Improving the bathymetry of the Southern Ocean with the ISOBatA project. ISOBatA Data delivered to IBCSO (version v.2)

This DOI publication presents the multibeam bathymetry dataset shared with the Alfred Wegener Institute to contribute to the International Bathymetric Chart of the Southern Ocean (IBCSO). The data were collected in the Southern Ocean (SO) as part of the ISOBatA PNRA project during 3 Antarctic expeditions with the Italian icebreaker Laura Bassi with the hull mounted EM304. Soundings collected have been corrected for sound velocity, processed with Qimera and formatted as ASCII XYZ grids in EPSG 9354 projection. The dataset that covers key areas in the Ross Sea and along the Macquarie Triple Junction and Emerald Fracture Zone were archived and made traceable to ensure wide dissemination and further usability.

The PNRA-funded ISOBatA project (Italian Southern Ocean Bathymetry from consistent exploitation of opportunistic seafloor datasets in the Antarctic region and surrounding areas) introduced an innovative approach to optimize acoustic (mainly bathymetric) and magnetometric data collection. The primary objective was to enhance bathymetric knowledge of the Southern Ocean by collecting multibeam echosounder data during the Laura Bassi cruises. The focus was on unexplored areas in: 1) the Ross Sea and 2) the region between the Macquarie Triple Junction (MQ TJ) and the Emerald Fracture Zone (EMZ).

The operational phase of ISOBatA spanned three expeditions: XXXVII (2021-2022), XXXVIII (2023), and XXXIX (2024) of the Laura Bassi Antarctic campaigns. In the first two years (XXXVII and XXXVIII), the project benefited from dedicated ship time, enabling efficient data collection through:

Strategic allocation of ship time to reduce speed during transfers and adjust routes along identified preferred corridors.

Planning data collection in preferred areas based on pre-existing metadata, such as IBCSO Coverage, SDL (Seismic Data Library), Italian Mooring Sites, Italian Coring and Box Coring Sites. This included transit routes through the Southern Ocean along MQ and EMZ and unmapped areas in the Ross Sea, such as the Italian MORSEA Mooring Sites.
In the third year (XXXIX), no dedicated time was available. ISOBatA collected data under two conditions: 1) without changing the ship's course or speed and 2) with simultaneous acquisition of acoustic equipment involved in other projects which reduced the spatial resolution of the data acquired by EM304.

Despite challenges due to weather conditions (rough seas and ice along the route), ship speed, and the lack of tide gauges, ISOBatA demonstrated the effectiveness of acoustic data collection, particularly in the Ross Sea, by utilizing downtime for opportunistic data collection during:

- Mooring maintenance operations (recovery and redeployment),
- Supporting supply vessels by clearing ice to reach the MZS Antarctic base,
- Medical assistance to fishing vessels (MEDEVAC),
- Sheltering during standby weather.

Onboard data sharing led to valuable interactions and collaborations with other onboard projects.

Acknowledgments: We acknowledge the MORSEA project's real-time sharing of collected XBTs and CTDs, which enabled us to apply the necessary sound velocity profiles. We also thank the PNRA Program for funding and support and the Laura Bassi research teams for the scientific interactions and collaborations.

Keywords: Southern Ocean, Bathymetry, ISOBatA, Laura Bassi, Antarctic, IBCSO.