The focus of this award is on the role of light-absorbing organic material (CDOM, for chromophoric dissolved organic material) in Arctic surface waters on sea ice retreat. The objectives are to 1) determine the sources of CDOM in the surface mixed layer of the western Arctic -- does it come from rivers, is it produced by phytoplankton, or by ice algae? 2) investigate how quickly and by what mechanism (photochemical or biological) the CDOM degrades, and 3) determine the impact of the CDOM on solar heating, thermal stratification, and ice melt. The PI and an associate will participate in a spring 2011 ice camp off Ellesmere Island in order to investigate these questions. The broader impacts of this research lie in its applications to understanding the recent and apparently ongoing retreat in the seasonal sea ice cover of the Arctic. It will directly impact the efforts of ocean modelers to simulate surface water processes that affect sea ice formation and melting.

Project Report

Summary: When plant matter dies and degrades (breaks down), some of the organic material that makes up the plant is released as dissolved organic material. A certain fraction of this material has light absorbing properties, and we call this chromophoric dissolved organic material (CDOM). You can think of this like a making a cup of tea, the action of pouring hot water over your bag of dead tea leaves breaks down the cell walls, releasing CDOM and turning the water a brown reddish color. The reason that we are interested in CDOM is that it is a strong absorber of solar energy especially in the UV and blue region of the visible spectrum. It can therefore be an important link between the penetration of sunlight and the warming of Arctic waters. Right now we know that CDOM is present in Arctic surface waters in the early spring, and we also know that high values are observed in sea ice. This preliminary data suggests that CDOM could be stored in the sea ice and released into surface waters in the early spring. The net result is the trapping of solar energy close to the surface and acceleration of surface warming. This leads to a positive feedback loop whereby warming leads to more ice melt and more CDOM release, leading to more warming and melting. We believe that CDOM could be a part of the missing puzzle piece that can help explain why sea ice is melting much faster than climate models have predicted. What we don’t know is what the ultimate source of the CDOM is, for example is it produced in the sea ice by algae, or is it incorporated into the ice during formation, in which case it comes from the water column and could quite likely be heavily terrestrially influenced. The source is important as it will determine how CDOM is impacted by climate change. If CDOM is produced by ice algae and stored in the ice, then the reduction of sea ice extent would mean less CDOM being produced and could result in warming slowing down due to the lack of CDOM. If the CDOM is produced on land and enters the Arctic Ocean via rivers then the continued warming on land, will increase CDOM in rivers which will in turn continue to accelerate the warming of Arctic surface waters. Our aim at the Catlin Ice Camp was to determine the sources and sinks of CDOM into and out of the surface Arctic Ocean, and to quantify the impact of this material on solar heating, ice melt and thermal stratification. It is hoped that this will provide information on how modifications in the cycling pathways of CDOM brought about by climate change in the Arctic (i.e. ice retreat, increased terrestrial runoff) will affect local mixing and ultimately, global thermohaline circulation driven by the sinking of cold Arctic waters. Research Methods The Catlin Ice Base 2011 (CIB) was located at N 78º 46.2’ W 104º 43.3’ in Deer Bay, Ellef Ringnes Island in the Canadian Arctic (see primary image). The camp was established in the first week of March 2011 and was continuously occupied until the 29th of April. Water column optical properties were consistent across the time period of observations. On average between 90 and 100% of the total water column absorption during this period was due to the presence of CDOM. Data from ice cores show that growth of ice algae in the bottom 20cm of the ice core (see ice core figure, green, Chl a) is correlated with increases in aCDOM at 374nm (see ice core figure, red, aCDOM), indicating that the seasonal growth of algae in the sea ice is a source of CDOM. Summary Ice algae are an important source of CDOM to the water column, they provide fresh material which can be quickly removed from the system by breakdown from sunlight and the bacteria in the microbial loop. The water under the ice has some CDOM even early in the spring before ice algae growth is high, this may be residual material from the previous summer. Educational activities I am a founding member of Science Alliance Live, which strives to connect scientific research to local communities through the arts For this project we developed a play called In Tuk in the Arctic (see photograph). In this play, children will meet Tuk, a Canadian Inuit dog, who protects Dr. Hill from polar bears, who helps her get over her homesickness, and who learns how to collect samples from the sea ice. Tuk discovers that studying the sea ice in the arctic can help children in Hampton Roads prepare for sea level rise. (Grades K-3).

National Science Foundation (NSF)
Division of Polar Programs (PLR)
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Henrietta N. Edmonds
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Old Dominion University Research Foundation
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