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Marietta M. De Leon, Aileen D. Fajardo, Nelson C. Agapay, Jr.:
Initial results of the vertical distribution pattern study of calcareous nannoplankton from SO - 114 cores, South China Sea
(Poster)

Some 25 multicore samples, collected in 1996 by the German research vessel, R/V SONNE, during its SO-114 cruise in the Philippine territorial limits of the South China Sea, are currently being examined for their calcareous nannoplankton content. The cores approximately range in length from 27 to 48cm. The main objectives of the study are to characterise the calcareous nannoplankton assemblages in the cores, in terms of their vertical and horizontal distribution patterns, and to correlate the results with available foraminiferal data. This is aimed at providing further information useful to future ecological and environmental interpretations.

This paper presents the initial findings of the investigations made on the first seven multicores. The core samples, which were recovered from water-depths ranging between 2500m to 3300m, represent the first seven stations visited by the vessel. They consist mostly of sand, silt, mud and ash.

Preliminary results reveal the presence of generally abundant, well-preserved, low- to medium-diversity calcareous nannoplankton in all multicores. Three species dominate the taxa recorded and are identified as: Florisphaera profunda, Gephyrocapsa oceanica and Emiliania huxleyi. At this stage of the study, no observation has been made regarding a pattern that is common to the seven cores since the cores' vertical nannoplankton distributions display different downcore trends.

The study also reveals sediment mixing in the samples, as exhibited by the presence of older calcareous nannoplankton alongside younger and Recent species. This mixing can probably be attributed in part to the location of the cores, they being proximal to the Luzon main island and the Manila Bay from where some of the sediments are derived. The mixing, however, tends to decrease with increasing water-depth and is restricted to fine-grained sediments. Furthermore, the adverse effect of the Mount Pinatubo eruption, and the subsequent deposition of ash falls, are very much evident in all of the seven cores examined. It appears to be a mass mortality of the calcareous nannoplankton caused by instantaneous deposition of ash. The ash-layers from Mount Pinatubo are marked by the absence of calcareous nannoplankton. This observation agrees with the results of foraminiferal studies done on similar cores.

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 [Division of Micropalaeontology] [Department of Geosciences] [Bremen University]

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