Browsing by Subject "POC"
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Item Examining The Binding of Radionuclides with Marine Biopolymers, A Comparative Study On Th, Pa, Be, Po And Pb Isotopes(2013-12-09) Chuang, Chia-YingNatural radioisotopes, Th, Pa, Pb, Po and Be, have been used as important proxies in oceanographic investigations for decades. Biopolymers, produced by both phytoplankton and bacteria, play an important role in the scavenging of these radionuclides, thus regulating the particulate organic carbon (POC)/isotope ratios in different oceanographic regions, which have been used to calculate POC flux. To study the binding mechanisms of colloidal organic material to these radionuclides, marine colloids isolated by cross-flow ultrafiltration from seawater, together with dissolved exopolymeric substances (EPS) produced by laboratory cultured diatoms were collected. By separating, identifying and characterizing radiolabeled organic carriers, the most efficient binding of many of these nuclides likely occurs to acid polysaccharide- and Fe-related protein-containing biomolecules. To differentiate between uptake to amorphous silica or associated biopolymers, radionuclides were incubated with diatom cultures of Phaeodactylum tricornutum. Partition coefficients (K_(d)) of radionuclides to different fractions of diatom cells, and the role of diatom related biopolymers were examined. More than 50% of selected radionuclides were bound to all-inclusive biopolymer fractions, and logK_(d) values of radioisotopes to whole diatom cells with or without silica frustules were similar, but logK_(d) values for cleaned silica frustules were orders of magnitude lower. Results from isoelectric focusing showed the most efficient binding sites occurring in acid-polysaccharides and iron-binding proteins. As revealed by 2D HSQC NMR spectra, the biopolymers in the HF insoluble fraction were mainly composed of carboxyl-rich, aliphatic-phosphoproteins. The concentrations of potential carrier phases for radionuclides and their K_(d) values were determined for particles collected by sediment traps deployed at the Oceanic Flux Program site off Bermuda. Chemical considerations, as well as factor analysis and correlations of logK_(d) values with chemical parameters, indicate that hydroxamate-siderophores (HS) are major classes of biopolymers that have a role in binding Po and Pa. MnO_(2) and FeO_(2), whose presence is closely related to that of HS, are also involved in binding of Pa and Po. The carbonate and biogenic silica phases are identified to be important in predicting removal and fractionation of Th and Be in the ocean.Item POC algorithms based on spectral remote sensing data and its temporal and spatial variability in the Gulf of Mexico(Texas A&M University, 2007-09-17) Son, Young BaekThis dissertation consists of three studies dealing with particulate organic carbon (POC). The first study describes the temporal and spatial variability of particulate matter (PM) and POC, and physical processes that affect the distribution of PM and POC with synchronous remote sensing data. The purpose of the second study is to develop POC algorithms in the Gulf of Mexico based on satellite data using numerical methods and to compare POC estimates with spectral radiance. The purpose of the third study is to investigate climatological variations from the temporal and spatial POC estimates based on SeaWiFS spectral radiance and physical processes, and to determine the physical mechanisms that affect the distribution of POC in the Gulf of Mexico. For the first and second studies, hydrographic data from the Northeastern Gulf of Mexico (NEGOM) study were collected on each of 9 cruises from November 1997 to August 2000 across 11 lines. Remotely sensed data sets were obtained from NASA and NOAA using algorithms that have been developed for interpretation of ocean color data from various satellite sensors. For the third study, we use the time-series of POC estimates, sea surface temperature (SST), sea surface height anomaly (SSHA), sea surface wind (SSW), and precipitation rate (PR) that might cause climatological variability and physical processes. The distribution of surface PM and POC concentrations were affected by one or more factors such as river discharge, wind stress, stratification, and the Loop Current/Eddies. To estimate POC concentration, empirical and model-based approaches were used using regression and principal component analysis (PCA) methods. We tested simulated data for reasonable and suitable algorithms in Case 1 and Case 2 waters. Monthly mean values of POC concentrations calculated with PCA algorithms. The spatial and temporal variations of POC and physical forcing data were analyzed with the empirical orthogonal function (EOF) method. The results showed variations in the Gulf of Mexico on both annual and inter-annual time scales.Item Seasonal dynamics of organic matter and inorganic nitrogen in surface waters of Alaskan Arctic streams and rivers(2015-12) Khosh, Matthew Solomon; McClelland, James W.; Dunton, Kenneth H; Liu, Zhanfei; Shank, Gerald C; Townsend-Small, AmyClimate-linked changes in hydrology and biogeochemical processes within Arctic watersheds are likely already affecting fluvial export of waterborne materials, including organic matter (OM) and dissolved inorganic nitrogen (DIN). Our understanding of Arctic watershed OM and DIN export response to climate change is hampered by a lack of contemporary baselines, as well as a dearth of seasonally comprehensive studies. This work focuses on characterizing OM and DIN concentrations and sources in six streams/rivers on the North Slope of Alaska during the entirety of the hydrologic year (May through October) in 2009 and 2010. The highest OM concentrations occurred during spring snowmelt, with results indicating that terrestrial vegetation leachates are the major source of dissolved OM, while particulate OM originates from a degraded soil source. Over the hydrologic year, soils became a progressively increasing source of dissolved OM, while autochthonous production made up a sizeable proportion of particulate OM during base flow conditions. DIN concentrations were low throughout the spring and summer and increased markedly during the late summer and fall. Our findings suggest that penetration of water into thawed mineral soils, and a reduction in nitrogen assimilation relative to remineralization, may increase DIN export from Arctic watersheds during the late summer and fall. Although recent studies of Arctic rivers have emphasized the importance of the spring thaw period on OM export, our understanding of the mechanisms that control water chemistry observations during this time are still lacking. Experimental leaching results, from experiments conducted in 2014, suggest that aboveground plant biomass is a major source of dissolved OM in Arctic catchments during the spring, and that the timing of freezing and drying conditions during the fall may impact dissolved OM leaching dynamics on that same material the following snowmelt. Improved knowledge of OM and DIN temporal trends and the mechanisms that control seasonal concentrations is essential for understanding export dynamics of these water constituents in Arctic river systems. Perhaps more importantly, increased understanding of the seasonal controls on OM and DIN export in Arctic rivers is critical for predicting how these systems will respond under future climate change scenarios.Item The Relationships of Particulate Matter and Particulate Organic Carbon with Hypoxic Conditions Along the Texas-Louisiana Shelf(2014-08-06) Zuck, Nicole AThe Mississippi-Atchafalaya river system discharges into the northern Gulf of Mexico and peaks during the spring freshet bringing high levels of nutrients that spur eutrophication in surface waters, often resulting in hypoxic (dissolved oxygen concentrations less than 1.4 mL/L) sub-pycnocline conditions. Hypoxia is generally manifest seasonally along the Louisiana coast over the shelf. In summer 2011, high rainfall in the Mississippi-Atchafalaya watershed caused high discharge into the northern Gulf of Mexico. In summer 2012 drought conditions in the watershed significantly reduced the discharge. Summer 2013 conditions returned to the climatologic average river discharge. Discrete samples were collected and continuous measurements were made via an onboard surface-water flow-through system, CTD casts, and by an undulating towed vehicle. Total particulate matter and particulate organic carbon samples were obtained from Niskin bottles on CTD casts. Samples were also taken to measure dissolved oxygen concentration and nutrients along with other hydrographic parameters. Water-column particulate matter and particulate organic carbon were analyzed to investigate the relationship between hypoxia and the composition of the particulate matter along the Texas-Louisiana shelf during different discharge rates in summer 2011 (for C:N of particulate matter), 2012 and 2013 for a larger suite of particle composition and relationship to hydrographic conditions of the Mississippi-Atchafalaya river system. The goal of this research is to determine if a statistically significant relationship is manifest, between shelf hypoxia and total particulate matter, as well as between particulate organic carbon and hypoxia, during periods of different river discharge (i.e. average, flood, or drought conditions). Correlations were identified between some variables, but no direct relationship between particulate matter and hypoxia was observed. There were however, some statistically significant changes in several parameters between summer 2013 and summer 2013.Item The Role of Particulate Matter in the Development of Hypoxia on the Texas-Louisiana Shelf(2013-07-31) Cochran, Emma MaryIn the northern Gulf of Mexico, hypoxia occurs annually during the summer on the Texas-Louisiana shelf. This study examines the distribution of particulate and dissolved components relative to hydrography, to better understand the processes controlling the development of hypoxia. Particulate matter on the Texas-Louisiana Shelf has three major sources ? river plumes, primary production, and resuspended sediments. The sources and processes controlling distribution and transport of particles are investigated using optical proxies (backscattering, chlorophyll fluorescence, Colored Dissolved Organic Matter fluorescence (CDOM)), temperature, salinity, dissolved oxygen (DO), and in-situ sampling during June and August 2011 cruises of the Mechanisms Controlling Hypoxia program (hypoxia.tamu.edu). Discrete samples of particulate matter (PM) and particulate organic carbon (POC) concentration were obtained for analysis and calibration of optical instruments interfaced with a profiling CTD, a towed undulating CTD (Acrobat), and the ship?s flow-through system along the shelf from south of Galveston, Texas, to east of the Mississippi delta. The results of this study support a previously hypothesized concept of three primary areas of organic and inorganic particle composition and processes that dominate those areas ? river-dominated water, highly productive surface waters, and clear, nutrient-poor low-productivity surface waters. The distribution and bulk composition of particulate matter in the northern Gulf of Mexico, plus the distribution of chlorophyll fluorescence and CDOM suggest that subpycnocline primary production plays a role in determining oxygen concentration in subpycnocline waters away from the river-dominated water.