A Couple of Papers from JQS

Below are a couple of papers from the latest edition of the Journal of Quaternary Science examining a possible solar link to climate:

JOURNAL OF QUATERNARY SCIENCE (2007) 22(7) 659–665

Climatic change during the last 4000 years in the southern Tarim Basin, Xinjiang, northwest China

WEI ZHONG,1* JI BIN XUE,1 QIANG SHU2 and LI GUO WANG2
1 School of Geography Science, South China Normal University, Guangzhou, P. R. China
2 School of Resource and Environmental Science, Xinjiang University, Urumqi, P. R. China

ABSTRACT: In this study, a ca. 4000 cal. yr ancient lacustrine (or wetland) sediment record at the southern margin of Tarim Basin is used to reconstruct the history of climate change. Six radiocarbon dates on organic matter were obtained. d18O and d13C of carbonate, pollen and sediment particle size were analysed for climate proxies. The proxies indicate that a drier climate prevailed in the area before ca. 1010 BC and during period 1010 BC–AD 500 climate then changed rapidly and continuously from dry to moist, but after about AD 500 climate generally shows dry condition. Several centennial-scale climatic events were revealed, with the wettest spell during AD 450–550, and a relatively wetter interval between AD 930–1030. Pollen results show that regional climate may influence human agricultural activities. Spectral analysis of mean grain size (MGS) proxy reveals statistically pronounced cyclic signals, such as ca. 200 yr, ca. 120 yr, ca. 90 yr, ca. 45 yr and ca. 33 or 30 yr, which may be associated with solar activities, implying that solar variability plays an important role in the decadal- and centennial-scale climate variations in the study area.

Possible solar forcing of climate in the southern Tarim Basin

Zhong et al. (2004) found that decadal- or centennial-scale climate events indicated by mean grain size (MGS) in the Niya section matches residual D14C variation remarkably well, suggesting a possible common solar forcing as inferred from D14C fluctuation. The humid periods (lower MGS values) inferred from the Niya section correspond to D14C maxima (solar minima) in most cases. Possibly, weaker solar irradiance results in a cold climate, leading to an increase in relative atmospheric humidity in the extreme arid southern Xinjiang. By applying the method of red-noise spectral analysis (REDFIT) for unevenly spaced time series proposed by Schulz and Mudelsee (2002) to deal with MGS proxy records in the Niya River section, we can find several statistically significant cyclic signals of ca. 200 yr, ca. 120 yr, ca. 90 yr, ca. 45 yr and ca. 33 or 30 yr (x2¼99%, Fig. 7). Most of these cycles are related to solar activity, the ca. 200 yr and 97–90 yr cycle are mostly likely to be related to the Suess and Gleissberg cycle respectively. The 33–30 yr cycle is possibly associated with the notable Brueckner cycle (Zhang, 1976).

JOURNAL OF QUATERNARY SCIENCE (2007) 22(7) 667–679

A multiproxy climate record from a raised bog in County Fermanagh, Northern Ireland: a critical examination of the link between bog surface wetness and solar variability

GRAEME T. SWINDLES,* GILL PLUNKETT and HELEN M. ROE
School of Geography, Archaeology and Palaeoecology, Queen’s University, Belfast, Northern Ireland, UK

ABSTRACT: A proxy climate record from a raised bog in County Fermanagh, Northern Ireland, is presented. The record spans the interval between 2850 cal. yr BC and cal. yr AD 1000 and chronological control is achieved through the use of tephrochronology and 14C dating, including a wiggle-match on one section of the record. Palaeoclimatic inferences are based on a combination of a testate amoebae-derived water table reconstruction, peat humification and plant macrofossil analyses. This multiproxy approach enables proxy-specific effects to be identified. Major wet shifts are registered in the proxies at ca. 1510 cal. yr BC, 750 cal. yr BC and cal. yr AD 470. Smaller magnitude shifts to wetter conditions are also recorded at ca. 380 cal. yr BC, 150 cal. yr BC, cal. yr AD 180, and cal. yr AD 690. It is hypothesised that the wet shifts are not merely local events as they appear to be linked to wider climate deteriorations in northwest Europe. Harmonic analysis of the proxies illustrates statistically significant periodicities of 580, 423–373, 307 and 265 years that may be related to wider Holocene climate cycles. This paper illustrates how the timing of climate changes registered in peat profiles records can be precisely constrained using tephrochronology to examine possible climatic responses to solar forcing. Relying on interpolated chronologies with considerable dating uncertainty must be avoided if the climatic responses to forcing mechanisms are to be fully understood.

Conclusions

………….Several shifts to wetter conditions are registered in the records, possibly related to wider climatic
deteriorations in northwest Europe. There are also a number of statistically significant periodicities in the record, that may be linked to climate-forcing parameters. The major wet phases generally occur at times of high 14C levels, tentatively suggesting a persistent influence of solar forcing on Holocene climate change. A wet shift at 750 cal. yr BC clearly lags a decrease in solar activity which begins at 850 cal. yr BC, but at other times in this record, the precise timing of wet shifts in relation to solar anomalies remains to be established. This study shows that tephra can be used as an effective alternative to wiggle-match radiocarbon dating to generate high-precision chronologies in order to investigate the solar forced contribution to climate change.