On subannual variability in the abyssal ocean
type: CreativeWork
description: The abyssal ocean is a critical yet understudied component of the climate system and is of growing economic interest. This thesis combines field observations and numerical modeling to advance our understanding of subannual variability in the abyssal ocean and its broader implications. First, hydrographic measurements from the Clarion-Clipperton Zone of the tropical eastern North Pacific are used to characterize the structure and variability of the bottom mixed layer (BML) in a region targeted for deep-sea mining. The observations reveal a spatially and temporally variable BML with a mean thickness of ∼250m and influenced by interactions with mesoscale eddies and abyssal thermal fronts. A simplified model of sediment transport suggests that such variations in BML structure could significantly influence the dispersal of sediments resuspended by seabed mining activities. Second, idealized model experiments are conducted to explore the genesis of benthic storms – episodes of strong near-bottom flows and sediment entrainment – underneath an unstable, surface-intensified jet resembling the Gulf Stream east of Cape Hatteras. In these experiments, the baroclinic instability of the jet gives rise to deep cyclonic and anticyclonic eddies through eddy barotropization and produces high levels of eddy kinetic energy at abyssal depths through the convergence of vertical eddy pressure fluxes. The near-bottom currents are comparable in magnitude to those observed during benthic storms, with vertical shears strong enough to produce BMLs up to 𝒪(100)m thick. Deep cyclonic eddies transport particles from near the bottom over the entire BML and could contribute to benthic nepheloid layers. The results suggest that the abyssal response to the intrinsic instability of surface-intensified currents could contribute significantly to subannual variability near the seafloor. Third, a model simulation of western North Atlantic circulation is performed to study the deep cyclones (DCs) observed …
abstract: The abyssal ocean is a critical yet understudied component of the climate system and is of growing economic interest. This thesis combines field observations and numerical modeling to advance our understanding of subannual variability in the abyssal ocean and its broader implications. First, hydrographic measurements from the Clarion-Clipperton Zone of the tropical eastern North Pacific are used to characterize the structure and variability of the bottom mixed layer (BML) in a region targeted for deep-sea mining. The observations reveal a spatially and temporally variable BML with a mean thickness of ∼250m and influenced by interactions with mesoscale eddies and abyssal thermal fronts. A simplified model of sediment transport suggests that such variations in BML structure could significantly influence the dispersal of sediments resuspended by seabed mining activities. Second, idealized model experiments are conducted to explore the genesis of benthic storms – episodes of strong near-bottom flows and sediment entrainment – underneath an unstable, surface-intensified jet resembling the Gulf Stream east of Cape Hatteras. In these experiments, the baroclinic instability of the jet gives rise to deep cyclonic and anticyclonic eddies through eddy barotropization and produces high levels of eddy kinetic energy at abyssal depths through the convergence of vertical eddy pressure fluxes. The near-bottom currents are comparable in magnitude to those observed during benthic storms, with vertical shears strong enough to produce BMLs up to 𝒪(100)m thick. Deep cyclonic eddies transport particles from near the bottom over the entire BML and could contribute to benthic nepheloid layers. The results suggest that the abyssal response to the intrinsic instability of surface-intensified currents could contribute significantly to subannual variability near the seafloor. Third, a model simulation of western North Atlantic circulation is performed to study the deep cyclones (DCs) observed …
author: Chen, Si-Yuan Sean
language: en_US
keywords: Abyssal ocean, Deep circulation, Bottom mixed layer
date published: 2025-09
date modified: 2026-07-27T22:05:08Z
provider: Woods Hole Oceanographic Institute
publisher: Networked Digital Library of Theses and Dissertations
type: WebPage
source organization: Massachusetts Institute of Technology and Woods Hole Oceanographic Institution

PropertyValue
property ID: Handle
value: https://hdl.handle.net/1912/72089

PropertyValue
property ID: DOI
value: 10.1575/1912/72089