باز‌سازی دیرینه اقلیمی و پوشش گیاهی در حوضه دشت ارژن فارس در پلیستوسن و هولوسن بر اساس مطالعه‌ی گرده‌های گیاهی

نوع مقاله: مقاله پژوهشی

نویسندگان

1 دانشجوی دکتری دانشگاه شهید بهشتی

2 استاد دانشگاه شهید بهشتی (نویسنده مسوول)

3 استادیار پژوهشکده اقیانوس‌شناسی و علوم جوی

چکیده

به منظور مطالعه پوشش گیاهی گذشته و دیرینه اقلیم در تالاب دشت اژن مغزه‌ای به طول 960 سانتیمتر از این تالاب برداشته شد. پیش از اقدام برای باز کردن، مغزه تحت اندازه‌گیری پذیرفتاری مغناطیسی قرار گرفت. سپس نمونه‌ها باز شده و با توجه به پذیرفتاری مغناطیسی در طول مغزه از آنها زیر‌نمونه تهیه شد و و مقاطع برای مطالعات گرده‌های گیاهی آماده‌سازی شد. چهار نمونه گیاهی هم در طول مغزه برداشته شده و برای سن‌سنجی به آزمایشگاه رادیوکربن پزنان لهستان ارسال گردید. از 15000 سال تا11000 سال قبل، پلیستوسن پسین پوشش گیاهی استپی با آب و هوای سرد و خشک غالب بوده است. دیاگرام گرده‌شناسی نشان داد گونه‌های درختی از جمله جنگل‌های بلوط و پسته-بادام در این منطقه تقریبا از 10000 سال قبل به بعد ظهور کرده و در هولوسن میانی درسطح گسترده‌ای گسترش پیدا کرده‌اند. احتمالا از این دوران به بعد بارش فصل گرم شرایط مناسب برای رشد بلوط را فراهم آورده است. از 1000 سال قبل بیشتر گونه‌های گندمیان در منطقه غلبه داشته‌اند. در حدود 5700 سال قبل هولوسن میانی پوشش درختی غلبه پیدا کرده و الگوی تقریبا منظمی را تا عهد حاضر طی می‌کند. این مشاهدات تایید کردند که اگر چه نوسانات در اقلیم درطول هولوسن میانی و پسین رخ داده است، اما الگوهای بارشی در این منطقه از 6000 سال قبل به بعد به الگوی تقریبا ثابت امروزی رسیده است و در این دوره گونه‌های درختی بلوط و جنگل‌های پسته- بادام دراین محیط گسترده شده‌اند. جنگل‌های بلوط از حدود 5700 سال قبل شروع به رشد کرده و ادامه پیدا کرده اند. فاز دوم گستردگی در گونه‌های بلوط در حدود 3000 سال قبل اتفاق افتاده و ظهور درخت گردو در این دوره نیز قابل توجه است و نشان دهنده فعالیت انسانی در این دوره است.

کلیدواژه‌ها


عنوان مقاله [English]

Paleoclimate reconstruction and vegetation dynamic based on palynology on Dasht E Arzhan Fars province Iran

نویسندگان [English]

  • Zahra Hosseini 1
  • S. Khaledi 2
  • A. Naderi Bani 3
1 PhD Student of Shahid Beheshti
2 Professor of Shahid Behshti university (Corresponding author)
3 Associated Professor I National Institute of Oceanography and Atmospheric Science
چکیده [English]

Abstract
Complex of climate related to topography and general circulation atmospheric interaction in Iran have been unintelligence. Modern climate in southwest Iran is governed by Red sea Trough and westerly depression and Siberian high pressure. In order to understand past climate and environment change and reconstruct at Arzhan wetland SW of Zagros Iran 960 Cm core were taken and a pollen diagram was derived through late Pleistocene and Holocene. The pollen records started at around 15100 Cal. BP and show an absence of arboreal plant in area during late Pleistocene up to 11000 Cal. BP. Pollen records in this zone present a cold steppe that indicated by Cousinia, Artemisia Centaura and Chenopodiaceae pollen with decrease of Poaceae. Younger Dryas in this part of Zagros have not presented by spatially pollen grain. It seems due to upland and local characteristic the basin has not experienced Younger Drays as other region of Zagros. From 10000 Cal. BP arboreal plant have begun to spread as Quercous woodland and Pistacio- Amygdalus scrub that dominated the area during last Holocene. At 8300Cal.BP Quercous woodland and Pistacia- Amygdalus scrub degraded during 600 years up to 7700 Cal BP after this phase Quercous woodland start to spread until 6300 Cal. BP. Middle Holocen at 6300 years ago Quercous woodland have degraded and start to spread. At 5000 Cal.BP. Through Holocen at this period Quercous woodland have maximum extended. Gaglans has appearanced at 3000 years ago and continued to present. Based on pollen diagram we reconstructed climate of past in this region. It seems the atmospheric circulation and climate regime have been stable and closed to modern climate in general.
Introduction
Complex of climate related to topography and general circulation atmospheric interaction in Iran have been unintelligence. Modern climate in southwest Iran is governed by Red sea Trough and westerly depression and Siberian high pressure and in order to understanding of this complex we need to obtain the climate conditions of past. One of the best method for reconstruction of paleoclimate change based on reconstructs of vegetation dynamics by pollen count. This method the first time have applicateed by Van Zist and Bottema in northwest of Iran and continued by Stevense et all,2001 and 2006, 2012, and Djamali and et al, 2009,2012,2015 and Joens et al,2015. Safaei Rad, 2014 in Persian and Davoodi and et al, 2015 in Persian and Azizi et al, 2012 in Persian and Akbari et al,2016 in Persian.
Arzhan wetland located on ′ 56 °51 تا ′ 59 °51 in sout west of zagros Fars province Iran. The climate parameter of this region show in table (1)
The number of frost days Minimum absolute temperature The maximum absolute temperature The average temperature of the coldest month Average temperature of the warmest month Annual average température
124 days 15˚C 38˚C 2.1˚C 21.1˚ 11

Table (1) Modern climatic factors


Materials and methods
In order to understand past climate and environment change and reconstruct at Arzhan wetland SW of Zagros Iran 960 Cm core were taken and a pollen diagram was derived through late Pleistocene and Holocene. We performed magnetic sensibility analysis in primary step and the second we initially to subsampled based on magnetic sensibility measure and in thirst we have prepare our samples according to Moor et al, 1995 methods. In this step we added Lycopodium to our samples in order to counting and frequency of pollen grain in samples than we counted pollen and derived pollen diagram during late Pleistocene and Holocene of Southwest of Iran( Figure 1)
In other hands for dating, we extracted four samples of piece of plant for obtained date and after preparing sent to Radio Carbon laboratory Poznan Poland.(Figure 2)

Results and discussion
Radio carbon dating represent 15000Cal. BP that covered late Pleistocene and Holocene at the region. The pollen diagram shows at late Pleistocene covered by cold and dry steppe with Cousinia and Artemisia whit dry summer. Represent of cousinia refer to cold and dry in the upland of Zagros mountain (El Moslemany, 1986 and 1987) also Djamali believe that cousinia pollen describe a dry conditions( Djamali et all, 2012) arboreal pollen represent during Holocene around 10000Cal B.P. and start to spread in this region. Quercous woodland and Pistasio- Amygdalus shrubs have spread from around 6000 years ago during middle Holocene. A maximum of spread of Oka woodland represent in 4000 and 3000 Cal.B.P so we referred them to increase of moisture of summer rainfall. Appearance of Guglans in 3000 years ago is important and refer to human activity in this region
Conclusion
The pollen records started at around 15100 Cal. BP and show an absence of arboreal plant in area during late Pleistocene up to 11000 Cal. BP. Pollen records in this zone present a cold steppe that indicated by Cousinia, Artemisia Centaura and Chenopodiaceae pollen with decrease of Poaceae. Younger Dryas in this part of Zagros have not presented by spatially pollen grain. It seems due to upland and local characteristic the basin has not experienced Younger Drays as other region of Zagros. From 10000 Cal. BP arboreal plant have begun to spread as Quercous woodland and Pistacio- Amygdalus scrub that dominated the area during last Holocene. At 8300Cal.BP Quercous woodland and Pistacia- Amygdalus scrub degraded during 600 years up to 7700 Cal BP after this phase Quercous woodland start to spread until 6300 Cal. BP. Middle Holocen at 6300 years ago Quercous woodland have degraded and start to spread. At 5000 Cal.BP. Through Holocen at this period Quercous woodland, have maximum extended. Gaglans has appearance at 3000 years ago and continued to present. Based on pollen diagram we reconstructed climate of past in this region. It seems the atmospheric circulation and climate regime have been stable and closed to modern climate in general.

کلیدواژه‌ها [English]

  • Paleo environment
  • Pleistocene
  • Holocene
  • Pollen
  • Dasht E Arzhan