Award: OCE-1851290

Large submarine sediment ripples, termed megaripples (Figure 1), are common in energetic in coastal and shelf environments, but little information exists on their biogeochemical functioning.

This project used a megaripple field in the inlet to Chotawhatchee Bay in the northern Gulf to investigate the effect of the megaripples on the decomposition of organic matter that passes the ripple field. The two main project objectives were: 1) demonstrate the general function of megaripples as biocatalytical filters, and 2) demonstrate that common inlet megaripples contribute to nutrient retention in coastal 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 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 nutrient re-mobilization through organic carbon mineralization in the flushed megaripple sand.

The project results characterize coastal megaripple fields as sites of intense organic matter degradation. The deflection of the strong tidal flows by the large ripples forces water into and through the highly permeable sediment forming the megaripples. Through this pore water exchange, organic matter and oxygen is transported into the megaripples where microbes colonizing the sand grains decompose particulate as well as dissolved organic material. This degradation remobilizes nutrients that support the growth of microalgae on the sediment surface.

This filtration process can effectively remove organic matter from the water column and accelerate its decomposition. Thereby, megaripples function as large biocatalytical filtration systems that contribute to the removal of organic materials from coastal waters.

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 the cycling of matter has not been addressed, albeit the geology and formation of megaripple fields has been subject of many studies. By producing data on the functioning of megaripples, the project addressed a knowledge gap that has implications on our understanding of the cycles of matter.

The project offered unique opportunities for both graduate and undergraduate students in learning state-of-the-art techniques. Results were disseminated via scientific journals, conference presentations and public lectures.

Last Modified: 07/30/2025
Modified by: Markus H Huettel