Raj K. Singh

Indian Ocean high-productivity event (10–8 Ma): Linked to global cooling or to the initiation of the Indian monsoons?

Uplift of the Himalayas and Tibetan Plateau (ca. 10-8 Ma) has been said to be the main cause of the origin or intensification of the Indian monsoon system, because mountains modulate the land-sea thermal contrast. The intensification of the monsoons, in turn, is seen as the cause of major changes in fauna and flora on land (as a result of changing precipitation patterns) as well as in the Indian Ocean, where the monsoons drive increased upwelling and thus increased productivity. We argue that the interactions between the elevation of the Himalayas and Tibetan Plateau, the onset of the monsoons, and their effects on the Indian Ocean biota remain uncertain. The timing of these events (uplift, monsoons, and biotic change) is not well constrained. Neogene deep-sea benthic foraminiferal faunal and isotope records of the Ninetyeast Ridge combined with published data show that a major increase in bio- genic productivity occurred at 10-8 Ma throughout the Indian Ocean, the equatorial Pacific, and southern Atlantic. We suggest that this Indian Ocean high-productivity event was not simply the result of monsoon-induced upwelling or nutrient delivery from the weathering of newly uplifted mountains, but may have been caused by strengthened wind regimes resulting from global cooling and the increase in volume of the Antarctic ice sheets.

Abrupt changes in Indian summer monsoon strength during 33,800 to 5500 years B.P.

Speleothem proxy records from northeastern (NE) India reflect seasonal changes in Indian summer monsoon strength as well as moisture source and transport paths. We have analyzed a new speleothem record from Mawmluh Cave, Meghalaya, India, in order to better understand these processes. The data show a strong wet phase 33,500–32,500 years B.P. followed by a weak/dry phase from 26,000 to 23,500 years B.P. and a very weak phase from 17,000 to 15,000 years B.P. The record suggests abrupt increase in strength during the Bolling-Allerod and early Holocene periods and pronounced weakening during the Heinrich and Younger Dryas cold events. We infer that these changes in monsoon strength are driven by changes in temperature gradients which drive changes in winds and moisture transport into northeast India.

SYSTEMATIC DECLINE IN BENTHIC FORAMINIFERAL SPECIES DIVERSITY LINKED TO PRODUCTIVITY INCREASES OVER THE LAST 26 MA IN THE INDIAN OCEAN

Deep-sea benthic foraminferal species diversity from the late Oligocene-Holocene sequence of Ocean Drilling Program (ODP) Site 757, Hole B, southeastern Indian Ocean (1652 m water depth), is examined in terms of the information function (H), equitability (E), number of species (S) and Sanders’ rarefied values. The values of these parameters reached their maximum about 18–15 Ma, and thereafter had a continuous stepwise decrease. Productivity increased significantly in the Indo-Pacific Ocean (the “biogenic bloom”) and the oxygen minimum zone (OMZ) intensified over large parts of the Indian Ocean beginning about 15 Ma. The diversity values show more abrupt changes since 10–8 Ma, when the strength of the Indian summer monsoon substantially increased and there were significant changes in Southern Hemisphere (SH) and Northern Hemisphere (NH) ice volume. Diversity values decreased abruptly 8–6 Ma (the Chron-6 negative Carbon Shift), 3.2–2.3 Ma (major NH glaciation) and 1.6–0.9 Ma, coinciding with increased percentages of Uvigerina proboscidea , a species indicative of high surface productivity. Thus, we suggest that fluctuations in species diversity at ODP Site 757 were related to changes in productivity during the studied interval.

Mahanadi: The Great River

Mahanadi, the ‘Great River’, is a major rain-fed peninsular river in East Central India that flows through states of Chhattisgarh and Odisha and meets the water requirement for irrigation, domestic and industrial purposes in part of these states. The farthest headwater of the river lies on Sihawa hills. It splits into various channels at Naraj in Odisha, and emerge into an arcuate shaped delta. Progressive shifting of the Mahanadi river course and its coastline can be observed at different stages in the Mahanadi delta. The upstream part of the river is dominated by Proterozoic sedimentary rocks of Chhattisgarh basin while downstream part by silicate rocks of Eastern Ghat Mobile belt. A large number of minor to major projects have already commenced or are under construction and the canals that come out from these projects regulate the agriculture practices in the basin. This river is very vulnerable to climate change as the spatial distribution of regional rainfall pattern enhances the chance of flood in its downstream sub-catchments, while the upstream sub-catchments face threats of draught. The deteriorating water quality of the Mahanadi and its seasonal variability is also a cause of concern.