We conducted year-round, monthly monitoring of the stable isotope composition of DIC and water in hypereutrophic Lake Kierskie, western Poland, along with isotope measures of calcite collected in sediment traps installed at 16 and 30 m water depth in the lake. Isotope data were supplemented by previously published data on physico-chemical variables in the lake water column. We sought to determine how carbon and oxygen isotopic disequilibria in calcite deposited in the lake’s laminated sediments vary seasonally, and what factors drive this variability. Deposition of calcite out of equilibrium with DIC and water was documented over the entire study period. For δ¹⁸O, the disequilibrium difference between successive months far exceeded the amplitude of the seasonal variability in the isotope composition of water. The biggest difference between the measured and calculated δ¹³C_calcite and δ¹⁸O_calcite values was observed during late autumn and winter sediment resuspension and redeposition (2.4‰ and 5.4‰, respectively). In the spring, δ¹³C_calcite and δ¹⁸O_calcite offsets from equilibria, 0.5‰ and 1.3‰, respectively, resulted from rapid precipitation of large calcite crystals. During summer, intense productivity and processes related to calcifying algae (“vital effects”) caused lower δ¹³C (0.5–1.8‰) and δ¹⁸O (2.8–2.9‰) in calcite. Differences between isotope values of calcite collected from the two water depths were small, and might have resulted from different settling velocities of small and large crystals, and/or preferential dissolution of smaller grains. We suggest that winter laminae should be excluded from isotope studies of varved sediments whenever possible, as they likely contain redeposited carbonate in which the isotope value is not indicative of conditions in the lake at the time of laminae formation. We also recommend supplementing isotope analysis of calcite in varved lake sediments with seasonally resolved analysis of carbonate content. It appears that major shifts in the proportion of carbonate deposited across seasons can cause notable changes in mean annual values of δ¹⁸O_calcite and δ¹³C_calcite, even if DIC and water isotopic compositions remain stable.

我们全年对波兰西部富营养化的Kierskie湖中DIC和水的稳定同位素组成进行了每月监测，并收集了在水深16和30 m处安装的沉积物捕集阱中方解石的同位素测量值。以前发表的有关湖水柱中理化变量的数据对同位素数据进行了补充。我们试图确定沉积在湖泊叠层沉积物中的方解石中的碳和氧同位素不平衡如何随季节变化，以及是什么因素驱动这种变化。在整个研究期间记录了方解石与DIC和水的不平衡沉积。对于δ ¹⁸O，连续几个月之间的不平衡差异远远超过了水同位素组成的季节性变化幅度。之间最大的区别测得的和计算出的δ ¹³ C ^_方解石和δ ^18个ö_方解石（分别为2.4‰和5.4‰）值晚秋冬沉积物再悬浮和再沉积过程中观察到。在春天，δ ¹³ Ç_方解石和δ ¹⁸ ö_方解石从平衡偏移，0.5‰和1.3‰，分别导致从大方解石晶体快速沉淀。在夏季，高生产力和与藻类钙化有关的过程（“生命效应”）导致较低的δ¹³ C（0.5-1.8‰）和δ ¹⁸O（2.8-2.9‰）方解石。从两个水深处收集的方解石同位素值之间的差异很小，这可能是由于大小晶体的沉降速度不同和/或较小颗粒的优先溶解造成的。我们建议应尽可能将冬季层流排除在瓣状沉积物的同位素研究中，因为它们可能含有重新沉积的碳酸盐，碳酸盐中的同位素值并不表示层流形成时湖泊的状况。我们还建议通过季节性解析的碳酸盐含量分析来补充瓦尔韦德湖沉积物中方解石的同位素分析。目前看来，在碳酸盐沉积跨季节的比例发生重大变化可能会导致δ的平均年值显着变化¹⁸ Ø_方解石和D ¹³ C_方解石，即使DIC和水的同位素组成保持稳定。