RADIOCARBON AGES OF SUYANGGAE PALEOLITHIC SITES IN DANYANG, KOREA

ABSTRACT The Suyanggae archeological complex is located in Aegok-li, Danyang County, Chungbuk Province, Korea (128°20'00"E, 365˚7'15"N, elevation 132 m). We investigated two Suyanggae Paleolithic localities (1 and 6). A total of 31 samples (18 localities) were analyzed for radiocarbon (14C) ages in three paleolithic cultural horizons of Suyanggae Locality 6 (SYG-6). The purpose of this paper is to report all dating results of SYG-6. It was found that ranges of 14C ages (BP) of cultural layers of SYG-6 are known to be 17,550 ± 80 ∼ 20,470 ± 70, 30,360 ± 350 ∼ 44,100 ± 1900, and 34,870 ± 540 ∼ 46,360 ± 510 BP for cultural layers 2, 3, and 4, respectively. We compared these age data with those of the previous study associated with Gunang Cave near Suyanggae Locality 1 (SYG-1). Based on the chronological information of the three archaeological sites, early humans lived in a rather cold environment from approximately 30,000 to 46,000 BP and disappeared between 30,000 ∼ 20,000 BP and then settled again in SYG-6 site during LGM period. This study demonstrates that archaeological study is important not only for understanding human occupations with their cultural development but also establishing climatic signals to which they have been adapted as a part of the human evolutional process.

Responses of gravel-bed rivers to periodic climate change

<p>Periodic variation in Earth's orbit leads to variation in temperature and precipitation at its surface that are expected to exert a profound influence on landscape evolution. Indeed, cyclical fluctuations in sediment yield and grain size are a ubiquitous feature of the geological record, and recurrence times of geomorphological features such as fluvial terraces and alluvial fans often appear to reflect orbital periodicities. However, making quantitative interpretations of these records requires a detailed understanding of the ways in which sediment is transported from mountainous source regions along alluvial channels to depositional sinks. Sediment transport processes may dampen (i.e. buffer, 'shred') or amplify climate signals, such as changes in channel elevation or sediment flux, and may introduce a lag between them and the responsible external forcing. Recent modelling studies, mostly focused on the potential transmission of climatic signals to sedimentary archives, have predicted a wide range of behaviour and have proven challenging to test in the field. Here, we aim to clarify this discussion and also consider the potential preservation of climatic signals by fluvial terraces along alluvial channels. Our starting point is a recently developed model describing the long-profile evolution of gravel-bed rivers. This model is the first of its kind to be derived from first principles using physical relationships that have been extensively tested in laboratory settings, and takes a non-linear diffusive form. We employ perturbation theory to obtain approximate analytical solutions to the relevant equations that describe how channel elevation and sediment flux vary in response to periodic fluctuations in discharge and sediment supply. Our solutions contain expressions for response amplitudes and lag times as functions of downstream distance, system 'diffusivity' and forcing frequency. Lag times can be a significant fraction of the forcing period, implying that care is required when interpreting the timings of terrace formation in terms of changes in discharge or sediment supply. We also show that at the onset of periodic forcing, or a change in the dominant forcing period, alluvial channels undergo a transient response as they adjust to a new quasi-steady state. Importantly, this result implies that suites of fluvial terraces can be preserved without the need for significant local base-level fall. Since the expressions presented here are defined in terms of fundamental properties of alluvial channels, they should be readily applicable to real settings.</p>

The impact of internal thermal regime of glaciers on climate caused advance and retreat

<p>Most glaciers in Sweden have polythermal temperature regimes, where a temperate core of ice is overlain by a cold surface layer. The cold surface layer prolongs the response time of a glacier, and therefore increases the time it takes for a glacier to start advancing during a cooling climate trend. In the late 1980s and 1990s, some glaciers in Sweden advanced due to prolonged periods of positive mass balance, for example Storglaciären. However, far from all glaciers advanced during this period, coincidentally relating to their cold surface layer thickness. This raises the question: what factors drive how and when a polythermal glacier advances, and what climatic signals can be read from traces of past advances and extents? Here, four polythermal glaciers are described in detail since the early 1900s, when they were close to, or at, their largest Holocene extents. These glaciers lie in relatively similar settings, and thus share many resemblances, but also show many differences. How these glaciers have changed since the early 1900s, how they look today, and what landforms they have left behind, provides an opportunity to explore factors behind their responses. The four studied glaciers are: Mikkaglaciären, Storglaciären, Rabots glaciär, and Mårmaglaciären. The dynamics of glaciers retreating are much better understood than glaciers advancing, as the overwhelming majority of existing data have been collected since the latter 1900s half, during a period of overall negative mass balance. The aim of the study is to describe the current properties of the studied glaciers. Using this knowledge and the landform assemblages in their glacier forefields, we suggest explanations to how they might have responded to climate change in the past and possible causes for differences in their response.</p>

Diffusion of climatic signals in ice cores by vein migration

<p>Ice-core analysis shows that climatic signals carried by dissolved impurities (e.g., sulphate) in the water veins exhibit peak broadening and damping with depth into the ice. Such diffusion distorts the signals progressively, limiting the retrievability of the past climatic variations, notably their time resolution. A mechanism put forward for the diffusion invokes continuous differential grain growth in creating gradients in impurity concentration in the vein water (Barnes et al., 2003). Separately, a mechanism known as “anomalous diffusion” has been proposed (Rempel et al., 2001) where vertical temperature gradients in the ice drive the migration of chemical peaks without diffusion — this migration causes age offset between the signals and the ice. Here, we show that climatic signals diffuse because of constant dynamical evolution of the vein network in polycrystalline ice that accompanies grain-boundary migration. In this new mechanism, the stochastic motion of vein segments carrying solute leads to a net diffusive transport of impurities when there is spatial gradient in the bulk impurity concentration or porosity. By modelling this phenomenon with a statistical-mechanical formulation in three dimensions, we find that the diffusivity <em>κ</em> for the bulk impurity concentration is given by <em>κ</em> = <em>K</em>(<em>T</em>)/3c, where <em>K</em> is the temperature-dependent grain growth rate and c (≈ 2 to 3) is a geometry constant, and that <em>κ</em> is independent of the mean grain size. The description of porosity follows an advection-diffusion equation that includes the other processes of Rempel et al. (2001) and Barnes et al. (2003). Our calculations for the Greenland summit ice cores and the EPICA ice core predict diffusivities of <em>κ</em> ∼ 10<sup>–8</sup> – 10<sup>–7 </sup>m<sup>2</sup> yr<sup>–1</sup>, which can explain the observed amount of peak broadening. Further including into this theory the regelative transport of the solute by water flow along the veins reveals a correction of ≈ 10% for the signal migration speed predicted by Rempel et al. (2001). Besides contributing a new diffusion mechanism, our study highlights the importance of grain-scale recrystallisation processes for understanding bulk ice properties.</p>

The millennial-scale climatic variability in central Asia during last glacial

<p>In the North Atlantic and the surrounding region, more than 20 rapid millennial-scale climatic fluctuations occurred during the last glacial-interglacial cycle (Dansgaard et al. 1993). These oscillations, known as Dansgaard-Oeschger (D-O) and H-events. Simulate studies suggest that the millennial-scale climatic signals can spread to a wide area by atmospheric and oceanic circulations. However, it lacks such record in central Asia which is climatically characterized by arid and sensitive to climate change.</p><p>Here, we present the record of millennial-scale fluctuations from loess deposits in Tajikistan in Central Asia. The frequency-dependent magnetic susceptibility (X<sub>fd</sub>, a moisture proxy) record in the Darai Kalon (DK) section (38º23′4″N, 69º50′1″N, 1561 m) can be readily matched with the NGRIP oxygen isotope curve, especially during the interval from 60-30 ka in which typical D-O cycles and H-events are well developed. Most of the long-lasting D-O cycles in Greenland, e.g., D-O 8, 12, and 14, are also evident in the Tajikistan loess. Similarly, the short-duration D-O cycles in Greenland, e.g., D-O 6, 7, 9, 10 cycles, have their damped counterparts in the Tajikistan loess. However, some significant differences in detail can be observed between the two records. The most distinct difference occurs in the case of last D-O cycle, which includes the well-documented Oldest Dryas (OD or H1), Bølling-Allerød (BA), and Younger Dryas (YD or H0) events, which are not clearly present in the X<sub>fd</sub> curve.</p><p>The magnetic results support that the climate is humid in interstadials and dry in stadials in central Asia. And, the variation of humidity is much more remarkable in central Asia than in Chinese Loess Plateau which is climatically dominated by Asian Monsoon. It exhibits the humidity in central Asia is sensitive to millennial-scale climate oscillations during the last glacial. The comparison results further indicate propagations of millennial-scale climatic signals were different between these two regions. We assumed the former one is the Westerlier which can directly and effectively force the millennial-scale climatic variability in central Asia, and the latter one is thermohaline circulation and Asian Monsoon, the complex propagation weakened the millennial-scale climatic variability Northern China.</p>