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Papers by Zicheng Yu
Geology, 1999
A 2100-yr decadal-resolution salinity and aridity proxy record of lacustrine ostracode-shell Mg/C... more A 2100-yr decadal-resolution salinity and aridity proxy record of lacustrine ostracode-shell Mg/Ca ratios from a closed-basin lake in the northern Great Plains shows statistically significant periodicities of 400, 200, 130, and 100 yr. These periodicities are similar to the three principal solar-oscillation periods (420, 218, 143 yr) as inferred from the atmospheric radiocarbon record, suggesting strong solar forcing of century-scale drought frequency with a fundamental 400-yr period and its 2nd, 3rd, and 4th harmonics. Our proxy record correlates visually and statistically (cross-spectral analysis) with the atmospheric ∆ 14 C record (solar proxy) and the GISP2 (Greenland Ice Sheet Project Two) δ 18 O record (climate proxy), showing that solar minima are in phase with drought periods in the northern Great Plains and cold periods in Greenland. This spectral similarity together with phase correlation indicates a possible teleconnection of century-scale global climate fluctuations through common solar forcing.
A 2100-yea r multiple proxy record at decadal resolution from a topographicall y closed (but hydr... more A 2100-yea r multiple proxy record at decadal resolution from a topographicall y closed (but hydrologically open) lake basin was used to reconstruct changes in lake salinity and evaporative intensity and to evaluate the reliability of different proxies for inferring climatic change in the glaciated Northern Great Plains (NGP). At Rice Lake, North Dakota, the ostracode-Mg/Ca ratios show good correlation with other ostracode, diatom and aeolian proxy records from other sites in the NGP. All of these records show signi cant century-scale periodicities, which have been related to solar variability as inferred from atmospheri c radiocarbon records. This coherent and consistent pattern suggests that these sites record climatic variability at regional scales. The interval of the Mediaeval Climatic Anomaly from |900 to 550 cal. yr BP contains two pronounce d dry periods. During the following 'Little Ice Age', a single period of frequent drought that peaked at |300 cal. yr BP was bracketed by wet periods before and after. In contrast, the ostracode-Sr/Ca ratios and ostracode-and molluscd 18 O records from Rice Lake have different patterns and do not correlate well with each other or with the same proxies at other sites. This lack of consistent pattern within a site and among several regional sites suggests seasonal and/or site-speci c in uences on these proxies. Variable contributions of groundwater , with low d 18 O values because of selective recharge from snowmelt, may have played an important role in determining the isotopic composition of the lake. The poor correlation of Sr/Ca with other proxies is caused by mediation of inorganic carbonate mineralogy, owing to active uptake of Sr in the formation of inorganic aragonite. Thus, our sediment data along with present-day lakewater chemistry suggest that carbonate-d 18 O records in the NGP cannot be interpreted simply in terms of climate because of signi cant local groundwate r in uences. Ostracode-Mg/Ca ratios tend to be a better indicator of past salinity because of the conservative nature of Mg in oligosaline waters (, 10‰ salinity).
Geology, 1999
A 2100-yr decadal-resolution salinity and aridity proxy record of lacustrine ostracode-shell Mg/C... more A 2100-yr decadal-resolution salinity and aridity proxy record of lacustrine ostracode-shell Mg/Ca ratios from a closed-basin lake in the northern Great Plains shows statistically significant periodicities of 400, 200, 130, and 100 yr. These periodicities are similar to the three principal solar-oscillation periods (420, 218, 143 yr) as inferred from the atmospheric radiocarbon record, suggesting strong solar forcing of century-scale drought frequency with a fundamental 400-yr period and its 2nd, 3rd, and 4th harmonics. Our proxy record correlates visually and statistically (cross-spectral analysis) with the atmospheric ∆ 14 C record (solar proxy) and the GISP2 (Greenland Ice Sheet Project Two) δ 18 O record (climate proxy), showing that solar minima are in phase with drought periods in the northern Great Plains and cold periods in Greenland. This spectral similarity together with phase correlation indicates a possible teleconnection of century-scale global climate fluctuations through common solar forcing.
A 2100-yea r multiple proxy record at decadal resolution from a topographicall y closed (but hydr... more A 2100-yea r multiple proxy record at decadal resolution from a topographicall y closed (but hydrologically open) lake basin was used to reconstruct changes in lake salinity and evaporative intensity and to evaluate the reliability of different proxies for inferring climatic change in the glaciated Northern Great Plains (NGP). At Rice Lake, North Dakota, the ostracode-Mg/Ca ratios show good correlation with other ostracode, diatom and aeolian proxy records from other sites in the NGP. All of these records show signi cant century-scale periodicities, which have been related to solar variability as inferred from atmospheri c radiocarbon records. This coherent and consistent pattern suggests that these sites record climatic variability at regional scales. The interval of the Mediaeval Climatic Anomaly from |900 to 550 cal. yr BP contains two pronounce d dry periods. During the following 'Little Ice Age', a single period of frequent drought that peaked at |300 cal. yr BP was bracketed by wet periods before and after. In contrast, the ostracode-Sr/Ca ratios and ostracode-and molluscd 18 O records from Rice Lake have different patterns and do not correlate well with each other or with the same proxies at other sites. This lack of consistent pattern within a site and among several regional sites suggests seasonal and/or site-speci c in uences on these proxies. Variable contributions of groundwater , with low d 18 O values because of selective recharge from snowmelt, may have played an important role in determining the isotopic composition of the lake. The poor correlation of Sr/Ca with other proxies is caused by mediation of inorganic carbonate mineralogy, owing to active uptake of Sr in the formation of inorganic aragonite. Thus, our sediment data along with present-day lakewater chemistry suggest that carbonate-d 18 O records in the NGP cannot be interpreted simply in terms of climate because of signi cant local groundwate r in uences. Ostracode-Mg/Ca ratios tend to be a better indicator of past salinity because of the conservative nature of Mg in oligosaline waters (, 10‰ salinity).