Logging, trapping, releasing and recovering…

… Or at least, we hope so. For the second time we are retrieving our moorings from Baker and Steffen fjords with great suspense (A year of mud). A year ago we deployed them for another year of data logging and sediment trapping and it is now time to see the job that they have done for us since last January. Earlier this week, whilst heading out for a sample of Huemules River, we spotted the surface buoys of the two moorings floating at their correct position. This gave us reassurance that they were still there, waiting to be picked up. But are all the loggers still working? Did a sediment trap flip over or even worse, did it break off? There is only one way to find out…

On Tuesday afternoon, we sailed out on the R/V Sur Austral on the cloudy blueish green waters of Baker Fjord. We passed Isla de los Muertos before arriving at the first mooring location under windy conditions. We quickly acknowledged that we could not safely retrieve the mooring under these conditions and decided to continue our way to Steffen fjord to retrieve our second mooring, which we did under fine but changing weather conditions. The sediment trap revealed an accumulation rate of 3.7 cm of sediment in 2018, which nicely supports our current age-depth model for the sediment cores collected in this fjord during the 2017 campaign (Better than manjar!). Since the weather conditions had not changed on our way back, we had to postpone the retrieval of the Baker mooring to the next morning.

Originally, four days were scheduled to retrieve the Baker mooring, service the logger, sequential sediment trap and acoustic release and redeploy it with fresh batteries, new shackles and upgraded kevlar ropes. Due to late arrival of the R/V Sur-Austral, we aimed to do the job in a single day, which meant a long day ahead for all of us on Wednesday. Fortunately, the wind had significantly subsided during the night, and an early departure from Tortel allowed us to be done with the retrieval by 9 am.

Retrieval of Baker mooring. All the equipment is back onboard but its clearly time to replace the shackles!

We quickly learned that once again, the turbidity logger had recorded another year worth of turbidity data, despite the last minute on-site repairs we had to do last year and the entangling of about 2m of rope around the logger and its wiper. This little but powerful device recorded hourly changes in suspended sediment concentrations for us over the last 370 days. Together with last year’s log, the results will allow us to understand seasonal variations in sediment supply, and ultimately get a better grasp on the processes recorded in the sediments at the bottom of the fjord.

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Despite the entangling of about 2m of rope around the logger and its wiper, this little device recorded hourly suspended sediment concentrations for us continuously over the last 370 days.

We were a bit less lucky with the sediment trap. Apparently, the motor battery drained faster than expected, which resulted in the sediment trap to stop turning in November 2018 instead of continuing switching bottles every two weeks until last week. As a result, the sediment of the last 2.5 months has accumulated in one single bottle instead of being neatly separated in distinct bottles. The bottle didn’t overfill though, so we’ll still be able to analyze the sediment composition, albeit at lower temporal resolution.

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The 24 bottles of the sequential sediment trap. Bottles B11 and 12 represent a particularly cold winter month with very limited river discharge. The last 4 bottles are empty because the trap stopped turning in November 2018.

As we had hoped, mooring redeployment happened the next day. We left Tortel at 6 am to take advantage of the fine morning weather conditions, and by noon the two moorings were back in the water. Since we were two days behind schedule, we decided to head south for Eyre fjord and Pio XI Glacier immediately after redeploying the moorings to begin the last chapter of our field expedition.

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