Skip to main content
eScholarship
Open Access Publications from the University of California

Scholarly Works (30 results)

  • Thesis
  • Peer Reviewed
UC Santa Cruz Electronic Theses and Dissertations (2012)

Eastern Boundary Current systems, running along the west coasts of Africa and the Americas, are among the most biologically productive oceanic ecosystems. Their disproportionately large contributions to global marine primary productivity (photosynthesis) and fish catch are supported by upwelling of deep, nutrient rich water, a process driven by the interaction of surface winds and Earth's rotation. Upwelling in these systems may be forced by two mechanisms: equatorward winds at the coastal boundary (coastal divergence), or a cross-shore gradient in the magnitude of winds (wind stress curl). Though bulk estimates of upwelled volume and the individual contributions of coastal divergence and wind stress curl have been estimated, their roles in regulating productivity remain unclear. Similarly, while nutrient supply from upwelling has been measured or modeled in specific regions, its dependence on variability in physical factors including topography, stratification, and latitude has not been adequately addressed. The measurement of primary productivity itself is laborious and complicated in situ, and satellite-borne ocean color sensors currently represent our best option for obtaining the large-scale estimates needed to constrain global carbon budgets. However, after over a quarter century of satellite primary productivity model development, performance has improved little.

The research in this dissertation employs a suite of cutting edge oceanographic tools - computer models, satellite sensors, and autonomous underwater platforms - to elucidate controls on primary productivity and its measurement in coastal upwelling systems. First, an idealized numerical model is used to evaluate the respective roles of stratification, continental shelf topography, latitude, and wind stress magnitude on upwelling source depth and nutrient delivery to the sunlit surface layer (Chapter 1). Next, this analysis is extended to investigate the impact of nearshore reduction in surface wind stress, a poorly constrained process with significant implications for bottom-up control of phytoplankton growth (Chapter 2). Finally, an extensive record of shipboard observations off the California Coast is analyzed to evaluate limitations on primary productivity estimation, and synergistic use of satellites with autonomous underwater gliders is identified as fertile ground for improvement (Chapter 3).

    Cover page: Controls on Primary Productivity and its Measurement in Coastal Upwelling Systems
    • Article
    • Peer Reviewed
    UC Santa Cruz Previously Published Works (2016)
    In Eastern Boundary Current systems, wind-driven upwelling drives nutrient-rich water to the ocean surface, making these regions among the most productive on Earth. Regulation of productivity by changing wind and/or nutrient conditions can dramatically impact ecosystem functioning, though the mechanisms are not well understood beyond broad-scale relationships. Here, we explore bottom-up controls during the California Current System (CCS) upwelling season by quantifying the dependence of phytoplankton biomass (as indicated by satellite chlorophyll estimates) on two key environmental parameters: subsurface nitrate concentration and surface wind stress. In general, moderate winds and high nitrate concentrations yield maximal biomass near shore, while offshore biomass is positively correlated with subsurface nitrate concentration. However, due to nonlinear interactions between the influences of wind and nitrate, bottom-up control of phytoplankton cannot be described by either one alone, nor by a combined metric such as nitrate flux. We quantify optimal environmental conditions for phytoplankton, defined as the wind/nitrate space that maximizes chlorophyll concentration, and present a framework for evaluating ecosystem change relative to environmental drivers. The utility of this framework is demonstrated by (i) elucidating anomalous CCS responses in 1998-1999, 2002, and 2005, and (ii) providing a basis for assessing potential biological impacts of projected climate change.
      Cover page: Optimal Environmental Conditions and Anomalous Ecosystem Responses: Constraining Bottom-up Controls of Phytoplankton Biomass in the California Current System.
      • Article
      • Peer Reviewed
      UC San Diego Previously Published Works (2018)
      Oceanic fronts are sites of increased vertical exchange that are often associated with increased primary productivity, downward flux of organic carbon, and aggregation of plankton and higher trophic levels. Given the influence of fronts on the functioning of marine ecosystems, an improved understanding of the spatial and temporal variability of frontal activity is desirable. Here, we document changes in the frequency of sea-surface fronts and the surface concentration of chlorophyll-a (Chla) in the California Current System that occurred during the Northeast Pacific anomalous warming of 2014–2015 and El Niño of 2015–2016, and place those anomalies in the context of two decades of variability. Frontal frequency was detected with the automated histogram method using datasets of sea-surface temperature (SST) and Chla from multiple satellite sensors. During the anomalous 2014–2016 period, a drop in the frequency of fronts coincided with the largest negative Chla anomalies and positive SST anomalies in the whole period of satellite observations (1997–2017 for Chla and 1982–2017 for SST). These recent reductions in frontal frequency ran counter to a previously reported increasing trend, though it remains to be seen if they represent brief interruptions in that trend or a reversal that will persist going forward.
        Cover page: CCE1: Decrease in the frequency of oceanic fronts and surface chlorophyll concentration in the California Current System during the 2014–2016 northeast Pacific warm anomalies
        • Article
        Impacts and Future Directions (2022)
        Transitioning from graduate student roles in academia to professional careers in industry and government affords ISEE’s Professional Development Program (PDP) alumni the opportunity to apply lessons and techniques learned at the PDP to new environments with new goals. In mission-focused government roles, PDP alumni apply their expertise in inquiry-style teaching to mentor junior staff and develop projects that meet governmental requirements, while preserving STEM learner identities. Alumni find that the principles of inquiry-style teaching have applicability across professional development spectrums — from mentoring high school interns through training postdoctoral researchers and managing teams of diverse career stages. In industry, where fast-paced corporate goals drive innovation, alumni have found that PDP principles in developing explicit content and practice learning outcomes have helped them develop unique roles within their companies. Additionally, across both industry and government roles, all PDP alumni on this panel report that PDP’s focus on leadership development, effective meeting strategies, and inclusive management practices have readied them for their post-academia careers.
          Cover page: Applying the PDP to Government and Industry Career PathwaysCreative Commons 'BY' version 4.0 license
          • Article
          • Peer Reviewed
          UC Santa Cruz Previously Published Works (2020)
          Spatial management is a valuable strategy to advance regional goals for nature conservation, economic development, and human health. One challenge of spatial management is navigating the prioritization of multiple features. This challenge becomes more pronounced in dynamic management scenarios, in which boundaries are flexible in space and time in response to changing biological, environmental, or socioeconomic conditions. To implement dynamic management, decision-support tools are needed to guide spatial prioritization as feature distributions shift under changing conditions. Marxan is a widely applied decision-support tool designed for static management scenarios, but its utility in dynamic management has not been evaluated. EcoCast is a new decision-support tool developed explicitly for the dynamic management of multiple features, but it lacks some of Marxans functionality. We used a hindcast analysis to compare the capacity of these 2 tools to prioritize 4 marine species in a dynamic management scenario for fisheries sustainability. We successfully configured Marxan to operate dynamically on a daily time scale to resemble EcoCast. The relationship between EcoCast solutions and the underlying species distributions was more linear and less noisy, whereas Marxan solutions had more contrast between waters that were good and poor to fish. Neither decision-support tool clearly outperformed the other; the appropriateness of each depends on management purpose, resource-manager preference, and technological capacity of tool developers. Article impact statement: Marxan can function as a decision-support tool for dynamic management scenarios in which boundaries are flexible in space and time.
            Cover page: Decision-support tools for dynamic management.
            • Article
            • Peer Reviewed
            UC Santa Cruz Previously Published Works (2018)
            Incidental catch of nontarget species (bycatch) is a major barrier to ecological and economic sustainability in marine capture fisheries. Key to mitigating bycatch is an understanding of the habitat requirements of target and nontarget species and the influence of heterogeneity and variability in the dynamic marine environment. While patterns of overlap among marine capture fisheries and habitats of a taxonomically diverse range of marine vertebrates have been reported, a mechanistic understanding of the real-time physical drivers of bycatch events is lacking. Moving from describing patterns toward understanding processes, we apply a Lagrangian analysis to a high-resolution ocean model output to elucidate the fundamental mechanisms that drive fisheries interactions. We find that the likelihood of marine megafauna bycatch is intensified in attracting Lagrangian coherent structures associated with submesoscale and mesoscale filaments, fronts, and eddies. These results highlight how the real-time tracking of dynamic structures in the oceans can support fisheries sustainability and advance ecosystem-based management.
              Cover page: Fisheries bycatch risk to marine megafauna is intensified in Lagrangian coherent structures.
              • Article
              • Peer Reviewed
              UC Santa Cruz Previously Published Works (2022)
              Marine heatwaves (MHWs)-periods of exceptionally warm ocean temperature lasting weeks to years-are now widely recognized for their capacity to disrupt marine ecosystems1-3. The substantial ecological and socioeconomic impacts of these extreme events present significant challenges to marine resource managers4-7, who would benefit from forewarning of MHWs to facilitate proactive decision-making8-11. However, despite extensive research into the physical drivers of MHWs11,12, there has been no comprehensive global assessment of our ability to predict these events. Here we use a large multimodel ensemble of global climate forecasts13,14 to develop and assess MHW forecasts that cover the worlds oceans with lead times of up to a year. Using 30 years of retrospective forecasts, we show that the onset, intensity and duration of MHWs are often predictable, with skilful forecasts possible from 1 to 12 months in advance depending on region, season and the state of large-scale climate modes, such as the El Niño/Southern Oscillation. We discuss considerations for setting decision thresholds based on the probability that a MHW will occur, empowering stakeholders to take appropriate actions based on their risk profile. These results highlight the potential for operational MHW forecasts, analogous to forecasts of extreme weather phenomena, to promote climate resilience in global marine ecosystems.
                Cover page: Global seasonal forecasts of marine heatwaves.
                • Article
                • Peer Reviewed
                UC Santa Cruz Previously Published Works (2019)
                In terrestrial systems, the green wave hypothesis posits that migrating animals can enhance foraging opportunities by tracking phenological variation in high-quality forage across space (i.e., resource waves). To track resource waves, animals may rely on proximate cues and/or memory of long-term average phenologies. Although there is growing evidence of resource tracking in terrestrial migrants, such drivers remain unevaluated in migratory marine megafauna. Here we present a test of the green wave hypothesis in a marine system. We compare 10 years of blue whale movement data with the timing of the spring phytoplankton bloom resulting in increased prey availability in the California Current Ecosystem, allowing us to investigate resource tracking both contemporaneously (response to proximate cues) and based on climatological conditions (memory) during migrations. Blue whales closely tracked the long-term average phenology of the spring bloom, but did not track contemporaneous green-up. In addition, blue whale foraging locations were characterized by low long-term habitat variability and high long-term productivity compared with contemporaneous measurements. Results indicate that memory of long-term average conditions may have a previously underappreciated role in driving migratory movements of long-lived species in marine systems, and suggest that these animals may struggle to respond to rapid deviations from historical mean environmental conditions. Results further highlight that an ecological theory of migration is conserved across marine and terrestrial systems. Understanding the drivers of animal migration is critical for assessing how environmental changes will affect highly mobile fauna at a global scale.
                  Cover page: Memory and resource tracking drive blue whale migrations.
                  • Article
                  • Peer Reviewed
                  UC Santa Cruz Previously Published Works (2023)
                  Forecasting weather has become commonplace, but as society faces novel and uncertain environmental conditions there is a critical need to forecast ecology. Forewarning of ecosystem conditions during climate extremes can support proactive decision-making, yet applications of ecological forecasts are still limited. We showcase the capacity for existing marine management tools to transition to a forecasting configuration and provide skilful ecological forecasts up to 12 months in advance. The management tools use ocean temperature anomalies to help mitigate whale entanglements and sea turtle bycatch, and we show that forecasts can forewarn of human-wildlife interactions caused by unprecedented climate extremes. We further show that regionally downscaled forecasts are not a necessity for ecological forecasting and can be less skilful than global forecasts if they have fewer ensemble members. Our results highlight capacity for ecological forecasts to be explored for regions without the infrastructure or capacity to regionally downscale, ultimately helping to improve marine resource management and climate adaptation globally.
                    Cover page: Ecological forecasts for marine resource management during climate extremes.
                    • Article
                    • Peer Reviewed
                    UC Santa Cruz Previously Published Works (2022)
                    Ensuring the long-term sustainability of tuna, billfish, and other transboundary fisheries resources begins with data on the status of stocks, as well as information concerning who catches what fish, when, where, and how. Despite recent improvements in fisheries monitoring and surveillance, such dynamics remain poorly understood across the high seas. Here we delineate and describe pelagic longline activity in the Pacific Ocean using a framework that integrates descriptive vessel information and tracking data with species-specific catch reports. When parsed by distinct vessel behaviors and attributes, disaggregated fisheries data highlight the existence of multi-national, multi-specific (i.e., targeting multiple species) fishing fleets, many of which target waters that span more than one management area. Our findings emphasize the need for increased coordination across regional and sub-regional governance bodies and suggest that effective and equitable management of the sector may require efforts to move beyond single-species, single-area controls and operational distinctions based primarily on vessel flag and/or gear type alone.
                      Creative Commons 'BY-NC-ND' version 4.0 license
                      Top