mean and 95%-confidence interval), respectively. The temporal variations of Pb isotopic composition from 1970 to mid-1990s reflect the changes in the consumption of Pb-enriched gasoline in the Southern Hemisphere, whereas the subsequent increase of the Pb isotope ratios is ascribed to a shift toward the natural isotopic signature. Accordingly, the anthropogenic Pb contribution decreased from (61 ± 3)% in 1980–1990 to (49 ± 10)% in 2010–2017. The measured ratios suggest that Australia has been a significant source of anthropogenic Pb to Antarctica, even in recent times. Differences and similarities among Pb content and isotopic composition in various sites across Antarctica have been displayed by principal component analysis, indicating that the altitude and the distance from the coast significantly affect the Pb content, while the Pb isotopic signatures are not influenced by these parameters.

Atmospheric pollution revealed by trace elements in recent snow from the central to the northern Tibetan Plateau

In order to determine the current levels, spatial distribution patterns, and potential pollution of trace elements (TEs) in the atmosphere of the Tibetan Plateau (TP), snow pit samples were collected in May 2016 from five TP glaciers: Qiyi (QY), Hariqin (HRQ), Meikuang (MK), Yuzhufeng (YZF), and Xiaodongkemadi (XDKMD). Concentrations of 13 TEs (Al, Ba, Cd, Co, Cr, Cu, Fe, Li, Pb, Sb, Sr, U, and Zn) in the snow were measured. The spatial distribution patterns and depth profiles of TEs from the studies sites revealed that the influence of dust on TEs was more significant on the MK and YZF glaciers than on the QY, HRQ, and XDKMD glaciers. The spatial distributions of TE EFFe values differed from their concentrations, however. The enrichment factor (EF) values and concentrations of some TEs in the YZF, QY, and XDKMD glaciers revealed that the pollution levels of these elements were significantly lower than those found in previous research. Examination based on EFs, principal component analysis, as well as the calculated non-dust contributions of TEs, revealed that dust was the principal source for most TEs in all five glaciers, while biomass burning was another potential natural source for TEs in some glaciers, such as QY. In contrast, Cd, Ba, Sr, Cu, Pb, Zn, and Sb were occasionally affected by anthropogenic sources such as road traffic emissions, fossil fuel combustion, and mining and smelting of nonferrous metals in and beyond the TP. Air mass backward trajectories revealed that potential pollutants were transported not only from local sources but also from Xinjiang Province in northwestern China, as well as South Asia, Central Asia, the Middle East, and Europe.

Stable isotopic composition in snowpack along the traverse from a coastal location to Dome A (East Antarctica): Results from observations and numerical modeling

Stable isotopic composition (δ18O and δD) in Antarctic snow/ice cores serves as the proxy of past temperature. However, the accuracy of temperature reconstruction is largely dependent on the relationship between water isotopes and local temperature (δ-T) derived from present conditions. Thus, it is crucial to quantitatively understand the spatial δ-T relationship and the influencing factors of δ18O and δD in surface snow besides temperature. In this work, we characterized the spatial and temporal variation of stable isotopes in surface snow using a comprehensive assessment of observations and simulations on the traverse from the coast to Dome A, the summit of East Antarctica ice sheet. The δ18O and δD from surface snow and snow pit samples show an insignificant variation at interannual scale, possibly suggesting that interannual changes in controlling factors are not remarkable during the investigation period. Along the traverse, the spatial δ18O-T slope is 0.91‰·oC−1 based on averages of δ18O measurements for snow pits and annual mean temperature at the sampling site. Results from the mixed cloud isotope model (MCIM) suggest that the effects of evaporative conditions and transportation paths of moisture on water isotopes for specific sites are insignificant. Therefore, it is more important to consider other effects on water isotopes (e.g. post-depositional processes) when interpreting ice core records, particularly in interior Antarctica.

Field Study of Mass Balance, and Hydrology of the West Khangri Nup Glacier (Khumbu, Everest)

The depiction of glaciers’ dynamics in the high altitudes of Himalaya and the hydrological fluxes therein is often limited. Although sparse seasonal (snow/ice) melt data may be available, dense precipitation networks are not available everywhere, and especially in the highest area, and the assessment of accumulation processes and mass balance may be difficult. Hydrological fluxes are little measured in the high altitudes, and few studies are available covering flow modeling and flow partitioning. Here, we investigate the snow accumulation, ice melt, and mass balance of West Khangri Nup (WKN) glacier (0.23 km2, mean altitude 5494 m asl), which is a part of the Khumbu glacier in the Everest region, where information of precipitation and hydro-glaciological dynamics in the highest altitudes was made available recently in fulfillment of several research projects. Weather, glaciological, snow pits, hydrologic, and isotopic data gathered during field campaigns (2010–2014) on the glacier and at the EVK2CNR Pyramid site were used to (i) set up the Poli-Hydro glacio-hydrological model to describe ice and snow melt and hydrological flows from the glacier, and (ii) investigate seasonal snow dynamics on this high region of the glacier. Coupling ice ablation data and Poli-Hydro simulation for ca. 5 years (January 2010–June 2014), we estimate that the WKN depleted ca. −10.46 m of ice water equivalent per year m IWE year−1 (i.e., annually ca. −2.32 meter of water equivalent per year m WE year−1). Then, using snowpack density and isotopic (δ18O) profiles on the WKN, we demonstrate that the local snowpack is recent (Fall–Winter 2013–2014) and that significant snow accumulation did not occur recently, so this area has not been a significant one of accumulation recently. Analysis of recent snow cover from LANDSAT images also confirms snow dynamics as depicted. Our study presents original data and results, and it complements present studies covering glaciers’ mass balance as well as an investigation of accumulation zones in the Everest region and the Himalayas, which is also potentially helpful in the assessment of future dynamics under ongoing climate change.

森林総合研究所十日町試験地における冬期の気象および雪質の調査資料 （9）（2014/15年～2018/19年 5冬期）

森林総合研究所十日町試験地における冬期の気象および雪質の調査資料 （9）（2014/15年～2018/19年 5冬期）

Underestimation of Snow Accumulation Rate in Central Antarctica (Vostok Station) Derived from Stake Measurements

It is shown that the snow stake measurements in central Antarctica systematically underestimate the value of the snow build-up. Two methods for the calculation of the corresponding correction to the snow stake measurements at Vostok station are developed to take this underestimation into account. The first method is based on the Sorge’s law to calculate the rate of compaction of snow layers using the vertical profile of snow density. The second method is based on the direct field measurements of this compaction. Two independent methods for the estimation of the snow accumulation rate in the vicinity of Vostok station are also considered: geodetic data on the rate of snow layer sinking and glaciological data from snow pits. The most reliable estimate of the snow accumulation rate in this region is 2.26 ± 0.10 g/cm2 per year, that is 8 ± 4% higher than uncorrected values from snow accumulation measurements.

Relating regional and point measurements of accumulation in southwest Greenland

Abstract. In recent decades, the Greenland ice sheet (GrIS) has frequently experienced record melt events, which have significantly affected surface mass balance (SMB) and estimates thereof. SMB data are derived from remote sensing, regional climate models (RCMs), firn cores and automatic weather stations (AWSs). While remote sensing and RCMs cover regional scales with extents ranging from 1 to 10 km, AWS data and firn cores are point observations. To link regional scales with point measurements, we investigate the spatial variability of snow accumulation (bs) within areas of approximately 1–4 km2 and its temporal changes within 2 years of measurements. At three different sites on the southwestern GrIS (Swiss Camp, KAN-U, DYE-2), we performed extensive ground-penetrating radar (GPR) transects and recorded multiple snow pits. If the density is known and the snowpack dry, radar-measured two-way travel time can be converted to snow depth and bs. We spatially filtered GPR transect data to remove small-scale noise related to surface characteristics. The combined uncertainty of bs from density variations and spatial filtering of radar transects is at 7 %–8 % per regional scale of 1–4 km2. Snow accumulation from a randomly selected snow pit is very likely representative of the regional scale of 1–4 km2 (with probability p=0.8 for a value within 10 % of the regional mean for KAN-U, and p>0.95 for Swiss Camp and DYE-2). However, to achieve such high representativeness of snow pits, it is required to determine the average snow depth within the vicinity of the pits. At DYE-2, the spatial pattern of snow accumulation was very similar for 2 consecutive years. Using target reflectors placed at respective end-of-summer-melt horizons, we additionally investigated the occurrences of lateral redistribution within one melt season. We found no evidence of lateral flow of meltwater in the current climate at DYE-2. Such studies of spatial representativeness and temporal changes in accumulation are necessary to assess uncertainties of the linkages of point measurements and regional-scale data, which are used for validation and calibration of remote-sensing data and RCM outputs.

Distribution and chemical composition of snow cover of the Sygyktinsky glacier (Kodar Ridge, south eastern Siberia)

Snow survey was carried out in the central part of the Sygyktinsky Glacier (Kodar Ridge, south eastern Siberia), and a map of the distribution of snow cover was constructed (average snow thickness was 97 cm). Stratigraphy and the chemical composition of the snow cover were studied in a snow pit. It was established that the chemical composition of the snow belongs to the chloride class, ammonium and sodium groups. At the same time, the ionic composition of snow reflects seasonal changes in atmospheric circulation in the region (local continental sources of ions prevail in winter, while the proportion of marine ions increases in the spring).

Continuous and autonomous snow water equivalent measurements by a cosmic ray sensor on an alpine glacier

Abstract. Snow water equivalent (SWE) measurements of seasonal snowpack are crucial in many research fields. Yet accurate measurements at a high temporal resolution are difficult to obtain in high mountain regions. With a cosmic ray sensor (CRS), SWE can be inferred from neutron counts. We present the analyses of temporally continuous SWE measurements by a CRS on an alpine glacier in Switzerland (Glacier de la Plaine Morte) over two winter seasons (2016/17 and 2017/18), which differed markedly in the amount and timing of snow accumulation. By combining SWE with snow depth measurements, we calculate the daily mean density of the snowpack. Compared to manual field observations from snow pits, the autonomous measurements overestimate SWE by +2 % ± 13 %. Snow depth and the bulk snow density deviate from the manual measurements by ±6 % and ±9 %, respectively. The CRS measured with high reliability over two winter seasons and is thus considered a promising method to observe SWE at remote alpine sites. We use the daily observations to classify winter season days into those dominated by accumulation (solid precipitation, snow drift), ablation (snow drift, snowmelt) or snow densification. For each of these process-dominated days the prevailing meteorological conditions are distinct. The continuous SWE measurements were also used to define a scaling factor for precipitation amounts from nearby meteorological stations. With this analysis, we show that a best-possible constant scaling factor results in cumulative precipitation amounts that differ by a mean absolute error of less than 80 mm w.e. from snow accumulation at this site.

Exceptionally High 2018 Equilibrium Line Altitude on Taku Glacier, Alaska

The Juneau Icefield Research Program (JIRP) has been examining the glaciers of the Juneau Icefield since 1946. The height of the transient snowline (TSL) at the end of the summer represents the annual equilibrium line altitude (ELA) for the glacier, where ablation equals accumulation. On Taku Glacier the ELA has been observed annually from 1946 to 2018. Since 1998 multiple annual observations of the TSL in satellite imagery identify both the migration rate of the TSL and ELA. The mean ELA has risen 85 ± 10 m from the 1946–1985 period to the 1986–2018 period. In 2018 the TSL was observed at: 900 m on 5 July; 975 m on 21 July; 1075 m on 30 July; 1400 m on 16 September; and 1425 m on 1 October. This is the first time since 1946 that the TSL has reached or exceeded 1250 m on Taku Glacier. The 500 m TSL rise from 5 July to 30 July, 8.0. md−1, is the fastest rate of rise observed. This combined with the observed balance gradient in this region yields an ablation rate of 40–43 mmd−1, nearly double the average ablation rate. On 22 July a snow pit was completed at 1405 m with 0.93 m w.e. (water equivalent), that subsequently lost all snow cover, prior to 16 September. This is one of eight snow pits completed in July providing field data to verify the ablation rate. The result of the record ELA and rapid ablation is the largest negative annual balance of Taku Glacier since records began in 1946.

Bistatic SAR Radar for Long-Term Snow Pack Monitoring

This article presents a short-range, bistatic radar system for in situ , long-term snow monitoring. The proposed system is capable of autonomously capturing time-lapsed, 2-D images of the snow cover. In this article, we report on system concept and initial results for average snow-water-equivalent (SWE) assessment. Average SWE of dry snow is estimated based on two-way-travel time, bistatic radar measurements and compared to observed snow pit data as well as monostatic radar estimates. Although current empirical results are limited, measurements are indicating good performance. The bistatic radar instrument is capable of 2-D imaging and wet snow assessment, but empirical validation is required.

Isotopic composition of oxygen in snow-and-firn thickness on the Eastern peak of Elbrus, the Caucasus

The isotopic composition of oxygen of the snow-and-firn and snow thickness on the Eastern peak of Elbrus had been studied. In 2006-2008, a number of snow samples were taken in the near-peak area of Elbrus to analyze the isotopic composition of them. The drilling was performed at the crater of the Eastern peak in 2006 (64 samples) while in 2017 the samples were taken from snow pit (25 samples). Another core to a depth of 23.8 m was extracted at the Western Plateau (118 samples) for the purpose to compare local 5 18 О values with samples from the Eastern peak. The δ 18 О values in the snow-and-firn thickness from the crater of the Eastern peak vary from -6.8 to -19.41 %o with the average value of -12.61 %o. It was revealed that snow layers with extremely low values of δ 18 О (down to -30 %) found on the eastern slope were absent on the western plateau. The loss of part of the annual isotope precipitation signal due to the winter extra light horizons could be caused by two reasons: wind drift of the freshly deposited snow, as well as the absence of part of the winter snowfalls with isotope-light precipitation at altitudes higher 5300 m. Seasonal variations of δ 18 О values, equal to 12 % and found in the snow-and-firn thickness on the Eastern peak, indicate that formation of the isotopic characteristics of snow is determined here by the equilibrium Rayleigh condensation and this is associated with the annual amplitude of the air temperature by a coefficient of 0.6 %o/°C. In the isotopic record obtained on the Western plateau of Elbrus, the relationship of values δ 18 О with the condensation temperature may be disturbed due to the frequent change of the main moisture-bearing air masses. This leads to significantly different δ 18 О values in precipitation at the same temperatures (the connection of seasonal δ 18 О values with the annual amplitude of air temperature varies from 0.3 to 1.12 % о /° С ).

Long-range terrestrial laser scanning measurements of annual and intra-annual mass balances for Urumqi Glacier No. 1, eastern Tien Shan, China

Abstract. The direct glaciological method provides in situ observations of annual or seasonal surface mass balance, but can only be implemented through a succession of intensive in situ measurements of field networks of stakes and snow pits. This has contributed to glacier surface mass-balance measurements being sparse and often discontinuous in the Tien Shan. Nevertheless, long-term glacier mass-balance measurements are the basis for understanding climate–glacier interactions and projecting future water availability for glacierized catchments in the Tien Shan. Riegl VZ®-6000 long-range terrestrial laser scanner (TLS), typically using class 3B laser beams, is exceptionally well suited for repeated glacier mapping, and thus determination of annual and seasonal geodetic mass balance. This paper introduces the applied TLS for monitoring summer and annual surface elevation and geodetic mass changes of Urumqi Glacier No. 1 as well as delineating accurate glacier boundaries for 2 consecutive mass-balance years (2015–2017), and discusses the potential of such technology in glaciological applications. Three-dimensional changes of ice and firn–snow bodies and the corresponding densities were considered for the volume-to-mass conversion. The glacier showed pronounced thinning and mass loss for the four investigated periods; glacier-wide geodetic mass balance in the mass-balance year 2015–2016 was slightly more negative than in 2016–2017. Statistical comparison shows that agreement between the glaciological and geodetic mass balances can be considered satisfactory, indicating that the TLS system yields accurate results and has the potential to monitor remote and inaccessible glacier areas where no glaciological measurements are available as the vertical velocity component of the glacier is negligible. For wide applications of the TLS in glaciology, we should use stable scan positions and in-situ-measured densities of snow–firn to establish volume-to-mass conversion.

Deposition of ionic species and black carbon to the Arctic snowpack: combining snow pit observations with modeling

Abstract. Although aerosols in the Arctic have multiple and complex impacts on the regional climate, their removal due to deposition is still not well quantified. We combined meteorological, aerosol, precipitation, and snowpack observations with simulations to derive information about the deposition of sea salt components and black carbon (BC) from November 2011 to April 2012 to the Arctic snowpack at two locations close to Ny-Ålesund, Svalbard. The dominating role of sea salt and the contribution of dust for the composition of atmospheric aerosols were reflected in the seasonal composition of the snowpack. The strong alignment of the concentrations of the major sea salt components in the aerosols, the precipitation, and the snowpack is linked to the importance of wet deposition for transfer from the atmosphere to the snowpack. This agreement was less strong for monthly snow budgets and deposition, indicating important relocation of the impurities inside the snowpack after deposition. Wet deposition was less important for the transfer of nitrate, non-sea-salt sulfate, and BC to the snow during the winter period. The average BC concentration in the snowpack remains small, with a limited impact on snow albedo and melting. Nevertheless, the observations also indicate an important redistribution of BC in the snowpack, leading to layers with enhanced concentrations. The complex behavior of bromide due to modifications during sea salt aerosol formation and remobilization in the atmosphere and in the snow were not resolved because of the lack of bromide measurements in aerosols and precipitation.

Melt‐Induced Fractionation of Major Ions and Trace Elements in an Alpine Snowpack

AbstractUnderstanding the impact of melting on the preservation of atmospheric compounds in high‐Alpine snow and glacier ice is crucial for future reconstruction of past atmospheric conditions. However, detailed studies investigating melt‐related changes of such proxy information are rare. Here we present a series of five snow pit profiles of 6 major ions and 34 trace elements at Weissfluhjoch, Switzerland, collected between January and June 2017. Atmospheric composition was preserved during the cold season, while melting toward the summer resulted in preferential loss of certain species from the snowpack or enrichment at the base of the snowpack. Increasing mobilization of major ions with meltwater (NH4+ < Cl− ~ Na+ < NO3− ~ Ca2+ ~ SO42−) can be related to their stronger enrichment at ice crystal surfaces during snow metamorphism. Results for trace elements show that less abundant elements such as Ce, Eu, La, Mo, Nd, Pb, Pr, Sb, Sc, Sm, U, and W were best preserved and may still serve as tracers to reconstruct past natural and anthropogenic atmospheric emissions from melt‐affected snow pit and ice core records. The obtained elution behavior matches the findings from another high‐Alpine site (upper Grenzgletscher) for major ions and the large majority of investigated trace elements. Both studies indicate that water solubility and location at the microscopic scale are likely to determine the relocation behavior with meltwater and also suggest that the observed species‐dependent preservation from melting snow and ice is representative for the Alpine region, reflecting Central European atmospheric aerosol composition.

Concentration, spatiotemporal distribution, and sources of mercury in Mt. Yulong, a remote site in southeastern Tibetan Plateau.

The unique geographic location of Mt. Yulong in the Tibetan Plateau (TP) makes it a favorable site for mercury (Hg) study. Various snow samples, such as surface snow, snow pit, and snowmelt water were collected from Mt. Yulong in the southeastern TP. The average concentration of Hg was found to be 37 ± 26ngL-1 (mean ± SD), comparable to Hg concentration from other parts of TP in the same year, though it was comparatively higher than those from previous years, suggesting a possible increase of Hg concentration over the TP. The concentration of Hg was higher in the lower elevation of the glaciers possibly due to the surface melting concentration of particulates. Higher concentration of Hg was observed in the fresh snow, suggesting the possibility of long-range transportation. The average concentration of Hg from the snow pit was 1.49 ± 0.78ngL-1, and the concentration of Hg in the vertical profile of the snow pit co-varied with calcium ion (Ca2+) supporting the fact that the portion of Hg is from the crustal origin. In addition, the principal component analysis (PCA) confirmed that the source of Hg is from the crustal origin; however, the presence of anthropogenic source in the Mt. Yulong was also observed. In surface water around Mt. Yulong, the concentration of HgT was found in the order of Lashihai Lake > Reservoirs > Rivers > Swamps > Luguhu Lake. In lake water, the concentration of HgT showed an increasing trend with depth. Overall, the increased concentration of Hg in recent years from the TP can be of concern and may have an adverse impact on the downstream ecosystem, wildlife, and human health.

RMetS National Meeting – Arctic prediction in a changing climate: understanding key processes and challenges

RMetS National Meeting – Arctic prediction in a changing climate: understanding key processes and challenges

Drone-Mounted Ultrawideband Radar for Retrieval of Snowpack Properties

Extracting snowpack parameters from snow cover on sea ice or land is a time-consuming and potentially high-risk task. Moreover, deriving such parameters by manually digging a snow pit evidently yields low area coverage. We, therefore, propose a practical solution to this problem by mounting an ultrawideband radar system onto an unmanned aerial vehicle (UAV) to obtain information such as snowpack depth, density, and stratigraphy in order to increase personnel safety and extend coverage area. In this paper, we describe the development of radar system hardware and its mounting onto a UAV, as well as initial tests with this radar as a snow measuring device. Preliminary results from both ground and airborne testing show that the radar system is capable of obtaining snow depth information that corresponds well to in situ validation data with a correlation of 0.87. The radar system also works well while mounted on a UAV platform with little additional signal noise from vibrational and translatory movements.

Erratum to: Deposition of atmospheric pollutant and their chemical characterization in snow pit profile at Dokriani Glacier, Central Himalaya

The uncertainty in assessing the numerous atmospheric pollutants transported via wind from arid and semi-arid regions is affecting the glacial ecosystem. In our study area due to the complexity of the system, a prominent seasonal difference noticed among major ions (Ca2+, Mg2+, SO42−, and NO3−). There is a need for understanding the ions cycling as a whole and the directionality of the feedback loops in the system. Therefore, we provide an appraisal of our current hypothesis for seasonal difference in major ion concentration from snow samples for two corresponding years (2013 and 2015) at Dokriani Glacier. A systematic study of chemical compositions in the shallow snow pit from Dokriani Glacier was undertaken for the pre-monsoon season to understand the cycling of major ions from atmosphere to solute acquisition process. The intimating connections of ions cycling in snow and its temporal behavior was observed and analyzed through various statistical tests. Among major ions, the SO42− has the highest concentration among anions on an average considered as 14.21% in 2013 and 29.46% in 2015. On the other side Ca2+ is the dominant cation contributing 28.22% in 2013 and 15.3% in 2015 on average. The average ratio of Na+/Cl− was higher in 2013 whereas lower in 2015. The backward trajectory analysis suggests the possible sources of the ions transported from Central Asia through the Western Disturbance (WD) as a prominent source of winter precipitation mainly in the Central Himalaya. Ionic concentration of Ca2+ in cations was highly dominated while in anion SO42− played the major role. Factor analysis and correlation matrix suggested that, the precipitation chemistry is mostly influenced by anthropogenic, crustal, and sea salt sources over the studied region. The elemental cycling through ocean, atmosphere and biosphere opens up new ways to understand the geochemical processes operating at the glacierized catchments of the Himalaya. Moreover, increasing the field-based studies in the coming decades would also have the certain advantage in overcoming the conceptual and computational geochemical modelling difficulties.

Relationship between the 2014–2015 Holuhraun eruption and the iron record in the East GRIP snow pit

ABSTRACTWe conducted a 2 m snow pit study in July 2017 at the East GRIP (Greenland Ice-Core Project; northeastern Greenland) deep ice-coring site. We collected snow samples at intervals of 0.05 m and analyzed their iron (Fe) and rare earth element (REE) concentrations. Pronounced seasonal variations in trace elements were observed during 2012–2017. The results indicated that the dissolved Fe (DFe), total dissolved Fe (TDFe), and total dissolved REEs (TDREEs) largely originated from mineral dust, which peaked in winter to early spring. In particular, the 2014–2015 Holuhraun eruption (31 August 2014 to 27 February 2015) can be clearly observed in the data at a depth of 90–125 cm. This event not only provided abundant acidic material (sulphate), but also released a large amount of DFe. Therefore, these results provide a possible way to use Greenland deep ice core data to construct a much longer history and better understand the relationship between eruptions and the release of iron in future studies.