Back to shore and that’s a wrap (for now)!

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We’ve come to a close of AT50-39!

It’s been a fabulously successful and productive cruise.  We have:
  • deployed the second Internal Wave Resolving Array in the Aleutians tidal beam,
  • deployed the Longline Array in the generation region along the slope,
  • deployed 3 EM APEX SQUID floats
  • conducted 6 dives with the REMUS 6000, collecting valuable data about the seabed and bottom boundary layer,
  • conducted several multibeam surveys with the shipboard EM124 to map areas not previously covered with shipboard surveys (including a survey that was critical for successful deployment of the IWR Array central mooring)
  • collected velocity profiles to ~700 m depth with the shipboard OS75 (many thanks the University of Hawaii Currents group who keep these sonars and the UHDAS data collection/processing running on the ARF).

OS75kHz velocity data from the yo-yo station north of the Aleutan ridge showing the M2 tide (courtesy of Caeli Griffin, SIO)

And we’ve done lots of CTDing (for instrument calibration casts, for interpreting and processing the CPIES data, and for  yo-yo CTDs to capture the M2 internal tide at a few locations).

36-hour CTD Cast north of the Aleutian Islands

HYCOM model output showing the northern and southern tidal beams emanating off of the Aleutian Ridge with the 36 hour station noted as filled in black circle (“NB”; figure courtesy of Mujeeb Abdulfatai, USM)

Right before we came back to port, we completed a 36-hour CTD yo-yo in the northern beam (the one generated at the Aleutian
Islands that propagates north into the Bering Sea). This sampling opportunity arose because the weather south of the Aleutians was pretty lousy and because we have access to some great HYCOM model output to guide us. Using HYCOM model output and with the help of some figures shared with us by Maarten Buijsman and his student Mujeeb AND some middle of the night consultations between the grad students Caeli and Grant with Amy and Drew, we were able to pick the perfect spot for this yo-yo. You can see from Caeli’s plot of the velocities, that we are resolving beautiful internal tide activity here.
As an aside, Greg noted that for one of our casts the audience in the computer lab watching the CTD screens was three rows deep. Apparently internal tides are exciting!

The CTD / winch console that the science party uses as they are making CTD profiles. Notice some must-haves at the console including: water bottle, coffee, logsheets, pen and duct tape (photo by Magdalena Andres)

Wonderful crew on the Atlantis

We’ve gotten great support from the Atlantis crew (from Bosun to SSSGs to Officers and Captain), starting with accommodating the installation of the AUV LARS in San Diego, to transporting the west coast TSE winch and our science gear on the transit from San Diego to Dutch Harbor (which was particularly helpful as Dutch Harbor is a logistically challenging location), and continuing with the day-to-day ops during AT50-39, working closely with us to optimize the science activities around the weather.  At some point we had 37 knot gusts and 30 knot sustained winds, but we were on station doing the yo-yo at the time (instead of transiting in the trough), so we barely even noticed the breeze….

Decorated shrunken styrofoam cups sent down that went to 5000 dbar (photo by Magdalena Andres)

 

Eddies have been spotted near the moored NGIW instruments

And one other fun fact: Windy (screen shot below from 17 July 2025) suggests that there is a big anticyclonic eddy brushing up against our IWR Array (big white dot), long line array and the SQUID floats which are still in the area — so in addition to the internal tide beam, we should have a super 12-month record of the mesoscale variability in the region to examine and compare with altimetry and SWOT when we recover the array.

Screenshot from Windy showing a large mesoscale eddy in close proximity to the IWR and long line array. (courtesy windy.com)

Thanks for the support,
Warm Regards,
Magdalena, Chief Scientist
on AT50-39