Paleoclimate of the past 4000 years at Lake Turkana, Kenya, based on the isotopic composition of authigenic calcite

Johnson, Thomas C.; Halfman, John D.; Showers, William J.

doi:10.1016/0031-0182(91)90158-n

Cited by 75 publications

(59 citation statements)

References 19 publications

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“…Relatively wet climates (higher relative lake levels) are characterized by less evaporation (P:E > 1) of water from the lake basin compared to the influx of precipitation and its run-off. (calcite) values in terms of lake-climate information is congruent with most arid environment lake studies (e.g., Benson et al 1991;Johnson et al 1991;Lister et al 1991;Li and Ku 1997;Seltzer et al 2000;.…”

Section: Supporting Proxy Data For Lake Level Changesupporting

confidence: 81%

“…In arid lake environments, such as Lake Elsinore, there are multiple studies purporting traditional interpretations of 18 O (calcite) values in terms of climate-forced relative lake level change (Benson et al 1991(Benson et al , 1996(Benson et al , 1998Li and Ku 1997;Li et al 2000;Seltzer et al 2000). Although the absolute value of lake level cannot be discerned from 18 O (calcite) values, it is possible to infer the general climate regime in terms of precipitation (inflow) versus evaporation (outflow) (P:E ratio) (Benson et al 1991;Johnson et al 1991;Lister et al 1991;Li and Ku 1997;Li et al 2000;Seltzer et al 2000;. Relatively dry climates (lower relative lake levels, P:E < 1.0) favor the evaporation of water from the lake basin preferentially removing 16 O from the lake water.…”

Section: Supporting Proxy Data For Lake Level Changementioning

confidence: 99%

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Late Holocene lake level dynamics inferred from magnetic susceptibility and stable oxygen isotope data: Lake Elsinore, southern California (USA)

Kirby

Poulsen

Lund

et al. 2004

Journal of Paleolimnology

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Southern California faces an imminent freshwater shortage. To better assess the future impact of this water crisis, it is essential that we develop continental archives of past hydrological variability. Using four sediment cores from Lake Elsinore in Southern California, we reconstruct late Holocene ($3800 calendar years B.P.) hydrological change using a twentieth-century calibrated, proxy methodology. We compared magnetic susceptibility from Lake Elsinore deep basin sediments, lake level from Lake Elsinore, and regional winter precipitation data over the twentieth century to calibrate the late Holocene lake sediment record. The comparison revealed a strong positive, first-order relationship between the three variables. As a working hypothesis, we suggest that periods of greater precipitation produce higher lake levels. Greater precipitation also increases the supply of detritus (i.e., magnetic-rich minerals) from the lake's surrounding drainage basin into the lake environment. As a result, magnetic susceptibility values increase during periods of high lake level. We apply this modern calibration to late Holocene sediments from the lake's littoral zone. As an independent verification of this hypothesis, we analyzed 18 O (calcite) , interpreted as a proxy for variations in the precipitation:evaporation ratio, which reflect first order hydrological variability. The results of this verification support our hypothesis that magnetic susceptibility records regional hydrological change as related to precipitation and lake level. Using both proxy data, we analyzed the past 3800 calendar years of hydrological variability. Our analyses indicate a long period of dry, less variable climate between 3800 and 2000 calendar years B.P. followed by a wet, more variable climate to the present. These results suggest that droughts of greater magnitude and duration than those observed in the modern record have occurred in the recent geological past. This conclusion presents insight to the potential impact of future droughts on the over-populated, water-poor region of Southern California.

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Section: Supporting Proxy Data For Lake Level Changesupporting

confidence: 81%

Section: Supporting Proxy Data For Lake Level Changementioning

confidence: 99%

Late Holocene lake level dynamics inferred from magnetic susceptibility and stable oxygen isotope data: Lake Elsinore, southern California (USA)

Kirby

Poulsen

Lund

et al. 2004

Journal of Paleolimnology

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“…Quasi-periodic oscillations at around 135 years have been observed elsewhere in the world, e.g. from Kenya (Johnson et al, 1991), from high latitudes in the Northern Hemisphere (Briffa et al, 1992;Scuderi, 1993) and in California (Burroughs, 1992). An ∼200-year oscillation has been reported in Californian dendrochronological studies (Burroughs, 1992), from marine cores near the Antarctic Peninsula (Leventer et al, 1996), from Tibetan ice cores (Thompson et al, 1997), and from peat deposits in Scotland (Chambers et al, 1997) and Denmark (Aaby, 1976).…”

Section: Variability Over the Period Of Meteorological Recordmentioning

confidence: 89%

Millennial to multi‐decadal variability in the climate of southern Africa

Tyson

Cooper

McCarthy

2002

Intl Journal of Climatology

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Wavelet analysis has been used to determine changes in the variability of southern Africa climate over the last three millennia. The structure of the variability in a 3000-year δ 18 O record has been compared with that in tree ring data for the last 600 years and both to the variability in annual rainfall and runoff during the 20th century. Preferred modes of variability are shown to have occurred in all the data sets. For overlap periods, the variability modes are in phase where the data are for a common seasonal rainfall regime.From the combined proxy and instrumental data it appears that an ∼1500-year oscillation in rainfall variability may have been present during the late Holocene. Considerable variability in South African climate has been shown to reside in the bands 500-800 and 60-120 years. The latter is manifest in stable isotope and tree ring proxy data and in measured rainfall and runoff, and shows a distinctive latitudinal variation over southern Africa. The ∼80-year variability has been present for at least 600 years in the tree ring data and at least 3000 years in the stable isotope data. During the 20th century, the variability in the 60-120-year range was confined south of 20°S in southern Africa.The existence of considerable multi-decadal climate variability in the range 16-20 years has been confirmed south of 15°S. Tree ring data show that the ∼18-year oscillation in climate has been present for at least 600 years. The 500-800-year, ∼80-year and ∼18-year variability has been both frequency-and amplitude-modulated over time, but never to the extent that the variability bands have lost their integrity. Their persistence is a striking feature of southern African climate.The millennial, centennial and multi-decadal variability in climate over southern Africa finds counterparts with temporal variability in similar time ranges reported elsewhere. Spatial teleconnections in variability likewise have been shown to occur. The changes in climate variability over the subcontinent are part of variability changes affecting the Earth system in many other regions.

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“…Down-core changes in lamination thickness, and abundance and isotopic composition of fine-grained calcite have been related to variability in the Omo River discharge and are thus interpreted to reflect the hydrologic balance within the Omo Basin (Halfman & Johnson, 1988;Halfman etal., 1989 (Barton & Torgersen, 1988). Johnson et al, 1991). These records did not recover sediments older than 4000 yr BP and reveal no evidence of a major highstand between roughly 3000 and 3 800 yr BP.…”

Section: Introductionmentioning

confidence: 63%

“…An early to mid Holocene high stand ( + 70 to 80 m) from 10000 to 4000 yr BP is consisten with records of lake level throughout northern intertropical east Africa and is predicted by computer simulations of monsoon climates modulated by millennial scale Milankovitch perturbations (Street & Grove, 1976;Hamilton, 1982;Street-Perrott & Harrison, 1983;Kutzbach & Street-Perrott, 1985;COHMAP, 1988;Pachur & Hoelzmann, 1991). Another, slightly lower, highstand (+ 60 to 80 m) is inferred between about 3800 and 3000 yr BP (Butzer et al, 1972;Owen etal., 1982) that is less consistent with other proxy records from east Africa (Halfman & & Johnson, 1988;Johnson et al, 1991). These elevations are relative to the 1976 level of the lake which has since declined by a few meters (Halfman, personal observations).…”

Section: Introductionmentioning

confidence: 66%

Fossil diatoms and the mid to late holocene paleolimnology of Lake Turkana, Kenya: a reconnaissance study

et al. 1992

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A 12 m sediment core recovered from the south basin of Lake Turkana, northwestern Kenya, reveals four major diatom assemblages that span approximately 5450 to 1070 years BP based on AMS radiocarbon analyses. The oldest assemblage, Zone D (5450 to 4850 yr BP), is dominated by Melosira nyassensis and Stephanodiscus spp. and is interpreted to reflect higher lake levels, fresher water and more variable seasonal mixing of the water column than the modern lake. Melosira dominates the assemblage in Zone C (4850 to 3900 yr BP) with some Surirella engleri and Stephanodiscus. This assemblage indicates a continuation of relatively high lake levels and seasonal mixing of a stratified lake. The brief peak of Surirella, interpreted as benthic, suggests an episode of slightly lower lake level. Thalassiosira rudolfi and Surirella predominate since the beginning of Zone B (3900 to 1900 yr BP), reflecting a decrease in lake level and increase in water column salinity. Increasing dominance of Surirella in Zone A (1900 to 1070 yr BP) may suggest that the lake continued to decrease in depth. Salinity probably rose to levels comparable with the modern lake. These results are consistent with paleoclimatic interpretations based on carbonate abundance, lamination thickness, oxygen isotope and bulk geochemistry profiles from this core and cores recovered from the north basin. It extends the known paleolimnology beyond 4000 yr BP of the earlier research to 5450 yr BP and into the early to mid Holocene pluvial phase in northern intertropical east Africa.

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Paleoclimate of the past 4000 years at Lake Turkana, Kenya, based on the isotopic composition of authigenic calcite

Cited by 75 publications

References 19 publications

Late Holocene lake level dynamics inferred from magnetic susceptibility and stable oxygen isotope data: Lake Elsinore, southern California (USA)

Late Holocene lake level dynamics inferred from magnetic susceptibility and stable oxygen isotope data: Lake Elsinore, southern California (USA)

Millennial to multi‐decadal variability in the climate of southern Africa

Fossil diatoms and the mid to late holocene paleolimnology of Lake Turkana, Kenya: a reconnaissance study

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