Ice Core Archives of Mineral Dust - Mineral Dust: A Key Player in the Earth System - page 456

18.1 Introduction

Snow and ice cover up to 25 % of the Earth's surface, approximately 15 million km 2
is on land and 25 million km 2 is sea ice that forms seasonally over the polar oceans.
Snow is deposited in many areas but glaciers will only grow in areas where the
annual snow accumulation exceeds the annual snow ablation. Although the largest
and most persistent ice sheets are found at the poles, many glaciers and smaller ice
sheets are found on lower latitude mountain ranges of sufficient height. As snow
accumulates, it compacts the underlying years' snowfall and produces layers that
become denser with depth. Fresh snow has a low density (300 kg/m 3 ) and rapidly
compacts to firn (density 500-800 kg/m 3 ). At densities greater than 830 kg/m 3 the
snow crystals have compressed into solid ice. The maximum possible density of ice
is 910 kg/m 3 , due to the trapping of air in the firn column, and subsequent presence
of air bubbles and clathrates in the ice matrix.
Ice sheets and glaciers can be hundreds to thousands of metres thick, offering
long climate records that are retrieved by drilling ice cores (Fig. 18.1 ). Deep ice
cores in central Greenland and Antarctica can be up to 4 km long and have produced
climate records covering the past 800 ka (thousands of years). Mountain glaciers are
usually less than 300 m thick and offer climate records from a few hundred to a few
thousand years long. Drilling operations are conducted in the summer, when weather
and temperature conditions are favourable; mountain glacier cores can be drilled in
a few weeks, deep drillings in Greenland and Antarctica usually require 3-5 years.
The ice is recovered in sequential drilling “runs”, returning 1-4 m of ice at a time.

Fig. 18.1 Map of the north and south polar regions showing ice core drilling sites in Antarctica
and Greenland. Antarctic locations include Berkner Island (BI), Byrd, Vostok (VK), Dome C
(DC), Dronning Maud Land (DML), Dumont D'Urville (DDU), Talos Dome (TD), Law Dome
(LD), Dome Fuji (DF), Dome B (DB) and Komsomolskaya (KMS). Greenland sites include Camp
Century (CC), NEEM, NorthGRIP (NGRIP), GRIP/GISP2 and DYE-3