Mohn, Christian, Schwarzkopf, Franziska U. , García, Patricia Jiménez, Orejas, Covadonga, Huvenne, Veerle A. I., Schumacher, Mia, Pérez‐Rodríguez, Irene, Sarralde Vizuete, Roberto, López‐Abellán, Luis J., Dale, Andrew C., Devey, Colin , Hansen, Jørgen L. S., Møller, Eva Friis and Biastoch, Arne (2025) Dynamics of Near‐Bottom Currents in Cold‐Water Coral and Sponge Areas at Valdivia Bank and Ewing Seamount, Southeast Atlantic. Journal of Geophysical Research: Oceans, 130 (1). e2024JC021667. DOI 10.1029/2024JC021667.

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Abstract

This study investigates near‐bottom currents and physical processes from simulations with the hydrodynamic model ROMS‐AGRIF at two seamounts of the northeast Walvis Ridge to obtain valuable insights about drivers of observed occurrences of benthic suspension feeders (cnidarians and sponges) in this data‐poor area. The spatial resolution in each model area was increased across two levels of nested grids from 1,500 m to 500 m resolution with 32 stretched terrain‐following (s‐) layers in the vertical with high resolution close to the bottom. The parent grids receive initial and boundary conditions from the basin‐scale model INALT20 and from solutions of the OTIS inverse tidal model. The model topography is based on GEBCO data with local refinements from multi‐beam data collected during different surveys in 2008, 2009, and 2010. Increasing model resolution is an important advancement for precisely evaluating the intrinsic dynamics within challenging rough terrain. We examined how near‐bottom currents vary over space and time and investigated potential links between observed Cnidarian and Porifera occurrences and ranges of physical variables and processes. We identified a close link between physical processes and species distributions and suggested that physical processes such as kinetic energy dissipation and internal wave dynamics may be considered in future research as proxies of food supply to benthic suspension feeders. Such mechanistic variables may also be used to supplement more traditional descriptors such as water mass and terrain properties in species distribution models, thus enhancing our ability to predict the occurrence of benthic communities characterized by cnidarians and sponges.

Plain Language Summary

We investigated the physical drivers of the distribution of cnidarians and sponges in two areas along the northeast Walvis Ridge, Valdivia Bank, and Ewing Seamount based on data from ocean model simulations over a period of 3 years. To get realistic boundary conditions for our simulations, we added bathymetric data from high‐resolution seafloor topography, water column data from a larger‐scale ocean circulation model, and information about tidal currents. By refining our model, we were able to better resolve the near‐bottom circulation and how it changes over time and space. Incorporating finer‐scale variability of physical variables and processes that represent important proxies for the transport and delivery of food to deep‐sea benthic fauna has the potential to greatly improve predictions of benthic filter feeding communities. Moreover, integration of such variables in future species distribution modeling may contribute to our current understanding of optimal environmental envelopes for important deep‐sea taxa, such as those that represent vulnerable marine ecosystems.

Key Points

High‐resolution nested hydrodynamic models simulate multiyear variations of bottom currents at two Walvis Ridge seamounts
Near‐bottom currents are influenced by flow‐topography interactions and internal tide dynamics
Kinetic energy dissipation and internal tide dynamics are important mechanisms driving food supply to benthic suspension feeders

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