T247 Lakes of the World through Time and Space: Archives of Climate Variability, Paleoenvironment, Geohazards, and Economic Resources (Posters)

Wednesday, 18 October 2023
8:00 AM - 5:30 PM
Hall B

BLUE-SHIFT ALTERATION OF SEDIMENTARY PIGMENTS IN LAKES NASIKIE ENGIDA AND MAGADI AS A RESULT OF ALKALINE CONDITIONS

Paper number: T247-28
Program: Technical Sessions
Time: 8:00 AM – 5:30 PM

Authors

Abstract

Pigments in an environmental setting allow us to understand the processes of primary production derived from both algal and prokaryotic organisms occurring in that system. Samples collected from cores in Lakes Nasikie Engida (ca. 2.6 ka) and Magadi (ca. 456 ka) in the East African Rift Valley as part of the Continental Scientific Drilling project were found to have unique pigments. These pigments were altered via several different pathways throughout the cores depending on their respective environments. A key pathway was a result of blue shifting which happens when the pigments are exposed to higher alkalinity, causing the fluorescence spectrum shift bluer. Samples in the modern analog Nasikie Engida retained most of their key structural identifiers for both chlorophylls and carotenoids, while pigments in Magadi were both degraded and more blue-shifted compared to younger sediments. It is hypothesized herein that this environment can shift the pigments bluer when they are exposed for long periods of time.

A variety of pigments were found in both systems, but the most diverse and most abundant number of pigments were in Nasikie Engida. In Nasikie Engida, allomerization from oxidative stress, transformation to pheophorbides as a result of grazing, and blue shifting of pigments was observed. Allomerization and grazing occur intermittently and at predictable intervals throughout the core, while the blue-shifting only affects certain carotenoids (e.g. rhodopinol). Haloxanthin, a carotenoid pigment found in halophilic bacteria, was more resistant to blue shifting although it was not completely unaffected. A variety of other chlorophylls and carotenoids were also observed including peridinin, bacteriochlorophyll a, and an unusual distribution of pyrochlorophyll a.

Pigments in Magadi were both less abundant and less diverse, however, this attribution is likely the result of pigments becoming blue-shifted from environmental exposure. The blue shifting alterations were observed most prominently over a period of ca. 85.5 ka. Mild alteration of pigments are seen in samples at ca. 15 ka and is most apparent at ca. 100.5 ka where pigments are unrecognizable from their original fluorescence spectrum. While there were fewer distinguishable pigments in Magadi, the presence of a unique carotenoid, 11',12'-Dihydrospheroidene, was observed in euxinic and other anoxic intervals.

Geological Society of America Abstracts with Programs. Vol. 55, No. 6

doi: 10.1130/abs/2023AM-394096

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