Temperature variability in southern Europe over the past 16,500 years constrained by speleothem fluid inclusion water isotopes

Abstract. In the Northern Hemisphere, the last 16.5 kyr were characterized by abrupt temperature transitions during stadials, interstadials, and the onset of the Holocene. These changes are closely linked to large-scale variations in the extent of continental ice-sheets, greenhouse gas concentrations, and ocean circulation. The regional impact of these rapid climate changes on Southwestern European environments is recorded by various temperature proxies, such as pollen and chironomids preserved in lake sediments. Speleothems and their fluid inclusions serve as valuable proxies, offering high-resolution chronologies and quantitative records of past temperature changes. These non-biogenic quantitative temperature records are essential to assess whether climate models can accurately simulate regionally divergent climatic trends and for understanding global and regional climate mechanisms in the past. Here, we present a record from five speleothems from two caves on the northeastern Iberian Peninsula (Ostolo and Medukilo caves). Using hydrogen isotopic composition of fluid inclusions, we developed a δ²H/T transfer function in order to reconstruct regional temperatures over the past 16.5 kyr (Ostolo-Mendukilo Fluid Inclusion Temperature record [OM-FIT]). Our findings reveal an increase of 6.0 ± 1.9 °C at the onset of Greenland Interstadial 1, relative to the cold conditions of the preceding Greenland Stadial 2.1a. Also, the OM-FIT record shows a temperature decline of approximately 5.3 ± 1.9 °C during the early phase of Greenland Stadial 1. The end of this cold phase and the onset of the Holocene are marked by a rapid warming of about 3–4 °C and reaching a maximum at 11.66 ± 0.03 kyr BP. The OM-FIT record also exhibits abrupt events during the last deglaciation and the Holocene, which are also reflected in the δ¹⁸O values of the calcite, including Heinrich Event 1, Greenland Interstadial 1d, and the 8.2 kyr event.