Signing off

The weather has been exceptionally fine on this trip -- warm and sunny with light winds and seas.  This evening we're about 500 nm from home and pushing through the remnants of TS Karen.  We're enjoying some wind, rain, and lively seas just south of the Gulf Stream.  The salinity snake was recovered earlier today after its boom buckled, but otherwise everything continues to go well as we roll along at a solid 11 kts towards home.  We expect a lumpy but uneventful trip across the Gulf Stream early tomorrow.

This will be our final SPURS blog post.  Thanks to the Captain and crew of R/V Endeavor for a very fun and successful cruise, thanks to the science party for their hard work and their contributions to this blog, and thanks to you for reading.

We expect to reach Woods Hole on Sunday.

The last bit

Guest Blogger:  Dave Rivera (PMEL)

After a few days of cruising, we were finally able to finish up the last of our mooring operations. Yesterday, October 6^th, we tracked and recovered the drifting PICO-E buoy, which had floated a little more than 650 nautical miles since breaking from its mooring line. In theory picking up a drifting buoy seems relatively straightforward as there was no mooring line or instruments to recover, but reality showed us that this type of operation would take a combined logistical effort and little bit of luck with the weather.

There are countless stories circulating the globe illustrating how people all over the country and abroad are affected by the current government shutdown. Sadly, the effects of the shutdown were also felt here, in the middle of the Atlantic. October 1^st, the first day of the government shutdown, was the last time our primary GPS tracking system provided us with coordinates for the drifting buoy so we were forced to use our back up system. Unfortunately due to the shutdown of NOAA computers and servers, we were unable to remotely access the GPS information needed for tracking, and were forced to utilize one of the few remaining NOAA Corps officers with access to NOAA-PMEL (Pacific Marine Environmental Laboratory) to update our positions from Seattle, a city that was five time zones away. Fortunately he was available and able to supply us with updated positions as we were nearing the presumed buoy location.

Of course getting buoy positions from Seattle was not our only obstacle as a number of small weather systems also hindered our ability to find the buoy on radar. In the end the only reliable tracking system we had available to us were our own eyes. Thanks to the efforts of the ships captain and crew, we closed in on the buoy around 0100 UTC (11 pm our time) and finished recovering the buoy 2 hours later.

This operation could be rated as one of the smoothest we have had on the cruise. Neither the periodic rain showers nor the lack of sunlight hindered us from maneuvering right up to the buoy, and capturing it using only a gaff and snap-hook on a pole- a method sailors and scientists are rarely able to use due to unsafe sea conditions. All in all we could not be happier with the result of our final mooring operations, and I would like to express my gratitude to the captain, crew, and fellow scientists for their efforts. 

Floats that sink

Guest Blogger:  Ben Hodges

The Argo program is an ongoing international effort to maintain a global fleet of 3000 or more autonomous profiling floats distributed throughout the world ocean.  These expendable instruments drift for 10 days at a depth of 1000 meters, and then, by changing their buoyancy, make a quick trip down to 2000 meters and back up to the surface, measuring temperature and salinity as they ascend.  Once at the surface, they determine their position and send the data they’ve collected to shore by satellite.  Each float is capable of repeating this 10-day cycle as many as 200 times or more.  Eventually though, they stop functioning—some break down due to a mechanical or electronic failure; others run aground; probably the most common cause of death is battery depletion.   The float shown below, at the Scripps Institution of Oceanography, was rescued from a premature demise by the Instrument Development Group there after it sprang a leak in its external oil bladder.

As old floats die, new ones must be deployed to replace them.  That’s where we come in.  SPURS is not affiliated with the Argo program, but while we’re out here, we’re happy to do our part to help maintain the Argo array.  Before we set sail from Ponta Delgada, colleagues from WHOI shipped eight SOLO II floats, similar to the one pictured above, to the Endeavor.  We deploy each one in its cardboard box by lowering it gently off the fantail after slowing down from cruising speed or as we pick up steam when leaving a CTD station.   The water-soluble tape securing the box quickly dissolves, and the float is released to begin its mission.  The biodegradable cardboard box eventually disintegrates.

Along our cruise track so far (white line in the figure below) we’ve deployed four of them (white circles).  We plan to continue along the red line, and deploy three more floats at the red circles (the eighth float is sick, and is headed back to the lab for a checkup).  The yellow dots are currently active Argo floats (including the ones we’ve just added), and the shading provides an indication of the density of floats in the area (thanks to Pelle Robbins for the data and concept for this figure). 

Oceanographers use the measurements made by Argo floats for many purposes. The floats directly measure current velocity at 1000 meters’ depth, and allow currents at other depths to be calculated based on spatial changes in seawater density and the rotation of the earth.   They also monitor the heat content of the ocean, which changes with the changing climate. 

As valuable as the information they provide is, it always feels a little strange to drop a 40-lb robot that costs as much as a car into the ocean and watch it drift away never to be seen again.   But gathering this data by any other method would be impossible—ships like the Endeavor can’t be everywhere all the time, and by their sheer number, Argo floats can.

For more information about the Argo program, visit http://www.argo.net.