Scientists are interested in the Mertz region as it one of 3 regions where deep water masses are formed. A polynya is an open body of water that is surrounded by ice, the area is kept open by the katabatic winds that come off Antarctica and blow the newly formed ice away from the coast. As sea ice is relatively fresh, so when it is forming it leaves behind very salty water. This cold, salty water is very dense and sinks down to the bottom of the ocean. This water flows around and is found in most of the ocean basins of the world.
In February 2010 the Mertz Glacier Tongue, that formed one side of the Mertz Polynya, broke off when another ice berg hit it. (It had already started to crack as it had probably grown too large and with all the pressure from winds, tides and other physical processes had become unstable.) The removal of this ice tongue from the region has completely changed the region. The location of the Mertz Polynya has shifted. Oceanographers are interested to see if this has changed the amount of deep water formation in this region and how this might impact the global oceans. The oceanographic moorings were put in to the area to continuously monitor the amount of salt, temperature and currents so that they can estimate the formation of the high salinity, dense waters.
Unfortunately these changes to the Mertz Glacier Tongue have also completely altered the sea ice. The area where the moorings are located was completely covered in thick sea ice this summer. The RV Tangaroa is only an ice strengthened ship and not an ice breaker - so despite the experienced Danish ice pilot, there was no chance we could get through.
Sunrise allows us to see how much sea ice there is and try to find a path through...
So change of plan... we spent most of our time looking for evidence of the high salinity, dense waters as they flowed off the Antarctic shelf and down a series of canyons. Searching for the end product, rather than the studying the formation of this water.
Nearer the end of the voyage we did get an opening on to the shelf to the east of the area we had hoped to get to. Over the last decade this area has often been covered in ice - so we went to explore, to see if there is high salinity water forming in this region as well. Possibly - the oceanographers still have to study the data. Unfortunately we had to retreat north very quickly as the sea ice was forming rapidly...
We were also looking at the biological productivity. We were looking for physical and chemical evidence for blooms of phytoplankton (the grass of the sea). On the shelf there was a large bloom....The large amount of productivity is obviously supporting a lot of animals - as we saw lots of birds, seals and penguins, and a few whales and orca. We had several very good photographers on board that got some amazing photos.
Some of Adrian Bass's amazing photos of the charismatic wildlife we saw.
So what has this got to do with geology? Well I was collecting some marine cores in the area - in the hope that changes in the mud provide clues about changes in the ocean currents over time - 1000s of years rather than the last few decades. We were also mapping the sea floor, providing the oceanographers with the information about where the canyons are exactly, and lots of ice berg scours, moraines and glacial features on the shelf. The latter provide us with evidence about the extent and dynamics of the glaciers since the last glacial (20,000 years ago).
I also collected some cores on the transit south and north to New Zealand, to fill in some gaps from some of my previous voyages. I hope that some of these cores will provide some important clues about changes in the Southern Ocean since the last glacial.
6 weeks is a long time to be away. Fortunately we had a great team on the ship with everyone getting along, most of the time. We had great food and in general we were very lucky with the weather, only losing a couple of days to storms on the voyage down. I did experience my first bout of sea sickness ever.... I will now have more sympathy for others on future voyages. Fortunately I got my sea legs after a day or so and was fine the rest of the trip. Unfortunately I always suffer from land sickness when I get home. The land was swaying for me for a couple days.
The team (Photo by Adrian Bass)
I now have enough samples and data to keep me going for the next decade... so I don't need to go to sea for a little while (at least a couple of years).
Sunset, with pancake ice starting to form (one of my photos)
More information and details (photos and fun) on the 36 blogs from the voyage (www.sciblogs.co.nz/fieldwork/).