Rock varnish is a manganiferous dark coating accreted on subaerially exposed rocks in drylands. It often contains a layered microstratigraphy that records past wetness variations. Varnish samples from latest Pleistocene and Holocene geomorphic features in the Lake Turkana basin, East Africa display a regionally replicable microstratigraphy record of Holocene millennial-scale wetness variability and a broad interval of wetter conditions during the African Humid Period (AHP). Three major wet pulses in the varnish record occurred during the generally wet interval of the early Holocene (11.5–8.5 ka) when the lake attained its maximum high stand (MHS) at 455–460 m. A >23 m drop from the MHS occurred between 8.5 and 8 ka. Subsequently two additional wet pulses occurred during the early to middle Holocene (8–5 ka) when the lake occupied its secondary high stand at 445 m. Collectively, these five wet phases represent an extended wet interval coincident with the AHP in the region. One moderate wet phase occurred during the subsequent climatic transition from the humid to arid regime (5–4.3 ka) after the lake level dropped rapidly from 445 m to <405 m. Five minor wet phases took place during the overall arid period of the late Holocene (4.3–0 ka) when the lake level oscillated below 405 m. These findings indicate that the AHP terminated rapidly around 5 ka in the Turkana basin in terms of lake level drop, but the regional shift in relative humidity from the AHP mode to its present-day condition lagged for about 700 years until 4.3 ka, hinting at a gradual phasing out in terms of moisture condition. These findings further suggest that Lake Turkana overflowed intermittently into the Nile drainage system through its topographic sill at 455–460 m during the early Holocene and has become a closed-basin lake thereafter for the past 8 ky.

岩石清漆是在干旱地区地下暴露的岩石上积聚的锰黑色涂层。它通常包含一个分层的微观地层，记录过去的湿度变化。东非图尔卡纳湖盆地最新的更新世和全新世地貌特征的清漆样品在非洲湿润时期（AHP）上显示了全新世千年尺度湿度变化的区域可复制的微观地层记录和较宽的湿润条件区间。当湖泊在455-460 m处达到最大高位（MHS）时，清漆记录中的三个主要湿脉冲发生在全新世早期的总体湿润时间段（11.5-8.5 ka）中。在8.5至8 ka之间发生了从MHS坠落> 23 m的情况。随后，在该湖处于其445 m处的第二高海拔时，在全新世早期至中期（8-5 ka）又发生了另外两个湿脉冲。总的来说，这五个湿相代表了与该地区AHP相一致的扩展湿润间隔。湖泊水位从445 m迅速下降到<405 m之后，随后的从湿润到干旱的气候转变（5-4.3 ka）发生了一个适度的湿相。在新世晚期（4.3-0 ka）的整个干旱时期，当湖泊水位在405 m以下振荡时，发生了五个次要的湿相。这些发现表明，就湖泊水位下降而言，图尔卡纳盆地的AHP在5 ka左右迅速终止，但相对湿度从AHP模式到目前状况的区域变化滞后了约700年，直到4.3 ka，暗示逐步淘汰水分条件。这些发现进一步表明，在全新世早期，图尔卡纳湖通过其位于455-460 m的地形基台间歇性地溢出到尼罗河排水系统中，此后在过去的8 ky内已成为一个封闭盆地湖。