Sampling the ocean piling up against the largest surviving giant floating glacier
this comes from a blog ....
The Adventures of K132* 2012
1
Arrival - 9 Jan
This is a new blog describing
the day-to-day
work for an experiment looking at a coastal ocean flow in
Over the past decade our group
(NIWA, IRL,
U. Otago) has done quite a bit of work in Southern McMurdo Sound
looking at how
the ocean beneath the
After a brief delay we got away
from
The late departure meant we
didn’t arrive
until 4:30 a.m. – the landing was followed by an hour long crawl
into Scott
Base on a big transporter bus. It was
actually snowing quite heavily by the time we made it in to base. This is unusual in itself – most of the
time
snow in
(*K132? It’s our experiment reference number and forms the basis of any communications and decisions here. It’s specifically associated with a grant from the prestigious Marsden Fund at the Royal Society of New Zealand to look at how melting ice influences ocean circulation.).
2
Preparations - 11 jan
The first few days of any work
down here
are taken up with preparations, training, meetings and checklists. This seems a chore but is pretty important
for keeping experiments running and having as few surprises as possible. Then the next task was to finalize our
freight and make last minute decisions on what to take up north on the
last leg
of our journey to the Italian Base. As
the flight up to the Italian Base is being operated by an
The freight is to be shipped out of Scott Base to Mario Zuchelli Base this afternoon, a day earlier than we originally thought so it was a bit of a scramble and gear didn’t have time to be re-checked. We’re hoping we won’t regret that later on, but these decisions need to be made all the time. Besides, it’s easier to spread out at our final destination; just a long way from spares! The one bit of serious testing we did do was to see how good we are at putting up the field tent. Pretty good it turns out – just not so good at putting it away. The tent is an excellent compromise between size, portability and resilience, regardless in the past we’ve had some challenging times putting these tents up in arduous conditions.
We’re not overly
concerned about the lack
of re-checking of the instrumentation as Brett Grant, my technical
whizz in
this endeavour, went through all the gear before it shipped out. We’ve worked together quite a bit over
the
past five years, both in Antarctica, and at sea in
We went for a walk around the pressure ridges near Scott Base after dinner. These are ripples and deformations in the sea ice as it is squeezed by the land, the ice shelf and the wider sea ice itself. Earlier in the season these ridges form a sharp jagged alien landscape. But now with the heat (-0.3 deg C! plus sunshine) the lumps of ice are all melting and all the dips between the ridges are filling with… liquid! Rather strange really. So these beautiful ponds of greeny-blue are forming almost before our eyes. An example of the rapidity of this development is the flagged trail set out for hikers to safely go through the ridges actually went straight into a pond.
3
Hurry Up and Wait 12Jan
The flight up to Mario Zuchelli
Station in
Part of this breakout opened up
water in
Anyway, the preceding
experiment involved
collaborative work with some pioneers of sea ice research from the
4
Buongiorno! Jan 14
Right on schedule we flew in to
As ever, anyone not used to dealing with oceanographers is surprised by the amounts of gear we travel with. The Italian team that greeted us at the airfield (a smooth bit of glacier) piled all our gear into the back of a truck and we were delivered to the base. The base has a whole new skyline to familiarize oneself with – along with the language and cultural differences. We met our Italian collaborator for the first time, Giannetta Fusco, who has worked in the region both at the base and aboard the Italian ship the Italica. She is proving a great host and showed us around the base, which has quite a different feel when compared to Scott Base or McMurdo Station. The Programme Director greeted us and wished us well in our scientific endeavours. We returned the favour with some fine NZ wines.
With focused process-based experiments where we look at how a specific set of mechanics works it is sometimes difficult to see how they fit into the big picture. From my perspective they contribute in two ways. First, the data in specific situations can be combined to build up a quantitative picture of behaviour. This directly gets included in models maybe as a new coefficient. The second way that this work proves useful is that it exposes mechanics that hitherto had not been considered relevant. Thus, extra aspects might be added to a model or a different model altogether might be used. When I say models here I mean both snazzy computer simulations through to things that as not much more that collections of thoughts on the back of an envelope.
Tomorrow starts with some survey work south of the ice tongue to look for a suitable site. Anyway must run – it’s pizza night at Mario Zuchelli Station.
5
Survey
Jan 15
We completed our first helicopter survey of the field location this morning. It was around a 30 minute flight south of the Station. In that time we stopped off for some brief tourism at Inexpressible Island where a number of Scott’s team were forced to spend the winter of 1912 in a snow cave surviving on seals before walking back to Cape Evans very early in the spring. This brought home the changes of the last century as we had barely finished our breakfast that would have been a week’s nutrients for those fellows - and quite a bit tastier than freeze-dried seal.
I must admit to some (much!) trepidation before the flight. There are competing needs here – we need ice that’s in a useful location, not too thick, not too thin and not all broken up and melting. The only ice likely to fit this bill is held in place by the seaward extension of the massive David Glacier – the Drygalski Ice Tongue. This icy behemoth some 80 km long, 15 km wide, 200 m thick and travelling at a couple of km a year is the last giant floating glacier left – for the time being. If features like this or its close relative the ice shelf, break up and allow increased flow of ice off the polar ice cap then sea level will likely increase rapidly. So fast might this increase be that it will not only become detectable in a human lifetime, it may actually dominate the activities of the human species for centuries to come.
Erich
von
Drygalski led a substantial German Antarctic voyage in the first years
of the
1900s. They worked over in the regions
south of the Indian Ocean and
My viewing of the satellite imagery suggested there was quite a bit of fast ice real estate just south of the Drygalski but this gave little indication of its thickness or condition. We flew about 5 km south of the southern edge of the massive ice tongue. Upon landing we shovelled off the small layer of crusty snow and started drilling using a kovacs. This thin drill is simply designed to measure ice thickness. I couldn’t watch as they drilled away – fully expecting them to get to 4 m and still not have broken through – well beyond the capabilities of our lightweight gear. But good news came soon enough when our Italian Navy Seal guide Davide broke through the bottom of the ice at around 2.6 m! This was a little thicker than I’d worked through in the past but possible. We drilled a few more holes in a 10 m vicinity to confirm this thickness – took a GPS location and departed.
I felt that the ice north of us towards the ice tongue would likely be thicker but we didn’t see any obvious rifting or steps so we flew a kilometre north and drilled again as this might be slightly more be protected from breakout in the coming weeks. Ice breakout can happen in a matter of hours – ocean swell from storms sometimes 1000s of km away literally flexes the sea ice to pieces.
A little surprisingly it turned out to be thinner – just a shade under 2 m, again confirmed with a few repeat holes nearby. This should be well within our drilling capabilities. Essentially, I think the region is made up of a jumble of large sea ice pieces that have broken out and refrozen. We took a wide sweeping departure with the helicopter as we left, showing fresh cracks seaward of our site and clear steps up to much thicker multi-year ice to the north and west. So I think we’ve chosen as well as we could hope.
6
Camp
Jan 18
We got the all-clear for heading out to the site this morning and set up our camp site. It was a stunning day and we had all day to drill a hole, set up the tent and do some sampling – easy! Step one was delivery of ourselves and our gear in helicopter sling-loads to the field site some 30 minutes helicopter flying south of the Italian station. These sling loads wrap up our boxes in big nets and chain them to the underside of the helicopter. When the load is on the ground at its destination point it is gently released. Hundreds of kilograms of gear can be moved in this way.
The setup proceeded slowly as it always does with the usual sequence of breakages and challenges that is essential in fieldwork and never more so than polar oceanography where everything takes three times as long as you expect. For these shallow “hydro-holes” in a remote location we use a combination of drilling techniques that gives us a not very pretty, but functional, hydro-hole. The ice is very soft and wet and almost immediately the holes we were drilling filled with slush which makes it hard going. Right as we broke through the last little piece the drill fell apart so that was good timing!
We then moved our tent over the hole and setup the gear inside. The first thing we did was get the acoustic current profiler in place – this is called ADCP for short-hand with the D standing for Doppler. It sends out pings like a fish finder but instead of simply listening to the amount of return signal as it bounces off small particles in the water it listens to the Doppler-shift in the signal. This way, after some geometry, we arrive at the water speed over a hundred or so metres of water depth. This unit will stay in for the duration hopefully giving a nice picture of the flow beneath the ice.
First thing we did was use a depth sounder to measure the depth. The charts put the depth in the vicinity of 600 m here. However, the sounder struggled to find something to lock on to so the results were inconclusive unfortunately. This meant we didn’t have the depth and would have to do the first profile slowly – essentially by feel.
Finally after all day setting up and with time getting away from us before pickup. I turned on the turbulence profiler - our reason for being here. And it didn’t work! Your worst nightmare! It was clear no power was getting to the unit so I bypassed the power conditioner and it worked but not very well as spikes from the generator corrupt the signal. The power was sufficient for us to profile slowly to get the depth and basic properties of the water column.
At the same time the winch was putting out a funny burning smell which is never good. Either it’s a problem with the fan in which case we’re probably ok as the air will help cool the unit. Or it’s something more sinister in which case there could be challenges ahead. The trouble is the winch is 130 kg and not easily moved around back to base for repair. Of course it’s just gone 100 years since Scott and his team reached the pole… second. So we’re not complaining.
And the data! Even the one profile recorded so far is interesting and probably the first such data from this complicated piece of the ocean where ice shelf water meets polynya water. In other words two radically different waters - but both associated with the birth of sea ice. The profile captured a warm (well… -1.9 oC) fresh layer just beneath the ice, then deep down there is a clear layer that is a little bit colder and saltier than the water around it. We hope to get a few more profiles over the next few days, especially in high resolution mode where we can really begin to unravel things.
7
Data!
Jan 19-23
The weather was too challenging
for us to
get to our field site for a few days which was frustrating as we were
all set
to go. On the plus side it’s not
often I
get to celebrate a birthday in Antarctica - or
We did have some modest
scientific
achievement in that we recovered four dust traps for a research team at
The next day’s waiting for weather involved a helicopter flight to within 5 km of the field site before we turned back by a wall of cloud over our field camp. This brought home to us how localised the good and bad weather can be around here. Finally, proving that patience is a huge virtue with Antarctic weather, we had a windless, sunny day at the camp and captured a serious amount of data. We took full advantage of the opportunity and had the equipment running pretty continuously through the day. It’s not a full tidal cycle but it is a substantial part of one.
Our main profiler is a Canadian-built instrument that can measure temperature and salinity down at perhaps the cm scale and to hundredths of degree accuracy. It also captures to tiny velocity variations in the ocean that act to stir up material and also represent energy lost from the main ocean currents. Equipment this sophisticated is rather delicate and needs a good deal of care and attention to detail to keep it running. However, give the harshness of the journey and conditions with which it must deal it’s a miracle it works at all, let alone consistently for hours on end.
The profile data show a myriad of slowly changing layers in the top 50 or so meters, sitting above a core fluid that remained pretty consistent in terms of its constituents. Just below the ice, the seawater was cooled down to near-freezing and suggested a pretty stable situation with regard to the condition and survival of this sea ice in the remainder of the season. Deeper, near the base of our profile at around 300 m depth (we can’t get right to the seafloor here as we couldn’t fly in a big enough winch) there was another layer with a clear signature that looks like it might have come from the nearby polynya – although with the warm weather the polynya itself is not obviously active. This we will need to tease apart when other data from other sources like ships and satellites come in.
We were able to get out to the field camp again the following afternoon for some follow-up profiles to provide us with a comparison. Things had changed dramatically in the top 50 m and now there was a warm fresh layer that had slid in just beneath the ice and was almost certainly causing melting. Also, with this change came a good deal more turbulence in the upper part of the ocean. If we can get out in the next day or two we hope to confirm the persistence of this warm layer, because if it remains it will have a dramatic effect on the sea ice structure.
A couple of emperor penguins came visiting during this most recent field day. They seemed a little less curious than previous encounters we’ve had as they didn’t come too close to camp. Other than that there have been a seal or two visiting the hydro-hole but nothing too disruptive. There are plenty of other holes in the area so I think they quickly decide they don’t need to share the space with oceanographic instruments. Also the bird life has a little more variety – i.e. more than just skua.
It is always tricky drawing global conclusions from such local finescale (– both in terms of duration and spatial extent) observations. However, the results give us a new perspective of some of the oceanographic processes in a basically unsampled bit of the ocean and give us a bit more certainty as to how to build ocean models. A quick look at the marine chart for the Victoria Land coast along the western Ross Sea shows a myriad of glacier tongues all jutting out into the ocean to varying degrees. While the Drygalski is far and away the biggest glacier tongue, they all certainly influence the local circulation. This in turn plays roles in regional aspects of both climate and ecosystem processes in what is a rather important part of the ocean (i.e. cold salty water for ocean thermohaline circulation and sea ice for habitat for algae that starts a massive food chain). Our new data give us some clues with regard to the way layers of ocean water collect and build up along the sidewall of the glacier. Also by sampling so late in the summer season we’re seeing some of the warmer waters and how they bathe the underside of the sea ice – reducing its resilience.
8
Stuck!
26feb
Despite being stuck on base due
to weather
for what is now the fourth day we feel incredibly lucky.
The station went from being the
This same swell started to eat
away at the
first year ice breaking it up into bite-sized floes – maybe 20-30
m across –
that stretched away into the distance as far as the eye could see. The wind continued to force the floes in
against the coast providing a spectacular vista. Brett
and I headed down to shore to watch the
waves and ice do their thing. The
quality of environmental documentaries these days is so high we are
familiar
with the look of such displays. But
nothing really compares with the reality happening right in front of
you.
Massive chunks of ice are tossed around as if they are weightless which
indeed,
whilst floating, they are in a way.
Penguins hopped on and off floes without a care in the world. I snuck off early to bed.
Brett, powered by youth, stayed up watching
the display and claimed to have seen an Orca blowing in the distance. He may have been having me on, but seeing as
Orca are a regular occurrence for us in
The wind changed direction
overnight,
picking up now to a not-inconsequential 40 knots. Hence
we are stuck on base despite it being a
bright sunny day. The helicopters (and
me) don’t want to be bouncing around in the wake of the mountains
to the west
of here. The wind made the sea of ice
disappear literally overnight. We now
have a sunny, wavy coastal vista that could be anywhere in the world if
it
wasn’t for the frozen volcano (
The ice floes end up in the
marginal ice
zone which surrounds
So now we are down to a scheduling squeeze. We have three more days to finish up here before our flight south. In that time we actually have to be able to get to our field camp to retrieve equipment that has been recording background properties, as well as the camp itself. We have also entertained the possibility that the ice upon which our camp is set up is now a floe too. We’ll deal with that if it happens. There’s a rule in oceanography – never expect anything you put in the ocean to come back. Certainly it’s nice when it does, but don’t assume it’ll happen. Sea ice oceanography, at least this time of year, is the same. I would say this, but from a distance people naturally focus on the cost of the equipment. The reality is, in the face of the operational costs of getting and staying (safely) here, the cost of the replaceable gear is far outweighed by the value of totally new observations (and ideas they spawn), in a new and important location and season.
9 Recovery Jan
26-
Finally came a break in the weather. The wind eased off and we got out to the sea ice camp. It was a nervous trip out as I thought open water on the horizon might be all that remained of our field camp. Fortunately, the water turned out to be much further south and our field area was as solid as it had ever been. Of course this is a slightly false sense of security as the ice can breakup in chunks at a moments notice. Satellite imagery from a few years back shows a 10x30 km piece of ice from the area we are on simply disconnecting from the coast over the space of a day. Something that big though stays together for a while and so with close helicopter support we’d be fine.
A reasonable pile of snow had
accreted
around the tent indicating that the local wind was from the South. This must’ve helped with the stability
of the
ice as it held the sea ice against the ice tongue rather than pushing
it offshore
as I’d pictured in my broken sleep during the previous night. We recorded some underwater video using our
trusty camera-on-a-flag-pole technique.
Not pretty, but effective. This
showed some hallmarks of ice shelf influence with platelets aggregated
into the
ice and a generally lumpy underside to the ice.
These are aspects our group, especially the two winter teams led
by Pat
Langhorne at the
Because of the difficulty getting out to our site and the looming return-deadline I decided to pull the camp as early as possible. Inevitably, I felt sure the weather would turn perfect for the remaining days. As it was, after some early success with the profiler, the decision was made for us by having a cable failure. This is readily fixable - but not in a tent. The problem occurred, we think, because the flow is so slow the profiler goes almost directly downwards making line tangle difficult to avoid. One of the tangles must’ve pulling so tight it broke wires within the cable - maybe.
We needn’t have worried about finishing early though as it took a couple of hours just to chip the tent out of the ice that had frozen around its edges. It all came flooding back to me that the downside of this tent is it takes forever to take down. This is a perfectly acceptable chore though as it also means it stays up in any weather. Besides, it only feels like proper sea ice science if you are scrabbling around on your hands and knees with an ice axe.
During the day Giannetta, our
Italian
collaborator, deployed a sea ice thermistor string.
Developed in
The other bit of gear that we recovered was an acoustic Doppler current profiler (ADCP for short). This sends out pings like a fish-finder but, as well as simply listening for the strength of the backscatter from the pings, it listens to their Doppler shift (i.e. like a passing ambulance siren) to gauge the speed of the water. The instrument was still pinging away when we recovered it so we knew it was still working - always a good thing. This will help us to determine the speed of the water, the strength of the tides and also to give us an idea of the amount of tiny suspended material in the water – beit ice crystals or biology.
The helicopters transport our
1500 kg of
gear using “sling loads” – big nets.
It’s a pretty effective way of quickly getting heavy gear
from place to
place and two loads will be sufficient for all our gear.
One sling load came back mid-afternoon while
we cleaned up camp. With the low wind
speeds we again took the opportunity to skim past the face of the
Nansen Ice
Sheet, making clear the myriad of patterns in the ice due to changes in
deposition and pressure.
The final sling load came back the next day and so began the laborious but important task of cleaning up the gear. Cleaning and rinsing everything as much as possible, from delicate instruments through to ropes and tents, makes them more likely to work next time.
10 Berg-tastic Jan
31-
Our last full day at Mario Zuchelli Station took sublime to new levels. We had the opportunity to use their coastal vessel, The Skua, for a few hours. It was great to look over the boat. There are no small boat operations out of Scott Base, nor have there needed to be for there has been a distinct lack of open water for the last decade or more. However this is changing and such operations may one day become part of the science support requirements. The Skua gets used for a range of sampling tasks as ice conditions allow. We took the vessel out to a modest grounded iceberg and sampled the ocean stratification and turbulence right by the berg in order to get a better understanding of how they melt when surrounded by open water rather than ocean capped by sea ice.
Rather than take our large
velocity-based
turbulence profiler I opted to bring a much more portable device, The
SCAMP,
that determines the amount of mixing from tiny temperature variations
over
distances as small as a mm. I’ve
struggled to get good results with this device in
One of the interesting things (to me!) about this sort of sampling is that it is actually doing quite simple things, albeit to incredibly high precision and with high signal to noise ratios. And also that these things were readily achievable to a degree decades ago. Where the challenge comes in is getting to enough places of importance and then getting enough data at the right times to represent the various conditions. There have been precious few attempts at directly measuring ocean mixing in Antarctic waters. Certainly, much of what goes on is as you would expect anywhere in the world’s oceans. It’s the departures from this, especially relating to unique features like the presence of massive ice shelves and glaciers, that need to be considered.
Being a small berg and seemingly well-grounded there was not much problem with the ice itself. However, even the slow, modest swell was enough to make holding the vessel off from the ice a challenge. The skipper did nicely bringing in the boat right over the spot I wanted and allowing me enough time to get the profiler into the water, the boat would then reverse out and stand off a few tens of meters whilst I paid out the thin line as the profiler slowly sank recording as it went. The thin kevlar line is only a few mm in diameter but is able to carry several hundred kilograms. Still, it takes some getting used to, throwing expensive equipment over the side of ships with nothing but a thin line for recovery. It could be tougher. There are deep ocean versions of our main profiler that have no line. When they return to the surface the operator has to rely on satellite communications, lights, keen eyes and nervous energy to get the gear and the data back.
One of the curious features of oceanography that a melting berg highlights is a set of processes relating to the combined and separate effects of heat and salt. If you were to throw some “seawater” into the ocean it would sink until it found a depth where the ocean density was the same as that of the injected water. The interesting thing is that the density of seawater mainly comprises the effects of temperature and salt concentration – and these two diffuse at different rates. So our injected patch of seawater might have quite different temperature and salt signatures to the water it found as its neighbour, even though it has matching density. The result then is the heat and/or salt start to diffuse and equilibrate such that the local density conditions might become unstable. Weird things happens – thin layers of constant density form- thermohaline staircases. If ocean models don’t capture this sort of effect they get the resulting circulation wrong.
11
Wrap-up
A busy last morning at Mario
Zuchelli
Station involved packing our pile of gear onto the back of a tractor
trailer
for the trip up the hill to the local airfield to be picked up by a
Twin Otter
aircraft. These planes work in remote
conditions throughout the world. Our
flight was the crew’s last flight of the season and they were
taking the
aeroplane to northern
We had excellent views on the
way
south. As we flew over our sea ice site
the aerial view revealed a large crack a little to the south of the
camp that
must’ve appeared in only the last four days.
Beyond that we passed over open water as well as vast areas of
pack ice
broken into a huge variety of scales.
These will either drift north and melt or be reintegrated into
multi
year ice contributing to a highly complex ocean skin that challenges us
constantly in terms of mapping its thickness, resilience and
suitability for
biological habitat. The challenges
around predicting future possibilities for the earth system and its
climate has
placed a strong spotlight on this aspect of
Now begins the task of collating, verifying and archiving the data. Actually much of this we’ve been doing as we go in the down-time between sampling. Once we’ve settled on good quality realisation of the results I have to tease it into some form of scientific story whereby the data fit into a context of need, questions, critique and implications. I’ll do this in conjunction with my various colleagues in the field, many of whom are vastly more knowledgeable than me on the topic.
And after all this I’m not going to tell you the punch line as to what we found! Before that happens I have to run my conclusions past my “peers” – essentially it gets torn apart and restructured by anonymous reviewers. One develops a very thick skin in this game. I have had papers that have had more space devoted to the reviews and response than the paper itself. This is a hugely critical part of science and a real challenge for field science where one simply cannot control every (any!) aspect. Certainly the process is not perfect.
The next mission is likely to take place in a years time and in many ways is even more challenging. We plan to sail to the Mertz Polynya area which until a few years ago was also home to a giant glacier tongue. This however was broken apart whn a large iceberg collided with it.
Thanks… MZS + PNRA, Helicopters NZ,Brett Grant, Giannetta Fusco, Giogio Budillon, Tim Haskell, AntNZ, Scott Base, Marsden Fund.
Collaborators
- Giannetta Fusco
