I’ve been going through the literature and data on ocean sediments looking for proxies with high resolution in the Holocene – something that I discussed a few months ago.
Kim et al 2004 and Lorenz et al 2006, two articles by the same group, discuss Holocene SST changes based on alkenones. Most of their proxies are rather low resolution – sometimes only 6 or 7 measurements in the past 7000 years.
However, SSDP-102 has a resolution of about 40 years during the past 2000 years. It’s taken in shallow waters (40 m) offshore Korea (most alkenone cores seem to be from depths of over 1000 m). Its highest values occur in the MWP – where values are significantly higher than the most recent values. MWP values are also higher than values around 6000 BP.
Here’s a plot of the data downloaded from http://www.pangaea.de here. Obviously it has a striking MWP and would make a nice addition to an apple-picking reconstruction. We’ve seen high MWP values in a couple of Pacific Warm Pool proxies (Stott et al 2004; Newton et al 2006).
I tried to compare these estimates to Levitus’ estimates of ocean temperatures and ran into a problem. The Levitus estimate for the closest 1×1 gridcell is much lower than the alkenone estimates as shown in the graph below. I’m not sure what this shows, other than one has to be cautious in splicing Levitus gricell temperatures with a proxy record (something that Jim Hansen might think about.)
Next here is a plot of Levitus 2001 ax1 gridcell values at surface (0.0 m) taken from here. The core is taken a little outside the closest gridcell with a Levitus value; it’s shallower and so it’s not surprising that the proxy values are higher than the gridcell value.
Just for interest, here’s how this core looked in the original figure by Kim et al 2004 (it’s not illustrated in Lorenz et al 2006). It’s very scrunched up and without re-plotting, most people probably wouldn’t notice the very strong MWP. I didn’t notice it when I read this article previously – I only noticed it by downloading data and re-plotting. This figure also shows the very low resolution of most of the alkenone records discussed in this article.
Kim et al 2004 Fig. 1. Caption: (a) Data points (open circles) and linear trends of alkenone SST reconstructions from the North Pacific realm. The magnitudes of SST change over the last 7000 years (1C/7 kyr) are indicated in the upper right corner and the core names are given in the lower left corner of each panel. The numbers refer to Table 1. r is the correlation coefficient.
Kim, Jung-Hyun; Rimbu, Norel; Lorenz, Stefan J; Lohmann, Gerrit; Nam, Seung-Il; Schouten, Stefan; Rühlemann, Carsten; Schneider, Ralph (2004): North Pacific and North Atlantic sea-surface temperature variability during the Holocene, Quaternary Science Reviews, 23 (20-22), 2141-2154, doi:10.1016/j.quascirev.2004.08.010
Stephan J. Lorenz, Jung-Hyun Kim, Norel Rimbu, Ralph R. Schneider and Gerrit Lohmann, 2006. Orbitally driven insolation forcing on Holocene climate trends: Evidence from alkenone data and climate modeling. PALEOCEANOGRAPHY, VOL. 21, PA1002, doi:10.1029/2005PA001152, 2006