Who: Ruth Musgrave

Dalhousie University

What: Internal tides and mixing at the continental shelf break

Internal tides at the coast can take the form of coastal trapped waves, propagating along the shelfbreak at both subinertial and superinertial frequencies. In this talk I will discuss the importance of mixing at the coast, then describe the nature of these waves and their influence on mixing with examples from observations and numerical models. At the end I will briefly talk about my planned research over the next few years at Dalhousie University.

When: Friday, October 25, 2019

Where: 10am, Needler Boardroom, Bedford Institute of Oceanography, Dartmouth, Nova Scotia

Who: Mathieu Dever

WHOI and Visiting Postdoctoral Fellow at Dalhousie University

What: What the Flux? On the Connectivity between Upper Ocean and the Interior at Submesoscales

Export flux of particulate organic matter from the euphotic zone to the ocean interior is traditionally viewed as a one-dimensional process driven by large, faster-sinking, particles raining down the water column. A fast-growing body of literature on ocean dynamics at scales ranging from 0.1-10 km (submeso-scales) highlights the presence of significant vertical currents O(10-100 m/day), where the flow becomes unbalanced, leading to an vertical ageostrophic recirculation.

In our work, we investigate the impact of the complex three-dimensional ocean circulation at submeso-scales on vertical fluxes of particles, as a function of particle sinking velocities. Using a process-oriented numerical model, we reveal that the role played by slow- and non-sinking particles is underestimated when quantifying vertical fluxes. The impact of remineralization in modulating the respective contributions of particle size-classes to the total vertical flux is also studied using a simple remineralization scheme, leading to unexpected and somewhat counter-intuitive conclusions.

In an effort to collect in-situ observations of the highlighted processes, we developed a bio-physical underway profiler called the EcoCTD. A quick introduction to the instrument and its potential for observing submesoscale processes are also featured in the presentation.

When: Friday, October 11, 2019

Where: 10am, Needler Boardroom, Bedford Institute of Oceanography, Dartmouth, Nova Scotia

Who: Uriel Zajaczkovski

What: Eddies in the Southern Ocean: an overview of generation mechanisms, energy sources and propagation dynamics

Satellite altimetry and output from an assimilating numerical model suggests that the generation of relatively large amplitude eddies is not a ubiquitous feature of the Southern Ocean but rather a phenomenon that is constrained to five isolated, well-defined hotspots. These hotspots are located downstream of major topographic features (where standing meanders enhance baroclinic instability) and in regions of elevated levels of available potential energy.

The eddy field in the Southern Ocean has two distinct propagation regimes. North and south of the Antarctic Circumpolar Current (ACC), eddies propagate westward with a mean meridional drift directed poleward for cyclonic eddies and equatorward for anticyclonic eddies. However eddies formed within the boundaries of the ACC have an effective eastward propagation with respect to the mean deep ACC flow, and the mean meridional drift is reversed, with warm-core anticyclonic eddies propagating poleward and cold-core cyclonic eddies propagating equatorward. This circulation pattern drives downgradient eddy heat transport, which could potentially transport a significant fraction of the net poleward ACC eddy heat flux.

When: Friday, October 4, 2019

Where: 10am, Needler Boardroom, Bedford Institute of Oceanography, Dartmouth, Nova Scotia