Table 2.
Past climatic variables for archaeological sites estimated from δ13C values in bison bone, associated dietary fractions of C4 plants, and correlations of C4 fractions with weather variables
| *NWS Station/ Archaeological Site | yr BP | MNI | Annual precipitation
|
June
precipitation
|
August minimum temperature
|
|||
|---|---|---|---|---|---|---|---|---|
| mm | P | mm | P | °C | P | |||
| *Gillette (2 east) | Present | 391.2 (95.5) | 71.4 (45.7) | 12.1 (1.5) | ||||
| CKM | 12,590 | 4 | 371.2 (12.0) | 0.09 | 62.2 (20.4) | 0.07 | 11.4 (0.1) | <0.001 |
| *Morrisey | Present | 306.1 (65.5) | 52.6 (25.9) | 14.2 (1.5) | ||||
| ABF | 12,590 | 9 | 378.9 (20.3) | <0.001 | 63.5 (3.5) | 0.02 | 11.5 (0.2) | <0.001 |
| ABAB | 12,390 | 14 | 363.6 (10.7) | <0.001 | 60.9 (1.8) | 0.05 | 11.3 (0.1) | <0.001 |
| ABHG | 11,910 | 11 | 397.6 (26.0) | <0.001 | 66.7 (4.4) | <0.01 | 11.7 (0.3) | <0.001 |
| *Upton | Present | 367.3 (77.7) | 65.3 (37.9) | 11.5 (1.6) | ||||
| HK | 7,280 | 12 | 415.5 (34.0) | <0.01 | 69.8 (5.8) | 0.26 | 11.9 (0.4) | 0.09 |
Values for present weather are from NWS reporting stations of closest geographic proximity (*) (numbers of reporting years ranged from 64 to 69 at Gillette, 20 to 33 at Morrisey, and 39 to 42 at Upton). For archaeological sites, we calculated the standard deviation of dietary C4 from standard deviations in δ13C values of each population of bison sampled. The standard error about the regression (sy.x) is ±37.35 mm for normal annual precipitation, ±8.25 mm for normal June average precipitation, and ±0.86°C for normal August minimum temperature. Past values in bold are significantly different from current weather at the nearest NWS station (two-tailed t test). Standard deviations are in parentheses. MNI, minimum number of individual bison sampled.