Investigating the controls on surface ocean dimethyl sulphide concentrations at regional to global scales

Miles, Christopher James (2012) Investigating the controls on surface ocean dimethyl sulphide concentrations at regional to global scales. Doctoral thesis, University of East Anglia.

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Abstract

This thesis details a series of investigations into the controls on surface ocean
concentrations of the climatically relevant, biogenic sulphur compound, dimethyl
sulphide (DMS) at regional to global scales. The primary focus is upon the role of
solar irradiance and metrics of biological activity in modulating DMS concentrations
using bivariate and multivariate statistical techniques in conjunction with three
different data sets from multiple spatial and temporal scales.
Firstly, a statistical investigation into the proposed strong positive relationship
between surface DMS concentration and the average mixed layer irradiance (solar
radiation dose: SRD) was undertaken using DMS data from a series of cruise tracks
from the Atlantic Meridional Transect (AMT) programme, primarily from the
oligotrophic Atlantic gyres. Positive correlations were found between DMS and (a)
SRD formulations using concurrently sampled in situ data (ρ=0.55 n=65 p<0.01), (b)
SRD formulations based on using climatological data (ρ=0.74 n=65 p<0.01) and (c)
a ultraviolet radiation dose (ρ= 0.67 n=54 p<0.01).
The next analysis investigated whether the inclusion of a biological variable
(chlorophyll or primary production) alongside irradiance could explain additional
variance in DMS concentrations. This analysis employed a database of cruise data
from a range of biogeochemical domains, latitudes and trophic conditions (AMT, the
Barents Sea, the Atmospheric Chemistry Studies in the Oceanic Environment
(ACSOE) research campaign and the DImethyl Sulphide biogeochemistry within a
COccolithophore bloom (DISCO) study. Using multiple linear regression (MLR)
analyses, it was found that the combination of, in situ rate of primary production and
underwater irradiance accounted for significant variance in DMS concentrations in
data from discrete depths within the euphotic zone (R2 = 0.55), from near-surface
waters (R2 = 0.66) and within depth profile integrated data (R2 = 0.40).
The final analysis is an investigation into global surface DMS dynamics using the
global surface seawater DMS database (http://saga.pmel.noaa.gov/dms/) and satellite
based retrievals of irradiance and primary production rates. A novel composite
approach which combines multiple MLR models applied to Longhurst biogeochemical provinces, and using monthly averaged data, explained maximum
variance. Models developed within a randomly selected training subset were able to
explain significant variance within the remaining validation subset using this
composite approach (predicted vs. observed ρ = 0.93, p = 0, n = 107). Previous
studies had been unable to identify a strong link between DMS and indicators of the
biological community (e.g. chlorophyll) at large scales. Our results suggest that a
link exists between ecosystem productivity and DMS concentrations, and moderated
by processes directly influenced by solar irradiance. These findings on large scale
ecosystem controls on DMS, based on remote-sensing datasets, provide an
advancement in the understanding and prediction of global-scale surface DMS
concentrations.

Item Type: Thesis (Doctoral)
Faculty \ School: Faculty of Science > School of Environmental Sciences
Depositing User: Brian Watkins
Date Deposited: 22 Aug 2013 14:31
Last Modified: 22 Aug 2013 14:31
URI: https://ueaeprints.uea.ac.uk/id/eprint/43162
DOI:

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