# Mass Exchange Dynamics of Surface and Subsurface Oil in Shallow-Water Transport

## TL;DR

This paper develops a large-scale model for oil spill transport in shallow water, focusing on the mass exchange between surface and subsurface oil driven by droplet dynamics and buoyancy, addressing microscale challenges.

## Contribution

It introduces an upscaled, environmentally relevant model for surface-subsurface oil exchange that maintains mass conservation and is applicable at large spatio-temporal scales.

## Key findings

- Model captures oil exchange mechanisms due to droplet dynamics and buoyancy.
- Addresses microscale challenges through upscaling for large-scale predictions.
- Ensures mass conservation in shallow-water oil spill simulations.

## Abstract

We formulate a model for the mass exchange between oil at and below the sea surface. This is a particularly important aspect of modeling oil spills. Surface and subsurface oil have different chemical and transport characteristics and lumping them together would compromise the accuracy of the resulting model. Without observational or computational constraints, it is thus not possible to quantitatively predict oil spills based upon partial field observations of surface and/or sub-surface oil. The primary challenge in capturing the mass exchange is that the principal mechanisms are on the microscale. This is a serious barrier to developing practical models for oil spills that are capable of addressing questions regarding the fate of oil at the large spatio-temporal scales, as demanded by environmental questions. We use upscaling to propose an environmental-scale model which incorporates the mass exchange between surface and subsurface oil due to oil droplet dynamics, buoyancy effects, and sea surface and subsurface mechanics. While the mass exchange mechanism detailed here is generally applicable to oil transport models, it addresses the modeling needs of a particular to an oil spill model [1]. This transport model is designed to capture oil spills at very large spatio-temporal scales. It accomplishes this goal by specializing to shallow-water environments, in which depth averaging is a perfectly good approximation for the flow, while at the same time retaining mass conservation of oil over the whole oceanic domain.