An interlaboratory study of TEX86 and BIT analysis of sediments, extracts and standard mixtures.

Two commonly used proxies based on the distribution of glycerol dialkyl glycerol tetraethers (GDGTs) are the TEX86 (TetraEther indeX of 86 carbon atoms) paleothermometer for sea surface temperature reconstructions and the BIT (Branched Isoprenoid Tetraether) index for reconstructing soil organic matter input to the ocean. An initial round-robin study of two sediment extracts, in which 15 laboratories participated, showed relatively consistent TEX86 values (reproducibility ±3-4°C when translated to temperature) but a large spread in BIT measurements (reproducibility ±0.41 on a scale of 0-1). Here we report results of a second round-robin study with 35 laboratories in which three sediments, one sediment extract, and two mixtures of pure, isolated GDGTs were analyzed. The results for TEX86 and BIT index showed improvement compared to the previous round-robin study. The reproducibility, indicating interlaboratory variation, of TEX86 values ranged from 1.3 to 3.0°C when translated to temperature. These results are similar to those of other temperature proxies used in paleoceanography. Comparison of the results obtained from one of the three sediments showed that TEX86 and BIT indices are not significantly affected by interlaboratory differences in sediment extraction techniques. BIT values of the sediments and extracts were at the extremes of the index with values close to 0 or 1, and showed good reproducibility (ranging from 0.013 to 0.042). However, the measured BIT values for the two GDGT mixtures, with known molar ratios of crenarchaeol and branched GDGTs, had intermediate BIT values and showed poor reproducibility and a large overestimation of the "true" (i.e., molar-based) BIT index. The latter is likely due to, among other factors, the higher mass spectrometric response of branched GDGTs compared to crenarchaeol, which also varies among mass spectrometers. Correction for this different mass spectrometric response showed a considerable improvement in the reproducibility of BIT index measurements among laboratories, as well as a substantially improved estimation of molar-based BIT values. This suggests that standard mixtures should be used in order to obtain consistent, and molar-based, BIT values

TRANSPIRATION RATES AND LEAF BOUNDARY LAYER PARAMETERS FOR PEANUT ANALYZED WITH THE TWO-DIMENSIONAL MODEL 2DLEAF

Rates of leaf transpiration and photosynthesis are both affected by the thickness of the boundary layer (BL) and by the rates at which gases diffuse through it. These BL properties are currently impossible to measure and must be estimated by using models in conjunction with measured rates of transpiration. Transpiration rates and BL for two Argentine peanut (Arachis hypogaea L.) cultivars, Florman INTA, Virginia type, and Manfredi 393 INTA, Spanish type, were studied with the two-dimensional model 2DLEAF which accounts for leaf anatomy, i.e. for leaf internal structure and stomatal density. Measurements on leaf cross-sections and leaf surface images demonstrated a significant difference between two cultivars. Published transpiration rates for peanut of Virginia and Spanish types measured in controlled environment and field conditions were used to determine two parameters of the leaf BL, its thickness, d, and the ratio of diffusion coefficients in the BL and in the intercellular space, B. Both parameters were different for two cultivars. Transpiration rate was presented (a) as a function of BL parameters d and B with four empirical parameters which depended on cultivar and stomatal aperture, and (b) as a function of stomatal aperture and d. Dependence (b) showed that the transpiration rate of Manfredi 393 INTA is higher than that of Florman at the same environmental conditions, and that this is completely due to the difference in leaf anatomy. It was shown that the values of BL thickness, d, grow with increasing stomatal aperture. For amphystomatous leaves of peanut, two empirical parameters, d and B, are necessary and sufficient to quantitatively describe the effect of the BL on transpiration