ALBERT

Description: Submitted in partial fulfillment of the requirements for the degree of Doctor of Philosophy at the Massachusetts Institute of Technology and the Woods Hole Oceanographic Institution April 1985

Description: The focus of this thesis is on rates of transport of metals both across the sediment/water interface and within the sediment column of nearshore sediments. The early diagenesis of several first-row transition metals exhibiting a variety of behaviors in the ocean -- Mn, Fe, Co, Ni, and Cu -- has been studied intensively at a site in Buzzards Bay, Mass. By limiting the study to a single site, independent measurements over the seasonal cycle of the concentrations of the metals in pore water, of the pore water constituents important to metal cycling, and of particle and solute transport rates could be made at the same site. In addition, a direct, in situ study of the interaction of chemical and transport processes was undertaken using radiotracer techniques. Thus, the study emphasizes the mechanisms of metal cycling near the interface of nearshore sediments. Transport rates were estimated using excess 234Th distributions for particle transport, and pore water 222Rn deficit distributions for solute transport. Particle transport rates, modeled by analogy to Fickian diffusion, ranged from 7-80x10-8 cmz/sec, with excess 234Th reaching to 2-2.5 cm below the interface. There was a significant seasonal variation in rates, with a warm-season average of 40x10-8 cm2/sec and a cold-season average of 20x10-8 cm 2/sec. 234Th-derived mixing rates were applied to Mn distributions through a mass balance model of Mn cycling. It was found that a particulate flux due to bioturbation, from the net dissolved Mn removal layer to a net dissolved Mn production layer adjacent to the interface, was as large as 38% of net dissolved Mn production. Mixing of particulate Fe sulfides may have a similar importance for Fe cycling. Solute transport was estimated using measured 222Rn/ 226 Ra disequilibrium. The pore water 222Rn deficit could be explained using a model including vertical molecular diffusion and exchange with overlying seawater via exchange of pore water with bottom water in rapidly flushed burrows. Cores taken in all seasons could be split into three groups: (1) December through March: the 222Rn deficit was explained by vertical molecular diffusion alone; (2) early summer (June): irrigation affected the 222Rn profile to a depth of at least 20cm; (3) late summer/fall: irrigation was still important near the interface, affecting 222Rn profiles to depths of 10-12 cm. 222Rn deficits were adequately explained by an exchange parameter (a) which decreased exponentially with depth below the interface, but not by a constant-α model. Previous studies have explained irrigation using a constant exchange parameter throughout the irrigated layer. For comparative purposes, an α averaged over the upper 20 cm of the sediment column was calculated at the Buzzards Bay site: the range of depth-averaged α values found, 4-12x10-7 sec-1, is in agreement with values reported previously for a variety of nearshore sediments, using pore water Si02 as a tracer, of 1-20x10-7 sec-1. 222Rn-derived irrigation rates were applied to pore water Mn and Fe distributions. It was estimated that irrigation may contribute 20-40% of the dissolved Mn flux across the interface and about 20% of the dissolved Fe flux. Study of pore water metal chemistry at the Buzzards Bay site included measurements of pore water Mn and Fe during all seasons, and measurements of Co, Cu, and Ni in two cores: one under late winter conditions when the interface is most oxidizing; one when sulfate reduction was very important in the upper centimeter of the sediments. Fe regeneration sufficient to produce enrichments on water column particles was observed only during periods of summer and fall when the interface was reducing; otherwise, oxidation of Fe to insoluble Fe(III) limited Fe fluxes. Mn, Co, Cu, and Ni fluxes varied inversely to Fe fluxes; the primary control on fluxes of these elements was their limited solubility in reducing marine systems. The control was least important for Mn and Co; fluxes of Ni and Cu were significantly greater than zero only when sulfate reduction was unimportant in the upper centimeter of the sediment column. Fluxes of Mn were sufficient to affect the water column Mn distribution, with enrichments on water column particulates of up to 10,000 ppm inferred from calculated fluxes. Tentative estimates of the turnover time of dissolved Co, Cu, and Ni in the water column relative to the benthic flux indicated that the flux may be a significant contributor to the coastal Co cycle (turnover time = 1 yr), but is less likely to be important to Cu and Ni cycles (turnover times greater than 2 yrs). In situ radiotracer migration experiments were carried out at the Buzzards Bay site. 54Mn, 59Fe, 60Co, and 63Ni were released into the sediments at depths ranging from 2.5 to 7 cm below the interface. The order of mobilities was Mn»Fe〉Co,Ni, which is similar to the solubility trend for these metals in reducing marine systems. 63Ni and 60Co were essentially particle-bound in these experiments; apparent diffusion coefficients calculated from their dispersion rates agreed with particle mixing rates from excess 234Th distributions. Solid:solution distribution coefficients were calculated from 54Mn dispersion and found to agree with directly measured values. The coefficient was approximately 15 (dpm/gm solid ÷ dpm/gm pore water) in the upper 0.5 cm and below 5 cm, and 5-10 from 0.5 to 5 cm. Distribution coefficients for 59Fe were approximately 120 below 0.5 cm. Although the trend of the distribution coefficients is clear, the quantitative results from these experiments are preliminary, in that the model used to explain metal ion dispersion, when applied to the nonreactive tracer, 36Cl, could only explain a portion of the 36Cl distribution. The agreement between calculated and directly measured s4Mn distribution coefficients, as well as the way the distributions of tracers varied as a function of apparent diffusion coefficient and time, provides evidence in favor of the adequacy of the model used.

Description: Financial support for parts of this work have come from: National Science Foundation grant #OCE-82-16425; Department of Commerce, NOAA, National Sea Grant College Program, under grant #NA80-AA-D-00077 (R/P/7); from the Coastal Research Center of the Woods Hole Oceanographic Institution; and from the WHOI Education Office.

Description: Submitted in partial fulfillment of the requirements for the degree of Doctor of Philosophy at the Massachusetts Institute of Technology and the Woods Hole Oceanographic Institution February 2013

Description: The sinking flux of particles is an important removal mechanism of carbon from the surface ocean as part of the biological pump and can play a role in cycling of other chemical species. This work dealt with improving methods of measuring particle export and measuring export on different scales to assess its spatial variability. First, the assumption of 238U linearity with salinity, used in the 238U–234Th method, was reevaluated using a large sample set over a wide salinity range. Next, neutrally buoyant and surface-tethered sediment traps were compared during a three-year time series in the subtropical Atlantic. This study suggested that previously observed imbalances between carbon stocks and fluxes in this region are not due to undersampling by traps. To assess regional variability of particle export, surface and water-column measurements of 234Th were combined for the first time to measure fluxes on ~20 km scales. Attempts to relate surface properties to particle export were complicated by the temporal decoupling of production and export. Finally, particle export from 234Th was measured on transects of the Atlantic Ocean to evaluate basin-scale export variability. High-resolution sampling through the water-column allowed for the identification of unique 234Th features in the intermediate water column.

Description: I was supported by NASA Headquarters under the NASA Earth and Space Science Fellowship Program (Grant NNX10AO72H). Specific projects were funded by grants from the National Science Foundation, including Carbon Flux Through the Twilight Zone – New Tools to Measure Change (OCE-0628416), WAPflux – New Tools to Study the Fates of Phytoplankton Production in the West Antarctic Peninsula (ANT-0838866), and GEOTRACES Atlantic Section: Trace Element Sources and Sinks Elucidated by Short- Lived Radium and Thorium Isotopes (OCE-0925158).

Description: Submitted in partial fulfillment of the requirements for the degree of Doctor of Philosophy at the Massachusetts Institute of Technology and the Woods Hole Oceanographic Institution September, 1970

Description: A series of laboratory experiments were conducted in a glass wave tank to investigate the propagation of internal gravity waves up a sloping bottom in a fluid with constant Brunt-Vaisala frequency. Measurements of the wave motion in the fluid interior were primarily taken with electrical conductivity probes; measurements in the boundary layer were made with dye streaks and neutrally buoyant particles. The results indicate that, outside of the breaking zone, the amplitude and horizontal wave number of the high-frequency waves increase lineariy with decreasing depth; this is shown to agree with existing linear, inviscid solutions. A zone of breaking or runup is induced by these high-frequency waves well upslope. Shadowgraph observations show that, if the wave characteristics are coincident, or nearly so, with the bottom slope, the upslope propagation of the low-frequency waves causes a line of regularly spaced vortices to form along the slope. Subsequent mixing in the vortex cells creates thin horizontal laminae that are more homogeneous than the adjacent layers. These laminae slowly penetrate the fluid interior, creating a step-like vertical density structure. Available linear theoretical solutions for the velocity in the viscous boundary layer, determined to be valid for certain experimental conditions, are used to develop a criterion for incipient motion of bottom sediment induced by shoaling internal waves. The maximum sediment sizes that can be placed into motion, according to this criterion, are larger than certain mean sediment sizes on the continental margin off New England. This suggests that internal waves might induce initial sediment movement. Speculation about the geological effects of breaking and vortex instabilities is also given. These processes, not definitely measured in the field as yet, might also be conducive to sediment movement.

Description: This work was supported by the Office of Naval Research.

Description: Submitted in partial fulfillment of the requirements of the degree of Master of Science at the Massachusetts Institute of Technology and the Woods Hole Oceanographic Institution June 2004

Description: Laterally extensive, well-developed clinoforms have been mapped in Early Cretaceous deposits located in the northeastern 27,000 km2 of the Colvile Basin, North Slope of Alaska. Using public domain 2-D seismic data, well logs, core photographs, and grain size data, depositional geometries within the Nanushuk and Torok formations were interpreted in order to constrain the transport conditions associated with progradation of the shoreline and construction of the continental margin out of detritus shed from the ancestral Brooks Range. Using STRATA, a synthetic stratigraphic modeling package, constructional clinoform geometries similar to those preserved in the North Slope clinoform volume (32,400 km3) were simulated. Sediment flux, marine and nonmarine diffusivities, and basin subsidence were systematically varied until a match was found for the foreset and topset slopes, as well as progradation rates over a 6 milion year period. The ability of STRATA to match the seismically interpreted geometries allows us to constrain measures of possible water and sediment discharges consistent with the observed development of the Early Cretaceous c1inoform suite. Simulations indicate that, in order to reproduce observed geometries and trends using constant input parameters, the subsidence rate must be very small, only a fraction of the most likely rate calculated from the seismic data. Constant sediment transport parameters can successfully describe the evolution of the prograding margin only in the absence of tectonic subsidence. However, further work is needed to constrain the absolute magnitude of these values and determine a unique solution for the NPR-A clinoforms.

Description: Submitted in partial fulfillment of the requirements for the degree of Doctor of Philosophy at the Massachusetts Institute of Technology and the Woods Hole Oceanographic Institution February 2004

Description: Onshore sediment transport and sandbar migration are important to the morphological evolution of beaches, but are not understood well. Here, a new model that accounts for accelerations of wave-orbital velocities predicts onshore sandbar migration observed on an ocean beach. In both the observations and the model, the location of the maximum acceleration-induced transport moves shoreward with the sandbar, resulting in feedback between waves and morphology that drives the bar shoreward until conditions change. A model that combines the effects of transport by waves and mean currents simulates both onshore and offshore bar migration observed over a 45-day period. A stochastic nonlinear Boussinesq model for the evolution of waves in shallow water is coupled with the wave-acceleration-driven sediment transport model to predict observed onshore sediment transport and sandbar migration given observations of the offshore wave field and initial bathymetry. The Boussinesq-wave model has skill in predicting wave spectra, as well as velocity and acceleration statistics across the surfzone, but it underpredicts acceleration skewness on top of the sandbar. As a result, the coupled wave-sediment transport model underpredicts sediment transport, and thus fails to move the sandbar onshore. Although the coupled wave and sediment model can be tuned to yield skillful predictions of onshore sandbar migration, in general, closer agreement between observed and modeled statistics of the wave field is essential for the successful application of wave models to predict sediment transport.

Description: Financial support was provided by the Army Research Office (DAAD1999-1-0250 and DAAD19-03-10072); the Office of Naval Research, Coastal Dynamics and Coastal Geosciences Programs (N00014-02-10145); the National Ocean Partnership Program (B- 428260); the National Science Foundation, Physical Oceanography (OCE-01l5850); and fellowships from Conselho Nacional de Desenvolvimento Cientifico (CNPq) - Brazil (201085/97-6), and from the Academic Programs Offce of the Woods Hole Oceanographic Institution.

Description: Submitted in partial fulfillment of the requirements for the degree of Doctor of Philosophy at the Massachusetts Institute of Technology and the Woods Hole Oceanographic Institution May 1998

Description: Observations of bedforms, suspended sediment and water velocities were used to examine sediment transport processes at the sandy LE0-15 site located off the New Jersey coast. The bedforms were observed during storms using a rotary sidescan sonar and were found to be wave orbital scale ripples. The onshore migration of these ripples was forced by non-linear wave velocities, and could be related to a simple bedload model. Observations of suspended sand flux were calculated from acoustic backscattering profiles and water velocity profiles. Suspended sand transport forced by wave velocities was found to occur primarily during the weaker offshore phase of wave motion, as part of a vortex ejection mechanism. This net offshore suspended sediment flux was an order of magnitude less than the flux associated with onshore ripple migration. Thus it is hypothesized that ripple migration was forced by unobserved bedload or near bottom suspended flux. The net suspended sediment flux due to mean currents was a factor of five less than the waveforced offshore suspended flux. These wave dominated events at LE0-15 represent a contradiction of the conceptual idea that waves are primarily responsible for suspending sediment and mean currents provide the transport mechanism.

Description: Submitted in partial fulfillment of the requirements for the degree of Master of Science at the Massachusetts Institute of Technology and the Woods Hole Oceanographic Institution September 1999

Description: This study uses geophysical and sedimentological data collected from the Lower Hudson River estuary to identify the depositional response of the estuary to high river discharge events. Erosional and depositional environments in the estuary are identified through the use of side-scan sonar, bottom penetrating sonar and surficial sediment sampling. Sediment cores are used to document deposit thicknesses and to obtain the spatial distribution of estuarine deposits. Results show a high degree of spatial and temporal variability in sedimentation within the estuary. Two primary deposits are identified underneath the turbidity maximum for the estuary. Approximately 300,000 metric tons of sediment were deposited within these two deposits during May and June of 1998. This short-term accumulation underneath the turbidity maximum of the estuary can account for 30 to 98 percent of the estimated, river-borne sediment load supplied to the estuary during the 1997-1998 water year. Both the tidally produced stratigraphy observed in sediment cores and the spatial distribution of identified deposits, support the theory that sedimentation underneath the turbidity maximum of the estuary is primarily the results of a convergence in bottom water flow, caused by the formation of a salinity front during ebb tide.

Description: This research was funded by the Hudson River Foundation and a National Science Foundation Coastal Trainee Fellowship.

Description: Submitted in partial fulfillment of the requirements for the degree of Doctor of Philosophy in Geochemistry at the Massachusetts Institute of Technology and the Woods Hole Oceanographic Institution September 2019.

Description: Mineral dust is generated in continental interiors and exported by winds to ocean basins, providing a sedimentary archive which is one of the few direct indicators we have of atmospheric circulation in the past. This archive can be utilized in regions of dust transport also affected by monsoons to examine how different climate forcing mechanisms impact the monsoon regions over glacialinterglacial, orbital, and millennial timescales. This thesis generates new eolian dust records from two monsoon regions to reconstruct changes in atmospheric circulation in response to forcing by high-latitude insolation and boundary condition change. In Chapters 2 and 3 I use 230Thxsnormalization to construct high-resolution eolian dust flux records from sedimentary archives downwind from the West African and East Asian Monsoon regions respectively. The West African margin dust records show variability associated with an interplay between Northern Hemisphere summer insolation forcing and North Atlantic cooling. The longest record at ODP Site 658, stretching back to 67 ka, shows evidence for a “Green Sahara” interval from 60-50 ka and a skipped precessional “beat” from 35-20 ka. This record also shows evidence for abrupt increases in dust flux associated with Greenland stadials. The Shatsky Rise record at ODP Site 1208, downwind of East Asian dust sources, shows variability associated with glacial-interglacial boundary conditions over the last 330 ka, exhibiting high dust during glacial times. The record also exhibits variability associated with a Northern Hemisphere summer insolation control at times overriding the glacialinterglacial signal. In Chapter 4 I demonstrate the feasibility of using radiogenic neodymium isotopes (143Nd/144Nd) at IODP Site U1430 in the Sea of Japan to fingerprint the provenance of eolian material at the core site from Asian dust sources. I then generate a 143Nd/144Nd record from isolated eolian material over the last 200 ka to examine Westerly Jet behavior in the Asian interior, which shows resolvable orbital-scale variability from 200 to 100 ka, and muted variability from 100 to 0 ka. The findings imply a quicker shift of the Westerly Jet to the north of the Tibetan Plateau during times of high Northern Hemisphere summer insolation and a strong Asian monsoon.

Description: This thesis research was supported by the National Science Foundation under Grant Nos. OCE-1030784 and EAR-1434138 and a Post-expedition activity award through the U.S. Science Support Program, Integrated Ocean Drilling Program. Kinsley was supported by fellowships from the MIT Department of Earth, Atmospheric, and Planetary Sciences in his first year of graduate school and the WHOI Academic Programs Office in his sixth year of graduate school.

Description: Submitted in partial fulfillment of the requirements for the degree of Doctor of Philosophy at the Massachusetts Institute of Technology and the Woods Hole Oceanographic Institution October, 1977.

Description: Sediment traps designed to yield quantitative data of particulate fluxes have been deployed and successfully recovered on four moorings in the deep sea. The traps were designed after extensive calibration of different shapes of containers. Further intercalibration of trap design was made in field experiments over a range of current velocities. Experiments with Niskin bottles showed that concentrations of suspended particulate matter obtained with standard filtration methods were low and had to be increased by an average factor of 1.5 to correct for particles settling below the sampling spigot. The trap arrays were designed to sample the particulate fluxes both immediately above and within the nepheloid layer. The data derived from the traps have been used to estimate vertical fluxes of particles including, for the first time, an attempt to distinguish between the flux of material settling from the upper water column (the "primary flux") and material which has been resuspended from some region of the sea floor (resuspension flux). From these data and measurements of the net nepheloid standing crop of particles one can also estimate a residence time for particles resuspended in the nepheloid layer. This residence time appears to be on the order of days to weeks in the bottom 15 m of the water column and weeks to months in the bottom 100 m. Between 80% and 90% of the particles collected in the six traps where particle size was measured were less than 63 μm. The mean size of particles collected in the nepheloid layer was about 20 μm, and above the nepheloid layer the mean was 11 μm. Less than 3% of the organic carbon produced in the photic zone at the trap sites was collected as primary flux 500 m above the sea floor. The primary flux measured at two sites was enough to supply 75% on the upper Rise and 160% on the mid Rise of the organic carbon needed for respiration and for burial in the accumulating sediments. From an intercomparison of the composition of particles falling rapidly (collected in traps), falling slowly or not at all (collected in water bottles), and resting on the sea floor (from a core top), it was determined that elements associated with biogenic matter, such as Ca, Sr, Cu, and I, were carried preferentially by the particles falling rapidly. Once the particles reached the bottom, the concentration of those elements was decreased through decomposition, respiration, or dissolution. Dissolution appears rapid in the vicinity of the sea floor, because despite an abundance of radiolarians, diatoms, and juvenile foraminifera collected in all traps, these forms were rare in core samples. The dynamic nature of thenepheloid layer makes it possible for particles to be resuspended many times before they are finally buried. This enables sediment to be carried long distances from its origin. The recycling of particles near the sea floor may increase dissolution of silicious and carbonate matter.

Description: Financial aid was provided in the form of a research assistantship from the Office of Naval Research through MIT and WHOI.

Description: Submitted in partial fulfillment of the requirements for the degree of Doctor of Philosophy at the Massachusetts Institute of Technology and the Woods Hole Oceanographic Institution June 2003

Description: This thesis examines the evolution of a mud-dominated coastal sedimentary system on multiple time scales. Fine-grained systems exhibit different properties and behavior from sandy coasts, and have received relatively little research attention to date. Evidence is presented for shoreline accretion under energetic conditions associated with storms and winter cold fronts. The identification of energetic events as agents of coastal accretion stands in contrast to the traditional assumption that low-energy conditions are required for deposition of fine-grained sediment. Mudflat accretion is proposed to depend upon the presence of an unconsolidated mud sea floor immediately offshore, proximity to a fluvial sediment source, onshore winds, which generate waves that resuspend sediment and advect it shoreward, and a low tidal range. This study constrains the present influence of the Atchafalaya River on stratigraphic evolution of the inner continental shelf in western Louisiana. Sedimentary and acoustic data are used to identify the western limit of the distal Atchafalaya prodelta and to estimate the proportion of Atchafalaya River sediment that accumulates on the inner shelf seaward of Louisiana's chenier plain coast. The results demonstrate a link between sedimentary facies distribution on the inner shelf and patterns of accretion and shoreline retreat on the chenier plain coast.

Description: Among my funding sources was a two-year fellowship from the Clare Booth Luce Foundation. I have received research grants from the Geological Society of America Foundation (Grant 6873-01) and the American Association of Petroleum Geologists (Kenneth H. Crandall Memorial grant).