Biological and physical controls on the flux and characteristics of sinking particles on the Northwest Atlantic margin

Author Posting. © American Geophysical Union, 2017. This article is posted here by permission of American Geophysical Union for personal use, not for redistribution. The definitive version was published in Journal of Geophysical Research: Oceans 122 (2017): 4539–4553, doi:10.1002/2016JC012549.Biogenic matter characteristics and radiocarbon contents of organic carbon (OC) were examined on sinking particle samples intercepted at three nominal depths of 1000 m, 2000 m, and 3000 m (∼50 m above the seafloor) during a 3 year sediment trap program on the New England slope in the Northwest Atlantic. We have sought to characterize the sources of sinking particles in the context of vertical export of biogenic particles from the overlying water column and lateral supply of resuspended sediment particles from adjacent margin sediments. High aluminum (Al) abundances and low OC radiocarbon contents indicated contributions from resuspended sediment which was greatest at 3000 m but also significant at shallower depths. The benthic source (i.e., laterally supplied resuspended sediment) of opal appears negligible based on the absence of a correlation with Al fluxes. In comparison, CaCO3 fluxes at 3000 m showed a positive correlation with Al fluxes. Benthic sources accounted for 42 ∼ 63% of the sinking particle flux based on radiocarbon mass balance and the relationship between Al flux and CaCO3 flux. Episodic pulses of Al at 3000 m were significantly correlated with the near-bottom current at a nearby hydrographic mooring site, implying the importance of current variability in lateral particle transport. However, Al fluxes at 1000 m and 2000 m were coherent but differed from those at 3000 m, implying more than one mode of lateral supply of particles in the water column.NSF Ocean Sciences Chemical Oceanography program Grant Numbers: OCE-0425677, OCE-0851350; Ocean and Climate Change Institute of WHOI2017-12-0

Lithogenic particle transport trajectories on the Northwest Atlantic Margin

Author Posting. © American Geophysical Union, 2021. This article is posted here by permission of American Geophysical Union for personal use, not for redistribution. The definitive version was published in Journal of Geophysical Research: Oceans 126(1), (2021): e2020JC016802, https://doi.org/10.1029/2020JC016802.The neodymium isotopic composition of the detrital (lithogenic) fraction (εNd‐detrital) of surface sediments and sinking particles was examined to constrain transport trajectories associated with hemipelagic sedimentation on the northwest Atlantic margin. The provenance of resuspended sediments and modes of lateral transport in the water column were of particular interest given the energetic hydrodynamic regime that sustains bottom and intermediate nepheloid layers over the margin. A large across‐margin gradient of ∼5 εNd units was observed for surface sediments, implying strong contrasts in sediment provenance, with εNd‐detrital values on the lower slope similar to those of “upstream regions” (Scotian margin) under the influence of the Deep Western Boundary Current (DWBC). Sinking particles collected at three depths at a site (total water depth, ∼3,000 m) on the New England margin within the core of the DWBC exhibited a similarly large range in εNd‐detrital values. The εNd‐detrital values of particles intercepted at intermediate water depths (1,000 and 2,000 m) were similar to each other but significantly higher than those at 3,000 m (∼50 m above the seafloor). These observations suggest that lithogenic material accumulating in the upper two traps was primarily advected in intermediate nepheloid layers emanating from the adjacent shelf, while that at 3,000 m is strongly influenced by sediment resuspension and along‐margin, southward lateral transport within the bottom nepheloid layer via entrainment in the DWBC. Our results highlight the importance of both along‐ and across‐margin sediment transport as vectors for lithogenic material and associated organic carbon transport.This research was funded by the NSF Ocean Sciences Chemical Oceanography program (OCE‐0425677; OCE‐0851350). JH was partly supported by the National Research Foundation of Korea (NRF) grant funded by the Korean Government (2020R1A2C1008378).2021-06-0

Transport of organic carbon from the California coast to the slope region : a study of Δ14C and δ13C signatures of organic compound classes

Author Posting. © American Geophysical Union, 2005. This article is posted here by permission of American Geophysical Union for personal use, not for redistribution. The definitive version was published in Global Biogeochemical Cycles 19 (2005): GB2018, doi:10.1029/2004GB002422.Surface sediments along a transect from an abyssal site in the northeastern Pacific (Station M, 34°50′N, 123°00′W) to a small mountainous river on the California coast (Santa Clara River) were studied to investigate the sources and cycling of organic matter on the continental margin. Sediment samples were separated into organic compound fractions (extractable lipids, amino acids (THAA), carbohydrates (TCHO), and the acid-insoluble fraction), and their carbon isotope ratios were measured. The Δ14C values of all the THAA and TCHO fractions were greater than −100‰, indicating relatively modern organic carbon (OC) source(s), and rapid cycling of these fractions. In contrast, the Δ14C values of extractable lipids and the acid-insoluble fraction were distinctly lower than those of the THAA and TCHO fractions. The Δ14C values of source OC to the sediments were estimated using a simple mixed layer model. These values were lower than the Δ14C signatures of pre-industrial plankton suggesting input of both old OC and contemporary plankton to the margin sediments. The source of old OC at the 2000-m site was likely from laterally transported coastal sediment. The estimated low Δ14C value of the transported OC suggests that old lipids and acid-insoluble material were selectively transported to the 2000-m site. The contribution of riverine POC to the margin sediments were estimated from Δ14C and δ13C values and indicate that relict OC exported by rivers was an important source of old lipids and acid-insoluble material to sedimentary OC on the shelf.This research was supported by NSF OCE Chemical Oceanography Program and ACS Petroleum Research Fund (to E. R. M. D.), the UCOP Marine Science Fellowship Program (to J. H.), and the Dreyfus Foundation for an Environmental Science Postdoctoral Fellowship grant (to T. K.)

Influence of atmospheric dust deposition on sinking particle flux in the northwest Pacific

We examined the flux and composition of sinking particles collected at a water depth of 800 m in the northwest Pacific from November 2017 to August 2018 to assess the impact of dust deposition on organic carbon export. The fluxes of total particulate matter and particulate organic carbon averaged over the study period were 88 ± 63 mg m-2 d-1 and 9.0 ± 5.8 mg m−2 d−1, respectively. Biogenic particles accounted for 82% of the sinking particles, on average. There were two notable pulses in the particle fluxes of both biogenic and lithogenic material in February and May 2018. These flux peaks were decoupled from net primary production in the surface waters but coincided with intervals of high rates of atmospheric dust deposition. The biogenic component of the two peaks was dominated by two different phytoplankton communities, which may have influenced carbon export efficiency. Correlations between the sinking particle flux and the lithogenic flux are found at several locations in the northwest Pacific, implying that East Asian dust deposition has a prevalent influence on the biological pump. Attention should be paid to the effects of changes in the continental dust supply to the oceans on oceanic carbon export

Lateral organic carbon supply to the deep Canada Basin

Author Posting. © American Geophysical Union, 2008. This article is posted here by permission of American Geophysical Union for personal use, not for redistribution. The definitive version was published in Geophysical Research Letters 35 (2008): L11607, doi:10.1029/2008GL034271.Understanding the processes driving the carbon cycle in the Arctic Ocean is important for assessing the impacts of the predicted rapid and amplified climate change in this region. We analyzed settling particle samples intercepted by a time-series sediment trap deployed in the abyssal Canada Basin (at 3067 m) in order to examine carbon export to the deep Arctic Ocean. Strikingly old radiocarbon ages (apparent mean 14C age = ∼1900 years) of the organic carbon, abundant lithogenic material (∼80%), and mass flux variations temporally decoupled from the cycle of primary productivity in overlying surface waters together suggest that, unlike other ocean basins, the majority of the particulate organic carbon entering the deep Canada Basin is supplied from the surrounding margins.This research was funded by the NSF Ocean Sciences Division (Chemical Oceanography program) and NSF Office of Polar Programs, Office of Naval Research, as well as the Ocean and Climate Change Institute and Arctic Research Initiative at the Woods Hole Oceanographic Institution

Blank Correction for Δ14C Measurements in Organic Compound Classes of Oceanic Particulate Matter

Contaminant carbon (blank carbon) was studied for its impact on the carbon isotope measurements (Delta-14C and delta-13C) of 3 organic compound classes of oceanic particulate organic matter. Two methods of blank correction and associated uncertainties were studied. First, the carbon blanks were quantified manometrically and the isotope ratios of the blank carbon were measured directly. Second, the isotope ratios of the blank carbon were estimated using the standard dilution method from the difference in Delta-14C values between unprocessed and processed standards. The 2 methods agreed within the uncertainties. The standard deviations of numerous Delta-14C measurements made on processed standard compounds were comparable to those of real samples. Blank correction using the standard dilution method is much less sensitive to the error in determination of blank carbon mass than is correction using the directly measured mass and Delta-14C values of the blank carbon. The standard dilution method is recommended for correcting Delta-14C analyses of small samples that involve incorporation of a significant amount of blank carbon.The Radiocarbon archives are made available by Radiocarbon and the University of Arizona Libraries. Contact [email protected] for further information.Migrated from OJS platform February 202