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Why Study Sea Ice?

Golden measuring sea ice SIPEX 07

Three researchers from the University of Utah–math professor Kenneth Golden, math doctoral student Christian Sampson, and electrical engineering grad student David Lubbers–are bound shortly for a two-month research mission on an icebreaker in Antarctica. This is the 15th excursion for Golden and the second trip for Lubbers. He was an undergraduate on his first trip in December 2010 and that experience influenced his academic future. Lubbers will be blogging periodically from the ship.

I’d like to tell you a little bit about the actual goal of this expedition.  So, why are we interested in studying sea ice?   It is a leading indicator of climate change, and a key component of Earth’s climate system. The dramatic decline in summer Arctic sea ice is being tracked by measuring its areal extent from satellite data.  This information is combined with ice depth data, where it exists, to monitor the volume of Arctic sea ice that survives the summer melt cycle.

In the Antarctic the sea ice almost entirely disappears in the summer and returns in the winter.  This is in contrast to the Arctic, where much of the ice survives the summer thaw to become multi-year ice.  However, much of what used to be multi-year Arctic ice is now melting away during the summer thaw.  It is believed that the melting is due to the warming of our climate.

Aside from acting as an indicator of climate change, sea ice plays a very active role in influencing the climate system.  The earth is continually bombarded by radiation from the sun, much of which is in the form of visible light.  Upon reaching earth this radiation is either absorbed or reflected back into space.  The term used to indicate how reflective the earth is in various places is “albedo,” which is the ratio of reflected sunlight to incident sunlight.  White sea ice and snow have a high albedo close to 1, so much of the incoming light is reflected back into space.  Seawater is dark and has a low albedo near 0, and as such it absorbs a lot of radiation that ultimately becomes heat.  The melting of Arctic ice in the summer significantly lowers the albedo by exposing darker ocean water and surface melt ponds.  Even a small section of exposed ocean will absorb a significantly greater amount of heat than ice would.  This accelerates the melting in this area, which in turn causes further decrease in albedo, and more melting, which is known as the ice-albedo feedback.

Sea ice is a porous material.  Under appropriate temperature and salinity levels a significant amount of water can flow through it.  A change in the fluid permeability of sea ice has far reaching consequences.  Permeable ice allows melt water to drain, reducing melt pond formation.  This alters the rate of ice sheet melt.  Permeable ice also allows surface flooding when the ice sheet is snow loaded, which is particularly important in the Antarctic.  The resulting slush on the surface can subsequently freeze, causing the ice pack to grow in thickness.  Aside from growth and melt, fluid transport is also responsible for the movement of nutrients through the ice that are critical to algal communities that sustain the polar ecosystem.

During our expedition we will use a network analyzer to determine how much electromagnetic radiation is transmitted through an ice sample, as well as how much is reflected by it.  Direct electrical conductivity measurements will be taken on ice core samples using an earth resistance meter.  We will measure the fluid permeability of the ice by drilling a hole partially through the ice and measuring how quickly it fills with fluid.  We have tight fighting sleeves that are inserted into these holes to block the horizontal component of fluid flow.  This ensures we only measure how much fluid is flowing through the bottom surface of each hole.  At each station where we stop, the ice will also be sampled for crystallographic study, so we can directly look at the ice microstructure.

The data collected will be correlated to further understand the relationship between the electrical and fluid permeability properties of the ice.  Changes in ice microstructure and fluid permeability are difficult to measure remotely, but there is a desire to monitor these changes on a large scale.  The linkage of these different but related properties will ultimately be used to develop methods that allow remote monitoring of ice microstructure changes using electromagnetic tests.  

If you are interested in more information on the recession of summer pack ice in the Arctic, or other topics of polar research, please see the links below.

http://www.ipcc-data.org/
http://nsidc.org/daac/
http://www.math.utah.edu/~golden/
http://www.antarctica.gov.au/