scholarly journals A comparison of the variability of biological nutrients against depth and potential density

2010 ◽  
Vol 7 (4) ◽  
pp. 1263-1269 ◽  
Author(s):  
J. While ◽  
K. Haines
Keyword(s):  
Temporal Variability ◽  
World Ocean ◽  
Biological Productivity ◽  
Potential Density ◽  
Dynamical Processes ◽  
Biogeochemical Models ◽  
Phosphate Silicate ◽  
Nutrient Variability ◽  
Series Study ◽  
Main Pycnocline

Abstract. The main biogeochemical nutrient distributions, along with ambient ocean temperature and the light field, control ocean biological productivity. Observations of nutrients are much sparser than physical observations of temperature and salinity, yet it is critical to validate biogeochemical models against these sparse observations if we are to successfully model biological variability and trends. Here we use data from the Bermuda Atlantic Time-series Study and the World Ocean Database 2005 to demonstrate quantitatively that over the entire globe a significant fraction of the temporal variability of phosphate, silicate and nitrate within the oceans is correlated with water density. The temporal variability of these nutrients as a function of depth is almost always greater than as a function of potential density, with he largest reductions in variability found within the main pycnocline. The greater nutrient variability as a function of depth occurs when dynamical processes vertically displace nutrient and density fields together on shorter timescales than biological adjustments. These results show that dynamical processes can have a significant impact on the instantaneous nutrient distributions. These processes must therefore be considered when modeling biogeochemical systems, when comparing such models with observations, or when assimilating data into such models.

scholarly journals A comparison of the variability of biological nutrients against depth and potential density

2009 ◽  
Vol 6 (5) ◽  
pp. 10177-10194
Author(s):  
J. While ◽  
K. Haines
Keyword(s):  
Light Field ◽  
World Ocean ◽  
Biological Productivity ◽  
Potential Density ◽  
Time Series Study ◽  
Biogeochemical Models ◽  
Phosphate Silicate ◽  
Series Study ◽  
Main Pycnocline

Abstract. The main biogeochemical nutrient distributions, along with ambient ocean temperature and the light field, control ocean biological productivity. Observations of nutrients are much sparser than physical observations of temperature and salinity, yet it is critical to validate biogeochemical models against these sparse observations if we are to successfully model biological variability and trends. Here we use data from the Bermuda Atlantic Time-series Study and from the World Ocean Database 2005, to demonstrate quantitatively that over the entire globe a significant fraction of the temporal variability of phosphate, silicate and nitrate within the oceans is correlated with water density. The variability of these nutrients with respect to depth and neutral density is estimated and it is shown that in most regions variability against density is significantly reduced. The largest reductions in variability were found within the main pycnocline. This in principle allows nutrient distributions to be inferred from physical hydrographic measurements, a fact that can usefully be applied to modeling, assimilating, and, in the long term, for biogeochemical forecasting.

scholarly journals Climatological distribution of dissolved inorganic nutrients in the Western Mediterranean Sea (1981–2017)

2021 ◽  
Author(s):  
Malek Belgacem ◽  
Katrin Schroeder ◽  
Alexander Barth ◽  
Charles Troupin ◽  
Bruno Pavoni ◽  
...  
Keyword(s):  
Mediterranean Sea ◽  
World Ocean ◽  
Western Mediterranean ◽  
Inorganic Nutrients ◽  
Data Product ◽  
Western Mediterranean Sea ◽  
Dissolved Inorganic Nutrients ◽  
In Situ Observations ◽  
Nutrient Variability

Abstract. The Western MEDiterranean Sea BioGeochemical Climatology (BGC-WMED) presented here is a product derived from in situ observations. Annual mean gridded nutrient fields for the period 1981–2017, and its sub-periods 1981–2004 and 2005–2017, on a horizontal 1/4° × 1/4° grid have been produced. The biogeochemical climatology is built on 19 depth levels and for the dissolved inorganic nutrients nitrate, phosphate and orthosilicate. To generate smooth and homogeneous interpolated fields, the method of the Variational Inverse Model (VIM) was applied. A sensitivity analysis was carried out to assess the comparability of the data product with the observational data. The BGC-WMED has then been compared to other available data products, i.e. the medBFM biogeochemical reanalysis of the Mediterranean Sea and the World Ocean Atlas18 (WOA18) (its biogeochemical part). The BGC-WMED product supports the understanding of inorganic nutrient variability in the western Mediterranean Sea, in space and in time, but can also be used to validate numerical simulations making it a reference data product.

scholarly journals An Assessment of Orthobaric Density in the Global Ocean

2005 ◽  
Vol 35 (11) ◽  
pp. 2054-2075 ◽  
Author(s):  
Trevor J. McDougall ◽  
David R. Jackett
Keyword(s):  
Southern Hemisphere ◽  
World Ocean ◽  
Ocean Basin ◽  
Ocean Modeling ◽  
Global Ocean ◽  
Potential Density ◽  
Vertical Coordinate ◽  
The World ◽  
Density Surface

Abstract Orthobaric density has recently been advanced as a new density variable for displaying ocean data and as a coordinate for ocean modeling. Here the extent to which orthobaric density surfaces are neutral is quantified and it is found that orthobaric density surfaces are less neutral in the World Ocean than are potential density surfaces referenced to 2000 dbar. Another property that is important for a vertical coordinate of a layered model is the quasi-material nature of the coordinate and it is shown that orthobaric density surfaces are significantly non-quasi-material. These limitations of orthobaric density arise because of its inability to accurately accommodate differences between water masses at fixed values of pressure and in situ density such as occur between the Northern and Southern Hemisphere portions of the World Ocean. It is shown that special forms of orthobaric density can be quite accurate if they are formed for an individual ocean basin and used only in that basin. While orthobaric density can be made to be approximately neutral in a single ocean basin, this is not possible in both the Northern and Southern Hemisphere portions of the Atlantic Ocean. While the helical nature of neutral trajectories (equivalently, the ill-defined nature of neutral surfaces) limits the neutrality of all types of density surface, the inability of orthobaric density surfaces to accurately accommodate more than one ocean basin is a much greater limitation.

scholarly journals Climatological distribution of dissolved inorganic nutrients in the western Mediterranean Sea (1981–2017)

2021 ◽  
Vol 13 (12) ◽  
pp. 5915-5949
Author(s):  
Malek Belgacem ◽  
Katrin Schroeder ◽  
Alexander Barth ◽  
Charles Troupin ◽  
Bruno Pavoni ◽  
...  
Keyword(s):  
Mediterranean Sea ◽  
World Ocean ◽  
Western Mediterranean ◽  
Inorganic Nutrients ◽  
Data Product ◽  
Western Mediterranean Sea ◽  
Dissolved Inorganic Nutrients ◽  
World Ocean Atlas ◽  
Nutrient Variability

Abstract. The Western MEDiterranean Sea BioGeochemical Climatology (BGC-WMED, https://doi.org/10.1594/PANGAEA.930447) (Belgacem et al., 2021) presented here is a product derived from quality-controlled in situ observations. Annual mean gridded nutrient fields for the period 1981–2017 and its sub-periods 1981–2004 and 2005–2017 on a horizontal 1/4∘ × 1/4∘ grid have been produced. The biogeochemical climatology is built on 19 depth levels and for the dissolved inorganic nutrients nitrate, phosphate and orthosilicate. To generate smooth and homogeneous interpolated fields, the method of the variational inverse model (VIM) was applied. A sensitivity analysis was carried out to assess the comparability of the data product with the observational data. The BGC-WMED was then compared to other available data products, i.e., the MedBFM biogeochemical reanalysis of the Mediterranean Sea and the World Ocean Atlas 2018 (WOA18) (its biogeochemical part). The new product reproduces common features with more detailed patterns and agrees with previous records. This suggests a good reference for the region and for the scientific community for the understanding of inorganic nutrient variability in the western Mediterranean Sea, in space and in time, but our new climatology can also be used to validate numerical simulations, making it a reference data product.

scholarly journals Observations of dissolved iron concentrations in the World Ocean: implications and constraints for ocean biogeochemical models

2007 ◽  
Vol 4 (2) ◽  
pp. 1241-1277 ◽  
Author(s):  
J. K. Moore ◽  
O. Braucher
Keyword(s):  
World Ocean ◽  
Deep Ocean ◽  
Euphotic Zone ◽  
Bimodal Distribution ◽  
Particulate Material ◽  
Ocean Model ◽  
Dust Deposition ◽  
Dissolved Iron ◽  
Biogeochemical Models ◽  
Iron Concentrations

Abstract. Analysis of a global compilation of dissolved iron observations provides insights into the controlling processes for iron distributions and some constraints for ocean biogeochemical models. The distribution of dissolved iron is consistent with the conceptual model developed for the scavenging of Th isotopes, whereby particle scavenging is a two-step process of scavenging mainly by colloidal and small particulates followed by aggregation and removal on larger sinking particles. Much of the dissolved iron (<0.4 μm) is present as small colloids (>~0.02 μm) and, thus, likely subject to aggregation and scavenging removal. Only the iron bound to soluble ligands (<~0.02 μm) is likely protected from scavenging removal. This implies distinct scavenging regimes for dissolved iron that appear consistent with the observational data: 1) high scavenging regime – where dissolved iron concentrations exceed the concentrations of strongly binding organic ligands; and 2) moderate scavenging regime – where dissolved iron is bound to both colloidal and soluble ligands. The removal rates for dissolved iron will be a function of biological uptake, number and size distributions of the colloidal and small particulate material, ligand dynamics, and the aggregation processes that lead to removal on larger particles. Inputs from dust deposition and continental sediments are key drivers of dissolved iron distributions. The observations provide several strong constraints for ocean biogeochemical models: 1) similar deep ocean concentrations in the North Atlantic and North Pacific (~0.6–0.8 nM), and much lower deep ocean dissolved iron concentrations in the Southern Ocean (~0.3–0.4 nM); 2) strong depletion of iron in the upper ocean away from the high dust deposition regions, with significant scavenging removal of dissolved iron below the euphotic zone; and 3) a bimodal distribution in surface waters with peaks less than 0.2 nM and between 0.6–0.8 nM. We compare the dissolved iron observations with output from the Biogeochemical Elemental Cycling (BEC) ocean model. The model output was in general agreement with the field data (r=0.76, for depths 103–502 m), but at lower iron concentrations (<0.3 nM) the model is consistently biased high relative to the observations.

scholarly journals The shape of the oceanic nitracline

2015 ◽  
Vol 12 (11) ◽  
pp. 3273-3287 ◽  
Author(s):  
M. M. Omand ◽  
A. Mahadevan
Keyword(s):  
Time Series ◽  
Mechanistic Model ◽  
World Ocean ◽  
Euphotic Zone ◽  
Vertical Gradient ◽  
Spatial And Temporal Variability ◽  
Surface Mixed Layer ◽  
World Ocean Atlas ◽  
Series Study

Abstract. In most regions of the ocean, nitrate is depleted near the surface by phytoplankton consumption and increases with depth, exhibiting a strong vertical gradient in the pycnocline (here referred to as the nitracline). The vertical supply of nutrients to the surface euphotic zone is influenced by the vertical gradient (slope) of the nitracline and by the vertical separation (depth) of the nitracline from the sunlit surface layer. Hence it is important to understand the shape (slope and curvature) and depth of the oceanic nitracline. By using density coordinates to analyze nitrate profiles from autonomous Autonomous Profiling EXplorer floats with In-Situ Ultraviolet Spectrophotometers (APEX-ISUS) and ship-based platforms (World Ocean Atlas – WOA09; Hawaii Ocean Time-series – HOT; Bermuda Atlantic Time-series Study – BATS; and California Cooperative Oceanic Fisheries Investigations – CalCOFI), we are able to eliminate much of the spatial and temporal variability in the profiles and derive robust relationships between nitrate and density. This allows us to characterize the depth, slope and curvature of the nitracline in different regions of the world's oceans. The analysis reveals distinguishing patterns in the nitracline between subtropical gyres, upwelling regions and subpolar gyres. We propose a one-dimensional, mechanistic model that relates the shape of the nitracline to the relative depths of the surface mixed layer and euphotic layer. Though heuristic, the model accounts for some of the seasonal patterns and regional differences in the nitrate–density relationships seen in the data.

scholarly journals Estimates of Ocean Macroturbulence: Structure Function and Spectral Slope from Argo Profiling Floats

2015 ◽  
Vol 45 (7) ◽  
pp. 1773-1793 ◽  
Author(s):  
Katherine McCaffrey ◽  
Baylor Fox-Kemper ◽  
Gael Forget
Keyword(s):  
Structure Function ◽  
World Ocean ◽  
Structure Functions ◽  
Potential Density ◽  
Argo Data ◽  
Ocean Variability ◽  
Salinity Variability ◽  
Salinity Data ◽  
Wavenumber Spectrum ◽  
Spectrum Slope

AbstractThe Argo profiling float network has repeatedly sampled much of the World Ocean. This study uses Argo temperature and salinity data to form the tracer structure function of ocean variability at the macroscale (10–1000 km, mesoscale and above). Here, second-order temperature and salinity structure functions over horizontal separations are calculated along either pressure or potential density surfaces, which allows analysis of both active and passive tracer structure functions. Using Argo data, a map of global variance is created from the climatological average and each datum. When turbulence is homogeneous, the structure function slope from Argo can be related to the wavenumber spectrum slope in ocean temperature or salinity variability. This first application of structure function techniques to Argo data gives physically meaningful results based on bootstrapped confidence intervals, showing geographical dependence of the structure functions with slopes near ⅔ on average, independent of depth.

scholarly journals Error assessment of biogeochemical models by lower bound methods (NOMMA-1.0)

2018 ◽  
Vol 11 (3) ◽  
pp. 1181-1198 ◽  
Author(s):  
Volkmar Sauerland ◽  
Ulrike Löptien ◽  
Claudine Leonhard ◽  
Andreas Oschlies ◽  
Anand Srivastav
Keyword(s):  
Lower Bound ◽  
Ocean Circulation ◽  
Real World ◽  
Time Derivative ◽  
World Ocean ◽  
Three Dimensional ◽  
Circulation Model ◽  
Noise Component ◽  
Biogeochemical Models

Abstract. Biogeochemical models, capturing the major feedbacks of the pelagic ecosystem of the world ocean, are today often embedded into Earth system models which are increasingly used for decision making regarding climate policies. These models contain poorly constrained parameters (e.g., maximum phytoplankton growth rate), which are typically adjusted until the model shows reasonable behavior. Systematic approaches determine these parameters by minimizing the misfit between the model and observational data. In most common model approaches, however, the underlying functions mimicking the biogeochemical processes are nonlinear and non-convex. Thus, systematic optimization algorithms are likely to get trapped in local minima and might lead to non-optimal results. To judge the quality of an obtained parameter estimate, we propose determining a preferably large lower bound for the global optimum that is relatively easy to obtain and that will help to assess the quality of an optimum, generated by an optimization algorithm. Due to the unavoidable noise component in all observations, such a lower bound is typically larger than zero. We suggest deriving such lower bounds based on typical properties of biogeochemical models (e.g., a limited number of extremes and a bounded time derivative). We illustrate the applicability of the method with two real-world examples. The first example uses real-world observations of the Baltic Sea in a box model setup. The second example considers a three-dimensional coupled ocean circulation model in combination with satellite chlorophyll a.

Bottom water production and its links with the thermohaline circulation

2004 ◽  
Vol 16 (4) ◽  
pp. 427-437 ◽  
Author(s):  
STANLEY S. JACOBS
Keyword(s):  
Temporal Variability ◽  
Bottom Water ◽  
Thermohaline Circulation ◽  
World Ocean ◽  
Antarctic Bottom Water ◽  
Water Production ◽  
Ongoing Work ◽  
Antarctic Continental Shelf ◽  
The World ◽  
The Antarctic

For more than a century it has been known that the abyssal basins of the world ocean are primarily occupied by relatively cold and fresh waters that originate in the Southern Ocean. Their distinguishing characteristics are acquired by exposure of surface and shelf waters to ‘ventilation’ by the polar atmosphere and to the melting and freezing of ice over and near the Antarctic continental shelf. Subsequent mixing with deep water over the continental slope results in ‘Bottom Water’ that forms the southern sinking limb of the global ‘Thermohaline Circulation.’ Over recent decades, oceanographers have wrestled with a variety of bottom water and thermohaline circulation problems, ranging from basic definitions to forcing and formation sites, source components and properties, generation processes and rates, mixing and sinking, pathways and transports. A brief review of these efforts indicates both advances and anomalies in our understanding of Antarctic Bottom Water production and circulation. Examples from ongoing work illustrate increasing interest in the temporal variability of bottom water in relation to climate change.

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