Tuesday, September 24, 2013


So Greg did something pretty cool last night. We were just chilling
out on station after midnight with the goal of deploying the seismic
gear after breakfast. Chilling out on station is not a good use of
ship time, and as we had already dropped a piston core and a
hydrocast, and were in the process of taking not one but two plankton
tows (one for the mixed layer at 25 m depth and one for the
chlorophyll maximum zone at the thermocline, around 200 m. A plankton
tow is exactly what it sounds like. We tow a net at a certain depth
for an hour to catch plankton –it also had the added benefit of making
our friendly Restech Keith smell like krill for the rest of the day).
Greg decided the thing to do would be expand our multibeam seafloor
survey from the grid we'd mapped that morning. The cool thing was that
after deciding this, he walked into the main lab, where we were in the
middle of a heated doubles ping pong match, and said "Hey budding
young scientists, does anyone want to look at our bathymetric data,
identify an area of interest, and design a survey plan?" To which
Jeremy and I replied "yes." (Sam and Kelly, the other half of our ping
pong foursome, were running the plankton tow.)
So we sat down and looked at the day's survey data to see what might
be interesting. Our waypoints and survey plan (and planning
scribblings) are plotted in the top photograph. The basemap is
satellite tomography (yeah, did you know they can measure seafloor
topography via satellite? It still blows my mind) which can resolve
good ocean-scale features, like ridges and trenches and abyssal plains
and the like. The finer stuff can't be resolved from satellite (which
is ok, because again: we're mapping the bottom of the ocean with
satellites), and can only be done with shipboard multibeam sonar.
These data are few and far between in the open ocean. Going back to
our survey map at the top, the line of better resolution data going
from southeast to northwest is a shiptrack from the only other survey
ship to have passed by here. Anyway, Jeremy and I sat down to look at
this, and the results from our survey this morning, which are not
included on the map above (the yellow dots you can see are the
waypoints from that survey). The morning's survey and 3.5MHz seismic
showed interesting seafloor features. Particularly, instead of the
gentle slope suggested by the satellites it has several 20 meter
terraces right along where the contours turn from dark blue to
slightly less dark blue. We couldn't survey during the plankton tow
because the ship can only go 1 knot at that time. That was supposed to
wrap up around 4am, which gave us 3.5 hours of survey time. And we had
to be at a certain location at 7:30 to start the seismic. So we
plotted a triangular course following contour lines of the ridge to
the north where we might hope to find those same terraces. We did this
old school, with a protractor and compass. We figured 10 knots over
three and a half hours gave us 35 nautical miles, so we designed a 29
nautical mile course, on the assumption that we may have to slow down
or quit early if conditions dictated it.
All these tasks completed, we wrote down way points in Lat/Long for
the bridge, and I went to bed, because it was three in the morning and
my shift had ended at midnight.
Jeremy took the waypoints up to the bridge and hand-delivered them,
which apparently is preferred, because there are sometimes
miscommunications over the phone. And they did it. Which is really
cool. We were the ones directing the ship.
Taking directions to the bridge is also extremely surreal, as at night
the bridge is completely black so the two officers driving the boat
can see out into open expanse of the ocean. So when Jeremy got up to
the bridge, he stood around the dark for a moment so his eyes could
adjust, then was greeted by a dark figure (it was one of the mates,
Jeff) standing next to an array of dimly lit computer/navigation
screens. After Jeff took the waypoints and plugged them into the
navigation computer (which literally took 10 seconds), the ship was
good to go and was soon pointed happily northeast towards the first
point Chris and Jeremy had selected.
The survey results, which you can see in the second picture, did
reveal some more of those 20 meter terrace features, but only on the
east-ward facing slopes of the ridges. We're not sure why that is,
although we might hypothesize that it's controlled by basement
topography (basement being the bedrock of this ocean ridge). We could
tell you for sure (probably) if we had time to run a proper seismic
survey over these features, but ship time is limited and we're here to
identify sites for ocean drilling to get sediment records of the last
15 million years of climate variability, not study the geomorphology
of the seafloor. But we explored a small area of the seafloor that was
preciously unexplored, and that was a pretty cool thing to do.

Posted by Chris (writing in the first person, except for right now)
and Jeremy (writing in the 3rd person)