A comprehensive study for the application of proxies based on glycerol dialkyl glycerol tetraethers in the Baltic Sea (TETRABAL)
Final Report Abstract
The aim of the present project was to understand the origin and functioning of a water temperature proxy (or indicator) to reconstruct the variability of Baltic Sea water temperature in the past using sediment cores. The temperature proxy (so called TEXL86) is based on membrane lipids (isoprenoid glycerol dialkyl glycerol tetraethers, iGDGTs) produced by Thaumarchaeota, a phylum of the Archaea, and which are well-preserved in Baltic Sea sediments. To calibrate this water temperature proxy, TEXL86 values measured on a well-dated sediment core were compared to observed water temperatures in the central Baltic Sea over the last 50 years. The highest correlation was found with water temperature at 80–120 m, what corresponds to the depth range in which Thaumarchaeota are thriving in the Baltic Sea (upper chemocline). A subsurface origin of the temperature signal was corroborated by similar iGDGT distributions and TEXL86 derived temperatures in sinking particles and surface sediments, as well as by the absence of a seasonal pattern in TEX L86 temperatures in sediment traps. iGDGT-based ratios even suggest different producers thriving in the water column of the Baltic Sea as a function of the oxygen content, i.e. near the oxic surface, in the hypoxic subsurface, and in the deep anoxic water. By applying the newly calibrated temperature proxy to a short sediment core, it was possible to reconstruct the variability of the subsurface water temperature over the last 160 years. The temperature record is in close agreement with water temperature simulations provided by climate models, but suggests that the simulations are overestimating the temperature by ca. 0.5 °C. Looking further back in time, the analysis of previous warm periods reveals that subsurface water temperatures were ca. 0.4 °C warmer-than-today about 6000 years ago (during the so-called Holocene Thermal Maximum), but ca. 0.3 °C colder-than-today during the more recent Medieval Climate Anomaly (ca. 800 years ago). Considering that the Baltic Sea is a marginal sea very sensitive to climate variability, the results obtained in the present study provide a unique opportunity to try anticipating the effect of the on-going temperature warming of the Baltic Sea.
Publications
- 2018. The invasive diatom Pseudosolenia calcar-avis and specific C25 isoprenoid lipids as a sedimentary time marker in the Black Sea. Geology 46, 507–510
Kaiser, J., Moros, M., Tomczak, M., Dellwig, O., Schulz-Bull, D., Arz, H.W.
(See online at https://doi.org/10.1130/G40294.1) - 2019. Changes in long chain alkenone distributions and Isochrysidales groups along the Baltic Sea salinity gradient. Organic Geochemistry 127, 92–103
Kaiser, J., Wang, K.J., Rott, D., Li, G., Zheng, Y., Amaral-Zettler, L., Arz, H.W., Huang, Y.
(See online at https://doi.org/10.1016/j.orggeochem.2018.11.012) - 2020. Impact of Eurasian Ice Sheet and North Atlantic climate dynamics on Black Sea temperature variability during the penultimate glacial (MIS 6, 130-184 ka BP). Paleoceanography and Paleoclimatology 35, e2020PA003882
Wegwerth, A., Kaiser, J., Dellwig, O., Arz, H.W.
(See online at https://doi.org/10.1029/2020PA003882) - 2020. Reconstructing N2-fixing cyanobacterial blooms in the Baltic Sea beyond observations using 6- and 7-methylheptadecane in sediments as specific biomarkers. Biogeosciences 17, 2579–2591
Kaiser, J., Wasmund, N., Kahru, M., Wittenborn, A.K., Hansen, R., Häusler, K., Moros, M., Schulz- Bull, D., Arz, H.W.
(See online at https://doi.org/10.5194/bg-17-2579-2020)
