Three cores were drilled at Dasuopu. We don’t hear much about Core #1. It was drilled in a flow zone and, despite being 160 m deep, is only back to 1922 in the most recent discussion.
I’m intrigued with this for a variety of reasons, including the fact that Guliya Core #3, the one that we’ve been discussing, was not drilled at the summit.
Dasuopu is a Thompson core and, needless to say, there is no systematic description of the core or archiving of the data. So it’s a “dance of the seven veils” to decode anything and results are inconsistent between one publication and another, seemingly with no reconciliation.
Thompson [QSR 2000] is one of the earliest accounts of the Dasuopu core (drilled in 1997). The accumulation rate at this glacier is rather high (said to have an accumulation of snow of 2.11 from Aug 1996 to Sep 1997 in this article), thus yielding a strong (“best-preserved”) annual signal in dO18. Figure 7 shows Core 1 back to 1974. Figure 8 shows Core 1 values down to 60 m. Temperature at bedrock was -13.8 deg C, the coldest then observed in tropical glaciers. Thompson: “ice is frozen at the bed indicates that cores 12 and 3 contain long records”.
Thompson et al [Science 2000] reported:
In 1997, three ice cores were recovered from the Dasuopu glacier (28°239N, 85°439E) with the use of an electromechanical drill in dry holes (Fig. 1). The first core (C1) was 159.9 m long and was drilled at 7000 m above sea level (a.s.l.) down the flow line from the top of the col, and two cores (C2 and C3), 149.2 and 167.7 m long, respectively, were drilled to bedrock 100 m apart on the col at 7200 m a.s.l. Visible stratigraphy showed no hiatus features in any of the cores.
They reported the following disposition of cores: C2- Lanzhou; C3- Ohio; C1 -split.
In 2004, Duan et al (including Thompson) reported:
The annual snow accumulation time series from Dasuopu ice core C1 and C2 are agreement during the period 1700 to 1995 [Thompson et al., (Science) 2000].
In my reading of Thompson et al 2000, I find no authority for this claim. In 2005, Davis et al (including Thompson) reported as shown below that Core 1 extends back only to 1922 AD(!), a finding which would seem to be inconsistent with the statement in Duan et al the previous year:
In 1997, another cooperative program between LIGG and OSU-BPRC culminated in the drilling of the Dasuopu glacier on the north slope of the central Himalayas (28N, 85E, 7200 m asl) [Thompson et al., 2000a]. Three ice cores were recovered, the first of which was drilled down-flow from the ice divide but did not reach bedrock. The time series extends back only to 1922 A.D. at 160 m, and below 74 m depth (corresponding to 1945 A.D.) the stratigraphy is severely compromised by ice flow. Cores 2 and 3 (DsC2 and DsC3) were drilled close to the ice divide, and both reached bedrock at 149 m and 168 m, respectively. DsC2 was taken frozen to LIGG, and DsC3 was returned completely frozen and intact to OSU-BPRC. Thus it was possible to sample all of DsC3 in great detail in a controlled environment, which was an advantage over the Dunde analysis.
The basal age of the ice in one of these mountain glaciers in relatively nearby cores of equivalent depth can therefore vary by an order of magnitude. Thompson obviously tries to find drilling locations that are least affected by flow, but, obviously, his picking at Dasuopu was not 100%. No fault there. Guliya was drilled before Dasuopu. I’ll try to locate corresponding information on drill locations at Guliya.
Duan, K., T. Yao, and L. G. Thompson (2004), Low-frequency of southern Asian monsoon variability using a 295-year record from the Dasuopu ice core in the central Himalayas, Geophys. Res. Lett., 31, L16209, doi:10.1029/2004GL020015.
Davis et al JGR 2005 http://www-bprc.mps.ohio-state.edu/Icecore/Abstracts/davis_jgr_2005.pdf
Thompson, 2000. Quat Sci Rev
Thompson, L.G., T. Yao, E. Mosley-Thompson, M.E. Davis, K.A. Henderson and P.-N. Lin. 2000. A high-resolution millennial record of the South Asian Monsoon from Himalayan ice cores. Science, 289, 1916-1919.
Zhao, H. X. and G. W. K. Moore, 2002: On the Relationship between Dasuopu Snow Accumulation and the Asian Summer Monsoon. Geophys. Res. Lett., 29(24),2222, doi:10.1029/2002GL015757.