ALBERT

Description: This data product contains dissolved silicon concentrations and isotopic composition, major ion concentrations and discharge for streams in Potter Peninsula, King George Island and Commonwealth Stream, McMurdo Dry Valleys, Antarctica.

Description: Yellowstone Plateau Volcanic Field, USA: Ge concentrations measured by inductively coupled plasma mass spectrometry (ICP-MS), Si concentrations measured by inductively coupled plasma optical emission spectrometry (ICP-OES), Ge/Si ratio, Si isotope compositions (d30Si and standard deviation SD) measured by Multicollector ICP-MS, concentrations in Ca, Na, Mg, K measured by ICP-OES, and concentrations in SO4 and Cl measured by ion chromatography in thermal waters, major rivers draining the Yellowstone Plateau Volcanic Field, and creeks flowing into Yellowstone Lake.

Description: The Action Group called ‘Standardized methods across Permafrost Landscapes: from Arctic Soils to Hydrosystems’ (SPLASH) is a community-driven effort aiming to provide a suite of standardized field strategies for sampling mineral and organic components in soils, sediments, and water across permafrost landscapes. This unified approach will allow data from different landscape interfaces, field locations and seasons to be shared and compared, thus improving our understanding of the processes occurring during lateral transport in circumpolar Arctic watersheds.

Description: Iron (Fe) plays a key role in mediating organic carbon (OC) decomposition rates in permafrost soils. Fe-bearing minerals stabilize OC through complexation, co-precipitation or aggregation processes and thus hinder degradation of OC. In addition, Fe(III) reduction can inhibit methanogenesis and decrease warming potential of greenhouse gases release. Ice-rich permafrost is subject to abrupt thaw and thermokarst formation, which unlocks OC and minerals from deep deposits and exposes OC to mineralization. These ice-rich domains include Yedoma sediments that have never thawed since deposition and Alas sediments that have undergone previous thermokarst processes during the Lateglacial and Holocene warming periods. The post-depositional history of these sediments may affect the distribution and reactivity of Fe-bearing minerals and the role Fe plays in mediating present day OC mineralization. Here we quantify Fe concentrations, Fe spatial and depth distribution, and Fe mineralogy in unthawed Yedoma and previously thawed Alas deposits from the Yedoma domain (West Siberia, Laptev Sea region, Kolyma region, New Siberian Islands and Alaska). Total Fe concentrations of ice-rich Yedoma deposits and previously thawed Alas deposits were determined using a portable X-ray fluorescence (XRF) device. This non-destructive method allowed a total iron concentration assessment of Yedoma domain deposits based on 1292 sediment samples. Portable XRF-measured concentrations trueness were calibrated from alkaline fusion and inductively coupled plasma optical emission spectrometry (ICP-OES) measurement method on a subset of 144 samples (R² = 0.81). Fe extractions of unthawed and previously thawed deposits display that, on average, 25% of the total iron is considered as reactive species, either as crystalline or amorphous oxides, or complexed with OC, with no significant difference between Yedoma and Alas deposits. We observe a constant total Fe concentration in Yedoma deposits, but a depletion or accumulation of total Fe in Alas deposits, which experienced previous thaw and/or flooding events, suggesting that redox driven processes during the Lateglacial and Holocene thermokarst formation impact the present day distribution of reactive Fe and its association with organic carbon in ice-rich permafrost.

Description: Glaciers and ice sheets export significant amounts of silicon (Si) to downstream ecosystems, impacting local and potentially global biogeochemical cycles. Recent studies have shown Si in Arctic glacial meltwaters to have an isotopically distinct signature when compared to non-glacial rivers. This is likely linked to subglacial weathering processes and mechanochemical reactions. However, there are currently no silicon isotope (d30Si) data available from meltwater streams in Antarctica, limiting the current inferences on global glacial silicon isotopic composition and its drivers. To address this gap, we present dissolved silicon (DSi), d30SiDSi, and major ion data from meltwater streams draining a polythermal glacier in the region of the West Antarctic Peninsula (WAP; King George Island) and a cold-based glacier in East Antarctica [Commonwealth Stream, McMurdo Dry Valleys (MDV)]. These data, alongside other global datasets, improve our understanding of how contrasting glacier thermal regime can impact upon Si cycling and therefore the d30SiDSi composition. We find a similar d30SiDSi composition between the two sites, with the streams on King George Island varying between -0.23 and C1.23h and the Commonwealth stream varying from -0.40 to C1.14h. However, meltwater streams in King George Island have higher DSi concentrations, and the two glacial systems exhibit opposite DSi–d30SiDSi trends. These contrasts likely result from differences in weathering processes, specifically the role of subglacial processes (King George Island) and, supraglacial processes followed by instream weathering in hyporheic zones (Commonwealth Stream). These findings are important when considering likely changes in nutrient fluxes from Antarctic glaciers under climatic warming scenarios and consequent shifts in glacial thermal regimes.

Description: The thawing of permafrost exposes organic matter to decomposition but also mineral constituents to water. To evaluate the potential to create mineral nutrients hotspots upon thawing, an inventory of the mineral element content and its local variability in permafrost terrain is needed. Based on measurements from major Arctic regions (Alaska, Greenland, Svalbard and Siberia), it is suggested that the mineral reserve in permafrost is firstly controlled by the local lithology. More specifically, the data highlight the potential for mineral nutrient hotspots to be generated upon thawing in soils derived from deltaic deposits, but not in thermokarst deposits. Finally, we suggest that portable X-ray fluorescence (pXRF) may present a quick and low-cost alternative to total digestion and ICP-AES measurements to build a mineral element inventory in permafrost terrain at a large spatial scale.

Description: Interactions between minerals and organic carbon (OC) in soils are key to stabilize OC and mitigate greenhouse gas emissions upon permafrost thaw. However, changes in soil water pathways upon permafrost thaw are likely to affect the stability of mineral OC interactions by inducing their dissolution and precipitation. This study aims to assess and quantify how mineral OC interactions are affected by dissolution and precipitation in thawed relative to unthawed layers. We hypothesize that a change in the radiogenic strontium (Sr) isotopic ratio (87Sr/86Sr) involved in mineral OC interactions upon changing water saturation conditions implies a destabilization of the mineral OC interaction. We quantified mineral OC interactions using selective extractions in soils facing gradual thaw (Eight Mile Lake, AK, USA) and in sediments with a thawing history of abrupt thaw (Duvanny Yar, Russia), and we measured the 87Sr/86Sr ratio of the selective extracts targeting the Sr associated to mineral OC interactions. Firstly, for water saturated layers with a higher proportion of mineral OC interactions, we found a difference in the 87Sr/86Sr ratio relative to the surrounding layers, and this supports the preservation of a Sr “stable” pool in these mineral OC interactions. We estimated that a portion of these mineral OC interactions have remained undissociated since their formation (between 4% and 64% by Sr isotope mass balance). Secondly, we found no difference in 87Sr/86Sr ratio between layers accumulating Fe oxides at redox interfaces regularly affected by water table changes (or upon thermokarst processes) relative to surrounding layers. This supports the dominance of a Sr “labile” pool inherited from processes of dissolution and precipitation of the mineral OC interactions. Thirdly, our estimations based on a Sr isotope mass balance support that, as a consequence of permafrost thaw, a larger proportion of Sr from primary mineral weathering (〉80%) controls the Sr in mineral OC interactions in the saturated zone of deeply thawed soils relative to poorly thawed soils (∼50%). In conclusion, we found that the radiogenic Sr isotope method, applied for the first time in this context, is promising to trace dissolution-precipitation processes of mineral OC interaction in thawing permafrost.

Description: Large Arctic rivers are key locations for nitrogen processing, which controls the supply of this limiting nutrient to the Arctic Ocean. In a warming Arctic, longer ice-free periods increase riverine productivity and modulate nitrogen consumption and delivery to the ocean. In this study, the annual variability of nitrate concentrations at the Lena River outlet (Samoylov station) was investigated. Significantly higher nitrate concentrations in water were observed sub-ice (winter) than in the open water (summer), and the higher nitrate concentrations follow phases of colder air temperature at the Lena catchment scale (ERA5 reanalysis data). We hypothesize that colder phases result in thicker river ice leading to darker under-ice conditions preferred by nitrifying microbial communities, thereby inducing increasing sub-ice nitrification. We tested this hypothesis using silicon isotopes known to fractionate upon freezing. The high nitrate concentrations in the winter are associated with heavier silicon isotope compositions in river water. This can be explained by the supersaturation and precipitation of amorphous silica preferentially incorporating the lighter silicon isotopes, leaving the water isotopically heavier. Supersaturation of amorphous silica can result from thicker ice formation upon colder air temperature at catchment scale. The silicon isotope data support phases of thicker ice formation, and indirectly support darker sub-ice conditions at the river base creating pulses of increasing nitrification. Our hypothesis is also supported by a change in the value of an index for dissolved organic carbon aromaticity (SUVA) during the colder phases: this suggests that conditions favour the decomposition of dissolved organic matter during periods of thicker river ice. Air temperature, nitrate concentration, silicon isotopes and SUVA are supporting evidence for pulses of sub-ice microbial activity in the river during winter. It follows that decreasing ice cover duration throughout the catchment is likely to decrease winter nitrate fluxes from the Lena River to the Arctic Ocean.

Description: Ice-rich permafrost has been subject to abrupt thaw and thermokarst formation in the past and is vulnerable to current global warming. The ice-rich permafrost domain includes Yedoma sediments that have never thawed since deposition during the late Pleistocene and Alas sediments that were formed by previous thermokarst processes during the Lateglacial and Holocene warming. Permafrost thaw unlocks organic carbon (OC) and minerals from these deposits and exposes OC to mineralization. A portion of the OC can be associated with iron (Fe), a redox-sensitive element acting as a trap for OC. Post-depositional thaw processes may have induced changes in redox conditions in these deposits and thereby affected Fe distribution and interactions between OC and Fe, with knock-on effects on the role that Fe plays in mediating present day OC mineralization. To test this hypothesis, we measured Fe concentrations and proportion of Fe oxides and Fe complexed with OC in unthawed Yedoma and previously thawed Alas deposits. Total Fe concentrations were determined on 1,292 sediment samples from the Yedoma domain using portable X-ray fluorescence; these concentrations were corrected for trueness using a calibration based on a subset of 144 samples measured by inductively coupled plasma optical emission spectrometry after alkaline fusion (R2 = 0.95). The total Fe concentration is stable with depth in Yedoma deposits, but we observe a depletion or accumulation of total Fe in Alas deposits, which experienced previous thaw and/or flooding events. Selective Fe extractions targeting reactive forms of Fe on unthawed and previously thawed deposits highlight that about 25% of the total Fe is present as reactive species, either as crystalline or amorphous oxides, or complexed with OC, with no significant difference in proportions of reactive Fe between Yedoma and Alas deposits. These results suggest that redox driven processes during past thermokarst formation impact the present-day distribution of total Fe, and thereby the total amount of reactive Fe in Alas versus Yedoma deposits. This study highlights that ongoing thermokarst lake formation and drainage dynamics in the Arctic influences reactive Fe distribution and thereby interactions between Fe and OC, OC mineralization rates, and greenhouse gas emissions.

Description: The stabilizing properties of mineral–organic carbon (OC) interactions have been studied in many soil environments (temperate soils, podzol lateritic soils, and paddy soils). Recently, interest in their role in permafrost regions is increasing as permafrost was identified as a hotspot of change. In thawing ice-rich permafrost regions, such as the Yedoma domain, 327–466 Gt of frozen OC is buried in deep sediments. Interactions between minerals and OC are important because OC is located very near the mineral matrix. Mineral surfaces and elements could mitigate recent and future greenhouse gas emissions through physical and/or physicochemical protection of OC. The dynamic changes in redox and pH conditions associated with thermokarst lake formation and drainage trigger metal-oxide dissolution and precipitation, likely influencing OC stabilization and microbial mineralization. However, the influence of thermokarst processes on mineral–OC interactions remains poorly constrained. In this study, we aim to characterize Fe, Mn, Al, and Ca minerals and their potential protective role for OC. Total and selective extractions were used to assess the crystalline and amorphous oxides or complexed metal pools as well as the organic acids found within these pools. We analyzed four sediment cores from an ice-rich permafrost area in Central Yakutia, which were drilled (i) in undisturbed Yedoma uplands, (ii) beneath a recent lake formed within Yedoma deposits, (iii) in a drained thermokarst lake basin, and (iv) beneath a mature thermokarst lake from the early Holocene period. We find a decrease in the amount of reactive Fe, Mn, Al, and Ca in the deposits on lake formation (promoting reduction reactions), and this was largely balanced by an increase in the amount of reactive metals in the deposits on lake drainage (promoting oxidation reactions). We demonstrate an increase in the metal to C molar ratio on thermokarst process, which may indicate an increase in metal–C bindings and could provide a higher protective role against microbial mineralization of organic matter. Finally, we find that an increase in mineral–OC interactions corresponded to a decrease in CO2 and CH4 gas emissions on thermokarst process.