Decadal Comparisons of Particulate Matter in Repeat Transects in the Atlantic, Pacific, and Indian Ocean Basins

Abstract

Basin‐wide sections of beam cp (proxy for particle concentration) in ocean basins collected during numerous oceanographic programs over the last four decades record variable concentrations in euphotic surface waters, very low concentrations through most of the water column, and very low to very high concentrations near the seafloor. Sections resampled at decadal intervals show that intense benthic nepheloid layers (BNLs) recur in the same general locations in these repeat sections, most often where eddy kinetic energy (EKE: cm2 s−2) is high in overlying waters. Areas beneath regions of low surface EKE consistently have weak to no BNLs. The decadal persistence of the close connection between surface and benthic EKE and presence or absence of BNLs is clear. Understanding the location and causes of intense versus weak BNLs helps in assessing scavenging of adsorption‐prone elements in the deep sea and quantifying the impact of deep ocean sediment dynamics on sediment redistribution.

Extent of impact of deep-sea nodule mining midwater plumes is influenced by sediment loading, turbulence and thresholds

“…7c, d, respectively. For these model runs, a dilution factor of 400,000 corresponds to a sediment concentration of 20 μg L −1 , which is around the reported background level in the CCFZ [47][48][49] . Accordingly, dilution factors of 100,000 and 40,000 correspond to plume concentrations of 80 μg L −1 and 200 μg L −1 , respectively.…”

230Th Normalization: New Insights on an Essential Tool for Quantifying Sedimentary Fluxes in the Modern and Quaternary Ocean

“…Fully assessing the merits of 230 Th normalization in regions of nepheloid layers will require identification of (1) the source(s) of the particles (resuspension of surface sediments locally, erosion and suspension of older sediments, or lateral transport from nearby topographic highs), (2) the diagenetic processes that affect the surface‐adsorption properties of resuspended particles, (3) the propagated effects of variability in nepheloid thickness and particle concentration on 230 Th scavenging, and (4) the 3‐D mass budget of 230 Th within regions of nepheloid layers. Until then, we recommend consulting global compilations of information about nepheloid layers (Gardner, Richardson, Mishonov, & Biscaye, ; Gardner, Mishonov, & Richardson, , ) and interpreting 230 Th‐normalized fluxes in these regions with caution.…”

Sources of Plutonium in the Pacific Ocean and Its Isotopic Ratio for Tracing of Ocean Circulation

“…The 239+240 Pu inventory in the water column is calculated by integrating the activity measured at each depth . The concentrations of particulate matter in the Pacific Ocean generally are high in surface waters (0.242–0.483 mg/L) and decrease rapidly to about 0.0121–0.0242 mg/L by 200–300 m as the organic matter is remineralized . In between the euphotic zone and seafloor, the concentration of small particles is generally very low. , It takes a long time (∼28.8 years) to settle from the surface to the bottom (∼4000 m) based on the Pu particles settling at a rate of 0.44 × 10 –3 cm s –1 . , Indeed, the sedimentation rate in the Pacific Ocean is often very low (0.52–1.82 cm/kyrs) .…”