Category Archives: Drifters

A tale of two drifters

We have recovered all of our (SIO, Feddersen) instruments, and the fun of sorting out and QCing the data has begun, however, I thought I’d share a sweet tale of loss and love. We were fortunate to only leave 2 instruments at Pt Sal, drifter 23 and 24, although I do believe their fate may have always been intertwined. Their tale begins during experiment preparation during final drifter assembly, when drifters were being labeled with a sharpie: 1… 27 – then 23 and 24 were shipped to Pt Sal, right next to each other in a large box. During IOP-1, both 23 and 24 rose to the occasion and provided excellent data from which internal waves, fronts, and surface waves were observed. However, on the final day of IOP-1, Sept. 17, drifter 23 (red in the figure) decided he/she wasn’t long for this world and sacrificed itself (for science, I presume) on the rocks, either that or that the point (0,0) in Pt Sal (x,y) is some sort of worm hole? (actually, we checked some mooring lines, which were kelp free! delaying recovery of 23). Regardless, we had finally lost a drifter, much to everyones dismay (delight?).

Now drifter 24 was sad, however, he/she performed admirably throughout IOP-2 collecting much data. On the final day of IOP-2 (Oct. 14), about 1 month after losing drifter 23, 24 decided enough was enough and attempted to reunite with 23. Upon release at 8:05, 24 went directly shoreward (green in figure), hitting the surfzone at 12:39. Realizing that 23 was 1 km to the south, 24 stumbled down the beach for 4 hours, getting about 200 m from 23’s final resting place. At this point, after stumbling down the beach for 4 hours (a difficult task for an old drifter from the 80s), 24 needed a rest. After a long 24 hour nap, drifter 24 made tje final push south toward 23, coming to rest about 100 m from his partner in science. Although we mourn the loss of these two drifters, we are happy they are once again together enjoying their retirement on a beautiful coastline. (in the figure, contours are at 2.5 m intervals, and the 20 m contour is thick)

 

IOP2 fun around Pt Sal

SIO-Whaler Sally Ann on her offshore (west) survey leg passing to the south of Ghost Reef on 10 October. Photo was take by Falk Feddersen from the RV Sounder

 

IOP2 has been a great deal of fun all around sampling both Pt Sal and Oceano with the Sounder, Kalipi and Oceanus.  Speaking of Oceanus, On 14 Oct, Mike Kovatch took some cool photos on of her from east of Pt Sal looking between Lion Rock on the left and Pt Sal on the right as the Oceanus was doing her onshore leg  and making the turn. 

 

We had three great days at Pt Sal and below are some plot of both the first day (9 Oct) and the last day (14 Oct).    On 9 October, Sally Ann and Sounder repeated the survey lines they did for the first IOP.  Survey lines and CTD data is shown beow.  Lots of repeatable frontal structure.

 

What might that frontal structure look like from the surface?  Well it looks like foam scum lines that are filled with algae. The two photos below are from 9 October which had Hs>2 m.   The first photo is looking north at Pt Sal and Lion Rock.  Note the big foam/algae streak (scum line) heading from Pt Sal to the right of Lion Rock.   The scum line can be very dense – even a few inches thick of foam!

Algae scum line coming off of Pt Sal and heading SE indicating the presence of a front where downwelling is occuring.

Close up of massive algae scum line coming off of Pt Sal on 9 October.

 

On IOP2 Day 6, 14 October, we again had 4 vessels doing joint surveys with the APL plane flying IR & visible and helping guide us.  The Sally Ann did a survey box much tighter near the strong bathymetric variations around Pt Sal.    The survey box below started east just offshore and south of Ghost Reef, passed Seal Rock and then Lion Rock, before turning north for a short leg and then offshore again between Pt Sal and Lion/Seal Rocks.

Here are some photos of those features.

A wave breaking at Ghost Reef up close on 15 Oct. The depth goes from 15 m to <4 m very rapidly (Mike Kovatch).

The NPS boat “SandCrab” racing to the south past Ghost reef to recover instruments. They did not stop for tea and biscuits (Mike Kovatch)

Waves breaking on Seal Rock just south of Pt Sal. Drifters recirculated behind this feature (F Feddersen)

All boats passed through many strong frontal features that had more wake, eddy, and recirculation properties than of NLIW.   Notice the repeatable front properties as the Sally Ann drove the box 4 times.

scripps oceanography uc san diego