Here is a plot of the upper 400 meters of the latest seaglider section off of Iquique (27 March – 07 April 2009, onshore to offshore track). On a hunch I plotted salinity contour lines on top of the oxygen (upper right) and backscattering (middle right) data. It seems that there is tight coupling between salinity and both O2 and bb. Before seeing these data, I would have guessed that variability in the deep oxycline would be driven by intrusions of water masses with different density and oxygen characteristics. Likewise with the bottom boundary of the intermediate depth scattering maximum. However, given what we see here, the story seems to be a bit more interesting than that! Why would salinity be more influential than density in regulating these distributions?
Re: density vs. salinity
Remember density is a dynamically active property; it needs to be stably stratified (i.e. light water above dense water). A corollary to this rule is that fluid likes to move along isopycnals rather than across, so intrusions move along isopycnals. This makes density a poor tracer. Salinity however has no such constraint (it affects density of course, but these affects can be compensated by temperature changes). I think in this case salinity is acting as a tracer for the low oxygen water mass.
Thanks for the explanation, Kipp. The number of years since my PO class are shamefully evident! Would love to get your impressions of the TS plots sometime.
Looks like you already got the answer to this one via the prof, Amanda, but I wonder if you’d see more similarities in distribution of oxygen and density if you shortened your density range from 24.0-26.5 to highlight more local density variations. Maybe, maybe not. Please enjoy my absolutely unsolicited free advice.
Thanks, Tristan. I’ll adjust my scale and let you know what I find. We encourage unsolicited advice around here – keep it coming! Oops, I guess that means that the advice is no longer “unsolicited.”
This is really cool to see. I’ve learned about all of these measurements in my marine biology classes at UC Santa Barbara, but I never knew exactly how they were taken. Thanks for sharing!
Glad you found us! We love hearing from visitors to the blog. BTW – I got my BS in Aquatic Biology from UCSB – go Gauchos!