Particles track from model and observations: A contribution to the OCEAN ICE work packages WP1 and WP2 (Deliverable D10.3)

This deliverable aims to assess the connectivity of currents around the Antarctic Peninsula, identify the structure of flows carrying particles from the Eastern to Western Antarctic Peninsula continental shelves through the Bransfield Strait, and ice keel-induced breaking of internal solitary waves (ISW). For the first two tasks, we utilised circulation data from the Weddell and Bellingshausen Seas in the Whole Antarctica Ocean Model (WAOM) to obtain and analyse particle trajectories using the Parcels model. For the third task, the non-hydrostatic model was applied. The pathways of water masses were characterised by calculating Lagrangian statistical parameters: the visitation frequency and the representative trajectory. The visitation frequency is the percentage of particles P that visit each 10×10 km grid column at least once during a 20-year modelling period. The representative particle trajectory is the individual particle trajectory that deviates the least from the rest of the individual trajectories. The latter characteristic was first introduced in the field of oceanography. The proportion of particles that turn to the Bellingshausen Sea is 21% of the total number of particles, while 70% turn northeast, and the proportion of remaining on the shelf is 9%. The farther to the west, the more particles are captured by the strong ACC. So, only 3.4% of the particles were transported west of 80°W, while only 0.1% reached the Amundsen Sea (105°W). This indicates a lack of connectivity between the circulation from the Weddell to the Amundsen Seas. In the Bransfield Strait, the representative trajectories align well with the distributions of visitation frequencies. They demonstrate essential dependence on the release season and the release depth. The wavelet analysis of recent high-resolution ice keel survey data collected during the MOSAIC expedition (https://mosaic-expedition.org/), which utilised a multi-beam sonar mounted on a remotely operated vehicle, revealed that the mean keel width can be categorised into two distinct classes. In the first class, the keel width was 30-40 m in summer and winter. In another class, the zone of pressure ridging can be much larger, ranging from 60 to 110 m. Another result of high-resolution measurements was the discovery of a fine structure of ridging zones with “sub-keels” of several meter scale that contribute to the ridge roughness, enhancing mixing by ISW. The shorter ISW wavelengths, relative to the keel, lead to more intense wave–keel interactions, resulting in enhanced wave breaking, vortex formation, turbulent dissipation, and sea ice melting. Similarly, a shorter distance between keels at a fixed horizontal scale of the ridge results in enhancing the dissipation of ISW.