Particulate organic matter in the Lena River and its delta: from the permafrost catchment to the Arctic Ocean
<p>Rapid Arctic warming accelerates permafrost thaw, causing an additional release of terrestrial organic matter (OM) into rivers and, ultimately, after transport via deltas and estuaries, to the Arctic Ocean nearshore. The majority of our understanding of nearshore OM dynamics and fate has be...
| Main Authors: | , , , , , , , , |
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| Format: | Article |
| Language: | English |
| Published: |
Copernicus Publications
2023-04-01
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| Series: | Biogeosciences |
| Online Access: | https://bg.copernicus.org/articles/20/1423/2023/bg-20-1423-2023.pdf |
| Summary: | <p>Rapid Arctic warming accelerates permafrost thaw, causing
an additional release of terrestrial organic matter (OM) into rivers and,
ultimately, after transport via deltas and estuaries, to the Arctic Ocean
nearshore. The majority of our understanding of nearshore OM dynamics and
fate has been developed from freshwater rivers despite the likely impact of
highly dynamic estuarine and deltaic environments on the transformation,
storage, and age of OM delivered to coastal waters. Here, we studied
particulate organic carbon (POC) dynamics in the Lena River delta and compared them
with POC dynamics in the Lena River main stem along a <span class="inline-formula">∼</span> 1600 km long
transect from Yakutsk, downstream to the delta. We measured POC, total
suspended matter (TSM), and carbon isotopes (<span class="inline-formula"><i>δ</i><sup>13</sup></span>C and <span class="inline-formula">Δ<sup>14</sup></span>C) in POC to compare riverine and deltaic OM composition and changes
in OM source and fate during transport offshore. We found that TSM and POC
concentrations decreased by 70 % during transit from the main stem to
the delta and Arctic Ocean. We found deltaic POC to be strongly depleted in
<span class="inline-formula"><sup>13</sup></span>C relative to fluvial POC. Dual-carbon (<span class="inline-formula">Δ<sup>14</sup></span>C and <span class="inline-formula"><i>δ</i><sup>13</sup></span>C) isotope mixing model analyses indicated a significant
phytoplankton contribution to deltaic POC (<span class="inline-formula">∼</span> 68 <span class="inline-formula">±</span> 6 %) and
suggested an additional input of permafrost-derived OM into deltaic waters
(<span class="inline-formula">∼</span> 18 <span class="inline-formula">±</span> 4 % of deltaic POC originates from Pleistocene
deposits vs. <span class="inline-formula">∼</span> 5 <span class="inline-formula">±</span> 4 % in the river main stem). Despite the
lower concentration of POC in the delta than in the main stem (0.41 <span class="inline-formula">±</span> 0.10 vs. 0.79 <span class="inline-formula">±</span> 0.30 mg L<span class="inline-formula"><sup>−1</sup></span>, respectively), the amount of
POC derived from Yedoma deposits in deltaic waters was almost twice as large
as the amount of POC of Yedoma origin in the main stem (0.07 <span class="inline-formula">±</span> 0.02 and 0.04 <span class="inline-formula">±</span> 0.02 mg L<span class="inline-formula"><sup>−1</sup></span>, respectively). We assert that estuarine and deltaic
processes require consideration in order to correctly understand OM dynamics
throughout Arctic nearshore coastal zones and how these processes may evolve
under future climate-driven change.</p> |
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| ISSN: | 1726-4170 1726-4189 |