The Bowman Lab

The dive team showed us this video that they took recently. It illustrates a couple of really interesting aspects of the relationship between sea ice and seawater. The stalactite-like projection extending down from the bottom of the sea ice is called a brine tube. Brine tubes form when some physical process causes very salty water to drain from porous ice. Since this brine is below the freezing point for relatively fresh seawater when the two come in contact the seawater freezes, forming a tube around the brine. You can still see the brine draining from the bottom of the tube. Anecdotal evidence suggests that these brine tubes are more active on sunny days suggesting that the ice warms up enough on these days to change its porosity. The ice where this video was taken is over 4 feet thick, only the bottom few inches likely warmed enough to drain. A rule of thumb exists for when the ice becomes so porous that the pores actually connect (like a block of very holey Swish cheese), called the “rule of 5s”. For ice that contains .5 % salt, at -5 C, 5 % of the total volume of water contained in the ice is liquid. This is a sufficient volume for the pores to connect and the brine to potentially drain from the ice interior.

This flushing has important implications for sea ice biology and the larger ecosystem. The brine flows out of the sea ice because it is denser than the underlying seawater that replaces it in the sea ice matrix. By now the ice algae have been active for some time and have probably depleted many of the nutrients within the sea ice brine. The incoming seawater replenishes these and allows primary production to continue. Recent research shows that the sea ice algae are not passive players in this process; they surround themselves with a gelatinous mixture of sugars and proteins that alters the physical structure of the ice. Among other things this enhances the porosity of the ice, encouraging an exchange of water.

Brine drainage might even effect have an impact on global climate. In an earlier post I talked about how specific salts form during the sea ice formation process (see “Pass the Salt”). One of the first salts to form, at a relatively warm temperature, is a form of calcium carbonate known as calcite. This is the same mineral that gives coral reefs their structure. It has been suggested that the flushing of sea ice “pumps” calcite into the water column. This pump is in essence a transfer of carbon from the atmosphere (where it exists as carbon dioxide) to the water column.

There’s a lot that we don’t know about brine drainage from sea ice. Here we’re observing it during the spring, but what about in the fall when sea ice is forming? A tremendous amount of salt is rejected from forming sea ice but due to logistical challenges researchers are rarely around to observe it (there have been some notable exceptions). And what about the sea ice bacteria that we study? Are they rejected along with the salt, or do they have some trick to help them stay in the ice?

Here’s a short YouTube video of the penguins we saw yesterday.  The sound comes on about halfway through for Shelly’s highly effective penguin call.

For the last couple of weeks we’ve been battling worsening sea ice conditions in McMurdo Sound.  Cracks between the different pans of land fast ice keep growing wider, and though they freeze quickly it can take weeks for the ice to be thick enough to travel over by McMurdo Station rules.  One particularly troublesome crack extends west from the Erebus Glacier Tongue effectively blocking all travel north of the tongue.  All throughout September we were able to travel over the crack safely, but it has widened significantly over the last two weeks.  Since our Tent Island sampling site is on the other side of the crack this presents a bit of a problem for us.

Today Shelly and I went out with Jen and another field safety staff member named Susan.  We thought that be traveling far out to the west, toward the center of McMurdo Sound, we’d be able to do an end-run around the crack.  We put a lot of miles on the snowmobiles heading west without the crack showing any sign of tapering off!  Unable to run around the end we measured the thickness of new ice over the crack in a few spots to try and find a safe crossing.  This was tough work.  It’s a wide crack and the irregular edges of the ice here had collected large rock-hard snowdrifts that had to be dug down to the ice surface.  When snow drifts and solidifies over a hollow space (like a crevasse or open water) it’s called a snow bridge.  Snow bridges and can be remarkably strong.  We had no doubt that the snow bridges and ice underneath would have supported our equipment and more, but the science teams have been issued strict instructions not to deviate from station rules.  Oh well!

As a consolation prize we were visited by a group of Emperor penguins at the farthest point west that we reached.  In contrast to the group that we saw a week ago, which was hunkered down for a storm, this group was quite active.  They spotted us from a ways away and, being naturally curious, came right on over.  We took a mandatory penguin-watching break and sat down to see what they would do.  It was a funny exchange; they got remarkably close to us and then stood and stared (while we stared back).  After about 45 minutes, cold and mindful of the fact that we still had a lot of work left to do, we finally get up and started getting ready to go.  Satisfied, all but one of the penguins wandered off to find more interesting things on the ice.  The remaining bird followed us over to our snowmobiles and kept staring even after we started them.  I think he (she?) would have taken a ride had it been offered.

Tomorrow Shelly and I will head back out to try and get some ice cores.  Since we can’t get to Tent Island we will have to try and find a site on this side of the crack that mimics our old site as close as possible.  That’s far less than ideal, any number of differences might exist between ice collected at the two sites, but that’s how field work goes sometimes!  It often seems that it goes that way most of the time…

I had a great conversation this morning with a group of oceanography students from Soap Lake High School in Washington (thanks to teacher Matt Brewer for facilitating). They’d done their homework and asked some really good questions. Among other things they asked me to draw some comparisons between Soap Lake (just down the road from their school) and the environments we are studying in Antarctica. The comparison is interesting enough that it’s worth expanding upon here.

Soap Lake isn’t a normal lake, it’s one of several saline lakes in the eastern part of Washington state. In fact Soap Lake falls into a special category of salt lakes; it’s an alkaline or “soda” lake. This means it has an unusually high pH brought on by the presence of certain minerals (primarily carbonate). Other famous soda lakes include Mono Lake in California.

As I’ve mentioned before in this blog frost flowers, and anything else at the sea ice surface, tend to be very salt. So how similar are these two salty environments? If we based our answer purely on the amount of salt present they are pretty similar. Frost flowers contain up to 15 % salt (ocean water is 3.5 %). The most saline water in Soap Lake, which forms a permanent layer at the bottom of the lake, is also close to 15 %. But quantity of salt isn’t everything. The composition of the salt probably has a bigger impact on these ecosystems.

Frost flowers are basically frozen seawater but they don’t contain the same normal ions, or charged elements, found in seawater; sodium, chloride, magnesium, sulfate, and carbonate among others. Mix a bunch of different ions together in water and evaporate the water, the ions will pair off to form the salt left in the bottom of the container. For example sodium might pair off with chloride to form halite, or table salt. A similar thing happens when water freezes. The ions will pair off at specific temperatures, the resulting salt will leave the water and settle to the bottom. In seawater calcium joins up with carbonate to form the salt calcite at only -2.3 C, not long after freezing started. As the temperature keeps going down other salts are lost. Sodium comes together with sulfate to form the salt mirabilite at -7.6 C. So before frost flowers even get a chance to form they are already deficient in calcium, sulfate, and carbonate (there is so much sodium present in seawater that little is lost during the production of mirabilite).

Soap Lake has an excess of carbonate, frost flowers are depleted in it. This is a critical difference. No one has yet come up with a way to measure the pH on the miniscule amounts of water in frost flowers, if we could we might find that these brines are more acidic than seawater (pH of 8.6) for the same reason that Soap Lake is more basic. This difference in pH could have a substantial impact on biology in the ice.

There are however, some Antarctic environments that could be very much like Soap Lake. In the nearby McMurdo Dry Valleys (which we are scheduled to visit toward the middle of the month) there are many saline lakes including Don Juan Pond, possibly the most saline lake in the world*. These lakes aren’t alkaline lakes. Instead of carbonate salts these lakes are dominated by the bizarre calcium chloride mineral antarcticite. They do share one important feature with Soap Lake however; high concentrations of sulfur in a layer of deep water that never comes to the surface. We don’t yet know a whole lot about the microbiology of these lakes, but these two things – a high concentration of sulfur and a permanent layer of deep water – have produced an interesting microbial ecosystem in Soap Lake. This ecosystem includes an incredibly dense community of bacteria capable of making their own organic carbon from carbon dioxide and found, as of yet, in no other lake on Earth (see article here). Of course studying Soap Lake and similar exotic bodies of water in our own backyards yields a wealth of information and techniques that make it possible to understand the ecology of lakes in the Dry Valleys and other places where access is limited.

*By the measure of water activity, the most biologically useful measure for how salty something is. Antarcticite is extremely hygroscopic, meaning it has a high affinity for water. As a result adding a few grams of antarcticite to a test tube containing cells and water would have a much bigger effect than adding a few grams of sodium chloride, as the cells would not be able to “compete” effectively for the water.

Thanks to the Advanced Biology and Physical Science students of Omak High School for a great Skype discussion this morning, and thanks to teacher Nancy Ridenour for facilitating!

The dust hasn’t settled from yesterday’s flights yet.  The McMurdo Station staff is scrambling to accommodate all the new workers and scientists, and there are twice as many people around everywhere you go.  Another flight should make it in sometime later today, and more flights are scheduled for Friday.   All the chaos has left Shelly and I with comparatively little to do.  We aren’t scheduled to revisit our ice core time series site at Tent Island until early next week, and we can’t continue work on the ice edge until the new safety personnel have finished settling in.  During winfly Jem and Dan handled safety for science parties out on the ice.  During the summer Dan shifts to the communications department, working as a “rigger” to install radio repeaters and other equipment on the high peaks around McMurdo Sound.  These radio repeaters allow outlying camps to communicate with McMurdo Station without the use of satellite phones.  Jen remains with the department involved in field safety, but has her hands full teaching the new personnel!

We expect things to settle down again by the middle of next week at which time we’ll try to pick the pace back up with our field work.  That is if the ice conditions allow.  Right now a large crack south of Tent Island is preventing all vehicle travel in that direction.  If it closes up just a little bit we’ll be able to drive over it with a Piston Bully.  If it doesn’t we’ll have to try and find a way around it, but no one’s found the end of it yet.

With luck, and if ice conditions allow, we’ll be soon be able to switch from using the Pisten Bully to using snowmobiles to reach the ice edge.  In addition to saving a significant amount of fuel we’ll gain a significant amount of time; we can travel a lot faster over bumpy snow drifts in a snowmobile.  To get ready for this shift Shelly and I took the mandatory snowmobile training course today.  We’ve both driven snowmobiles in Alaska but it was good to get some instruction in snowmobile repairs.  The thought of being stuck way out at the ice edge with temperatures dropping and a snowmobile that won’t start isn’t pleasant, but I think we can deal with the most common problems now.

Otherwise it’s time to relax a little and catch up on other work.  Fortunately McMurdo’s a pretty active place.  In addition to two gyms, a basketball court, library, and movie lounge it seems that every night there’s an event (or multiple events) to keep us entertained.  Last night there were two “secret life” talks, where McMurdo staffers talk about previous jobs they’ve had.  One worked as a space shuttle technician at the Kennedy Space Center for eleven years, the other as a scientist right here in Antarctica!

On Saturday night we got some new satellite images showing that much of the new pack ice that’s been forming off of Cape Royds had sheared away from the landfast ice in McMurdo Sound, leaving a very large lead open west of the Cape. Not wanting to waste the opportunity Shelly and I made a last minute decision to head out and see if frost flowers were forming. Dan graciously gave up his day off to join us. We got off to a late start, we’ve all been pushing pretty hard of late and are getting slower in the morning! The need to bridge a large crack in the ice that’s gotten worse over the last couple of days slowed us further, and by the time we got to Tent Island (roughly half way to the ice edge off of Cape Royds) we were running out of time and the weather was deteriorating.

A kilometer or two later we noticed a funny bump on the horizon, almost directly on our old tracks heading out to Cape Royds. Visibility was still okay in that direction but we couldn’t really make out what it was. Distances are very hard to determine on sea ice, it could have been an iceberg at the ice edge 10 km further on or a seal much closer in. As we got closer the bump slowly resolved into a clump of Emperor penguins just off Inaccessible Island, the first penguins we’ve seen on this trip!

We expected to run into the smaller, more numerous Adelie penguins at some point; they have a colony at Cape Royds. Finding Emperor’s was quite a surprise. They are truly bizarre birds, and it’s difficult to imaging just what they were doing so far from either their colony (the closest one is at Cape Crozier, on the other side of Ross Island) or the ice edge. Both Emperors and Adelies are known for wandering long distances for their own purposes however, researchers in the Dry Valley’s have been surprised by Adelie penguins wandering past them in the direction of the Antarctic interior.

These Emperors weren’t nearly that lost – the ice edge was only 7 km away. I don’t know too much about these birds, but my understanding is that we are now in the time when both parents have left the chicks (who hatched back in late July, early August) at Cape Crozier and the other colonies to hunt. So these foraging parents probably decided to take a little sidetrip deeper into McMurdo Sound.

We spent around 30 minutes watching the group, they seemed to be hunkering down in anticipation of the approaching bad weather. By the time we were ready to move on the weather had deteriorated to the point where we decided to turn back. Conditions haven’t improved much, there’s no wind but heavy snowfall and little visibility. We were supposed to get the first two flights of the summer season today (the first flights in a month), they’ve been delayed for 24 hours. This is no problem to us, but frustrating for the McMurdo staff who have been here all winter – they can leave once these flights make it in!

Thanks to the students of Nespelem Middle School for an excellent Skype conversation this morning. I was really impressed by the depth of some of the questions asked! Thanks also to teacher Sheri Edwards for facilitating and writing a nice article about it here.

It seems like Shelly and I have been doing nothing but filter water for the last several days, but the end is in sight. I think we’ll finish off the last of our samples this evening, then it will be time to turn our attention to getting some new material. It’s difficult to know when our next opportunity to get on the sea ice will be. On Monday the main science season starts. Three planes each week will bring new scientists and staff for the station. There will be a LOT more people around and many more demands on the safety personnel. For the last four weeks there has been only one other group doing science on the sea ice, a team led by Prof. Adam Marsh at the University of Delaware. This group studies the physiology of polychaete worms that live in the sediment of McMurdo Sound. I’m a tad jealous of them because they collect their samples by diving underneath the sea ice, something that I’ve wanted to do ever since I learned it was possible (probably by watching Jaque Cousteau as a kid).

Every Sunday evening one of the science groups gives a public talk in the dining hall on their work. Last week Adam and his team presented, this Sunday it’s our turn. I learned some fascinating things about some of the marine ecology of McMurdo Sound. The benthic, or seafloor life in the Sound is very dense, looking much like a tropical coral reef.  Except in place of hard corals McMurdo Sound has large, delicate sponges. The deeper you go the bigger and denser life gets. This is a result of icebergs continually scouring the shallows, removing everything before it has a chance to get large.

The polychaete worms Marsh’s group studies like to live in places other organisms won’t, such as the sewage outflow site for McMurdo Station. Until recently McMurdo didn’t treat its sewage, and the sediments at the old outflow are particularly rich in organics. Bacteria are quick to colonize such spots and consume the organic material so quickly that all the oxygen is used up. The worms can tolerate lower levels of oxygen than most animals, and also like the high concentration of organics. They burrow through it leaving tunnels that allow new oxygen-rich water to enter. This allows other organisms to follow along and further degrade the organic material.

The group is particular interested in a genus of polychaete worms called Capetella. This genus, in addition to being especially tolerant to low oxygen conditions, is highly resistant to many toxins found in marine sediments. In the old days everything from McMurdo Station was disposed of by simply dropping it into the Sound. As a result some places in the Sound are highly contaminated with heavy metals, PCBs, and other chemicals. Bacteria can degrade many of these materials over time, but without oxygen they perform this service very slowly. Microbial degradation is likely much enhanced by actively burrowing Capetella.

Joining Adam in McMurdo are fellow benthic ecologist Stacy, graduate students Stephanie and Annemarie, and middle school teacher Mike. Mike is in Antarctica through the National Science Foundation’s Polartrec program which pairs teachers with scientists in the field. Mike dives with the team and shares the experience with his and other classrooms via a blog (with lots of great photos). Check it out if you’re curious about what’s it’s like to dive under the ice in Antarctica!

Last week’s successful sampling efforts have left us with a lot to do this week.  On Monday Dan and I went back out to the ice edge to sample mature first year ice, the final sample in our four part set of ultra-large samples from this area.  Completing that was a huge relief, although melting and filtering all of that ice (900 kg total between frost flowers, young sea ice, and first year ice) is going to be quite a task.  We still have to aquire some equally large samples from glaciers in the Dry Valleys, but logistically this should be much simpler.  Sampling at the ice edge went off okay despite the fact that the motor we normally use to power the coring equipment wouldn’t work.  This sort of thing is pretty normal in the cold, so we switched to a smaller backup motor and finished up pretty quick.

Ahead of schedule we decided to do a little reconnaissance of some cracks in the ice near Barne Glacier, an impressive glacier that flows into McMurdo Sound from Mt. Erebus.  The absence of multiyear ice from McMurdo Sound and the abnormally warm winter have left the McMurdo Sound sea ice more difficult to travel over than in normal years.  One of Dan and Jen’s jobs prior to the start of the summer season is to map out safe travel routes over the sea ice and identify problematic cracks.  Fractures are everywhere on sea ice.   Most are not dangerous but some can become wide cracks (essentially small leads) over time if the winds and tides exert enough stress on the ice.  A crack can widen to a half meter of more overnight and then be camouflaged under a layer of snow. 

The route we’ve been taking out to the ice edge is in danger of being blocked off by a crack just like this, right now it can only be crossed safely in a couple of spots.  Normally an alternate route can be found inside of (east of) Tent and Inaccessible Islands, heading north past Cape Evans and the Barne Glacier.  Right now this passage is blocked by a large crack south of Tent Island that might heal in the coming weeks, but we confirmed another impassible crack at the Barne Glacier effectively shutting off this route.  We were very lucky to get such good access to the ice edge early in the season; the summer science groups will start arriving next week and some that work around McMurdo Sound will be hard pressed to reach their normal study areas.

The Barne Glacier was as beautiful up close as it looked like it might be from a distance.  At the base of the glacier the sea ice pulls away, leaving an easy access point for seals.  Seals were lying all around the ice at the base of the glacier and we could see a number breathing through the thin ice there.  After the glacier we headed to our second objective for the day, a site near Tent Island where we are taking periodic ice cores for a time series of microbial community composition during the seasonal transition.  Here’s where the day got a little bit interesting.  We were within sight of being done and back to McMurdo in time for dinner (which rarely happens when we head out) when the ice corer become very stuck in the ice.  As I mentioned earlier the large motor that we normally use wouldn’t start in the cold.  This motor drives the corer slowly, but with a tremendous amount of torque.  Instead we were using a much smaller, faster, and weaker motor.  Midway through drilling the core barrel stuck in the ice, firmly frozen in place.  This happens sometimes with very cold ice. 

The next couple of hours unfolded comically as we went to more extreme lengths to get the core barrel back out of the ice.  After about thirty minutes we realized that no tool at our disposal was going to get the barrel to back out by turning, so we decided to excavate.  This was a little unnerving, core barrels are expensive and made of fiberglass, so they are easily damaged.  The last time I saw one get dug out in a similar situation it sustained serious damage.  We slowly but surely chainsawed and picked a pit around the corer and eventually got it free.  Totally exhausted we finished up and headed for home.

 

It’s been good frost flower growing weather in McMurdo Sound over the last few days and we benefitted with an excellent collection on Friday.  Heading out with Dan and Jen we got as close to our old sampling site at Cape Royds as we could, which it turns out wasn’t very close.  The ice had sheared off further from the old edge than we had thought; you could see our old tracks go right off the ice edge!  In this case the edge didn’t mean open water though, temperatures have been hovering between -30 and -40 C (approximately -20 to -40 F) driving a lot of new ice formation.  The photo above shows the whole evolution of new ice edge, starting with the first satellite image of the area for the season on September 21.  The middle image is from the 22^nd, and the right image is from the 23^rd.  On the 21^st the thick black line is the new lead between the land fast ice to the south (bottom in the image) and the drifting pack ice to the north.  Only 24 hours later in the middle image the lead has frozen so solidly that it is indistinguishable in the satellite image from the older young ice present elsewhere on the 21^st.  That sudden growth of young ice seems have held everything in place between the 22^nd and 23^rd.  Despite a persistent breeze from the south there is almost no change to the location of individual ice floes.  Yesterday the wind really ripped through McMurdo Station and we don’t have the next satellite image yet.  It’s entirely possible that an even newer lead has opened between the land fast ice and the pack ice!

Virtually every surface of the young ice that we visited or could see from standing on top of the Pisten Bully on the 23^rd was completely covered in frost flowers.  Out in the pack ice, where young is continually forming throughout the winter, the frost flower environment is impressively vast.  Spatially it’s much like looking out over a vast grassland.  It’s partially their extent that makes frost flowers interesting.  Because the ice surface temperatures are so low any microbial metabolism within frost flowers must be low, but the cumulative effect within all the frost flowers present at any one time could have interesting consequences.

On this sampling effort we needed to go really big.  Our final analysis requires a lot of DNA, so we need a lot of bacteria!  Taking advantage of the fact that we could drive nearly to the frost flowers we almost doubled our haul from September 19^th, pulling in 300 kg of frost flowers (661 lbs) and equal amounts of young sea ice and seawater.  Now comes the really hard part, getting all that material melted down and filtered!  It will take us more than a week to get caught up on that part of the process, and in the meantime we still have to collect an equally large quantity of mature first year ice to round out our sample set.  We might have to divide-and-conquer tomorrow to avoid falling behind schedule, with Shelly filtering and me getting more ice cores.  Whether we can do that depends on whether we can get Dan or Jen to spend a whole day helping me in the field…

I haven’t yet spend a lot of time on this blog talking about working or living conditions here at McMurdo (both are pretty good).  To give a little introduction to Crary Lab, the excellent new science building where we’ve been spending much of our time, I’ve prepared a short video tour of the -1 C cold room where we do most of our sample processing.  To go along with it there’s a 360 degree photosynth of the room, and as a bonus a similar photosynth of the station from the Crary rooftop (I needed an excuse to play around with photosynth some more).

 

I know there are several teachers with classes reading this blog.  We would like to visit a select number of classrooms via Skype (or an alternate media, possibly Vyew) over the next 2-3 weeks to share some of our experiences and to let students ask questions.  As you might be able to tell from reading this blog we have to retain a certain amount of flexability in our schedule in order to take advantage of changing conditions.  As a result we don’t know how many calls we can accomodate.  Priority will be given to teachers with whom I’ve already communicated with on this subject (including teachers of the PSBB Millenium School), followed by first-come first-serve.  You can sign up via Google Docs here.  Once I have the information specified on the sign up sheet I will email you to arrange a specific day and time that works for your class and to work out any technical issues.