Crusius John

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Now showing 1 - 11 of 11
  • Article
    Glacial influence on the geochemistry of riverine iron fluxes to the Gulf of Alaska and effects of deglaciation
    (American Geophysical Union, 2011-08-25) Schroth, Andrew W. ; Crusius, John ; Chever, Fanny ; Bostick, Benjamin C. ; Rouxel, Olivier J.
    Riverine iron (Fe) derived from glacial weathering is a critical micronutrient source to ecosystems of the Gulf of Alaska (GoA). Here we demonstrate that the source and chemical nature of riverine Fe input to the GoA could change dramatically due to the widespread watershed deglaciation that is underway. We examine Fe size partitioning, speciation, and isotopic composition in tributaries of the Copper River which exemplify a long-term GoA watershed evolution from one strongly influenced by glacial weathering to a boreal-forested watershed. Iron fluxes from glacierized tributaries bear high suspended sediment and colloidal Fe loads of mixed valence silicate species, with low concentrations of dissolved Fe and dissolved organic carbon (DOC). Iron isotopic composition is indicative of mechanical weathering as the Fe source. Conversely, Fe fluxes from boreal-forested systems have higher dissolved Fe concentrations corresponding to higher DOC concentrations. Iron colloids and suspended sediment consist of Fe (hydr)oxides and organic complexes. These watersheds have an iron isotopic composition indicative of an internal chemical processing source. We predict that as the GoA watershed evolves due to deglaciation, so will the source, flux, and chemical nature of riverine Fe loads, which could have significant ramifications for Alaskan marine and freshwater ecosystems.
  • Article
    Glacial flour dust storms in the Gulf of Alaska : hydrologic and meteorological controls and their importance as a source of bioavailable iron
    (American Geophysical Union, 2011-03-18) Crusius, John ; Schroth, Andrew W. ; Gasso, Santiago ; Moy, Christopher M. ; Levy, Robert C. ; Gatica, Myrna
    Iron is an essential micronutrient that limits primary productivity in much of the ocean, including the Gulf of Alaska (GoA). However, the processes that transport iron to the ocean surface are poorly quantified. We combine satellite and meteorological data to provide the first description of widespread dust transport from coastal Alaska into the GoA. Dust is frequently transported from glacially-derived sediment at the mouths of several rivers, the most prominent of which is the Copper River. These dust events occur most frequently in autumn, when coastal river levels are low and riverbed sediments are exposed. The dust plumes are transported several hundred kilometers beyond the continental shelf into iron-limited waters. We estimate the mass of dust transported from the Copper River valley during one 2006 dust event to be between 25–80 ktons. Based on conservative estimates, this equates to a soluble iron loading of 30–200 tons. We suggest the soluble Fe flux from dust originating in glaciofluvial sediment deposits from the entire GoA coastline is two to three times larger, and is comparable to the annual Fe flux to GoA surface waters from eddies of coastal origin. Given that glaciers are retreating in the coastal GoA region and in other locations, it is important to examine whether fluxes of dust are increasing from glacierized landscapes to the ocean, and to assess the impact of associated Fe on marine ecosystems.
  • Article
    Groundfish overfishing, diatom decline, and the marine silica cycle : lessons from Saanich Inlet, Canada, and the Baltic Sea cod crash
    (American Geophysical Union, 2009-12-31) Katz, Timor ; Yahel, Gitai ; Yahel, Ruthy ; Tunnicliffe, Verena ; Herut, Barak ; Snelgrove, Paul V. R. ; Crusius, John ; Lazar, Boaz
    In this study, we link groundfish activity to the marine silica cycle and suggest that the drastic mid-1980s crash of the Baltic Sea cod (Gadus morhua) population triggered a cascade of events leading to decrease in dissolved silica (DSi) and diatom abundance in the water. We suggest that this seemingly unrelated sequence of events was caused by a marked decline in sediment resuspension associated with reduced groundfish activity resulting from the cod crash. In a study in Saanich Inlet, British Columbia, Canada, we discovered that, by resuspending bottom sediments, groundfish triple DSi fluxes from the sediments and reduce silica accumulation therein. Using these findings and the available oceanographic and environmental data from the Baltic Sea, we estimate that overfishing and recruitment failure of Baltic cod reduced by 20% the DSi supply from bottom sediments to the surface water leading to a decline in the diatom population in the Baltic Sea. The major importance of the marginal ocean in the marine silica cycle and the associated high population density of groundfish suggest that groundfish play a major role in the silica cycle. We postulate that dwindling groundfish populations caused by anthropogenic perturbations, e.g., overfishing and bottom water anoxia, may cause shifts in marine phytoplankton communities.
  • Preprint
    Depth of the vadose zone controls aquifer biogeochemical conditions and extent of anthropogenic nitrogen removal
    ( 2017-06) Szymczycha, Beata ; Kroeger, Kevin D. ; Crusius, John ; Bratton, John F.
    We investigated biogeochemical conditions and watershed features controlling the extent of nitrate removal through microbial dinitrogen (N2) production within the surficial glacial aquifer located on the north and south shores of Long Island, NY, USA. The extent of N2 production differs within portions of the aquifer, with greatest N2 production observed at the south shore of Long Island where the vadose zone is thinnest, while limited N2 production occurred under the thick vadose zones on the north shore. In areas with a shallow water table and thin vadose zone, low oxygen concentrations and sufficient DOC concentrations are conducive to N2 production. Results support the hypothesis that in aquifers without a significant supply of sediment-bound reducing potential, vadose zone thickness exerts an important control of the extent of N2 production. Since quantification of excess N2 relies on knowledge of equilibrium N2 concentration at recharge, calculated based on temperature at recharge, we further identify several features, such as land use and cover, seasonality of recharge, and climate change that should be considered to refine estimation of recharge temperature, its deviation from mean annual air temperature, and resulting deviation from expected equilibrium gas concentrations.
  • Preprint
    Mobility of authigenic rhenium, silver, and selenium during postdepositional oxidation in marine sediments
    ( 2002-07-04) Crusius, John ; Thomson, John
    Sedimentary records of redox-sensitive trace elements hold significant potential as indicators of paleoceanographic environmental conditions. Records of Re can reveal the intensity of past reducing conditions in sediments at the time of deposition (Crusius et al., 1996), while records of Ag may record the magnitude of past diatom fluxes to the seafloor. Confidence in paleoenvironmental reconstruction from records of either metal, however, requires it to have experienced negligible redistribution since deposition. This study examines diagenetic re-arrangements of Re and Ag that occur in response to exposure to bottom-water O2 in environments of low sedimentation rate, including Madeira Abyssal Plain turbidites and eastern Mediterranean basin sapropels. Authigenic Re was remobilized quantitatively by oxidation, but poorly retained by the underlying sediments. All records are consistent with previous work demonstrating that only a limited re-immobilization of Re occurs preferentially in Corg-rich, reducing sediments (Crusius and Thomson, 2000). Silver was also mobilized quantitatively by oxidation, but was subsequently immobilized more efficiently in all cases as sharp peaks immediately into anoxic conditions below active oxidation fronts, and these peaks remain immobile in anoxic conditions during long-term burial. Comparison of Ag, S and Se records from various cores suggests that Ag is likely to have been immobilized as a selenide, a mechanism previously proposed for Hg in similar situations (Mercone et al., 1999). Coexisting narrow peaks of Ag and Hg with Se offer a means of assessing whether oxidative burndown has ever occurred at the top of Corg- and sulfide-rich sedimentary units. While these results suggest that caution must be used when inferring paleoenvironmental information from records of Ag and Re in cores with low sediment accumulation rates (<5 cm ka-1), they should not affect the promise that authigenic Ag and Re records hold for paleoenvironmental reconstruction in sediments with higher accumulation rates and where anoxic conditions have been maintained continuously.
  • Preprint
    Bioturbation depths, rates and processes in Massachusetts Bay sediments inferred from modeling of 210Pb and 239 + 240Pu profiles
    ( 2004-07-20) Crusius, John ; Bothner, Michael H. ; Sommerfield, Christopher K.
    Profiles of 210Pb and 239+240Pu from sediment cores collected throughout Massachusetts Bay (water depths of 36-192 m) are interpreted with the aid of a numerical sedimentmixing model to infer bioturbation depths, rates and processes. The nuclide data suggest extensive bioturbation to depths of 25-35 cm. Roughly half the cores have 210Pb and 239+240Pu profiles that decrease monotonically from the surface and are consistent with biodiffusive mixing. Bioturbation rates are reasonably well constrained by these profiles and vary from ~0.7 to ~40 cm2 yr-1. As a result of this extensive reworking, however, sediment ages cannot be accurately determined from these radionuclides and only upper limits on sedimentation rates (of ~0.3 cm yr-1) can be inferred. The other half of the radionuclide profiles are characterized by subsurface maxima in each nuclide, which cannot be reproduced by biodiffusive mixing models. A numerical model is used to demonstrate that mixing caused by organisms that feed at the sediment surface and defecate below the surface can cause the subsurface maxima, as suggested by previous work. The deep penetration depths of excess 210Pb and 239+240Pu suggest either that the organisms release material over a range of >15 cm depth or that biodiffusive mixing mediated by other organisms is occurring at depth. Additional constraints from surficial sediment 234Th data suggest that in this half of the cores, the vast majority of the presentday flux of recent, nuclide-bearing material to these core sites is transported over a timescale of a month or more to a depth of a few cm below the sediment surface. As a consequence of the complex mixing processes, surface sediments include material spanning a range of ages and will not accurately record recent changes in contaminant deposition.
  • Article
    Submarine groundwater discharge to a small estuary estimated from radon and salinity measurements and a box model
    (Copernicus Publications, 2005-06-24) Crusius, John ; Koopmans, D. ; Bratton, John F. ; Charette, Matthew A. ; Kroeger, Kevin D. ; Henderson, Paul B. ; Ryckman, L. ; Halloran, K. ; Colman, John A.
    Submarine groundwater discharge was quantified by a variety of methods for a 4-day period during the early summer of 2004, in Salt Pond, adjacent to Nauset Marsh, on Cape Cod, USA. Discharge estimates based on radon and salinity took advantage of the presence of the narrow channel connecting Salt Pond to Nauset Marsh, which allowed constructing whole-pond mass balances as water flowed in and out due to tidal fluctuations. The data suggest that less than one quarter of the discharge in the vicinity of Salt Pond happened within the pond itself, while three quarters or more of the discharge occurred immediately seaward of the pond, either in the channel or in adjacent regions of Nauset Marsh. Much of this discharge, which maintains high radon activities and low salinity, is carried into the pond during each incoming tide. A box model was used as an aid to understand both the rates and the locations of discharge in the vicinity of Salt Pond. The model achieves a reasonable fit to both the salinity and radon data assuming submarine groundwater discharge is fresh and that most of it occurs either in the channel or in adjacent regions of Nauset Marsh. Salinity and radon data, together with seepage meter results, do not rule out discharge of saline groundwater, but suggest either that the saline discharge is at most comparable in volume to the fresh discharge or that it is depleted in radon. The estimated rate of fresh groundwater discharge in the vicinity of Salt Pond is 3000-7000 m3 d-1. This groundwater flux estimated from the radon and salinity data is comparable to a value of 3200-4500 m3 d-1 predicted by a recent hydrologic model (Masterson, 2004; Colman and Masterson, 2004), although the model predicts this rate of discharge to the pond whereas our data suggest most of the groundwater bypasses the pond prior to discharge. Additional work is needed to determine if the measured rate of discharge is representative of the long-term average, and to better constrain the rate of groundwater discharge seaward of Salt Pond.
  • Article
    Nutrient gradients in Panamanian estuaries : effects of watershed deforestation, rainfall, upwelling, and within-estuary transformations
    (Inter-Research, 2013-05-22) Valiela, Ivan ; Giblin, Anne E. ; Barth-Jensen, Coralie ; Harris, Carolynn ; Stone, Thomas A. ; Fox, Sophia E. ; Crusius, John
    To test whether deforestation of tropical forests alters coupling of watersheds, estuaries, and coastal waters, we measured nutrients in 8 watershed-estuarine systems on the Pacific coast of Panama where watershed forest cover ranged from 23 to 92%. Watersheds with greater forest cover discharged larger dissolved inorganic nitrogen concentrations and higher N/P into estuary headwaters. As freshwater mixed with seawater down-estuary, within-estuary biogeochemical processes erased the imprint of watershed deforestation, increased ammonium, lowered nitrate concentrations, and otherwise altered down-estuary water column composition. As estuarine water left mangrove estuaries, ammonium, nitrate, and phosphate, but not dissolved organic nitrogen, were exported to receiving near-shore waters. Mangrove estuaries in this region thus provide important ecological services, by uncoupling coastal waters from changes in terrestrial land covers, as well as by subsidizing adjoined receiving coastal waters by providing nutrients. The pattern of land-sea coupling and exports was disrupted during La Niña-influenced conditions. In one instance when La Niña conditions led to upwelling of deeper layers, high concentrations of marine-derived ammonium were inserted into estuaries. In another instance, La Niña-associated high rainfall diluted nutrient concentrations within estuaries and lowered salinity regionally, and the fresher upper layer impaired coastal upwelling. Regional rainfall has increased during the last decade. If La Niña rainfall continues to increase, disruptions of current land-estuary-sea couplings may become more frequent, with potentially significant changes in nutrient cycles and ecological services in these coupled ecosystems.
  • Preprint
    Ensuring confidence in radionuclide-based sediment chronologies and bioturbation rates
    ( 2006-09-11) Crusius, John ; Kenna, Timothy C.
    Sedimentary records of naturally occurring and fallout-derived radionuclides are widely used as tools for estimating both the ages of recent sediments and rates of sedimentation and bioturbation. Developing these records to the point of data interpretation requires careful sample collection, processing, analysis and data modeling. In this work, we document a number of potential pitfalls that can impact sediment core records and their interpretation. This paper is not intended as an exhaustive treatment of these potential problems. Rather, the emphasis is on potential problems that are not well documented in the literature, as follows: 1) The mere sampling of sediment cores at a resolution that is too coarse can result in an apparent diffusive mixing of the sedimentary record at rates comparable to diffusive bioturbation rates observed in many locations; 2) 210Pb profiles in slowly accumulating sediments can easily be misinterpreted to be driven by sedimentation, when in fact bioturbation is the dominant control. Multiple isotopes of different half lives and/or origin may help to distinguish between these two possible interpretations; 3) Apparent mixing can occur due simply to numerical artifacts inherent in the finite difference approximations of the advection diffusion equation used to model sedimentation and bioturbation. Model users need to be aware of this potential problem. Solutions to each of these potential pitfalls are offered to ensure the best possible sediment age estimates and/or sedimentation and bioturbation rates can be obtained.
  • Article
    Deforestation of watersheds of Panama : nutrient retention and export to streams
    (Springer, 2013-03-19) Valiela, Ivan ; Barth-Jensen, Coralie ; Stone, Thomas A. ; Crusius, John ; Fox, Sophia E. ; Bartholomew, Megan
    A series of eight watersheds on the Pacific coast of Panama where conversion of mature lowland wet forest to pastures by artisanal burning provided watershed-scale experimental units with a wide range of forest cover (23, 29, 47, 56, 66, 73, 73, 91, and 92%). We used these watersheds as a landscape-scale experiment to assess effects of degree of deforestation on within-watershed retention and hydrological export of atmospheric inputs of nutrients. Retention was estimated by comparing rainfall nutrient concentrations (volume-weighted to allow for evapotranspiration) to concentrations in freshwater reaches of receiving streams. Retention of rain-derived nutrients in these Panama watersheds averaged 77, 85, 80, and 62% for nitrate, ammonium, dissolved organic N, and phosphate, respectively. Retention of rain-derived inorganic nitrogen, however, depended on watershed cover: retention of nitrate and ammonium in pasture-dominated watersheds was 95 and 98%, while fully forested watersheds retained 65 and 80% of atmospheric nitrate and ammonium inputs. Watershed forest cover did not affect retention of dissolved organic nitrogen and phosphate. Exports from more forested watersheds yielded DIN/P near 16, while pasture-dominated watersheds exported N/P near 2. The differences in magnitude of exports and ratios suggest that deforestation in these Panamanian forests results in exports that affect growth of plants and algae in the receiving stream and estuarine ecosystems. Watershed retention of dissolved inorganic nitrogen calculated from wet plus dry atmospheric deposition varied from 90% in pasture- to 65% in forest-dominated watersheds, respectively. Discharges of DIN to receiving waters from the watersheds therefore rose from 10% of atmospheric inputs for pasture-dominated watersheds, to about 35% of atmospheric inputs for fully forested watersheds. These results from watersheds with no agriculture or urbanization, but different conversion of forest to pasture by burning, show significant, deforestation-dependent retention within tropical watersheds, but also ecologically significant, and deforestation-dependent, exports that are biologically significant because of the paucity of nutrients in receiving tropical stream and coastal waters.
  • Article
    Resuspension by fish facilitates the transport and redistribution of coastal sediments
    (Association for the Sciences of Limnology and Oceanography, 2012-07) Katz, Timor ; Yahel, Gitai ; Reidenbach, Matthew A. ; Tunnicliffe, Verena ; Herut, Barak ; Crusius, John ; Whitney, Frank ; Snelgrove, Paul V. R. ; Lazar, Boaz
    Oxygen availability restricts groundfish to the oxygenated, shallow margins of Saanich Inlet, an intermittently anoxic fjord in British Columbia, Canada. New and previously reported 210Pb measurements in sediment cores compared with flux data from sediment traps indicate major focusing of sediments from the oxygenated margins to the anoxic basin seafloor. We present environmental and experimental evidence that groundfish activity in the margins is the major contributor to this focusing. Fine particles resuspended by groundfish are advected offshore by weak bottom currents, eventually settling in the anoxic basin. Transmittance and sediment trap data from the water column show that this transport process maintains an intermediate nepheloid layer (INL) in the center of the Inlet. This INL is located above the redox interface and is unrelated to water density shifts in the water column. We propose that this INL is shaped by the distribution of groundfish (as resuspension sources) along the slope and hence by oxygen availability to these fish. We support this conclusion with a conceptual model of the resuspension and offshore transport of sediment. This fish-induced transport mechanism for sediments is likely to enhance organic matter decomposition in oxygenated sediments and its sequestration in anoxic seafloors.