Impact of frontal ablation on the ice thickness estimation of marine-terminating glaciers in Alaska

Frontal ablation is a major component of the mass budget of calving glaciers, strongly affecting their dynamics. Most global-scale ice volume estimates to date still suffer from considerable uncertainties related to (i) the implemented frontal ablation parameterization or (ii) not accounting for frontal ablation at all in the glacier model. To improve estimates of the ice thickness distribution of glaciers, it is thus important to identify and test low-cost and robust parameterizations of this process. By implementing such parameterization into the ice thickness estimation module of the Open Global Glacier Model (OGGM v1.1.2), we conduct a first assessment of the impact of accounting for frontal ablation on the estimate of ice stored in glaciers in Alaska. We find that inversion methods based on mass conservation systematically underestimate the mass turnover and, therefore, the thickness of tidewater glaciers when neglecting frontal ablation. This underestimation can amount to up to 19 % on a regional scale and up to 30 % for individual glaciers. The effect is independent of the size of the glacier. Additionally, we perform different sensitivity experiments to study the influence of (i) a constant of proportionality (k) used in the frontal ablation parameterization, (ii) Glen’s temperature-dependent creep parameter (A) and (iii) a sliding velocity parameter (fs) on the regional dynamics of Alaska tidewater glaciers. OGGM is able to reproduce previous regional frontal ablation estimates, applying a number of combinations of values for k, Glen’s A and fs. Our sensitivity studies also show that differences in thickness between accounting for and not accounting for frontal ablation occur mainly at the lower parts of the glacier, both above and below sea level. This indicates that not accounting for frontal ablation will have an impact on the estimate of the glaciers’ potential contribution to sea-level rise. Introducing frontal ablation increases the volume estimate of Alaska marine-terminating glaciers from 9.18±0.62 to 10.61±0.75 mm s.l.e, of which 1.52±0.31 mm s.l.e (0.59±0.08 mm s.l.e when ignoring frontal ablation) are found to be below sea level

Increase of ice discharge from Greenland's peripheral tidewater glaciers over recent decades

The Greenland Ice Sheet is losing mass at increasing rates. Substantial amounts of this mass loss occur by ice discharge. The ice sheet is surrounded by thousands of peripheral glaciers, which are dynamically decoupled from the ice sheet, and which account for ~10 % of the global glacier ice volume outside the two main ice sheets. Rather low-lying along the coasts, these peripheral glaciers are also losing mass at increasing, but disputed, rates. The total absence of knowledge about the role and share of solid ice discharge in this mass loss adds to the controversy. Since the quantification of ice discharge is still pending, a full understanding of ice mass loss processes in this globally important glacier region is substantially hampered. Here, we present the first estimation of ice discharge from Greenland's peripheral tidewater glaciers. For each of these 760 glaciers, we combine an idealized rectangular flux gate cross sections derived from modelling with the Open Global Glacier Model with surface ice flow velocities derived from the ITS_LIVE and MEaSUREs remote sensing datasets to calculate glacier specific ice discharge on both annual and multi-annual time scales over the period 1985 to 2018. For the few glaciers not covered by either of the employed original datasets or modelling methods we use a regression tree-based extrapolation scheme to estimate the necessary input data for our calculation. Our findings indicate a significant overall increase of ice discharge over the study period although several individual glaciers show contrasting developments. This increase became especially apparent across the southern parts of Greenland. Our results also show that the total of the ice discharge from Greenland's peripheral tidewater glaciers is dominated by few major contributors and that this dominance is completely time-independent

Calibration of a frontal ablation parameterization applied to Greenland's peripheral calving glaciers

Greenland's Peripheral Glaciers (PGs) are glaciers that are weakly or not connected to the Ice Sheet. Many are tidewater, losing mass via frontal ablation. Without comprehensive regional observations or enough individual estimates of frontal ablation, constraining model parameters remains a challenging task in this region. We present three independent ways to calibrate the calving parameterization implemented in the Open Global Glacier Model (OGGM) and asses the impact of accounting for frontal ablation on the estimate of ice stored in PGs. We estimate an average regional frontal ablation flux for PGs of 7.94±4.15 Gtyr-1 after calibrating the model with two different satellite velocity products, and of 0.75±0.55 Gt yr-1 if the model is constrained using frontal ablation fluxes derived from independent modelled Surface Mass Balance (SMB) averaged over an equilibrium reference period (1961-1990). This second method is based on the assumption that most PGs during that time have an equilibrium between mass gain via SMB and mass loss via frontal ablation. This assumption can serve as a basis to assess the order of magnitude of dynamic mass loss of glaciers when compared to the SMB imbalance. By comparing the model output after applying both calibration methods, we find that the model is not able to predict individual tidewater glacier dynamics if it relies only on SMB estimates and the assumption of a closed budget to constrain the model. The differences between the results from both calibration methods serve as an indication of how strong the dynamic imbalance might have been for PGs during that reference period

Quantifying heating biases in marine air temperature observations, ~1790 - present

Accurate, long-term time series of near-surface air temperature (AT) are the fundamental datasets on which the magnitude of anthropogenic climate change is scientifically and societally addressed. Across the ocean, these (near-surface) climate records use Sea Surface Temperature (SST) instead of Marine Air Temperature (MAT) and blend the SST and AT over land to create datasets. MAT has often been overlooked as a data choice as daytime MAT observations from ships are known to contain warm biases due to the storage of accumulated solar energy. Two recent MAT datasets, CLASSnmat (1881 – 2019) and UAHNMAT (1900 – 2018), both use night-time MAT observations only. Daytime MAT observations in the International Comprehensive Ocean–Atmosphere Data Set (ICOADS) account for over half of the MAT observations in ICOADS, and this proportion increases further back in time (i.e. pre-1850s). If long-term MAT records over the ocean are to be extended, the use of daytime MAT is vital. To adjust for the daytime MAT heating bias, and apply it to ICOADS, we present the application of a physics-based model, which accounts for the accumulated energy storage throughout the day. As the ‘true’ diurnal cycle of MAT over the ocean has not been, to-date, adequately quantified, our approach also removes the diurnal cycle from ICOADS observations and generates a night-time equivalent MAT for all observations. We fit this model to MAT observations from groups of ships in ICOADS that share similar heating biases and metadata characteristics. This enables us to use the empirically derived coefficients (representing the physical energy transfer terms of the heating model) obtained from the fit for use in removal of the heating bias and diurnal cycle from ship-based MAT observations throughout ICOADS which share similar characteristics (i.e. we can remove the diurnal cycle from a ship which only reports once daily at noon). This adjustment will create an MAT record of night-time-equivalent temperatures that will enable an extension of the marine surface AT record back into the 18th century

Modalidad auxiliar de investigación: Acta de Evaluación de trabajo de grado en modalidad auxiliar de investigación, para obtener el título de Doctor en Cirugía Dental, en el proyecto titulado “Impacto en la calidad de vida relacionado a enfermedad periodontal en usuarios que asisten a las Unidades Comunitarias de Salud Familiar en el año 2022”

Acta finalización de proceso de grado de cincuenta estudiantes, quienes finalizaron su trabajo de investigación durante periodo de enero 2022 a diciembre 2022, lo que justifica finalización de requisito en Modalidad Auxiliar de investigación del proyecto del Centro de Investigaciones de la Facultad de Odontología de la Universidad de El Salvador, titulado: “Impacto en la calidad de vida relacionado a enfermedad periodontal en usuarios que asisten a las Unidades Comunitarias de Salud Familiar en el año 2022” para obtener el título de Doctor en Cirugía Dental de la Facultad de Odontología de la universidad de el salvador. Por tanto, se da por finalizado su trabajo de grado en modalidad auxiliar de investigación, el día trece de febrero de dos mil veintitrés