Basal stress controls ice-flow variability during a surge cycle of Hagen Bræ, Greenland

Basal conditions play an essential role in the dynamics of outlet glaciers, but direct observations at the bed of glaciers are challenging to obtain. Instead, inverse methods can be used to infer basal parameters from surface observations. Here, we use a simple ice-flow model as a forward model in an inversion scheme to retrieve the spatio-temporally variable basal stress parameter for Hagen Bræ, North Greenland, from 1990 to 2020. Hagen Bræ is a surge-type glacier with up to an order of magnitude variability of winter velocities near the grounding line. We find that downstream changes in the basal stress parameter can explain most of the variation of flow velocity, and we further identify a region of high resistance ~20–40 km from the grounding line. We hypothesise that this region of high resistance plays an important role in controlling glacier discharge.

High resolution aerosol concentration data from the Greenland NorthGRIP and NEEM deep ice cores

Records of chemical impurities from ice cores enable us to reconstruct the past deposition of aerosols onto the polar ice sheets and alpine glaciers. Through that, they allow us to gain insight into changes of the source, transport and deposition processes that ultimately determine the deposition flux at the coreing location. However, the low concentrations of the aerosol species in the ice and the resulting high risk of contamination poses a formidable analytical challenge, especially if long, continuous and highly resolved records are needed. Continuous Flow Analysis, CFA, the continuous melting, decontamination and analysis of ice-core samples has mostly overcome this issue and has quickly become the de-facto standard to obtain high-resolution aerosol records from ice cores after its inception at the University of Bern in the mid 90s. Here we present continuous records of calcium (Ca2+), sodium (Na+), ammonium (NH4+), nitrate (NO3−1) and electrolytic conductivity at 1 mm depth resolution from the NGRIP (North Greenland Ice Core Project) and NEEM (North Greenland Eemian Ice Drilling) ice cores produced by the Bern Continuous Flow Analysis group in the years 2000 to 2011. Both of the records have previously been used in a number of studies but have never been published in the full 1 mm resolution. Alongside the 1 mm datasets we provide decadal averages, a detailed description of the methods, relevant references, an assessment of the quality of the data and its usable resolution. Along the way we will also give some historical context on the development of the Bern CFA system.

Molecular characteristics of Bombus (Alpinobombus) polaris from North Greenland with comments on its general biology and phylogeography

The bumble bee Bombus polaris (Curtis 1835) is known from the northernmost region of Greenland. But how it can survive there, where in terms of geographic origin it came from, and which species in addition to B. pyrrhopygus (Friese 1902) genetically it is most closely related to are insufficiently answered questions that have motivated us to carry out this study. On the basis of a molecular analysis of the cytochrome oxidase I gene of a B. (Alpinobombus) polaris from North Greenland (82° 48′ N; 42° 14′ W), we conclude that the female specimen we analysed was most closely related to the Canadian populations of B. polaris. Geographic proximity, occurrence of B. polaris on Ellesmere Island and wind direction are likely factors that have aided B. polaris to establish itself in northern and eastern Greenland. The presence of five haplotypes in the studied sequences from Greenland indicates a moderately high level of genetic diversity of B. polaris in Greenland, reflecting the successful adaptation of B. polaris populations. In the broader context of entomological life in the high Arctic, our results on B. polaris allow us to conclude that the survival of pollinating species in the high Arctic under the changing climate scenario depends not only on the weather but also on an individual’s opportunity to continue to locate suitable food sources, i.e. pollen and nectar in the case of B. polaris. This aspect, briefly touched upon in this study, is of relevance not just to B. polaris, but the Arctic entomofauna generally.

The Franklinian Composite Tectono-Sedimentary Element, North Greenland

The Franklinian margin composite tectono-sedimentary element (CTSE) in North Greenland is dominated by Neoproterozoic - lowermost Devonian sedimentary strata that include early syn-rift through passive margin TSEs of mixed carbonate and siliciclastic facies. The sedimentary successions are well exposed in much of northern Greenland, but locally were strongly affected by the Ellesmerian Orogeny, resulting in a fold and thrust belt that deformed the northernmost exposures. An exposed palaeo-oilfield attests to the petroleum potential of the basin. Several formations have good source potential and several others have good reservoir properties. Palaeo-heat flow indicators show that temperatures increase to the north, where much of the basin is over-mature. Because of the remoteness of the area and the restricted locations where petroleum potential is likely to remain, the basin is not currently a target for exploration.

Metamorphism obscures primary taphonomic pathways in the early Cambrian Sirius Passet Lagerstätte, North Greenland

Correct interpretation of soft-bodied fossils relies on a thorough understanding of their taphonomy. While the focus has often been on the primary roles of decay and early diagenesis, the impacts of deeper burial and metamorphism on fossil preservation are less well understood. We document a sequence of late-stage mineral replacements in panarthropod fossils from the Sirius Passet Lagerstätte (North Greenland), an important early Cambrian Burgess Shale–type (BST) biota. Muscle and gut diverticula were initially stabilized by early diagenetic apatite, prior to being pervasively replaced by quartz and then subordinate chlorite, muscovite, and chloritoid during very low- to low-grade metamorphism. Each new mineral replicates the soft tissues with different precision and occurs in particular anatomical regions, imposing strong biases on the biological information retained. Muscovite and chloritoid largely obliterate the tissues’ original detail, suggesting that aluminum-rich protoliths may have least potential for conserving mineralized soft tissues in metamorphism. Overall, the fossils exhibit a marked shift toward mineralogical equilibration with the matrix, obscuring primary taphonomic modes. Sequential replacement of the phosphatized soft tissues released phosphorus to form new accessory monazite (and apatite and xenotime), whose presence in other BST biotas might signal the prior, more widespread, occurrence of this primary mode of preservation. Our results provide critical context for interpreting the Sirius Passet biota and for identifying late-stage overprints in other biotas.

Towards reconstructing the Arctic atmospheric methane history over the 20th century: measurement and modeling results for the NGRIP firn

Systematic measurements of atmospheric methane (CH4) mole fractions at the northern high latitudes only began in the early 1980s, and whilst CH4 measurements from Greenland ice cores covered the period before ~1900, no reliable observational record is available for the intermediate period. In this study, we reconstruct the atmospheric CH4 for that period, when the mole fraction started to increase rapidly. We use a set of trace gas data measured from firn (an intermediate stage between snow and glacial ice formation) air samples collected at the NGRIP (North Greenland Ice Core Project) site in 2001, in combination with a firn air transport model whose performance is validated by using a set of published firn air data at the NEEM (North Greenland Eemian ice Drilling) site. We examine a variety of possible firn diffusivity profiles using a suite of measured trace gases, and reconstruct the CH4 mole fraction by an iterative dating method. We find that, given the currently available firn air data sets from Greenland, reliable reconstruction of the Arctic CH4 mole fraction is possible only back to the mid 1970s. For the earlier period, it is difficult to identify the atmospheric CH4 history that consistently reproduce the depth profiles of CH4 in firn at both NGRIP and NEEM sites. Therefore, the currently proposed Arctic CH4 history should still be considered preliminary and uncertain, and should not be treated as the known history for constraining firn-air transport models.

Supplemental Material: Metamorphism obscures primary taphonomic pathways in the early Cambrian Sirius Passet Lagerstätte, North Greenland

Materials, methods and bulk rock geochemical characterization.<br>

Supplemental Material: Metamorphism obscures primary taphonomic pathways in the early Cambrian Sirius Passet Lagerstätte, North Greenland

Materials, methods and bulk rock geochemical characterization.<br>