Scientist Profile: Neill Mackay

Since the first of our scientist profiles appeared, contributions have been coming thick and fast! Today, Neill Mackay, a second year PhD student at the University of East Anglia, tells us a bit about his research interests:

What is your involvement with the DIMES project?

Neill collecting water samples from the CTD rosette

DIMES is the fuel for my PhD. I'm interested in the diapycnal mixing in Drake Passage, and while on land I'm attempting to model the tracer (dye) evolution using an offline version of the numerical model MITgcm, comparing its outputs to the tracer measurements we are making on the cruises. Ultimately I'm hoping to come up with a model for the 3D distribution of diapycnal diffusivity (a quantity measuring mixing across ocean density surfaces) over the whole of the DIMES tracer region which could be applied to other parts of the ocean.

What do you personally want to get out of this cruise?

More tracer profiles! The more real data I have to compare with the model and make adjustments to it, the better the end product should be.

What do you enjoy about going to sea?

I'm well known amongst colleagues as the grumpy one when it comes to being at sea, so I'd have to say....going home!

Halftime hits!

As we reach the halfway stage of the cruise, I'd just like to say a quick thanks to everyone who is following for supporting the blog. Google reliably informs me that we have now had over 5000 page hits, with people viewing in the UK, US, Spain, Argentina, France, the Netherlands, New Zealand, Australia and many more!

In other news, we should complete the last of our work in Shag Rocks Passage tonight before moving eastwards along the North Scotia Ridge towards South Georgia. We have enjoyed really flat seas in the last couple of days, just going to show that it isn't always stormy down here!

Scientist Profile: Ben Mills

An important member of our tracer team on board, Ben took a few minutes to tell us a little about his background and research interests:

Where are you are working/studying?

I’m in the final year of my PhD at the University of East Anglia in Norwich (UK). My work focuses on the Earth’s combined biological, geological and chemical cycles, and the evolution of this ‘Earth system’ over the last 4.5 billion years. I make simple mathematical models, and attempt to unravel the mysteries presented in the geologic record, with varying degrees of success...

You can see some of my recent work here.

What is your involvement with the DIMES project?

I’m a bit of a stow-away on this cruise, not being an oceanographer and all that. The tracer experiments are run by our research group at UEA, and they needed an extra hand to help with  the 24hr sampling. They also mentioned that there would be free food.

What do you personally want to get out of this cruise?

This is the first time I’ve been to sea, so for me it’s been a great experience already. As a computer modeller, I rely completely on other people's data, so it is nice to give something back by helping with the sampling.

What do you enjoy about going to sea/working in oceanography?

It’s fun. Lots of cool places and wildlife to see. Everyone is interesting and friendly. Did I mention the free food?

Wildlife pictures from the bridge

Second officer Mike has given us these great shots of what we believe to be a fin whale and some hourglass dolphins seen from the ship in the last couple of days. Many thanks to him!

Scientist Profile: Uriel Zajaczkovski

In today’s blog update, we spoke to Uriel, who is a PhD student on the UK DIMES 3 cruise. We started by asking him about his background and the research he is undertaking:

I am studying at Scripps Institution of Oceanography under the guidance of Sarah Gille. My research is currently focused on how heat is transported from the equator to high latitudes. In particular, the Southern Ocean circulation plays an important role in the Earth’s climate system by controlling the oceanic meridional (north-south) heat transport in the Southern Hemisphere. Despite this fundamental role, the details of how heat is being transported still remain unclear.

Uriel in the main lab

What is your involvement with the DIMES project?

One of DIMES’s goals is to quantify mixing along and across isopycnals. A suitable coordinate system for the study of isopycnal mixing in the Southern Ocean is therefore needed. Eddy diffusivities via Taylor’s approach can only be estimated for homogeneous and random motions; dispersion effects from the mean shear flow must be filtered out. Otherwise diffusivity estimates in regions of high horizontal shear, such as the Antarctic Circumpolar Current fronts, are expected to behave non-asymptotically at large lags. Therefore the estimation of a robust mean flow is of vital importance in order to achieve stable estimates of isopycnal mixing. For the past few months, I have been working on the estimation of the mean density, temperature and salinity fields of the Southern Ocean by combining in situ Argo float measurements and satellite altimeter data. The percentage of variance captured by the altimeter can be as high as 40% at the density surface where the tracer (dye) was injected. Moreover, the signal to noise ratio shows a substantial improvement. This suggests that when altimeter data are used in combination with in situ Argo float measurements, fewer observations are required to produce a stable estimate of time-averaged density field. 

What do you personally want to get out of this cruise?

I am here mostly for the experience and to learn as much as I can about microstructure profilers. It is also a good opportunity to meet colleagues and find out what they are working on.

What do you enjoy about going to sea and working in oceanography?

Being at sea for long periods of time can be really fun if one has the right attitude, and the possibility to explore remote places is definitely a plus. For me, one of the most exciting things about Physical Oceanography is the fact that it is a relatively new branch of Physics. A lot of controversy still remains in the most basic subjects and our understanding is being re-shaped and broadened every day. These are very exciting times for oceanographers!

Uriel works the evening shift on ship and has taken the opportunity to grab a couple of great sunset pictures. Enjoy!

All go for tow-yo!

The conductivity-temperature-depth (CTD) package.

After an aborted start prior to visiting Stanley, we have now got into one of the most exciting parts of our science programme. Normally when we do a CTD station we send the package to the bottom and return it to the surface in the same location, firing bottles on the upcast. However, we are currently operating the CTD in a different way to study the along-stream changes in water properties as we move south to north across Shag Rocks Passage.

This alternative mode of operation is known as doing a “tow-yo”, and involves lowering and raising the CTD whilst the ship is steaming slowly in the direction of the current. This allows us to track the temperature, salinity and velocity changes following the water as it moves through the passage. Typically, we will “yo-yo” the CTD (send it down and up) for 3 or 4 cycles, firing bottles only on the last cast. Sampling the water in this way will allow us to detect any changes in dye concentration as the water transits the passage, giving us an indication as to the extent and possible mechanisms by which water is mixing vertically.

Paul and Steve looking at the CTD deck unit.

Operating the CTD as a “tow-yo” requires great care, both from the winch drivers and the bridge, in order to stop the angle on the wire becoming too great, which can damage it. Nevertheless, we are currently enjoying great weather conditions and are hopeful that we should be able to “tow-yo” for the next couple of days.

Will and Dave driving the winch that lowers the CTD.

Edging eastwards

Our steam back towards Shag Rocks Passage continued today, meaning that we should arrive back in the science area around 5 a.m. tomorrow. Having observed some of the tracer (dye) in the Argentine Basin at the start of the cruise, we took the opportunity this morning to do a station on the continental slope to the east of the Falkland Islands. This should enable us to understand more clearly the mixing pathways across the ridge. All the scientists on board were relieved to be working again after a frustrating few days and are looking forward to getting some more exciting results in the coming days.

A plethora of penguins!

Apologies for the lack of blog updates in the last couple of days, but unfortunately a medical issue meant that the ship has had to return to the Falkland Islands. Whilst this was disappointing from the science perspective, it has given the scientists, technicians and crew a little bit of down-time. Yesterday, a group of eight visited Volunteer Point in the north of East Falkland to see the king and gentoo penguin colonies, whilst another group went for a shorter expedition to Gypsy Cove, where we saw three groups of Magellanic (or jackass) penguins. Most of the scientists have spent this morning exploring Stanley and buying penguin-themed souvenirs! A group of us also visited the Stanley Museum, which had some fascinating exhibits on the warrah, an extinct fox-like creature that once inhabited the Falklands, and on the 1982 Conflict. Stanley also features a 1 to 1 billion scale model of the solar system, created by a local artist.  The sun appears as a metre diameter sphere in the centre of town, with the planets then found to scale to the west of the main town. Earth appears about the size of a marble a couple of hundred metres away, whilst Pluto is a tiny ball bearing close to the summit of Mount Tumbledown several kilometers to the west. Thank you to Tom and Lou for all the photos.

RRS James Cook from the launch

The shipwreck of the Lady Elizabeth

Magellanic penguins at Gypsy Cove

Magellanic penguins at Yorke Bay

The sun, at the start of the Solar System Trail, in Stanley

The Earth and moon with the sun and RRS James Cook in the background!

Ben in penguin attire with king penguins at Volunteer Point!

RRS James Cook by night

Adorable gentoo penguins swimming at Volunteer Point

Gentoos and kings at Volunteer Point beach

We sailed this evening from Stanley at 6 p.m. and should return to Shag Rocks Passage on Saturday.

Tracer Tales

In today’s installment, Dr. Marie-Jose Messias has kindly written a few words explaining the operation of the space-age looking equipment used in the tracer container to detect the concentration of dye in the seawater:

 

Marie-Jose analysing tracer results

The inert molecule CF₃SF₅

The tracer team - Neill, Ben, Dhruv, Steve, Marie_jose and Andy

“Our mission is to better understand how water from the Antarctic Circumpolar Current (ACC) invades the rest of the world’s oceans. To do this, 80 kg of tracer (trifluoromethyl sulphur pentafluoride, CF₃SF₅) were released into the Pacific side of the ACC in 2009. Since then, we have been tracking its dispersion vertically (diapycnal mixing) and horizontally (isopycnal mixing) by collecting water at different depths along its path towards the Atlantic and measuring its tracer content. Our measuring instrument (which we have named Electric Barbarella 3000) is very sensitive, and able to detect a concentration of 5 atomoles (10^-18 moles/liter) or 0.5 micrograms of tracer within a kilometre cube of seawater. It uses a method called ‘purge and trap analysis’ and is coupled to a gas chromatograph.  Everything is carried through the instrument by a flow of the ‘carrier gas’, Nitrogen (N₂).  Water samples flow through into a calibrated volume and then are transferred to a ‘sparge tower’ under vacuum. The sparge tower is where the dissolved gasses (including our tracer CF₃SF₅) present in the water are removed by bubbles of nitrogen gas. Gases are carried from the water into a ‘trap’, which is cooled to -110°C, causing the gases to condense and become trapped. We cool the trap by immersing it in liquid nitrogen vapor. After 3 minutes of sparging, the trap is lifted out of the liquid nitrogen and heated to +110° C. This releases the trapped gases into the gas chromatograph, where the tracer is separated from the other gasses by going through a series of chromatographic columns. The amount of tracer present is quantified by an electron capture detector (the electrophile CF₃SF₅ ‘captures’ the electrons). Thus we can tell how much tracer we have in each water sample! The running time per sample is 9 minutes, giving us just enough time to compile and check the results from the previous run, and to fetch the new samples, and maybe make a quick cup of tea...  Next sample please!”

Fleeting Falklands visit

We had a very quick stop in the Falkland Islands today and enjoyed some great weather on both our arrival and departure into Stanley. Many of the scientists aboard partook in some wildlife watching as the ship steamed into the harbour, and we even managed to grab a few shots of the town before our 10.30 a.m. departure. We were sad to say goodbye to four of our science party who left the ship in the Falklands but we are now steaming back to Shag Rocks Passage. Many thanks to Heather Bouman and Luc Rainville for the great photos. Luc has also contributed a video of some dolphins riding the bow wave of the ship this morning. Apologies for the low-resolution but I am uploading over a slow connection!

Alberto

Ben

Luc, Alberto and Brian on the foredeck

Marie-Jose and Alex

Magellanic penguins from the ship

Entering Stanley Harbour

Two Sisters

Luc outside the cathedral

View from the shore

Dolphins at the bow of the ship this morning