This is the final update for the 2021 occupation of A20. The last week continued to run smoothly
and we completed the final station (90) at 01:17 on April 13th UTC (photo below). On Friday
(April 9th) we completed the 35 nm spaced stations and began three and half days of closely
spaced stations. Knowing this was coming, everyone was prepared for stations in rapid
succession. The stations first tightened to 13 nm, but depths were >4500 m. Spacing then
decreased to 11 nm when we entered the French Guiana EEZ. The final six stations were only
~4.5 nm apart, with depths between 70 – 350 m. They were completed in only 9 hours. The back
log of samples collected during the last couple of days will be analyzed on the transit to port.
Also, during the final stations, we entered into the Amazon River outflow plume. Surface
salinities dropped from ~36 to ~15, a strikingly low value for over 100 nautical miles from the
coast and hundreds of miles from the mouth of the Amazon. The underway pCO2 system
measured an incredibly low value of 47 μatm (compared ~300 μatm encountered further north).
Despite the weather delay at the beginning of the cruise, we were still able to complete the
section with higher resolution than the 2012 occupation.
On station 69 it was noticed that the block on the winch was making metallic scraping noises. It
was decided to replace the block before the next cast as a preventative measure. The process was
quick and only caused a 45-minute delay before the next station. Afterwards the block was taken
apart and showed severe damage to one of the bearings. Replacement parts have been ordered
and will be loaded in St. Thomas for A22.
The seas have continued to be calm, and temperatures have risen into the 80s. With relative
humidity of ~80% being outside has become oppressive during the day. Samplers have taken to
cooling off using extra water from the Niskin bottles. With the 30th birthday of the 2nd mate, on
Saturday we had another BBQ on the bow. A light sprinkle threatened to ruin the BBQ, but it
passed quickly. The clouds provided beautiful colors during sunset (photo below).
and we completed the final station (90) at 01:17 on April 13th UTC (photo below). On Friday
(April 9th) we completed the 35 nm spaced stations and began three and half days of closely
spaced stations. Knowing this was coming, everyone was prepared for stations in rapid
succession. The stations first tightened to 13 nm, but depths were >4500 m. Spacing then
decreased to 11 nm when we entered the French Guiana EEZ. The final six stations were only
~4.5 nm apart, with depths between 70 – 350 m. They were completed in only 9 hours. The back
log of samples collected during the last couple of days will be analyzed on the transit to port.
Also, during the final stations, we entered into the Amazon River outflow plume. Surface
salinities dropped from ~36 to ~15, a strikingly low value for over 100 nautical miles from the
coast and hundreds of miles from the mouth of the Amazon. The underway pCO2 system
measured an incredibly low value of 47 μatm (compared ~300 μatm encountered further north).
Despite the weather delay at the beginning of the cruise, we were still able to complete the
section with higher resolution than the 2012 occupation.
On station 69 it was noticed that the block on the winch was making metallic scraping noises. It
was decided to replace the block before the next cast as a preventative measure. The process was
quick and only caused a 45-minute delay before the next station. Afterwards the block was taken
apart and showed severe damage to one of the bearings. Replacement parts have been ordered
and will be loaded in St. Thomas for A22.
The seas have continued to be calm, and temperatures have risen into the 80s. With relative
humidity of ~80% being outside has become oppressive during the day. Samplers have taken to
cooling off using extra water from the Niskin bottles. With the 30th birthday of the 2nd mate, on
Saturday we had another BBQ on the bow. A light sprinkle threatened to ruin the BBQ, but it
passed quickly. The clouds provided beautiful colors during sunset (photo below).
Figure 1. Sunset on April 10, 2021 (left) Deploying the CTD rosette at the final station (right).
Having completed the science goals of the cruise we are now on a 3-day steam to St. Thomas.
There is discussion on if we will be able to see ash from the recent volcanic eruption of La
Soufrière on St Vincent. In St. Thomas, nine of the science party and several crew members will
disembark and replacements, who are currently undergoing the pre-boarding isolation, will board
to take their place during the return voyage to Woods Hole on the A22 cruise.
Weekly updates from the A22 cruise led by Chief Scientist Viviane Menezes and Co-Chief Jesse
Anderson should follow soon after their departure on April 20, 2021.
Final Counts:
90 stations
11 SOFAR drifters
8 BGC-Argo floats
7 Core Argo floats
Ryan Woosley – Chief Scientist
Andreas Thurnherr – Co-Chief Scientist
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