A 25,000 year tropical climate history from Bolivian ice cores

A 25,000 year tropical climate history
from Bolivian ice cores

Science, Volume 282(5295), 1858-1864, 1998.

Thompson, L.G., M.E. Davis, E.M.Thompson,
T.A.Sowers, K.A. Henderson, V.S. Zagorodnov,
P.N. Lin, V.N. Mikhalenko, R.K. Campen,
J.F.Bolzan, J.Cole-Dai and B.Francou.

Ice cores that were recovered from the summit of Sajama mountain in Bolivia provide carbon-14-dated tropical records and extend to the Late Glacial Stage (LGS). Oxygen isotopic ratios of the ice decreased 5.4 per mil between the Early Holocene and Last Glacial Maximum, which is consistent with values from other ice cores. The abrupt onset and termination of a Younger Dryas-type event suggest atmospheric processes as the probable drivers. Regional accumulation increased during the LGS, during deglaciation and over the past 3000 years, which is concurrent with higher water levels in regional paleolakes. Unlike polar cores, Sajama glacial ice contains eight times less dust than the Holocene ice, which reflects wetter conditions and extensive snow cover.

Download Sajama Data from the WDC Paleo Archive:
Data Description
d18O, Particle, and Ion Data presented as
5, 3, and 0.5 meter averages or 100-yr averages

Accumulation Reconstruction , Age Model, Sowers' d18Oatm data, plus
Sowers and Campen gas composition data and gas composition data description .

Fig. 2
Seasonal variations in d18Oice (per mil), insoluble dust, and NO3 - concentrations (ppm, parts per million) allow layer counting in the upper part of C-1. Dating is calibrated by the identification of the 1964 3H peak (gray bars). The sample values in each plot are smoothed with a three-point (1, 2, 1) filter. Data are plotted so that annual tick marks correspond to the austral winter.
Fig. 3
Depth profiles of d18Oice for C-1; d18Oice for C-2; and concentrations of dust, Cl-, NO3-, and SO42 - for C-1. Dust concentrations are the number of insoluble particles with diameters of 0.63 and 16.0 µm per milliliter of sample, and anion concentrations are in ppm. Locations of 14C samples in the core are denoted by diamonds.
Fig. 4
d18Oatm values from GISP 2  are compared to the Sajama d18Oatm record. The shaded areas denote Sajama data points that lie outside ±0.05 per mil of the corresponding GISP 2 data and contain elevated dAr/N2 values.

Fig. 5
All data used to constrain the Sajama time scale are illustrated to show the depth-age relationship. Diamonds denote 14C data, triangles denote d 18Oice matching points, and squares signify absolute dates. Solid symbols represent the data points used to construct the Holocene time scale (). The dates from the 14C data points at 78.3 m were averaged (denoted by the line between them) because of their low individual carbon weights Table 1.

Fig. 6
The 100-year averages of d18Oice; insoluble dust; and Cl-, NO3-, and SO42- concentrations from C-1 are shown for the past 25,000 years. Dating is based on 14C dates and on matching d18Oatm and d18Oice with GISP 2. Two accumulation histories (p = 1.5 and 2.0) were calculated with Eq. 1. The two accumulation records were combined (averaged), and the data presented are deviations from the mean of the combined record.

Fig. 7
The global extent of the LGS and a climatic reversal (cooling) during deglaciation is illustrated by the stable isotope records from two tropical sites [Sajama and Huascarán ()], two Northern Hemisphere sites [Guliya () and GISP 2 ()], and two Southern Hemisphere sites [Byrd station () and Vostok ()]. All records shown are 100-year averages, except records for Vostok (200-year averages) and Guliya (400-year averages). dD, 8 d18O + 10.

To read or view the full study, please visit the Science website.
It was published in Science Volume 282(5295), 1858-1864, 1998.

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