Conservative tracer study of horizontal sediment mixing rates in a bathyal basin, California borderland

In situ tracer (50–125 μm plastic particles) experiments conducted using the DSV Alvin over a two year period in the 1240 m deep Santa Catalina Basin (eastern Pacific) have yielded near-surface (0–1.5 cm) horizontal bioturbation rates of order 1–10 cm2yr–1. Vertical biodiffusivities obtained from the same and similar particulate tracers at the same site are approximately an order of magnitude less. Mixing of near-surface, coarse sediment in Santa Catalina Basin is anisotropic. Deeper within the sediment horizontal bioturbation is not diffusive on a two-year time scale, but would appear to be a form of mixing termed nonlocal symmetric by Boudreau and Imboden (1987), whereby particles are moved appreciable distances advectively. The finding that bioturbation in near-surface sediments is anisotropic in Santa Catalina Basin and the likelihood that this phenomenon is widespread in deep-ocean sediments calls into question the present parameterization of the effect sediment mixing has on various early diagenetic processes. Specifically, the contribution of bioturbation to organic carbon remineralization rates via microbial intermediaries may be underestimated. Bioturbation rates represent more than simply vertical mass transfer coefficients and should be incorporated into models of early diagenesis accordingly

Spatial variation in short-term (234Th) sediment bioturbation intensity along an organic-carbon gradient

Natural and human-induced spatial gradients provide a useful vehicle with which to better understand diverse marine processes. On the Palos Verdes margin (S. California), historical and ongoing waste-water discharge has created an along-shelf gradient in organic C and total N, as well as various trace metals and other pollutants (e.g., DDT). To better understand the impact of such pollution on bioturbation and to develop a more general understanding of the controlling factors of sediment bioturbation intensity, a series of stations representing severely, moderately and negligibly impacted sediments was studied. Vertical profiles of the naturally occurring radionuclide, 234Th, as well as the abundance and species composition of macrofauna were measured from box cores collected at three sites during July 1992. During a March 1993 cruise, radionuclide profiles were collected at an additional eleven sites on the margin. Excess 234Th profiles are, in general, consistent with a steady-state model that balances vertical biodiffusive mixing with radioactive decay. Biodiffusivities determined from the 234Th profiles yield a spatial pattern in which sediments near the outfall are mixed at intensities of ≈10 cm2/yr, and bioturbation intensities are five times as rapid at sites 5–7 km from the outfall. Average mixing intensities are between these extremes (28 cm2/yr) at a nearby unimpacted site. Despite the overall consistency of this pattern the reasons behind it remain unclear. Structural aspects of the macrofauna either do not vary between the three intensively studied stations (e.g., depth distribution, size) or do so in a manner that would suggest an opposite effect on the biodiffusivity (e.g., abundance). There is also little variability in trophic groupings along the enrichment gradient. Behavioral modifications, such as: (1) sublethal pollution effects caused by elevated contaminant (e.g., organic carbon and DDT) concentrations, and (2) inhibition by a tube-building polychaete, Mediomastus sp., are postulated to suppress mixing intensities near the outfall. The results of this study suggest that, at least in shallow-water settings, the general controls of bioturbation intensity are still poorly understood

Particle bioturbation in Massachusetts Bay: Preliminary results using a new deliberate tracer technique

To better understand temporal and particle size-dependent bioturbation processes, we conducted a study of sediment mixing in Massachusetts Bay using a newly developed deliberate tracer technique. Sediments from a 32-m, fine-grained site were collected and the 38–62 (“silt”) and 63–125 (“sand”) μm fractions isolated. These particle-size fractions were labeled with two different noble metals (Au: silt & Ag: sand) using a thermal diffusion technique. Mixtures of the tracers were spread onto the seafloor in April and July 1992 by divers and were tube-cored (3 replicates) ˜ 80 d later in each case. Vertical profiles of the tracers were measured at μg/g (Ag) and ng/g (Au) levels by instrumental neutron activation analysis. During the spring experiment, Au (silt) was mixed to depths \u3e 15 cm and displayed multiple subsurface maxima, whereas Ag (sand) was confined to the upper 5 cm of the bed and showed a near monotonic decrease in concentration with depth. In the fall experiment, the tracers displayed more congruent down-core profiles consisting of near-surface maxima and several subsurface peaks. Two nonlocal bioturbation modes are suggested by the tracer data: reverse conveyor-belt transport and head-down deposit feeding or excavation. A particle caching strategy by an unidentified macrofaunal species is postulated to explain the subsurface peaks, but remains conjectural without better species-level natural history information regarding solid-phase bioturbation

Experimental tests for particle size-dependent bioturbation in the deep ocean

The potential for particle size-dependent bioturbation rates was experimentally tested at 1,240 m in the Santa Catalina Basin (eastern Pacific). Spherical glass bead tracers in five size classes (8- 16, 17-31, 32-62, 63-125, and 126-420 μm) were spread over the sediment surface and tube cored 997 d later. Downcore concentrations of glass beads were enumerated in each of the five size categories and Page's L-test was used to test the null hypothesis of equal vertical penetration of all size classes of tracer. In all cores the null hypothesis was rejected; finer tracers penetrated deeper into the sediment. In two of the three cores, vertical biodiffusivities were computed from concentration profiles of downcore tracers. These also showed size dependence, with biodiffusivities ranging from 1 cm² yr¯¹ for the 8-1 6-μm fraction to 0.1 cm² yr¯¹ for the 125-420-μm size class. These data demonstrate that vertical bioturbation rates are particle size-dependent in Santa Catalina Basin. The likely cause is preferential ingestion and downward transport of fine particles by deposit feeders

Particulate organic matter export by two contrasting small mountainous rivers from the Pacific Northwest, U.S.A.

We investigated the export of particulate organic matter (POM) to the ocean by two contrasting small, mountainous rivers, the Umpqua and Eel Rivers, by collecting suspended sediment samples over a range of discharges and analyzing them for a variety of constituents, including organic carbon, nitrogen, biomarkers with distinct biochemical sources, and isotopic compositions (δ¹³C and Δ¹⁴C). Concentrations of all measured constituents in both rivers increased as a function of discharge, resulting in their export being dominated by short-lived, wintertime high-discharge events. In the Umpqua River, marked compositional contrasts between low- and high-discharge conditions were consistent with a shift in the provenance of POM from biogenic sources dominated by non-vascular plant sources at low flows to contributions from vascular plant sources of moderate ¹⁴C ages (~300 years before present) dominating at high flows. In contrast, POM from the Eel River, which was highly diluted by mineral sediment at all discharges, had significant contributions from petrogenic sources and displayed lower concentrations of recognizable biomarkers. Both rivers had comparable yields of biogenic POM, which appeared to be moderately degraded and originated primarily from surface soils in erosion prone areas of the watersheds. While tectonic/geologic differences help explain the contrasts in sediment and petrogenic POM yields between the two watersheds, ecological factors such as vegetation coverage, productivity, and soil carbon are more important in influencing the composition of biogenic POM mobilized from these systems.Keywords: Oregon Coast Range, Northern California, Mendocino triple junction, Eel River, Efffective discharge, Carbon, Continental shelf, Debris flow, United States, Sediment transpor

Inhibition of plasmin-mediated TAFI activation may affect development but not progression of abdominal aortic aneurysms

Objective: Thrombin-activatable fibrinolysis inhibitor (TAFI) reduces the breakdown of fibrin clots through its action as an indirect inhibitor of plasmin. Studies in TAFI-deficient mice have implicated a potential role for TAFI in Abdominal Aortic Aneurysm (AAA) disease. The role of TAFI inhibition on AAA formation in adult ApoE-/- mice is unknown. The aim of this paper was to investigate the effects of TAFI inhibition on AAA development and progression. Methods: Using the Angiotensin II model of AAA, male ApoE-/- mice were infused with Angiotensin II 750ng/kg/min with or without a monoclonal antibody inhibitor of plasmin-mediated activation of TAFI, MA-TCK26D6, or a competitive small molecule inhibitor of TAFI, UK-396082. Results: Inhibition of TAFI in the Angiotensin II model resulted in a decrease in the mortality associated with AAA rupture (from 40.0% to 16.6% with MA-TCK26D6 (log-rank Mantel Cox test p = 0.16), and 8.3% with UK-396082 (log-rank Mantel Cox test p = 0.05)). Inhibition of plasmin-mediated TAFI activation reduced the incidence of AAA from 52.4% to 30.0%. However, late treatment with MA-TCK26D6 once AAA were already established had no effect on the progression of AAA in this model. Conclusions: The formation of intra-mural thrombus is responsible for the dissection and early rupture in the angiotensin II model of AAA, and this process can be prevented through inhibition of TAFI. Late treatment with a TAFI inhibitor does not prevent AAA progression. These data may indicate a role for inhibition of plasmin-mediated TAFI activation in the early stages of AAA development, but not in its progression

Spatiotemporal variation in Oregon salt marsh expansion and contraction (GIS data)

The dataset is a layer file created in ArcGIS Pro 2.2. The dataset includes digitized outlines of the seaward edges of five Oregon salt marshes (Nehalem, Netarts, Salmon, Alsea, and Coquille). These are roughly decadal from 1939 to 2018 and were hand-digitized using historical aerial photography (1939 to the late 1990s) scanned at the University of Oregon’s Map & Aerial Photography Library and aerial imagery downloaded from the Oregon Statewide Imagery Program (https://www.oregon.gov/geo/Pages/imagery_data.aspx). Historical aerial imagery were georeferenced using ≥ 10 control points that were placed at stable locations including road and channel intersections, and using a second order polynomial transformation. Salt marsh areas were determined using a stable upslope edge (Pacific Marine & Estuarine Fish Habitat Partnership current extent map https://www.pacificfishhabitat.org/data/). The dataset also includes rates of salt marsh seaward edge change which was calculated using the USGS Digital Shoreline Analysis System (DSAS; https://www.usgs.gov/centers/whcmsc/science/digital-shoreline-analysis-system-dsas?qt-science_center_objects=0#qt-science_center_objects) in ArcMap 10.7.1 over roughly decadal periods from 1939 to 2018 and integrated over the period of record. DSAS automatically placed transects at 5 m intervals perpendicular to digitized marsh edges. When calculating the rate of edge change integrated over all digitized edges, regressions were fit for any transect that passed through ≥ 6 edges. Error estimates associated with the regressions were calculated with 95% confidence intervals. These rates and uncertainties can be found in the attribute tables of each shapefile.Research context: These data were collected to assess potential drivers of marsh lateral rates of expansion/contraction over the last ~80 y in five Oregon estuaries: Nehalem Bay, Netarts Bay, Salmon River Estuary, Alsea Bay, and Coquille River Estuary (focusing on marshes relatively unimpacted by dikes). These systems vary in terms of bay morphology, mean annual fluvial sediment supply, and relative sea level changes. These forcings were assessed by comparing net lateral rates of edge change within and across estuaries. Further, to assess the importance of changing land use and hydroclimate on marsh morphodynamics, roughly decadal rates of marsh expansion/contraction were compared for each estuary. These rates were binned into four distinct periods to assess the relative importance of the PDO and history of timber harvest in uplands on marsh expansion/contraction (1939 to 1944, 1944 to 1977, 1977 to 2000, and 2000 to 2018). Results will elucidated both spatiotemporal patterns of marsh lateral change and provided an idea of future trajectories under changing climate and land use scenarios