Collaborative research: unraveling connectivity constraints and pathways of sargassum and the nature of their variability by building on a maxey-riley framework for drift modeling

This three-year, $395,626 project grant from the National Science Foundation Division of Ocean Sciences aims to develop a physical-biological transport model of pelagic sargassum seaweed. Funded under the Geosciences program (CFDA 47.050), the grant supports basic research to expand understanding of the integrated Earth system through the atmospheric, earth, and ocean sciences.

Specifically, the awardee LGL Ecological Research Associates, Inc. will build on Maxey-Riley frameworks for drift modeling to account for the combined effects of ocean currents, wind drag, and sargassum raft inertia as a function of growth and mortality responses to temperature and nutrients. Laboratory experiments and satellite tracking of deployed sargassum rafts will help validate transport modeling incorporating buoyancy-dependent drift and wave effects. Tools from ergodic nonlinear dynamics and transition path theory will quantify connectivity and uncertainty. The model aims to unravel constraints on sargassum pathways and variability, with implications for water quality and marine resources affected by pelagic blooms.

Abstract

Satellite imagery has revealed abundant pelagic sargassum seaweed in the sargasso sea, the northwestern gulf of mexico and, in the last decade, a new recurrent zonal band, referred to as the great atlantic sargassum belt (gasb), often extending from the west coast of africa to the caribbean sea. The magnitude of pelagic sargassum in the tropical and subtropical atlantic represents a new form of coastal hazard with direct impact on the water quality and living marine resources of the nearshore ecosystem. This project seeks to develop and implement a physical-biological transport model of sargassum responding in a novel manner to the ocean and atmospheric circulations and changing environmental conditions. The model will account for the combined effects of ocean currents and wind drag mediated by sargassum raft inertia, which will be a function of growth and mortality in response to ambient temperature and nutrient availability. This project would use first-principle-based maxey?riley framework of fluid mechanics for the study of inertial particle motion to develop a framework for modeling sargassum drift. The investigators have extended and tested this application to investigating the drift of isolated objects floating at the ocean surface. This foundation, and further recent theoretical developments, will contribute to building a mechanistic physical?physiological model formulation for the movement of sargassum rafts represented as networks of elastically interacting floating inertial particles whose configurations change according to a growth model. In the model, these changes in sargassum raft size and shape will correspondingly affect their transport. The required carrying flow to conduct the proposed sargassum connectivity investigation will be obtained from reanalysis systems and a multidata synthesis. The sargassum transport model will be tested in the field by satellite tracking sargassum rafts deployed in the florida current. Laboratory experiments in an air-water flume facility will be carried out to quantify buoyancy dependent leeway and constrain wave-induced drift effects. Tools for connectivity analysis and uncertainty quantification will be brought from ergodic nonlinear dynamics theory including set-oriented methods for framing asymptotically almost-invariant sets and the transition path theory for discrete markov chains. This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the foundation's intellectual merit and broader impacts review criteria.