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. / Graduation date: 1980
| Identifer | oai:union.ndltd.org:ORGSU/oai:ir.library.oregonstate.edu:1957/27704 |
| Date | 27 July 1979 |
| Creators | DeVries, Thomas J. |
| Contributors | Pearcy, William G. |
| Source Sets | Oregon State University |
| Language | en_US |
| Detected Language | English |
| Type | Thesis/Dissertation |
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