Late Holocene ice core records of climate and environment from the tropical Andes, Peru

Abstract

A 1 500-year history of climatic and environmental variations from the Quelccaya ice cap (13o56'S, 70o50'W, 5 670 m a.s.l.) is compared to a similar 3 000-year ice core record from the col of Huascarán (9o06'S, 77o 36'W, 6 048 m a.s.l.). The parameters which are presented are oxygen isotopic ratios (δ18O), considered to be indicative of temperature, insoluble dust, and (for Huascarán only) nitrate concentrations (NO3) which is indicative of vegetation fluctuations in the Amazon rainforest. The Huascarán δ18O and NO3 profiles for the most recent 3 000 years show that there has been a general decrease in temperature along with a decrease inbiological activity in the Amazon Basin, with the lowest values occurring during the "Little Ice Age" (LIA), 200 to 500 yrs BP. This was followed by an abrupt change in 8180, which increased to the levels of 3 000 years ago. This abrupt warming has dominated the last two centuries in the records from both sites. NO3 levels in Huascarán have also increased during this time, albeit less dramatically. There is evidence for slight isotopic enrichment (warming) between 1 150 and 900 yrs BP, which may be related to the "Medieval Warm Period". The Huascarán dust concentration record shows a fairly constant background level over the last 3 000 years, which was interrupted by a dust event between 2 000 and 1 800 years BP (0-200 A.D.) and centered on 1 900 years BP (100 A.D.). A less intense peaks occurred from 1 400 to 1 600 years BP (400 to 600 A.D.) and 1300 to 1030 years BP (700 to 960 A.D). Examination of the dust associated with this event indicates that it is wind-blown material which is very similar in composition to the granodiorite of which the Cordillera Blanca massif is composed. The more recent peaks are temporally correlative with the much greater 400 to 620 A.D. dust event in the Quelccaya ice core, thus suggesting that it may have been widespread. The more recent dust event in the Quelccaya record from 830 to 960 A.D. is recorded at lower concentrations in the Huascarán ice cores, which gives support to the linkage of the early part of the Quelccaya dust record to prehistoric agriculture activity in the Late Titicaca basin (Thompson et al, 1988).