Fig. 3: Recurrent central Arabian humid episodes over the late Miocene to late Pleistocene are associated with increasing regional aridity and higher Northern Hemisphere meridional temperature gradients.

a, Key stages of Northern Hemisphere (NH) cooling, including late Miocene cooling¹⁷ associated with ephemeral glaciation³⁵ and ice-rafted debris³⁶, as well as the Pliocene/Pleistocene gradual increase in the Northern Hemisphere in glacial period ice volume⁴⁶ and the timing of Northern Hemisphere ice-sheet advancement⁴⁷. b, Latitudinal temperature gradient (°C) calculated using the SST differences between Arabian Sea site ODP 722 and North Atlantic site ODP 982¹⁷ (see Methods for calculations). The solid coloured line has shading that varies according to the calculated temperature gradient and the black dashed line is the linear trend line. c, Major global events are shown including the Messinian Salinity Crisis³⁷, restriction of the Central American Seaway and Indonesian Throughflow⁴⁸, intensification of Walker–Hadley circulation¹⁶ and the MPT⁴⁹. d, Sahara dust flux from North Atlantic marine core 659 indicating high and low inputs, which are indicated by orange to yellow shading, respectively, and the 99% percentile shown in pink shading¹. e, SSTs from the Arabian Sea based on an alkenone unsaturation method with warmer to cooler SSTs indicated by red to blue shading, respectively^17,33. f, This study; U–Pb-derived ages (filled circles) and U–Th-derived ages using LA-MC-ICP-MS (filled diamonds) and solution MC-ICP-MS (filled squares), with the 95% confidence interval uncertainty indicated by the horizontal error bars. The ages of gypsum ‘crust’ samples are indicated by asterisk symbols and the colours of the filled symbols refer to the individual speleothem isotopic composition shown in the box plots in g. g, The average modern rainfall δ¹⁸O (‰ VPDB) value⁵⁰ is indicated by the blue dashed line converted to VPDB scale (see Methods for details). Box plots of speleothem δ¹⁸O (‰ VPDB) values (n = 1,138), with each colour denoting an individual speleothem growth period. Circles show all individual datapoints, squares indicate outliers and diamonds indicate extreme outliers. Mean values of –14.2 (1σ = 0.9), –13.0 (1σ = 0.9), –12.0 (1σ = 1.7), and –8.5 (1σ = 2.8) are shown near clustered groups. The background shading shows the U–Pb histogram frequency in Fig. 2g and is indicated by the colour bar.