Tropical Ice Core Climate Studies

Elemental and isotopic composition of trapped gases in the Huascaran and Sajama ice cores from South America.

Drilling ice cores on the summit of a strato volcano (Sajama) in SW Bolivia in June 1997.  Elevation = 6,500m


Elemental and isotopic composition of trapped gases in the Huascaran and Sajama ice cores from South America

Active from 3/1/97-2/29/99

Funding agency: NSF Climate Dynamics

Project description: A set of very exciting climate records extending into the last glacial period have recently been developed from the Huascar?n ice core from the Peruvian Cordillera (9o6'S; 77o36'W, 6048 m above sea level) [Thompson et al. , 1995] . The isotopic temperature record from this core demonstrated that, during the last glacial period, temperatures at Huascar?n were colder than today, supporting various lines of evidence that the tropics were indeed colder during the last glacial period. In addition, measurements of the chemical composition of the ice core suggest higher dust concentrations in glacial ice from Huascar?n. These findings are consistent with ice core records from Greenland and Antarctica which extend into the last glacial period. The high degree of covariation between all these records during the termination argues that there are strong teleconnections between these sites which are probably responding to the same (or similar) forcing functions. In this proposal, we propose to measure the elemental and isotopic composition of the trapped gases in the Huascar?n ice core. Specifically we propose to analyze the 18O/16O of O2 (d18Oatm) and the [CH4] along the Huascar?n core. These records will hopefully provide definitive evidence for the existence of glacial ice at Huascar?n. In addition, the gas records will help refine the timescale for the Huascar?n core to within 500 years of that ascribed to the GISP II ice core from central Greenland. The gas records will also allow us to transfer the Huascar?n climate records into a "common temporal framework" where we can determine whether the climate events recorded in the ice cores are local or global climate events In addition, we expect to investigate the leads and lags between all these climate records and many other records covering the last deglaciation. The ultimate goal in this research is gain insight into the mechanisms which caused the Earth to move out of the last glacial period by establishing the sequence of events which led to the deglaciation. Placing the tropical climate events from Huascar?n in this sequence will help decipher the nature of the forcing mechanisms responsible for the last termination. As the Huascar?n records provide a single point calibration of the tropics, it is important to construct a similar set of records from another tropical site extending into the last glacial period. We propose to do this by analyzing the trapped gases in a suite of samples from the Sajama ice core (18oS; 69oW, 6548 m above sea level) which will be drilled in Bolivia by Lonnie Thompson during the summer of 1997. Our goal is to obtain glacial stage ice from Sajama and correlate the two ice cores through their gas records. Comparisoin of the isotopic temperature records from the two sites should reveal the broad geographic (tropical) temperature signal for comparison with isotope temperature records from Greenland and Antarctica. Even if glacial stage ice is not recovered from Sajama, our gas records will provide dating control in the Holocene so we can compare the Sajama climate records with Holocene records from around the globe.