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On Moorings

12/14/2010, 11:06 PM by Lollie Garay
Povl (l) and Raul (r)study ice images.<br/><br/>Credit: Tish Yager
Povl (l) and Raul (r)study ice images.
Photo Credit: Tish Yager

Dec 13- 7 PM local time (= Dec 14 02:00 GMT)

72°24.2'S, 118°12.3'W

Air temp is -3.4C

Winds are 15 kts

Wind chill is -18C

 Awhile back I mentioned that before reaching the polynya, moorings were going to be recovered. The Mooring Team PIs are: Stan Jacobs, Hartmut Hellmer and Adrian Jenkins, (Lamont-Doherty Earth Observatory). Stan’s Technicians are Povl Abrahamsen and Raul Guerrero. Their research project is the Amundsen Sea Influence on West Antarctic Ice Sheet Stability and Sea Level Rise

The main purpose of the project is too look at water masses in the region and how they move over an annual cycle. The mooring "string" is an apparatus that has CTDs and current meters that measure continuously. Unfortunately, they can only store the data until you can come back and collect them. Thus, you MUST collect them, else they have no value. They are designed so that the tops of them are far below the sea surface so that icebergs don't catch on and drag them around. They are connected by an acoustic release to a very heavy weight that holds them to the seafloor until you send a signal. When they work, the sound signal causes the acoustic release to open up and let go of the weight. Then the whole string floats to the surface in about 10 minutes or less. So, why is this important?

From the ConOps document: “West Antarctica is a marine ice sheet grounded below sea level in an evolving ocean. Its stability in a changing climate hinges on the balance between surface accumulation, ice stream flow, iceberg calving and in situ basal melting of its fringing ice shelves. In the Amundsen Sea's greater Pine Island Bay, deep shelf ice is melting orders of magnitude faster than elsewhere around Antarctica, driven by intrusions of 'warm' deep water onto the continental shelf. Remote sensing studies have correlated that melting with thinning ice shelves, increased velocity of inflowing ice streams and drawdown of the adjacent ice sheet. Multi-year time series of ocean properties and currents are needed to better understand seasonal and interannual variability of deep-water access to the continental shelf and ice shelf cavities.

To clarify Amundsen Sea influence on the regional ice shelves and the effects of ice sheet change on the coastal ocean, 14 moorings were anchored to the sea floor in the eastern and central Amundsen Sea during NBP09-01 (January 2009) to record the thermohaline field and ocean circulation over a period of 2 years. The measurements obtained will be used to assess and model seasonal and interannual changes in ocean properties and circulation, and ocean interactions with the atmosphere and cryosphere”.

Technicians Raul and Povl use ice images with an overlain cruise track to figure out the best route (see images). Chief Tish says that it’s hard to get to the moorings with so much ice (they had to back up and ram the ice a bit). And,” it's hard to recover a mooring if there's too much ice around (it gets trapped under the ice when it comes to the surface)”.

I’ve attached a schematic of the moorings and a map (with bathymetry of the shelf) where all of them are located. According to Tish, today they got BSR #14! Tomorrow they will go get #8, then #7, then #9 (7,8, and 9 are in the open polynya). She adds, “We wanted to get 11 and 12, but they were in too heavy of ice conditions (you can only pop them up to the surface if you have some open water). Today's recovery was a bit of a miracle since we were in heavy ice, but they were able to determine that the mooring was located under a little opening in the ice (which we waited for - as the ice drifted over the site). I took a picture, but unfortunately, you can't very well see the tiny little green float that shows the arrival of the mooring at the surface. It's just a string of little green floats with some mossy-looking instruments strung on a line - so it's not particularly photogenic.” Having seen similar recoveries in the Amazon Plume of the Mid Atlantic earlier this year, I can vouch for the fact that they are REALLY hard to see in the open ocean until they are very close! (Think needle in a haystack!) We look forward to hearing about the successful recovery of the moorings.

On a lighter note, we have a fun anecdote from Rasmus: “After spending a few minutes every day in the front of the ship I noticed that almost every penguin and seal always tries to get away from the ship by going over the ice and rarely jump into the water (only when they really have to). I talked Maggie and we figured that this probably is the most efficient way for them to escape their natural predator’s leopard seals and orcas that don’t do well on ice. I attached a couple of funny picture of an Adelie penguin and an emperor penguin running away in their own clumsy way. Also today I got a bit lucky getting a crab eater seal while it is jumping out of the water to get away from the ship. When it got on the ice however it crawled the wrong way and after a minute it got cut off by the ship (5 meter away) at which point it stood up and looked very surprised, followed by an 180 degree turn a few seconds later!”

(BTW, a correction to a previous blog: Rasmus is a Danish PhD student working on the Swedish predator invasion project).

And finally, Peng Yi, a graduate student working with PI Ala Aldahan (chemical oceanographer, not onboard) reports that the “People Newspaper “ the most important newspaper in China” is very interested in the Antarctic ASPIRE expedition, and is publishing his weekly diaries! I downloaded a copy of the manuscript and had one of my students (James) who is fluent in Chinese read it to the class ☺

It’s so wonderful to hear that an international audience is following the voyage and is interested in the science. We’ve received emails from France, Denmark, the Netherlands, and of course many US cities.

Until the next post, Lollie

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Question of the Day

  • What are Polynyas and why are they important to study?

    Polynyas, are recurring areas of seasonally open water surrounded by ice.

    Energy and material transfer between the atmosphere, polar surface ocean, and the deep sea in polynas provide polar ecosystems with just the right ingredients needed for high productivity and intense biogeochemical recycling.

    Polynyas may be the key to understanding the future of Polar Regions since their extent is expected to increase with anthropogenic warming.