Winter/Spring 2013


Observations of the Space-time Structure of Flow, Vorticity and Stress over Orbital-scale Ripples

Jenna Hare

Department of Oceanography
Dalhousie University

3:30 p.m., Thursday, January 17, 2013

Abstract: Results are presented from a laboratory investigation of the spatial and temporal structure at turbulence-resolving scales of the flow, vorticity and stress over equilibrium orbital-scale sand ripples. The ripples were created in 0.153 mm median diameter sand, at 10 s period and an excursion of 0.5 m, using the oscillating tray apparatus described in Hay et al. (JGR-Oceans, 2012). Vertical profiles of velocity above the bed were obtained at 40 Hz and 3 mm vertical resolution using a wide-band coherent Doppler profiler (MFDop). Through runs at different positions of the MFDop relative to a particular ripple crest, phase-averaged measures of the flow over a full ripple wavelength were obtained as a function of phase during the forcing cycle. These measurements are used to determine the formation of the lee vortex and the position of the point of reattachment. The evolution of the phase-averaged Reynolds stress and turbulent kinetic energy near the bed was also obtained.


No POMSS This Week

Thursday, January 24, 2013


Physical and Geotechnical Investigation of Sediment Remobilization Processes

Nina Stark

Department of Oceanography
Dalhousie University

3:30 p.m., Thursday, January 31, 2013

Abstract: Sediment remobilization processes have a high impact on the environment, society and economy. However, such processes are complex and highly variable in time and space. This presentation will give an insight into state-of-the-art methods and current results with regard to in-situ geotechnical and physical investigations of sediment remobilization processes in the coastal zone.


Components of extreme sea level: how are they changing?

Dr. Kevin Horsburgh

Head, Marine Physics and Ocean Climate Research Group
Natural Environment Research Council, UK

3:30 p.m., Thursday, February 7, 2013


Acoustic Detection of Double Diffusive Interfaces

Nick Dourado

Department of Oceanography
Dalhousie University

3:30 p.m., Thursday, February 14, 2013

Abstract: A general introduction to double diffusive convection (DDC), using a laboratory scale DDC model, will serve as the basis for a discussion of how acoustic backscatter measurements can be used to detect fluid microstructure in the ocean. This presentation will review laboratory observations of DDC using high-frequency broadband acoustics made by Andone Lavery and Tetjana Ross.


Title: TBA

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Institute

3:30 p.m., Thursday, February 21, 2013


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Institute

3:30 p.m., Thursday, February 28, 2013


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3:30 p.m., Thursday, March 7, 2013


Controlling errors in nearshore bathymetry using remote sensing and data assimilation

Greg Wilson

Oregon State University

3:30 p.m., Thursday, March 14, 2013


No POMSS This Week

C-DOGS

Thursday, March 21, 2013


Inter-species Discrimination of Cetacean Vocalizations with an Automated Aural Classifier

Carolyn Binder

Department of Oceanography
Dalhousie University

3:30 p.m., Thursday, March 28, 2013

Abstract: Passive acoustic methods are in widespread use to detect, classify and localize marine mammals; however, these passive sonar systems are often triggered by other transient sources, producing large numbers of false positives. In order to isolate the true detections and to positively identify marine mammals, large volumes of data are collected that need to be processed by a trained analyst. To reduce acoustic analyst workload, an automatic detector can be implemented with a high false positive rate. Detections from this then feed into an automatic classifier to both significantly reduce the number of false detections and classify the marine mammal species. This process requires the development of a classifier capable of performing inter-species classification. A prototype aural classifier has been developed at Defence R&D Canada that uses perceptual signal features which model the features employed by the human auditory system. The first part of this talk will focus on the results of applying the aural classifier to discriminate cetacean vocalizations from five species: North Atlantic right, humpback, bowhead, minke, and sperm whales. In the second part of the talk an experimental design for assessing the robustness of the perceptual features to propagation effects will be presented. Propagation effects on vocalizations from two of the previously studied species . bowhead and humpback whales . are investigated by comparing classification results for the original vocalizations to results obtained after vocalizations were retransmitted over ranges of 2 to 10 km. Additional insight is gained from transmission of synthetic bowhead and humpback vocalizations, designed to have features similar to the most important aural features for classification of bowhead and humpback vocalizations.


Reoccurrence of winter convection in the warming Labrador Sea

Igor Yashayaev

Bedford Institute of Oceanography

3:30 p.m., Thursday, April 4, 2013


A Tidal Energy Resource Assessment: Results and Challenges

Justine McMillan

Department of Oceanography
Dalhousie University

3:30 p.m., Thursday, April 11, 2013


No seminar this week

Thursday, April 18, 2013


Could marine mammals be acoustically detected at a tidal energy site?
(Synopsis of combined honours project in marine biology and oceanography)

Chloe Malinka

Department of Oceanography
Dalhousie University

3:30 p.m., Thursday, April 25, 2013

ABSTRACT: Passive acoustic monitoring for marine mammals at tidal energy developments requires an understanding of site-specific acoustic detection ranges. Since underwater sound is used as a tool for detecting marine mammal presence via their vocalizations, sounds mimicking that of marine mammals were projected to assess the feasibility of a marine mammal monitoring system at a proposed small-scale tidal energy site (Fundy Tidal Inc.) in Grand Passage, NS. Baseline ambient noise levels were determined, and methods of pseudo-sound reduction were explored. This work contributes to the future acoustic monitoring of marine mammal presence in the vicinity of the turbine, and will potentially aid in understanding interactions between marine mammals and in-stream turbines.


No seminar this week

Thursday, May 2, 2013


No seminar this week

Thursday, May 9, 2013


Downscaling Ocean Conditions: Initial Experiments with a Quasi-Geostrophic Ocean Model

Anna Katavouta

Department of Oceanography
Dalhousie University

3:30 p.m., Thursday, May 16, 2013


No seminar this week

Thursday, May 23, 2013


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Speaker

Institute

3:30 p.m., Thursday, May 30, 2013


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Institute

3:30 p.m., Thursday, June 6, 2013


Glider observations of internal waves and internal tides near Luzon Strait

Shaun Johnston

Scripps Institution of Oceanography
University of California at La Jolla

3:30 p.m., Thursday, June 13, 2013

Tidal flow through the Luzon Strait produces large internal waves that propagate westward into the South China Sea and eastward into the Pacific. Internal tidal energy fluxes were obtained from June-August 2011 from 5 time series stations by 2 underwater gliders in the South China Sea. Underwater gliders profiled every 2 hours to 500 m, which is deep enough given the shallow thermocline to compute mode-1 fluxes from vertical mode fits to tidal displacements and currents. Westward, mode-1 diurnal and semidiurnal fluxes exceeded 40 and 30 kW/m. To our knowledge, these flux observations are the first from both velocity and density measurements by gliders. Fluxes compare well with a mooring near a generation site in southern Luzon Strait and a regional model. Furthermore, the zonal-depth structure of the internal tide is obtained by binning measurements, which cover four spring-neap cycles and over 100 km along 20 degrees 39' N. Westward phase propagation is found for currents and displacements, while roughly constant phase is found along beams. Both these features of the phase suggest a narrow-banded internal tide.

Another set set of sustained observations was made by gliders from 7 overlapping missions, April 2007 through July 2008. A particular focus is high frequency internal waves, where the operational definition of high involves periods shorter than a glider profile taking 3-6 hours. Internal wave vertical velocity is estimated from measurements of pressure and glider orientation through two methods: (1) use of a model of glider flight balancing buoyancy and drag along the glider path, and (2) high pass filtering of the observed glider vertical velocity. By combining high frequency vertical velocities from glider flight with low frequency estimates from isopycnal depth variations between dives, a spectrum covering 5 decades of frequency is constructed. A map of the standard deviation of vertical velocity over the survey area shows decay from the Luzon Strait into the Pacific. The growth of high frequency vertical velocity with propagation into the South China Sea is observed through two two-week time series stations. The largest observed vertical velocities are greater than 0.2 m/s, and are associated with displacements approaching 200 m. The high frequency waves are observed at regular intervals of one day as they ride on the diurnal tidal internal waves generated in the Strait.


On Buoyancy Driven, Coastally-Trapped Currents:
Theory, scientific questions and proposed approach

Mathieu Dever

Department of Oceanography
Dalhousie University

3:30 p.m., Thursday, June 20, 2013

Abstract: Buoyancy driven, coastally-trapped currents usually exist when a large input of buoyant water is discharge into denser water (e.g. estuaries, fjords, straits). These currents can cover anything between 50 km (e.g. Delaware coastal current) and 2000 km (e.g. Alaska Coastal Current). Because of their contribution to cross-shelf dynamics and freshwater transport, buoyancy driven currents are key contributors to shelf dynamics. A review of the driving mechanisms of these currents and how they interact with wind forcing and bottom topography is provided. Since 2008, a large quantity of observations has been collected over the Scotian Shelf and across the Nova Scotia Current (NSC) as part of the Ocean Tracking Network project. Different platforms (gliders, ADCPs, CTDs,.) have been used, providing unprecedented spatial and temporal coverage. Based on these observations, 3 key scientific aspects are investigated: The role of wind forcing vs buoyancy driven motion within the NSC, anticyclonic eddies forming between the coast and the current creating a strong mesoscale flow in the opposite direction, and a possible technique to monitor the transport associated with the NSC. This presentation mainly focuses on the different approaches and methods proposed to study these phenomena and bring answers.