Project Overview

Summary:

In January 2016, Dr. Villy Kourafalou at the University of Miami’s Rosenstiel School of Marine and Atmospheric Science was awarded an RFP-V grant of $2,262,767 to lead the GoMRI project entitled Influence of River Induced Fronts on Hydrocarbon Transport consisted of 3 collaborative institutions and approximately 24 research team members (including students).

1. Objectives

The overarching study objective was to understand, quantify and be able to predict the role of river plume induced fronts and circulation regimes in enhancing, modifying or altering the transport pathways of hydrocarbons, in the presence of complex topography, shelf flows and strong oceanic currents. Prior to this project, strong evidence had emerged that such fronts and currents played a crucial, but poorly understood, role controlling oil pathways in the Gulf of Mexico (GoM) during the Deepwater Horizon (DwH) incident. This project was the first comprehensive study to elucidate the related processes. Two major hypotheses were examined: a) large river plumes create distinct circulation regimes, separated with strong fronts that are of fundamental importance for hydrocarbon transport; b) accurate estimates of hydrocarbon pathways need to take into account the thickness of oil. This study elucidated under what conditions river plumes may help entrain oil and guide it toward the coastline (prevailing case west of the Mississippi Delta) or may help push oil offshore, acting as a barrier for onshore pathways (prevailing case east of the Mississippi Delta). The latter was also connected to river plume interaction with offshore flows, specifically the Loop Current (LC) system.

2. Methodology

The study area covered the entire GoM, including the Florida Straits. This project employed novel analyses of satellite data, targeted field surveys, and data-guided, high resolution physical, biochemical and oil spill simulations to explore details on hydrocarbon transport, with updated methodologies to estimate and model oil thickness. Both the true conditions of the DwH incident and a variety of relevant alternative scenarios were studied. A known active leakage site, the Taylor Energy platform near the Mississippi Delta (leaking oil since 2004) was used for in situ estimates of oil spreading and thickness under different conditions in the surrounding environment, which is dominated by Mississippi influence and LC intrusions. These in situ data were used to calibrate oil thickness estimation from remote sensing, allowing a more accurate initialization of the proposed oil spill simulations. This approach has filled important knowledge gaps and resulted in advanced understanding of the conditions controlling the complex hydrocarbon pathways in the GoM. A unique campaign employed multi-platform observations around the Taylor Energy platform and resulted in unprecedented data on the transport and fate of oiled waters near a major river plume. Combined with the project’s high resolution numerical models, this campaign played an important role in establishing the importance of river fronts on hydrocarbon transport and fulfilling the project’s objectives.

Research Highlights

 As of December 31, 2019, this project’s research resulted in  9 peer-reviewed publications and 27 scientific presentations and 16 datasets being submitted to the GoMRI Information and Data Cooperative (GRIIDC), which are/will be made available to the public. The project also engaged 2 Masters and PhD students over its award period. Significant outcomes of this project’s research are under GoMRI Research Theme 1 and are highlighted below.

• The fronts created by the Mississippi River played a significant role on the transport and fate of oil during the 2010 DeepWater Horizon incident.

This important study finding established a missing component of the complex conditions that resulted in hydrocarbon transport and fate under the DwH incident. Prior to the study, impacts of coastal circulation were limited to wind and wave effects. Currents driven by the buoyancy of the fresher river waters and the resulting fronts with saltier offshore waters were proven to be an important factor in guiding hydrocarbon pathways.

• Rivers create fronts in the coastal ocean that can act as barriers when oil from a deep release is traveling toward the coast; but rivers also create currents that can either help keep oil offshore or guide oil along and toward the coast.

The study provided details on how exactly the river induced fronts influence hydrocarbon pathways. These details strongly depend on the dynamics of river plumes. The spreading of riverine waters under these dynamics has three distinct regimes for the Mississippi River: west of the Delta (toward Louisiana-Texas), east of the Delta (toward Miassissippi-Alabama-Florida) and offshore (toward the Gulf interior). Hydrocarbon transport varies under each of these regimes that are defined by the fronts.

• In the Gulf of Mexico, the southward offshore transport and fate of hydrocarbons released near the Mississippi Delta is strongly influenced by the interaction of the river’s coastal currents and fronts with the deep circulation, namely the Loop Current and eddies around it.

Mississippi waters often form a narrow offshore jet, especially when the Loop Current is extended in the Gulf and can reach far northward, approaching the Delta. Additional conditions need to be met, both in terms of coastal circulation (ie favorable winds to bring the riverine waters in the right place) and in terms of deep ocean circulation (ie a counter-clockwise eddy must be near the clockwise Loop Current, to create the offshore jet flow in between). Once oil is entrained in this offshore jet, it has the potential to travel large distances, along branches of waters of Mississippi origin, reaching the Straits of Florida and beyond. The study elucidated, for the first time, how these branches evolve, not only near the surface, but also at depth, under the influence of the Loop Current and associated eddies.

• New tools for monitoring and predicting oil transport and fate

The study advanced a comprehensive oil trajectory model by adding oil thickness. A method was developed to produce shape files from satellite observations for reliable model initialization. For the first time, a method to produce maps of Sea Surface Salinity (SSS) from ocean color satellite data was developed; this was advantageous for evaluating model results of oil trajectories in a river dominated domain where SSS gradients are strong.

  Proposal Abstract - RFP-V PI Villy Kourfalou