A LATE HOLOCENE DECADAL-RESOLUTION TEMPERATURE RECORD FROM SOUTH GREENLAND: A CASE STUDY IN THE APPLICATION OF BRGDGTS TO ARCTIC LAKES

Greenland has a unique geographical position and geomorphological features, which play a key role in both regional and global climatic change. Obtaining high-resolution climate records from Greenland is essential for understanding the key forcing mechanisms of northern hemisphere climate change in the Holocene. Here, we use the Methylation of Branched Tetraethers/Cyclization of Branched Tetraethers (MBT/CBT) Index, an organic geochemical proxy for mean annual air temperature, to produce a decadally-resolved temperature record spanning the last 2000 years. The sediment core was collected in July 2016 from Lake 578 (W45°36’, N61°04’) in south Greenland, and the age model is based on ²¹⁰Pb and ¹³⁷Cs activity and ¹⁴C dating of terrestrial macrofossils. To examine relationships between branched glycerol dialkyl glycerol tetraethers (brGDGTs) and temperature, we also collected monthly samples with a sediment trap and compared brGDGTs distributions with corresponding in situ temperature. We find that temperature variation derived from the MBT/CBT index at Lake 578 is robust despite known complicating factors associated with the application of MBT/CBT proxy to lake sediments. Our temperature reconstruction reveals a gradual cooling trend from the core bottom (~200 AD) to the top (2016 AD), which is in accordance with the decreasing trend of Northern Hemisphere insolation. However, other forcing factors were also likely to have been involved. The climate of the south Greenland coast is influenced by adjacent sea surface temperatures. We posit that decadal temperature changes in South Greenland may result from the variable intensity of polar water flux. When the cold East Greenland Current is stronger and becomes the dominant control of the South Greenland region, our site experiences colder conditions. In general, the application of the MBT/CBT index to Lake 578 sediments provides promise for generating other temperature records from the Arctic.