11 May 2023
 | 11 May 2023
Status: this preprint is open for discussion.

The global correlation between internal-tide generation and the depth-distribution of cold-water corals

Anna-Selma van der Kaaden, Dick van Oevelen, Christian Mohn, Karline Soetaert, Max Rietkerk, Johan van de Koppel, and Theo Gerkema

Abstract. Internal tides are known to be an important source of mixing in the oceans, especially in the bottom boundary layer. The depth of internal-tide generation therefore seems important for benthic life and the formation of cold-water coral mounds, but internal-tidal conversion is generally investigated in a depth-integrated sense. Using both idealized and realistic simulations on continental slopes, we found that the depth of internal-tide generation increases with increasing slope steepness and decreases with intensified shallow stratification. The depth of internal-tide generation also shows a typical latitudinal dependency. Using a global database of cold-water corals, we found that the depth-pattern of internal-tide generation is remarkably similar to the depth-pattern of cold-water corals globally: shallowest near the poles and deepest around the equator with a shoaling around 25 degrees South and North and shallower north of the equator than south of the equator.

We further found that cold-water corals are, more than what would be expected by chance, associated to the (super)critical reflection of internal tides (i.e., situated on topography that is steeper than the internal tidal beam) and to trapped internal tides (i.e., above the critical latitude of 70 degrees for semidiurnal tides and 30 degrees for diurnal tides). The (super)critical reflection of internal tides and trapped internal tides therefore provide an interesting new angle of food supply mechanisms that has not yet been considered in cold-water coral studies. With climate change, stratification is expected to increase. Based on our results, this would cause a shoaling of internal-tide generation, possibly creating new shallower suitable habitat for cold-water corals on continental slopes.

Anna-Selma van der Kaaden et al.

Status: open (until 06 Jul 2023)

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Anna-Selma van der Kaaden et al.

Anna-Selma van der Kaaden et al.


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Short summary
Cold-water corals (CWCs) and tidal waves in the interior of the ocean have only been connected in case-studies. We now demonstrate this connection globally using hydrodynamic simulations and a cold-water coral database. Internal tide generation shows a similar depth-pattern with slope steepness and latitude as CWCs. Our results suggest that increased stratification from climate change will likely shoal internal tide generation, creating new suitable CWC-habitat shallower on continental slopes.