35,000 years of hydrological variability in northern New Zealand from speleothem magnetism

Speleothem magnetism is the study of the origin and geo-enviromagnetic significance of magnetic minerals in speleothems. Allogenic magnetic particles are transported to speleothem sites from soils and sediments by hydrological and aeolian processes. The two main hydrologic transport mechanisms are infiltration through karst porosity and entrainment in fluvial transport. Cave ventilation constitutes a third input mechanism, supplying aeolian particulate matter. Water percolating from the surface tends to discriminate towards smaller, pedogenic magnetic mineral grains, whereas fluvial and aeolian processes discriminate towards larger, non-pedogenic (lithogenic) grains. If magnetic populations in speleothem calcite samples can be thoroughly characterised, individual components can be recognised which relate to specific processes of transport, and the contributions of these components can be used to reconstruct variability in the strength of these processes over the depositional period of the speleothem