Reconstruction of Past Antarctic Temperature Using Present Seasonal d¹⁸O–Inversion Layer Temperature: Unified Slope Equations and Applications

Reconstructing the history of polar temperature from ice core water isotope (d¹⁸O) calibration has remained a challenge in paleoclimate research, because of our incomplete understanding of various temperature–d¹⁸O relationships. This paper resolves this classical problem in a new framework called the unified slope equations (USE), which illustrates the general relations among spatial and temporal d¹⁸O–surface temperature slopes. The USE is applied to the Antarctica temperature change during the last deglaciation in model simulations and observations. It is shown that the comparable Antarctica-mean spatial slope with deglacial temporal slope in d¹⁸O–surface temperature reconstruction is caused, accidentally, by the compensation responses between the d¹⁸O–inversion layer temperature relation and the inversion layer temperature itself. Furthermore, in light of the USE, we propose that the present seasonal slope of d¹⁸O–inversion layer temperature is an optimal paleothermometer that is more accurate and robust than the spatial slope. This optimal slope suggests the possibility of reconstructing past Antarctic temperature changes using present and future instrumental observations. SIGNIFICANCE STATEMENT: This paper develops a new framework called the unified slope equations (USE) to provide, for the first time, a general relation among various spatial and temporal water isotope–temperature slopes. The application of the USE to Antarctic deglacial temperature change shows that the optimal paleothermometer is the seasonal slope of the inversion layer temperature.