Stable isotope composition of tropical high-altitude fresh-waters on Mt. Kenya, Equatorial East Africa

Rietti-Shati, Miri; Yam, Ruth; Karlén, Wibjörn; Shemesh, Aldo

doi:10.1016/s0009-2541(99)00233-8

Cited by 63 publications

(33 citation statements)

References 11 publications

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“…They also suggest that anomalously heavy snowfall events recorded in diatom d 18 O contributed to Neoglacial ice advances inferred from lacustrine sediments and dated to >5.7 ka, 3.2-2.3 ka and 1.3-1.2 ka (Karlen et al, 1999). Increased glacier meltwater contribution and temperatures up to 48C warmer are inferred between 2.3 ka and 1.5 ka from biogenic opal in Mt Kenya's Hausberg tarn (Rietti-Shati et al, 2000).…”

Section: Discussion and Interpretationmentioning

confidence: 96%

Quaternary glaciation in Africa: key chronologies and climatic implications

Mark

Osmaston

2008

J Quaternary Science

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Multiple episodes of Quaternary glaciation are evidenced on >10 distinct mountain localities throughout Africa, with the best dated sites from Kilimanjaro and Mt Kenya in equatorial East Africa. A general paucity of radiogenic dates constrains the glacial chronology, and regional sequences have largely been based on correlations by relative weathering of features. Excellent glacial moraine preservation and other features of erosion put limits on the spatial extent of palaeoglaciers, and have facilitated advances in palaeo-equilibrium line altitude (ELA) analyses. All radiocarbon dates (n < 30) provide minimum ages of deglaciation, and are consistent with a widespread synchronous advance during the Last Glacial Maximum (LGM, 21 AE 2 ka). K-Ar dates on Kilimanjaro lava flows initially recognised up to three glaciations prior to the LGM. Over 100 cosmogenic radionuclide (CRN) 36 Cl exposure ages on glacial erratics and bedrock from Kilimanjaro and Mt Kenya date 16 landforms, confirming maximum glacial extent prior to Marine Isotope Stage (MIS) 10. No glacial geological features have been dated to MIS 6. While on Kilimanjaro the CRN ages confirm a clear LGM (MIS 2) maximum, Mt Kenya lacks definitive LGM moraines. Lateglacial advances or stillstands on both mountains are suggested by low-relief moraines dating to 14.6 AE 1.2 ka (two boulders) on Mt Kenya and 16.3 AE 1.9 ka and 15.8 AE 2.5 ka on Kilimanjaro. Multiple moraines upvalley have early Holocene ages ranging from 11.2 AE 0.8 to 8.6 AE 0.2 ka. Isolated and equivocal dates on both mountains also provide speculative evidence that the maximum extent since MIS 5e may have occurred close to 30 ka, similar to sites in South America. New palaeoclimatic understanding from lake and ocean proxies suggests hypotheses for the source of low-latitude climate changes causing the advances that can be tested with improved dates. A high degree of intra-regional variance in ELA is observed, with differences by aspect reflecting precipitation gradients. Future work should include more CRN dates, improved mapping and inverse climate-mass balance modelling.

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Section: Discussion and Interpretationmentioning

confidence: 96%

Quaternary glaciation in Africa: key chronologies and climatic implications

Mark

Osmaston

2008

J Quaternary Science

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“…Kenya (0 • S, 37 • E), which has a climate similar to Mt. Kilimanjaro, precipitation and lake water δD values were also found to be influenced by the "amount effect" rather than by the "altitude effect" (Rietti-Shati et al, 2000). However, due to the lack of measured source water δD data, we can only speculate about the factors which can explain the absent linear relation.…”

Section: Soil N-alkane δD Values Along Mt Kilimanjaromentioning

confidence: 87%

Assessment of soil <i>n</i>-alkane δ<i>D</i> and branched tetraether membrane lipid distributions as tools for paleoelevation reconstruction

et al. 2009

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Abstract. δ 18 O values of pedogenic minerals forming from soil water are commonly used to reconstruct paleoelevation. To circumvent some of the disadvantages of this method, soil n-alkane δD values were recently proposed as a new tool to reconstruct elevation changes, after showing that soil nalkane δD values track the altitude effect on precipitation δD variations (r 2 =0.73 along Mt. Gongga, China). To verify the suitability of soil n-alkane δD values as a paleoelevation proxy we measured the δD of soil n-alkanes along Mt. Kilimanjaro (Tanzania). At midslope, soil n-alkane δD values are possibly influenced by the present precipitation belt, causing D-depletion in precipitation, and hence in the soil n-alkanes. Consequently, soil n-alkane δD values do not linearly relate with altitude (r 2 =0.03), suggesting that, in this case, they can not serve as an unambiguous proxy to infer past elevation changes. In contrast, it was recently shown that the MBT/CBT temperature proxy, which is based on the distribution of branched glycerol dialkyl glycerol tetraether (GDGT) membrane lipids, is linearly related with MAT, and thus altitude (r 2 =0.77), at Mt. Kilimanjaro. This suggests that this proxy may be more suitable for paleoelevation reconstruction for this region. However, application of the MBT/CBT proxy on the altitude gradient along Mt. Gongga showed that, although the MBT/CBT-derived temperature lapse rate (−5.9 • C/1000 m) resembles the measured temperature lapse rate (−6.0 • C/1000 m), there is a relatively large degree of scatter (r 2 =0.55). Our results thus show that both Correspondence to: F. Peterse (francien.peterse@nioz.nl) proxies can be subject to relatively large uncertainties in their assessment of past elevation changes, but that a combination of the soil n-alkane δD and MBT/CBT proxies can likely result in a more reliable assessment of paleoelevation.

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“…4). A number of factors were probably responsible for the d 18 O maximum, including: a small increase in the d 18 O of water vapour over the Indian Ocean source region (Jouzel et al, 2000); a substantial decrease in convective uplift, cloud cover and precipitation over East Africa during the last glacial, leading to a decrease in the magnitude of the isotopic 'amount effect' (Bonnefille et al, 1992;Hostetler and Clark, 2000;Barker et al, 2001); lower lake levels, which would help to eliminate seepage losses to groundwater, leading to hydrological closure (Rietti-Shati et al, 2000); increased evaporation resulting from decreased cloud cover and humidity and/or increased wind strength; and decreased water temperatures leading to enhanced d 18 O diatom values (Leng and Barker, 2006). This scenario suggests extended seasonal dominance by the dry, northeast (boreal winter) monsoon (Sirocko et al, 2000).…”

Section: Discussionmentioning

confidence: 99%

Towards an understanding of late Quaternary variations in the continental biogeochemical cycle of silicon: multi‐isotope and sediment‐flux data for Lake Rutundu, Mt Kenya, East Africa, since 38 ka BP

Street-Perrott

Barker

Leng

et al. 2008

J Quaternary Science

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2008. Towards an understanding of late Quaternary variations in the continental biogeochemical cycle of silicon: multi-isotope and sediment-flux data for Lake Rutundu, Mt Kenya, East Africa, since 38 ka BP.ABSTRACT: Silicon is an essential nutrient for marine diatoms, which dominate the export of organic carbon to the deep ocean. Despite the dominance of the oceanic Si budget by fluvial inputs and the role of the land biosphere in controlling Si losses from rocks and soils to rivers, few studies have considered how continental biogeochemical Si fluxes varied on an orbital timescale. We reconstruct changes in Si cycling by the catchment-lake ecosystem of Lake Rutundu, Mt Kenya (3078 m a.s.l.), over the last ca. 38 ka, using a novel combination of lake-sediment fluxes and stable-isotope (d 13 C, d 15 N, d 18 O, d 30 Si) data. Under glacial conditions (38.3-14.3 ka BP), high diatom productivity was maintained by substantial losses of dissolved SiO 2 and soil nutrients from a sparse, leaky, terrestrial ecosystem. During the following period of enhanced monsoon rainfall and seasonality (14.3-9.5 ka BP), rapid Si cycling by fire-prone, mesic grassland was associated with substantial aeolian transport of opal phytoliths by smoke plumes, but greatly reduced nutrient losses in runoff. Invasion of tall, subalpine shrubs after 9.5 ka BP further enhanced landscape stability, leading to very low sediment fluxes of both phytoliths and diatoms. This case study offers new insights into processes that may have operated at biome to continental scales during the late Quaternary.

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Stable isotope composition of tropical high-altitude fresh-waters on Mt. Kenya, Equatorial East Africa

Cited by 63 publications

References 11 publications

Quaternary glaciation in Africa: key chronologies and climatic implications

Quaternary glaciation in Africa: key chronologies and climatic implications

Assessment of soil <i>n</i>-alkane δ<i>D</i> and branched tetraether membrane lipid distributions as tools for paleoelevation reconstruction

Towards an understanding of late Quaternary variations in the continental biogeochemical cycle of silicon: multi‐isotope and sediment‐flux data for Lake Rutundu, Mt Kenya, East Africa, since 38 ka BP

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Stable isotope composition of tropical high-altitude fresh-waters on Mt. Kenya, Equatorial East Africa

Cited by 63 publications

References 11 publications

Quaternary glaciation in Africa: key chronologies and climatic implications

Quaternary glaciation in Africa: key chronologies and climatic implications

Assessment of soil &lt;i&gt;n&lt;/i&gt;-alkane δ&lt;i&gt;D&lt;/i&gt; and branched tetraether membrane lipid distributions as tools for paleoelevation reconstruction

Towards an understanding of late Quaternary variations in the continental biogeochemical cycle of silicon: multi‐isotope and sediment‐flux data for Lake Rutundu, Mt Kenya, East Africa, since 38 ka BP

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Assessment of soil <i>n</i>-alkane δ<i>D</i> and branched tetraether membrane lipid distributions as tools for paleoelevation reconstruction