COMPILED REPORTS OF THE
U.S. ICE CORE RESEARCH WORKSHOP

1.5 SPECIALTY GROUP REPORT: SOLUBLE AND INSOLUBLE CONSTITUENTS

Ice cores contain a historical record of aerosols and soluble gases relatable to global climate and to biogeochernical cycles of elements such as C, N, S, and Cl. These components affect the Earth's radiation balance directly via absorption and scattering of light, and indirectly by influencing cloud nucleation processes. The aerosol concentrations and composition both contribute to and respond to global climate change.

General Problem Areas

The overall objective for the examination of soluble and insoluble constituent records is to document the Earth's climatic history using a global array of ice cores which span glacial/interglacial transitions, focus upon specific abrupt events (e.g. volcanic activity, Younger Dryas) and document recent anthropogenic influences upon the chemical and physical properties of the atmosphere. These environmental records, when obtained from a variety of analytical approaches, provide a unique opportunity to understand more thoroughly some of the complex processes which control global climate. These processes include the long distance transport and degree of atmosphere loading of continental dust, the production and release of trace gases and aerosols from the oceans, and the injection of volcanically derived material. 'Me source strengths of these components as a function of time and in response to varying environmental conditions needs to be assessed.

Specific Problem Areas

Soluble Constituents:

Nitrate continues to be one of the most difficult ionic species in glacial ice to quantify in terms of discrete sources. The relative importance of biological, tropospheric, solar and stratospheric sources of nitrate and the modulating factors and processes need to be assessed.

Sulfate is a major component of the aerosol in the polar regions. The origin of this sulfate aerosol is of considerable importance because of its role in the formation and transport of acid precipitation and its effects on the optical properties and climate of the atmosphere. There are three major potential sources of this sulfate: anthropogenic emissions, stratospheric sulfate (largely of volcanic origin), and biogenic emissions of reduced sulfur gases.

Methanesulfonic acid (MSA) is an atmospheric oxidation product of DMS which is of interest as a potential tracer for the cycling of organosulfur emissions. The incorporation of MSA into aerosols and subsequent preservation in ice cores provides a unique opportunity to study the history of the input of organo-sulfur compounds into the ancient atmosphere and its relationship to global climate.

In addition the d15N of N03- and the d34S of SO42- should be determined to help ascertain the sources of these constituents. It is hoped that marine biogenic, terrestrial biogenic as well as volcanic and anthropogenic sources can be distinguished based on differences in their isotopic signatures.

Ice cores should be recognized for their value as a unique tool for the examination of global atmospheric chemistry through time. Investigators should be encouraged to conduct analyses for a wide range of constituents including all of the major anions and cations, as well as trace constituents such as F, Fe, Mn, Al, and silica. Analyses of major constituents yield information concerning basic input sources and their modulating factors and set the stage for the interpretation of other records. F is a tracer for local volcanic eruptions. The other species yield information concerning the concentration and composition of particulate matter which is integrally linked to climate and atmospheric circulation. Organic constituents such as aldehydes which are important for understanding cloud processes as well as other organic constituents with biological sources should also be investigated.

Oceanic emissions play a major role in the atmospheric cycling of the halogens (Cl, Br, I). In particular, there is a large enrichment of iodine in marine aerosols. A historical record of sea surface iodine emissions from the high latitude oceans should be preserved in ice cores. This signal would contain information about the productivity of the oceans and about the state of the atmosphere during various climatic regimes.

Insoluble Particulates:

Variations in the concentration of dust document the major and minor shifts in global temperature. In all ice cores containing glacial/interglacial transitions, increased particulate deposition characterizes the cool periods. The concentration, size distribution, and chemical composition of the material entrained in the atmosphere directly affects the radiation balance by differential absorption and scattering of shortwave and longwave radiation.

The insoluble particulate matter (continental dust, volcanic ash, diatoms, and pollen) preserved in the ice provide an opportunity to examine both long and short term variations in the contribution of various sources to the atmospheric particulate mass. The contributions as a function of time (hence, of varying environmental conditions) when interpreted along with the other ice core parameters (i.e., isotopes, chemistry, accumulation) will allow documentation of climatic and environmental history over the last -150,000 years. The ultimate objective is to better understand the role of particulates in the global environmental system.

Particulates are of specific interest, not only because of the demonstrated close link with temperature and wind strength, but also the particulate loading of the atmosphere responds quickly to changes in surface conditions and circulation intensity. Excluding melting and percolation, particulates are quickly incorporated into the firn and the input signal is not altered substantially by post-depositional processes. Greater emphasis should be placed upon particle identification and size distribution determinations. It should be possible to link many of the major dust events in both glacial and interglacial ice to similar dust events in other ice cores.

Ice Core Dating:

The establishment of an annual time scale is essential for the proper analysis and interpretation of each ice core and should be given highest priority. Since no single constituent is perfectly preserved each year, at least 3 independent properties should be measured simultaneously as a cross-check. This approach will require the ability to make continuous, high-resolution measurements along the entire length of each core. Therefore those techniques that are least destructive, can be performed most rapidly after core procurement (e.g. on site), and are most consistently reliable should be considered. The resulting time scale and interpretations must be made available shortly after core collection for use in core allocation.

To date only DC (surface) conductivity has been proven to generally satisfy all of the above criteria. Therefore, priority should be given to the development and testing of alternate dating methods. Those which show some potential include: 1) AC conductivity (dielectric constant), 2) liquid conductivity, 3) NO3- ion (using UV spectrophotometry), 4) H202, and 5) laser light scattering. Well-established, but time-consuming measurements such as d180, 82H and microparticles should be made intermittently or at a later date to confirm the dating of the core.

At greater depths (e.g. pre-Holocene), resolution becomes the limiting factor. Thus it is essential to identify those techniques that will remain useful for dating annual layers after the others have failed. Ultimately, less precise but longer time scale methods such as radioactive isotope dating should be used on an intermittent basis if sample size requirements can be kept within reason.

Throughout the cores, marker horizons such as volcanic events, 10Be peaks, and the glacial/interglacial transitions should be used for cross correlation of the ice cores and absolute dating where possible. Finally, geophysical ice flow modeling should be used to complement the dating methods at depth.

Analyses to be Performed

Particulates

Microparticulates 
     total count 
     size distribution 
     elemental analysis 
     particle morphology

Pollen
Diatoms

Major Anions and Cations

Cl, N03, SO4, Na, NH4, K, Ca, Mg, Acidity

Trace Constituents

F, Methane Sulfonic Acid, Aldehydes
Fe, Mn, Al, Silica, Sr, Organic Acids, I

Other Constituents

Hydrogen Peroxide

Detail - Continuous analyses

Subannual to examine seasonal cycling and natural cycling and variability
Much detail around episodic phenomena such as volcanic events
Much detail over interglacial/glacial transition period to examine response of 
various constituents to this climate change.

Specific Experiments

Greenland Deep Drilling - Summit

Greenland Shallow Core Studies

Antarctic Deep Core Studies

Antarctic Shallow to Intermediate Core Studies

High Elevation Sites and Low Latitude Shallow to Intermediate Core Studies

S. America 
China
Himalayas 
Indonesia
Alaska

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