Hot-spring inputs and climate drive dynamic shifts in archaeal communities in Lake Magadi, Kenya Rift Valley
<p>The methane index (MI) is an organic geochemical index that uses isoprenoid glycerol dialkyl glycerol tetraethers (GDGTs) as a proxy for methane cycling. Here, we report results from sediments in core MAG14-2A that span almost 500 <span class="inline-formula">ka</span>...
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| Main Authors: | , , , , , , , , |
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| Format: | Article |
| Language: | English |
| Published: |
Copernicus Publications
2025-08-01
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| Series: | Biogeosciences |
| Online Access: | https://bg.copernicus.org/articles/22/3931/2025/bg-22-3931-2025.pdf |
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| Summary: | <p>The methane index (MI) is an organic geochemical index that uses isoprenoid glycerol dialkyl glycerol tetraethers (GDGTs) as a proxy for methane cycling. Here, we report results from sediments in core MAG14-2A that span almost 500 <span class="inline-formula">ka</span> in Lake Magadi, Kenya. The deposits show abrupt shifts between high and low MI values through calcareous, tuffaceous and zeolitic silts. The MI switches “off” (MI <span class="inline-formula"><</span> 0.2) and “on” (MI <span class="inline-formula">></span> 0.5) through the core with bulk organic matter enriched in <span class="inline-formula"><sup>13</sup>C</span> during “MI-off” periods (<span class="inline-formula">∼</span> <span class="inline-formula">−</span>18 ‰) in the upper part of the core, whereas <span class="inline-formula"><sup>13</sup>C</span> is lower (<span class="inline-formula">−</span>22 ‰ to <span class="inline-formula">−</span>25 ‰) in lower parts of the sedimentary sequence. Sediments deposited when the MI switches “on” showed <span class="inline-formula"><i>δ</i><sup>13</sup>C<sub>OM</sub></span> values as low as <span class="inline-formula">−</span>89.4 ‰, but most values were within the range of <span class="inline-formula">−</span>28 ‰ to <span class="inline-formula">−</span>30 ‰, which is consistent with contributions from methanogens rather than methanotrophs. Thus, the likely source of these high MI values in Lake Magadi is methanogenic archaea. Our results show that hydrothermal inputs of bicarbonate-rich waters into Lake Magadi combined with further evaporative concentration cause a shift in the dominant archaeal communities, alternating between two stable states.</p> |
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| ISSN: | 1726-4170 1726-4189 |