عنوان

Foraminifer evidence of monsoon upwelling off Oman during the late Quaternary

TLpq303923081

انگلیسی

Foraminifer evidence of monsoon upwelling off Oman during the late Quaternary

[Thesis]

D. M. Anderson

Brown University

1991

306

Ph.D.

Brown University

1991

In the northwest Arabian Sea, Ekman transport driven by the southwest-monsoon winds upwells cool, nutrient-rich waters along the coast of Oman. Variations in upwelling are recorded in plankton fossils (foraminifers) and other sediments off Oman, forming a marine-geologic record of monsoon circulation. I found that by comparing fossil assemblages between nearshore and offshore sites I could reconstruct the history of the coastal upwelling gradient which today characterizes coastal upwelling in coretop sediments. A nearshore-offshore gradient similar in magnitude to the present exists during all interglacial times during the late Quaternary interval from 0-300 k.y. The gradient is reduced or absent during glacial times implying diminished southwest winds, not strong enough to produce an environmental gradient in the surface waters. Some differences exist between the time series of nearshore and offshore upwelling, and sensitivity tests performed with a one-dimensional model of upwelling indicate that part of these differences may result from changes in the jet structure of the low-level winds. In shallow sediments along the continental margin variations in productivity are recorded by changes in shell accumulation during the late Quaternary. Accumulation is greatest during interglacial times when the species composition indicates nearshore waters are cold relative to sites offshore, consistent with increased coastal upwelling. These variations were examined in the interval 0-20 k.y. using accelerator mass-spectrometry to measure the C content of the foraminifer shells. Shell accumulation rates were low during the last glacial maximum, increased at the time of deglaciation, and reached maximal values in the mid-Holocene. The amplitude and timing of variations in these measures of coastal upwelling implicate glacial-interglacial climate and summer insolation variations as the dominant external controls on monsoon wind strength off Oman during the late Quaternary, consistent with numerical climate simulations.

Earth sciences

Geology

Geology

Paleoecology

D. M. Anderson

p

[Thesis]

276903

a

Y