The proper choice of proxies for relevant strontium isotope baselines used for provenance and mobility studies in glaciated terranes - Important messages from Denmark

Strontium (Sr) isotope based provenance and mobility studies of ancient humans and animals necessitate representa-tive isoscapes/baselines. However, regions/terranes that were shaped and affected by glaciers during the last Ice Ages and are covered by glaciogenic sediments present a challenge with regards to the choice of suitable surface proxy ar-chives. Recent studies proposed that only Sr-87/Sr-86 signatures from pristine areas are relevant for this purpose. To test this theory, 160 new Sr concentrations [Sr] and Sr-87/Sr-86 signatures composed from similar to 960 subsamples of soil leachates and plants, complemented with 55 surface waters from agriculturally unaffected pristine forest sites from all over Denmark (island of Bornholm excluded) were analyzed. The results reveal that average Sr-87/Sr-86 signatures of all three proxies (plants: 0.7115 +/- 0.0025; 2 Sigma, n = 162; soil leachates: 0.7118 +/- 0.0037; 2 Sigma; n = 161, surface waters: 0.7104 +/- 0.0030; 2 Sigma, n = 55) are elevated compared to larger water bodies (creeks, rivers, lakes). In mixing diagrams, the data converge in a shared high [Sr] low 87Sr/86Sr endmember, which points to either remnant natural carbonates and/or organic components retaining carbonate Sr in the studied Podzols/Luvisols. The indications for more abundant carbonates in the past, compared to today's acid leached soils, implies that Sr-87/Sr-86 values measured from pristine forest locations and heathlands do not adequately reflect the biosphere compositions that prevailed similar to 12,000-2000 thou-sand years ago. Consequently, pristine forests in Denmark seem to be unsuitable proxy archive environments for constructing Sr isotope baselines for determining the provenance and mobility of ancient humans and animals. Hence, Sr-87/Sr-86 values measured in these pristine areas are non-representative and inadequate, and their use will lead to wrong interpretations. Finally, our study sheds light on the complexity of defining relevant and representative isoscapes/baselines in significantly changing environments and areas where the surface biosphere conditions do not necessary reflect the underlying geology.