Benthic iron flux influenced by climate‐sensitive interplay between organic carbon availability and sedimentation rate in Arctic fjords

2021 ◽  
Author(s):  
Lisa C. Herbert ◽  
Qingzhi Zhu ◽  
Alexander B. Michaud ◽  
Katja Laufer‐Meiser ◽  
Christopher K. Jones ◽  
...  
Keyword(s):  
Organic Carbon ◽  
Sedimentation Rate ◽  
Carbon Availability ◽  
Arctic Fjords

Total organic carbon and the preservation of organic-walled microfossils in Precambrian shale

Geology ◽  
2020 ◽  
Author(s):  
C.R. Woltz ◽  
S.M. Porter ◽  
H. Agić ◽  
C.M. Dehler ◽  
C.K. Junium ◽  
...  
Keyword(s):  
Species Richness ◽  
Organic Carbon ◽  
Total Organic Carbon ◽  
Microbial Degradation ◽  
Sedimentation Rate ◽  
Surface Pattern ◽  
Causal Factors ◽  
Eukaryotic Diversity ◽  
High Concentrations ◽  
Fossil Preservation

Much of our understanding of early eukaryote diversity and paleoecology comes from the record of organic-walled microfossils in shale, yet the conditions controlling their preservation are not well understood. It has been suggested that high concentrations of total organic carbon (TOC) inhibit the preservation of organic fossils in shale, and although this idea is supported anecdotally, it has never been tested. Here we compared the presence, preservational quality, and assemblage diversity of organic-walled microfossils to TOC concentrations of 346 shale samples that span the late Paleoproterozoic to middle Neoproterozoic in age. We found that fossil-bearing samples have significantly lower median TOC values (0.32 wt%, n = 189) than those containing no fossils (0.72 wt%, n = 157). Preservational quality, measured by the loss of surface pattern, density of pitting, and deterioration of wall margin, decreases as TOC increases. Species richness negatively correlates with TOC within the ca. 750 Ma Chuar Group (Arizona, USA), but no relationship is observed in other units. These results support the hypothesis that high TOC content either decreases the preservational quality or inhibits the preservation of organic-walled microfossils altogether. However, it is also possible that other causal factors, including sedimentation rate and microbial degradation, account for the correlation between fossil preservation and TOC. We expect that as TOC varies in space and time, so too does the probability of finding well-preserved fossils. A compilation of 13,940 TOC values spanning Earth history suggests significantly higher median TOC levels in Mesoproterozoic versus Neoproterozoic shale, potentially biasing the interpreted pattern of increased eukaryotic diversity in the Tonian.

scholarly journals Coastal urbanization alters carbon cycling in Tokyo Bay

2020 ◽  
Vol 10 (1) ◽  
Author(s):  
Atsushi Kubo ◽  
Jota Kanda
Keyword(s):  
Organic Carbon ◽  
Sedimentation Rate ◽  
Dissolved Inorganic Carbon ◽  
Sewage Treatment ◽  
Tokyo Bay ◽  
Net Community Production ◽  
Labile Organic Carbon ◽  
Treatment Facilities ◽  
Coastal Urbanization ◽  
Freshwater Inputs

AbstractThe carbon budget of Tokyo Bay, a highly urbanized coastal basin, was estimated using a box model that incorporated inorganic and organic carbon data over an annual cycle (2011–2012). The surface water represented net autotrophic system in which the annual net community production (NCP) was 19 × 1010 gC year−1. The annual loading of dissolved inorganic carbon and total organic carbon (TOC) from freshwater inputs was 11.2 × 1010 and 4.9 × 1010 gC year−1, respectively. The annual TOC sedimentation rate was 3.1 × 1010 gC year−1, similar to the annual air–sea CO2 uptake (5.0 × 1010 gC year−1). Although the NCP and TOC loading from freshwater inputs were respectively 3.0 and 2.7 times lower than those in the 1970s, the TOC sedimentation rate was similar. Therefore, a relatively high carbon efflux from Tokyo Bay likely occurred in the 1970s, including CO2 efflux to the atmosphere and/or export of labile organic carbon to the open ocean. The changes in carbon flow between the 1970s and 2011–2012 resulted from improved water quality due to increased sewage treatment facilities and improved sewage treatment efficiency in the catchment, which decreased the amount of labile organic carbon flowing into the bay.

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