Revisiting afro-alpine Lake Garba Guracha in the Bale Mountains of Ethiopia: rationale, chronology, geochemistry, and paleoenvironmental implications

Abstract

Previous paleolimnological studies demonstrated that the sediments of Garba Guracha, situated at 3950 m asl in the afro-alpine zone of the Bale Mountains of Ethiopia, provide a complete Late Glacial and Holocene paleoclimate and environmental archive. We revisited Garba Guracha in order to retrieve new sediment cores and to apply new environmental proxies, e.g. charcoal, diatoms, biomarkers, and stable isotopes. Our chronology is established using 210 Pb dating and radiocarbon dating of bulk sedimentary organic matter, bulk n-alkanes, and charcoal. Although bedrock was not reached during coring, basal ages confirm that sedimentation started at the earliest * 16 cal kyr BP. The absence of a systematic age offset for the n-alkanes suggests that ''pre-aging'' is not a prominent issue in this lake, which is characterised by a very small afro-alpine catchment. X-ray fluorescence scans and total organic carbon contents show a prominent transition from minerogenic to organic-rich sediments around 11 cal kyr BP coinciding with the Holocene onset. While an unambiguous terrestrial versus aquatic source identification seems challenging, the n-alkane-based P aq proxy, TOC/N ratios, d 13 C values, and the sugar Electronic supplementary material The online version of this article (

Nonuniform Late Pleistocene glacier fluctuations in tropical Eastern Africa

“…4 ). The basal ages of the core suggest that sedimentation in the Togona Valley started after ~16 cal ka BP ( 20 ). This leads to the conclusion that the outlet glacier in this valley retreated rapidly from its LPG stage III position.…”

The Holocene lake-evaporation history of the afro-alpine Lake Garba Guracha in the Bale Mountains, Ethiopia, based on δ18O records of sugar biomarker and diatoms

“…The timing of the AHP termination has been debated, and seems to be related to individual proxy responses (Castañeda et al, 2016). Erica and fire experienced maxima and minima during this period at Garba Guracha, but consistently decreased towards absolute minima from 5.2-2.5 cal ka BP (Gil-Romera et al, 2019), while the Botryococcus braunii content (Umer et al, 2007) and TOC values drop later at 4.5 cal ka BP (Bittner et al, 2020). This asynchronous proxy response may be related to the differential sensitivity of proxies to environmental change and individual drivers (Castañeda et al, 2016).…”

“…They incorporate information about changes in the catchment, including varying erosion, often without significant anthropogenic disturbance or desiccation (Arnaud et al, 2016). In eastern Africa, high-altitude paleolimnological research has been carried out at Lake Ashenge (2442 m asl; Marshall et al, 2009), Lake Dendi (2840 m asl; Wagner et al, 2018), Sacred Lake (2350 m asl on Mount Kenya; Barker et al, 2001Barker et al, , 2011Street-Perrott et al, 2008;Loomis et al, 2015Loomis et al, , 2017, and Lake Garba Guracha (3950 m asl on the Bale Mountains; Umer et al, 2007;Tiercelin et al, 2008;Bittner et al, 2020).…”

“…Their work indicates that Garba Guracha is one of the longest, most continuous high-resolution Late Quaternary environmental archives from highland Africa. With a new core, Bittner et al (2020) established a higher resolution chronology and analyzed XRF and biomarkers. Gil-Romera et al (2019) carried out charcoal and pollen analyses on the same core to show that fire has been a constant disturbance at millennial time scales in the Afromontane vegetation of the Bale Mountains, driving the long-term ecological dynamics of Erica spp.…”

Natural archives of long-range transported contamination at the remote lake Letšeng-la Letsie, Maloti Mountains, Lesotho

“…Although low Hg values have been reported for southern Africa in the past, leading to the suggestion of an African mercury "anomaly" (e.g. Black et al, 2011), this has tended to be related to unexpectedly low Hg levels in biota which would have been expected to biomagnify Hg through the aquatic food-web. However, given the atmospheric life-time of Hg may conceivably be around one year and hence Hg deposited to remote lake sediments could potentially be derived from any global source, an African anomaly may be less relevant.…”