Nekton remains, diatoms, and holocene upwelling off Peru Public Deposited

http://ir.library.oregonstate.edu/concern/graduate_thesis_or_dissertations/5999n654s

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  • Partly laminated sediments on the upper continental slope (200-600 m) off central Peru contain a diverse assemblage of fish debris, diatoms, and the remains of a variety of other nektonic, planktic, and benthic organisms. Approximately 97 percent of the fish scales recovered from the best preserved cores come from the anchoveta (79 percent) , Peruvian hake (16 percent) , and sardine (2 percent). Most of the diatoms belong to the genera Chaetoceros, Skeletonema, Thalassionema, Thalassiosira, Coscinodiscus, and Rhizosolenia. A discontinuous sedimentary record at 11°S. and 13°S. shows that the species composition of diatom and fish debris assemblages has changed very little in the past 15,000 years. However, the relative abundance of diatom species and genera, and to a lesser extent, fish species and genera, has fluctuated throughout the Holocene. These fluctuations may be attributed to changes of primary and secondary productivity in the overlying water column and to subsequent chemical and physical alteration of the depositional environment. An explanation of Holocene upwelling and productivity was developed based on the distribution of fish debris, diatoms, and silicoflagellates in sediments deposited during the Second Neoglacial Period (about 2700-1800 yr. B.P.) from core 7706-40 at 11°15'S. Floral and faunal assemblages, variously enriched in sardine and saury scales, diatoms of the species Rhizosolenia shrubsolei, R. bergonii, and Skeletonema costatum, and the silicoflagellate genera Dictyocha and Distephanus, suggest that periods of global atmospheric cooling were accompanied by both enhanced productivity and warmer surface water off the coast of Peru. Abundant sardine scales in sediments deposited during the close of the last ice age (11,700-11,400 yr. B.P.) and a tropical oceanic assemblage of diatoms (Coscinodiscus nodulifer, Asteromphalus spp., Rhizosolenia bergonii) deposited together with large numbers of Skeletonerna costatum and Rhizosolenia shrubsolei at 11°15'S. during the 'Little Ice Age' (200-500 yr. B.P.) are further evidence supporting the proposed explanation of Holocene upwelling and productivity patterns. Latitudinal compression of atmospheric and oceanic circulation in the South Pacific Ocean and a southward shifting Intertropical Convergence Zone are phenomena frequently attributed to climatic cooling. Intensified oceanic circulation and weakened southeast trade winds directly off Peru that may have resulted from the compressed and shifted circulation belts could have interacted to produce the paradoxical simultaneity of warm surface water and high productivity signals preserved in Peruvian marine sediments during some episodes of global atmospheric cooling. Further testing of this and competing hypotheses depends upon the availability of cores from the northern and southern reaches of the Peruvian continental margin that exhibit greater temporal continuity.
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  • description.provenance : Approved for entry into archive by Patricia Black(patricia.black@oregonstate.edu) on 2012-02-13T21:14:11Z (GMT) No. of bitstreams: 1 DevriesThomasJ1980.pdf: 970038 bytes, checksum: a0c0c422fc016d5dcf289d2b37c0bf9b (MD5)
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  • description.provenance : Approved for entry into archive by Patricia Black(patricia.black@oregonstate.edu) on 2012-02-13T21:19:40Z (GMT) No. of bitstreams: 1 DevriesThomasJ1980.pdf: 970038 bytes, checksum: a0c0c422fc016d5dcf289d2b37c0bf9b (MD5)
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