What is Seafloor Roughness?

Seafloor roughness refers to the abyssal hills in the ocean basins. Imagine the interior of an egg carton: it's not smooth, but covered with small dimples and bumps that help protect the eggs from cracking or breaking. Similarly, the bathymetry beneath the vast ice and the ocean around Antarctica is not smooth, but filled with hills and valleys. These variations typically occur at scales of about 10 kilometres, which are quite small compared to large-scale bathymetric features like canyons and ridges that can extend hundreds to thousands of kilometres across an ocean basin.

These small-scale bathymetric features in the ocean can be observed through directly from a ship. However, they are often not resolved by satellite gravity measurements, the main data source available for a large portion of the Antarctic margin. As a result, seafloor roughness has always been overlooked and not adequately represented in ocean and climate models.

How to Measure the Effect of Seafloor Roughness?

In our study, we examine the impact of seafloor roughness by comparing two widely used bathymetry datasets, BedMachine Antarctica Version 2 (BedMachine) and Shuttle Radar Topography Mission at 15 arc sec resolution (SRTM15). Both datasets effectively capture large-scale topographic features. However, SRTM15 includes detailed small-scale seafloor roughness that BedMachine lacks. To assess the role of this seafloor roughness, we run a high-resolution regional ocean model of the Denman Glacier region with these two bathymetry datasets. This comparison allows us to evaluate how small-scale variations in the seafloor impact the ocean circulation and hence the melting of the East Antarctica. 

How Does Roughness Reduce Melting?

Seafloor roughness significantly influences the melting of ice shelves by acting as a brake on the ocean circulation.  Our study shows that seafloor roughness can slow down the circulation over the continental shelf. As a result, the ocean heat transport onto the continental shelf and ice shelf cavity drops, leading to a reduction in ice shelf melting. Our findings indicate that this reduction can be as much as 4 gigatonnes per year. However, available bathymetry observations in nearby Vincennes Bay suggest that even the rougher bathymetry product, SRTM15, underestimates the seafloor roughness. This implies that its impact on ocean circulation and ice shelf melting may also be underestimated. To explore this further, we conduct an additional simulation where we artificially introduce roughness to match the observations. This new simulation shows an even larger impact, with up to 8.4 gigatonnes per year reduction in the total meltwater discharge.

A Call for More Observation 

We know too little about the bathymetry, so we urgently need more detailed observations of the bathymetry around the Antarctic regions. By getting a clearer picture of these underwater landscapes, we could better understand the dynamics at play and develop more accurate models to predict future climate change.