Search for: All records

Abstract. Over the last 30 years, in situ cosmogenic nuclides (CNs) have revolutionizedsurficial processes and Quaternary geologic studies. Commonly measured CNsextracted from common mineral quartz have long half-lives (e.g.,10Be, 26Al) and have been applied over timescales from a fewhundred years to millions of years. However, their long half-lives alsorender them largely insensitive to complex histories of burial and exposure ofless than ca. 100 kyr. On the other hand, in situ cosmogenic 14C (in situ 14C) isalso produced in quartz, yet its 5.7 kyr half-life renders it very sensitiveto complex exposure histories during the last ∼25 ka, aparticularly unique and powerful tool when analyzed in concert withlong-lived nuclides. In situ 14C measurements are currently limited torelatively coarse-grained (typically sand-sized or larger, crushed or sieved tosand) quartz-bearing rock types, but while such rocks are common, they arenot ubiquitous. The ability to extract and interpret in situ 14C fromquartz-poor and fine-grained rocks would thus open its unique applicationsto a broader array of landscape elements and environments. As a first step toward this goal, a robust means of interpreting in situ 14Cconcentrations derived from rocks and minerals spanning wider compositionaland textural ranges will be crucial. We have thus developed aMATLAB®-based software framework to quantifyspallogenic production of in situ 14C from a broad range of silicate rock andmineral compositions, including rocks too fine grained to achieve purequartz separates. As expected from prior work, production from oxygendominates the overall in situ 14C signal, accounting for >90 %of production for common silicate minerals and six different rock types atsea level and high latitudes (SLHL). This work confirms that Si, Al, and Mgare important targets but also predicts greater production from Na thanfrom those elements. The compositionally dependent production rates for rockand mineral compositions investigated here are typically lower than that ofquartz, although that predicted for albite is comparable to quartz,reflecting the significance of production from Na. Predicted productionrates drop as compositions become more mafic (particularly Fe-rich). This framework should thus be a useful tool in efforts to broaden the utility ofin situ 14C to quartz-poor and fine-grained rock types, but futureimprovements in measured and modeled excitation functions would bebeneficial. 

Abstract The impact of late Cenozoic climate on the East Antarctic Ice Sheet is uncertain. Poorly constrained patterns of relative ice thinning and thickening impair the reconstruction of past ice-sheet dynamics and global sea-level budgets. Here we quantify long-term ice cover of mountains protruding the ice-sheet surface in western Dronning Maud Land, using cosmogenic Chlorine-36, Aluminium-26, Beryllium-10, and Neon-21 from bedrock in an inverse modeling approach. We find that near-coastal sites experienced ice burial up to 75–97% of time since 1 Ma, while interior sites only experienced brief periods of ice burial, generally <20% of time since 1 Ma. Based on these results, we suggest that the escarpment in Dronning Maud Land acts as a hinge-zone, where ice-dynamic changes driven by grounding-line migration are attenuated inland from the coastal portions of the East Antarctic Ice Sheet, and where precipitation-controlled ice-thickness variations on the polar plateau taper off towards the coast.