Dataset Information

A late Holocene pollen record from proglacial Oblong Tarn, Mount Kenya.

ABSTRACT: High-elevation ecosystems, such as those on Mount Kenya are undergoing significant changes, with accelerated glacial ice losses over the twentieth century creating new space for alpine plants to establish. These ecosystems respond rapidly to climatic variability and within decades of glacial retreat, Afroalpine pioneering taxa stabilize barren land and facilitate soil development, promoting complex patches of alpine vegetation. Periglacial lake sediment records can be used to examine centennial and millennial scale variations in alpine and montane vegetation compositions. Here we present a 5300-year composite pollen record from an alpine tarn (4370 m asl) in the Hausberg Valley of Mount Kenya. Overall, the record shows little apparent variation in the pollen assemblage through time with abundant montane forest taxa derived and transported from mid elevations, notably high abundances of aerophilous Podocarpus pollen. Afroalpine taxa included Alchemilla, Helichrysum and Dendrosenecio-type, reflecting local vegetation cover. Pollen from the ericaceous zone was present throughout the record and Poaceae percentages were high, similar to other high elevation pollen records from eastern Africa. The Oblong Tarn record pollen assemblage composition and abundances of Podocarpus and Poaceae since the late Holocene (~4000 cal yr BP-present) are similar to pollen records from mid-to-high elevation sites of nearby high mountains such as Mount Elgon and Kilimanjaro. These results suggest a significant amount of uphill pollen transport with only minor apparent variation in local taxa. Slight decreasing trends in alpine and ericaceous taxonomic groups show a long-term response to global late Holocene cooling and a step decrease in rate of change estimated from the pollen assemblages at 3100 cal yr BP in response to regional hydroclimatic variability. Changes in the principal component axis scores of the pollen assemblage were coherent with an independent mid-elevation temperature reconstruction, which supported the strong influence of uphill pollen transport from montane forest vegetation and association between temperatures and montane vegetation dynamics. Pollen accumulation rates showed some variability related to minerogenic sediment input to the lake. The Oblong Tarn pollen record provides an indication of long term vegetation change atop Mount Kenya showing some decreases in local alpine and ericaceous taxa from 5300-3100 cal yr BP and minor centennial-scale variability of montane taxa from mid elevation forests. The record highlights potentials, challenges and opportunities for the use of proglacial lacustrine sediment to examine vegetation change on prominent mountain massifs.

SUBMITTER: Courtney Mustaphi CJ

PROVIDER: S-EPMC5604990 | biostudies-literature | 2017

REPOSITORIES: biostudies-literature

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A late Holocene pollen record from proglacial Oblong Tarn, Mount Kenya.

Courtney Mustaphi Colin J CJ Gajewski Konrad K Marchant Rob R Rosqvist Gunhild G

PloS one 20170919 9

High-elevation ecosystems, such as those on Mount Kenya are undergoing significant changes, with accelerated glacial ice losses over the twentieth century creating new space for alpine plants to establish. These ecosystems respond rapidly to climatic variability and within decades of glacial retreat, Afroalpine pioneering taxa stabilize barren land and facilitate soil development, promoting complex patches of alpine vegetation. Periglacial lake sediment records can be used to examine centennial ...[more]

PMID: 28926642

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Project description:Climate is currently warming due to anthropogenic impact on the Earth’s atmosphere. To better understand the processes and feedbacks within the climate system that underlie this accelerating warming trend, it is useful to examine past periods of abrupt climate change that were driven by natural forcings. Glaciers provide an excellent natural laboratory for reconstructing the climate of the past as they respond sensitively to climate oscillations. Therefore, we study glacier systems and their behavior during the transition from colder to warmer climate phases, focusing on the period between 15 and 10 ka. Using a combination of geomorphological mapping and beryllium-10 surface exposure dating, we reconstruct ice extents in two glaciated valleys of the Silvretta Massif in the Austrian Alps. The mountain glacier record shows that general deglaciation after the Last Glacial Maximum (LGM) was repeatedly interrupted by glacier stabilization or readvance, perhaps during the Oldest Dryas to Bølling transition (landform age: 14.4 ± 1.0 ka) and certainly during the Younger Dryas (YD; 12.9–11.7 ka) and the Early Holocene (EH; 12–10 ka). The oldest landform age indicates a lateral ice margin that postdates the ‘Gschnitz’ stadial (ca. 17–16 ka) and predates the YD. It shows that local inner-alpine glaciers were more extensive until the onset of the Bølling warm phase (ca. 14.6 ka), or possibly even into the Bølling than during the subsequent YD. The second age group, ca. 80 m below the (pre-)Bølling ice margin, indicates glacier extents during the YD cold phase and captures the spatial and temporal fine structure of glacier retreat during this period. The ice surface lowered approximately 50–60 m through the YD, which is indicative of milder climate conditions at the end of the YD compared to its beginning. Finally, the third age group falls into a period of more substantial warming, the YD–EH transition, and shows discontinuous glacier retreat during the glacial to interglacial transition. The new geochronologies synthesized with pre-existing moraine records from the Silvretta Massif evidence multiple cold phases that punctuated the general post-LGM warming trend and illustrate the sensitive response of Silvretta glaciers to abrupt climate oscillations in the past.

Dataset Information

A late Holocene pollen record from proglacial Oblong Tarn, Mount Kenya.

Publications

A late Holocene pollen record from proglacial Oblong Tarn, Mount Kenya.

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