@article{19976177f537467f97a61e1ee50bac68,
title = "Signatures of global climatic events and forcing factors for the last two millennia from the active mudflats of Rohisa, southern Saurashtra, Gujarat, western India",
abstract = "The limited extent of instrumental records going back in time and control of various climatic variables on Indian Summer Monsoon (ISM) has reinvigorated the unprecedented effort in documenting climate changes for the last two millennia. Although extensive studies on late Holocene ISM reconstruction are available, comprehensive understanding on the influence of natural forcing factors on ISM and their plausible signatures is not arrived at till date. In view of this, the present study attempts to address the ISM variations during the last two millennia with special emphasis on natural forcing factors (solar and volcanic) and climate variables (ocean-atmospheric processes). The Saurashtra peninsula of Gujarat in western India receives majority of rainfall during ISM and hence it provides an ideal test-bed to study the ISM variability. A multiproxy approach has been adopted on a sediment core retrieved from the active mudflat of Southern Saurashtra which was chronologically supported by 210Pb, 137Cs and 14C. The present study demonstrates vacillating climate with strengthened ISM during Roman Warm Period and Medieval Warm Period (2000−950 cal yr BP) as a result of increased solar irradiance interrupted by reduced ISM during Dark Ages of Cold Period (∼1500 cal yr BP). The plausible occurrence of volcanic eruption before the onset of Little Ice Age (500−200 cal yr BP) caused the southward migration of Intertropical Convergence Zone (ITCZ) leading to enhanced western disturbances in the study area thereby resulting in cool and wet climate in the region. The study also emphasizes the increased El Nino events with gradual decline in the ISM since Little Ice Age. Further, the study underscores a climate warming during the last two centuries that corroborates well with the instrumental records. Thus, the present study has implication towards understanding the significant role of volcanic activity and solar variability in controlling the millennia scale climate oscillations with additional feedback mechanisms.",
keywords = "GEOTRACES, Geochemistry, Late holocene, Little ice age, Medieval warm period, Meghalayan age, Roman warm period, Volcanic forcing",
author = "Banerji, {Upasana S.} and Ravi Bhushan and Jull, {A. J.T.}",
note = "Funding Information: This research was funded by the Ministry of Earth Sciences, Govt. of India under GEOTRACES Project. We thank Mr. Balaji D. and Mr. J.P. Bhavsar for their kind help and support during the fieldwork. We are grateful to Prof. J.S. Ray for his support and help during trace element measurement by Q-ICP-MS. We thank anonymous reviewers for their critical comments and suggestions that helped improving the manuscript. We thank Dr. D. Chakrabarty for proof reading the manuscript. Funding Information: During 1546−503 cal yr BP, a marginal increase in the detrital component with consistent values (Fig. 3) suggests improved and consistent hydrological conditions, further supported by increased and consistent values of in−situ productivity and weathering till 800 cal yr BP. TOC/TN too shows enhanced contribution of terrestrial organic matter (Fig. 4). The time period coinciding with MWP suggests marginally high terrestrial flux with consistent productivity and weathering suggests warm and wet conditions. Previously, based on various evidences from western Europe, the MWP was identified as persistent warm period between 1000 and 1200 AD with temperatures nearly 1–2 °C higher than the average temperature recorded between 1931 and 60 AD (Lamb, 1965). Globally, MWP is known as a duration of warm and humid climate in the Europe (Lamb, 1965; Brown, 1998) and other parts of globe (Dippner and Voss, 2004; Gao et al., 2006; LeGrande et al., 2006). The study on flood deposits of Mahi river basin, mainland Gujarat demonstrated warm climate with monsoon strengthening during MWP (Sridhar, 2009). The palynological investigation on the sediment core from Khedla Quila Lake, south-western Madhya Pradesh also connote a warm and moderately humid climate phase during 534–1444 AD (Quamar and Chauhan, 2014). However, the monsoon strength during RWP was more compared to MWP as indicated by weathering and productivity proxies. Study on a sediment core retrieved from the Peruvian coast suggested intense El Nino flooding event along the coast during MWP (Rein et al., 2004). Indian subcontinent presently experiences low rainfall or drought during El Nino event (Mooley and Parthasarathy, 1983). Thus it can be suggested that unlike RWP, the plausible occurrence of El Nino inhibited the extreme ISM during MWP. Nevertheless, there occurred warm and wet climate compared to present during MWP. Funding Information: During 1546?503?cal?yr BP, a marginal increase in the detrital component with consistent values (Fig. 3) suggests improved and consistent hydrological conditions, further supported by increased and consistent values of in?situ productivity and weathering till 800?cal?yr BP. TOC/TN too shows enhanced contribution of terrestrial organic matter (Fig. 4). The time period coinciding with MWP suggests marginally high terrestrial flux with consistent productivity and weathering suggests warm and wet conditions. Previously, based on various evidences from western Europe, the MWP was identified as persistent warm period between 1000 and 1200 AD with temperatures nearly 1?2??C higher than the average temperature recorded between 1931 and 60 AD (Lamb, 1965). Globally, MWP is known as a duration of warm and humid climate in the Europe (Lamb, 1965; Brown, 1998) and other parts of globe (Dippner and Voss, 2004; Gao et al., 2006; LeGrande et al., 2006). The study on flood deposits of Mahi river basin, mainland Gujarat demonstrated warm climate with monsoon strengthening during MWP (Sridhar, 2009). The palynological investigation on the sediment core from Khedla Quila Lake, south-western Madhya Pradesh also connote a warm and moderately humid climate phase during 534?1444 AD (Quamar and Chauhan, 2014). However, the monsoon strength during RWP was more compared to MWP as indicated by weathering and productivity proxies. Study on a sediment core retrieved from the Peruvian coast suggested intense El Nino flooding event along the coast during MWP (Rein et al., 2004). Indian subcontinent presently experiences low rainfall or drought during El Nino event (Mooley and Parthasarathy, 1983). Thus it can be suggested that unlike RWP, the plausible occurrence of El Nino inhibited the extreme ISM during MWP. Nevertheless, there occurred warm and wet climate compared to present during MWP. This research was funded by the Ministry of Earth Sciences, Govt. of India under GEOTRACES Project. We thank Mr. Balaji D. and Mr. J.P. Bhavsar for their kind help and support during the fieldwork. We are grateful to Prof. J.S. Ray for his support and help during trace element measurement by Q-ICP-MS. We thank anonymous reviewers for their critical comments and suggestions that helped improving the manuscript. We thank Dr. D. Chakrabarty for proof reading the manuscript. Publisher Copyright: {\textcopyright} 2019 Elsevier Ltd and INQUA",
year = "2019",
month = feb,
day = "25",
doi = "10.1016/j.quaint.2019.02.015",
language = "English (US)",
volume = "507",
pages = "172--187",
journal = "Quaternary International",
issn = "1040-6182",
publisher = "Elsevier Ltd",
}