Plastics Distribution and Degradation on Lake Huron Beaches
The resistivity of plastic debris to chemical and mechanical weathering processes poses a serious threat to the environment. Numerous marine beaches are littered with plastic fragments that entangle and become ingested by organisms including birds, turtles and plankton. Although many studies have been conducted to determine the amount and effects of plastics pollution on marine organisms, relatively little is known about the distribution and quantity of polymer types along lacustrine beaches. Plastic particles sampled from selected beaches on Lake Huron were analyzed using Fourier Transform Infrared Spectroscopy (FTIR) to determine polymer composition. The majority of the plastic fragments are industrial pellets composed of polypropylene and polyethylene. Varying degrees of oxidation are indicated by multiple irregular peaks in the lower wavenumber region on the FTIR spectra. The oxidized pellets also represent the plastic particles with the most pronounced surface textures, as identified using Scanning Electron Microscopy (SEM). Crazes and flakey, fibrous, or granular textures are consistent with chemical weathering processes, whereas gauges and pits occur through abrasion during mechanical weathering. Further textural and compositional analysis will indicate which polymer types are more resistant to weathering processes. Additional investigation of the distribution of plastic debris along the beaches of Lake Huron will indicate the amount and primary transport directions of resistant plastic debris polluting one of Ontario's Great Lakes.
Chemistry in Clean Marine Air
Model-measurement comparisons of HOx in extremely clean air ([NO]<3 ppt) are reported. Measurements were made during the second Southern Ocean Photochemistry Experiment (SOAPEX-2), The free-radical chemistry was studied using a zero-dimensional box-model based upon the Master Chemical Mechanism (MCM). Two versions of the model were used, with different levels of chemical complexity, to explore the role of hydrocarbons upon free-radical budgets under very clean conditions. The "detailed" model was constrained to measurements of CO, CH4 and 17 NMHCs, while the "simple" model contained only the CO and CH4 oxidation mechanisms, together with inorganic chemistry. The OH and HO2 (HOx) concentrations predicted by the two models agreed to within 5-10%. The model results were compared with the HOx concentrations measured by the FAGE (Fluorescence Assay by Gas Expansion) technique during four days of clean Southern Ocean marine boundary layer (MBL) air. The models overestimated OH concentrations by about 10% on two days and about 20% on the other two days. HO2 concentrations were measured during two of these days and the models overestimated the measured concentrations by about 40%. Better agreement with measured HO2 was observed by using data from several MBL aerosol measurements to estimate the aerosol surface area and by increasing the HO2 uptake coefficient to unity. This reduced the modelled HO2 overestimate by ~40%, with little effect on OH, because of the poor HO2 to OH conversion at the low ambient NOx concentrations. Local sensitivity analysis and Morris One-At-A-Time analysis were performed on the "simple" model, and showed the importance of reliable measurements of j(O1D) and [HCHO] and of the kinetic parameters that determine the efficiency of O(1D) to OH and HCHO to HO2 conversion. A 2σ standard deviation of 30-40% for OH and 25-30% for HO2 was estimated for the model calculations using a Monte Carlo technique coupled with Latin Hypercube Sampling (LHS).
Multiproxy Comparison of Climatic and Oceanographic Conditions in the Subtropical North Atlantic During the Last 20,000 Years
The Bermuda Rise is an important location for monitoring changes in the deep ocean circulation and climatic conditions in the western subtropical Atlantic Ocean. This is true in part because fine sediments from a far larger area are transported laterally and deposited here, where their rapid accumulation allows great temporal resolution for paleoceanographic studies. Applying the unsaturation ratio in alkenone biomarkers, a commonly utilized indicator of sea-surface temperature, is thus problematic at this crucial location. Prior analysis of GGC5, a sediment core from the Bermuda Rise, demonstrated that the 14C age of alkenone biomarkers are offset in age on average > 5,000 years compared with coarser, sand-sized, microfossil foraminifera shells that are more likely to accumulate vertically and remain in situ. This is attributed to the complicated bottom ocean circulation in the form of re-circulating gyres that characterize the region. It also suggests that the alkenones may be from as distant a location as Nova Scotia in origin. This study presents results from a new indicator of sea-surface temperatures, the TEX86 organic compound produced by marine archaea, which has recently been shown to have minimal 14C age offset from foraminifera shells in the same samples at the Bermuda Rise, along with the more established Uk'37 alkenone unsaturation ratio. These are then compared with prior reconstructions, especially the 231Pa/230Th tracer for the strength of the deep ocean circulation, as well as the climatic indices of δ18O, and an older Uk'37 record. The TEX86 shows a high resemblance to δ18O and 231Pa/230Th (r2 = 0.8), suggesting the sea surface temperature (SST), ocean circulation, and salinity / global ice volume are strongly related. The analyses from Bermuda Rise are then compared with RAM, Uk'37 and Uk37 estimates of SST from a core on the Iberian Margin, SU8118. These SST proxies show similar trends and highly compare with those in the Bermuda Rise. Together, they demonstrate that the climate was colder during the deglacial Heinrich iceberg discharge event (H1) than during the Last Glacial Maximum (LGM) by approximately 5°C at the Bermuda Rise and 7°C at the Iberian Margin. The 231Pa/230Th at Bermuda Rise illustrates that the ocean circulation was slower during H1 than the LGM. In fact, the 231Pa/230Th approached 0.093, its production ratio and suggests a dramatic reduction in ocean heat transport. The δ18O reconstruction is also characterized by an increase near H1 from approximately 1.75 to 2.5 ‰, equivalent to several degrees cooling. The comparison of these several proxies in two different regions of the subtropical North Atlantic provides strong evidence that the climate was more extreme during a time interval in the deglaciation than during LGM, most likely due to greatly diminished oceanic meridional overturning circulation.
High Resolution Geophysical Survey of Western Long Island Sound Offshore New York: An Estuary Floor Shaped by Bottom Currents and Human Activity
Western Long Island Sound near metropolitan New York averages 16m in water depth, with a few elongated
depression up to 40 m deep. In June 2006, we surveyed the westernmost section of Long island Sound with
the R/V HUGH SHARP. Analysis of the high-resolution multibeam bathymetric data collected during that survey
reveals a series of sedimentary features that are consistent with a net westward direction of bottom currents.
These features include: (1) Large sedimentary waves spaced ab out 100 m west of two km-scale features
outcropping through the sediments; (2) Prominent sediment drifts or scour marks west of numerous
shipwrecks and bouldery outcrops; (3) Series of subtle, sub-parallel sedimentary furrows aligned in a general
EW direction along the north slope of the surveyed area (similar features have been documented in north-
central Long Island Sound - (Poppe et al., J. Coastal Res. 2002). The lack of short wavelength sedimentary
waves is consistent with the known muddy substrate and weak bottom currents (<10 cm/s) documented in
western Long Island Sound. Fields of pockmarks affecting areas of gas-charged sediments may indicate
localized, active venting of fluids and/or gas. The high-resolution bathymetry also highlights numerous
anthropogenic disturbances such as pipelines, cables, shipwrecks, anchor drag marks, and dredge spoils.
Three-Dimension Temperature Structure of Cold Eddy-Upwelling System off Northeastern Taiwan in Summer and Winter
According to the World Ocean Atlas 2005 with the research and development of the computer programs about data analysis and figure manifestation, the three-dimension temperature structures for Cold eddy-upwelling system off northeastern Taiwan in summer and winter are displayed and studied. The influences of Kuroshio, Taiwan warm current and continental shelf current on the cold eddy-upwelling system are analyzed. The results show: (1) In the summer, as August, the cold eddy is divided into two layers, the upper (13-100m) and the bottom (138-150m). In the winter, as February, the cold eddy only exists the water layer between 109m and 150m, according the isotherm distribution. (2) The upwelling in the center of the cold eddy is continuing. Because the bottom colder water from the shelf of the East China Sea and the warmer water from the bottom of Taiwan Strait, which wedge the water layer between 100m and 138m, the isotherm which token Cold eddy is not close there. (3) At the region where Kuroshio intrudes the shelf of the East China Sea toward northeast is stronger, Cold Eddy-upwelling system becomes stronger. At the layer where Kuroshio intrudes the shelf toward northwest is strong, Cold Eddy-upwelling system becomes weaker or disappear.
Numerical Simulation of Supercritical Trapped Internal Waves Over Topography
The flow of density stratified fluids such as the atmosphere and oceans over topography has long been known to generate a variety of waves. We have developed a fully nonlinear theory for supercritical internal waves trapped over isolated topography. The theory yields a nonlinear elliptic problem and can include background shear. A pseudospectral, iterative solver is used to study this problem with shear background currents over valley-like topography. Trapped waves are found to have very large amplitudes for certain background currents. Small changes in the shear of the background current tend to have an interesting impact on the size of the wave. Of particular interest is the transition between large and small amplitude waves; the iterative solver produces different transition points depending on how the background current was changed and thereby yields a hysteresis loop. Several background current-density stratification combinations have led to regions of breaking and trapped cores.
Vigorous internal tides induced potential pumping of nutrients to upper layers of the South China Sea
Barotropic tides propagate westward from the Northwest Pacific Ocean (NPO), impinge on two prominent meridional-running ridges in the Luzon Strait, and generate dramatic internal (baroclinic) tides propagating towards the South China Sea (SCS) and the NPO. In the northern SCS, the interaction of these internal tides with steep shoaling topography, e.g. Dongsha Plateau, may transport nutrient-rich subsurface waters upward to the euphotic layer and enhance vertical mixing, which may in turn elevate biological growth in the upper oceans. A 3-D baroclinic tide model coupled with a biogeochemical model is developed to simulate the internal tides and to evaluate their influence on the nutrient concentrations as well as the primary productivity in the upper layer. Results derived from scenario model runs suggest that the pumping of nutrients by the action of internal tides could support 3.5-6.6% of the daily primary productivity which is 410 mg-C/m/m/d on average.
Benthic-Pelagic Coupling on the Louisiana Continental Shelf
An expansive area of bottom-water hypoxia occurs annually during the summer on the Louisiana continental shelf (LCS). The formation of these hypoxic waters has been linked to spring Mississippi River nutrient loading. Inferred in this linkage is the remineralization of nutrients, in both the sediments and water-column, to support primary production (PP) across the LCS. Benthic-pelagic interactions also mediate bottom-water O2 concentrations and provide a nitrogen sink through production of N2. To investigate the role of benthic- pelagic coupling processes we measured water-column PP, sediment-water interface fluxes of nutrients, N2, O2, and DIC, and concentrations of biogeochemically active substrates in sediments across the LCS during 5 cruises spanning 2006 and 2007. Measurements of PP indicated that a substantial fraction of PP (25-50%) occurred below the pycnocline. Thus, N and P remineralized from the sediments were directly available to primary producers, even when the water-column was strongly stratified. Sediment N2 fluxes (range = 0.0-1.2 mmoles N2 m-2 d-1) indicated a large potential sink for Mississippi River N loads. Sediment oxygen consumption (SOC) rates (range = 0-24 mmoles O2 m-2 d-1) were dependent on bottom-water O2 concentrations (range = 13-135 mmoles O2 m-3). Total sediment metabolism rates, approximated from sediment DIC fluxes (range = 8-21 mmoles C m-2 d- 1), did not vary significantly across the LCS and were insensitive to changes in bottom-water O2 concentrations. The accumulation of reduced anaerobic end-products under conditions of low bottom-water O2 concentrations may be important in maintaining hypoxia through summer.
Seasonal and episodic effects (dust storm) on nutrient dynamics in the upwelling across shelf break on the East China Sea to the Kuroshio Water, northeastern Taiwan
An upwelling has been frequently observed at shelf break on the East China Sea to the Kuroshio Water, northeastern of Taiwan, a traditional fishing ground. There is however limited information on its magnitude, seasonal dynamics, and biogeochemical processes. In addition, the upwelling also locates on the track of the Asian dust storm occurred in late winter to early spring. To reveal the seasonal nutrient dynamics and its potential impacts by the Asian dust storm, transect stations across the upwelling was visited with 1-3 months interval during November 2003 to January 2005. Results of T-S diagrams showed that the upwelling was mostly characteristics of the subsurface Kuroshio Water with seasonal fluctuation. Depth profiles of water temperature indicate that the upwelling was persistent year round, and the most intensified upwelling was observed during the winter period where the subsurface water upwelled to the water surface with the center of cold dome moving shelfward to the East Chinas Sea. Concentration of dissolved inorganic nitrogen averaged over 100 m was however the highest during the dust storm intrusion with mean value of 8.68 μM. As expected, nitrate concentration was significantly related to water temperature and phosphate in each cruise. Interestingly, the molar ratio of nitrate to phosphate (i.e., N/P ratio) is significantly larger than 16 during the dust storm period, and the N/P ratio are equal to or smaller than 16 in the other seasons. To compare, nitrate concentration was estimated using empirical function deriving from water temperature and nitrate for all pooled data except that in the dust storm period. Measured nitrate concentrations are similar to the estimated values except that during the dust storm period which needed significant amount of extraneous nitrate to compensate the estimation. It suggests that aerosol deposition via the Asian dust storm might be the potential external source for inorganic nutrients, thereafter it might have important effects on the biogeochemical fluxes in the oligotrophic Kuroshio Water.
Particulate Scavenging and Lateral Transport Processes in the Gaoping Submarine Canyon Deduced From Pb-210 and Po-210 Observations
Pb-210 and Po-210 were measured on the suspended particulate matter(SPM) and filtered water samples collected in profile from five stations in the Gaoping Submarine Canyon (GPSC) during a cruise aboard R/V Ocean Researcher III in late November, 2006. These stations were selected along the axis of the GPSC, and denoted as CW1 through CW5 sequentially from the shallow part near the mouth of the Gaoping River to the deep-water region of the canyon. Except for CW4, the SPM profiles generally show a rapid increase to a maximum near bottom, the value of which is an order of magnitude higher than that observed above, suggesting a significant particulate resuspension or lateral input in the bottom layer. The SPM concentrations obtained at canyon head stations(CW1 to CW3) vary between 0.36 and 19.17 mg/kg. These values are generally higher than those obtained farther outward(CW4 and CW5), which range from 0.01 to 2.13 mg/kg, indicating a decrease away from the shore. The dissolved Pb-210 and Po-210 profiles observed from CW1 and CW2 are fairly uniform for the entire water column, with a mean of about 14 and 12 dpm/100kg, respectively. The other stations show a large variation in dissolved Pb-210 and Po-210 with a mean of about 23 and 14 dpm/100kg, respectively. At stations CW1, CW2 and CW3, the particulate Pb-210 and Po-210 profiles generally display a maximum around 28-38 and 27-48 dpm/100kg, respectively, in the bottom layer, suggesting significant particulate resuspension and scavenging. Variable Pb-210 and Po-210 activities in the particulates at CW4 and CW5 are observed in the surface layer. Both the dissolved and the total (dissolved + particulate) Po-210 to Pb-210 activity ratios vary between 0.1 and 1.7, mostly less than 1.0, with a mean of 0.7 and 0.8, indicating a variable deficiency of Po-210 relative to Pb- 210 in this study area. Total activities of Pb-210 are generally higher than those of Po-210. The Ra-226 profiles show much lower activities than those of the corresponding Pb-210 and Po-210, indicating large excesses of both Pb-210 and Po-210 over its parent , Ra-226. Assuming at steady-state, the mean residence times for the dissolved and particulate Pb-210 in the surface mixed layer are 0.6-1.3 and 0.8-3.9 years, respectively. The residence times of dissolved and particulate Po-210 are 0.4-2.6 and 0.1-0.4 years, respectively. The mean residence times are estimated to be on the order of days if advection terms are taken into account.
Anthropogenic Lead Invasion to the Abyssal North Pacific Ocean
The North Pacific abyssal water is considered as one of the most pristine waters of the world ocean that has not been contaminated by anthropogenic subtances such as bomb tritium and chloroflurocarbon. Here we report measurements of seawater dissolved lead (Pb) concentration and stable Pb isotopic composition to show that anthropogenic Pb has invaded this water. The anthropogenic Pb input triples dissolved Pb concentration along the deep-water flow path and increases 206Pb/207Pb ratio from ~1.16 in the upper 600 m of the water column to ~1.19 at 4000-5000 m. Simple model calculation using our data implies that anthropogenic Pb is transported by sinking particle and released to the deep ocean and that the anthropogenic Pb source has a 206Pb/207Pb ratio decreasing with time during the past few centuries.