Transcript Past rainfall reconstruction using speleothem from Nakarallu cave

Past rainfall reconstruction using speleothem from
Nakarallu cave, Kadapa, Andhra Pradesh, India
Naveen Gandhi, Nitesh Sinha, S. Chakraborty, H. P.
Borgaonkar, M. G. Yadava and R. Ramesh
• -1.5‰ /100 mm
• -0.22 ‰ / 0C
• large changes in speleothem δ18O are mainly by variations in δ18Op
Speleothem research in India
Regions studied so far
Our site of study
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Time periods covered so far
• Present- AD 4000 (Uttrakhand, Kotlia et al., 2014; QI)
• 15700-14700 BP (Kurnool, AP; Lone et al, 2014; PALAEO3)
• 11200-3670 BP (Meghalaya; Berkelhammer et al, 2012; AGU
Monograph)
• Present-4000 BP (Andaman; Laskar et al, 2013; G3)
• Present-3400 BP (Chhattisgarh; Yadava and Ramesh 2005; The
Holocence)
• AD 600-1500 (Chhattisgarh; Sinha et al, 2007; GRL)
• AD 1075-2008 (Chhattisgarh; Sinha et al, 2011; GRL)
• AD 1399-2007 (Shillong; Sinha et al, 2011; GRL)
• AD 1560-2006 (Uttarakhand; Kotlia et al, 2012; QI)
• AD 1666-1996 (Karnataka; Yadava et al, 2004; The Holocence)
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Major findings so far
Kotlia et al., 2014; Present-AD 4000
• Central Himalaya influenced by ISM and westerlies
• Higher precipitation during 0.5-0.25 ka BP (part of LIA) due to strong
westerlies
• Driest period ~3.2 ka BP
Lone et al, 2014; 15700-14700 BP
• Abrupt change in ISM during the last deglaciation
• Onset of T1a at 1480 BP in the Indian subcontinent
• Strong monsoon during later phase of H1
Berkelhammer et al, 2012; 11200-3670 BP
• ISM weakened during 4071-3670 BP and remained in the state for almost
180 years
Laskar et al, 2013; Present-4000 BP
• Strongest ISM activity during MWP (800-1200 BP)
• Decreasing trend in ISM in the transition from MWP to LIA
• Small reductions in ISM around 1500 and 450-800 BP
Yadava and Ramesh 2005; 0-3400 BP
• 14 years arid phase around 2000 BP
• Higher than present ISM activity at 600 BP
• An arid phase observed before 1200 BP
Continue….
Sinha et al, 2007; AD 600-1500
• Monsoon weakened during 14th and mid 15th century
Sinha et al, 2011; AD 1075-2008; AD 1399-2007
• Intra-seasonal variability of ISM produces quasi east-west
precipitation dipole (enhanced-deficient) over the Indian subcontinent
• Precipitation in central and NE India oscillating between
periods of active (AD 1700-2007) and break (AD 1400-1700)
dominated regimes. The abrupt switch was at AD 1650-1700.
Kotlia et al, 2012; AD 1590-2006
• LIA (AD 1590-1850) and post LIA (after AD 1850) were mostly
wet and dry periods, respectively.
Yadava et al, 2004; AD 1666-1996
• Highest rainfall ~ AD 1666 and lowest rainfall ~AD 1900 in the
period AD 1666-1996
Sampling site: Kadapa, Andhra Pradesh, INDIA
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Sample
232Th 238U
U/Th
AN14-06-59-NK1305-001
0.4 77716.5 218550
AN14-06-60-NK1305-010 16.9
7776
460
AN14-06-61-NK1305-014
0.8 62084.2 73420
AN14-06-62-NK1305-023
0.8 66159 83313
AN14-06-63-NK1305-033
0.4 5229.1 13819
AN14-06-64-NK1305-040
1.5 51990.1 35334
AN14-06-65-NK1305-046
0.3 20206.6 58132
AN14-06-66-NK1305-052
0.9 44851.2 51171
AN14-06-67-NK1305-054
0.6
5980 10740
AN14-06-68-NK1305-061
0.8 4038.6 5367
AN14-06-69-NK1305-064
1.5 3856.7 2541
AN14-06-70-NK1305-070
2.5 4471.9 1783
AN14-06-71-NK1305-077
4.6 8928.6 1938
AN14-06-72-NK1305-085
0.3 5410.5 20963
AN14-06-73-NK1305-090
4.2
5753 1361
AN14-06-74-NK1305-093
0.5 4870.9 10263
AN14-06-75-NK1305-096
0.1 4618.7 32030
AN14-06-76-NK1305-108
6.1 5159.7
847
AN14-06-77-NK1305-113
6.7 5278.2
785
AN14-06-78-NK1305-133
2.2 5183.9 2401
AN14-06-79-NK1305-142
0.2 3397.2 22204
AN14-06-80-NK1305-153
0.3 4925.3 14880
AN14-06-81-NK1305-168
0.4 5653.8 16140
AN14-06-82-NK1305-174
0.2 197.1 1225
AN14-06-83-NK1305-185
2.1
49
23
AN14-06-84-NK1305-187
0.3 164.2
616
AN14-06-85-NK1305-199
1.8 4838.1 2625
AN14-06-86-NK1305-209
5.7 4707.1
827
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Speleothem Sample Analysis
Sample
Cross-Section
of the Sample
Weighing (~100 µg)
Preparation of 100% pure
H3PO4
•
Commercially 98% pure is
available
• Add P2O5 and heat (180oC)
for 2-3hrs
• Leave it for over night
Ortho-Phosphoric Acid (120oC)
• Transfer to the bottle
(H3PO4)
immediately to reduce the
chance of getting moisture
Adding acid to the sample
δ13C and δ18O variations with radiocarbon ages
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Kadapa Cave
Point to notice:
•
•
•
Resolution
Spatial Variation
Calibration
Baratang cave
(Yadava et al., 2005)
Scales are inverse
(Laskar et al., 2013)
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Stalactite from Bitto cave , Uttrakhand, INDIA
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Thank You