Eastern Canadian Arctic Lake water Isotope Samples, 1992-2021

Lacustrine δ2H and δ18O isotope proxies are powerful tools for reconstructing past climate and precipitation changes in the Arctic. However, robust paleoclimate record interpretations depend on site-specific lake water isotope systematics, which are poorly described in the eastern Canadian Arctic due to insufficient modern lake water isotope data. We use modern lake water isotopes (δ18O and δ2H) collected between 1994-1997 and 2017–2021 from a transect of sites spanning a Québec-to-Ellesmere Island gradient to evaluate the effects of inflow seasonality and evaporative enrichment on the δ2H and δ18O composition of lake water. Four lakes near Iqaluit, Nunavut sampled biweekly through three ice-free seasons reflect mean annual precipitation isotopes with slight evaporative enrichment. In a 23° latitudinal transect of 181 lakes, through-flowing lake water δ2H and δ18O fall along local meteoric water lines. Despite variability within each region, we observe a latitudinal pattern: southern lakes reflect mean annual precipitation isotopes, whereas northern lakes reflect summer-biased precipitation isotopes. This pattern suggests that northern lakes are more fully flushed with summer precipitation, and we hypothesize that this occurs because the ratio of runoff to precipitation increases with latitude as vegetation cover decreases. Therefore, proxy records from through-flowing lakes in this region should reflect precipitation isotopes with minimal influence of evaporation, but vegetation changes in lake catchments across a latitudinal transect and through geologic time may influence the seasonality of lake water isotopic compositions. Thus, we recommend that future lake water isotope proxy records are considered in context with temperature and ecological proxy records.

湖泊氢同位素δ²H与氧同位素δ¹⁸O代用指标是重建北极古气候与降水变化的有力工具。然而，可靠的古气候记录解译依赖于特定站点的湖水同位素系统特征，而加拿大北极东部地区因现代湖水同位素数据匮乏，相关研究鲜有报道。本研究利用1994-1997年与2017-2021年间采集的现代湖水同位素（δ¹⁸O与δ²H）数据，这些数据采自横跨魁北克至埃尔斯米尔岛纬度梯度的样带采样点，旨在评估入流季节变化与蒸发富集作用对湖水δ²H与δ¹⁸O组成的影响。对努纳武特地区伊魁特附近的4个湖泊在3个无冰季内每两周进行一次采样，其湖水同位素信号反映了年平均降水同位素组成，仅存在微弱的蒸发富集。在跨度23个纬度的181个湖泊样带中，吞吐型湖水的δ²H与δ¹⁸O分布于当地大气降水线。尽管各区域内部存在差异，但我们观测到清晰的纬度分布规律：南部湖泊的湖水同位素信号反映年平均降水同位素组成，而北部湖泊则对应夏季主导型降水的同位素信号。该规律表明，北部湖泊可被夏季降水充分置换更新，我们据此提出假说：随着纬度升高，植被覆盖度降低，径流量与降水量之比随之上升，进而导致这一现象。因此，该区域吞吐型湖泊的代用指标记录应可反映受蒸发作用影响极小的降水同位素信号，但横跨纬度样带的湖泊流域植被变化以及地质历史时期的植被变迁，可能会改变湖水同位素组成的季节特征。据此，我们建议未来在解读湖水同位素代用指标记录时，应结合温度与生态代用指标记录开展综合分析。