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 September 2014

Description: The great geologic and climatic diversity of the Fraser River basin in southwestern Canada render it an excellent location for understanding biogeochemical cycling of sediments and terrigenous organic carbon in a relatively pristine, large, temperate watershed. Sediments delivered by all tributaries have the potential to reach the ocean due to a lack of main stem lakes or impoundments, a unique feature for a river of its size. This study documents the concentrations of a suite of dissolved and particulate organic and inorganic constituents, which elucidate spatial and temporal variations in chemical weathering (including carbonate weathering in certain areas) as well as organic carbon mobilization, export, and biogeochemical transformation. Radiogenic strontium isotopes are employed as a tracer of sediment provenance based on the wide variation in bedrock age and lithology in the Fraser basin. The influence of sediments derived from the headwaters is detectable at the river mouth, however more downstream sediment sources predominate, particularly during high discharge conditions. Bulk radiocarbon analyses are used to quantify terrestrial storage timescales of organic carbon and distinguish between petrogenic and biospheric organic carbon, which is critical to assessing the role of rivers in long-term atmospheric CO2 consumption. The estimated terrestrial residence time of biospheric organic carbon in the Fraser basin is 650 years, which is relatively short compared to other larger rivers (Amazon, Ganges-Brahmaputra) in which this assessment has been performed, and is likely related to the limited floodplain storage capacity and non-steady-state post-glacial erosion state of the Fraser River. A large portion of the dissolved inorganic carbon load of the Fraser River (〉80%) is estimated to derive from remineralization of dissolved organic carbon, particularly during the annual spring freshet when organic carbon concentrations increase rapidly. This thesis establishes a baseline for carbon cycling in a largely unperturbed modern mid-latitude river system and establishes a framework for future process studies on the mechanisms of organic carbon turnover and organic matter-mineral associations in river systems.

Description: Principle funding for this thesis was provided by grants from the National Science Foundation (OCE-0851015, OCE-0851101, and EAR-1226818). Financial support for field and analytical work was also provided by the WHOI Ocean Ventures Fund, James and Jane Orr, the WHOI Deep Ocean Exploration Institute for supporting the 2011 Geodynamics Program study tour, the MIT Student Assistance Fund, NSF grant OCE-0928582, the LightHawk organization, the WHOI Coastal Ocean Institute, the MIT PAOC Houghton Fund, the Friends of Switzerland Stratton Fellowship, and the WHOI Academic Programs 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: In this thesis we present results from inversion of data using dense arrays of collocated seismic and magnetotelluric stations located in the Cascadia subduction zone region of central Washington. In the migrated seismic section, we clearly image the top of the slab and oceanic Moho, as well as a velocity increase corresponding to the eclogitization of the hydrated upper crust. A deeper velocity increase is interpreted as the eclogitization of metastable gabbros, assisted by fluids released from the dehydration of upper mantle chlorite. A low velocity feature interpreted as a fluid/melt phase is present above this transition. The serpentinized wedge and continental Moho are also imaged. The magnetotelluric image further constrains the fluid/melt features, showing a rising conductive feature that forms a column up to a conductor indicative of a magma chamber feeding Mt. Rainier. This feature also explains the disruption of the continental Moho found in the migrated image. Exploration of the assumption of smoothness implicit in the standard MT inversion provides tools that enable us to generate a more accurate MT model. This final MT model clearly demonstrates the link between slab derived fluids/melting and the Mt. Rainier magma chamber.

Description: Funding for this work was made possible by the American Society for Engineering education through a National Defense Science and Engineering Fellowship, and by the National Science Foundation through two grants for the CAFE and CAFE MT projects.

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 2014

Description: Marine particles include living and non-living solid components of seawater, representing a dynamic and chemically diverse mixture of phases. Through a combination of method development, basin-scale particulate collection and analyses, modeling, and field experiments, this thesis examines both the distributions of marine particulate trace metals and the underlying processes—inputs, scavenging, vertical and horizontal transport, and biotic uptake—in which marine particles participate. I first present the results of an intercalibration exercise among several US laboratories. We use inter-lab and intra-lab total elemental recoveries of these particles to determine our state of our intercalibration and to identify means of future improvement. We present a new chemical method for dissolution of polyethersulfone filters and compare it to other total particle digestion procedures. I then present the marine particulate distributions of the lithogenic elements Al, Fe, and Ti in the North Atlantic GEOTRACES section. A one-dimensional multi-box model that describes lithogenic particle distributions is also proposed and its parameter sensitivities and potential implications are discussed. I conclude with presentation of results from a series of bottle incubations in iron-limited waters using isotopically labeled Fe-minerals. We demonstrate solubilization of minerals ferrihydrite and fayalite via transfer of isotopic label into suspended particles.

Description: Funding was provided by the Williams College Tyng Fellowship, the MIT/WHOI Academic Programs Office, the International and US GEOTRACES Offices, and U.S. National Science Foundation (NSF) #0960880 and #0963026 and PLR #0838921 to P.J. Lam.

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 2014

Description: Here I use a simple numerical model of reef profile evolution to show that the presentday morphology of carbonate islands has developed largely in response to late Pleistocene sea level oscillations in addition to variable vertical motion and reef accretion rates. In particular, large amplitude ‘ice-house’ sea-level variability resulted in long lagoonal depositional hiatuses, producing the morphology characteristic of modern-day barrier reefs. Reactivation of carbonate factories, transport of coarse reef material and rapid infilling of shallow water accommodation space since deglaciation makes these unique sites for reconstructing Holocene climate. Integration of new tropical cyclone reconstructions from both backbarrier reef (central Pacific) and carbonate bank (the Bahamas) settings with existing storm archives suggests a coordinated pattern of cyclone activity across storm basins since the late Holocene. Seesawing of intense tropical cyclone activity between the western Pacific (~0-1000 yrs BP) and North Atlantic/Central Pacific (~1000-2500 yrs BP) appears closely tied with hydrographic patterns in the tropical Pacific and El Niño-like variability. Decoupling of North Atlantic (inactive) and South Pacific (active) tropical cyclone patterns during the mid-Holocene suggests precession driven changes in storm season insolation may constrain ocean-atmosphere thermal gradients and therefore cyclone potential intensity on orbital timescales.

Description: I was funded by the Ocean and Climate Change Institute, a MIT Presidential fellowship, SERDP and the WHOI Academic Programs 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 2014

Description: At the land-ocean interface, terrestrial groundwater interacts with seawater to form a subterranean estuary, which can play host to dynamic biogeochemical cycling of nutrients, trace metals and radionuclides. This chemically altered groundwater enters the ocean through submarine groundwater discharge (SGD), a process that is driven by a number of physical processes acting on aquifers and the coastal ocean. In this thesis, seasonal variability in chemical cycling and associated loading to the coastal ocean was observed in a monthly time series within the Waquoit Bay (MA, USA) subterranean estuary. The position of the aquifer mixing zone moved seaward with an increase in hydraulic gradient, resulting in low salinity conditions and reduced mixing, while a decrease in gradient led to landward movement, high salinity groundwater and enhanced mixing. At this location, seasonal variability in sea level, not groundwater level, was the dominant variable driving the hydraulic gradient and therefore SGD. Fluxes of sediment bound cations to the ocean increased coincidently with sea level rise due to desorption. There was enhanced nitrogen attenuation during winter, potentially due to longer groundwater residence times, with greater nutrient delivery to coastal waters during the spring and summer bloom. Interannual climate fluctuations that control sea level and precipitation may ultimately control the timing and magnitude of chemical and water flux via SGD. In addition to temporal variability, aquifer lithology influences chemical export. This thesis also demonstrates that SGD from karst subterranean estuaries may play a role in local and global element budgets. The potential for the chemical signature of SGD to be recorded in the coral record was tested through a combination of coral culture experiments and field and modeling studies in the Yucatan Peninsula. Coral barium was well correlated with precipitation for a twelve-year record, with coral geochemistry reflecting the passage of a hurricane in 2002. While additional complexities in deciphering coral records remain, this proxy offers the potential to extend SGD records into the past.

Description: This research was supported by a National Defense Science and Engineering Graduate Fellowship, a National Estuarine Research Reserve Graduate Fellowship from the National Oceanic and Atmospheric Administration, and grants from the U.S. Geological Survey (G10AC00210) and the U.S. National Science Foundation (OCE-0425061, OCE-0751525 and OCE-0524994). Additional funds were provided by the WHOI Academic Programs Office, WHOI Ocean and Climate Change Institute, and MIT endowed funds.

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 2013.

Description: Iron is a redox active trace metal micronutrient essential for primary production and nitrogen acquisition in the open ocean. Dissolved iron (dFe) has extremely low concentrations in marine waters that can drive phytoplankton to Fe limitation, effectively linking the Fe and carbon cycles. Understanding the marine biogeochemical cycling and composition of dFe was the focus of this thesis, with an emphasis on the role of the size partitioning of dFe (〈0.2μm) into soluble (sFe〈0.02μm) and colloidal (0.02μm〈cFe〈0.2μm) size fractions. This was accomplished through the measurement of the dFe distribution and size partitioning along basin-scale transects experiencing a range of biogeochemical influences. dFe provenance was investigated in the tropical North Atlantic and South Pacific Oceans. In the North Atlantic, elevated dFe (〉1 nmol/kg) concentrations coincident with the oxygen minimum zone were determined to be caused by remineralization of a high Fe:C organic material (vertical flux), instead of a laterally advected low oxygen-high dFe plume from the African margin. In the South Pacific Ocean, dFe maxima near 2000m were determined by comparison with dissolved manganese and 3He to be caused by hydrothermal venting. The location of these stations hundreds to thousands of kilometers from the nearest vents confirms the "leaky vent" hypothesis that enough dFe escapes precipitation at the vent site to contribute significantly to abyssal dFe inventories. The size partitioning of dFe was also investigated in order to trace the role of dFe composition on its cycling. First, the two most commonly utilized methods of sFe filtration were compared: cross flow filtration (CFF) and Anopore filtration. Both were found to be robust sFe collection methods, and sFe filtrate through CFF (10 kDa) was found to be only 74±21% of the sFe through Anopore (0.02μm) filters at 28 locations, a function of both pore size differences and the natural variability in distribution of 10kDa- 0.02μm colloids. In the North Atlantic, a colloidal-dominated partitioning was observed in the surface ocean underlying the North African dust plume, in and downstream of the TAG hydrothermal system, and along the western Atlantic margin. However, cFe was depleted or absent at the deep chlorophyll maximum. A summary model of dFe size partitioning in the North Atlantic open ocean is presented in conclusion, hypothesizing that a constant dFe exchange between soluble and colloidal pools modulates the constant partitioning of nearly 50% dFe into the colloidal phase throughout the subsurface North Atlantic Ocean, while sFe and cFe cycle independently in the upper ocean.

Description: Funding for this research was provided by an MIT Presidential Fellowship, an NSF Graduate Research Fellowship (# 0645960), a fellowship from the Martin Family Society of Fellows for Sustainability, several NSF Chemical Oceanography grants (OCE-0751409, OCE-07020278, OCE- 0926204, and OCE-0926197), and the Center for Microbial Oceanography: Research and Education (NSF OIA #EF-0424599).

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 February 2012

Description: Global warming has led to a significant increase in Greenland ice sheet (GrIS) melt and runoff since 1990, resulting in escalated export of fresh water and associated sediment to the surrounding North Atlantic and Arctic Oceans. Similar to alpine glacial systems, surface meltwater on ice sheet surface drains to the base (subglacial) where it joins a drainage system and can become chemically enriched from its origin as dilute snow- and ice-melt. In this thesis, I examine the interdependence of glacial hydrology and biogeochemical cycling in terms of export of carbon and iron from the Greenland ice sheet. I develop a new isotope mixing-model to quantify water source contributions to the bulk meltwater discharge draining a GrIS outlet glacier. Results illustrate (a) the new application of a naturally occurring radioisotope (radon-222) as a quantitative tracer for waters stored at the glacier bed, and (b) the seasonal evolution of the subglacial drainage network from a delayed-flow to a quick-flow system. Model results also provide the necessary hydrological context to interpret and quantify glacially-derived organic carbon and iron fluxes. I combine bulk- and molecular-level studies of subglacial organic carbon to show that GrIS discharge exports old (radiocarbon depleted), labile organic matter. Similar investigations of dissolved and particulate iron reveal that GrIS discharge may be a significant flux of labile iron to the North Atlantic Ocean during the summer meltseason. Both carbon and iron are subject to proglacial processing prior to export to the marine environment, and exhibit strong seasonal variability in correlation with the subglacial drainage evolution. Low, chemically concentrated fluxes characterize the spring discharge, whereas higher, chemically dilute fluxes typify the summer discharge. Collectively, this thesis provides some of the first descriptions and flux estimates of carbon and iron, key elements in ocean biogeochemical cycles, in GrIS meltwater runoff.

Description: This research was supported the WHOI Arctic Research Initiative (EBK, SBD, MAC), the National Science Foundation (EBK, SBD), NASA (SBD), a National Science and Engineering Research Council of Canada Postgraduate Doctoral Fellowship (MPB), an American Geophysical Union Horton Hydrology Award (MPB), the Ocean Ventures Fund (MPB), and the WHOI Climate Change Institute (MPB).

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 January 1993

Description: Although the association between soft-sediment invertebrates and a specific sediment type has been documented for many habitats, most studies have been correlative and have failed to convincingly demonstrate any single mechanism to explain this association. Sediment type has generally been characterized by grain size, however, many other potential causal factors correlate with grain size, including organic content, microbial content, stability, food supply, and larval supply. One hypothesis for animal-sediment associations is that settling larvae are transported as passive particles and are sorted into different sedimentary habitats much like sediment grains. To test the hypothesis that near-bed hydrodynamics may modify larval settlement, field and flume experiments were conducted where larval settlement was compared between microdepositional environments (small depressions) and non-trapping environments (flush treatments). Depressions have been observed to trap passive particles, and these experiments were therefore designed to test whether settling larvae would be trapped in depressions like passive particles. Flume flow simulations were carried out with the polychaete Capitella sp. I and the bivalve Mulinia latera/is. Experiments with flush and depression sediment treatments were conducted in the absence of the potentially confounding effects of suspended sediment and organic matter and therefore offered a highly controlled, explicit test of passive hydrodynamic deposition of larvae in depressions. Although larvae of both species were generally able to actively select a high-organic sediment over a low-organic alternative with a comparable grain size, elevated densities of both species were observed in depressions for a given sediment treatment. Thus, both species appeared to be vulnerable to hydrodynamic trapping. M. latera/is larvae, however, often made a "poor choice" by settling in high numbers in depressions containing the low-organic sediment while Capitella sp. I larvae were generally able to "escape" from depressions if the sediment was unsuitable. In field experiments carried out at Station R in Buzzards Bay, Massachusetts, significantly higher densities of Mediomastus ambiseta juveniles, spionid polychaete juveniles, bivalves, gastropod larvae, and nemerteans were observed in depressions compared with flush treatments over 5 relatively short experimental periods (3 or 4 days each) during the summer of 1990. Of the abundant taxa, only Capitella spp. was not significantly more abundant in depressions compared with flush treatments, although numbers tended to be higher in depressions. Experiments were conducted over a short time period to minimize potential biological interactions between taxa and reduce the likelihood that organic material would accumulate in depressions and provide a cue for settling larvae. Thus, higher numbers in depressions suggest that larvae were passively entrained. These flume and field experiments suggest that near-bed hydrodynamics may modify settlement at some scales, and that both active and passive processes may operate in determining larval distributions in shallow-water, muddy habitats. In deep-sea ecosystems, the role of near-bed hydrodynamics is also of interest because of the potential role that larval settlement in organic patches may play in maintaining the immense species diversity characteristic of many deep-sea ecosystems. To try to understand the role of organic patches in deep-sea communities, several investigators have used colonization trays containing sediments that have been treated in different ways. These experiments have been criticized in the past because the sediment surface in the trays was elevated above the bottom and may therefore have interfered with natural boundary layer flow. Flume simulations of flow over these colonization trays revealed serious flow artifacts generated by the trays, and that flow across the sediment surface of the trays was characterized by turbulent eddies, accelerated velocities and boundary layer thickening. These sorts of flow characteristics would not be expected over natural sediments, and an alternative colonization tray was designed to eliminate these artifacts. To test the hypothesis that different types of food patches would result in different types of larval response, and determine how near-bed hydrodynamics may influence larval settlement, flush colonization trays filled with prefrozen sediment were deployed in tandem with artificial depressions south of St. Croix, U.S.V.I at 900 m depth. Colonization trays and artificial depressions were either unenriched or enriched with Thalassiosira sp. and Sargassum sp. two types of algae chosen to mimic natural food patches on the sea floor. Unexpectedly high densities of organisms colonized trays after only 23 days. The Thalassiosira trays were colonized by high densities of a relatively low diversity, opportunistic fauna, Sargassum trays were colonized by lower densities of a higher diversity fauna, and unenriched trays were colonized by very low numbers of a very diverse fauna. All tray faunas were markedly different in composition from the natural, ambient fauna. These fmdings suggest that different patch types did, indeed, result in a specialized faunal response to each of the "patch" types. Depressions on the sea floor provide a natural mechanism for food patch formation because passive particles such as detritus and algae tend to be entrained in the depressions. To determine whether dominant colonizers would be entrained in depressions like passive particles or could differentiate between depression "patch" types in a flow environment that might be expected to make active selection more difficult, artificial depressions were unenriched or enriched with Sargassum sp. or Thalassiosira sp. Total densities of organisms and densities of the most abundant species were substantially lower in artificial depressions than in trays. Densities in Thalassiosira depressions were lower than in Sargassum depressions and densities in unenriched depressions were extremely low, suggesting that dominant colonizers were not passively entrained in depressions and that colonization was specialized and highly active for these taxa. A different fauna was also observed in natural depressions compared with flush sediments, suggesting that natural depressions do contribute to species coexistence. Long-term tray deployments designed to test whether different faunas would be present in "patches" of different ages indicated that time may also play an important part in a deep-sea patch mosaic.

Description: This was funded by NSF and ONR, NOAA, NSERC (Canada), WHOI Ocean Ventures Fund and the WHOI Ditty Bag Fund.

Description: Submitted in partial fulfillment of the requirements for the degree of Master of Science at the Massachusetts Institute of Technology and Woods Hole Oceanographic Institution February 1994

Description: Planktonic foraminiferal flux was collected at four sediment trap locations spanning a 34° latitude range in the North Atlantic during 1988-1990. Satellite-derived sea surface temperature (SST) and CTD data were integrated with time-corrected flux data to determine the effects of seasonal hydrographic changes on foraminiferal production and species succession in surface waters. The thermal structure of the upper water column controls foraminiferal production by regulating levels of phytoplankton production and by directly influencing the preferred temperature habitats of individual species in the community. Sediment traps deployed at the two southern sites (34°N and 48°N) were part of the U.S. Joint Global Ocean Flux Study (JGOFS) and were located in regions influenced by upwelling events induced by mesoscale eddy activity. The timing of maximum foraminiferal production at each trap location coincides with the northward progression of the spring bloom in the North Atlantic. The magnitude of total flux during bloom periods varies considerably with location and is positively correlated with the amount of primary productivity in surface waters. Foraminiferal production is highest at JGOFS 48 and probably results from the greater influence of mesoscale variability in this region on local hydrographic conditions. The upwelling associated with cyclonic cold-core eddies appears to be an effective mechanism for increasing local foraminiferal production in the North Atlantic by enhancing food availability. The preferred production of individual species during upwelling periods may depend on the vertical distribution of chlorophyll in the water column. Seasonal variation in SST is also an important factor controlling the relative abundance of species with preferred thermal habitats. A distinct seasonal species succession occurs at both JGOFS sites but is absent at higher latitudes due to decreases in both faunal diversity and seasonal temperature variations with increasing latitude in the North Atlantic. Foraminiferal :flux data, expressed in terms of relative abundance, is the best direct method of comparing species distributions of living populations with fossil assemblages in the sedimentary record. Preferred temperature ranges for G. ruber, G. bulloides, and N. pachyderma are estimated in this study. The tolerance limits for these species and other ecological inferences derived from these flux data may prove useful for paleoceanographic reconstruction in deep-sea cores. Future studies will be necessary, however, to establish the consistency of these results among different ocean basins.

Description: This research was funded by National Science Foundation Grant No. ATM-9115619.

Description: Submitted in partial fulfillment of the requirements for the degree of Doctor of Philosophy at the Massachusetts Institute of Technology and Woods Hole Oceanographic Institution February 1994

Description: Ambient noise in the sea has been observed for over 100 years. Previous studies conclude that the primary source of microseisms is nonlinear interaction of surface gravity waves at the sea surface. Though this source relationship is generally accepted, the actual processes by which the wave generated acoustic noise in the water column couples and propagates to and along the sea floor are not well understood. In this thesis, the sources and propagation of sea floor and sub-sea floor microseismic noise between 0.2 and 10 Hz are investigated. This thesis involves a combination of theoretical, observational and numerical analysis to probe the nature of the microseismic field in the Blake Bahama Basin. Surface waves are the primary mechanism for noise propagation in the crust and fall into two separate groups depending on the relative wavelength/water depth ratio. Asymptotic analysis of the Sommerfeld integral in the complex ray parameter plane shows results that agree with previous findings by Strick (1959) and reveal two fundamental interface wave modes for short wavelength noise propagation in the crust: the Stoneley and pseudo-Rayleigh wave. For ocean sediments, where the shear wave velocity is less than the acoustic wave velocity of water, only the Stoneley interface wave can exist. For well consolidated sediments and basalt, the shear velocity exceeds the acoustic wave velocity of water and the pseudo-Rayleigh wave can also exist. Both interface waves propagate with retrograde elliptic motion at the sea floor and attenuate with depth into the crust, however the pseudo-Rayleigh wave travels along the interface with dispersion and attenuation and "leaks" energy into the water column for a half-space ocean over elastic crust model. For finite depth ocean models, the pseudo-Rayleigh wave is no longer leaky and approaches the Rayleigh wave velocity of the crust. The analysis shows that longer wavelength noise propagates as Rayleigh and Stoneley modes of the ocean+crust waveguide. These long wavelength modes are the fundamental mechanism for long range noise propagation. During the Low Frequency Acoustic Seismic Experiment (LFASE) a four-node, 12- channel borehole array (SEABASS) was deployed in the Blake Bahama Basin off the coast of eastern Florida (DSDP Hole 534B). This experiment is unique and is the first use of a borehole array to measure microseismic noise below the sea floor. Ambient background noise from a one week period is compared between an Ocean Bottom Seismometer (OBS) and SEABASS at sub-bottom depths of 10, 40, 70 and 100 meters below the sea floor. The 0.3 H z microseism peak is found to be nearly invariant with depth and has a power level of 65 and 75 dB rel 1 (nm/ s2)2)/ H z for the vertical and horizontal components respectively. At 100 m depth, the mean microseismic noise levels above 0.7 Hz are 10 dB and 15-20 dB quieter for the vertical and horizontal components respectively. Most of this attenuation occurs in the upper 10 m above 1.0 Hz, however higher modes in the spectra show narrow bandwidth variability in the noise field that is not monotonic with depth. Dispersion calculations show normal mode Stoneley waves below 0.7 Hz and evidence of higher modes above 0.8 Hz. A strong correlation between noise levels in the borehole and local sea state conditions is observed along with clear observation of the nonlinear frequency doubling effect between ocean surface waves and microseisms. Particle motion analysis further verifies that noise propagates through the array as Rayleigh/Stoneley waves. Polarization direction indicates at least two sources; distant westerly swell during quiescent times and local surface waves due to a passing storm. Above 1.0 Hz the LFASE data shows little coherence and displays random polarization. Because of this, we believe scattered energy is a significant component of the noise field in the Blake Bahama Basin. A fully 3-D finite difference algorithm is used to model both surface and volume heterogeneities in the ocean crust. Numerical modeling of wave propagation for hard and soft bottom environments shows that heterogeneities on the order of a seismic wavelength radiate energy into the water column and convert acoustic waves in the water into small wavelength Stoneley waves observed at the borehole. Sea floor roughness is the most important elastic scattering feature of the ocean crust. Comparisons of 2D and 3D rough sea floor models show that out-of-plane effects necessitate the use of 3D methods. The out-of-plane energy that is present in the LFASE data comes from either heterogeneities in the source field (i.e. mixed gravity wave directions) or, equally likely, scattering of the source field from surface or volume heterogeneities in the sea floor.

Description: This research was supported by Office of Naval Research grants N00014-89-C-0018, N00014-89-J-1012, N00014-90-C-0098, N00014-90-J-1493 and N00014-93-1-1352.

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 Doctor of Philosophy at the Massachusetts Institute of Technology and the Woods Hole Oceanographic Institution February 1999

Description: In this thesis the analysis of natural ice events is carried out based on direct measurements of ice-borne seismo-acoustic waves generated by ice fracturing processes. A major reason for studying this phenomenon is that this acoustic emission is a significant contributor to Arctic ocean ambient noise. Also the Arctic contains rich mineral and oil resources and in order to design mining facilities able to withstand the harsh environmental conditions, we need to have a better understanding of the processes of sea ice mechanics. The data analyzed in this thesis were collected during the Sea Ice Mechanics Initiative SIMI’94 experiment which was carried out in the spring of 1994 in the Central Arctic. One of the contributions of this thesis was the determination of the polarization characteristics of elastic waves using multicomponent geophone data. Polarization methods are well known in seismology, but they have never been used for ice event data processing. In this work one of the polarization methods so called Motion Product Detector method has been successfully applied for localization of ice events and determination of polarization characteristics of elastic waves generated by fracturing events. This application demonstrates the feasibility of the polarization method for ice event data processing because it allows one to identify areas of high stress concentration and "hot spots" in ridge building process. The identification of source mechanisms is based on the radiation patterns of the events. This identification was carried out through the analysis of the seismo-acoustic emission of natural ice events in the ice sheet. Previous work on natural ice event identification was done indirectly by analyzing the acoustic energy radiated into the water through coupling from elastic energy in the ice sheet. After identification of the events, the estimation of the parameters of fault processes in Arctic ice is carried out. Stress drop, seismic moment and the type of ice fracture are determined using direct near-field measurements of seismo-acoustic signals generated by ice events. Estimated values of fracture parameters were in good agreement with previous work for marginal ice zone. During data processing the new phenomenon was discovered: "edge waves", which are waves propagating back and forth along a newly opened ice lead. These waves exhibit a quasi-periodic behavior suggesting some kind of stick-slip generation mechanism somewhere along the length of the lead. The propagation characteristics of these waves were determined using seismic wavenumber estimation techniques. In the low frequency limit the dispersion can be modeled approximately by an interaction at the lead edges of the lowest order, antisymmetric modes of the infinite plate.

Description: Support for this thesis was provided by Office of Naval Research.

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

Description: A review of six methods for deriving sediment quality criteria SQC was conducted. Each approach was analyzed according to cost, difficulty, applicability and reliability. Results of this analysis led to the recommendation that the state of Massachusetts should use a combination of the Equilibrium Partitioning modeling approach and the Threshold Effects Level/Probable Effects Level correlative approach to SQC derivation. Criteria should then be applied as screening values for evaluation of sediment toxicity. One significant component of sediment quality that all criteria approaches lack is the bioaccumulation/biomagnification of contaminants. Nor are there accurate, easily implemented models for benthically-coupled organisms such as Mya arenaria. In this document a bioaccumulation model for PAHs and PCBs was developed. The model considers contaminant partitioning into organism lipid and protein and incorporates organism exposure to contaminants through sediment and ingestion of contaminated food particles. Results show the model predicts PCB accumulation in M. arenaria with only a slight variation from observed data. Partitioning into sedimentary soot fraction was added to the model for PARs. Results showed an increase in model accuracy, but predicted concentrations still remain greater than observed concentrations. A combination of sediment quality criteria used as screening criteria and the bioaccumulation model for M.arenaria will improve the accuracy of site assessment of PAH and PCB compounds.

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 2011

Description: The sinking flux of particulate matter into the ocean interior is an oceanographic phenomenon that fuels much of the metabolic demand of the subsurface ocean and affects the distribution of carbon and other elements throughout the biosphere. In this thesis, I use a new suite of observations to study the dynamics of marine particulate matter at the contrasting sites of the subtropical Sargasso Sea near Bermuda and the waters above the continental shelf of the Western Antarctic Peninsula (WAP). An underwater digital camera system was employed to capture images of particles in the water column. The subsequent analysis of these images allowed for the determination of the particle concentration size distribution at high spatial, depth, and temporal resolutions. Drifting sediment traps were also deployed to assess both the bulk particle flux and determine the size distribution of the particle flux via image analysis of particles collected in polyacrylamide gel traps. The size distribution of the particle concentration and flux were then compared to calculate the average sinking velocity as a function of particle size. I found that the average sinking velocities of particles ranged from about 10-200 m d-1 and exhibited large variability with respect to location, depth, and date. Particles in the Sargasso Sea, which consisted primarily of small heterogeneous marine snow aggregates, sank more slowly than the rapidly sinking krill fecal pellets and diatom aggregates of the WAP. Moreover, the average sinking velocity did not follow a pattern of increasing velocities for the larger particles, a result contrary to what would be predicted from a simple formulation of Stokes’ Law. At each location, I derived a best-fit fractal correlation between the flux size distribution and the total carbon flux. The use of this relationship and the computed average sinking velocities enabled the estimation of particle flux from measurements of the particle concentration size distribution. This approach offers greatly improved spatial and temporal resolution when compared to traditional sediment trap methods for measuring the downward flux of particulate matter. Finally, I deployed specialized in situ incubation chambers to assess the respiration rates of microbes attached to sinking particles. I found that at Bermuda, the carbon specific remineralization rate of sinking particulate matter ranged from 0.2 to 1.1 d-1, while along the WAP, these rates were very slow and below the detection limit of the instruments. The high microbial respiration rates and slow sinking velocities in the Sargasso Sea resulted in the strong attenuation of the flux with respect to depth, whereas the rapid sinking velocities and slow microbial degradation rates of the WAP resulted in nearly constant fluxes with respect to depth.

Description: The Scurlock Bermuda Biological Station for Research Fund provided travel support to and from Bermuda. A grant from the National Science Foundation (NSF) Carbon and Water Program (06028416) enabled all the Sargasso Sea research as well as the opportunity to develop and test much of the methodology presented in this thesis. Internal awards from the WHOI Rinehart Access to the Sea Program and the WHOI Coastal Oceans Institute provided early funding that supported my first season of research in Antarctica and were instrumental in securing the larger external NSF Office of Polar Programs (OPP) Western Antarctic Peninsula Flux Project (OPP 0838866) grant for a second year of science in the region. The NSF OPP Palmer Long-Term Ecological Research Project and the Food for Benthos on the Antarctic Continental Shelf Project provided logistical support in the region. Phoebe Lam and Scott Doney’s grant from the WHOI Ocean Carbon and Climate Institute supported a semester of my time. The Henry G. Houghton Fund and the MIT Student Assistance Fund subsidized educational costs, textbooks, equipment, and travel expenses to conferences. In my first year I was supported by funding from Scott Doney’s NSF grant (OCCE-0312710).

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 2011

Description: Coastal barriers are particularly susceptible to the predicted effects of accelerated of sea-level rise and the potential for increased impacts of intense storms. Over centennial scales, barriers are maintained via overtopping during storms, causing deposition of washover fans on their landward sides. This study examines three washover fans on the south shore of Martha’s Vineyard using a suite of data including vibracores, ground penetrating radar, high resolution dGPS, and LiDAR data. From these data, the volumes of the deposits were determined and range from 2.1—2.4 x 104 m3. Two overwashes occurred during Hurricane Bob in 1991. The water levels produced by this storm have a return interval of ~28 years, resulting in an onshore sediment flux of 2.4—3.4 m3/m/yr. The third washover was deposited by a nor’easter in January 1997, which has a water level return interval of ~6 years, resulting in a flux of 8.5 m3/m/yr. These fluxes are smaller than the flux of sediment needed to maintain a geometrically stable barrier estimated from shoreline retreat rates, suggesting that the barrier is not in long-term equilibrium, a result supported by the thinning of the barrier over this time interval.

Description: Funding for this research was provided by an Emery Fellowship through the Woods Hole Oceanographic Institution Academic Programs Office, the National Science Foundation (grants NSF-GEO-0815875 and NSF-OCE-0840894), and the Department of Defense Strategic Environmental Research and Development Program (contract W912HQ-09-C-0043).

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 at the Massachusetts Institute of Technology and the Woods Hole Oceanographic Institution December 1985

Description: Samples from time-series sediment traps deployed in three distinct oceanographic settings (North Pacific, Panama Basin, and Black Sea) provide strong evidence for rapid settling of marine particles by aggregates. Particle water column residence times were determined by measuring the time lag between the interception of a flux event in a shallow trap and the interception of the same event in a deeper trap at the same site. Effective sinking speeds were determined by dividing the vertical offset of the traps (meters) by the interception lag time (days). At station Papa in the North Pacific, all particles settle at 175 m day-1, regardless of their composition, indicating that all types of material may be settling in common packages. Evidence from the other two sites (Panama Basin and Black Sea) shows that particle transport may be vertical, lateral, or a combination of directions, with much of the Black Sea flux signal being dominated by lateral input. In order to ascertain whether marine snow aggregates represent viable transport packages, surveys were conducted of the abundance of these aggregates at several stations in the eastern North Atlantic and Panama Basin using a photographic technique. Marine snow aggregates were found in concentrations ranging from ~1 mm3 liter-1 to more than 500 mm3 liter-1. In open ocean environments, abundances are higher near the surface (production) and decline with depth (decomposition). However, in areas near sources of deep input of resuspended material, concentrations reach mid-water maxima, reflecting lateral transport. A model is proposed to relate the observed aggregate abundances, time series sediment flux and inferred circulation. In this model, depthwise variations in sediment flux and aggregate abundance result from suspension from the sea floor and lateral transport of suspended aggregates which were produced or modified on the sea floor. Temporal changes in sediment flux result from variations in the input of fast-sinking material which falls from the surface, intercepts the suspended aggregates, and transports them to the sea floor. A new combination sediment trap and camera system was built and deployed in the Panama Basin with the intent of measuring the flux of marine snow aggregates. This device consists of a cylindrical tube which is open at the top and sealed at the bottom by a clear plate. Material lying on the bottom plate is illuminated by strobe lights mounted in the wall of the cylinder and photographed by a camera which is positioned below the bottom plate. Flux is determined as the number of aggregates arriving during the time interval between photographic frames (# area-1 time-1). Results show that essentially all material arrives in the form of aggregates with minor contributions of fecal pellets and solitary particles. Sinking speeds (m day-1), calculated by dividing the flux of aggregates (# m-2 day-1) by their abundance (# m-3), indicate that the larger (4-5mm) aggregates are flocculent and sink slowly (~1m day-1) while the smaller aggregates (1-2.5mm) are more compact and sink more quickly (~36m day-1). These large, slow-sinking aggregates may have been re-suspended from the sediment water interface at nearby basin margins.

Description: This research was supported by ONR contract numbers N00014-82-C-0019 and N00014-85-C-0001, NSF grant numbers OCE-83-09024, OCE-84-17106, and DPP-85-01152 and the WHO1 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 September 1987

Description: This thesis presents an application of the Grant-Madsen-Glenn bottom boundary layer model (Grant and Madsen, 1979; Glenn and Grant, 1987) to predictions of sediment transport on the continental shelf. The analysis is a two-stage process. Via numerical experiment, we explore the sensitivity of sediment transport to variations in model parameters and assumptions. A notable result is the enhancement of suspended sediment stratification due to wave boundary layer effects. When sediment stratification is neglected under conditions of large wave bottom velocities, concentration predictions can be more than an order of magnitude higher than any observed during storm conditions on the continental shelf. A number of limitations to application emerged from the analysis. Solutions to the stratified model are not uniquely determined under a number of cases of interest, potentially leading to gross inaccuracies in the prediction of sediment load and transport. Load and sediment transport in the outer Ekman Layer, beyond the region of emphasis for the model, can be as large or larger than the near-bottom estimates in some cases; such results suggest directions for improvements in the theoretical model. In the second step of the analysis, we test the ability of the model to make predictions of net sediment transport that are consistent with observed sediment depositional patterns. Data from the Mid-Atlantic Bight and the Northern California coast are used to define reasonable model input to represent conditions on two different types of shelves. In these examples, the results show how the intensification of wave bottom velocities with decreasing depth can introduce net transport over a region. The patterns of erosion/deposition are shown to be strongly influenced by sediment stratification and moveable bed roughness. Also predicted by the applications is a rapid winnowing out of fine grain size components when there is even a small variation of bed grain size texture in the along-flow direction.

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 2010

Description: Quorum sensing (QS) via acylated homoserine lactones (AHLs) was discovered in the ocean, yet little is known about its role in the ocean beyond its involvement in certain symbiotic interactions. The objectives of this thesis were to constrain the chemical stability of AHLs in seawater, explore the production of AHLs in marine particulate environments, and probe selected behaviors which might be controlled by AHL-QS. I established that AHLs are more stable in seawater than previously expected and are likely to accumulate within biofilms. Based on this result, I chose to study AHL-QS in the bacterial communities inhabiting biofilms attached to Trichodesmium spp. and detrital (photosynthetically-derived sinking particulate organic carbon, POC) particles. These hot spots of microbial activity are primary sites of interaction between marine primary producers and heterotrophs and crucial components of the biological pump. Biofilm communities associated with Trichodesmium thiebautii colonies in the Sargasso Sea differed considerably from seawater microbial communities. In addition, there was no overlap between the communities associated with tuft and puff colonies. These results suggest that bacterial communities associated with Trichodesmium are not random; rather, Trichodesmium selects for specific microbial flora. Novel 16S rRNA gene sequences are present both in clone libraries constructed from DNA extracted from colonies of Trichodesmium spp. and in culture collections derived from wild and laboratory cultivated Trichodesmium spp., supporting the idea that the phycosphere of Trichodesmium is a unique microenvironment. Using high performance liquid chromatography-mass spectrometry, I demonstrated that bacteria isolated from Trichodesmium synthesize AHLs. In addition, I detected AHLs in sinking particles collected from a site off of Vancouver Island, Canada. AHLs were subsequently added to laboratory cultures of non-axenic Trichodesmium colonies and sinking POC samples. This is the first time AHLs have been detected in POC and indicates that AHL-QS was occurring in POC. Further, I showed that AHLs enhanced certain organic-matter degrading hydrolytic enzyme activities. My results suggest that AHL-QS is a factor regulating biogeochemically relevant enzyme activities on sinking POC and within the biofilms attached to Trichodesmium colonies and thereby may impact the timing and magnitude of biogeochemical fluxes in the ocean.

Description: My personal funding came from an MIT Presidential Fellowship, National Science Foundation Graduate Fellowship, and the WHOI Academic Programs Office. My research was funded by grants from the National Science Foundation (Chemical Oceanography award # 0825407), the Office of Naval Research (N0014-06-1-0134) and the Ocean Life Institute (award CH12702).

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.