Short-Campaign GNSS Observations of Horizontal Velocity and Vertical Tidal Response Across the Drygalski Ice Tongue, East Antarctica

The Drygalski Ice Tongue is a tide-influenced floating extension of the David Glacier in East Antarctica, where field observations are constrained by polar logistics. We investigated how horizontal ice motion and vertical tidal response vary along and across the tongue. To extend earlier observations, we analysed a 2025–2026 Global Navigation Satellite System (GNSS) campaign comprising 12 stations and 248 station-days. Kinematic GNSS coordinate series were produced with Bernese 5.4 and subsequently analysed under four stochastic covariance descriptions for horizontal and apparent vertical-rate estimation. Comparisons with a regional Mario Zucchelli Station (MZS)/Terra Nova Bay tide reference characterized station-level up-component response to tidal forcing, and two tide-removal paths were evaluated for apparent vertical-rate analysis. Floating-tongue speeds increased downstream, spanning 663.9–749.4 m/yr, with a clockwise turn toward the southeast and north-to-south differences in fitted campaign rates. The main horizontal patterns persisted across all four tested covariance descriptions. Vertical tidal response was weak in the near-grounding group, spatially heterogeneous in the transition sector, and near-unity downstream. Across the four covariance descriptions, neither tide-removal approach yielded a model-robust apparent vertical-rate field. The campaign resolved spatial patterns of horizontal motion and vertical tidal response, while covariance testing identified the limits of apparent vertical-rate inference from short GNSS records.