Brief communication: Impact of common ice mask in surface mass balance estimates over the Antarctic ice sheet

Regional climate models compute ice sheet surface mass balance (SMB) over a mask that defines the area covered by glacier ice, but ice masks have not been harmonised between models. Intercomparison studies of modelled SMB therefore use a common ice mask. The SMB in areas outside the common ice mask, which are typically coastal and high-precipitation regions, is discarded. Ice mask differences change integrated SMB by between 40.5 and 140.6 Gt yr(-1) (1.8 % to 6.0 % of ensemble mean SMB), equivalent to the entire Antarctic mass imbalance. We conclude there is a pressing need for a common ice mask protocol

Impact of acute coronary syndrome on clinical outcomes after revascularization with the dual-therapy CD34 antibody-covered sirolimus-eluting Combo stent and the sirolimus-eluting Orsiro stent

OBJECTIVES: To compare the efficacy and safety of the dual-therapy CD34 antibody-covered sirolimus-eluting Combo stent (DTS) and the sirolimus-eluting Orsiro stent (O-SES) in patients with and without acute coronary syndrome (ACS) included in the SORT OUT X study.BACKGROUND: The incidence of target lesion failure (TLF) after treatment with modern drug-eluting stents has been reported to be significantly higher in patients with ACS when compared to patients without ACS. Whether the results from the SORT OUT X study apply to patients with and without ACS remains unknown.METHODS: In total, 3146 patients were randomized to stent implantation with DTS (n = 1578; ACS: n = 856) or O-SES (n = 1568; ACS: n = 854). The primary end point, TLF, was a composite of cardiac death, target-lesion myocardial infarction (MI), or target lesion revascularization (TLR) within 1 year.RESULTS: At 1 year, the rate of TLF was higher in the DTS group compared to the O-SES group, both among patients with ACS (6.7% vs. 4.1%; incidence rate ratio: 1.65 [95% confidence interval, CI: 1.08-2.52]) and without ACS (6.0% vs. 3.2%; incidence rate ratio: 1.88 [95% CI: 1.13-3.14]). The differences were mainly explained by higher rates of TLR, whereas rates of cardiac death and target lesion MI did not differ significantly between the two stent groups in patients with or without ACS CONCLUSION: Compared to the O-SES, the DTS was associated with a higher risk of TLF at 12 months in patients with and without ACS. The differences were mainly explained by higher rates of TLR.</p

Determining the Freshwater Fluxes from Antarctica with Earth Observation Data, Models, and In Situ Measurements: Uncertainties, Knowledge Gaps, and Prospects for New Advances [Meeting Summary]

Workshop on Antarctic Ice Shelf Processes in Models and Earth Observation

Characteristics of surface “melt potential” over Antarctic ice shelves based on regional atmospheric model simulations of summer air temperature extremes from 1979/80 to 2018/19

We calculate a regional surface “melt potential” index (MPI) over Antarctic ice shelves that describes the frequency (MPI-freq, %) and intensity (MPI-int, K) of daily maximum summer temperatures exceeding a melt threshold of 273.15 K. This is used to determine which ice shelves are vulnerable to melt-induced hydrofracture and is calculated using near-surface temperature output for each summer from 1979/80 to 2018/19 from two high-resolution regional atmospheric model hindcasts (using the MetUM and HIRHAM5). MPI is highest for Antarctic Peninsula ice shelves (MPI-freq 23-35%, MPI-int 1.2-2.1 K), lowest (2-3%, < 0 K) for Ronne-Filchner and Ross ice shelves, and around 10-24% and 0.6-1.7 K for the other West and East Antarctic ice shelves. Hotspots of MPI are apparent over many ice shelves, and they also show a decreasing trend in MPI-freq. The regional circulation patterns associated with high MPI values over West and East Antarctic ice shelves are remarkably consistent for their respective region but tied to different large-scale climate forcings. The West Antarctic circulation resembles the central Pacific El Niño pattern with a stationary Rossby wave and a strong anticyclone over the high-latitude South Pacific. By contrast, the East Antarctic circulation comprises a zonally symmetric negative Southern Annular Mode pattern with a strong regional anticyclone on the plateau and enhanced coastal easterlies/weakened Southern Ocean westerlies. Values of MPI are 3-4 times larger for a lower temperature/melt threshold of 271.15 K used in a sensitivity test, as melting can occur at temperatures lower than 273.15 K depending on snowpack properties

Epigenetic control of embryonic stem cell fate

In embryonic stem cells, alterations in chromatin modifications influence the balance between self-renewal and differentiation

Reconciling fundamental climate variables for determining the Antarctic Mass Balance

The Antarctic ice sheet is the largest ice sheet on Earth, it has the potential to raise the global mean sea level by 58 metres if it melts completely. Even though it is not the largest contributor to present-day sea level rise, recent studies have shown that the Antarctic ice sheet has increased its mass loss between 1993 and 2018. It is therefore important to monitor and understand how the ice sheet evolves to understand present and future rates of sea level rise.This Ph.D. thesis focuses on reconciling climate variables to estimate the surface mass balance and the total mass balance of Antarctica. The surface mass balance is the sum of the accumulation (snowfall and rainfall), and the ablation (sublimation, evaporation, and runoff). Total mass balance includes both SMB and the discharge across the grounding line. In this thesis, a regional atmospheric climate model is used to model the atmosphere and the output used to compute the surface mass balance. To get a realistic representation of the subsurface snow and ice layers, a firn model has also been developed for the Antarctic ice sheet. This thesis investigates the uncertainties in modelled mass balance from different regional climate models and different methods. There are three geodetic methods to derive the mass balance from remote sensing; altimetry, mass budget, and gravimetric measurements. Two of these, altimetry and mass budget, require knowledge of the firn pack over the ice sheet. When using the mass budget method to estimate the mass balance the surface mass balance and the discharge values are need. The surface mass balance is here found to be  1968.0±279.3 Gt year-1 over the grounded part of Antarctica and over the total Antarctic ice sheet it is 2574.4 Gt year-1 from the period 1979 to 2021. Applying the altimetry method, the satellite ICESat-2 has been used to measure the surface elevation change. To isolate the surface elevation change, that is due the ice dynamics, we have to correct for the firn compaction rate, for which we use the firn model, and correct for the vertical bedrock movement. When we have corrected for the nonice dynamic signals we can convert the volume change to mass change if the correct conversion density is known. This thesis therefore also presents new work for determining the appropriate density parametrization to be able to make a realistic conversion from volume change to mass balance change of the Antarctica ice sheet between 2018 and 2021. Finally, this thesis also shows some results for the Greenland ice sheet to show the applicability of the methods of this thesis for both ice sheets. <br/