Check out these internal waves

Dispatch from the R/V Oceanus

Tow-yo sampling is not the most invigorating of field work. It involves watching a screen and calling out depths every few minutes as the CTD moves up and down in the water column. This continues for hours on end (our October 5th sampling lasted for eight hours straight).

To fight against the inevitable hebetude, we have all adopted our own strategies. Steve likes to make up rhymes. Maddie drinks espresso. Dean watches the live CTD temperature and salinity plots and ponders the oceanographic processes behind them. Personally, I like to save a slice of pie from dinner and eat it very very slowly.

The good news is that the monotony is worth it. The results of our recent tow-yo survey on October 5th captured an internal wave propagating up the shelf, visible in the series of plots below. The plots show temperature over depth along the inner and mid-shelf for four consecutive transects. As you can see in the plots, the internal wave is evident moving along the sharp temperature interface. The wave moves up the shelf before flattening out into a surge as it nears shore. See also how the wave displaces the warm pocket of nearshore water towards the west (best seen by comparing plots 2 and 3). In the last two plots, you can see the next shore-ward propagating internal wave making an appearance.

Something else to note is the seasonal characteristics of the mixed layer. The upper layer is very well mixed and homogeneous in temperature down to about 20 meters. These plots are quite a contrast to the profiles from September, which were stratified throughout the water column and lacked a mixed layer. In this case, the increase in wind must be the culprit. We have certainly been feeling the effects of the windy weather on-board.

We plan to sample more internal waves and other interesting features with the tow-yo in the days ahead. We will also increase our sampling to a continuous 26 hours. We hope a longer record will help us better resolve the waves’ propagation and serve as a valuable addition to the remote sensing efforts and mooring array data. It might also mean that we’ll need more pie.

– Jenessa Duncombe and the R/V Oceanus team

Figures courtesy of Steve Pierce