Search

Reconstructing past climate seasonality is fundamental to understanding the nature of past climate changes. This is especially true in the Arctic, where climate is intensely seasonal and proxies that can distinguish climate conditions of multiple seasons in a single year are relatively rare. We propose that submerged aquatic mosses, which are abundant subfossils in some Arctic lake sediments and have distinctive seasonal growth morphologies, can be used to estimate past lake water oxygen isotope composition (δ18O lw) across multiple seasons. Aquatic mosses are abundant, well preserved, and grow continuously in Arctic lakes whenever light is available, with some species displaying unique seasonal morphologies influenced by water temperature. Although Greenland paleorecords suggest that aquatic moss oxygen isotope values (δ18O om) reflect the δ18O values of lake water, no modern calibration between δ18O om and δ18O lw exists in Greenland. We present a modern δ18O om vs. δ18O lw calibration using multiple moss species or morphotypes from eight lakes and ponds near Pituffik (Thule), northwest Greenland. We find strong linear relationships (r2 = 0.76-0.85) between the δ18O om and δ18O lw values of multiple species or morphotypes across the range of relatively low δ18O lw values at Pituffik, and our results indicate isotopic fractionations are similar to those found previously at lower latitudes. To assess the potential of mosses as archives of seasonal δ18O lw values, we analyzed δ18O om in season-specific segments of moss strands, with seasons identified based upon growth morphology. Moss inferred lake water δ18O values (δ18O lwom) are higher in autumn than spring or summer, likely due to increasing contributions of 18O enriched precipitation and the cumulative effects of lake water evaporation throughout the ice-free season. For moss subsampled throughout summer, δ18O lwom values generally increased through the season in parallel with observed δ18O lw values. Potential temperature dependent fractionation effects during biosynthesis, however, remain unconstrained and should be further addressed with future research. Overall, these findings suggest that aquatic mosses from lake sediments could be used to directly resolve climate seasonality of the past. • Aquatic moss strand δ18O values reflect lake water values through multiple seasons. • Summer subsampled moss strands show weekly to monthly evolution of lake water δ18O. • Aquatic moss vs. lake water δ18O calibrations are similar for species tested here. • Aquatic moss δ18O needs testing down core to evaluate past seasonal signals. • Temperature-dependent fractionation and pre-treatment effects need more research. [ABSTRACT FROM AUTHOR]

The impact of warming, acidification, and deoxygenation on deep-sea environments is a growing concern. Historical records are sparse, particularly at high latitudes, making climate change projections challenging. Indirect proxies, such as trace element composition of marine carbonates, such as coral skeletons, can offer an alternative method to fill data gaps but have not been realised. Here, using Laser Ablation Triple-Quadrupole Inductively Coupled Plasma Mass Spectrometry (LA-QQQ-ICP-MS), we examined micrometre-scale element variation within and between individual colonies of the bamboo coral Keratoisis sp. obtained from the Eastern Canadian Arctic. These data are used to assess the influence of biological variability on geochemical tracers for reconstructing past environmental conditions (temperature: Mg/Ca, Li/Mg, Sr/Ca, Ba/Ca, U/Ca; [Ba] SW : Ba/Ca). We place these data into context, based on a survey of literature data, using refined calibrations for high-Mg calcitic Octocorals. We find reproducible (2σ relative coefficient of variation) values of Mg/Ca (3%) and Ba/Ca (6%) along the radial growth axis of all colonies and internodes of Keratoisis sp., indicating that these signals are likely suitable for environmental reconstructions. After revising the available multi-taxa calibrations for Mg/Ca (0.316 ± 0.026 °C/mmol/mol, R2 = 0.87, p < 0.001) and Ba/Ca ([Ba/Ca μmol/mol] = 0.148 ± 0.005 [Ba SW nmol/kg], R2 = 0.97, p < 0.001), we show that vital effects within and among Keratoisis sp. colonies strongly influence reconstructed temperature and [Ba] SW , but this can be somewhat mitigated by combining multiple internode transects from one colony into a single composite series. Despite the ontogenetic variability, all colonies reveal a gradual deep-water cooling trend since the early 21st century and synchronised, multi-year spikes in Ba/Ca (and hence [Ba] SW) that suggest substantial and coherent barium inputs to the seafloor. Our study confirms the reliability of Mg/Ca and Ba/Ca proxies in high-Mg bamboo corals for detecting multi-annual temperature and seawater barium variations in cold-water environments, but further investigation into micro-scale element behaviour influenced by biotic processes in these corals is needed to enhance confidence in reconstructions at finer spatial and temporal resolutions. We conclude that employing empirical calibrations based on multi-taxa approaches can increase the certainty of capturing regional changes in the environment more accurately than a single species calibration, while leveraging multiple element series to account for biological-induced variability improves single colony reconstructions. • Trace element patterns in Arctic Keratoisis vary between and within colonies. • Leveraging element patterns across internodes improves reproducibility of signals. • Integrating intra-specificity in living proxies enhances deep-water reconstructions. [ABSTRACT FROM AUTHOR]