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Title: Cobalt and copper distributions in the waters of Santa Monica Basin, California,
Description: The trace metals cobalt and copper are removed from the oceans interior by scavenging on to particle surfaces, but the mechanisms for removal of these two metals are probably quite different. Cobalt appears to be scavenged by manganese oxide particles, whereas organic compounds are the main carrier phase for copper. Remobilization of these metals in marine sediments therefore proceeds by different pathways. The differences in the pathways of remobilization are accentuated in oxygen-deficient environments: manganese oxide reduction is accelerated at low oxygen levels and organic carbon is preserved. Cobalt fluxes from sediments underlying oxygen-deficient waters should be enhanced and copper fluxes reduced. We report here measurements of the cobalt and copper distributions in the waters of an oxygen-deficient marine basin in the Southern California Bight. Cobalt concentrations near the bottom are raised four times above the background level, whereas copper concentrations show no increase. These measurements confirm features of existing models for the oceanic cycles of these metals., Cited By (since 1996):18, Oceanography, CODEN: NATUA, ,
Author: Johnson, Stout, Berelson, Sakamoto-Arnold
Date: 1988-01-01T00:00:00Z

Title: Benthic manganese fluxes along the Oregon-California continental shelf and slope
Description: Here we examine the factors that influence the manganese (Mn) benthic flux from eastern North Pacific marine sediments, with a primary emphasis on continental shelf locations off Oregon and California and studies that involve the use of in situ benthic chambers. Typical shelf-to-shallow margin (<~350m) sites have benthic Mn efflux rates that average ~8±5μmolm-2d-1. In contrast, for the Eel River continental shelf region the benthic Mn efflux can be an order of magnitude higher than other shelf settings with benthic effluxes exceeding ~50μmolm-2d-1. Based on prior work and some new results, continental margin and slope sites (350-~4000m) have benthic Mn efflux rates that average ~1±1μmolm-2d-1. The combination of the benthic flux and Mn solid-phase data, indicate that for the continental shelf off the Umpqua and Eel Rivers, approximately 15±10% of the total Mn that is delivered to the seafloor is remobilized. The compiled data set shows that the benthic Mn efflux co-varies with the organic carbon oxidation rate with a Mn to organic carbon oxidation (Cox) ratio of ~0.8mmol Mn mol-1. Although this ratio can be as high as ~5 for some Eel River sites, the generally close correspondence between Mn and organic carbon implies that the organic carbon oxidation rate exerts some primary control over the rate of the Mn efflux. The amount of organic carbon oxidized by Mn-oxides, however, represents a small fraction (i.e., generally <1%) of the total organic carbon oxidized in these seafloor sediments. © 2012 Elsevier Ltd., Cited By (since 1996):5, Oceanography, CODEN: CSHRD
Author: McManus, Berelson, Severmann, Johnson, Hammond, Roy, Coale
Date: 2012-01-01T00:00:00Z

Title: The flux of iron from continental shelf sediments,
Description: The flux of dissolved iron from sediments to the water column was measured with flux chambers along the California coast over a five-year period. High fluxes were observed from sediments on the continental shelf. The measured fluxes were an average of 75 times larger than flux values derived from pore-water iron gradients. The iron flux was significantly correlated with the oxidation of organic matter, which allows an extrapolation to the global shelf. The input from shelf sediments is at least as significant as the global input of dissolved iron from aerosols, which has been presumed to be the dominant external iron source. Evidence of this input is seen 100's of kilometers offshore where it can enable the high productivity of broad coastal regions seen in satellite images. Copyright 2004 by the American Geophysical Union., Cited By (since 1996):125, Oceanography, CODEN: GPRLA, ,
Author: Elrod, Berelson, Coale, Johnson
Date: 2004-01-01T00:00:00Z

Title: A time series of benthic flux measurements from Monterey Bay, CA,
Description: In situ incubation chamber measurements of benthic nutrient recycling rates were made on the Monterey Bay shelf at 100m during various years and seasons. Variability in nutrient (Si, PO 4 2+, NH 3, NO 3 -) and trace metal (Mn, Fe (II), Cu) fluxes correlate with variability in the amount of organic carbon oxidized on the sea floor. Patterns of primary productivity show a mid-year maxima, consistent with the timing of increased rates of benthic C org and opal recycling. High rates of C org rain to the shelf promote nitrate consumption at a rate that equals or exceeds ammonia efflux. Low rates of C org rain promote greater efflux of DIN; thus these margin sediments provide a negative feedback to local productivity cycles. The efflux of iron (II) from shelf sediments is sufficient to support > 100% of new production, yet Fe flux is positively correlated with C org recycling which lags the maximum in new production. On account of this time lag, diagenetically recycled Fe is not likely a micro-nutrient trigger of new production, but could serve as a positive feedback. Bio-irrigation rates are seasonally variable by 30% but maximal during the maximum productivity months. © 2003 Elsevier Science Ltd. All rights reserved., Cited By (since 1996):65, CODEN: CSHRD, , , Oceanography
Author: Berelson, McManus, Coale, Johnson, Burdige, Kilgore, Colodner, Chavez, Kudela, Boucher
Date: 2003-01-01T00:00:00Z

Title: Phosphorus regeneration in continental margin sediments,
Description: Benthic incubation chambers have been deployed in a variety of geochemical environments along the California Continental Margin. These include both high and low oxygen environments and sites where the rate of organic matter oxidation on the seafloor (Cox) ranges from < 1 mmol m-2 day-1 to more than 7 mmol m-2 day-1 through a depth range of 100-3500 m. This range in the rate of organic matter oxidation along with variations in the concentration of bottom water oxygen allow us to elucidate the diagenetic conditions under which P regeneration may be decoupled from organic matter cycling. Under conditions where bottom water oxygen concentration is low (<50 μM), and the rate of organic matter oxidation is also low (< 1 mmol m-2 day-1), P regeneration may be less than that expected from the decay of organic debris and, in some cases, there is a flux of phosphate into the sediments. At stations where bottom water oxygen is low, and the degradation rate of organic material is greater than 1 mmol m-2 day-1, phosphate may be released at a rate exceeding the production expected from the oxidation of organic matter. At stations having high bottom water oxygen concentrations, rates of organic matter decomposition < ∼7 mmol m-2 day-1, and where benthic irrigation is not significant, P regeneration is consistent with that expected from the decomposition of organic debris. In addition, our data indicate that high benthic iron fluxes are observed in regions exhibiting a decoupling between organic matter and phosphate, whereas low to zero iron fluxes are observed in regions where P regeneration is either consistent with or less than that expected from the decomposition of organic material. These results support previous work suggesting a coupling between iron cycling and phosphate cycling in suboxic environments. Data presented here show that this coupling may result in either preferential phosphate burial or release relative to organic material in suboxic environments. Copyright © 1997 Elsevier Science Ltd., Cited By (since 1996):105, ,
Author: Mcmanus, Berelson, Coale, Johnson, Kilgore
Date: 1997-01-01T00:00:00Z

$Diagenetic fractionation of Ge and Si in reducing sediments$

Title: Diagenetic fractionation of Ge and Si in reducing sediments,
Description: The average Ge/Si ratio in the ocean is determined by the budgets for each of these elements. Previous budget formulations have assumed that the only important sink for both elements is burial as opal, based on studies of the Si cycle and the close oceanic coupling observed between inorganic Ge and Si distributions. However, these budgets implied two paradoxes: (1) hydrothermal flow through ocean ridges is smaller than predicted by other tracers, and (2) the lower Ge/Si ratio of opal deposited during glacial times compared to that deposited during interglacial times required enhanced weathering during cooler, drier climates. Both paradoxes could be resolved if a significant sedimentary sink for Ge other than opal burial could be identified, and the objective of this study was to search for one. Two pore water profiles collected in Equatorial Pacific sediments show that Ge and Si behave similarly in the upper 10 cm of sediment, indicating no evidence for a significant non-opal sink for Ge in oxic sediments. By contrast, profiles in several cores from the California Margin demonstrate that in reducing sediments, Ge diagenesis is poorly coupled to Si diagenesis: significant Ge removal is evident, both downcore and sometimes in the near-surface. Benthic flux chamber measurements at three continental slope stations, all with an oxic layer less than 1 cm thick and large iron gradients in near-surface pore waters, showed that 55 ± 9% of the Ge released by opal dissolution is sequestered. However, at two locations with anoxic sediments but little pore water Fe+2 in the upper 2 cm, flux measurements indicated little fractionation from the oceanic ratio during diagnesis, implicating the importance of iron for fractionating Ge from Si during diagenesis. If the Ge sequestration observed in the iron-rich CA margin sediments is typical of all slope sediments (using a depth range of 200-1000 m), then the Ge sink is sufficient to bring the hydrothermal budget based on Ge into concurrence with that based on other tracers. The temporal variation in oceanic Ge/Si could be explained if Ge and Si inputs remain constant and the effective diagenetic fractionation of Ge increases by a factor of 2-3 during glacial times. Increased fractionation would require that glacial periods are characterized by increased opal dissolution in iron-rich reducing sediments; this could be caused by (1) thinning of the oxygenated sediment layer in response to decreased bottom water oxygen concentrations or increased rain of organics to the sea floor, (2) increased rain of iron-rich detrital sediments in areas receiving high opal rain, (3) increased rain of opal to sediments in margin areas. If the oceanic Ge/Si ratio reflects increased rain of diatom opal or organic carbon in margin areas during glacial periods, it may indicate an increase in the efficiency of the biological pump for CO2 during glacial times. Copyright (C) 2000 Elsevier Science Ltd., Cited By (since 1996):38, Oceanography, ,
Author: Hammond, McManus, Berelson, Meredith, Klinkhammer, Coale
Date: 2000-01-01T00:00:00Z

Title: A time series of benthic flux measurements from Monterey Bay, CA,
Description: , , , In situ incubation chamber measurements of benthic nutrient recycling rates were made on the Monterey Bay shelf at 100 m during various years and seasons. Variability in nutrient (Si, PO42+, NH3, NO3−) and trace metal (Mn, Fe (II), Cu) fluxes correlate with variability in the amount of organic carbon oxidized on the sea floor. Patterns of primary productivity show a mid-year maxima, consistent with the timing of increased rates of benthic Corg and opal recycling. High rates of Corg rain to the shelf promote nitrate consumption at a rate that equals or exceeds ammonia efflux. Low rates of Corg rain promote greater efflux of DIN; thus these margin sediments provide a negative feedback to local productivity cycles. The efflux of iron (II) from shelf sediments is sufficient to support >100% of new production, yet Fe flux is positively correlated with Corg recycling which lags the maximum in new production. On account of this time lag, diagenetically recycled Fe is not likely a micro-nutrient trigger of new production, but could serve as a positive feedback. Bio-irrigation rates are seasonally variable by 30% but maximal during the maximum productivity months., ,
Author: Berelson, McManus, Coale, Johnson, Burdige, Kilgore, Colodner, Chavez, Kudela, Boucher
Date: 2003-01-01T00:00:00Z

Title: The flux of iron from continental shelf sediments: A missing source for global budgets
Description: The flux of dissolved iron from sediments to the water column was measured with flux chambers along the California coast over a five-year period. High fluxes were observed from sediments on the continental shelf. The measured fluxes were an average of 75 times larger than flux values derived from pore-water iron gradients. The iron flux was significantly correlated with the oxidation of organic matter, which allows an extrapolation to the global shelf. The input from shelf sediments is at least as significant as the global input of dissolved iron from aerosols, which has been presumed to be the dominant external iron source. Evidence of this input is seen 100’s of kilometers offshore where it can enable the high productivity of broad coastal regions seen in satellite images.
Author: Elrod, Berelson, Coale, Johnson

Title: Organic matter diagenesis in the sediments of the San Pedro Shelf along a transect affected by sewage effluent,
Description: A study was conducted to examine the rate of organic matter degradation within the sediments adjacent to the Whites Point Los Angeles County sewage outfall system on the San Pedro Shelf. Benthic chamber deployments were made at three stations in a transect away from the outfall pipe during three cruise periods (October 1990, February and October 1991). The fluxes of phosphate, silicate and radon-222 showed the most significant difference (factor of 3) between stations proximal and distal to the sewage effluent outfall pipe; the fluxes of nitrate, ammonia, alkalinity and TCO2 showed some gradient (a factor of 1.5-2) and the uptake of oxygen showed no variability between sites. Carbon oxidation in these sediments is driven primarily by net oxygen consumption and secondarily by net sulfate reduction. Net sulfate reduction accounts for about 30% of the carbon oxidation near the outfall pipe and 10-15% at the distal sites. Measurements of radon-222 fluxes and radon emanation rates from sediments indicate that the intensity of bio-irrigation is greater by a factor of 2 at sites away from the outfall pipe, but also shows that bio-irrigation does take place at the site adjacent to the pipe. The total amount of particulate organic carbon (POC) oxidized in the sediments around the outfall is ∼2 × 107 g C/d. An estimate of carbon burial in this region is 4 × 107 g C/d. The outfall system could supply ∼3 × 107 g C/d of which 12-20% is estimated to have been deposited in the region. Hence, effluent-derived POC, although it may be a part of the total organic carbon pool undergoing diagenesis and burial on the sea floor, is not likely the only source of carbon to this system. Primary productivity in the surface ocean could supply 9-13 × 107 g C/d to the sea floor. A balanced carbon budget requires that half the primary production is exported to the sea floor, although this budget does not account for other sources of POC to the region. © 2002 Elsevier Science Ltd. All rights reserved., Cited By (since 1996):13, CODEN: CSHRD, ,
Author: Berelson, Johnson, Coale, Li
Date: 2002-01-01T00:00:00Z

Title: On the formation of the manganese maximum in the oxygen minimum,
Description: A simple model that accounts for the formation of the Mn maximum in the oxygen minimum is presented here. In this model, Mn is proposed to cycle in a constant proportion to carbon, as do nitrogen and phosphorous. Superimposed on the Mn-carbon cycle is the removal of Mn(II) via scavenging onto sinking particles and transport by vertical diffusion. Scavenging is assumed to follow the rate law observed in the laboratory for Mn(II) oxidation. Manganese (II) concentrations were calculated with the model at stations in the Pacific and Atlantic Oceans and compared with measurements of dissolved Mn. All parameters in the model were based on laboratory measurements or field observations. The model reproduced Mn(II) maxima of the correct concentration and at the correct depth. This agreement was observed at a range of oxygen concentrations. The calculations demonstrate that the Mn maximum can form because of a reduction in the pseudo-first order scavenging rate constant (k′) within the oxygen minimum. The value of k′ will decrease in regions of the water column with low oxygen and pH (k′ = k0 [O2] {OH-}2). These regions will accumulate higher dissolved Mn(II) concentrations before the rate of Mn(II) removal, k′ [Mn(II)], equals the input from remineralization of POC and a steady state is reached. An additional source of Mn, such as flux from continental margin sediments or dissolution of Mn oxides, is not necessary to account for formation of the Mn maximum., Cited By (since 1996):51, ,
Author: Johnson, Coale, Berelson, Gordon
Date: 1996-01-01T00:00:00Z

Title: Biogenic matter diagenesis on the sea floor,
Description: Benthic chamber measurements of the reactants and products involved with biogenic matter diagenesis (oxygen, ammonium, nitrate, silicate, phosphate, TCO2, alkalinity) were used to define fluxes of these solutes into and out of the sediments off southern and central California. Onshore to offshore transects indicate many similarities in benthic fluxes between these regions. The pattern of benthic organic carbon oxidation as a function of water depth, combined with published sediment trap records, suggest that the supply of organic carbon from vertical rain can just meet the sedimentary carbon oxidation + burial demand for the central California region between the depths 100-3500 m. However, there is not enough organic carbon raining through the upper water column to support its oxidation and burial in the basins off southern California. Lateral transport and focusing of refractory carbon within these basins is proposed to account for the carbon buried. The organic carbon burial efficiency is greater off southern California (40-60%) compared to central California (2-20%), even though carbon rain rates are comparable. Oxygen uptake rates are not sensitive to bottom water oxygen concentrations nor to the bulk wt. % organic carbon in surficial sediments. Nitrate uptake rates are well defined by the depth of oxygen penetration into the sediments and the overlying water column nitrate concentration. Nitrate uptake accounts for about 50% of the total denitrification taking place in shelf sediments and denitrification (0.1-1.0 mmolN/m2d) occurs throughout the entire study region. The ratio of carbon oxidized to opal dissolved on the sea floor is constant (0.8 ± 0.2) through a wide range of depths, supporting the hypothesis that opal dissolution kinetics may be dominated by a highly reactive phase. Sea floor carbonate dissolution is negligible within the oxygen minimum zone and reaches maximal rates just above and below this zone (0.2-2.0 mmol/m2d)., Cited By (since 1996):72, Oceanography, ,
Author: Berelson, McManus, Coale, Johnson, Kilgore, Burdige, Pilskaln
Date: 1996-01-01T00:00:00Z

Title: Geochemistry of barium in marine sediments,
Description: Variations in the accumulation rate of barium in marine sediments are thought to be indicative of variations in marine biological productivity through time. However, the use of Ba as a proxy for paleoproductivity is partly dependent upon its being preserved in the sediment record in a predictable or consistent fashion. Arguments in favor of high Ba preservation are partly based on the assumption that sediment porewaters are generally at saturation with respect to pure barite. The idea is that because nondetrital sedimentary Ba predominantly exists as barite, porewater saturation would promote burial. We present sediment porewater, sediment solid phase, and benthic incubation chamber data suggesting that solid-phase Ba preservation may be compromised in some geochemical settings. We propose that under suboxic diagenetic conditions, characterized by low bottom water oxygen and high organic carbon respiration rates, Ba preservation may be reduced. Independent of the mechanism, if this assertion is true, then it becomes important to know when the Ba record is unreliable. We present evidence demonstrating that the sedimentary accumulation of authigenic U may serve as a proxy for when the Ba record is unreliable. We then provide an example from the Southern Ocean during the last glacial period where high authigenic U concentrations coincide with high Pa:Th ratios and high accumulation rates of biogenic opal, but we find low accumulation rates of sedimentary Ba. Thus, for the study sites presented here during the last glacial, we conclude that Ba is an unreliable productivity proxy., Cited By (since 1996):163, ,
Author: McManus, Berelson, Klinkhammer, Johnson, Coale, Anderson, Kumar, Burdige, Hammond, Brumsack, McCorkle, Rushdi
Date: 1998-01-01T00:00:00Z

Title: Cadmium flux in Los Angeles/Long Beach harbours and at sites along the California continental margin,
Description: Fluxes of dissolved cadmium were measured in situ using benthic flux chambers at stations in Los Angeles/Long Beach harbour and at sites on the California continental margin. Cadmium fluxes ranged from -0.212 to 0.118 μmol m-2 d-1 indicating that Cd flux may either be into or out of sediments. Correlations between Cd flux and carbon oxidation rate and between carbon oxidation rate and sulfate reduction indicate that anaerobic microbial degradation was the major process controlling both the sign and the magnitude of cadmium fluxes at stations in Los Angeles and Long Beach harbours. A simple box model based on sediment fluxes and water column concentrations indicates cadmium has a residence time of 47 days within the Los Angeles/Long Beach harbour system, similar to the hydraulic residence time. Sedimentary flux is, therefore, sufficient to account for water column cadmium concentration in inner harbour areas, suggesting that the sediments are the dominant source and sink of cadmium in these areas of the harbour. Comparison of the cadmium: phosphate ratio for the Los Angeles/Long Beach harbour water column with those reported for the northeast Pacific suggests that distributions of Cd in the study area were elevated over expected values but appear to be dominated by natural physical and biogeochemical processes. © 2001 Academic Press., Cited By (since 1996):9, Oceanography, CODEN: ECSSD, ,
Author: Colbert, Coale, Berelson, Johnson
Date: 2001-01-01T00:00:00Z

Title: Manganese flux from continental margin sediments in a transect through the oxygen minimum,
Description: The flux of manganese from continental margin sediments to the ocean was measured with a free-vehicle, benthic flux chamber in a transect across the continental shelf and upper slope of the California margin. The highest fluxes were observed on the shallow continental shelf. Manganese flux decreased linearly with bottom water oxygen concentration, and the lowest fluxes occurred in the oxygen minimum zone (at a depth of 600 to 1000 meters). Although the flux of manganese from continental shelf sediments can account for the elevated concentrations observed in shallow, coastal waters, the flux from sediments that intersect the oxygen minimum cannot produce the subsurface concentration maximum of dissolved manganese that is observed in the Pacific Ocean., Cited By (since 1996):47, Oceanography, CODEN: SCIEA, ,
Author: Johnson, Berelson, Coale, Coley, Elrod, Fairey, Iams, Kilgore, Nowicki
Date: 1992-01-01T00:00:00Z

Title: Benthic fluxes and pore water studies from sediments of the central equatorial north Pacific,
Description: Benthic exchange rates of radon-222, oxygen, nitrate, ammonia, and silica were determined using an in situ benthic flux chamber and by modeling pore water profiles at three sites in the central equatorial north Pacific. A comparison of these results reveals several artifacts of pore water collection and processing. Whole-core squeezer (WCS) silica profiles are influenced by adsorption during squeezing and yield calculated fluxes that are too large. Pore water ammonia profiles show near-surface maxima that appear to be an artifact of core recovery. Near-surface nitrate measurements may also be suspect due to oxidation of the ammonia released, causing anomalously large nitrate gradients that yield overestimates of benthic exchange rates. Fluxes of radon, oxygen, and nitrate calculated from WCS profiles agree with chamber fluxes to better than 40% at all sites. Fluxes of silica and nitrate calculated from pore water data collected at coarser scales (> 1 cm intervals) agree within 50% with chamber measurements. Previous flux estimates from pore water and solid phase models established at two of these sites using data collected 6 years prior to this work differ from these chamber measurements, in some cases by up to a factor of 5 due to modeling uncertainties and temporal variabilities in the delivery of organic matter to a site. The benthic oxygen consumption rates measured at these sites are similar (they average 0.36 ± 0.03 mmol m-2 day-1) and are consistent with a trend of oxygen uptake vs. water depth previously established by others on a transect through the oligotrophic north Pacific gyre. © 1990., Cited By (since 1996):62, Rocks and Cores, ,
Author: Berelson, Hammond, O'neill, Xu, Chin, Zukin
Date: 1990-01-01T00:00:00Z

Title: Fluxes of dissolved organic carbon from California continental margin sediments,
Description: Fluxes of dissolved organic carbon (DOC) from marine sediments represent a poorly constrained component of the oceanic carbon cycle that may affect the concentration and composition of DOC in the ocean. Here we report the first in situ measurements of DOC fluxes from continental margin sediments (water depths ranging from 95 to 3,700 m), and compare these fluxes with measured benthic fluxes from 20 other coastal and continental margin sediments. With this combined data set data we have estimated that benthic DOC fluxes are less than ~10% of sediment carbon oxidation rates, and that the integrated DOC flux from sediments in water depths less than 2,000 m is ~180 Tg C/yr. These fluxes are roughly equivalent to the riverine DOC flux, and the organic carbon burial rate in marine sediments. Benthic DOC fluxes therefore represent an important net source of DOC to the oceans. We also note that: (1) benthic DOC fluxes represent a loss of organic carbon from sediments; (2) in many sediments these fluxes appear to be controlled by molecular diffusion (i.e., by pore water concentration gradients); (3) pore water DOC may be an important intermediate in sediment carbon burial and preservation. These observations therefore suggest a linkage between benthic DOC fluxes and sediment carbon preservation that may be mediated by pore water DOC concentrations and cycling. The magnitude and fate of DOC effluxing from marine sediments is thus important to understanding carbon cycles and budgets in the marine environment., Cited By (since 1996):55, ,
Author: Burdige, Berelson, Coale, McManus, Johnson
Date: 1999-01-01T00:00:00Z