scholarly journals Global ocean storage of anthropogenic carbon

2012 ◽  
Vol 9 (7) ◽  
pp. 8931-8988 ◽  
Author(s):  
S. Khatiwala ◽  
T. Tanhua ◽  
S. Mikaloff Fletcher ◽  
M. Gerber ◽  
S. C. Doney ◽  
...  
Keyword(s):  
Ocean Circulation ◽  
Global Scale ◽  
Global Ocean ◽  
Observational Methods ◽  
Robust Estimates ◽  
Anthropogenic Carbon ◽  
Ocean Models ◽  
Biogeochemical Parameters ◽  
Range Of Values ◽  
Made In

Abstract. The global ocean is a significant sink for anthropogenic carbon (Cant), absorbing roughly a third of human CO2 emitted over the industrial period. Robust estimates of the magnitude and variability of the storage and distribution of Cant in the ocean are therefore important for understanding the human impact on climate. In this synthesis we review observational and model-based estimates of the storage and transport of Cant in the ocean. We pay particular attention to the uncertainties and potential biases inherent in different inference schemes. On a global scale, three data based estimates of the distribution and inventory of Cant are now available. While the inventories are found to agree within their uncertainty, there are considerable differences in the spatial distribution. We also present a review of the progress made in the application of inverse and data-assimilation techniques which combine ocean interior estimates of Cant with numerical ocean circulation models. Such methods are especially useful for estimating the air-sea flux and interior transport of Cant, quantities that are otherwise difficult to observe directly. However, the results are found to be highly dependent on modeled circulation, with the spread due to different ocean models at least as large as that from the different observational methods used to estimate Cant. Our review also highlights the importance of repeat measurements of hydrographic and biogeochemical parameters to estimate the storage of Cant on decadal timescales in the presence of the variability in circulation that is neglected by other approaches. Data-based Cant estimates provide important constraints on ocean forward models, which exhibit both broad similarities and regional errors relative to the observational fields. A compilation of inventories of Cant gives us a "best" estimate of the global ocean inventory of anthropogenic carbon in 2010 of 155 Pg C with an uncertainty of ±20%. This estimate includes a broad range of values suggesting that a combination of approaches is necessary in order to achieve a robust quantification of the ocean sink of anthropogenic CO2.

scholarly journals Global ocean storage of anthropogenic carbon

2013 ◽  
Vol 10 (4) ◽  
pp. 2169-2191 ◽  
Author(s):  
S. Khatiwala ◽  
T. Tanhua ◽  
S. Mikaloff Fletcher ◽  
M. Gerber ◽  
S. C. Doney ◽  
...  
Keyword(s):  
Ocean Circulation ◽  
Global Scale ◽  
Global Ocean ◽  
Observational Methods ◽  
Robust Estimates ◽  
Anthropogenic Carbon ◽  
Ocean Models ◽  
Biogeochemical Parameters ◽  
Range Of Values ◽  
Made In

Abstract. The global ocean is a significant sink for anthropogenic carbon (Cant), absorbing roughly a third of human CO2 emitted over the industrial period. Robust estimates of the magnitude and variability of the storage and distribution of Cant in the ocean are therefore important for understanding the human impact on climate. In this synthesis we review observational and model-based estimates of the storage and transport of Cant in the ocean. We pay particular attention to the uncertainties and potential biases inherent in different inference schemes. On a global scale, three data-based estimates of the distribution and inventory of Cant are now available. While the inventories are found to agree within their uncertainty, there are considerable differences in the spatial distribution. We also present a review of the progress made in the application of inverse and data assimilation techniques which combine ocean interior estimates of Cant with numerical ocean circulation models. Such methods are especially useful for estimating the air–sea flux and interior transport of Cant, quantities that are otherwise difficult to observe directly. However, the results are found to be highly dependent on modeled circulation, with the spread due to different ocean models at least as large as that from the different observational methods used to estimate Cant. Our review also highlights the importance of repeat measurements of hydrographic and biogeochemical parameters to estimate the storage of Cant on decadal timescales in the presence of the variability in circulation that is neglected by other approaches. Data-based Cant estimates provide important constraints on forward ocean models, which exhibit both broad similarities and regional errors relative to the observational fields. A compilation of inventories of Cant gives us a "best" estimate of the global ocean inventory of anthropogenic carbon in 2010 of 155 ± 31 PgC (±20% uncertainty). This estimate includes a broad range of values, suggesting that a combination of approaches is necessary in order to achieve a robust quantification of the ocean sink of anthropogenic CO2.

The geography of numerical mixing in a suite of global ocean models

2021 ◽  
Author(s):  
Ryan Holmes ◽  
Jan Zika ◽  
Stephen Griffies ◽  
Andrew Hogg ◽  
Andrew Kiss ◽  
...  
Keyword(s):  
Ocean Circulation ◽  
General Circulation ◽  
Horizontal Resolution ◽  
Global Ocean ◽  
Vertical Diffusivity ◽  
Mixing Parameters ◽  
Ocean Models ◽  
Numerical Mixing ◽  
Comparable Magnitude ◽  
Ice Model

<p>Numerical mixing, the physically spurious diffusion of tracers due to the numerical discretization of advection, is known to contribute to biases in ocean circulation models. However, quantifying numerical mixing is non-trivial, with most studies utilizing specifically targeted experiments in idealized settings. Here, we present a precise method based on water-mass transformation for quantifying numerical mixing, including its spatial structure, that can be applied to any conserved variable in global general circulation ocean models. The method is applied to a suite of global MOM5 ocean-sea ice model simulations with differing grid spacings and sub-grid scale parameterizations. In all configurations numerical mixing drives across-isotherm heat transport of comparable magnitude to that associated with explicitly-parameterized mixing. Numerical mixing is prominent at warm temperatures in the tropical thermocline, where it is sensitive to the vertical diffusivity and resolution. At colder temperatures, numerical mixing is sensitive to the presence of explicit neutral diffusion, suggesting that much of the numerical mixing in these regions acts as a proxy for neutral diffusion when it is explicitly absent. Comparison of equivalent (with respect to vertical resolution and explicit mixing parameters) 1/4-degree and 1/10-degree horizontal resolution configurations shows only a modest enhancement in numerical mixing at the eddy-permitting 1/4-degree resolution. Our results provide a detailed view of numerical mixing in ocean models and pave the way for future improvements in numerical methods.</p>

Global Ocean Meridional Overturning

2007 ◽  
Vol 37 (10) ◽  
pp. 2550-2562 ◽  
Author(s):  
Rick Lumpkin ◽  
Kevin Speer
Keyword(s):  
Ocean Circulation ◽  
Global Scale ◽  
The Arctic ◽  
Global Ocean ◽  
Mixing Processes ◽  
Boundary Currents ◽  
Antarctic Continent ◽  
Meridional Overturning ◽  
Global Ocean Circulation ◽  
The Antarctic

Abstract A decade-mean global ocean circulation is estimated using inverse techniques, incorporating air–sea fluxes of heat and freshwater, recent hydrographic sections, and direct current measurements. This information is used to determine mass, heat, freshwater, and other chemical transports, and to constrain boundary currents and dense overflows. The 18 boxes defined by these sections are divided into 45 isopycnal (neutral density) layers. Diapycnal transfers within the boxes are allowed, representing advective fluxes and mixing processes. Air–sea fluxes at the surface produce transfers between outcropping layers. The model obtains a global overturning circulation consistent with the various observations, revealing two global-scale meridional circulation cells: an upper cell, with sinking in the Arctic and subarctic regions and upwelling in the Southern Ocean, and a lower cell, with sinking around the Antarctic continent and abyssal upwelling mainly below the crests of the major bathymetric ridges.

scholarly journals Simulation of anthropogenic CO<sub>2</sub> uptake in the CCSM3.1 ocean circulation-biogeochemical model: comparison with data-based estimates

2011 ◽  
Vol 8 (6) ◽  
pp. 10895-10933
Author(s):  
S. Wang ◽  
J. K. Moore ◽  
F. W. Primeau ◽  
S. Khatiwala
Keyword(s):  
Ocean Circulation ◽  
Model Comparison ◽  
Industrial Revolution ◽  
Large Fraction ◽  
Detailed Comparison ◽  
Global Ocean ◽  
Inversion Method ◽  
Biogeochemical Model ◽  
Climate System Model ◽  
Anthropogenic Carbon

Abstract. The global ocean has taken up a large fraction of the CO2 released by human activities since the industrial revolution. Quantifying the oceanic anthropogenic carbon (Cant) inventory and its variability is important for predicting the future global carbon cycle. The detailed comparison of data-based and model-based estimates is essential for the validation and continued improvement of our prediction capabilities. So far, three global estimates of oceanic Cant inventory that are "data-based" and independent of global ocean circulation models have been produced: one based on the ΔC* method, and two are based on reconstructions of the Green function for the surface-to-interior transport, the TTD method and the maximum entropy inversion method (KPH). The KPH method, in particular, is capable of reconstructing the history of Cant inventory through the industrial era. In the present study we use forward model simulations of the Community Climate System Model (CCSM3.1) to estimate the Cant inventory and compare the results with the data-based estimates. We also use the simulations to test several assumptions of the KPH method, including the assumption of constant climate and circulation, which is common to all the data-based estimates. Though the integrated estimates of global Cant inventories are consistent with each other, the regional estimates show discrepancies up to 50 %. The CCSM3 model underestimates the total Cant inventory, in part due to weak mixing and ventilation in the North Atlantic and Southern Ocean. Analyses of different simulation results suggest that key assumptions about ocean circulation and air-sea disequilibrium in the KPH method are generally valid on the global scale, but may introduce significant errors in Cant estimates on regional scales. The KPH method should also be used with caution when predicting future oceanic anthropogenic carbon uptake.

scholarly journals <sup>14</sup>C-age tracers in global ocean circulation models

2014 ◽  
Vol 7 (5) ◽  
pp. 7033-7074 ◽  
Author(s):  
W. Koeve ◽  
H. Wagner ◽  
P. Kähler ◽  
A. Oschlies
Keyword(s):  
Gas Exchange ◽  
Ocean Circulation ◽  
Model Evaluation ◽  
Global Ocean ◽  
Exchange Constant ◽  
Model Parameters ◽  
Water Age ◽  
14C Age ◽  
Ocean Models ◽  
Global Ocean Circulation

Abstract. The natural abundance of 14C in total CO2 dissolved in seawater is a property applied to evaluate the water age structure and circulation in the ocean and in ocean models. In this study we use three different representations of the global ocean circulation augmented with a suite of idealised tracers to study the potential and limitations of using natural 14C to determine water age, the time elapsed since a body of water had contact with the atmosphere. We find that, globally, bulk 14C-age is dominated by two equally important components, one associated with aging, i.e. the time component of circulation and one associated with a "preformed 14C-age". This latter quantity exists because of the slow and incomplete atmosphere/ocean equilibration of 14C in particular in high latitudes where many water masses form. The relative contribution of the preformed component to bulk 14C-age varies regionally within a given model, but also between models. Regional variability, e.g. in the Atlantic Ocean is associated with the mixing of waters with very different end members of preformed 14C-age. In the Atlantic, variations in the preformed component over space and time mask the circulation component to an extent that its patterns are not detectable from bulk 14C-age alone. Between models the variability of age can also be considerable (factor of 2), related to the combinations of physical model parameters, which influence circulation dynamics, and gas exchange in the models. The preformed component was found to be very sensitive to gas exchange and moderately sensitive to ice cover. In our model evaluation exercise, the choice of the gas exchange constant from within the current range of uncertainty had such a strong influence on preformed and bulk 14C-age that if model evaluation would be based on bulk 14C-age it could easily impair the evaluation and tuning of a models circulation on global and regional scales. Based on the results of this study, we propose that considering preformed 14C-age is critical for a correct assessment of circulation in ocean models.

scholarly journals Model constraints on the anthropogenic carbon budget of the Arctic Ocean

2018 ◽  
Author(s):  
Jens Terhaar ◽  
James C. Orr ◽  
Marion Gehlen ◽  
Christian Ethé ◽  
Laurent Bopp
Keyword(s):  
Ocean Acidification ◽  
Arctic Ocean ◽  
Ocean Circulation ◽  
The Arctic ◽  
Global Ocean ◽  
Cmip5 Models ◽  
Lateral Transport ◽  
Coarse Resolution ◽  
The Arctic Ocean ◽  
Anthropogenic Carbon

Abstract. The Arctic Ocean is projected to experience not only amplified climate change but also amplified ocean acidification. Modeling future acidification depends on our ability to simulate baseline conditions and changes over the industrial era. Such centennial-scale changes require a global model to account for exchange between the Arctic and surrounding regions. Yet the coarse resolution of typical global models may poorly resolve that exchange as well as critical features of Arctic Ocean circulation. Here we assess how simulations of Arctic Ocean storage of anthropogenic carbon (Cant), the main driver of open- ocean acidification, differ when moving from coarse to eddy admitting resolution in a global ocean circulation-biogeochemistry model (NEMO-PISCES). The Arctic's regional storage of Cant is enhanced as model resolution increases. While the coarse- resolution model configuration ORCA2 (2°) stores 2.0 Pg C in the Arctic Ocean between 1765 and 2005, the eddy-admitting versions ORCA05 and ORCA025 (1/2° and 1/4°) store 2.4 and 2.6 Pg C. That result from ORCA025 falls within the uncertainty range from a previous data-based Cant storage estimate (2.5 to 3.3 Pg C). Yet those limits may each need to be reduced by about 10 % because data-based Cant concentrations in deep waters remain at ∼ 6 μmol kg−1, while they should be almost negligible by analogy to the near-zero observed CFC-12 concentrations from which they are calculated. Across the three resolutions, there was roughly three times as much anthropogenic carbon that entered the Arctic Ocean through lateral transport than via the flux of CO2 across the air-sea interface. Wider comparison to nine earth system models that participated in the Coupled Model Intercomparison Project Phase 5 (CMIP5) reveals much larger diversity of stored anthropogenic carbon and lateral transport. Only the CMIP5 models with higher lateral transport obtain Cant inventories that are close to the data-based estimates. Increasing resolution also enhances acidification, e.g., with greater shoaling of the Arctic's average depth of the aragonite saturation horizon during 1960–2012, from 50 m in ORCA2 to 210 m in ORCA025. To assess the potential to further refine modeled estimates of the Arctic Ocean's Cant storage and acidification, sensitivity tests that adjust model parameters are needed given that century-scale global ocean biogeochemical simulations still cannot be run routinely at high resolution.

scholarly journals Prospects for improving the representation of coastal and shelf seas in global ocean models

2016 ◽  
Author(s):  
Jason Holt ◽  
Pat Hyder ◽  
Mike Ashworth ◽  
James Harle ◽  
Helene T. Hewitt ◽  
...  
Keyword(s):  
Global Scale ◽  
Global Ocean ◽  
Goods And Services ◽  
Process Representation ◽  
Current State ◽  
Basin Scale ◽  
Shelf Seas ◽  
Dense Water Formation ◽  
Global Modelling ◽  
Ocean Models

Abstract. Accurately representing coastal and shelf seas in global ocean models represents one of the grand challenges of Earth System science. They are regions of immense societal importance, through the goods and services they provide, hazards they pose and through their role in global scale processes and cycles, e.g. carbon fluxes and dense water formation. However, they are poorly represented in the current generation of global ocean models. In this contribution we aim to identify and quantify the important physical processes, and their scales, needed to address this issue in the context of the options available to resolve these scales globally and the evolving computational landscape. We find barotropic and topographic scales are well resolved by the current state-of-the-art model resolutions (e.g. nominal 1/12°) and here the focus is on process representation. We identify tides, vertical coordinates, river inflows and mixing schemes as four areas where modelling approaches can readily be transferred from regional to global modelling with substantial benefit. We demonstrate this through basin scale northern North Atlantic simulations and analysis of global profile data, which particularly shows the need for increased vertical resolution in shallower water. In terms of finer scale processes, we find that a 1/12° global model resolves the 1st baroclinic Rossby Radius for only ~ 20 % of regions

scholarly journals Photoacclimation by phytoplankton determines the distribution of global subsurface chlorophyll maxima in the ocean

2021 ◽  
Vol 2 (1) ◽  
Author(s):  
Yoshio Masuda ◽  
Yasuhiro Yamanaka ◽  
Sherwood Lan Smith ◽  
Takafumi Hirata ◽  
Hideyuki Nakano ◽  
...  
Keyword(s):  
Resource Allocation ◽  
Ocean Circulation ◽  
Circulation Model ◽  
Mechanistic Explanation ◽  
Global Scale ◽  
Global Ocean ◽  
Driving Mechanism ◽  
Chlorophyll Distribution ◽  
Resource Allocation Strategy ◽  
Ocean Observations

AbstractSubsurface chlorophyll maxima are widely observed in the ocean, and they often occur at greater depths than maximum phytoplankton biomass. However, a consistent mechanistic explanation for their distribution in the global ocean remains lacking. One possible mechanism is photoacclimation, whereby phytoplankton adjust their cellular chlorophyll content in response to environmental conditions. Here, we incorporate optimality-based photoacclimation theory based on resource allocation trade-off between nutrient uptake and light harvesting capacity into a 3D biogeochemical ocean circulation model to determine the influence of resource allocation strategy on phytoplankton chlorophyll to carbon ratio distributions. We find that photoacclimation is a common driving mechanism that consistently explains observed global scale patterns in the depth and intensity of subsurface chlorophyll maxima across ocean regions. This mechanistic link between cellular-scale physiological responses and the global scale chlorophyll distribution can inform interpretation of ocean observations and projections of phytoplankton responses to climate change.

scholarly journals The oceanic sink for anthropogenic CO2from 1994 to 2007

Science ◽  
2019 ◽  
Vol 363 (6432) ◽  
pp. 1193-1199 ◽  
Author(s):  
Nicolas Gruber ◽  
Dominic Clement ◽  
Brendan R. Carter ◽  
Richard A. Feely ◽  
Steven van Heuven ◽  
...  
Keyword(s):  
Carbon Dioxide ◽  
Linear Regression ◽  
Ocean Circulation ◽  
Uptake Rate ◽  
Regional Differences ◽  
Global Ocean ◽  
Anthropogenic Carbon ◽  
Storage Rate ◽  
Repeat Hydrography ◽  
Global Increase

We quantify the oceanic sink for anthropogenic carbon dioxide (CO2) over the period 1994 to 2007 by using observations from the global repeat hydrography program and contrasting them to observations from the 1990s. Using a linear regression–based method, we find a global increase in the anthropogenic CO2inventory of 34 ± 4 petagrams of carbon (Pg C) between 1994 and 2007. This is equivalent to an average uptake rate of 2.6 ± 0.3 Pg C year−1and represents 31 ± 4% of the global anthropogenic CO2emissions over this period. Although this global ocean sink estimate is consistent with the expectation of the ocean uptake having increased in proportion to the rise in atmospheric CO2, substantial regional differences in storage rate are found, likely owing to climate variability–driven changes in ocean circulation.

scholarly journals Towards accounting for dissolved iron speciation in global ocean models

2011 ◽  
Vol 8 (2) ◽  
pp. 2775-2810 ◽  
Author(s):  
A. Tagliabue ◽  
C. Völker
Keyword(s):  
Ocean Circulation ◽  
General Circulation ◽  
Environmental Variability ◽  
World Ocean ◽  
Global Scale ◽  
Global Ocean ◽  
Test Bed ◽  
Fe Species ◽  
Effective Manner ◽  
Fe Speciation

Abstract. The trace metal iron (Fe) is now routinely included in state-of-the-art ocean general circulation and biogeochemistry models (OGCBMs) because of its key role as a limiting nutrient in regions of the world ocean important for carbon cycling and air-sea CO2 exchange. However, the complexities of the seawater Fe cycle, which impact its speciation and bioavailability, are highly simplified in such OGCBMs to avoid high computational costs. In a similar fashion to inorganic carbon speciation, we outline a means by which the complex speciation of Fe can be included in global OGCBMs in a reasonably cost-effective manner. We use our Fe speciation to suggest the global distribution of different Fe species is tightly controlled by environmental variability (temperature, light, oxygen and pH) and the assumptions regarding Fe binding ligands. Impacts on bioavailable Fe are highly sensitive to assumptions regarding which Fe species are bioavailable. When forced by representations of future ocean circulation and climate we find large changes to the speciation of Fe governed by pH mediated changes to redox kinetics. We speculate that these changes may exert selective pressure on phytoplankton Fe uptake strategies in the future ocean. We hope our modeling approach can also be used as a ''test bed'' for exploring our understanding of Fe speciation at the global scale.

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