It’s a dangerous practice to let your eye get teased into visual comparisons, but I was struck by a comparison between the G Bulloides series from the Arabian Sea (which is an upwelling proxy) and Stott’s Warm Pool SST proxies. The two figures excerpted below both cover the Holocene. On the left is Gupta et al 2003 Figure 2 showing G Bulloides primarily from 723A in the Arabian Sea (I’m going to discuss a potentially problematic splice of 723A with RC2730 on another occasion); on the right is a plot of Mg/Ca-derived SST (blue) for MD81 in the Pacific Warm Pool from Stott et al 2004. In each case, one sees a similar-looking uptick dating more or less to the MWP and an elevated Holocene Optimum.
Figure 1. Left – G Bulloides from Arabian Sea 723A; right – Mg-Ca estimated SST from Warm Pool MD81
Now here are both series plotted in a consistent format from archived information. Holocene Optimum levels are higher in the G. Bulloides upwelling proxy than for the Warm Pool SST proxy, but, to me, anyway, there seems to be some similarity.
Figure 2. Top – Arabian Sea G Bulloides from 723A; bottom- Mg-Ca derived SST estimate from MD81
I think that this impression carries over to the data when plotted on a centennial scale as below. Within the very loose dating schemes of these ocean sediment cores, I find myself being persuaded that there is actually some similarity in detail between 723A G Bulloides and the Pacific Warm Pool Mg-Ca proxy – if you indulge in a little re-alignment of peaks. I’d be inclined to align the downticks just before 1000 in 723A and just after 1000 in MD81 and try to date these features with more precise proxies. (Note that the left-right are reversed in this diagram to make it consistent with centennial-scale conventions ending on the right.) Note that Stott specifically marked an MWP at his website figure showing a slightly varied version of the figure below, where the match might even be a little better.’ In either case, the MWP appears as rather a distinct period in both proxies on a Holocene scale.
Top -‘ 723A G Bulloides; bottom – Mg-Ca derived SST from MD81.
Now there’s an interesting tie-in back to Lorenz et al where they primarily (and incorrectly IMHO) used upwelling sites to characterize the tropics.’ Here’s a graphic from a relatively recent PPT presentation by Oppo showing both G Bulloides and Mg-Ca SST estimates for the Arabian Sea. The top chart shows G Bulloides from 723A – with a familiar look (compare to above) -‘ while Mg-Ca’ proxies for both bulloides and ruber show an’ increase through the Holocene to about 2000 BP (the opposite to the G Bulloides upwelling proxy). It’s not clear why the Mg-Ca series don’t carry through to more modern values.’ ‘ Note that’ Oppo’s G Bulloides series does not carry forward to the 20th century, while the Moberg G Bulloides series does. What I’ll report on in another post is a very questionable splice in the Moberg proxy.