Award: OCE-1851424

Large sand ripples on the seafloor, termed megaripples (Figure 1), are common features in energetic coastal environments with strong currents and/or wave action, but little information exists on their biogeochemical cycling of organic matter.

This project used a shallow-water megaripple field in the inlet to Choctawhatchee Bay in Florida to investigate the effect of megaripples on decomposition of organic matter that passes over the megaripple field and is filtered out or captured in the permeable sand. The two main project objectives were: 1) demonstrate the general function of megaripples as highly effective biocatalytical filters, and 2) demonstrate that common inlet megaripples contribute to carbon and nutrient retention in the bays. The overall hypothesis was that sand megaripples act as large filter systems that rapidly convert entrained dissolved and solid organic matter into inorganic carbon and nutrients.

The project deployed non-invasive aquatic eddy covariance instruments equipped with newly developed robust sensors to quantify sedimentary remineralization processes. In-situ measurements combined with laboratory experiments and analyses quantified carbon and nutrient re-mobilization through organic carbon mineralization in the megaripple sand.

The project results characterize coastal megaripple fields as metabolic hotspots with intense organic matter degradation. The deflection of the strong tidal flows by the large megaripples forces water into and through the highly permeable sand. Through this pore water exchange, organic matter and oxygen are transported into the megaripples rich on microbes that facilitate decomposition of both particulate and dissolved organic matter.

Globally, megaripple fields are common features on the seafloor in high-energy environments like inlets, the shelf edge, straits, and submarine canyons, and thus are likely to have a significant influence on carbon and nutrient cycling. Surprisingly, their role for cycling of organic matter has not been addressed well, albeit the geology and formation of megaripples has been a subject of many studies.

By producing data on the biogeochemical functioning of megaripple fields, the project addressed a knowledge gap that has implications on our understanding of the cycles of organic matter in our oceans.

Last Modified: 08/21/2025
Modified by: Peter Berg