The coastal ocean most directly links deep water to human society, and as such has long been the subject of fascination, study, and appreciation. The small-scale processes our group focuses on play a dramatic role in the coastal ocean, setting the distribution of everything from pollutants to biologically essential nutrients that underlie the health of our fisheries and nearshore ecosystems.
Some of our work focuses on the role of so-called internal tide ‘solitons’ that are fairly ubiquitous in coastal areas. Many of our projects through the world involve study of internal waves (waves propagating not on the surface but on density interfaces within the ocean interior), often created by tidal flow over topography. When such waves propagate into increasingly shallow water, they often steepen up into very sharp, steep soliton trains. Though the primary action is sub-surface, near-surface convergences and divergences create the appearance of ‘slicks’ on the ocean surface that are often visible (e.g. this photo**). The full complexity of the sub-surface structure of such waves can be visualized with a new fiber optic temperature sensing system, innovative technology developed for this application by Rob Pinkel and Drew Lucas. An example of such measurements can be seen in Figures ** drew_fig1 and drew_fig3. (get captions from Drew for these).
Internal waves play a particularly complex role in the sharp and often deep canyons that are frequently found on the West Coast of North America. Amy Waterhouse led 2012 fieldwork with Ruth Musgrave that investigated internal tide breaking and associated turbulence in Eel Canyon, near Mendocino (http://journals.ametsoc.org/doi/10.1175/JPO-D-16-0073.1 and project website: https://sites.google.com/site/mixingatthemargins/blog). Closer to home, several group members have active projects in La Jolla Canyon, in our own backyard. Here large internal tides interact with mean flows and the sharp canyon bathymetry to greatly enhance the amount of turbulence, and turbulent upwelling of biologically essential nutrients within the canyon. We suspect this why La Jolla Canyon is oft observed to be a biological hot spot! (link to Jess C-G work?). Graduate student Maddie Hamann recently led a UC Ship Funds project to more closely study processes within LJ Canyon, and she is providing a figure ***. Complimenting that, Drew Lucas is maintaining a uniquely long-term wire-walker record within the Canyon (**Figure?). Do you want a link to the RBR real time data website here?
The complex interaction between coastal currents, their instabilities, internal waves, turbulence, and ecosystems is important not just in canyons, but throughout coastal California and around the world. Amy Waterhouse and Jen MacKinnon are participating in a large Office of Naval Research funded project to assess the interplay of these processes near Pt Sal California. Graduate student André Palóczy will be leading an affiliated UC Ship Funds project to focus on the role sub-mesoscale coastal current instabilities play in mediating cross-shelf exchange of heat, nutrients and pollutants. More information on that project can be found here: https://scripps.ucsd.edu/projects/innershelf/. Watch for updates as that fieldwork season arrives, September 2017.
CASE: Schematic of plume dispersal pathways in a complex, time-dependent environment.
The density of the plume as it reaches the surface is a function of the density in the ambient waters at the time of discharge. Since most mixing happens within meters from the discharge location, the near-bottom ambient temperature and salinity is of primary importance. The near-bottom temperature varies with the internal tide, implying time variability in the plume density.
On occasion, the surfacing plume can be cold enough (i.e. dense enough) and the adjacent, aged plume waters warm enough, that the surfacing plume waters can subduct and spread at depth (red and blue arrows on the right hand panel). In such circumstances, tracking lateral dispersion is complicated by the difficulty of measuring currents at depth along a particular trajectory. Thus the three-dimension environmental variability of the discharge location, as well as discharge/environment feedback, are critical to predicting plume dispersal.
Is there a DCM in your coffee?