Carbon cycle dynamics and ecology revealed by the carbon isotopic composition of single organic microfossils during the Late Devonian Biotic Crisis
Carbon cycle dynamics and ecology revealed by the carbon isotopic composition of single organic microfossils during the Late Devonian Biotic Crisis
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DOI：
10.1111/gbi.12482
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发表时间：
2021-12
期刊：
影响因子：
3.7
通讯作者：
Phoebe A. Cohen;C. Junium;Ezekiel King Phillips;B. Uveges
中科院分区：
文献类型：
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作者：
Phoebe A. Cohen;C. Junium;Ezekiel King Phillips;B. Uveges
本文采用一种新的方法对纽约阿巴拉契亚盆地（AB）三个地点的单一有机壁微化石（OWM）进行了δ13C分析，这些地点跨越了晚泥盆纪生物危机（LDBC）。我们的数据提供了对AB地区frasian - fammenian碳循环性质的新见解，也为古生代页岩序列中普遍存在的神秘OWM的古生态学提供了可能的约束。OWM的碳同位素组成与正常的原生海相有机质一致，范围为- 32 ~ - 17‰，但所有样品的平均碳同位素组成均为- 25‰，与大块沉积物（δ13Cbulk）相比，13C‐始终富集~0 ~ 10‰。我们观察到平面层（光滑壁）和棘棘层（棘棘）的δ13COWM之间没有差异，表明我们的数据是由生态信号驱动的，而不是由分类信号驱动的。我们假设δ13COWM和δ13Cbulk之间的偏移部分是由于AB水柱中δ13C梯度大，其中OWM利用了地表附近相对13C富集的溶解无机碳。因此，产生总有机碳平衡的生物正在吸收13C耗尽的C源，包括但不限于呼吸有机碳或发酵副产物。我们还观察到，从海岸相到开阔海相，δ13COWM和δ13Cbulk均有3‰的系统性减少，这可能反映了相对封闭的AB组中来自河流的13C富集溶解无机碳（DIC）的影响。这反过来又可能导致了LDBC期间的低氧底水条件。这是首次将真核生物的单个微化石δ13Corg分析结果与深时化石记录中的整体δ13Corg进行直接比较。
We apply a new approach for the δ13C analysis of single organic‐walled microfossils (OWM) to three sites in the Appalachian Basin of New York (AB) that span the Late Devonian Biotic Crisis (LDBC). Our data provide new insights into the nature of the Frasnian–Famennian carbon cycle in the AB and also provide possible constraints on the paleoecology of enigmatic OWM ubiquitous in Paleozoic shale successions. The carbon isotope compositions of OWM are consistent with normal marine organic matter of autochthonous origins and range from −32 to −17‰, but average −25‰ across all samples and are consistently 13C‐enriched compared to bulk sediments (δ13Cbulk) by ~0–10‰. We observe no difference between the δ13COWM of leiospheres (smooth‐walled) and acanthomorphic (spinose) acritarch OWM, indicating that our data are driven by ecological rather than taxonomic signals. We hypothesize that the offset between δ13COWM and δ13Cbulk is in part due to a large δ13C gradient in the AB water column where OWM utilized relatively 13C‐enriched dissolved inorganic carbon near the surface. Thus, the organisms producing the balance of the total organic carbon were assimilating 13C‐depleted C sources, including but not limited to respired organic carbon or byproducts of fermentation. We also observe a systematic decrease in both δ13COWM and δ13Cbulk of 3‰ from shoreward to open‐ocean facies that may reflect the effect of 13C‐enriched dissolved inorganic carbon (DIC) derived from riverine sources in the relatively enclosed AB. The hypothesized steep carbon isotope gradient in the AB could be due to a strong biological pump; this in turn may have contributed to low oxygen bottom water conditions during the LDBC. This is the first time single‐microfossil δ13Corg analyses of eukaryotes have been directly compared to bulk δ13Corg in the deep‐time fossil record.