scholarly journals GNOM v1.0: An optimized steady-state model of the modern marine neodymium cycle

2021 ◽  
Author(s):  
Benoît Pasquier ◽  
Sophia K. V. Hines ◽  
Hengdi Liang ◽  
Yingzhe Wu ◽  
Seth G. John ◽  
...  
Keyword(s):  
Steady State ◽  
Ocean Circulation ◽  
Large Scale ◽  
Matrix Representation ◽  
Ocean Model ◽  
Isotopic Signatures ◽  
Open Questions ◽  
Steady State Model ◽  
Biogeochemical Parameters

Abstract. Spatially distant sources of neodymium (Nd) to the ocean that carry different isotopic signatures (εNd) have been shown to trace out major water masses, and have thus been extensively used to study large-scale features of the ocean circulation both past and current. While the global marine Nd cycle is qualitatively well understood, a complete quantitative determination of all its components and mechanisms, such as the magnitude of its sources and the paradoxical conservative behavior of εNd, remains elusive. To make sense of the increasing collection of observational Nd and εNd data, we develop the global neodymium ocean model (GNOM) v1, the first inverse model of the global marine biogeochemical cycle of Nd. The GNOM is embedded in a data-constrained steady-state circulation that affords spectacular computational efficiency, which we leverage to estimate biogeochemical parameters via systematic objective optimization. Owing to its matrix representation, the GNOM model is additionally amenable to novel diagnostics that allow us to investigate open questions about the Nd cycle with unprecedented accuracy. The GNOM is open-source and freely accessible, is written in Julia, and its code is easily understandable and modifiable for further developments and experiments.

scholarly journals The anthropic argument against infinite past and the Eddington-Lemaitre universe

2000 ◽  
pp. 33-37 ◽  
Author(s):  
M.M. Cirkovic
Keyword(s):  
Steady State ◽  
Large Scale ◽  
Cosmological Models ◽  
State Model ◽  
The Past ◽  
Philosophy Of Cosmology ◽  
Ongoing Effort ◽  
Steady State Model ◽  
Nature Of Time ◽  
Additional Constraints

This study in the philosophy of cosmology is a part of an ongoing effort to investigate and reassess the importance of the anthropic (Davies-Tipler) argument against cosmologies containing the past temporal infinity. Obviously the prime targets of this argument are cosmological models stationary on sufficiently large scale, the classical steady state model of Bondi, Gold and Hoyle being the best example. Here we investigate the extension of application of this argument to infinitely old non-stationary models and discuss additional constraints necessary to be imposed on such models for the edge of the anthropic argument to be preserved. An illustrative counterexample is the classical Eddington-Lemaitre model, in the analysis of which major such constraints are presented. Consequences of such an approach for our understanding of the nature of time are briefly discussed.

scholarly journals Interannual characteristics of an 80 km resolution diagnostic Arctic ice–ocean model

1991 ◽  
Vol 15 ◽  
pp. 155-162 ◽  
Author(s):  
John E. Ries ◽  
William D. Hibler
Keyword(s):  
Ocean Circulation ◽  
Large Scale ◽  
Eddy Viscosity ◽  
Barents Sea ◽  
Arctic Basin ◽  
Ocean Model ◽  
The Arctic ◽  
Atmospheric Forcing ◽  
Ice Edge ◽  
Arctic Ice

Seasonal simulations with large-scale coupled ice–ocean models have reproduced many features of the ice and ocean circulation of the Arctic Ocean and the Greenland and Norwegian seas (e.g. Hibler and Bryan, 1987; Semtner, 1987). However, the crude resolution and high lateral eddy viscosity used by these models prevent the simulation of many of the smaller-scale seasonal features and tend to produce sluggish circulation. Similarly, the use of a single year’s atmospheric forcing prevents the simulation of features on an interannual time-scale. As an initial step towards addressing these issues, an 80 km diagnostic Arctic ice–ocean model is constructed and integrated over a three-year period using daily atmospheric forcing to drive the model. To examine the effect of topographic resolution and eddy viscosity on model results, similar simulations were performed with a 160 km-resolution model. The results of these simulations are compared with one another, with buoy drift in the Arctic Basin, and with observed ice-edge variations. The model results proved most sensitive to changes in horizontal resolution. The 80 km results provided a more realistic and robust circulation in most areas of the Arctic and improved the modelled ice edge in the Barents Sea, while also successfully simulating the interannual variation in the region. Although it performed better than the 160 km model, the 80 km model still produced too large an ice extent in the Greenland Sea. No significant improvement in the ice-edge prediction was observed by varying the lateral eddy viscosity. The results indicate that problems remain in the vertical resolution in shallow regions, in treating penetrative convection, and in the simulation of inflow into the Arctic Basin through the Fram Strait.

scholarly journals The Effects of Mesoscale Ocean–Atmosphere Coupling on the Large-Scale Ocean Circulation

2009 ◽  
Vol 22 (15) ◽  
pp. 4066-4082 ◽  
Author(s):  
Andrew Mc C. Hogg ◽  
William K. Dewar ◽  
Pavel Berloff ◽  
Sergey Kravtsov ◽  
David K. Hutchinson
Keyword(s):  
Spatial Scale ◽  
Ocean Circulation ◽  
Large Scale ◽  
Ocean Model ◽  
Small Scale ◽  
Western Boundary ◽  
Ekman Pumping ◽  
Boundary Current ◽  
Ocean Atmosphere ◽  
Gyre Circulation

Abstract Small-scale variation in wind stress due to ocean–atmosphere interaction within the atmospheric boundary layer alters the temporal and spatial scale of Ekman pumping driving the double-gyre circulation of the ocean. A high-resolution quasigeostrophic (QG) ocean model, coupled to a dynamic atmospheric mixed layer, is used to demonstrate that, despite the small spatial scale of the Ekman-pumping anomalies, this phenomenon significantly modifies the large-scale ocean circulation. The primary effect is to decrease the strength of the nonlinear component of the gyre circulation by approximately 30%–40%. This result is due to the highest transient Ekman-pumping anomalies destabilizing the flow in a dynamically sensitive region close to the western boundary current separation. The instability of the jet produces a flux of potential vorticity between the two gyres that acts to weaken both gyres.

scholarly journals Inverse-model estimates of the ocean's coupled phosphorus, silicon, and iron cycles

2017 ◽  
Vol 14 (18) ◽  
pp. 4125-4159 ◽  
Author(s):  
Benoît Pasquier ◽  
Mark Holzer
Keyword(s):  
Steady State ◽  
Ocean Circulation ◽  
Large Scale ◽  
The Other ◽  
Global Ocean ◽  
Nutrient Concentrations ◽  
Iron Source ◽  
Fractional Contribution ◽  
Wide Range ◽  
Phosphorus Export

Abstract. The ocean's nutrient cycles are important for the carbon balance of the climate system and for shaping the ocean's distribution of dissolved elements. Dissolved iron (dFe) is a key limiting micronutrient, but iron scavenging is observationally poorly constrained, leading to large uncertainties in the external sources of iron and hence in the state of the marine iron cycle. Here we build a steady-state model of the ocean's coupled phosphorus, silicon, and iron cycles embedded in a data-assimilated steady-state global ocean circulation. The model includes the redissolution of scavenged iron, parameterization of subgrid topography, and small, large, and diatom phytoplankton functional classes. Phytoplankton concentrations are implicitly represented in the parameterization of biological nutrient utilization through an equilibrium logistic model. Our formulation thus has only three coupled nutrient tracers, the three-dimensional distributions of which are found using a Newton solver. The very efficient numerics allow us to use the model in inverse mode to objectively constrain many biogeochemical parameters by minimizing the mismatch between modeled and observed nutrient and phytoplankton concentrations. Iron source and sink parameters cannot jointly be optimized because of local compensation between regeneration, recycling, and scavenging. We therefore consider a family of possible state estimates corresponding to a wide range of external iron source strengths. All state estimates have a similar mismatch with the observed nutrient concentrations and very similar large-scale dFe distributions. However, the relative contributions of aeolian, sedimentary, and hydrothermal iron to the total dFe concentration differ widely depending on the sources. Both the magnitude and pattern of the phosphorus and opal exports are well constrained, with global values of 8. 1  ±  0. 3 Tmol P yr−1 (or, in carbon units, 10. 3  ±  0. 4 Pg C yr−1) and 171.   ±  3.  Tmol Si yr−1. We diagnose the phosphorus and opal exports supported by aeolian, sedimentary, and hydrothermal iron. The geographic patterns of the export supported by each iron type are well constrained across the family of state estimates. Sedimentary-iron-supported export is important in shelf and large-scale upwelling regions, while hydrothermal iron contributes to export mostly in the Southern Ocean. The fraction of the global export supported by a given iron type varies systematically with its fractional contribution to the total iron source. Aeolian iron is most efficient in supporting export in the sense that its fractional contribution to export exceeds its fractional contribution to the total source. Per source-injected molecule, aeolian iron supports 3. 1  ±  0. 8 times more phosphorus export and 2. 0  ±  0. 5 times more opal export than the other iron types. Conversely, per injected molecule, sedimentary and hydrothermal iron support 2. 3  ±  0. 6 and 4.   ±  2.  times less phosphorus export, and 1. 9  ±  0. 5 and 2.   ±  1.  times less opal export than the other iron types.

scholarly journals Predicting ocean-induced ice-shelf melt rates using a machine learning image segmentation approach

2022 ◽  
Author(s):  
Sebastian Harry Reid Rosier ◽  
Christopher Bull ◽  
G. Hilmar Gudmundsson
Keyword(s):  
Deep Learning ◽  
Ocean Circulation ◽  
Large Scale ◽  
Ice Sheet ◽  
Ground Truth ◽  
Ocean Model ◽  
Ice Shelf ◽  
Computational Expense ◽  
Shelf Slope ◽  
Wide Range

Abstract. Through their role in buttressing upstream ice flow, Antarctic ice shelves play an important part in regulating future sea level change. Reduction in ice-shelf buttressing caused by increased ocean-induced melt along their undersides is now understood to be one of the key drivers of ice loss from the Antarctic Ice Sheet. However, despite the importance of this forcing mechanism most ice-sheet simulations currently rely on simple melt-parametrisations of this ocean-driven process, since a fully coupled ice-ocean modelling framework is prohibitively computationally expensive. Here, we provide an alternative approach that is able to capture the greatly improved physical description of this process provided by large-scale ocean-circulation models over currently employed melt-parameterisations but with trivial computational expense. We introduce a new approach that brings together deep learning and physical modelling to develop a deep neural network framework, MELTNET, that can emulate ocean model predictions of sub-ice shelf melt rates. We train MELTNET on synthetic geometries, using the NEMO ocean model as a ground-truth in lieu of observations to provide melt rates both for training and to evaluate the performance of the trained network. We show that MELTNET can accurately predict melt rates for a wide range of complex synthetic geometries and outperforms more traditional parameterisations for > 95 % of geometries tested. Furthermore, we find MELTNET's melt rate estimates show sensitivity to established physical relationships such as a changes in thermal forcing and ice shelf slope. This study demonstrates the potential for a deep learning framework to calculate melt rates with almost no computational expense, that could in the future be used in conjunction with an ice sheet model to provide predictions for large-scale ice sheet models.

scholarly journals Circulation beneath the Filchner Ice Shelf, Antarctica, and its sensitivity to changes in the oceanic environment: a case-study

1998 ◽  
Vol 27 ◽  
pp. 99-104 ◽  
Author(s):  
K. Grosfeld ◽  
R. Gerdes
Keyword(s):  
Sea Ice ◽  
Mass Loss ◽  
Ocean Circulation ◽  
Large Scale ◽  
Ocean Model ◽  
Current Situation ◽  
Weddell Sea ◽  
Ice Formation ◽  
Shelf Area ◽  
Ice Shelf

We investigate the sensitivity of the ocean circulation in the Filchner Trough to changes in the large-scale oceanic environment and its impact on the mass balance of the Filchner Ice Shelf, Antarctica. Three experiments with a three-dimensional ocean model describe (i) the current situation, (ii) a scenario with increased ocean temperatures, and (iii) a scenario with reduced sea-ice formation rates on the adjacent continental shelf. in the final discussion brief results of a combined scenario with increased ocean temperatures and reduced sea-ice formation are presented. The changes from the current situation affect the circulation in the Filchner Trough, and melting and freezing processes beneath the ice shelf. The latter affect the amount and properties of Ice Shelf Water (ISW), a component of Antarctic Bottom Water. Net basal melt rates provide an overall measure for the changes: while the control run yields 0.35 m a−1 net melting averaged over the Filchner Ice Shelf area, the warming scenario results in a more than twofold increase in ice-shelf mass loss. Reduced production of High Salinity ShelfWater due to smaller sea-ice formation rates in the second scenario leads, on the other hand, to a decrease in basal mass loss, because the deep cavity is less well ventilated than in the control run. ISW is cooled and the ice shelf is stabilized under this scenario, which is arguably the more likely development in the southern Weddell Sea.

scholarly journals Interannual characteristics of an 80 km resolution diagnostic Arctic ice–ocean model

1991 ◽  
Vol 15 ◽  
pp. 155-162 ◽  
Author(s):  
John E. Ries ◽  
William D. Hibler
Keyword(s):  
Ocean Circulation ◽  
Large Scale ◽  
Eddy Viscosity ◽  
Barents Sea ◽  
Arctic Basin ◽  
Ocean Model ◽  
The Arctic ◽  
Atmospheric Forcing ◽  
Ice Edge ◽  
Arctic Ice

Seasonal simulations with large-scale coupled ice–ocean models have reproduced many features of the ice and ocean circulation of the Arctic Ocean and the Greenland and Norwegian seas (e.g. Hibler and Bryan, 1987; Semtner, 1987). However, the crude resolution and high lateral eddy viscosity used by these models prevent the simulation of many of the smaller-scale seasonal features and tend to produce sluggish circulation. Similarly, the use of a single year’s atmospheric forcing prevents the simulation of features on an interannual time-scale. As an initial step towards addressing these issues, an 80 km diagnostic Arctic ice–ocean model is constructed and integrated over a three-year period using daily atmospheric forcing to drive the model. To examine the effect of topographic resolution and eddy viscosity on model results, similar simulations were performed with a 160 km-resolution model. The results of these simulations are compared with one another, with buoy drift in the Arctic Basin, and with observed ice-edge variations. The model results proved most sensitive to changes in horizontal resolution. The 80 km results provided a more realistic and robust circulation in most areas of the Arctic and improved the modelled ice edge in the Barents Sea, while also successfully simulating the interannual variation in the region. Although it performed better than the 160 km model, the 80 km model still produced too large an ice extent in the Greenland Sea. No significant improvement in the ice-edge prediction was observed by varying the lateral eddy viscosity. The results indicate that problems remain in the vertical resolution in shallow regions, in treating penetrative convection, and in the simulation of inflow into the Arctic Basin through the Fram Strait.

scholarly journals Inverse-model estimates of the ocean's coupled phosphorus, silicon, and iron cycles

2017 ◽  
Author(s):  
Benoît Pasquier ◽  
Mark Holzer
Keyword(s):  
Steady State ◽  
Ocean Circulation ◽  
Large Scale ◽  
Three Dimensional ◽  
Nutrient Utilization ◽  
Global Ocean ◽  
Nutrient Concentrations ◽  
Iron Source ◽  
Fractional Contribution ◽  
Wide Range

Abstract. The ocean's nutrient cycles are important for the carbon balance of the climate system and for shaping the ocean's distribution of dissolved elements. Dissolved iron (dFe) is a key limiting micronutrient, but iron scavenging is observationally poorly constrained leading to large uncertainties in the external sources of iron and hence in the state of the marine iron cycle. Here we build a model of the ocean's coupled phosphorus, silicon, and iron cycles embedded in a data-assimilated steady-state global ocean circulation. The model includes the redissolution of scavenged iron, parameterization of subgrid topography, and small, large, and diatom phytoplankton functional classes. Phytoplankton concentrations are implicitly represented in the parameterization of biological nutrient utilization through an equilibrium logistic model. Our coupled nutrient model thus carries only three nutrient tracers whose three-dimensional steady-state distributions can be found efficiently using a Newton solver. The very efficient numerics allow us to use the model in inverse mode to objectively constrain many biogeochemical parameters by minimizing the mismatch between modelled and observed nutrient and phytoplankton concentrations. We consider a family of possible solutions corresponding to a wide range of external iron source strengths. Iron source and sink parameters cannot jointly be optimized because of local compensation between regeneration, recycling, and scavenging. All optimized solutions have a similar mismatch with the observed nutrient concentrations and very similar large-scale dFe distributions. However, the relative contributions of aeolian, sedimentary, and hydrothermal iron to the total dFe concentration differ widely depending on the sources. Both the magnitude and pattern of carbon and opal export are well constrained with global values of (10.3 ± 0.4) Pg C yr−1 and (171. ± 3.) Tmol Si yr−1. We diagnose the carbon and opal export supported by aeolian, sedimentary, and hydrothermal iron. The geographic patterns of the export supported by each iron type are well constrained across the family of solutions. Sedimentary-iron supported export is important in shelf and large-scale upwelling regions, while hydrothermal iron contributes to export mostly in the Southern Ocean. The globally integrated export supported by a given iron type varies systematically with the fractional contribution of its source to the total iron source. Aeolian iron is most efficient in supporting export in the sense that its fractional contribution to export exceeds its fractional contribution to the total source by as much as ~ 30 % for carbon and ~ 20 % for opal export. Conversely, sedimentary and hydrothermal iron are less efficient with a fractional export that is less than their fractional sources. For the same fractional contribution to the total source, hydrothermal iron is less efficient than sedimentary iron for supporting carbon export but about equally efficient for supporting opal export.

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