One of Loehle’s proxies – the one that ends in the 16th century – has occasioned some interest and I took some time to investigate it. It is an alkenone SST estimate from ocean sediment core MD95-2011 from the Norwegian Sea (66 58.19N, 07 38.36E and 1048 m). The series ends in the 16th century because it was a piston core and the top of it was lost. However box core JM97-948/2A was drilled i the same location and provides a high resolution series right to the 1990s.
Both cores are in high-accumulation zones and have been closely sampled – a sample spacing of 0.5 cm in core JM97-948/2A and 1.0 cm in core MD95-2011 – yielding resolution of about 3.4 years and 8.4 years, respectively. Both have been discussed in a number of scientific reports and a number of relevant data sets have been archived at http://www.pangaea.de, a repository for much ocean sediment data.
The archive includes dO18 values for both N pachy dex and N pachy sin for both MD95 and JM97; the combined data being shown in the plot below, with a slight difference in color denoting the change in core. Do these measurements indicate that dO18 values in the Norwegian Sea are at unprecedented levels? You tell me.
Figure 1. dO18 for Md95 and JM97. In the archive, the dates for the JM97 series are incorrectly reported. I asked CA reader Richart T about this and he was able to confirm that there was an error. I’ve plotted the data by re-calculating the dates in the JM97 dO18 series to match the date model. JM97 data from http://doi.pangaea.de/10.1594/PANGAEA.510799?format=textfile and MD95 data from http://doi.pangaea.de/10.1594/PANGAEA.510782?format=textfile. Dating from http://doi.pangaea.de/10.1594/PANGAEA.510806?format=textfile. X-axis in kyrs.
While dO18 is sometimes used as a temperature proxy (e.g. Lonnie Thompson’s ice core), it has not been used as one here. SST was estimated in two different ways for this core – (1) by an analog based on foram distributions; (2) alkenone SST. The SST estimates from foram distribution are archived for both MD95 and Jm97 and are plotted below; for alkenone SST, only the MD95 values are archived. I’ve been informed that JM97 values have been calculated but they have not been archived or reported, apparently because of inconsistency problems. Here is a plot:
Figure 2. SST estimates. Black – from foram distributions; red dots – alkenone SST from MD95. SST estimate and abundance of forams for MD95 from http://doi.pangaea.de/10.1594/PANGAEA.510781?format=html and for JM97 from http://doi.pangaea.de/10.1594/PANGAEA.510801?format=html. Alkenone SST for MD95 from loc=”http://doi.pangaea.de/10.1594/PANGAEA.438810?format=textfile.
Calvo E., Grimalt J. O. and Jansen, E. (2002) High resolution UK37 sea surface temperature reconstruction in the Norwegian Sea during the Holocene. Quaternary Science Reviews, 21, 1385-1394. https://bora.uib.no/bitstream/1956/385/2/2001PA000654.pdf
Andersson, C. Bjørg Risebrobakken,2 Eystein Jansen,1,2,3 and Svein Olaf Dahl4 2003. Late Holocene surface ocean conditions of the Norwegian Sea (Vøring Plateau), Paleooceanography.
Risebrobakken, B; Jansen, E; Andersson, C et al. (2003): High-resolution study of Holocene paleoclimatic and paleoceanographic changes in the Nordic Seas, Paleoceanography