Figure 1. Prediction surface (a) and standard error surface (b) of the spatial variation in δ¹⁸O_p values calculated using Ordinary Kriging.

(Prediction errors: n = 258; mean = 0.001; RMS = 0.563; standardised mean = 0.001; standardised RMS = 1.002; average standard error = 0.516). All values were retained for coincident points or multiple samples from the same site. Symbology for prediction surface and standard error surface classified using defined intervals and geometric intervals respectively. Ordinary Kriging carried out using the Geostatistical Analyst extension for ArcGIS for Desktop 10.3.1 (http://desktop.arcgis.com/en/arcmap/10.3/guide-books/extensions/geostatistical-analyst/understanding-ordinary-kriging.htm) © EuroGeographics for the administrative boundaries.