Effects of ocean turbulence on the large-scale stratification and Small-Scale Particle Distributions
type: CreativeWork
description: Part I: “The Middepth Ocean.” Away from polar regions, the ocean stratification from 1–3 km depth exhibits little horizontal variability and a strikingly exponential vertical structure. The stratification is maintained by a large-scale balance between the upwelling of cold water from the abyss and the downward mixing of heat by turbulence. At smaller scales, however, the upwelling and mixing exhibit tremendous spatial variability, belying the simple structure of the stratification. Observations of mixing are too sparse to extrapolate accurately to large scales, and the millennial timescales associated with diapycnal mixing render it challenging to constrain with models. By studying the basin-averaged buoyancy budget in light of what is known about the stratification and overturning, we deduce that the vertical profile of the isopycnal-averaged turbulent diffusivity must increase with depth, but it must do so more slowly than the stratification decays. In recognition of the importance of the distribution of mixing to the stratification and upwelling, we then extend theoretical models of middepth dynamics to account for structure in the turbulent diffusivity profile. We develop a fully predictive theory for the stratification and upwelling profiles that explains why bottom-enhanced mixing is essential to the observed exponential stratification. The upshot is that as long as the mixing is appreciably bottom-enhanced, the basin-averaged diapycnal upwelling will vary roughly linearly with depth and the stratification will be exponential; conversely, without any structure in the mixing, the stratification will not be exponential. This result tightens constraints on the large-scale distribution of mixing and implies that the vertical structure of mixing is important to characterize correctly in ocean models. Part II: “Inertial Particles.” The motion of solid objects in the ocean such as plastic debris or freely floating oceanographic instruments may differ from that of the…
abstract: Part I: “The Middepth Ocean.” Away from polar regions, the ocean stratification from 1–3 km depth exhibits little horizontal variability and a strikingly exponential vertical structure. The stratification is maintained by a large-scale balance between the upwelling of cold water from the abyss and the downward mixing of heat by turbulence. At smaller scales, however, the upwelling and mixing exhibit tremendous spatial variability, belying the simple structure of the stratification. Observations of mixing are too sparse to extrapolate accurately to large scales, and the millennial timescales associated with diapycnal mixing render it challenging to constrain with models. By studying the basin-averaged buoyancy budget in light of what is known about the stratification and overturning, we deduce that the vertical profile of the isopycnal-averaged turbulent diffusivity must increase with depth, but it must do so more slowly than the stratification decays. In recognition of the importance of the distribution of mixing to the stratification and upwelling, we then extend theoretical models of middepth dynamics to account for structure in the turbulent diffusivity profile. We develop a fully predictive theory for the stratification and upwelling profiles that explains why bottom-enhanced mixing is essential to the observed exponential stratification. The upshot is that as long as the mixing is appreciably bottom-enhanced, the basin-averaged diapycnal upwelling will vary roughly linearly with depth and the stratification will be exponential; conversely, without any structure in the mixing, the stratification will not be exponential. This result tightens constraints on the large-scale distribution of mixing and implies that the vertical structure of mixing is important to characterize correctly in ocean models. Part II: “Inertial Particles.” The motion of solid objects in the ocean such as plastic debris or freely floating oceanographic instruments may differ from that of the…
author: Rogers, Mason
keywords: Middepth ocean, Stratification, Inertial particles
date published: 2025-09
date modified: 2026-07-27T22:05:02Z
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/1912/72322

PropertyValue
property ID: DOI
value: 10.1575/1912/72322