Changes in vertical ice extent along the East Antarctic Ice Sheet margin in western Dronning Maud Land – initial field and modelling results of the MAGIC-DML collaboration

Constraining numerical ice sheet models by comparison with observational data is crucial to address the interactions between cryosphere and climate at a wide range of scales. Such models are tested and refined by comparing model predictions of past ice geometries with field-based reconstructions from geological, geomorphological, and ice core data. However, for the East Antarctic Ice sheet, there is a critical gap in the empirical data necessary to reconstruct changes in ice sheet geometry in the Dronning Maud Land (DML) region. In addition, there is poor control on the regional climate history of the ice sheet margin, because ice-core locations, where detailed reconstructions of climate history exist, are located on high inland domes. This leaves numerical models ofregional glaciation history in this near-coastal area largely unconstrained. MAGIC-DML is an ongoing Swedish-US-Norwegian-German-UK collaboration with a focus on improvingice sheet models of the western DML margin by combining advances in modeling with filling critical data gaps regarding the timing and pattern of ice-surface changes. A combination of geomorphological mapping using remote sensing data, field observations, cosmogenic nuclide surface exposure dating, and numerical ice sheetmodeling are being used in an iterative manner to produce a comprehensive reconstruction of the glacial historyof western DML. Here, we present an overview of the project, field evidence for formerly higher ice surfaces and in-situ cosmogenic nuclide measurements from the 2016/17 expedition. Preliminary field evidence indicate that interior sectors of DML have experienced a general decrease in ice sheet thickness since the late Miocene, with potential episodes of increasing thickness in the late Pleistocene (700-300 ka, 250-75 ka). To aid in interpreting these field data, new high-resolution ice sheet model reconstructions, constraining ice sheet configurations during key episodes, are presented

Mid-Pleistocene ice sheet fluctuations from cosmogenic nuclide field constraints in western Dronning Maud Land, Antarctica

The East Antarctic Ice Sheet (EAIS) is generally assumed to have been relatively insensitive to Quaternary climat echange. However, recent studies have shown potential instabilities in coastal, marine sectors of the EAIS. In addition, long-term climate reconstructions and modelling experiments indicate the potential for significant changes in ice volume and ice sheet configuration since the Pliocene. Hence, more empirical evidence for ice surface and ice volume changes is required to discriminate between contrasting inferences. MAGIC-DML is an ongoing Swedish-US-Norwegian-German-UK collaboration focused on improving ice sheetm odels by filling critical data gaps that exist in our knowledge of the timing and pattern of ice surface changes along the western Dronning Maud Land (DML) margin and combining this with advances in numerical techniques. As part of the project, field studies in the 2016/17 and 2017/18 austral summers targeted selected sites spanning accessible altitudes in the Heimefrontfjella, Vestfjella, Ahlmannryggen, Borgmassivet, and Kirwanveggen nunatakranges for in situcosmogenic nuclide sampling. Comparing concentrations of nuclides with widely differing half-lives in bedrock and erratics from a range of altitudes above modern ice surfaces can provide information on ice sheet fluctuations and complex burial and exposure histories, and thus, past configurations of non-erosive ice. Quartz-bearing rock types were sampled and analyzed for 10Be (t1/21.4 My),14C (t1/25.7 ky),26Al (t1/2705ky), and 21Ne (stable), and mafic lithologies for36Cl (t1/2301 ky). Results thus far for 3210Be and 26Al isotope pairs complemented with seven21Ne measurements have yielded some consistent patterns of paleoglaciation for the western DML margin. Eight out of fourteen bedrock samples from high-elevation (1700-2238 m a.s.l.) ridges and summits return some of the oldest exposure ages in Antarctica and have consistent 10Be,26Al, and 21Ne minimum apparent exposure ages of 1.8-4.1 Ma. Initial results therefore indicate that parts of the ice sheet marginal to the Antarctic plateau, along the Heimefrontfjella range, generally have experienced a decrease in ice thickness since the late Miocene. Another six bedrock samples (1556-1732 ma.s.l.) fall in the 300-700 ka range, and they all show significant burial. At face value, perhaps this indicates aregional ice sheet surface above 1700 m a.s.l. for much of the Plio-early Pleistocene. All other samples analyzedto date are erratics from lower elevation and more coastal sites (10 from nunataks at 553-1400 m a.s.l., and 6 froma surface moraine at 1385 m a.s.l.), exhibiting ages between 59 and 275 ka, save for two (4 and 6 ka). Whereas almost all of the nunatak erratics (including the young ones) show significant burial durations, five of the six surface moraine samples do not. These 2016/17 field samples are not yet leading to conclusive age constraints but already start to paint a picture of the western DML margin being relatively stable although there was possibly one or more episodes of relatively limited ice thickening during the last 700 ka

Finishing the euchromatic sequence of the human genome

The sequence of the human genome encodes the genetic instructions for human physiology, as well as rich information about human evolution. In 2001, the International Human Genome Sequencing Consortium reported a draft sequence of the euchromatic portion of the human genome. Since then, the international collaboration has worked to convert this draft into a genome sequence with high accuracy and nearly complete coverage. Here, we report the result of this finishing process. The current genome sequence (Build 35) contains 2.85 billion nucleotides interrupted by only 341 gaps. It covers ∼99% of the euchromatic genome and is accurate to an error rate of ∼1 event per 100,000 bases. Many of the remaining euchromatic gaps are associated with segmental duplications and will require focused work with new methods. The near-complete sequence, the first for a vertebrate, greatly improves the precision of biological analyses of the human genome including studies of gene number, birth and death. Notably, the human enome seems to encode only 20,000-25,000 protein-coding genes. The genome sequence reported here should serve as a firm foundation for biomedical research in the decades ahead

A Moser/Bernstein type theorem in a Lie group with a left invariant metric under a gradient decay condition

We say that a PDE on the hyperbolic space Hn of constant sectional curvature −1, n ≥ 2, is geometric if, whenever u is a solution of the PDE on a domain Ω of Hn, the composition uφ := u◦φ is also a solution on φ−1 (Ω) for any isometry φ of Hn. We prove that if u ∈ C1 (Hn) is a solution of a geometric PDE satisfying the comparison principle and if lim sup r→∞ e 2r sup Sr ∇u = 0, (1) where Sr is a geodesic sphere of Hn centered at a fixed point o ∈ Hn with radius r, then u is constant. However, given C > 0, there exists a bounded non-constant harmonic function v ∈ C∞ (Hn) such that limr→∞ e r sup Sr ∇v = C. (2) We prove (1) by showing a similar result for left invariant PDEs on a Lie group and by endowing Hn with a Lie group structure

A Moser/Bernstein type theorem in a Lie group with a left invariant metric under a gradient decay condition

We say that a PDE on the hyperbolic space Hn of constant sectional curvature −1, n ≥ 2, is geometric if, whenever u is a solution of the PDE on a domain Ω of Hn, the composition uφ := u◦φ is also a solution on φ−1 (Ω) for any isometry φ of Hn. We prove that if u ∈ C1 (Hn) is a solution of a geometric PDE satisfying the comparison principle and if lim sup r→∞ e 2r sup Sr ∇u = 0, (1) where Sr is a geodesic sphere of Hn centered at a fixed point o ∈ Hn with radius r, then u is constant. However, given C > 0, there exists a bounded non-constant harmonic function v ∈ C∞ (Hn) such that limr→∞ e r sup Sr ∇v = C. (2) We prove (1) by showing a similar result for left invariant PDEs on a Lie group and by endowing Hn with a Lie group structure

Characterization of the High-Resolution Infrared Radiation Sounder Using Lunar Observations

The High-Resolution Infrared Radiation Sounder (HIRS) has been operational since 1975 on different satellites. In spite of this long utilization period, the available information about some of its basic properties is incomplete or contradictory. We have approached this problem by analyzing intrusions of the Moon in the deep space view of HIRS/2 through HIRS/4. With this method we found: (1) The diameters of the field of view of HIRS/2, HIRS/3, and HIRS/4 have the relative proportions of 1.4 ° to 1.3 ° to 0.7 ° with all channels; (2) the co-registration differs by up to 0.031 ° among the long-wave and by up to 0.015 ° among the shortwave spectral channels in the along-track direction; (3) the photometric calibration is consistent within 0.7% or less for channels 2–7 (1.2% for HIRS/2), similar values were found for channels 13–16; (4) the non-linearity of the short-wavelength channels is negligible; and (5) the contribution of reflected sunlight to the flux in the short-wavelength channels can be determined in good approximation, if the emissivity of the surface is known

Opportunistic Constant Target Matching—A New Method for Satellite Intercalibration

Opportunistic constant target matching is a new method for satellite intercalibration. It solves a long-standing issue with the traditional simultaneous nadir overpass (SNO) method, namely, that it typically provides only data points with cold brightness temperatures for humidity sounding instruments on sun-synchronous satellites. In the new method, a geostationary infrared sensor (SEVIRI) is used to select constant target matches for two different microwave sensors (MHS on NOAA 18 and Metop A). We discuss the main assumptions and limitations of the method and explore its statistical properties with a simple Monte Carlo simulation. The method was tested in a simple case study with real observations for this combination of satellites for MHS Channel 3 at 183 ± 1 GHz, the upper tropospheric humidity channel. For the studied 3-month test period, real observations are found to behave consistently with the simulations, increasing our confidence that the method can be a valuable tool for intercalibration efforts. For the selected case study, the new method confirms that the bias between NOAA 18 and Metop A MHS Channel 3 is very small, with absolute value below 0.05 K

An Uncertainty Quantified Fundamental Climate Data Record for Microwave Humidity Sounders

To date, there is no long-term, stable, and uncertainty-quantified dataset of upper tropospheric humidity (UTH) that can be used for climate research. As intermediate step towards the overall goal of constructing such a climate data record (CDR) of UTH, we produced a new fundamental climate data record (FCDR) on the level of brightness temperature for microwave humidity sounders that will serve as basis for the CDR of UTH. Based on metrological principles, we constructed and implemented the measurement equation and the uncertainty propagation in the processing chain for the microwave humidity sounders. We reprocessed the level 1b data to obtain newly calibrated uncertainty quantified level 1c data in brightness temperature. Three aspects set apart this FCDR from previous attempts: (1) the data come in a ready-to-use NetCDF format; (2) the dataset provides extensive uncertainty information taking into account the different correlation behaviour of the underlying errors; and (3) inter-satellite biases have been understood and reduced by an improved calibration. Providing a detailed uncertainty budget on these data, this new FCDR provides valuable information for a climate scientist and also for the construction of the CDR