Preliminary insights into Miocene palaeoprecipitation and palaeotemperature using speleothem fluid inclusion isotopes from eastern North Greenland

The Miocene epoch was a warm period characterised by elevated atmospheric CO₂ levels compared to the present day. These CO₂ concentrations are similar to those predicted for future climate scenarios, making the Miocene an important period to deepen our understanding of warmer climates. While Greenland ice cores have provided highly valuable data for the late Quaternary, terrestrial palaeoclimate archives extending deeper in time in the Arctic remain sparse, leaving a significant gap in our knowledge of Greenland's climate history.

Speleothems are an excellent archive for obtaining high-resolution terrestrial climate data. During speleothem formation, dripwater can be trapped as fluid inclusions, preserving the isotopic signature of ancient meteoric water. This study focuses on four speleothems from a cave in eastern North Greenland. U-Pb dating indicates that the speleothems were deposited during the middle and late Miocene. We analysed the stable H isotopic composition of primary fluid inclusions to reconstruct the isotopic composition of palaeo-dripwater. Carbon and oxygen isotopes of the speleothem calcite were also measured in order to estimate quantitative temperatures for eastern North Greenland during middle and late Miocene. Our initial results show that during such an elevated CO₂ world, mean annual air temperatures were substantially elevated above modern values.

Macroscopically, all speleothems are comprised of translucent and light brown calcite. Microscopically, the dominant fabric is coarsely crystalline columnar calcite. Fluid inclusion petrography shows the presence of both fluid inclusion-rich and inclusion-poor areas in the late Miocene speleothems, while primary fluid inclusions are abundant in the two middle Miocene speleothems. The mean water content obtained from crushing varies from 0.2 µL to 1.0 µL between the speleothems.