Orkney Passage moorings

A relatively clear sky and flat seas at 60S in the Orkney Passage. The sky textures are many and varied. They express a huge suite of colour and a range of patterns. The clarity of cloud formations is unique to the high latitudes, where aerosol pollution is far less prevalent than in the lower latitudes. We have been blessed with some mild weather, offering us a respite from the raging seas and howling winds that have been the norm. It is good weather for work and for sleep. 

Port side looking towards the rear (aft or stern) of the JC Ross on a relatively clear day in the Orkney Passage.

Eleanor captured this image of swimming penguins. I cannot get enough of these photos! Penguins seem to be infinitely entertaining.

I awoke this morning, 17 April, to a rather unusual site from my cabin window. The seas were calm, the sky revealed some blue, and the winds were still. The view over this calm water reveals far more details about the fauna of this region than otherwise visible with roaring seas.  What is that  fin?  Is that a minke or southern right whale?  See those penguins in the distance?

Imagine a calm early morning in a small boat. Then imagine not seeing any land on the horizon.  Then put the water temperature at just above freezing. Finally, add to the mix a suite of exotic fauna, from birds to whales to penguins.  That is nearly the scene today.  The main difference is that we are in the comforts of a  large metal ship with massive diesel engines. It is relatively quiet for such a machine, or at least my mind has learned to filter its noise from my awareness.  Indeed, during many moments standing on deck outside, or even looking through a window in the comforts of a warm cabin, one can realise sweet expressions of silence and stillness among the natural forces that surround us.

There are storm clouds on the horizon in more than one direction. But for now, we experience some calm.  This is ideal weather for our work, so we make the most of it.  Last night's shift did a full suite of CTD and VMPs.  Today, 17 April, we will deploy one CTD and then send Boaty McBoatface on his third mission into the abyss of the Orkney Passage. During his mission, Boaty will measure turbulence and the fine scale of ocean properties within the mountains and valleys that sit beneath the waves. 

Povl Abrahamsen of BAS, listening to the acoustic pings being sent to an Orkney Passage mooring. Once we get close to the mooring, Povl sends an acoustic signal to the mooring from this yellow box. The signal informs the mooring that it can release its weights and float back to the surface for recovery and eventual redeployment. 

Recovery of one of the ADCPs on an Orkney Passage mooring. The yellow ball is made of hard plastic foam that is able to withstand pressures down to 3000m in the ocean. It provides the housing for the acoustic transducers that are pointed downward at an angle. These transducers send acoustic signals into the water column, with their wave signals returned to the ADCP after scattering off of particles in the water. Through some geometry and acoustic wave analysis, we can then infer the horizontal current velocity. It all seems rather straightforward to an acoustic engineer who may work on dry land. But what makes seagoing measurement device design so difficult is the need to ensure they work day after day under extreme conditions. It is a very disappointing day when an instrument is recovered, only to find a battery went wrong or a wire corroded.  Fortunately, these moorings appear to have done well during their two years of service to ocean science.     

DynOPO mooring recovery on 14-15 April

As we awoke on the morning of 15 April, we had -5C air temperature after a snow fall the previous night. For some reason, the night watch has generally been privileged to witness such snow storms!  The deck is slippery with ice this morning. A blue sky peeks through the gray storm clouds.

We are on the second day of recovering the DynOPO moorings. There are seven Orkney Passage moorings as part of the DynOPO project. They were deployed two years ago on a JC Ross cruise led by Povl Abrahamsen. On the present cruise, Povl is leading in their recovery and will coordinate the redeployment later in the week.  His team of scientists and crew recovered four moorings on 14 April, and recovered the remaining three on 15 April.  It was a masterful effort by the team, working for roughly 12 hours throughout very cold weather.

The weather, though cold, has been ideal, particularly due to the mild wind and low swell. It is amazing how a full day of productive work can turn the spirits, especially after many days of weather delays. Work has hit a nice rhythm for the past few days, with VMPs, a successful 2nd mission of the auto-sub Boaty (future post), and now the successful mooring recovery.  In addition to these logistical successes, data from the VMPs and Boaty's 2nd mission look interesting scientifically.  And preliminary data from the moorings indicate they did their job for the past two years. 

This is perhaps the most amazing and dramatic photo of the blog thus far.  Eleanor captured this image of a southern right whale just off the back deck during recovery of an Orkney Passage mooring. Whales have been incredibly socialable throughout this cruise, approaching the ship during feeding, and in general just hanging around.  This whale offered us an iconic image of oceanography in the high latitudes. And no need to fret, as the rope loop in the photo is not going to wrap around the whale. We are just as curious about the whale as he/she is of us, and do our best to do no harm!

This is a design diagram for the Orkney Passage mooring OP1.  It shows all of the floats (yellow dots) and instruments attached to the wire.  It also shows the depths (distance from surface) and distance from bottom.  The ''Aquadopp'' provides a local measure of the ocean currents; the ''SBE'' measures temperature; and the single large yellow dot house the ADCP.  The bottom is anchored with three old steel railway wheels.

 A brief on ocean moorings

 Moorings offer us an array data with a relatively small amount of invested people-time. They are the bread and butter of long-term observational oceanography and climate science.  Their time series capture the many time scales of ocean phenomena, from the seconds of random turbulent fluctuations, the hours of tidal motions, the seasonal fluctuations of currents, the interannual variations from the Southern Annular Mode and El Nino / Southern Oscillation, and the decadal and longer time scales of climate change. to centuries.

A schematic of the Orkney Passage moorings, as deployed in 2015. These are the moorings that we recovered on 14-15 April, and will be redeployed later in the week. The panel shows the moorings with a background potential temperature field. Note the different degree of instrumentation on the various moorings, with OP1 and OP2 the most heavily loaded. The numbers on the top of each panel (46 to 56) represent CTD stations made across the section. This image comes from the 2015 cruise, labelled ''JR310''.  The present cruise is labelled ''JR16005''.

The design of each mooring is the subject of scrutiny and thought. What do we wish to measure: currents, temperature, salinity, biology, turbulence?  How can we make our wish list compatible with a limited budget?  What is feasible to deploy and to recover given the extreme weather down here? 

Some of these moorings have been here for a few years, and we hope they will continue to be turned around for many years into the future.  There are changes happening down here.  Such monitoring from moorings is vital to uncovering the dynamical reasons for these changes: are they natural or are they anthropogenic?

Recovering an instrument from one of the Orkney Passage moorings. Note that Andy Davies, our resident mooring recovery expert from Woods Hole, has taken a liking to the orange gear from BAS. It was very cold and long work, motivating many layers to stay warm.  (Photo Eleanor Frajka-Williams)

Povl Abrahamsen in the deck laboratory space, with a portion of the instruments recovered from the seven Orkney Passage moorings. Povl is here wearing his Columbia University shirt, which is where he went to school as an undergraduate.  Povl deployed these instruments on a cruise in 2015, and is in charge of recovery and redeployment on the present cruise.