The University of Southampton
University of Southampton Institutional Repository

Shear enhanced nutrient supply at the Mesoscale

Shear enhanced nutrient supply at the Mesoscale
Shear enhanced nutrient supply at the Mesoscale
Phytoplankton live almost exclusively in the sunlit waters of the euphotic zone. However, in addition to sunlight, phytoplankton require a regular supply of nutrients to grow. In the open ocean such nutrients are abundant in the dark waters below the euphotic zone. Hence, to a large extent it is the physical mechanisms driving the transfer of nutrient rich water into the euphotic zone which dictate patterns of phytoplankton growth. Using a combination of observation and high resolution computer modelling this thesis investigates whether shear associated with mesoscale features leads to locally enhanced turbulent mixing and a shear-enhanced nutrient supply. Measurements of turbulent diffusivity and nutrient concentrations have been made in a region containing an eddy dipole, a strong mesoscale feature, consisting of a cyclonic eddy and an anti-cyclonically rotating mode-water eddy. The effect of this strong mesoscale feature on vertical turbulent mixing is assessed by investigating whether variations in vertical shear associated with the mesoscale feature enhance the observed vertical turbulent mixing. Using these observations of turbulent diffusivity, augmented by further measurements from two other ocean regions, a new parametrization of shear-enhanced vertical turbulent mixing is developed. The new shear-enhanced mixing parametrization is implemented in a high-resolution computer model of a mode-water eddy. This model is then used to examine the effect of interactions between the eddy and the wind on vertical nutrient fluxes. The shear enhancement to nutrient supply by mesoscale circulation is found to be potentially of much greater significance than has previously been considered. Modelling suggests that when forced by high variability winds mode-water eddies appear to be capable of locally enhancing the vertical turbulent nutrient flux by up to an order of magnitude. The work in this thesis suggests that vertical turbulent flux may well be underestimated as a stimulus to new production.
Forryan, Alexander
4e753ae9-7f12-495f-933a-2c5a1f554a0e
Forryan, Alexander
4e753ae9-7f12-495f-933a-2c5a1f554a0e
Martin, Adrian P.
9d0d480d-9b3c-44c2-aafe-bb980ed98a6d
Popova, Katya
3ea572bd-f37d-4777-894b-b0d86f735820
Srokosz, Meric
1e0442ce-679f-43f2-8fe4-9a0f0174d483

Forryan, Alexander (2010) Shear enhanced nutrient supply at the Mesoscale. University of Southampton, School of Ocean and Earth Science, Doctoral Thesis, 356pp.

Record type: Thesis (Doctoral)

Abstract

Phytoplankton live almost exclusively in the sunlit waters of the euphotic zone. However, in addition to sunlight, phytoplankton require a regular supply of nutrients to grow. In the open ocean such nutrients are abundant in the dark waters below the euphotic zone. Hence, to a large extent it is the physical mechanisms driving the transfer of nutrient rich water into the euphotic zone which dictate patterns of phytoplankton growth. Using a combination of observation and high resolution computer modelling this thesis investigates whether shear associated with mesoscale features leads to locally enhanced turbulent mixing and a shear-enhanced nutrient supply. Measurements of turbulent diffusivity and nutrient concentrations have been made in a region containing an eddy dipole, a strong mesoscale feature, consisting of a cyclonic eddy and an anti-cyclonically rotating mode-water eddy. The effect of this strong mesoscale feature on vertical turbulent mixing is assessed by investigating whether variations in vertical shear associated with the mesoscale feature enhance the observed vertical turbulent mixing. Using these observations of turbulent diffusivity, augmented by further measurements from two other ocean regions, a new parametrization of shear-enhanced vertical turbulent mixing is developed. The new shear-enhanced mixing parametrization is implemented in a high-resolution computer model of a mode-water eddy. This model is then used to examine the effect of interactions between the eddy and the wind on vertical nutrient fluxes. The shear enhancement to nutrient supply by mesoscale circulation is found to be potentially of much greater significance than has previously been considered. Modelling suggests that when forced by high variability winds mode-water eddies appear to be capable of locally enhancing the vertical turbulent nutrient flux by up to an order of magnitude. The work in this thesis suggests that vertical turbulent flux may well be underestimated as a stimulus to new production.

Text
AF_Thesis_FINAL_VERSION_no_Auth_Dec_Aug_2011.pdf - Other
Download (7MB)

More information

Published date: May 2010
Organisations: University of Southampton

Identifiers

Local EPrints ID: 195037
URI: http://eprints.soton.ac.uk/id/eprint/195037
PURE UUID: b6789802-a2ea-4219-b1fa-5d8784b10e5d

Catalogue record

Date deposited: 15 Aug 2011 15:44
Last modified: 14 Mar 2024 04:01

Export record

Contributors

Author: Alexander Forryan
Thesis advisor: Adrian P. Martin
Thesis advisor: Katya Popova
Thesis advisor: Meric Srokosz

Download statistics

Downloads from ePrints over the past year. Other digital versions may also be available to download e.g. from the publisher's website.

View more statistics

Atom RSS 1.0 RSS 2.0

Contact ePrints Soton: eprints@soton.ac.uk

ePrints Soton supports OAI 2.0 with a base URL of http://eprints.soton.ac.uk/cgi/oai2

This repository has been built using EPrints software, developed at the University of Southampton, but available to everyone to use.

We use cookies to ensure that we give you the best experience on our website. If you continue without changing your settings, we will assume that you are happy to receive cookies on the University of Southampton website.

×