As noted in my previous post, Marcott, Shakun, Clark and Mix disappeared two alkenone cores from the 1940 population, both of which were highly negative. In addition, they made some surprising additions to the 1940 population, including three cores whose coretops were dated by competent specialists 500-1000 years earlier.
While the article says that ages were recalibrated with CALIB6.0.1, the differences between CALIB6.0.1 and previous radiocarbon calibrations is not material to the coretop dating issues being discussed here. Further, Marcott’s thesis used CALIB6.0.1, but had very different coretop dates. Marcott et al stated in their SI that “Core tops are assumed to be 1950 AD unless otherwise indicated in original publication”. This is not the procedure that I’ve observed in the data. Precisely what they’ve done is still unclear, but it’s something different.
In today’s post, I’ll examine their proxy #23, an alkenone series of Isono et al 2009.