Last ice sheet recession and landscape emergence above sea level in east central Sweden, evaluated using 14C produced in situ in quartz

<p>The aim of this study is to test the Holocene relative sea-level (RSL) curve (or shoreline displacement curve) for east central Sweden using ¹⁴C produced <em>in situ</em> in quartz-bearing bedrock (<em>in-situ</em> ¹⁴C). The original RSL curve is instead based on radiocarbon dating of organic material from isolation basins. Having an accurate RSL curve is crucial from at least two aspects. In Sweden&#8217;s safety assessments for a planned spent nuclear fuel repository and for the existing repository for low- and intermediate level waste, the RSL curve is used to constrain the emergence above sea level in landscape development models. Also, the RSL is used to constrain model estimates of rates and depths of glacial and subaerial erosion from cosmogenic ¹⁰Be and ²⁶Al produced <em>in situ</em> in quartz in bedrock surfaces.</p><p>Avoiding vein quartz and hydrothermally altered bedrock, five samples of granitoid bedrock were taken along an elevation transect extending southwards from Forsmark, the location of the planned spent nuclear fuel repository. Because all samples derive from bedrock outcrops positioned below the highest postglacial shoreline, they target the timing of progressive landscape emergence above sea level. To further assess the accuracy of <em>in-situ</em> ¹⁴C dating, we took an additional five samples from bedrock outcrops 100 km west of Forsmark, above the highest postglacial shoreline. The <em>in-situ</em> ¹⁴C concentrations in these samples should reflect local deglaciation ages.</p><p>The ten new <em>in-situ</em> ¹⁴C measurements provide robust age constraints that compare favorably with the original RSL curve derived from radiocarbon&#160;dating of organic material in isolation basins and with the regional deglaciation chronology. Inferences of limited rates and depths of bedrock erosion over the past 1 Myr, inferred from ¹⁰Be and ²⁶Al inheritance and which are critically dependent on the RSL curve, therefore glean strong support from these new <em>in-situ</em> ¹⁴C measurements.</p>