9 July 2007:
At last a chance for another brief update. So much has been going on
that we have all been extremely busy and with one exception, which I
will come to later, the cruise has been a great success so far.
Having initially deployed the two
tracer patches (one with and one without surfactant), the ASIS buoys and
the URI float within only a few km of each other, we have seen their
paths subsequently diverge. While both ASIS buoys have progressed to the
south and westward at a mean speed of about 0.8 kt, the University of
Rhode Island (URI) float moved initially to the northeast (a second URI
float malfunctioned and was retrieved but it will not be redeployed).
The URI float was in a three day cycle in which it spent significant
periods below the mixed layer and was presumably driven by subsurface
currents while ASIS was predominantly wind driven. Following remote
reprogramming the URI float spent longer periods in the mixed layer and
subsequently followed a course more similar to ASIS. Nevertheless by
last night the separation between ASIS and the URI float was approaching
200km! Meanwhile the tracer patches moved towards the south and west.
The first of these has now been abandoned due to SF6 levels approaching
background but the other is still good for a few days.
We have this morning retrieved the
URI float and are proceeding towards ASIS 1 and 2 to redeploy it along
with a new (third) tracer patch later this evening. Interspersed with
sampling the tracer patches for SF6 and helium-3 we have made
deployments of the now repaired NIOZ Catamaran (you will recall that it
was earlier damaged and capsized) and the PML surface sampler, both for
microlayer and near-surface gradient work. Matt Salter has also
collected microlayer samples by RIB for surfactant and bacterial
diversity analysis on several occasions. We have also successfully
deployed the NOC wave and bubble buoy on a couple of occasions and we
also managed to lay out a surfactant patch in the path of one of the
ASIS buoys, which subsequently passed through it. We took advantage of
the fact that both ASIS buoys were moving in the same direction on
parallel paths about 14 km apart. Thus we should have a good comparison
between the two. Damping of capillary waves within the patch was quite
clearly observable looking across the surfactant patch boundary through
binoculars. There are also plans to release surfactant in the path of
the NOC buoy next week; from this one we will also get sea surface
photographs so the time in and out of the surfactant will be pretty
precisely known. Overall the surfactant releases seem to have been a
great success, at least from an operational point of view, but we will
of course have to await full data analysis on our return home.
Overnight and where possible when
the ship has been into the wind the University of Hawaii group have been
measuring DMS fluxes while Steve Archer from PML has been monitoring DMS
in surface waters. Comparison of transfer velocities derived from this
data set with tracer, CO2- and O2-derived fluxes and transfer
velocities, and the wave and bubble data will we hope, allow us to
assess any "divergence" of gas transfer velocities between gases of
differing solubilities at intermediate to high wind speeds. This is one
of our major aims and like the surfactant deployments is rather novel.
Sadly it has not been good news
across the board. Brian Ward's (Old Dominion University) ASIP (Air-Sea
Interaction Profiler) malfunctioned during its third deployment and
sank. It now lies crushed at the bottom of the Atlantic. Brian remains
philosophical however, and he plans to work on a replacement on his
2 July 2007:
We had a few hours delay to
sailing due to a blown transformer on the NIOZ Catamaran and thus we had
to wait a for a replacement to be couriered from the Midlands. So far we
have put out both SF6/3He tracer patches, one around 43°37.5'N, 17°03.0'W on 21 June and the other at around 43°31.5'N, 18°01.7'W on
26 June. The latter patch was deliberately smaller than the first and
this was the one we covered with a much larger patch of surfactant,
about 5 times the area of the SF6 patch. This was to try and minimise
the possibility of the surfactant slipping away from the SF6. Initially
it looked like this indeed might be happening but the next day we sent
Matt Salter out in the RIB to investigate. The surfactant had spread out
to cover a much larger area than the initial deployment and completely
overlaid the other tracers which seemed to be somewhere near the centre,
exactly what we had hoped for. The surfactant release was done as a
series of parallel streaks about 250 m apart and about 2.5-3 km in
length. These could be seen clearly from the deck as they spread out
laterally and we have some really cool photos of them. We also
successfully released the NOC wave rider buoy, the two ASIS buoys and
the URI floats; however one of the URI floats had to be recovered today
due to a malfunction. Not sure if it will be redeployed yet.
Unfortunately the NIOZ catamaran suffered a major engineering failure on
its first test. A motor came loose due to breakage of the sampler boom
and sawed its way through one of the hulls. This caused listing and eventual
capsize which drowned the electronics.
However the crew were as always
able to expertly retrieve it and amazingly the samples remained intact.
After several days of intensive repairs it now seems operational although a
planned deployment today may be postponed due to worsening weather.
Today surveying for SF6 in the surfactant patch and hope to move on to
the non-surfactant patch again later today before the low pressure
passes through over the weekend. The University of Hawaii have been measuring eddy
covariance DMS fluxes in and out of the surfactant although Steve
Archer's DMS concentrations are low around 1-1.5 n molar. Meanwhile pCO2 measured by the Montana SAMI
sensor and the URI sensor, both in underway mode, has been around
340-350 ppm which we think is about adequate for the CO2 flux
measurements on ASIS. There is significant redundancy with respect to CO2 because in
addition to ASIS (Miami) and the underway data (URI) we will have direct
flux estimates from AUTOFLUX (NOC).
Unfortunately the CASIX pCO2 data
have however been spuriously high throughout, having been well over 400
ppm, and at one stage around 480 ppm! The second ASIS was released N of
the surfactant and we predict it will pass through the surfactant patch
and out the other side, so we will get a good series of contrasting "in"
and "out" measurements. It will be interesting to see what the coming
low will do to the surfactant.