Evaluation of the distributions of hydroxylated glycerol dibiphytanyl glycerol tetraethers (GDGTs) in Holocene Baltic Sea sediments for reconstruction of sea surface temperature: the effect of changing salinity

Abstract

Abstract. Hydroxylated glycerol dibiphytanyl glycerol tetraethers (OH-GDGTs) produced by both marine and freshwater thaumarchaea are increasingly used for the reconstruction of past sea surface temperature (SST). They occur throughout the modern Baltic Sea, but it is unknown if OH-GDGTs can be used for assessing past SST in this area, where salinity has changed considerably over the Holocene. Three commonly applied OH-GDGT proxies for SST reconstruction, i.e., the OH-GDGT%, RI-OH, and RI-OH′ indices, were tested using a thaumarchaeotal culture enriched from the Baltic Sea grown at 4 and 22 ∘C, as well as 12 surface sediments from the Baltic Sea and the adjacent Skagerrak. In the culture experiments all three proxies showed the expected response with the rise in temperature, but their absolute values were not always in line with existing marine core-top calibrations, especially for the OH-GDGT% index. Of the two proxies based on the distribution of OH-GDGTs, the RI-OH index shows no increase with increasing mean annual SST, whilst the RI-OH′ index shows only a linear correlation with SST when the sediments from the Bothnian Sea and Bothnian Bay area, with a reduced salinity and increased lateral sediment influx, are omitted from the dataset. Two sedimentary Holocene records from the Arkona and Gotland basins were studied, the latter in high resolution. In the brackish phase of the Baltic Sea (the Littorina Sea stage), the RI-OH′ index shows a good correlation with the TEX86L, an established temperature proxy in the Baltic Sea, and can be used to identify important climatic events. However, during the preceding Ancylus Lake phase the RI-OH′ (and RI-OH) index records values that are far too high, resulting in anomalously high SST estimates. This is probably because freshwater thaumarchaea adjust their OH-GDGTs differently, as has been shown for thaumarchaea in Lake Lugano's water column. In the Littorina Sea, Ancylus Lake, and Yoldia Lake phases of the Baltic basin, the record of the RI-OH′ index thus most likely reflects changes in both temperature and salinity. Overall, our study indicates that a reduced salinity increases the values of the RI-OH′ (and RI-OH) indices substantially, and this should be considered when applying these proxies in other settings.

Biomarker characterization of the North Water Polynya, Baffin Bay: implications for local sea ice and temperature proxies

“…In addition to temperature, recent studies have shown that several other environmental and geochemical factors can influence the degree of GDGT cyclization, such as growth phase (Elling et al, 2014), ammonia oxidation rates (Hurley et al, 2016), and oxygen concentrations (Qin et al, 2015) but not likely salinity (Wuchter et al, 2004(Wuchter et al, , 2005. Although the effects of these environmental parameters on OH-GDGT cyclization have not been rigorously tested, emerging evidence suggests that salinity, sea ice, seasonality, and terrestrial input may be complicating factors in some oceanic settings (Fietz et al, 2013;Kang et al, 2017;Lü et al, 2019;Park et al, 2019;Wei et al, 2020;Sinninghe Damsté et al, 2022).…”

“…However, BAYSPAR does not include surface sediment for sensitive oceanographic regions like Baffin Bay (Tierney and Tingley, 2014). For this reason, developing local correlation-constrained calibrations can be particularly useful to capture the nuances of oceanographic variability in regions where global dataset coverage is lacking or where the temperature relationship deviates from global linear calibrations (e.g., Harning et al, 2019;Park et al, 2019;Fietz et al, 2020;Sinninghe Damsté et al, 2022). Moreover, exploring the potential influence of additional environmental variables (e.g., salinity, DO, nutrients) will help us better understand the mechanisms behind (and functionality of) this commonly applied paleotemperature proxy.…”

Archaeal Hydroxylated Isoprenoid GDGTs in Asian Lake Sediments: A New Tool for Terrestrial Paleotemperature Reconstructions

“…Sinninghe Damsté, Warden, et al. (2022) also noted higher RI‐OH values in lake sediments than marine sediments in several Baltic Sea sediment cores and attributed them to the effect of salinity. Recently, Xiao et al.…”

“…Sinninghe Damsté, Warden, et al (2022) also noted higher RI-OH values in lake sediments than marine sediments in several Baltic Sea sediment cores and attributed them to the effect of salinity. Recently, Xiao et al (2023) and Varma et al (2024) both found an unusually large range of RI-OH values in tropical oceans and attributed it to the effect of water depth.…”

Disentangling Effects of Sea Surface Temperature and Water Depth on Hydroxylated Isoprenoid GDGTs: Insights From the Hadal Zone and Global Sediments

“…All the original data have been deposited publicly to the repository of Zenodo (https://doi.org/10.5281/zenodo.7114938). All the supporting data can be found in the cited references (Chen et al., 2020; Davtian & Bard, 2023; Davtian et al., 2019, 2021; Fietz et al., 2013, 2016; Huguet et al., 2013; Kaiser & Arz, 2016; Kremer et al., 2018; Lamping et al., 2021; L. Liu et al., 2022; Lü et al., 2015; Morcillo‐Montalba et al., 2021; Sinninghe Damste et al., 2022; Wei et al., 2020; Yang, 2017; Yang et al., 2018).…”