Limnological Investigation of Antarctic Lakes and their Paleoclimate Implications
By: Pawan Govil
Summarized by: Baron Hoffmeister
What data were used?: A 78 cm sediment core from a freshwater lake in Larsemann Hills, East Antarctica was used to interpret historic climate patterns from the late Quaternary period.
Methods: The sediment core was analyzed using grain size distribution, as well as biological productivity indicators such as organic carbon and biogenic silica. Biogenic silica makes up diatom cell walls and is commonly called opal. This study used radiocarbon dating to measure total organic carbon present, and the biogenic silica was also evaluated using a wet alkaline extraction. A wet alkaline extraction is a method that isolates plasmid DNA or RNA from bacteria. This was used to determine the biogeochemical attributes of this lake.
Results: Using radiocarbon dating, this study found that this core is from the Holocene Epoch, a time that began around 11,700 years ago. This core was dated to be 8,300 years old. Most of the material in the core was sand, and clay and silt were rarer (sand, clay, and silt are defined by grain size in geology- sand is the coarsest grain size in this example; figure 1)The silica content within this was very low, indicating a very low abundance of silicate microfossils. The total carbon was low or negligible in the lower part of the core, likely due to the high sedimentation rates of sand during this time. The area of the core that had the most organic carbon was the top of the core that contained the small amounts of clay and silt. This study showed that this was due to a build of algae. The particles of clay and silt prevented oxygen from decomposing the organic matter. This indicates that during this time, approximately 4,000 years ago, there were low sedimentation rates and low oxygen levels in this lake. This algal mat at the top of the core indicates warming temperatures during this time, and that the lake had little interference with glacial ice. The fine grained sediments were deposited due to ice meltwater (as water slows down, fine grained sediments drop out of water suspension) and can be seen in the upper core. The lower portion of the core contains high sand content, which implies glacial river input (i.e.,fluvioglacial) before 6,000 ago. The overall paleoproductivity implications of the core are as follows. From 8,300 ago to around 6,000 years ago there was a period of warming. Around 4,000 ago, the warm temperatures allowed the lake to be free of ice and exposed to sunlight, and therefore this was the highest level of productivity and can be reflected in the upper core’s higher total carbon content.
Why is this study important?: Antarctica and its surrounding oceans influence climate across the entire planet. Antarctica holds around 90% of the world’s ice and about 70% of the world’s freshwater trapped in ice. The ability to be able to interpret past climate conditions that influenced climate patterns in Antarctica can allow scientists to better predict current day climatic changes in Antarctica and its effects globally. More information about Antarctica and its ice sheets can be found here.
The big picture: Today, the ice sheets are melting at a rate that has never been seen before. The effects of this could be catastrophic to life on Earth. Studies like these can allow scientists to better understand current-day climate patterns that could potentially help reduce the impact of widespread climate change.
Citation: Govil, P. (2019). Limnological Investigation of Antarctic Lakes and their Paleoclimatic Implications. Ministry of Earth Sciences, (24), 289-303. Retrieved May 24, 2020.