Winter 2020

Winter 2020 Seminars

A-340  Earth & Marine Sciences Building
Fridays, 10:40 a.m. - 11:45 p.m. (unless otherwise noted*)

Seminar Coordinator: Pratigya Polissar

For disability-related accommodations: call (831) 459-4730 or email Rondi Robison

 


    January 10

  • Leah Johnson, Brown University

    Lagrangian evolution of a submesoscale front
    A wealth of research in the past decade has unveiled the importance of small fronts in the upper ocean buoyancy budget, yet process study type observations are rare due to the challenges of resolving the relevant spatial and temporal scales. Here, a neutrally buoyant, subsurface Lagrangian float was deployed in a small mixed layer front within the California Current System as part of the ONR AESOP program. Its trajectory was acoustically tracked, allowing the region surrounding the drifting float to be intensely surveyed by a ship towing a Triaxus profiler. This Lagrangian approach provides uniquely detailed measurements of the frontal structure and evolution within and below the boundary layer. Initially, downfront winds incite mixing and the float repeatedly traverses the boundary layer. As winds relax and vigorous mixing subsides, the system enters a different dynamical regime as the front develops an overturning circulation associated with large vertical velocities that ultimately tilt isopycnals over and stratify the upper ocean within a day. A buoyancy flux scaling approach (commonly used with observations to isolate dominant frontal dynamics) fails as most scalings collapse to similar values in this parameter space. Instead, a thorough account and analysis reveal evidence that wind driven inertial motions, boundary layer friction and frontal instabilities work in concert to dictate the evolution of the front.

     


  • January 17

  • No Seminar


  • January 24

  • Phoebe Lam, UC Santa Cruz

    Unexpected iron cycling at the Peru Margin

    The GP16 Eastern Pacific Zonal Transect cruise from Peru to Tahiti in 2013 along 12-15°S crossed the large eastern tropical South Pacific oxygen deficient zone (ODZ) in the eastern half of the transect, which was expected to be an important source of dissolved iron into the ocean interior.  Contrary to expectations, there was no significant iron plume in the heart of the ODZ around 250 m that extended beyond the coastal margin, despite the ODZ penetrating several thousand of kilometers into the interior.  Surprisingly, a deep coastal iron plume in oxygenated waters centered around 2000 m was observed to penetrate >1000 km into the interior. In this talk, I examine the reasons behind the unexpected high Fe from the oxygenated deep slope relative to the more reducing ODZ above. 


  • January 31

  • Adi Torfstein, Institute of Earth Sciences, Hebrew University, Jerusalem, and InterUniversity Institute for Marine Sciences, Eilat, Israel

    The interplay between dust, export production and seawater compositions in the oligotrophic Gulf of Aqaba, northern Red Sea

    Real time observations of particulate fluxes, their compositions, related biogeochemical cycles and the distribution patterns of trace metals in deep open ocean waters are extremely rare, and more so in the context of continuous, highly resolved records. This observational gap, that largely stems from logistical difficulties maintaining sampling campaigns in distal oceanic settings, hampers our ability to fully understand fundamental aspects of the marine environment.
     
    The Gulf of Aqaba (GOA), northern Red Sea, is a deep oligotrophic water body surrounded by hyper-arid deserts with no major tributaries, limiting terrigenous influxes to surface waters, except for seasonal dust storms. Importantly, the northern GOA is highly accessible and therefore provides a unique opportunity to study the dynamics and impact of abrupt perturbations such as dust storms and biological blooms.
     
    In this talk I will present coeval, multi-annual, time series from the GOA of atmospheric dust loads, bulk and export production particulate fluxes (based on sediment traps), and dissolved trace metal perturbations. The results are used to quantify the rate and magnitude of seasonal and short term perturbations associated with dust storms, fluvial episodes and bottom resuspension events. 

  • February 7

  • Ondřej Prášil, The Czech Academy of Sciences

    How modelling can stimulate our understanding of ecophysiology of diazotrophic cyanobacteria

    Recently we have applied physiological cell flux models to field and laboratory data on various experiments with diazotrophic cyanobacteria, mostly with Crocosphaera. In my talk I will show how relatively simple modelling of existing data can provide new mechanistic and quantitative information about ecophysiology of diazotrophs. 

    Specifically, I plan to provide few examples on: i) how the ability to fix nitrogen even in the presence of ammonium gives Crocosphaera competitive advantage over non-nitrogen-fixing phytoplankton; ii)  how heterogeneous rates of N2 fixation in unicellular diazotroph populations confer them an energetic advantage and allow to expand their ecological niche; iii) how Crocosphaera uses different O2 management strategies to maintain microanaerobic environment for N2 fixation; iv) the importance of C transfer from the host diatom to symbiotic heterocyst-forming diazotrophs and its role in supporting the required growth and N2-fixing activity of the diatom-diazotroph association.


  • February 14

  • Nicole Shibley, Yale

    Inferring Mixing from Echosounder Observations of Double-Diffusive Staircases in the Arctic Ocean

    Double-diffusive convection is a small-scale convective mixing process that may occur in the ocean where temperature and salinity both increase with depth. In the interior Arctic Ocean, this process is widely present and is responsible for transporting heat upwards to the overlying sea ice cover. In this talk, I will show how acoustic observations may be used to infer mixing levels associated with double diffusion and to understand the persistence of double diffusion in a setting of weak background turbulence. 


  • February 21

  • No Seminar


  • February 26

  • Ari Friedlaender, UC Santa Cruz

    Using top predators and integrative approaches to study ocean ecosystem structure, function, and health

    Advances in biologging and ocean sensing technology can now be integrated to enhance our understanding of the structure, function, and conservation needs of marine ecosystems.  The distribution of large marine predators can be used to indicate where emergent properties of ocean ecosystems organize to create enhanced primary and secondary productivity and complete food webs.  By evaluating the foraging behavior and habitat use of top predators we can gain remarkable insights as to the structure and function of key environmental parameters across a range of spatial and temporal scales, and this information can be used to not only better understand how top predators utilize habitat but also to help identify areas of ecological and conservation importance.   Using examples from California and Antarctica, I will present new concepts and results from collaborative ocean studies in my lab and how these can integrate with the current Ocean Sciences Department to augment its scope of expertise and breadth of knowledge, opportunities for collaboration among labs, and the number and diversity of students being taught/mentored in the department.


  • February 28

  • Stefan Koenigstein, UC Santa Cruz and NOAA Fisheries

    Climate change and the resilience of marine fish stocks, food webs, and human users

    Increasing human pressures and intensifying climate change can have severe impacts on marine organisms and ecosystems, and on human users such as fisheries and tourism. Ecosystem models can be used to investigate how the dynamics of marine fish populations and top predators are shaped by environmental drivers, food web interactions, and fisheries. 
    I will present work from the California Current, the Barents Sea (Norway), and the Northern Humboldt Current (Peru). The developed models integrate field data, lab experiments, and perceptions and adaptation options of local user groups, to assess the responses of marine systems to interacting drivers under current conditions and future changes. Looking further into societal adaptation strategies for strengthening resilience to global change, I will finally present an ocean education game for high schools which integrates a wide range of ocean uses and impacts.

  • March 6

  • OS Open House


  • March 13

  • Anela Choy, UCSD Scripps Institution of Oceanography

    Food web oceanography in deep-pelagic Pacific ecosystems

    The oceanic water column occupies Earth's largest living space and is fueled almost entirely by primary production from sunlit surface waters. Diverse assemblages of animals inhabit epipelagic, mesopelagic, and bathypelagic depths and form complex food webs that stretch and connect energy flow across distant depth horizons. I will present insights gained into the structure and function of these food webs using a diversity of approaches including in situ observation (with remotely operated vehicles), gut content analysis, and biochemical trophic tracers (stable isotopes and trace metals). I will also present evidence of anthropogenic change impacting deep-pelagic ecosystems, which are critical to sustaining fisheries, climate regulation, and ecosystem services for global societies.