Essential Maintenance: All Authorea-powered sites will be offline 9am-10am EDT Tuesday 28 May
and 11pm-1am EDT Tuesday 28-Wednesday 29 May. We apologise for any inconvenience.

Maria Osińska

and 1 more

This study investigates the impact of glacial water discharges on the hydrodynamics of Admiralty Bay (AB) in the South Shetland Islands, a wide bay adjacent to twenty marine-terminating glaciers. From December 2018 until February 2023, AB water properties were measured on 136 days. This dataset showed that a maximally two-layered stratification occurs in AB, and that glacial water is always the most buoyant water mass. Using the Delft3D Flow, a three-dimensional hydrodynamical model of AB was developed. During tests, the vertical position and initial velocity of glacial discharges have been shown to be insignificant for the overall bay circulation. Fourteen model scenarios have been calculated with an increasing glacial influx added. The AB general circulation pattern consists of two cyclonic cells. Even in scenarios with significant glacial input, water level shifts and circulation are predominantly controlled by the ocean. Glacial freshwater is carried out of AB along its eastern boundary in a surface layer no thicker than 60 m. Within the inner AB inlets, significant glacial influx produces buoyancy-driven vertical circulation. Using an innovative approach combining hydrographic and modeling data, a four-year, unprecedentedly high-resolution timeseries of glacial influx volumes into AB has been produced. On average, glacial influx summer values are >10 times greater than in spring and winter and 3 times higher than in autumn. The annual glacial influx into AB was estimated at 0.525 Gt. Overall, it was demonstrated how the topography and forcing controlling the hydrodynamics of an Antarctic bay differs from that of well-studied northern-hemisphere fjords.

Agnieszka Herman

and 1 more

Sea ice-waves interactions have been widely studied in the marginal ice zone, at relatively low wind speeds and wave frequencies. Here, we focus on very different conditions typical of coastal polynyas: extremely high wind speeds and locally-generated, short, steep waves. We overview available parameterizations of relevant physical processes (nonlinear wave-wave interactions, energy input by wind, whitecapping and ice-related dissipation) and discuss modifications necessary to adjust them to polynya conditions. We use satellite-derived data and spectral modelling to analyze waves in ten polynya events in the Terra Nova Bay, Antarctica. We estimate the wind-input reduction factor over ice in the wave-energy balance equation at 0.56. By calibrating the model to satellite observations we show that exact treatment of quadruplet wave-wave interactions (as opposed to the default Discrete Interaction Approximation) is necessary to fit the model to data, and that the power n>4 in the sea-ice source term S_ice~f^n (where f denotes wave frequency) is required to reproduce the observed very strong attenuation in spectral tail in frazil streaks. We use a very-high resolution satellite image of a fragment of one of the polynyas to determine whitecap fraction. We show that there are more than twofold differences in whitecap fraction over ice-free and ice-covered regions, and that the model produces realistic whitecap fractions without any tuning of the whitecapping source term. Finally, we estimate the polynya-area-integrated wind input, energy dissipation due to whitecapping, and whitecap fraction to be on average below 25%, 10% and 30%, respectively, of the corresponding open-water values.