scholarly journals Quantifying 210Po/210Pb Disequilibrium in Seawater: A Comparison of Two Precipitation Methods With Differing Results

2021 ◽  
Vol 8 ◽  
Author(s):  
Montserrat Roca-Martí ◽  
Viena Puigcorbé ◽  
Maxi Castrillejo ◽  
Núria Casacuberta ◽  
Jordi Garcia-Orellana ◽  
...  
Keyword(s):  
Water Column ◽  
Methodological Issue ◽  
Deep Ocean ◽  
Future Research ◽  
Upper Ocean ◽  
Deep Waters ◽  
Poc Export ◽  
Particle Export ◽  
Seawater Samples ◽  
Lead 210

The disequilibrium between lead-210 (210Pb) and polonium-210 (210Po) is increasingly used in oceanography to quantify particulate organic carbon (POC) export from the upper ocean. This proxy is based on the deficits of 210Po typically observed in the upper water column due to the preferential removal of 210Po relative to 210Pb by sinking particles. Yet, a number of studies have reported unexpected large 210Po deficits in the deep ocean indicating scavenging of 210Po despite its radioactive mean life of ∼ 200 days. Two precipitation methods, Fe(OH)3 and Co-APDC, are typically used to concentrate Pb and Po from seawater samples, and deep 210Po deficits raise the question whether this feature is biogeochemically consistent or there is a methodological issue. Here, we present a compilation of 210Pb and 210Po studies that suggests that 210Po deficits at depths >300 m are more often observed in studies where Fe(OH)3 is used to precipitate Pb and Po from seawater, than in those using Co-APDC (in 68 versus 33% of the profiles analyzed for each method, respectively). In order to test whether 210Po/210Pb disequilibrium can be partly related to a methodological artifact, we directly compared the total activities of 210Pb and 210Po in four duplicate ocean depth-profiles determined by using Fe(OH)3 and Co-APDC on unfiltered seawater samples. While both methods produced the same 210Pb activities, results from the Co-APDC method showed equilibrium between 210Pb and 210Po below 100 m, whereas the Fe(OH)3 method resulted in activities of 210Po significantly lower than 210Pb throughout the entire water column. These results show that 210Po deficits in deep waters, but also in the upper ocean, may be greater when calculated using a commonly used Fe(OH)3 protocol. This finding has potential implications for the use of the 210Po/210Pb pair as a tracer of particle export in the oceans because 210Po (and thus POC) fluxes calculated using Fe(OH)3 on unfiltered seawater samples may be overestimated. Recommendations for future research are provided based on the possible reasons for the discrepancy in 210Po activities between both analytical methods.

scholarly journals Nitrogen cycling in the Southern Ocean Kerguelen Plateau area: evidence for significant surface nitrification from nitrate isotopic compositions

2015 ◽  
Vol 12 (5) ◽  
pp. 1459-1482 ◽  
Author(s):  
F. Dehairs ◽  
F. Fripiat ◽  
A.-J. Cavagna ◽  
T. W. Trull ◽  
C. Fernandez ◽  
...  
Keyword(s):  
Water Column ◽  
Mixed Layer ◽  
Nitrate Uptake ◽  
Deep Ocean ◽  
Kerguelen Plateau ◽  
Mass Balance Calculation ◽  
Particulate Nitrogen ◽  
Isotopic Compositions ◽  
Deep Waters ◽  
Plateau Area

Abstract. This paper presents whole water column data for nitrate N, O isotopic composition for the Kerguelen Plateau area and the basin extending east of Heard Island, aiming at understanding the N-cycling in this naturally iron fertilized area that is characterized by large re-current phytoplankton blooms. The KEOPS 2 expedition (October–November 2011) took place in spring season and complements knowledge gathered during an earlier summer expedition to the same area (KEOPS 1, February–March 2005). As noted by others a remarkable condition of the system is the moderate consumption of nitrate over the season (nitrate remains >20 μM) while silicic acid becomes depleted, suggesting significant recycling of nitrogen. Nitrate isotopic signatures in the upper water column do mimic this condition, with surprising overlap of spring and summer regressions of δ18ONO3 vs. δ15NNO3 isotopic compositions. These regressions obey rather closely the 18&amp;varepsilon;/15&amp;varepsilon; discrimination expected for nitrate uptake (18&amp;varepsilon;/15&amp;varepsilon; = 1), but regression slopes as large as 1.6 were observed for the mixed layer above the Kerguelen Plateau. A preliminarily mass balance calculation for the early bloom period points toward significant nitrification occurring in the mixed layer and which may be equivalent to up to 47% of nitrate uptake above the Kerguelen Plateau. A further finding concerns deep ocean low δ18ONO3 values (<2‰) underlying high chlorophyll waters at the Polar Front Zone and which cannot be explained by remineralization and nitrification of the local particulate nitrogen flux, which is too small in magnitude. However, the studied area is characterized by a complex recirculation pattern that would keep deep waters in the area and could impose a seasonally integrated signature of surface water processes on the deep waters.

scholarly journals The Atmospheric Bridge Communicated the δ<sup>13</sup>C Decline during the Last Deglaciation to the Global Upper Ocean

2020 ◽  
Author(s):  
Jun Shao ◽  
Lowell D Stott ◽  
Laurie Menviel ◽  
Andy Ridgwell ◽  
Malin Ödalen ◽  
...  
Keyword(s):  
Nutrient Transport ◽  
Deep Ocean ◽  
Upper Ocean ◽  
Last Deglaciation ◽  
Planktic Foraminifera ◽  
Proxy Records ◽  
Deep Waters ◽  
Eastern Equatorial Pacific ◽  
The Last Deglaciation ◽  
Atmospheric Pco2

Abstract. During the early last glacial termination (17.2–15 ka) atmospheric δ13C declined sharply by 0.3–0.4 ‰ as atmospheric pCO2 rose. This was the initial part of the atmospheric δ13C excursion that lasted for multiple thousand years. A similar δ13C decline has been documented in marine proxy records from both surface and thermocline-dwelling planktic foraminifera. The foraminiferal δ13C decline has previously been attributed to a flux of respired carbon from the deep ocean that was subsequently transported within the upper ocean (i.e. bottom up transport) to sites where the signal is recorded. Here, we provide modeling evidence that when respired carbon upwells in the Southern Ocean, negative δ13C anomalies in the global upper ocean were instead transferred from the atmosphere (i.e. top down transport). Due to this efficient atmospheric bridge, the pathway of δ13C transport was likely to be different from nutrient transport during the early deglaciation. This implies that the usage of planktic δ13C records for identifying the carbon source(s) responsible for the atmospheric pCO2 rise during the early deglaciation is limited. The model results also suggest that thermocline waters in upwelling systems like the eastern equatorial Pacific, and even upper deep waters above 2000 m, can be affected by this atmospheric bridge during the early deglaciation. Our results imply that caution must be applied when interpreting early deglacial marine δ13C records from depths that are potentially affected by the atmosphere.

scholarly journals Nitrogen cycling in the Southern Ocean Kerguelen Plateau area: evidence for significant surface nitrification from nitrate isotopic compositions

2014 ◽  
Vol 11 (9) ◽  
pp. 13905-13955 ◽  
Author(s):  
F. Dehairs ◽  
F. Fripiat ◽  
A.-J. Cavagna ◽  
T. W. Trull ◽  
C. Fernandez ◽  
...  
Keyword(s):  
Water Column ◽  
Mixed Layer ◽  
Nitrate Uptake ◽  
Deep Ocean ◽  
Kerguelen Plateau ◽  
Mass Balance Calculation ◽  
Particulate Nitrogen ◽  
Isotopic Compositions ◽  
Deep Waters ◽  
Plateau Area

Abstract. This paper presents whole water column data for nitrate N, O isotopic composition for the Kerguelen Plateau area and the basin extending east of the island, aiming at understanding the N-cycling in this naturally iron fertilized area that is characterized by large re-current phytoplankton blooms. The KEOPS 2 expedition (October–November 2011) took place in spring season and complements knowledge gathered during an earlier summer expedition to the same area (KEOPS 1, February–March 2005). As noted by others a remarkable condition of the system is the moderate consumption of nitrate over the season (nitrate remains > 20 μM) while silicic acid becomes depleted, suggesting significant recycling of nitrogen. Nitrate isotopic signatures in the upper water column do mimic this condition, with surprising overlap of spring and summer regressions of δ18ONO3 vs. δ15NNO3 isotopic compositions. These regressions obey rather closely the 18&amp;varepsilon;/15&amp;varepsilon; discrimination expected for nitrate uptake (18&amp;varepsilon;/15&amp;varepsilon; = 1), but regression slopes as large as 1.6 were observed for the mixed layer above the Kerguelen Plateau. A preliminary mass balance calculation for the early bloom period points toward significant nitrification occurring in the mixed layer and which could account for up to 80 % of nitrate uptake above the Kerguelen Plateau. A further finding concerns deep ocean low δ18ONO3 values (< 2‰) underlying high chlorophyll waters at the Polar Front Zone and which cannot be explained by remineralisation and nitrification of the local particulate nitrogen flux, which is too small in magnitude. However, the studied area is characterised by a complex recirculation pattern that would keep deep waters in the area and could impose a seasonally integrated signature of surface water processes on the deep waters.

scholarly journals Distribution of 210Pb and 210Po in the Arctic water column during the 2007 sea-ice minimum: Particle export in the ice-covered basins

2018 ◽  
Vol 142 ◽  
pp. 94-106 ◽  
Author(s):  
Montserrat Roca-Martí ◽  
Viena Puigcorbé ◽  
Jana Friedrich ◽  
Michiel Rutgers van der Loeff ◽  
Benjamin Rabe ◽  
...  
Keyword(s):  
Sea Ice ◽  
Water Column ◽  
The Arctic ◽  
Arctic Water ◽  
Particle Export

scholarly journals 4SM: A Novel Self-calibrated Algebraic Ratio Method for Satellite Derived Bathymetry and Water Column Correction

2017 ◽  
Author(s):  
Yann George MOREL
Keyword(s):  
Water Column ◽  
Radiative Transfer Equation ◽  
Atmospheric Correction ◽  
Ratio Method ◽  
Published Data ◽  
Deep Waters ◽  
Bare Land ◽  
Depth Sounding ◽  
Radiance Data ◽  
The Ideal

All empirical water column correction methods have consistently been reported to require existing depth sounding data for the purpose of calibrating a simple depth retrieval model; they yield poor results over very bright or very dark bottoms. In contrast, we set out to (i) use only the relative radiance data in the image along with published data, and several new assumptions, (ii) in order to specify and operate the simplified radiative transfer equation (RTE), (iii) for the purpose of retrieving both the satellite derived bathymetry (SDB) and the water column corrected spectral reflectance over shallow seabeds. Sea truth regressions show that SDB depths retrieved by the method only need tide correction. Therefore it shall be demonstrated that, under such new assumptions, there is no need (i) for formal atmospheric correction, (ii) nor for conversion of relative radiance into calibrated reflectance , (iii) nor for existing depth sounding data, to specify the simplified RTE and produce both SDB and spectral water column corrected radiance ready for bottom typing. Moreover, the use of the panchromatic band for that purpose is introduced. Altogether, we named this process the Self-Calibrated Supervised Spectral Shallow-sea Modeler (4SM). This approach requires a trained practitioner, though, to produce its results within hours of downloading the raw image. The ideal raw image should be a &ldquo;near-nadir&rdquo; view, exhibit homogeneous atmosphere and water column, include some coverage of optically deep waters and bare land, and lend itself to quality removal of haze, atmospheric adjacency effect, and sun/sky glint.

scholarly journals Missing links in the study of solute and particle exchange between the sea floor and water column

2020 ◽  
Vol 77 (5) ◽  
pp. 1602-1616 ◽  
Author(s):  
Saskia Rühl ◽  
Charlie Thompson ◽  
Ana M Queirós ◽  
Stephen Widdicombe
Keyword(s):  
Water Column ◽  
Current Knowledge ◽  
Anthropogenic Impacts ◽  
Future Research ◽  
Sea Floor ◽  
Marine Habitats ◽  
Exchange Processes ◽  
Ecosystem Level ◽  
Particle Exchange

Abstract Exchanges of solutes and solids between the sea floor and water column are a vital component of ecosystem functioning in marine habitats around the globe. This review explores particle and solute exchange processes, the different mechanisms through which they interact at the ecosystem level, as well as their interdependencies. Solute and particle exchange processes are highly dependent on the characteristics of the environment within which they takes place. Exchange is driven directly by a number of factors, such as currents, granulometry, nutrient, and matter inputs, as well as living organisms. In turn, the occurrence of exchanges can influence adjacent environments and organisms. Major gaps in the present knowledge include the temporal and spatial variation in many of the processes driving benthic/pelagic exchange processes and the variability in the relative importance of individual processes caused by this variation. Furthermore, the accurate assessment of some anthropogenic impacts is deemed questionable due to a lack of baseline data and long-term effects of anthropogenic actions are often unknown. It is suggested that future research should be transdisciplinary and at ecosystem level wherever possible and that baseline surveys should be implemented and long-term observatories established to fill the current knowledge gaps.

scholarly journals Modelling the biogeochemical effects of heterotrophic and autotrophic N<sub>2</sub> fixation in the Gulf of Aqaba (Israel), Red Sea

2018 ◽  
Vol 15 (24) ◽  
pp. 7379-7401 ◽  
Author(s):  
Angela M. Kuhn ◽  
Katja Fennel ◽  
Ilana Berman-Frank
Keyword(s):  
Water Column ◽  
Red Sea ◽  
N2 Fixation ◽  
Large Scale ◽  
Gulf Of Aqaba ◽  
Nutrient Concentrations ◽  
Nutrient Ratios ◽  
Biogeochemical Models ◽  
Deep Waters ◽  
Direct Measurements

Abstract. Recent studies demonstrate that marine N2 fixation can be carried out without light by heterotrophic N2 fixers (diazotrophs). However, direct measurements of N2 fixation in aphotic environments are relatively scarce. Heterotrophic as well as unicellular and colonial photoautotrophic diazotrophs are present in the oligotrophic Gulf of Aqaba (northern Red Sea). This study evaluates the relative importance of these different diazotrophs by combining biogeochemical models with time series measurements at a 700 m deep monitoring station in the Gulf of Aqaba. At this location, an excess of nitrate, relative to phosphate, is present throughout most of the water column and especially in deep waters during stratified conditions. A relative excess of phosphate occurs only at the water surface during nutrient-starved conditions in summer. We show that a model without N2 fixation can replicate the observed surface chlorophyll but fails to accurately simulate inorganic nutrient concentrations throughout the water column. Models with N2 fixation improve simulated deep nitrate by enriching sinking organic matter in nitrogen, suggesting that N2 fixation is necessary to explain the observations. The observed vertical structure of nutrient ratios and oxygen is reproduced best with a model that includes heterotrophic as well as colonial and unicellular autotrophic diazotrophs. These results suggest that heterotrophic N2 fixation contributes to the observed excess nitrogen in deep water at this location. If heterotrophic diazotrophs are generally present in oligotrophic ocean regions, their consideration would increase current estimates of global N2 fixation and may require explicit representation in large-scale models.

Internal waves in JASIN

1983 ◽  
Vol 308 (1503) ◽  
pp. 389-405 ◽  
Keyword(s):  
Internal Waves ◽  
Internal Tide ◽  
Deep Ocean ◽  
Upper Ocean ◽  
Velocity Measurements ◽  
High Frequencies ◽  
Topographic Features ◽  
Rockall Trough ◽  
Moored Current Meters ◽  
The Continuum

The internal wavefield during the Joint Air—Sea Interaction (JASIN) experiment was monitored by moored current meters and moored and towed thermistor chains. The observations were concentrated in the upper ocean near the centre of Rockall Trough, but velocity measurements were also made near topographic features and throughout the water column. Observed spectra are compared with results from the deep ocean, as represented by the Garrett-Munk (GM) model of the spectral continuum, and are generally found to have spectral levels equal to or greater than the GM spectrum. The greatest deviation from the GM spectrum occurs at high frequencies and wavenumbers where the observed spectra often exhibit a spectral shoulder and high vertical coherence. These features, also found in other upper-ocean spectra, are explained by a model composed of three vertically standing modes. The spatial variation of internal wave variance is related to topography: variance is highest near rough topography. The ratio of variance in the semidiurnal tidal band to variance in a band in the continuum is approximately constant. The possibility of a dynamical link between the two frequency bands requires further investigation. The semidiurnal internal tide varies temporally and spatially. Rockall Bank is identified as the source of an energetic beam of tidal oscillations during a one-week period.

scholarly journals The Mediterranean Sea Overturning Circulation

2019 ◽  
Vol 49 (7) ◽  
pp. 1699-1721 ◽  
Author(s):  
Nadia Pinardi ◽  
Paola Cessi ◽  
Federica Borile ◽  
Christopher L. P. Wolfe
Keyword(s):  
Mediterranean Sea ◽  
Water Column ◽  
Eastern Mediterranean ◽  
Deep Ocean ◽  
Western Mediterranean ◽  
The Other ◽  
Strait Of Gibraltar ◽  
Water Formation ◽  
Dense Water Formation ◽  
Meridional Overturning

AbstractThe time-mean zonal and meridional overturning circulations of the entire Mediterranean Sea are studied in both the Eulerian and residual frameworks. The overturning is characterized by cells in the vertical and either zonal or meridional planes with clockwise circulations in the upper water column and counterclockwise circulations in the deep and abyssal regions. The zonal overturning is composed of an upper clockwise cell in the top 600 m of the water column related to the classical Wüst cell and two additional deep clockwise cells, one corresponding to the outflow of the dense Aegean water during the Eastern Mediterranean Transient (EMT) and the other associated with dense water formation in the Rhodes Gyre. The variability of the zonal overturning before, during, and after the EMT is discussed. The meridional basinwide overturning is composed of clockwise, multicentered cells connected with the four northern deep ocean formation areas, located in the Eastern and Western Mediterranean basins. The connection between the Wüst cell and the meridional overturning is visualized through the horizontal velocities vertically integrated across two layers above 600 m. The component of the horizontal velocity associated with the overturning is isolated by computing the divergent components of the vertically integrated velocities forced by the inflow/outflow at the Strait of Gibraltar.

scholarly journals On the Linkage between Antarctic Surface Water Stratification and Global Deep-Water Temperature

2011 ◽  
Vol 24 (14) ◽  
pp. 3545-3557 ◽  
Author(s):  
Ralph F. Keeling ◽  
Martin Visbeck
Keyword(s):  
Water Temperature ◽  
North Atlantic ◽  
Deep Water ◽  
Surface Waters ◽  
Feedback Loop ◽  
Deep Ocean ◽  
Static Stability ◽  
Deep Waters ◽  
Water Stratification ◽  
The Antarctic

Abstract The suggestion is advanced that the remarkably low static stability of Antarctic surface waters may arise from a feedback loop involving global deep-water temperatures. If deep-water temperatures are too warm, this promotes Antarctic convection, thereby strengthening the inflow of Antarctic Bottom Water into the ocean interior and cooling the deep ocean. If deep waters are too cold, this promotes Antarctic stratification allowing the deep ocean to warm because of the input of North Atlantic Deep Water. A steady-state deep-water temperature is achieved such that the Antarctic surface can barely undergo convection. A two-box model is used to illustrate this feedback loop in its simplest expression and to develop basic concepts, such as the bounds on the operation of this loop. The model illustrates the possible dominating influence of Antarctic upwelling rate and Antarctic freshwater balance on global deep-water temperatures.

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