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Saturday, January 31, 2015

Laboratory versus the Real World

Since I suspect that the Herbert et al. tropical SST reconstruction data using UK'37 will require some re-calibration, I am becoming a Mg/Ca kinda guy, I looked for a few comparisons using the same core or region.  DuBois et al. used the Herbert method and LuDuc et a. did a comparison of UK'37 and Mg/Ca.

Nothing is simple though.  The lat/lon are the first two numbers in the legend with the core identifier and method.  From the read me with the DuBois 2009 data we have this:

Cores ME0005A-27JC, ME0005A-43JC and TR163-31P were analyzed for alkenone unsaturation at Dalhousie University following standard laboratory procedures detailed by Kienast et al. (2006), whereas cores TR163-19P and TR163-22P where analyzed at Brown University following similar laboratory procedures detailed by Herbert et al. (1998). 
The age models for these cores were adopted as published in earlier studies (ME0005A-27JC from Kienast et al. 2007, ME0005A-43JC from Benway et al. 2006, TR163-19P from Lea et al. 2000, TR163-22P from Lea et al. 2006, TR163-31P from Martin et al. 2002). 
The alkenone unsaturation index UK037 is calculated as UK'37 = (C37:2)/(C37:3 + C37:2), where (C37:2) and (C37:3) are concentrations of the diunsaturated and triunsaturated C37 methyl alkenones. For conversion into temperature estimates, we used the culture calibration of Prahl et al. (1988) (UK'37 = 0.034T + 0.039). Replicate analyses of selected samples indicate an analytical precision of about ±0.01 UK'37 units (0.3°C). 

So we have lab quality of about +/- 0.3C but real world temperature ranges of about +/- 3.0 C degrees.  The eastern tropical Pacific should be about the worst case.  There is a great deal of ENSO related upwelling and northward circulation.  The UK'37 method can be "calibrated" to regional temperatures but you may not be able to capture the variance.  So while the eastern Pacific is an interesting region, temperature reconstructions are going to be a beyatch.  So let's just say Eastern Tropical Pacific is going to be put on hold.

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