Icebergs, penguins, and the Lamont moorings

One of my favourite icebergs during the cruise. It followed us for a day in early April when we were doing a CTD section. We called it the ''pesky iceberg'' as it came quite close to a few of the CTD stations. Note the blue tint to the iceberg. Also note the lower flat portion on the right.  Binoculars revealed a field of penguin poop on that portion, left by the colony of penguins making this iceberg their home.

 

A group of chin-strap penguins near the ship, and coming from the iceberg in the above photo. Penguins in water are fast and sleek.  Consequently, they are difficult to photograph. This photo was one of many that I fired as they were swimming around the ship.  Only after I cropped the photo to zoom into the penguins did I discover just how wonderful this photo is.  Look close to see different poses of the penguins. They are quite amazing to watch as they zoom around trying to catch fish.

(Note: The remainder of this post concerns a mooring recovery/redeployment on 22 March.)

An iceberg neighbourhood around the Lamont moorings

The air temperature is -1C during the day and colder at night. The wind and humidity make it quite cold to stand on the Monkey Island overlook above the navigation bridge. Ocean swells are frequent, even with the relatively calm winds today. In the Southern Ocean, there is a good chance that a storm sits somewhere nearby, sending us the gift of ocean swell and the attendant motion. For today, the conditions are good for doing seagoing oceanography in this part of the planet.

We are located at the furthest south location of our cruise, at 63,32' S (read "63 degrees and 32 minutes latitude south) near 45 degrees west longitude. There are icebergs all around the ship.  Icebergs are floating islands of freshwater ice that broke away from one of the ice shelves rimming Antarctica. These ancient ice chunks are compelling and somewhat mysterious features of our ocean-scape.

Parts of the icebergs reveal deep blue shades of very pure ice (made blue for reasons similar to why the sky is blue), whereas other parts are the more familiar white.  These brilliant colours, along with their contoured patterns formed during calving, form an impressionistic image next to the gray sky and dark waters.  I find it difficult to remove my gaze from these creations, and I take one photo after another.

Wherever there are icebergs, there are bergy bits. Bergy bits are small chunks of icebergs that have been eroded away from the mother iceberg.  They represent the eventual fate of all icebergs during their melt into the surrounding liquid sea.

Some of the icebergs floating around us during the recovery and redeployment of the Lamont moorings on 22 March.  We purposefully remained distant from the icebergs, for safety reasons. Some of the distant icebergs are far larger than the ship.

I wonder which part of the Antarctic ice shelf these icebergs broke away from.  When did that happen?  How old is the ice? I understand that some ice shelves can be many thousands of years old.  Answers to these questions could be found by consulting a glaciologist with expertise on icebergs.  But for me today, answering these questions is less compelling than the fascination at simply watching the ice float on the nearby ocean. They are part of our neighborhood, keeping us company as we do our ocean field work.

Georgina is the ship's second officer. She was the officer in charge on the navigation bridge when I went up there to check out the vast expanse of icebergs in our neighbourhood. She was ever watchful, looking out towards the many icebergs.

Ship's radar on the navigation bridge, showing a light blip for each of the icebergs surrounding us.

For our safety, it is important to stay far away from icebergs. Hence, as wonderful as they are for "sight seeing scientists", icebergs are a bother for the navigation bridge. Radar technology allows us to view the extensive field of icebergs floating nearby.  Even so, vigilant visual watch is maintained by the officer on duty and the watchkeeper.  It is astonishing how eyes can become sensitive to objects on the distant horizon, readily picking out an iceberg, whale, or oceanographic instrument on the surface.

A bit about the science of icebergs and sea ice

The cryosphere refers to that portion of the planet that is frozen water, either on land or sea.  When studying ice floating on the ocean, it is useful to distinguish icebergs from sea ice since they have very distinct histories.  As noted above, icebergs are chunks of freshwater ice that broke away from an ice shelf.  In contrast, sea ice is frozen seawater, with some sea ice living through summer but most sea ice in the Southern Ocean newly forming each year.

The ice shelves that form icebergs are generally attached to one of the many ice sheets covering Antarctica.  Scientists have great concern that ice shelves are melting more rapidly as a result of excessively warm (due to human induced climate warming) ocean waters impinging on their underside.  As ice shelves melt, the ice sheets behind them loose their buttresing, thus allowing continental ice to flow into the liquid ocean.  Imagine releasing a cork from a champagne bottle.

Adding more land ice to the ocean increases sea level.  Our cruise is not directly studying these "ice-shelf / ocean" processes that contribute to ice shelf melting.  But these issues are on many of our minds. Indeed, some of the scientists onboard (e.g., Keith Nicholls from BAS) are part of allied projects investigating facets of the science.  There are good reasons to conduct this research, as sea level rise is among the most dramatic and societally impactful results of human induced ("anthropogenic") climate change.

The seasonal cycle of sea ice is massive in the Southern Ocean.  During summertime, most sea ice melts back to near the continental shelf margins.  In late winter, sea ice can extend well into the Antarctic Circumpolar Current to our north.

We entered the Southern Ocean during autumn, during which time sea ice extent is advancing to the approaching winter cold and dark.  For our science, we hope to avoid sea ice as it will make our work with moorings, CTDs, VMPs, and the auto-sub Boaty McBoatface logistically difficult if not impossible. Fortunately, the sea ice extent this year is quite low.  Hence, there is a good chance we will successfully avoid encountering sea ice.

The low sea ice in this particular Southern Ocean autumn contrasts to that of two years ago. At that time, the first DynOPO cruise came here during a period of especially large sea ice extent. These sorts of up/down fluctuations of sea ice extent illustrates the inter-annual variability typical of the climate down here.  This variability, which occurs naturally (i.e., "natural variability"), is superimposed on long term trends of anthropogenic climate change that are ubiquitous on the planet today.

Members of the crew looking over the side at the mooring that was being recovered.

Recovering and redeploying the Lamont moorings M2 and M3

We recovered and then redeployed two moorings today (M2 and M3), starting very early in the morning at daybreak. Povl Abrahamsen of BAS was in charge of both operations (he is an expert at ocean moorings), with help from Andy Davies from WHOI and others from the JC Ross crew. These two moorings are supported by Lamont-Doherty Earth Observatory, which is part of Columbia University in the USA. They are among the longest continuous in situ ocean measurements in the Southern Ocean.  Given our proximity to the moorings, and the presence of mooring experts onboard, we are "turning around" these two moorings to keep the data stream flowing to the broader research community.

Crew member slinging a rope with a hook to grab onto the mooring line. The yellow mooring floats are made from glass spheres surrounded by hard plastic.

Note that "in situ" ocean measurements refer to measurements taken by inserting an instrument directly into the seawater.  In situ measurements are the traditional means for sampling the ocean.  In addition, since the late 1970s, satellites have offered remote measurements of certain ocean properties from space, such as sea surface height and sea surface temperature.

As explained in the "Kurt's Mooring" post (22 March), a mooring is a cable anchored to the bottom, holding a suite of instruments and floats. Details of each mooring are a function of the desired measurements. Moorings M2 and M3 do not reach to the ocean surface.  Part of the reason is that the near surface ocean is highly turbulent and has a lot of wave energy (as we have experienced on this cruise!).  Such back/forth motion can stress the mooring cables and instruments, which can lead to damage over time.  Additionally, it is important to minimize the chances of moorings becoming damaged by icebergs passing by this region.  Finally, it is wise to keep moorings away from the near surface to reduce chances of becoming tangled in fishing gear.

Bringing the top portion of the mooring onto the back deck.  The mooring line is often tangled when bringing it onto the deck, thus necessitating a massive detangling process. This step is the start of a long process of bringing the mooring instruments onto the deck. Note that only those crew members on a safety leash can get close to the back portion of the deck.

A mooring location is recorded from its prior deployment of a few years ago.  When we reach the location, Povl sends an acoustic signal to the mooring, telling it to release its anchor that holds it to  the ocean seabed.  The mooring is always patiently listening for such signals, awaiting the time when it is to be recovered.  When it hears the signal, it releases hold and the floats then bring the whole string of instruments to the surface.

A lot can happen to a mooring over its multi-year deployment, even when deep in the ocean and away from surface waves and turbulence. And even if healthy, a high latitude mooring could find itself sitting underneath an iceberg or sea ice, in which case we would not be able to recover it. Fortunately, both the M2 and M3 moorings were successfully recovered today and they all appeared healthy. After recovery, the instruments were taken off the cable in order to download their data onto ship computers. Then, new instruments were pulled from their crates for redeployment of the moorings.

The turnaround for a mooring recovery/deployment takes a few hours, depending on amount of instrumentation on the mooring and the length of the mooring cable. Furthermore, we often do a CTD cast near the mooring location to help calibrate the mooring instruments.  There are many hands that participate in turning around a mooring.  As said at my son's school: "many hands make light work".  Even so, those working on the cold, windy, and rocky deck are extremely tired after doing mooring work.

I hope to have a future post about the DynOPO moorings located in the Orkney Passage.  We have about six of these moorings to recover on this cruise, with much of that work ongoing as I write today, 14 April.