Stable carbon isotope record of Lake Challa
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| Sprache: | en |
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PANGAEA
2011
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| _version_ | 1867169514959929344 |
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| author | Sinninghe Damsté, Jaap S Verschuren, Dirk Ossebaar, Jort Blokker, Jord van Houten, Rianne van der Meer, Marcel T J Plessen, Birgit Schouten, Stefan |
| author_facet | Sinninghe Damsté, Jaap S Verschuren, Dirk Ossebaar, Jort Blokker, Jord van Houten, Rianne van der Meer, Marcel T J Plessen, Birgit Schouten, Stefan |
| collection | Datos científicos de ciencias marinas y ambientales |
| contents | The debate of climate versus CO2 in controlling the long-term dynamics of tropical African vegetation has focused on events at the upper tree-line, since the relevant paleodata tend to be from mid-elevation sites (~2000-3000 m). Less well known is the relative importance of CO2 in regulating the dynamics of tropical lowland (<1500 m) vegetation, particularly that of the dry open woodlands, bush- and grasslands covering much of eastern equatorial Africa. Here we examine the stable carbon isotopic composition of n-alkanes in the sediment record of Lake Challa, a lowland crater lake near Mt. Kilimanjaro, covering the last 25,000 years. The distributions of the n-alkanes, with dominance of the long-chain odd-carbon-numbered components, and their isotopic composition reveal a mixed origin. The C23 and C25 n-alkanes are depleted in 13C, with d13C values between-30 and-50 per mil. In shallow lakes these n-alkanes are thought to derive from non-emergent aquatic plants, but this is unlikely in this steep-sided crater lake as it lacks a significant littoral habitat. The C27+ n-alkanes are predominantly derived from leaf wax lipids of terrestrial plants, brought into the lake predominantly by local soil run-off. Their d13C values, in particular that of the n-C31 alkane, reveal a marked transition in local lowland vegetation from being dominated (~70-100%) by C4 plants during the glacial period until 16.5 cal kyr BP, to a more mixed C3/C4 composition (~30-60% C4) during the Holocene. The start of the late-glacial trend towards a greater proportion of C3 plants coincided with the start of increasing monsoon rainfall, ~1500 years after the onset of the rise in atmospheric CO2 and ~3500 years after the onset of post-glacial warming. The transition was interrupted during the dry Younger Dryas period (13.0-11.7 cal kyr BP), when C4 plants again became much more prevalent, almost reaching their glacial-period abundance. Notably, the principal trend in leaf-wax ?13C values infers C4 dominance during both wet and dry phases of the glacial period, and a mixed C3/C4 vegetation during both wet and dry phases of the Holocene. Our results indicate that long-term variation in pCO2 exerted important control on the composition of drought-adapted savanna vegetation in this currently semi-arid lowland region of equatorial East Africa. |
| format | Dataset Open Access |
| id | pangaea_https___doi_org_10_1594_PANGAEA_881214 |
| institution | PANGAEA |
| language | en |
| publishDate | 2011 |
| publisher | PANGAEA |
| record_format | pangaea |
| spellingShingle | Stable carbon isotope record of Lake Challa Sinninghe Damsté, Jaap S Verschuren, Dirk Ossebaar, Jort Blokker, Jord van Houten, Rianne van der Meer, Marcel T J Plessen, Birgit Schouten, Stefan Lake_Challa; Mount Kilimanjaro, Tanzania; NIOZ_UU; NIOZ Royal Netherlands Institute for Sea Research, and Utrecht University; PCUWI; Piston corer, UWITEC The debate of climate versus CO2 in controlling the long-term dynamics of tropical African vegetation has focused on events at the upper tree-line, since the relevant paleodata tend to be from mid-elevation sites (~2000-3000 m). Less well known is the relative importance of CO2 in regulating the dynamics of tropical lowland (<1500 m) vegetation, particularly that of the dry open woodlands, bush- and grasslands covering much of eastern equatorial Africa. Here we examine the stable carbon isotopic composition of n-alkanes in the sediment record of Lake Challa, a lowland crater lake near Mt. Kilimanjaro, covering the last 25,000 years. The distributions of the n-alkanes, with dominance of the long-chain odd-carbon-numbered components, and their isotopic composition reveal a mixed origin. The C23 and C25 n-alkanes are depleted in 13C, with d13C values between-30 and-50 per mil. In shallow lakes these n-alkanes are thought to derive from non-emergent aquatic plants, but this is unlikely in this steep-sided crater lake as it lacks a significant littoral habitat. The C27+ n-alkanes are predominantly derived from leaf wax lipids of terrestrial plants, brought into the lake predominantly by local soil run-off. Their d13C values, in particular that of the n-C31 alkane, reveal a marked transition in local lowland vegetation from being dominated (~70-100%) by C4 plants during the glacial period until 16.5 cal kyr BP, to a more mixed C3/C4 composition (~30-60% C4) during the Holocene. The start of the late-glacial trend towards a greater proportion of C3 plants coincided with the start of increasing monsoon rainfall, ~1500 years after the onset of the rise in atmospheric CO2 and ~3500 years after the onset of post-glacial warming. The transition was interrupted during the dry Younger Dryas period (13.0-11.7 cal kyr BP), when C4 plants again became much more prevalent, almost reaching their glacial-period abundance. Notably, the principal trend in leaf-wax ?13C values infers C4 dominance during both wet and dry phases of the glacial period, and a mixed C3/C4 vegetation during both wet and dry phases of the Holocene. Our results indicate that long-term variation in pCO2 exerted important control on the composition of drought-adapted savanna vegetation in this currently semi-arid lowland region of equatorial East Africa. |
| title | Stable carbon isotope record of Lake Challa |
| topic | Lake_Challa; Mount Kilimanjaro, Tanzania; NIOZ_UU; NIOZ Royal Netherlands Institute for Sea Research, and Utrecht University; PCUWI; Piston corer, UWITEC |
| url | https://doi.org/10.1594/PANGAEA.881214 |