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UC San Diego UC San Diego Electronic Theses and Dissertations UC San Diego UC San Diego Electronic Theses and Dissertations Title Phytoplankton in Surface Ocean Fronts : Resolving Biological Dynamics and Spatial Structure Permalink https://escholarship.org/uc/item/61r5x33r Author De Verneil, Alain Joseph Publication Date 2015 Peer reviewed|Thesis/dissertation eScholarship.org Powered by the California Digital Library University of California UNIVERSITY OF CALIFORNIA, SAN DIEGO Phytoplankton in Surface Ocean Fronts: Resolving Biological Dynamics and Spatial Structure A dissertation submitted in partial satisfaction of the requirements for the degree Doctor of Philosophy in Oceanography by Alain Joseph de Verneil Committee in charge: Professor Peter J.S. Franks, Chair Professor Jorge Cortés Professor Michael R. Landry Professor Mark D. Ohman Professor Daniel L. Rudnick 2015 Copyright Alain Joseph de Verneil, 2015 All rights reserved. The Dissertation of Alain Joseph de Verneil is approved, and it is acceptable in quality and form for publication on microfilm and electronically: Chair University of California, San Diego 2015 iii DEDICATION To my family, Mama, Papa and Mary-Pat, Christine and Matt, Mamy and Papy, Paul Dano, and Claude duVerlie iv TABLE OF CONTENTS Signature Page .................................................................................................................iii Dedication........................................................................................................................ iv Tables of Contents ............................................................................................................ v List of Figures................................................................................................................. vii Acknowledgements........................................................................................................... x Vita................................................................................................................................. xiv Abstract of the Dissertation ............................................................................................ xv Chapter 1. Introduction ..................................................................................................... 1 1.1. Flows at a Front.............................................................................................. 2 1.2.Thesis Outline ............................................................................................... 11 References........................................................................................................... 13 Chapter 2. A pseudo-Lagrangian method for remapping ocean biogeochemical tracer data: Calculation of Net Chl-a growth rates ................................................................... 18 Abstract ............................................................................................................... 18 2.1. Introduction.................................................................................................. 19 2.2. Data .............................................................................................................. 23 2.3. Pseudo-Lagrangian Method ......................................................................... 29 2.4. Calculation of Net Rates of Change of Chl-a .............................................. 37 2.5. Discussion .................................................................................................... 48 2.6. Conclusions.................................................................................................. 51 Acknowledgements............................................................................................. 55 References........................................................................................................... 56 Chapter 3. Fine-Scale Vertical and Horizontal Layers of Salinity and Chlorophyll-a Fluorescence at a Front: Formation by Cross-Frontal Vertical Shear ............................ 63 Abstract ............................................................................................................... 63 3.1. Introduction.................................................................................................. 64 3.2. Data .............................................................................................................. 65 3.3. Evidence of fine structure and possible mechanisms................................... 69 3.4. Diagnosis of cross-frontal shear................................................................... 79 3.5. Biological Consequences and Conclusions.................................................. 83 Acknowledgements............................................................................................. 85 References........................................................................................................... 86 v Chapter 4. Submesoscale Mixed Layer and Symmetric Instabilities: Physical Dynamics and Biological Responses ............................................................................................... 90 Abstract ............................................................................................................... 90 4.1. Introduction.................................................................................................. 90 4.2. Submesoscale phenomena, terminology, and set-up ................................... 92 4.3. Symmetric Instability................................................................................. 107 4.4. Mixed Layer Instability.............................................................................. 121 4.5. Conclusions................................................................................................ 127 Acknowledgements........................................................................................... 129 References......................................................................................................... 130 Chapter 5. Conclusions................................................................................................. 136 Measuring biological rates in the ocean............................................................ 136 Recognizing fine-scale variability .................................................................... 140 Diagnosing short-term frontal dynamics........................................................... 141 References......................................................................................................... 144 vi LIST OF FIGURES Figure 1.1. (a) A geostrophic flow arises between water masses with two different densities, separating two phytoplankton assemblages. (b) A geostrophic current has a maximum magnitude at the surface, and decreases with depth. This creates shear, which alters the horizontal and vertical distribution of an initially............................................. 4 Figure 1.2. (a) Plan view of an intensifying front. Geostrophic currents (white arrows) advect water in the x direction. The density gradient sharpens in the x direction, causing the geostrophic currents to accelerate. Regions of positive and negative divergence of the Qg are shown in white and black contours, respectively. (b)............................................ 7 Figure 1.3. Plan views of a meandering front. (a) The horizontal density gradient (black arrows) points to the dense side of the front. Regions of positive and negative ∇2ψ are indicated in white. The horizontal gradient of ∇2ψ is denoted in red. (b) Regions of downwelling and upwelling, shown in white and black................................................... 9 Figure 2.1. E-front. Aviso Sea surface height anomaly average for (a)€ Survey 1 (July 29- August 3) and (b) Survey 2 (August€ 21 -25, 2012). Black line shows the location and direction of the survey relative to the frontal feature...................................................... 24 Figure 2.2. Objective maps of Density (a,c) and Chlorophyll-a fluorescence (b,d) for Surveys 1 and 2, at 27 m depth. White arrows in (a,c) indicate the horizontal currents, displayed at one-fourth resolution. Black contours in (b,d) show the streamlines of the flow. Note the strong, stationary frontal feature in both................................................. 27 Figure 2.3. Pseudo-Lagrangian procedure. (a) Streamlines of flow are calculated from the survey data. Observations on the same streamline are identified. (b) Flow direction is reversed, and the survey time is reversed. (c) Positions are back-advected for a time tobs from their sampling, to arrive at their inferred initial ..................................................... 33 Figure 2.4. Sequential steps in the pseudo-Lagrangian transformation, showing objectively mapped Chl-a fluorescence with the initial survey distribution completed after 3.45 days (a), moving back in time to (b) 2.57, (c) 0.87, and (d) 0 days after the survey began. Black lines are the streamlines; red line is the ship track; .................................. 35 Figure 2.5. Rate calculation method. Starting with two observations connected by a streamline (a), we forward-advect the first observation (b) along its streamline until the ship collects the second observation on the same streamline (c). The first water parcel’s new position X" is used with the objective map of tracer.............................................. 38 Figure 2.6. Calculated net Chl-a growth rates for Survey 2. Red dots indicate the
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