Date of Award

Winter 2019

Project Type

Thesis

Program or Major

Civil Engineering

Degree Name

Master of Science

First Advisor

Nancy Kinner

Second Advisor

Kai Ziervogel

Third Advisor

Tom Ballestero

Abstract

While extensive research has been conducted on minerals aggregating with spilled oil, surface-forming organic aggregates, called marine snow, have only recently been studied as a transport mechanism. This knowledge gap in understanding the fate of oil was highlighted following the 2010 Deepwater Horizon (DWH) blowout in the Gulf of Mexico when a significant percentage of the spilled oil reached the seafloor as a result of association with marine snow. Research following the DWH blowout suggests both marine snow and mineral aggregates are significant oil exposure pathways that must be considered during an oil spill response. The U.S. Geological Survey and others have noted that understanding particle fluxes in areas of petroleum exploration and extraction is urgently needed. The motivation for this thesis research is to inform response decision-making and understanding of the potential association of spilled oil with marine snow in Cook Inlet, Alaska. During Summers 2018 and 2019 and January 2019, the particle flux in southeastern Cook Inlet was measured with a surface-tethered sediment trap, deployed for 1 to 3 h, below the mixed layer, at a depth of 20 m. Fluxes were similar at three sites along the axis of Kachemak Bay, and significantly larger at Anchor Point. In both summers, there was a strong and consistent organic flux indicating high primary productivity across the region. In Kachemak Bay the total flux ranged from 104-152 g m-2 d-1. At Anchor Point, there was significantly higher sedimentation with a mean flux of 297 g m-2 d-1. Throughout the region, 20-36% of the particle composition was organic.

In the laboratory phase of this study, roller-bottles with surface water from Kachemak Bay were used to explore the interaction of surface oil and natural assemblages. The results corroborate studies in the Gulf of Mexico and other regions; there is potential for surface oil to impact the benthic environment to varying degrees in areas of high primary productivity that are directly connected to the seafloor by a strong biological particle flux. In roller-bottle experiments, the addition of oil enhanced aggregation. Estimates from microscopy and image analysis suggest that 0.6 to 9.3% of the total oil added to surface waters became incorporated in non-floating aggregates. The results suggest oil sorption to surface organics in lower Cook Inlet in May-June conditions is likely and similar to what has been found in other regions.

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