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Iceberg Alley

12/29/2010, 6:08 PM by Lollie Garay
Sharon leads the way into Iceberg Alley<br/><br/>Credit: Tish Yager
Sharon leads the way into Iceberg Alley
Photo Credit: Tish Yager

Dec 29

Iceberg Alley

In yesterday’s blog I mentioned Sharon Stammerjohn’s work with the trace metal team. Sharon is a physical oceanographer and Assistant Professor in the Ocean Sciences Dept. of UC Santa Cruz. Grad student Evan Randall-Goodwin, also from UCSC, is working with her. I first met Sharon on the 2007 Oden expedition and I can tell you that she knows oceans!!

On a recent evening, Sharon directed the NBP deep into Iceberg Alley, an area near the Thwaites Glacier. This area is so shallow (~200m) that icebergs get stranded on it! The Thwaites Glacier (75° 30S 106°45W) is a large fast-flowing glacier whose acceleration has been the focus of many research studies. The glacier flows into Pine Island Bay. In March of 2002, an iceberg measuring 85km long and 65km wide broke off of the Thwaites ice tongue (the part that projects our from the coastline), and was named B22 (National Ice Center).

Sharon has contributed this description of her research focus on the NBP: “My component focuses on the ocean physical environment (vertical structure and circulation) and how sea ice, atmospheric variability and coastal processes affect the spatial variability in ocean properties. Because of the remoteness of the Amundsen Sea, ocean observations are relatively sparse, particularly for the polynya region, so we are busily acquiring vertical ocean profiles of temperature, salinity, dissolved oxygen, fluorescence and light transmittance at high spatial resolution throughout the polynya area. These data will allow us to identify different water mass types and their variability as influenced by atmospheric variability, sea ice and glacial ice (e.g., icebergs and coastal ice shelves). “

“Of particular interest is the influence of iceberg and ice shelf meltwater in modifying water properties and ocean circulation in this region. These meltwaters contain iron-rich micronutrients, which are helping to fuel the high phytoplankton concentrations observed here. This is what motivated the ocean measurements we took along the Dotson ice shelf, i.e., to better characterize this ‘iron curtain’, as well as the transects in and out of ‘iceberg alley’ along the shallow eastern border of the polynya.”

“Changes in bathymetry are also very distinct across the polynya region, which is bisected by a deep trough that leads from the outer continental shelf break to the coast and disappears under the Dotson and Getz ice shelves. Ocean depths range from 700 meters to over a 1000 meters in these troughs (deeper towards the coast), with much shallower depths (350-500 meters) to either side of the trough system. This bathymetry plays a big role in defining the ocean circulation, particularly the delivery of Antarctic circumpolar deep water flowing at depth from the shelf break towards the coast. This salty water mass is up to several degrees above freezing, so where it interacts with iceberg keels and the bottoms of ice shelves, iron-rich meltwater is produced. This creates a slightly cooler and fresher version of this water mass, which is more buoyant and rises or is mixed with surface waters, thus delivering its micronutrients to the sun-lit areas of the polynya. “

“Changes in ocean circulation will thus lead to changes in meltwater production or its spatial extent, and this is what we are trying to better understand. To this end, we are also focusing on the bigger picture of ice-atmosphere-ocean variability and how this particular year of field observations compares to ice-climate variability and trends observed over the last ~30 years. To do this, we rely on satellite-derived variables (e.g., of regional sea ice and sea surface temperature) and on numerically analyzed meteorological variables (e.g., of regional sea-level pressure and winds) to characterize the year-to-year variability in ice-atmosphere interactions. For example, offshore of the polynya region, the winter duration of seasonal sea ice is decreasing, while storm forcing appears to be increasing. It’s very likely that these changes in sea ice and atmospheric circulation are driving ocean circulation changes, which in turn are driving meltwater production rates. “

Tish adds that they think that either the icebergs themselves or the sediment kicked up from the bottom as they move is a source of iron for the polynya. A map of the underway fluorescence (see image) shows over-the-top GREEN (in purple)! The color indicates high chlorophyll levels. According to Tish, this is higher than the levels in the Amazon Plume we studied this summer!

Sharon is on her 9th Antarctic research cruise and shares her personal reflections on this one:

“We have been really lucky with Neptune who has granted us fair weather, plenty of sunny days, and awesome scenery of the southern polynya coast, the Dotson ice shelf, the numerous and variously shaped icebergs bordering the polynya to the east, and the heavily deformed sea ice floes bordering the polynya to the north and west. As a Christmas Eve celebration, we had a lovely walkabout on an ice floe - and we couldn't have asked for a more magical setting. There were just enough clouds to catch the low sun angle, turning the horizon a beautiful pink blush, making a nice backdrop to the ice sculpted surface of the heavily deformed ice floe. From somewhere a football and Frisbee appeared, and we played for hours, running, tackling and basically relishing in the opportunity to move about on frozen ocean.”

What’s life on the ship like? “Most excellent. There’s such a great group of folks on board, both crew and science. Spirits are high, despite the long work hours, and there appears to be no shortage of good humor and camaraderie. In short, a very supportive and energized work environment.”

Sounds like a great place to work!

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.