More Like this

1. Impact of the Elemental Composition of Exported Organic Matter on the Observed Dissolved Nutrient and Trace Element Distributions in the Upper Layer of the Ocean

   https://doi.org/10.1029/2020GB006902  

   Quay, Paul ( October 2021 , Global Biogeochemical Cycles)

   Systematic regional variations in the ratio of nutrient depth gradients of dissolved inorganic carbon (ΔDIC):nitrate (ΔNO₃):phosphate (ΔPO₄) in the upper layer (300 m) of the Pacific Ocean are observed. Regional variations in the ΔDIC/ΔNO₃/ΔPO₄are primarily the result of three processes, that is, the C/N/P of organic matter (OM) being exported and subsequently degraded, nitrogen fixation, and air‐sea CO₂gas exchange. The link between the observed dissolved ΔDIC/ΔNO₃/ΔPO₄and the C/N/P of exported OM is established using surface layer dissolved DIC, NO₃, and PO₄budgets. These budgets, in turn, provide a means to indirectly estimate the C/N/P of OM being exported from the surface layer of the ocean. The indirectly estimated C/N/P of exported OM reach maxima in the subtropical gyres at 177/22/1, that is, significantly greater than the Redfield ratio and a minimum in the equatorial ocean at 109/16/1 with both results agreeing with available observed particle C/N/P and ocean biogeochemical models. The budget approach was applied to a bioactive trace element (TE) using the measured dissolved Cadmium (Cd) to PO₄gradients to estimate the Cd/P of exported OM in the Pacific Ocean. Combining the budget method with the availability of high‐quality dissolved nutrient and TE data collected during the GOSHIP and GEOTRACES programs could potentially provide estimates of the C/N/P/TE of exported OM on global ocean scales which would significantly improve our understanding of the link between the ocean's biological pump and dissolved nutrient distributions in the upper ocean.

    

   more » « less
2. Origin and Accumulation of an Anthropogenic CO 2 and 13 C Suess Effect in the Arctic Ocean

   https://doi.org/10.1029/2019GB006423  

   Ko, Young Ho ; Quay, Paul D. ( February 2020 , Global Biogeochemical Cycles)

   We determined the impact of anthropogenic CO₂(C_ant) accumulation on the δ¹³C of dissolved inorganic carbon in the Arctic Ocean (i.e., the¹³C Suess effect) based on δ¹³C measurements during a GEOTRACES cruise in 2015. The δ¹³C decrease was estimated from the amount of C_antchange derived by the transit time distribution approach and the ratio of the anthropogenic δ¹³C/dissolved inorganic carbon change (RC). A significant C_antincrease (up to 45 μmol kg⁻¹) and δ¹³C decrease (up to −0.9‰) extends to ~2,000 m in the Canada and Makarov Basin. We find distinctly different RC values for the intermediate water (300–2,000 m) and upper halocline water (<200 m) of −0.020 and −0.012‰ (μmol kg⁻¹)⁻¹, respectively, which identifies two sources of C_antaccumulation from North Atlantic and North Pacific. Furthermore, estimated RC for intermediate waters is the same as the RC observed in the Greenland Sea and the rate of anthropogenic dissolved inorganic carbon increase estimated for intermediate waters at 0.9 μmol kg⁻¹yr⁻¹is identical to the estimated rate in the Iceland Sea. These observations indicate that the high rate of C_antaccumulation and δ¹³C decrease in the Arctic Ocean is primarily a result of the input of C_ant, via ventilation of intermediate waters, from the Nordic Sea rather than local anthropogenic CO₂uptake within the Arctic Basin. We determine the preindustrial δ¹³C (δ¹³C_PI) distributions and find distinct δ¹³C_PIsignatures of the intermediate and upper halocline waters that reflect the difference in δ¹³C_PI–PO₄relationship of Atlantic and Pacific source water.

    

   more » « less
3. Evaluating the Glacial‐Deglacial Carbon Respiration and Ventilation Change Hypothesis as a Mechanism for Changing Atmospheric CO 2

   https://doi.org/10.1029/2020GL091296  

   Stott, Lowell D. ; Shao, Jun ; Yu, Jimin ; Harazin, Kathleen M. ( February 2021 , Geophysical Research Letters)

   The prevailing hypothesis to explain pCO₂rise at the last glacial termination calls upon enhanced ventilation of excess respired carbon that accumulated in the deep sea during the glacial. Recent studies argue lower [O₂] in the glacial ocean is indicative of increased carbon respiration. The magnitude of [O₂] depletion was 100–140 µ mol/kg at the glacial maximum. Because respiration is coupled toδ¹³C of dissolved inorganic carbon (DIC), [O₂] depletion of 100–140 µ mol/kg from carbon respiration would lower deep waterδ¹³C_DICby ∼1‰ relative to surface water. Prolonged sequestration of respired carbon would also lower the amount of¹⁴C in the deep sea. We show that Pacific Deep Waterδ¹³C_DICdid not decrease relative to the surface ocean and Δ¹⁴C was only ∼50‰ lower during the late glacial. Model simulations of the hypothesized ventilation change during deglaciation lead to large increases inδ¹³C_DIC, Δ¹⁴C, andε¹⁴C that are not recorded in observations.

    

   more » « less
4. Integrated carbon, sulfur, and nitrogen isotope chemostratigraphy of the Ediacaran Lantian Formation in South China: Spatial gradient, ocean redox oscillation, and fossil distribution

   https://doi.org/10.1111/gbi.12226  

   Wang, W. ; Guan, C. ; Zhou, C. ; Peng, Y. ; Pratt, L. M. ; Chen, X. ; Chen, L. ; Chen, Z. ; Yuan, X. ; Xiao, S. ( January 2017 , Geobiology)

   The Ediacaran Doushantuo Formation in South China is a prime target for geobiological investigation because it offers opportunities to integrate chemostratigraphic and paleobiological data. Previous studies were mostly focused on successions in shallow‐water shelf facies, but data from deep‐water successions are needed to fully understand basinal redox structures. Here, we report δ¹³C_carb, δ¹³C_org, δ³⁴S_pyr, δ³⁴S_CAS, and δ¹⁵N_seddata from a drill core of the fossiliferous Lantian Formation, which is a deep‐water equivalent of the Doushantuo Formation. Our data confirm a large (>10‰) spatial gradient in δ¹³C_carbin the lower Doushantuo/Lantian formations, but this gradient is probably due to the greater sensitivity of carbonate‐poor deep‐water sediments to isotopic mixing with¹³C‐depleted carbonate cements. A pronounced negative δ¹³C_carbexcursion (EN3) in the upper Doushantuo/Lantian formations, however, is spatially consistent and may be an equivalent of the Shuram excursion. δ³⁴S_pyris more negative in deeper‐water facies than in shallow‐water facies, particularly in the lower Doushantuo/Lantian formations, and this spatial pattern is interpreted as evidence for ocean redox stratification: Pyrite precipitated in euxinic deep waters has lower δ³⁴S_pyrthan that formed within shallow‐water sediments. The Lantian Formation was probably deposited in oscillating oxic and euxinic conditions. Euxinic black shales have higherTOCandTNcontents, but lower δ³⁴S_pyrand δ¹⁵N_sedvalues. In euxinic environments, pyrite was predominantly formed in the water column and organic nitrogen was predominantly derived from nitrogen fixation orNH₄⁺assimilation because of quantitative denitrification, resulting in lower δ³⁴S_pyrand δ¹⁵N_sedvalues. Benthic macroalgae and putative animals occur exclusively in euxinic black shales. If preserved in situ, these organisms must have lived in brief oxic episodes punctuating largely euxinic intervals, only to be decimated and preserved when the local environment switched back to euxinia again. Thus, taphonomy and ecology were the primary factors controlling the stratigraphic distribution of macrofossils in the Lantian Formation.

    

   more » « less
5. Carbon cycle dynamics and ecology revealed by the carbon isotopic composition of single organic microfossils during the Late Devonian Biotic Crisis

   https://doi.org/10.1111/gbi.12482  

   Cohen, Phoebe A. ; Junium, Christopher K. ; King Phillips, Ezekiel ; Uveges, Benjamin T. ( December 2021 , Geobiology)

   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 consistently¹³C‐enriched compared to bulk sediments (δ¹³C_bulk) by ~0–10‰. We observe no difference between the δ¹³C_OWMof 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 δ¹³C_OWMand δ¹³C_bulkis in part due to a large δ¹³C gradient in the AB water column where OWM utilized relatively¹³C‐enriched dissolved inorganic carbon near the surface. Thus, the organisms producing the balance of the total organic carbon were assimilating¹³C‐depleted C sources, including but not limited to respired organic carbon or byproducts of fermentation. We also observe a systematic decrease in both δ¹³C_OWMand δ¹³C_bulkof 3‰ from shoreward to open‐ocean facies that may reflect the effect of¹³C‐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 δ¹³C_organalyses of eukaryotes have been directly compared to bulk δ¹³C_orgin the deep‐time fossil record.

    

   more » « less