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Responses of the upriver valley sediment to Holocene environmental changes in the Paju area of Korea
Nahm, Wook-Hyun,Kim, Ju-Yong,Lim, Jaesoo,Yu, Kang-Min Elsevier 2011 Geomorphology Vol.133 No.1
<P><B>Abstract</B></P><P>Multidisciplinary paleoproxy data from five sedimentary cores (UJ-03, 06, 07, 10, and 12) recovered from the broad, flat upriver valley in the Paju area of Korea are presented. Twelve AMS radiocarbon dates from cores UJ-03 and 12 provided a high-resolution Holocene record for the sedimentary sequence, ranging from about 8000YBP to the present. From 6400 to 4400<SUP>14</SUP>CYBP (7100–5000cal. YBP), the sediments were dominantly poorly sorted, medium to coarse sands containing angular to subangular pebbles, suggesting that the materials were locally derived. The increased abundance of coarse-grained sediment was attributed to intensified rainfall during the mid-Holocene, despite the dense regional vegetational cover. This period probably corresponded to the Holocene Climate Optimum in the Korean Peninsula. Total organic carbon (TOC) values showed a marked increase from 4400 to 2100<SUP>14</SUP>CYBP (5000–2200cal. YBP), which coincided with an observed decrease in particle size (i.e., a decrease in sand content). These changes indicated the onset of paludification on the silty or sandy valley bottom. Contemporaneously, relative abundances of <I>Pinus</I> and herbaceous pollen increased, and the East Asian summer monsoon became weakened. Several intermittent depositional layers were observed, ranging from 2100<SUP>14</SUP>CYBP (2200cal. YBP) to the present, which contained a high concentration of rootlets, sand, or clay particles. These types of recurring sedimentation events are attributable to climatic shifts and/or human impacts, such as timber harvest and land clearing. The upriver valley catchment was probably sensitive to flash floods due to poorly vegetated slopes, accelerating rates of erosion as a consequence of land use change. This research indicates that the response of a valley system such as that in Paju to climate- or human-induced environmental changes can vary greatly on local and regional scales.</P> <P><B>Highlights</B></P><P>► Response of a valley system to climate- or human-induced changes was traced. ► The increased abundance of coarse grains was attributed to intensified rainfall. ► This period may correspond to the Holocene Climate Optimum in Korea. ► A marked increase in TOC from 4400<SUP>14</SUP>CYBP may indicate the onset of paludification. ► Several depositional layers were observed from 2100<SUP>14</SUP>CYBP to the present.</P>
Holocene paleosols of the Upo wetland, Korea: Their implications for wetland formation
Nahm, Wook-Hyun,Kim, Jin-Kwan,Yang, Dong-Yoon,Kim, Ju-Yong,Yi, Sangheon,Yu, Kang-Min Elsevier 2006 QUATERNARY INTERNATIONAL Vol.144 No.1
<P><B>Abstract</B></P><P>A 4.490m long core UP-1 was recovered from the marginal part of the Upo wetland. The wetland is a typical riverine wetland in Korea and has been designated as a Protected Wetland in accordance with the International Ramsar Treaty. We studied the Holocene environmental changes of the Upo wetland and the depositional conditions under which the Upo wetland formed. The core is divided into four units on the basis of grain size distribution, abundance of mottles and vertical color variation. Unit 1 has undergone pedogenic processes, resulting in variably weak to moderate soil profile development. Unit 1 paleosols are regarded as synsedimentary soils of floodplain origin, and the radiocarbon data suggest that the whole paleosol profile spans the last 5790years. The boundaries between the soil horizons are not clear-cut, probably due to a repeated cycle of accumulation, denudation and soil-forming processes. The recurrence of these processes initiated the development of the Upo wetland. The lower boundary of Unit 2 lies at about 2300<SUP>14</SUP>CyrBP, the beginning of the Subatlantic age in Korea. The lack of intense soil formation and abundant clay content in Unit 2 indicate that the geomorphologically stable wetland was developed around the coring site at that time. This means that the depositional environment changed from a floodplain to a stable, continuously submerging wetland setting. An abrupt change in sediment textures was detected in Unit 3, which commenced formation around 1000–900<SUP>14</SUP>CyrBP, indicative of geological events such as inundations or inflows of slope-wash sediments. Anthropogenic deforestation and plowing around the Upo wetland area might have started at that time.</P>