NOAA/WDS Paleoclimatology - Lake Tanganyika 1500 Year TEX86 LST, BSi, and Charcoal Data

Instrumental observations suggest that Lake Tanganyika, the largest rift lake in East Africa, has become warmer, increasingly stratified and less productive over the past 90 years. These trends have been attributed to anthropogenic climate change. However, it remains unclear whether the decrease in productivity is linked to the temperature rise, and whether the twentieth-century trends are anomalous within the context of longer-term variability. Here, we use the TEX86 temperature proxy, the weight per cent of biogenic silica and charcoal abundance from Lake Tanganyika sediment cores to reconstruct lake-surface temperature, productivity and regional wildfire frequency, respectively, for the past 1,500 years. We detect a negative correlation between lake-surface temperature and primary productivity, and our estimates of fire frequency, and hence humidity, preclude decreased nutrient input through runoff as a cause for observed periods of low productivity. We suggest that, throughout the past 1,500 years, rising lake-surface temperatures increased the stratification of the lake water column, preventing nutrient recharge from below and limiting primary productivity. Our records indicate that changes in the temperature of Lake Tanganyika in the past few decades exceed previous natural variability. We conclude that these unprecedented temperatures and a corresponding decrease in productivity can be attributed to anthropogenic global warming, with potentially important implications for the Lake Tanganyika fishery.

仪器观测结果显示，东非最大的裂谷湖坦噶尼喀湖（Lake Tanganyika）在过去90年间持续变暖、水体层化加剧且初级生产力下降。上述变化趋势被归因于人为气候变化。然而，目前仍不清楚初级生产力下降是否与升温存在关联，且20世纪的变化趋势在长期气候变率背景下是否属于异常现象。本研究利用坦噶尼喀湖沉积物岩芯中的TEX86温度代用指标、生物硅重量百分比以及炭屑丰度，分别重建了过去1500年的湖表温度、初级生产力与区域野火发生频率。研究发现湖表温度与初级生产力之间呈负相关关系；同时，我们对野火频率（进而对湿度）的估算排除了径流养分输入减少是观测到的低生产力时段成因的可能性。本研究认为，在过去1500年间，湖表温度升高加剧了湖水柱的层化作用，阻碍了下层水体的养分补给，进而限制了初级生产力。我们的记录显示，坦噶尼喀湖在过去数十年间的温度变化已超出此前的自然变率范围。综上，这些前所未有的温度异常与同步发生的初级生产力下降可归因于人为全球变暖，该结果对坦噶尼喀湖渔业或具有重要的潜在影响。