Journal of Geological Society of India (Online archive from Vol 1 to Vol 78)

Anil K. Gupta ¹, Moumita Das ¹

Affiliations
1 Department of Geology and Geophysics, Indian Institute of Technology, Kharagpur 721302, IN

Abstract

We produced a 12.9 Ma census data of deep-sea benthic foraminifera from subtropical Ocean Drilling Program (ODP) Hole 752A, Broken Ridge, southeastern Indian Ocean to understand paleoceanographic and paleoclimatic changes and their relation to Southern Ocean climate variability as well as latitudinal shifts in the Subtropical Convergence Zone (SCZ). We employed knowledge of the ecology of Recent deep-sea benthic foraminifera from different ocean basins for environmental interpretations at Hole 752A. Benthic faunal data suggest a major transition in deep-sea environments of the southeastern Indian Ocean across 5.5-4.5 Ma roughly coinciding with the end of the Indo-Pacific "biogenic bloom". The benthic biofacies suggest well-oxygenated and nutrient poor deep waters from 12.9 to 10 Ma with variable flux of organic matter. The interval 10-5.5 Mais marked by high and sustainedflux of organic matter at the time when productivity increased many fold throughout the Indian and Pacific Oceans during which time the biogenic bloom peaked and the Indian summer monsoon intensified. Antarctic ice volume significantly increased and southern component deep-water formation enhanced during this time. This southern cooling in the late middle to late Miocene probably pushed the SCZ towards north above Hole 752A. Since 4.5 Ma, the organic flux was low to intermediate and pulsed.

Keywords

Paleoceanographic changes, Benthic foraminifera, ODP Site 752, Broken Ridge, SE Indian Ocean.

Full Text

     

Moumita Das ¹, Anil K. Gupta ¹, David M. Anderson ²

Affiliations
1 Departrnent of Geology and Geophysics, Indian Institute of Technology, Kharagpur 721 302, IN
2 NOAA Paleoclimatology Program, 325 Broadway, Code E/GC, Boulder, CO 80302, US

Abstract

We analyzed a 1000-year census record of benthic foraminifera in core RC 2730 (water depth 698 m), off the Oman Margin, northwestern Arabian Sea, to understand the influence of surface productivity on bottom water environments in response to changes in the intensity of the southwest (SW) monsoon winds. We employed knowledge of the ecology of recent deep-sea benthic foraminifera from different ocean basins for environmental interpretation of benthic assemblages. Benthic faunal data suggest that the interval 1200 - 1400 A.D. is marked by an increased influx of organic matter to the northwestern Arabian Sea floor that resulted from higher surface productivity during a stronger SW monsoon. This interval corresponds to the Medieval Warm Period and a wet phase in India. The organic flux was low during the Little Ice Age (1450- 1850 A.D.) when the SW monsoon was weak. Over the last millennium, the SW monsoon was weakest during the Maunder Minimum, and since then it has shown a continuous intensification, coinciding with increased surface air temperatures.

Keywords

Last millennium, Foraminifera, Organic flux, Southwest monsoon, Northwestern Arabian Sea.

Full Text