Does it matter whether proxies are used upside-down or not?
Maybe not in Mann-world (where, in response to our criticism at PNAS, Mann claimed that it was impossible for him to use series upside-down). But, unlike Mann, Darrell Kaufman acknowledges responsibility for using proxies upside-up. Unfortunately, he and the PAGES2K authors don’t seem to be very diligent in ensuring that they do so.
Shortly after release of PAGES2K, I observed that they used both Hvitarvatn and Quelccaya upside-down (the latter on Neukom’s watch.) I also observed that correct orientation of Hvitarvatn ought to have a knock-on impact on Big Round Lake, which matched Hvitarvatn about as closely as two distinct proxies could be expected. Thus far, Kaufman’s already corrected upside-down Hvitarvatn: Big Round Lake should be in play as well. This inconsistency is something that ought to have been “assessed” in an assessment report, but wasn’t.
In a previous post earlier today, I questioned whether PAGES2K ought to have inverted the orientation of the Okshola speleothem O18 series since the Holocene trend (as inverted) is now opposite to the Holocene trend of the high-quality Renland ice core O18 series. The Okshola series is the only speleothem O18 series in the PAGES2K network: on other occasions, I’ve questioned the appropriateness of using “singleton” proxies in an assessment report. The fact that serious questions can arise over even the orientation of a series is eloquent support for this policy.
In the present post, I’m going to look at another singleton O18 series in PAGES2K – the single ocean sediment O18 series in the network (P1003), where once again, I seriously question whether PAGES2K have used the series in the correct orientation.
In the diagram below, I’ve shown O18 values (inverted) of sediments from an Arctic ocean core, showing the contrast between the LGM and the Holocene Optimum: this is a loud contrast which ought to show which way is up. While ice core O18 series have more negative values in glacial periods, the opposite happens with ocean sediment O18: O18 values in Arctic ocean sediments became less positive (from ~4 to ~3 %%). This is true over dozens of cores. The reason is logical enough: the continental glaciers in ice ages contain ice with depleted O18 values and this results in the oceans being less depleted in O18.
Figure 1. Top panel – O18 for PS1243-1 (from pangaea.de). Bottom panel – long version P1003 from Sundqvist et al 2014 archive. (I haven’t seen a technical publication.)
In the next figure, I’ve shown the two-millennium section of P1003 used by PAGES2K in two mirror orientations. In the top panel, I’ve shown the series in PAGES2K uninverted orientation, while in the bottom panel, I’ve shown the series in the inverted orientation that is consistent with the observed relationship between values in the LGM and Holocene Optimum.
Figure 2. P1003 O18 series (PAGES2K) version. top – in PAGES2K orientation; bottom – inverse orientation to match LGM-Holocene Optimum orientation.
Had the series been oriented to show elevated O18 values to show elevated values in glacial periods, it would also have resulted in a Little Ice Age being colder than both the medieval warm period and the modern warm period – a phenomenon that is not disputed even by the Team for the Arctic, and a somewhat declining trend through the two most recent millennia, reducing the inconsistency of this proxy with other series. As a clincher, Kristensen et al 2004 (Paleooceanography), a technical publication of P1-003MC, used the orientation shown in the bottom panel – opposite to PAGES2K as shown in the excerpt shown below (the scale is different, but if you look closely, you can see the match):