A downcore calibration of the TEX86L temperature proxy for the Baltic Sea. (1st December 2022)

• Record Type: Journal Article
• Authors: Wittenborn, Anna K.; Radtke, Hagen; Dutheil, Cyril; Arz, Helge W.; Kaiser, Jérôme
• Is Part Of: Continental shelf research. Volume 251(2022)
• Publication Date: 2022-12-01
• Subjects: iGDGTs -- TEX86L Temperature -- Calibration -- Sediment -- Monitoring data -- Reanalysis -- Hindcast simulation -- Baltic Sea; Continental shelf -- Periodicals; Submarine geology -- Periodicals; 551.41
• DOI: 10.1016/j.csr.2022.104875
• Languages: English
• ISSNs: 0278-4343

Abstract

Abstract: The Baltic Sea is a marginal sea sensitive to climate change. Relatively high sedimentation rates allow reconstructing Holocene climate variability with a high temporal resolution. The different TEX86 proxies (TEX86, T E X 86 L and T E X 86 H ) based on Thaumarchaeota membrane lipids (isoprenoid glycerol dialkyl glycerol tetraethers; i GDGTs) represent a unique opportunity to estimate past water temperature variability as other temperature proxies are not applicable in the Baltic Sea. Although numerous TEX86 calibrations are available, the Baltic Sea represents a particular environment characterized by brackish and permanently stratified waters. Since surface sediments used to establish temperature calibrations are restricted in space and time, a downcore calibration approach is proposed here, which consists of comparing TEX86, T E X 86 L and T E X 86 H values from a well-dated sediment core with observed water temperatures in the central Baltic Sea over the last 45 years. The most reliable relationship is between T E X 86 L and water temperature at 80–120 m, the depth range in which Thaumarchaeota are thriving in the Baltic Sea. This result is corroborated by the absence of a seasonal pattern in the T E X 86 L index derived from a sediment trap time series. Comparing T E X 86 L water temperature estimates from a sediment core covering the last 160 years with hindcast simulations suggests that T E X 86 L estimates might be affected by changes in redox conditions. This is most likely related to a change in the depth habitat of Thaumarchaeota. The application of the new calibration on a long sediment core from the central Baltic Sea validates its efficiency to reconstruct subsurface water temperature in the Baltic Sea over the mid-to late Holocene. Highlights: Downcore TEX L 86 calibration for the Baltic Sea. Most reliable relationship between TEX L 86 and subsurface water temperature. Close agreement between TEX L 86 temperature estimates and simulations.