نوع مقاله : مقاله پژوهشی

نویسندگان

1 آب و هواشناسی دیرینه، دانشکده جغرافیا، دانشگاه تهران

2 اقلیم شناسی، دانشکده جغرافیا، دانشگاه تهران

چکیده

به منظور بازسازی آب‌وهوای منطقه جنوب شرق ایران، مغزه‌ای به طول 5/5 متر از رسوبات کف دریاچه سردریا، در دامنه کوه تفتان، برداشت شد. روی مغزه مورد نظر آنالیز‌های زیست‌شیمی، شامل سنجش سیلیکات‌های زیست‌زا و مقدار کل مواد آلی و غیرآلی، به انجام رسید. نتایج سن‌سنجی نشان داد مغزه مورد نظر 578 سال اخیر را پوشش می‌‌دهد. شواهد نشان می‌‌دهد تغییرات سیلیکات‌های زیستزا روند کاهشی دارند که می‌‌تواند حاکی از افزایش تدریجی دمای تابستانه در منطقه باشد. تغییرات مقدار کل کربن آلی و غیرآلی، که روندی مشابه را نشان می‌‌دهند، بین سال‌های 1460 و 1650، پیک‌های افزایشی مشخصی دارند که هم‌زمان است با عصر یخبندان کوچک در دیگر نقاط دنیا. به طور کلی، شواهد نشان می‌‌دهد در عصر یخبندان کوچک دوره‌های متناوب خشکی‌های شدید در منطقه رخ داده که با خشک‌شدگی کامل سطح دریاچه همراه بوده است. این در حالی است که تحقیقات نشان می‌دهند عصر یخبندان کوچک شرایط مرطوب‌تری را در نواحی غربی و شمال غربی به وجود آورده است. این نتایج تأییدکننده واکنش‌های متضاد آب‌وهوایی منطقه جنوب شرق  نسب به نیمه غربی کشور طی هولوسن است.

کلیدواژه‌ها

موضوعات

عنوان مقاله [English]

Reconstruction the climatic changes of the last 600 years in Southeast Iran, study area, the Lake Sardarya, Taftan Volcano

نویسندگان [English]

  • Daryoush Nooro allahi 1
  • Ghasem Azizi 2

1 Paleoclimatology, Faculty of Geography, University of Tehran

2 Climatology, Faculty of Geography, University of Tehran

چکیده [English]

Introduction:
In order to recognize the mechanism of local climatic settings and to be able to establish the future climatic scenarios is essential to understand the past climatic and environmental conditions of the each area. This is also important to explore the response of local areas to the global climatic variations. The palaeoclimate researches carried out in Iran mainly considered the general pattern of Holocene climatic shifts located mostly on western half of the country  (Stevens et al, 2001: Djamali et al, 2009: Griffiths et al, 2001: van Zeis et al, 1967) and few in number in eastern part  (Hamze et al, 2016). These palaeoclimate researches have reconstructed the climatic and environmental changes in the sites located in north and the Zagros range which are roughly controlled by similar synoptic systems. This record first will help filling the existing data gap of the eastern part of Iran as an area to be subjected by monsoon rainfall nowadays and probably in a variable rate in the past.
Materials and methods:
A 5.5 Meters Core was taken in May 2017 using a Livingstone corer  (Livingstone, 1955) from the middle part of the Sar Darya Lake in 1-m water depth. Samples kept in the plastic waterproof barrels and transported to the University of Bremen, Germany for the subsampling and further analysis. A number of 28 samples were dried and grounded and then the total carbon  (TC) and total nitrogen  (TN) measure with a Euro-EA Elemental Analyser. For CNS the sample is weigh in in Sn-capsules. For TOC the sample is weigh in in Ag-capsules, and treated by 80°C with 3% and 20% HCl to destroy carbonates. TIC=TC-TOC. Measurement range is from 0, 01-100%. In the next step in order to raise the resolution a number of 78 samples selected to be used with Fourier transform infrared spectroscopy  (FTIRS) method. This method confirmed to have high potential for the organic and inorganic content estimation (Rosen et al/////)For FTIRS analyses of the samples in diffuse reflectance mode, a VERTEX 70 FTIRS spectrometer  (BrukerOptik GmbH, Germany) equipped with a diffuse reflectance accessory  ("Praying Mantis" Harrick Inc., USA) was used. Sample pretreatment, IR spectroscopy measurement conditions and processing procedures applied to the raw spectra are described by Vogel et al.  (2016).
Results and discussion:
The radiocarbon dating carried out by the analytical center of the environmental science atmospheric and ocean research institute, the University of Tokyo. The dating results show that the core expands the last 578 years, BP. In the zone considered as the little ice age the  (1460-1650 AD) the average TIC is 1.6% much higher than the upper part of the core with an average of 0.6%. This high rate is also observed in the TOC with an average of 0.6 higher than the upper part of the core with an average of 0.3%. The highest peaks of TIC and TOC with values of 8.2 and 8.4 respectively occurred in this zone. This zone is not only characterized by high TIC and TOC values but also with high standard deviation (TIC 1.9 and TOC 1.2) implying the high variation of the carbonate content of the core during this phase. Also both TIC and TOC have a low values in the lowermost of the core  (1417-1460 AD).
Conclusion, Keywords:
The primarily assumption regarding the TIC of the lake sediment is that the low lake level phases increase the carbonate content of the sediment. However this effect could also affected by the other parameter such as the erosion action of the lake  . Additionally, although the TIC and TOC are mostly used for tracking the source of organic matter in the lake environment, show a high potential for investigating the abrupt lake level change (Yuan et al, 2006).  (Heinecke et al, 2016). In the core, high TIC and TOC follows the Ca and Fe patterns which could represent the E/P ratio in the core accordingly. The high TOC and TIC suggested as a result of dry and warm climate (Haberzettl1 et al, 2005) it seems the organic content of the sediment is controlled by the lake level changes as a result. During the LIA the high TIC values indicate a low lake level with low amount of runoff input to the lake. However, the low TIC in the lowermost section of the core, before the LIA and perhaps the last part of the MCA is therefore likely to be the result of high clastic input. During this period a very low TIC content could be related to an high organic content as a result of addition fresh water discharge into the lake which commensurate with silt or silt-clay sediments representing high precipitation and run off inputs.

کلیدواژه‌ها [English]

  • Climatic Reconstruction
  • the Lake Sardarya
  • Little Ice Age