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University of Southampton Research Repository Eprints Soton University of Southampton Research Repository ePrints Soton Copyright © and Moral Rights for this thesis are retained by the author and/or other copyright owners. A copy can be downloaded for personal non-commercial research or study, without prior permission or charge. This thesis cannot be reproduced or quoted extensively from without first obtaining permission in writing from the copyright holder/s. The content must not be changed in any way or sold commercially in any format or medium without the formal permission of the copyright holders. When referring to this work, full bibliographic details including the author, title, awarding institution and date of the thesis must be given e.g. AUTHOR (year of submission) "Full thesis title", University of Southampton, name of the University School or Department, PhD Thesis, pagination http://eprints.soton.ac.uk UNIVERSITY OF SOUTHAMPTON FACULTY OF ENGINEERING, SCIENCE AND MATHEMATICS National Oceanography Centre, Southampton School of Ocean and Earth Science Particle Fluxes in the North-East Atlantic and Southern Ocean By Ian Salter Thesis for the degree of Doctor of Philosophy September 2007 Graduate School of the National Oceanography Centre, Southampton This PhD dissertation by Ian Salter has been produced under the supervision of the following persons Supervisors: Dr. Richard S. Lampitt Prof. Alan E.S. Kemp Chair of Advisory Panel: Dr Rachel A. Mills “Begin at the beginning and go on till you come to the end; then stop”. (Lewis Carrol) DECLARATION OF AUTHORSHIP • I, Ian Salter, declare that the thesis entitled Particle fluxes in the North East Atlantic and Southern Ocean and the work presented in it are my own. I confirm that: • This work was done wholly or mainly while in candidature for a research degree at this University • Where any part of this thesis has been previously submitted for a degree or any other qualification at this University or any other institution, this has been clearly stated; • Where I have consulted the published work of others, this is always clearly attributed; • Where I have quoted from the work of others, the source is always given. With the exception of such quotations, this thesis is entirely my own work; • I have acknowledged all main sources of help; • Where the thesis is based on work done by myself jointly with others, I have made clear exactly what was done by others and what I have contributed myself; • Parts of this work have been published as: Salter, I., Lampitt, R., Sanders, R., Poulton, A., Kemp, A., Boorman, B., Saw, K., Pearce, R. “Estimating carbon, silica, and diatom export from a naturally fertilised phytoplankton bloom in the Southern Ocean using PELAGRA: A novel drifting sediment trap.” Deep-Sea Research II, In Press. Signed:……………………………………………………………………………… Date:………………………………………………………………………………… ACKNOWLEDGMENTS My sincere thanks go to my supervisor Dr. Richard Lampitt for giving me the initial opportunity, and subsequent freedom and support to explore my own ideas. I would also like to thank my co-supervisor, Prof. Alan Kemp who has been a great help, particularly during the long write-up. I would like to thank my Mum and Dad for the sacrifices that they have made to provide me with the opportunities that they did not have, and always supporting me in every decision I have ever made. I would like to thank my brother for always being on the other end of the phone when I needed him, despite being at the other end of the world, and also my sister, Louise for her support and greeting cards. There are many people at the National Oceanography Centre who deserve my thanks. I would particularly like to acknowledge the support of Richard Sanders, Martha Gledhill, and Peter Statham. I would also like to thank Raymond Pollard for organising and implementing the excellent CROZEX programme which I am very proud to have been involved with. And lastly, but by no means least, I would like to thank Maria to whom I dedicate this work. I would probably have to write another thesis of equal length to ever fully acknowledge the support and patience that she has shown towards me throughout this journey; it simply would not have been possible without her. UNIVERSITY OF SOUTHAMPTON ABSTRACT FACULTY OF ENGINEERING, SCIENCE, AND MATHEMATICS SCHOOL OF OCEAN AND EARTH SCIENCE Doctor of Philosophy PARTICLE FLUXES IN THE NORTH-EAST ATLANTIC AND SOUTHEN OCEAN Ian Salter Concerns regarding the climatic implications of the increase in atmospheric CO2 concentrations throughout the anthropocene have provided the impetus to obtain a mechanistic understanding of oceanic processes and their role in regulating atmospheric pCO2. One important mechanism is the functioning of the biological pump which partitions carbon between the atmosphere and ocean reservoirs over relevant time scales. Current uncertainties revolve around the accuracy of upper ocean particle flux measurements, and the effect of iron and ballast minerals on the strength and efficiency of the biological carbon pump. This study documents the design and deployment of a neutrally buoyant sediment trap (PELAGRA). In the north-east Atlantic organic carbon fluxes were measured using this new technology and compared to indirect estimates of export based on 234Th and nutrient budgets. The vertical fluxes of 234Th into the traps were less than those estimated from the 234Th water column budget, which is interpreted to be the result of previous export events removing 234Th from the water column and the lateral advection of gradients of total 234Th/238U disequilibria confounding the Eulerian budgeting approach adopted. Successful simultaneous deployments in July 2006 at different depths provided a direct measurement of the attenuation of flux with depth, which at 1.8 is substantially greater than the canonical value of 0.856. PELAGRA deployments in the Southern Ocean were conducted as part of the CROZEX project, which examined the role of iron supply on bloom dynamics and subsequent export. Using a mass balance approach to account for the seasonal depletion of dissolved silica acid in surface waters and Si fluxes from the euphotic zone, potential surface export(100m) of organic carbon from +Fe bloom area was estimated to be in the order of 11-15 g C m-2, which is higher than previous estimates obtained from artificial fertilisation experiments. The issue of temporal decoupling between production and export processes was addressed by employing retrospective estimates of production. Particle export efficiency in the +Fe region to the north of the plateau (25-70%) was higher than similar estimates in the –Fe region (11-20%). Diatom size was well correlated with a range of calculated export ratios(100m). The main diatoms involved in the export from the surface were E. Antarctica in the +Fe region and F. kerguelensis in the –Fe region. E. Antarctica fluxes also dominated deep-water (3000m) diatom fluxes in the +Fe region, and its importance is attributed to the regions proximity to the Crozet Islands, where resting spores and dissolved iron are advected into the bloom area during the winter. Deep-water carbon fluxes measured to the south of the plateau. Deep-water carbon fluxes measured south of the plateau (0.09 g C m-2 yr-1) are consistent with previous measurements in a similar environment. In the +Fe region to the north, deep water fluxes were 0.4 g C m-2 yr-1 indicating that natural iron fertilisation can increase the strength of the biological carbon pump by a factor of 4. Comparison of fluxes with satellite-derived productivity also suggests that the efficiency of the biological pump in transferring organic carbon to the deep-ocean is increased by a factor of 3 in the presence of iron. The flux and composition of amino acids, in relation to the dominant mineral phases that comprised the particulate flux in the NE Atlantic and the Southern Ocean was also examined. The fraction of carbon that could be accounted for by the total hydrolysable amino acids varied very little (20-30%) with sample composition. Protein amino acids were used to quantify the degradation state of the settling particulate material. Specific amino acids seem to infer diatomaceous rather than calcareous as the dominant organic matter source. Multiple linear regression analysis reveals that mineral fluxes can only explain a very small amount of the variability in amino acid composition, which does not support previous hypotheses that relate mineral fluxes and organic carbon fluxes through the differential protective capacity of various mineral phases. List of Contents 1 Introduction 1 1.1 Background 1 1.2 The biological carbon pump 3 1.3 Present uncertainties in our knowledge 5 1.3.1 Vertical attenuation of sinking particle fluxes in the 5 sub-surface ocean 1.3.2 The ballast theory 6 1.3.3 Impact of iron on carbon export 7 1.4 The Crozet Natural Iron Bloom and Export Experiment 8 1.5 Study areas 8 1.5.1 North-East Atlantic: PAP 8 1.5.2 Southern Ocean: Crozet Islands 9 1.6 Objectives 10 1.7 Structure of thesis 11 1.8 Publications 12 2 Particle export from the euphotic zone: Estimates using a novel 14 drifting sediment trap, 234Th, and new production Data 15 Abstract 16 2.1 Introduction 17 2.1.1 Hydrodynamics 18 2.1.2 Swimmers 19 2.2 Methods 20 2.2.1 The PELAGRA trap 20 2.2.1.1 Sediment trap components 23 2.2.1.2 Compressibility and coefficient of thermal 24 expansion 2.2.1.3 Ballasting 24 2.2.1.4 Measurements during cruises 25 2.2.2 Nutrients 25 2.2.3 Primary productivity (14C) 26 2.2.4 New and regenerated production (15N) 26 2.2.5 Export flux
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