Huascarán Ice Core Data: Readme file --------------------------------------------------------------------- World Data Center for Paleoclimatology, Boulder and NOAA Paleoclimatology Program --------------------------------------------------------------------- NOTE: PLEASE CITE ORIGINAL REFERENCE WHEN USING THIS DATA!!!!! NAME OF DATA SET: Huascarán Ice Core Data LAST UPDATE: 8/2013 (addition of annions data file). Original receipt by WDC Paleo 1/2001 CONTRIBUTOR: Lonnie G. Thompson, Byrd Polar Research Center of The Ohio State University IGBP PAGES/WDCA CONTRIBUTION SERIES NUMBER: 2001-008 SUGGESTED DATA CITATION: Thompson, L.G., 2001, Huascarán Ice Core Data, IGBP PAGES/World Data Center A for Paleoclimatology Data Contribution Series #2001-008. NOAA/NGDC Paleoclimatology Program, Boulder CO, USA. ORIGINAL REFERENCE: Thompson, L.G., E. Mosley-Thompson, M.E. Davis, P-N. Lin, K.A. Henderson, J. Cole-Dai, J.F. Bolzan and K-b. Liu. 1995. Late Glacial Stage and Holocene tropical ice core records from Huascarán, Peru. Science, 269, 46-50. GEOGRAPHIC REGION: South America, Peruvian Andes PERIOD OF RECORD: 19.5 KYrBP - present LIST OF FILES: Readme_Huascaran.txt (this file), ASCII text data files: age.txt Age-scale/averaging doc. all-mo.txt Linearized profiles 100yr. annualc.txt Cal. Annual avg for 100yr. annualt.txt Thermal Annual avg - 100yr. hs12-5m.txt 5m/.5m/every averages hs1layer.txt C1 layer depths/thickness hs2layer.txt C2 layer depths/thickness hs2-100a.txt Revised C2 100-yr averages. annions.txt decadal averages of major anions (Chloride, Nitrate, Sulfate) DESCRIPTION: General Information about the Huascarán Ice Cores Site Description and Analysis In July-August 1993, two ice cores to bedrock were recovered from the col between the north and south peaks of Nevado Huascarán, Peru (9řS, 77ř30'W, col elevation 6050 m) and were subsequently transported back to the cold room facility at the Byrd Polar Research Center (BPRC). Core 1 (HSC1, 160.40 m) was sectioned in the field into 2677 samples decreasing in thickness from 13 cm at the top to 3 cm at the base, which were then melted and poured into 2 or 4 oz. plastic (HDPE) bottles, and sealed with wax. Core 2 (HSC2, 166.08 m), drilled approximately 100 m from the HSC1 site, was returned frozen in 1 m sections. Ice motion vectors determined from stake movements from 1991-93 indicate that the drill sites are proximal to the divide between ice flow towards the east and west outlets of the col. Visible observations and borehole temperatures indicate that the glacier is 'polar' type, i.e., it remains frozen to the bed (Thompson et al., Science, v.269, 1995, p. 46-50). Each ice sample from HSC2 was prepared in a Class 100 clean room environment, and analyzed for major anion concentrations (Cl-, NO3-, and SO42-) on a Dionex 2010i ion chromatograph, d18O on a Finnigan Mat mass spectrometer (Craig, 1957), and for particulate concentration and size distribution using a Coulter TA-II particle counter (Thompson, OSU IPS Report 46, 1973). A complete d18O profile was also produced from the bottled samples from HSC1. Contamination during field preparation and transport of these samples precluded the development of a second complete record of particles and anion concentrations. For display purposes, variable averaging on the core depth scale was utilized to show the major large-scale events in the record without the confusion of the large annual variations superimposed upon the upper portion. Hence, for HSC2, 5-m integrated averages were calculated for between the surface and 140 meters depth and then 50-cm averages were generated between 140 and 160 meters. Between 160 and 166 meters, every sample value was plotted. A similar scheme was used for HSC1 (all values plotted for 155-160.4 m). These data are included in hs12-5m.txt in this data archive, and the graph can be seen in Thompson et al., 1995 (Fig. 3). Development of the time/depth relationship Tropical South American climate is marked by annual dry seasons (July-October) which were identifiable in the ice core record as elevated values in all relevant measurements. The nitrate (NO3-) record from the Huascarán ice core provided the most definitive seasonal marker, but the final time scale was constructed from a comparison of four major parameters (NO3-, d18O, dust and SO42-). Each annual maximum corresponds to the middle of the dry season, assumed to occur on the 1st of August. The rapid layer- thinning below 120 m limited annual resolution to the most recent 270 years. However, the high accumulation and strong preservation of seasonal cycles also made possible the subannual resolution of d18O variations for a period of at least 100 years (1894-1993). The accuracy of the time scale is of paramount importance in the development of relationships between ice core proxy data and tropical climate conditions. Several horizons in recent times were useful for confirming the layer counting as a reliable method, and indicate almost certain ages for the uppermost 50 years. In 1980, during the original reconnaissance expedition to Huascarán, a 10 m firn core was extracted and analyzed for d18O at BPRC (Thompson et al., JGR, v. 89d3, 1984, p. 4638-4646). Aside from minor accumulation variation and slight signal attenuation, the 1993 cores duplicated the earlier stable isotope profile over the common portion, and confirmed the layer counting to 1980 as absolute. Additionally, a magnitude 7.7 earthquake struck coastal Peru in May 1970, generating large mud flows following the collapse of a large portion of the Huascarán glacier from the north peak. The event was recognized in the ice core by a sharp two-year rise in particulates from the newly-created sediment source. A third time horizon was provided by the HSC2 36Cl profile (Synal et al., Glaciers From the Alps, Paul Scherrer Inst., 1997, p. 99-102), a substance produced by neutron activation during the explosion of atomic devices in the presence of a 35Cl source, such as sea water. An abrupt >100-fold rise in 36Cl concentration occurred at ~54 m depth, which dates (by layer counting) to 1951-53. This was in direct response to the October 31, 1952 U.S. 'Ivy' surface test of an experimental nuclear device on the Eniwetok Atoll in the Pacific Ocean (11řN, 162řE) (Carter and Moghissi, Health Physics, v. 33, 1977, p. 55-71). Finally, in both HSC1 and HSC2, the 1883 eruption of Krakatau, Indonesia (6řS, 105ř30'E) was identified by an anomalous sulfate concentration of ~400 ppb at 110 m depth, more than twice the level of any other local (within 10 m) event. A date of mid- year 1884 was thus considered to be an absolute time marker for both cores within the error of the time lag (less than one year).