Hydrosphere

Climate history from lakes

Lakes are distributed widely across the globe, and depending on their location, they can be particularly sensitive to changing climate.  For example, global warming is having a significant impact on lakes in polar and alpine environments, while variation in rainfall patterns impacts on lakes in semi-arid regions.  In order to understand the climate history that can be obtained from lakes, we need to briefly consider how temperature and precipitation affect different types of lakes.   In cold, polar-regions, lakes are normally covered by ice for many months of the year.  During spring, the ice melts and winds help mix the water up, which also ensures...

Cave deposits (speleothems) as archives of environmental change

Speleothems, from the Greek words for cave and deposit, include the familiar descending stalactites, upward-growing stalagmites and more continuous sheets called flowstones.  They grow slowly, at rates of between 1 mm a year to 0.001 mm a year.   This growth can persist for many thousands of years before being interrupted.  As with trees, speleothems commonly display annual layers which may be visible when a sample is polished, or recognised through chemical analyses.  Ideally, a sample will accumulate regular, parallel layers,  allowing the investigator to study its growth through time, and see changes in environmental conditions. These speleothems grow in caves within limestone rock.  Typically the...