Fine-scale strata formation in biologically and physically dominated estuarine systems within the lower Chesapeake and York River subestuary

To investigate the relationship between biological and physical mixing in forming strata, the lower mainstem of Chesapeake Bay has been contrasted with the York River Subestuary. By using radioisotope profiles from sediment cores, comparisons are made in terms of depth and rate of sediment mixing, deposition and accretion. Within the lower Chesapeake Bay two sites were selected as biologically dominated, both are located within the bay stem plains and are characterized by muddy sand and an abundance of large, deep-dwelling organisms. X-radiographs indicate complete biological reworking of sediments. 210Pb profiles reveal low sediment accretion rates within the mainstem sites (\u3c0.1 cm y-1), but significant differences in biological mixing depths (25 vs 40 cm) and biodiffusivity (\u3e80 vs 6--30 cm3 y-1). Within the upper York River, transient, longitudinal erosional furrows regularly form within a broad flat secondary channel. Varying furrow morphologies were observed depending on tidal flow, ranging from: (1) no bedforms during the higher flow conditions such as spring tide; to (2) large patches of meandering furrows as the mean flow decreases; to (3) large, variably spaced (5--7 m) linear furrows during the lowest mean current conditions of neap tide. A 35 month time series using kasten cores reveals that along with ∼ 25 cm differences in mixing depths due to the fortnightly time formation and destruction of furrows, a ∼ 100 cm depth scale signal of mixing exists annual to interannual time frame which is unrelated to the formation of erosional furrows. Throughout much of the energetic microtidal York River, the seabed is characterized by deep physical mixing (25--200 cm). A strong cross-estuary gradient is observed with one side, including channel, flank and shoal, dominated by frequent deep erosion and re-deposition (physical mixing), while physical mixing is reduced on the other side resulting in a greater preservation of biological mixing. Within the physically dominated side of the river, the mixed layer is characterized by 210Pb profiles with one or more segments ( ∼ 25--100 cm thick) of nearly uniform excess activity. X-radiographs reveal that the mixed layer consists of centimeter to decimeter scale units of finely to coarsely laminated strata bounded by hiatal surfaces, indicative of physical mixing. The physical mixing results in an impoverishment benthic community which is composed primarily of small, opportunistic species. Mixing in the biologically dominated side of the river is generally shallow (\u3c40 cm), with low 210Pb biodiffusion rates (0.43--3.35 cm 2 y-1). 210Pb based particle residence time within the mixed layer are on the order of centuries. Estimates of the sediment mass in the physically mixed layer is equivalent to ∼ 70 years of river sediment yield, this is consistent with century-scale residence times. Although sediment mixing within the Lower Chesapeake Bay is controlled by biological processes and sediment mixing in much of the York River is controlled by physical processes, in both places particle residence times in the seabed are generally on the century time-frame. However, when considering the cycling of pore-water nutrients, organic matter and particle bound contaminants, the type of seabed mixing is as important as the particle residence time in determining the ultimate fate and fluxes of these constituents

Particle triggered reactions as an important mechanism of alkalinity and inorganic carbon removal in river plumes

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 Geophysical Research Letters 48(11), (2021): e2021GL093178, https://doi.org/10.1029/2021GL093178.The effects of heterogeneous reactions between river-borne particles and the carbonate system were studied in the plumes of the Mississippi and Brazos rivers. Measurements within these plumes revealed significant removal of dissolved inorganic carbon (DIC) and total alkalinity (TA). After accounting for all known DIC and TA sinks and sources, heterogeneous reactions (i.e., heterogeneous CaCO3 precipitation and cation exchange between adsorbed and dissolved ions) were found to be responsible for a significant fraction of DIC and TA removal, exceeding 10% and 90%, respectively, in the Mississippi and Brazos plume waters. This finding was corroborated by laboratory experiments, in which the seeding of seawater with the riverine particles induced the removal of the DIC and TA. The combined results demonstrate that heterogeneous reactions may represent an important controlling mechanism of the seawater carbonate system in particle-rich coastal areas and may significantly impact the coastal carbon cycle.This research was funded by the National Science Foundation (NSF) and the Bi-National Science Foundation U.S-Israel award number OCE-BSF 1635388.2021-11-2

Core data collected in the Brazos River Plume, TX during 2017-2018

Dataset: Brazos Plume Core DataCore data collected in the Brazos River Plume, TX during three cruises conducted in 2017 and 2018. Cores were analyzed for grain size and mercury content. For a complete list of measurements, refer to the full dataset description in the supplemental file 'Dataset_description.pdf'. The most current version of this dataset is available at: https://www.bco-dmo.org/dataset/844548NSF Division of Ocean Sciences (NSF OCE) OCE-182922

Data supplementing article "Dramatic hydrodynamic and sedimentary responses in Galveston Bay and adjacent inner shelf to Hurricane Harvey"

This is data set used to plotting the figure that describes the relationship between surface landward current at buoy station g06010 and section-averaged landward current at the entrance of Galveston Bay

Clay-fraction strontium and neodymium isotopes, K/Al ratios, and bulk grain size from IODP Sites U1456 and U1457

This study presents data collected from International Ocean Discovery Program (IODP) Expedition 355 Arabian Sea Monsoon to investigate changes in sediment provenance as well as the effect of sediment transport processes on deep-sea sediment samples. From Site U1457, 83 sediment samples were analyzed, complemented by 44 samples from Site U1456. Samples were analyzed for bulk grain-size using a Malvern Mastersizer 2000. The clay fraction was separated, digested, and analyzed for K/Al ratios using inductively couple plasma optical emission spectroscopy (ICP-OES). Radiogenic strontium (87Sr/86Sr) was measured using a Neptune Plus multicollector inductively coupled plasma mass spectrometer (MC-ICP-MS) and a Triton Plus multicollector thermal ionization mass spectrometer (TIMS). A subset of 38 samples were analyzed for radiogenic neodymium composition (143Nd/144Nd) using TIMS

Clay-fraction strontium and neodymium isotopes in the Indus Fan: Implications for sediment transport and provenance

© The Author(s), 2020. Published by Cambridge University Press. Reconstructing the provenance of siliciclastic marine sediment is important for understanding sediment pathways and constraining palaeoclimate and erosion records. However, physical fractionation of different size fractions can occur during sediment transport, potentially biasing records derived from bulk sediment. In this study, records of radiogenic Sr and Nd isotopic composition and K/Al ratio of the separated clay fraction, as well as bulk grain size, are presented, measured from deep-sea sediments recovered from International Ocean Discovery Program (IODP) Sites U1456 and U1457 in the Arabian Sea. These new records are compared with published bulk sediment records to investigate the influence of sediment transport on these proxies and to constrain provenance evolution and its relationship to climate variability since middle Miocene time. Correlations between grain size and the bulk sediment isotopic composition confirm that transport processes are influencing the bulk sediment record. This relationship, although present, is not as strong in the clay-fraction isotopic records. Heterogeneity of bulk sediment likely drives differences between bulk and clay records, thought to be largely controlled by sediment transport processes. The isotopic records reveal variations in provenance that correlate with climatic change at 8-7 Ma, as well as an increase in overall provenance variability beginning at c. 3.5 Ma, likely linked to monsoon strength and glacial-interglacial cycles. The clay-fraction records highlight the potential value of measuring proxy records from multiple size fractions to help constrain provenance records as well as investigate sediment transport and/or weathering and erosion processes recorded in deep-sea sediment archives