Ammonium concentration in ice cores: A new proxy for regional temperature reconstruction?

Abstract

We present a reconstruction of tropical South American temperature anomalies over the last ∼1600 years. The reconstruction is based on a highly resolved and carefully dated ammonium record from an ice core that was drilled in 1999 on Nevado Illimani in the eastern Bolivian Andes. Concerning the relevant processes governing the observed correlation between ammonium concentrations and temperature anomalies, we discuss anthropogenic emissions, biomass burning, and precipitation changes but clearly favor a temperature‐dependent source strength of the vegetation in the Amazon Basin. That given, the reconstruction reveals that Medieval Warm Period– and Little Ice Age–type episodes are distinguishable in tropical South America, a region for which until now only very limited temperature proxy data have been available. For the time period from about 1050 to 1300 AD, our reconstruction shows relatively warm conditions that are followed by cooler conditions from the 15th to the 18th century, when temperatures dropped by up to 0.6°C below the 1961–1990 average. The last decades of the past millennium are characterized again by warm temperatures that seem to be unprecedented in the context of the last ∼1600 years.

Ice sheets and nitrogen

“…Ammonium increased by about a factor 3 from 1700 to 2000 (figure 3), which was then interpreted as an Amazon Basin increase of about 0.68C over this period. Kellerhals et al [39] suggest that the mechanism for the observed relationship is that higher temperatures lead to greater emissions of NH 3 from soils, and from vegetation through Figure 3. Ammonium concentration in the Illimani core over the last 1600 years.…”

“…An unusual trend has been observed in ammonium concentrations in an ice core from the Bolivian Alps (Illimani). The year-to-year variations [39] have been calibrated against temperature anomalies in the Amazon Basin (most airmasses at Illimani track back over the Amazon): a remarkably good correlation was found. This was used to propose that ammonium in this ice core could be used as a proxy for temperature across the Amazon Basin further back in time.…”

“…Ammonium concentration in the Illimani core over the last 1600 years. The authors [39] interpreted the rise since 1700 as being due to a modest temperature rise across the Amazon Basin, leading to increased ammonium emissions. (Online version in colour.)…”

An 800 year high-resolution black carbon ice-core record from Lomonosovfonna, Svalbard

“…deviation, in such a way that this threshold takes background variations into account, which is of prime importance in the case of non-specific proxies having other sources than biomass burning, such as biogenic emissions in the case of formate (Legrand and De Angelis, 1996) and ammonium (Eichler et al, 2009;Fischer et al, 2015;Kellerhals et al, 2010). Every annual average above this threshold can thus be considered as a year with significant biomass burning emissions, and finally the centennial frequency of such episodes was obtained.…”

Radiocarbon dating of glacier ice: overview, optimisation, validation and potential

“…The methodology of 14 C analysis of the different carbonaceous particle fractions was adopted to study the suitability of WIOC for 14 C dating of old ice, finding that it is of purely biogenic origin prior to industrialisation (Jenk et al, 2006(Jenk et al, , 2007. Since then this novel 14 C approach has been applied for the dating of a number of ice cores from different highaltitude mountain glaciers (Table 1) Sigl et al, 2009;Kellerhals et al, 2010;Herren et al, 2013;Zapf et al, 2013;Aizen et al, 2016). Meanwhile the method has been further optimised and was additionally validated by determining the age of independently dated ice.…”