| The Antarctic Peninsula has warmed about six times faster than the global mean in recent decades making it among the most sensitive of global climate changes. The South Shetland Islands is located at the north of Antarctic Peninsula, and Fildes Peninsula,8.0 km long and 2.5-4.5 km wide, located on the southwest of King George Island, South Shetland Island. It has an area of 38 km2, and it is one of the largest ice-free areas on King George Island. During Last Glacial Maximum and early Holocene, Fildes Peninsula was covered by ice, and gradually evolved into coastal ice-free area due to glacier melting and glacial isostatic adjustment (GIA). Variety of paleoclimatic carriers existed in Fildes Peninsula, and many related researches have been carried out, however environmental evolution of Grande Valley and marine record of historical climate therein during Holocene were missing. Accurate chronological sequence is fundamentally important for paleoecological and paleoenvironmental studies, however, the establishment of the radiocarbon chronology in fluvioglacial deposits was still difficult due to the instable sources of deposits, which directly affected the reliability of reconstructed paleoclimatic and paleoenvironmental records. That’s also why the sediment core GA-2 in Grande Valley, Fildes Peninsula was not systematically studied.This paper is to use glacimarine sediment core GA-2 in Grande Valley, sediment core T in Tuanjie Lake, sediment core J in Kitezh Lake and sediment core CH in Long Lake to look for a new method for selecting bulk sediment samples for radiocarbon dating in fluvioglacial environment and reconstruct climate changes during Holocene in Fildes Peninsula, Antarctica.51 surficial lake sediments are selected to study distribution feature of heavy metal elements Cu, Zn, Pb, Ni, Cr, Cd, Co, As, Sb, Hg and nutrient elements P, Se using contour map and analyze the main influence factors and current situation of environment in Fildes Peninsula. 1. An efficient method for selecting bulk sediment samples for radiocarbon dating in fluvioglacial depositsGrande Valley was a typical fjord environment during Holocene in Fildes Peninsula, Antarctica. We performed AMS 14C dating on 20 bulk sediments of the glacial-marine sediment core GA-2 for exploring a new method for selecting dating samples in fluvioglacial deposits. The ages of samples along the sediment core were not in chronological order as they should be. To overcome the difficulty in obtaining a reliable chronology, we selected five samples based on lithological characteristics and grain size distributions of the sediments and used their dates to build a chronology of the sediment core. The validity of the chronology was confirmed by comparing the inferred geochemical and geophysical parameters with previous studies. The core was formed between 6600 and 2000 a BP during the Holocene period according to AMS 14C dating. The criteria we used to select samples can be generalized and applied to pre-select dating samples for radiocarbon dating, especially for those formed in a complex environment and influenced by old carbon sources and glacier activities. Finally, we successfully applied this method to the selection of bulk sediment dating samples in the sediment J, CH in Fildes Peninsula and the sediment core GA-2 collected in Arctic, which testifies to the its effectiveness.2. Depositional environment and climate changes during Holocene in Grande Valley, Fildes PeninsulaThe core was formed between 6600 and 2000 a BP during the Holocene period according to AMS 14C dating. The median grain size, lithological characteristics, loss on ignition (LOI550℃), magneticsusceptibility and geochemical elements of the sediments were analyzed, and three-stages depositional environments and an alternate climate change pattern, warm-cool-warm-cold, during 6600-2000 a BP were identified. This study reconstructed the environmental evolution of Grande Valley during Holocene, made up the missing marine record of historical climate for the western coast of Fildes Peninsula and laid the foundation forstudy of the climate and environment changes therein. The sea level records obtained from marine sediment core GA-2 and seal guano deposit core HF4 allow for detailed reconstruction of Holocene sea level variation.3. Preliminary study of climate changes during Late Holocene from lacustrine deposits in Fildes PeninsulaA typical rapid sedimentary layer was observed in Tuanjie Lake according to lithology changes from mud to coarse sand gravel at 1.31 m below the surface layer. The layer formed about 500-600 a BP on the basis of AMS 14C dating of the mosses, and it may be caused by a large number of terrigenous material input due to climate cooling and glacier advancing. That was highly consistent with the start time of Little Ice Age (LIA). The sediment core J was formed between 2900 and 560 a BP during the Late Holocene period according to AMS 14C dating. The median grain size, lithological characteristics, loss on ignition (LOI550℃), magnetic susceptibility were analyzed, and three main environmental and climatic change periods were identified: Neoglacial-Medieval Warm Period (MWP)-Little Ice Age (LIA). Neoglacial was between 2900 and 1100 a BP, Medieval Warm Period (MWP) between 1100 and 650 a BP and Little Ice Age (LIA) started at 650 a BP consistent with the rapid sedimentary layer. Little Ice Age (LIA) was the first time to be found in lacustrine deposits in Flides Peninsula, consistent with the records in the dirt sediments of seals, dirt sediments of penguins and marine sediments therein, which laid the foundation for further study about LIA.4. Distribution feature of heavy metal elements from surficial lacustrine deposits in Fildes PeninsulaHeavy metal elements Cu, Zn, Pb, Ni, Cr, Cd, Co, As, Sb, Hg and nutrient elements P, Se of 51 surficial lake sediments were analyzed, and we found the elements had accumulated in some lakes by coefficient of variation which close to the areas of human activities and the habitat of seals and seabirds in Fildes Peninsula. To directly observe the enrichment areas of heavy metal elements, the contour maps of elements were drew using software surfer 8.0, and these maps show that human and seals activities may be the main influence factors of heavy metal elements enrichment. We compared the contents of elements in surficial lacustrine deposits, surficial soils, dirt sediments of penguins with soil environmental quality standards (GB15618-1995) in China, and found the effect on Fildes Peninsula of human activities was weaker than penguins. Surficial lacustrine deposits and soils not only was accord with soil environmental quality standards of 2 levels, but also with soil environmental quality standards of 1 levels in addition to the element Cd which mean they were still clear. Even so, we still need attach great importance to the protection of environment in future scientific research. |
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