Paleoclimate and Paleoceanographic Changes During the Last 250 Years Inferred by High Resolution Sedimentary and Mineralogical Compositions of two Box-cores Collected in the Central Peruvian Margin
Abstract
Two box cores from the central Peruvian margin (off Pisco, 13°30'S; and off Callao, 12°S) record the histories of the mineral input to the sediments during the last 250 years. The high resolution description throughout the X-Ray digital analyses shows that both cores presented laminations (less than 5 mm thick) and bands formed by the succession of light (high X-ray gray level) and dark layers (low X-ray gray level), which are deposited without bioturbation under anoxic conditions. The preliminary microscopic observations (smear slide under polarized light) confirm the lithological description and show that the light and dark laminae correspond to layers rich in mineral particles and diatom remains, respectively. X ray difractometry (DRX) and Attenuated Transmission Refractometry (ATR) performed on samples from light lamina show that the mineral fraction is dominated by quartz, feldspar, kaolinite and illite. The quartz content quantification throughout Fourier Transform Infrared (FTIR) spectrometry analyses, at high resolution, shows the same patterns at both sites. Chronologically these results reveal three periods over the last 250 years, though with rather similar interdecadal periodicity (40 to 50 years). The earliest one from 1750 to 1835 AD, which enclose the end of the Little Ice Age, is characterised by high quartz content confirmed also by grey level values. These high quartz concentrations can tentatively be explained by the expression of more than one source of detrital transport (Eolian, fluvial or marine). The second one, dated from 1835 to 1950 AD, starts with an abrupt decrease of quartz content by ca. 1850, which then oscillated around the low values with the same interdecadal periodicity. Finally, the third period, which corresponds to the last 50 years, shows a positive trend reflecting an increase of the terrigenous input, which may be linked to changes in the eolian forcing. In addition, the results show significant signatures of the mineral fraction (quartz, feldspar, kaolinite and illite) in layers including El Niño events (1982-83, 1986-87 and 1997-98), with the largest peak during the 1997-98 episode.
- Publication:
-
AGU Fall Meeting Abstracts
- Pub Date:
- December 2005
- Bibcode:
- 2005AGUFMPP51D0629S
- Keywords:
-
- 0473 Paleoclimatology and paleoceanography (3344;
- 4900)