Effects of light and phosphorus on summer DMS dynamics in subtropical waters using a global ocean biogeochemical model

2016 ◽  
Vol 13 (2) ◽  
pp. 379 ◽  
Author(s):  
Italo Masotti ◽  
Sauveur Belviso ◽  
Laurent Bopp ◽  
Alessandro Tagliabue ◽  
Eva Bucciarelli
Keyword(s):  
General Circulation ◽  
North Atlantic Ocean ◽  
Model Simulation ◽  
Global Ocean ◽  
Longitudinal Distribution ◽  
Biogeochemical Model ◽  
Relative Role ◽  
Sargasso Sea ◽  
Ecological Processes ◽  
Climatological Data

Environmental context Models are needed to predict the importance of the changes in marine emissions of dimethylsulfide (DMS) in response to ocean warming, increased stratification and acidification, and to evaluate the potential effects on the Earth’s climate. We use complementary simulations to further our understanding of the marine cycle of DMS in subtropical waters, and show that a lack of phosphorus may exert a more important control on surface DMS concentrations than an excess of light. Abstract The occurrence of a summer DMS paradox in the vast subtropical gyres is a strong matter of debate because approaches using discrete measurements, climatological data and model simulations yielded contradictory results. The major conclusion of the first appraisal of prognostic ocean DMS models was that such models need to give more weight to the direct effect of environmental forcings (e.g. irradiance) on DMS dynamics to decouple them from ecological processes. Here, the relative role of light and phosphorus on summer DMS dynamics in subtropical waters is assessed using the ocean general circulation and biogeochemistry model NEMO-PISCES in which macronutrient concentrations were restored to monthly climatological data values to improve the representation of phosphate concentrations. Results show that the vertical and temporal decoupling between chlorophyll and DMS concentrations observed in the Sargasso Sea during the summer months is captured by the model. Additional sensitivity tests show that the simulated control of phosphorus on surface DMS concentrations in the Sargasso Sea is much more important than that of light. By extending the analysis to the whole North Atlantic Ocean, we show that the longitudinal distribution of DMS during summer is asymmetrical and that a correlation between the solar radiation dose and DMS concentrations only occurs in the Sargasso Sea. The lack of a widespread summer DMS paradox in our model simulation as well as in the comparison of discrete and climatological data could be due to the limited occurrence of phosphorus limitation in the global ocean.

scholarly journals Marine productivity response to Heinrich events: a model-data comparison

2012 ◽  
Vol 8 (5) ◽  
pp. 1581-1598 ◽  
Author(s):  
V. Mariotti ◽  
L. Bopp ◽  
A. Tagliabue ◽  
M. Kageyama ◽  
D. Swingedouw
Keyword(s):  
North Atlantic ◽  
General Circulation ◽  
Circulation Model ◽  
Global Ocean ◽  
Biogeochemical Model ◽  
Heinrich Events ◽  
The North ◽  
Heinrich Event ◽  
The North Atlantic ◽  
Marine Productivity

Abstract. Marine sediments records suggest large changes in marine productivity during glacial periods, with abrupt variations especially during the Heinrich events. Here, we study the response of marine biogeochemistry to such an event by using a biogeochemical model of the global ocean (PISCES) coupled to an ocean-atmosphere general circulation model (IPSL-CM4). We conduct a 400-yr-long transient simulation under glacial climate conditions with a freshwater forcing of 0.1 Sv applied to the North Atlantic to mimic a Heinrich event, alongside a glacial control simulation. To evaluate our numerical results, we have compiled the available marine productivity records covering Heinrich events. We find that simulated primary productivity and organic carbon export decrease globally (by 16% for both) during a Heinrich event, albeit with large regional variations. In our experiments, the North Atlantic displays a significant decrease, whereas the Southern Ocean shows an increase, in agreement with paleo-productivity reconstructions. In the Equatorial Pacific, the model simulates an increase in organic matter export production but decreased biogenic silica export. This antagonistic behaviour results from changes in relative uptake of carbon and silicic acid by diatoms. Reasonable agreement between model and data for the large-scale response to Heinrich events gives confidence in models used to predict future centennial changes in marine production. In addition, our model allows us to investigate the mechanisms behind the observed changes in the response to Heinrich events.

scholarly journals Skill assessment of the PELAGOS global ocean biogeochemistry model over the period 1980–2000

2009 ◽  
Vol 6 (11) ◽  
pp. 2333-2353 ◽  
Author(s):  
M. Vichi ◽  
S. Masina
Keyword(s):  
Organic Carbon ◽  
Mixed Layer ◽  
General Circulation ◽  
Net Primary Production ◽  
Global Ocean ◽  
Biogeochemical Model ◽  
Data Set ◽  
Surface Ocean ◽  
Ocean Biogeochemistry

Abstract. Global Ocean Biogeochemistry General Circulation Models are useful tools to study biogeochemical processes at global and large scales under current climate and future scenario conditions. The credibility of future estimates is however dependent on the model skill in capturing the observed multi-annual variability of firstly the mean bulk biogeochemical properties, and secondly the rates at which organic matter is processed within the food web. For this double purpose, the results of a multi-annual simulation of the global ocean biogeochemical model PELAGOS have been objectively compared with multi-variate observations from the last 20 years of the 20th century, both considering bulk variables and carbon production/consumption rates. Simulated net primary production (NPP) is comparable with satellite-derived estimates at the global scale and when compared with an independent data-set of in situ observations in the equatorial Pacific. The usage of objective skill indicators allowed us to demonstrate the importance of comparing like with like when considering carbon transformation processes. NPP scores improve substantially when in situ data are compared with modeled NPP which takes into account the excretion of freshly-produced dissolved organic carbon (DOC). It is thus recommended that DOC measurements be performed during in situ NPP measurements to quantify the actual production of organic carbon in the surface ocean. The chlorophyll bias in the Southern Ocean that affects this model as well as several others is linked to the inadequate representation of the mixed layer seasonal cycle in the region. A sensitivity experiment confirms that the artificial increase of mixed layer depths towards the observed values substantially reduces the bias. Our assessment results qualify the model for studies of carbon transformation in the surface ocean and metabolic balances. Within the limits of the model assumption and known biases, PELAGOS indicates a net heterotrophic balance especially in the more oligotrophic regions of the Atlantic during the boreal winter period. However, at the annual time scale and over the global ocean, the model suggests that the surface ocean is close to a weakly positive autotrophic balance in accordance with recent experimental findings and geochemical considerations.

scholarly journals Skill assessment of the PELAGOS global ocean biogeochemistry model over the period 1980–2000

2009 ◽  
Vol 6 (2) ◽  
pp. 3511-3562 ◽  
Author(s):  
M. Vichi ◽  
S. Masina
Keyword(s):  
Primary Production ◽  
General Circulation ◽  
Equatorial Pacific ◽  
Global Ocean ◽  
Biogeochemical Model ◽  
Winter Period ◽  
Spatial And Temporal Variability ◽  
Data Set ◽  
Carbon Production ◽  
Ocean Biogeochemistry

Abstract. Global Ocean Biogeochemistry General Circulation models are useful tools to study biogeochemical processes at gobal and large scales under current climate and future scenario conditions. The accuracy of the future estimate is however dependent on the adequate representation of the current ocean biogeochemical features. To this purpose, the results of an interannual simulation of the global ocean biogeochemical model PELAGOS have been objectively compared with multi-variate observations from the last 20 years of the XX century. The model was assessed in terms of spatial and temporal variability of chlorophyll and primary production derived from satellite sensors, with a specific focus on the simulation of carbon production/consumption rates observed in the equatorial Pacific ocean and at the long-term JGOFS stations. The predicted chlorophyll is acceptable in the northern mid-latitude regions and equatorial Pacific, but is underestimated in the upwelling regions of the Atlantic and Indian Oceans and markedly overestimated in the Southern Ocean. This latter bias is linked to the inadequate representation of the mixed layer seasonal cycle in the region, which favours primary production during austral spring. Simulated primary production is comparable with satellite estimates both at the global scale and when compared with an independent data-set in the equatorial Pacific. A comparison with other models showed that PELAGOS results are as good as the estimates from state-of-the-art diagnostic models based on satellite data. The skill in reproducing the interannual varibility was assessed in the equatorial Pacific and against the decadal JGOFS timeseries BATS and HOT. In the tropical Pacific our analysis suggests that interannual variability of primary production is related to the climate variability both in the observations and in the model. At the JGOFS stations PELAGOS has skill to simulate the observed bacterial biomass and shows realistic means of primary and bacterial production at BATS. These results have been further strenghtened with an analysis of spatial variability of microbial carbon production/consumption and comparison with observations along a transect in the Atlantic ocean. Within the limits of the model assumption and known biases, PELAGOS predicts that the system is net heterotrophic if the boreal winter period only is considered and especially in the more oligotrophic regions. However, at the annual time scale and over the global ocean, the model suggests that surface ocean is close to a slightly positive autotrophic balance in accordance with recent experimental findings and geochemical evidences.

Using the depth of the centre of gravity as an indicator on the state of the general ocean circulation

2021 ◽  
Author(s):  
Benjamin Schmiedel ◽  
Fabien Roquet
Keyword(s):  
Potential Energy ◽  
Ocean Circulation ◽  
General Circulation ◽  
Model Simulation ◽  
Ocean Model ◽  
The State ◽  
Relative Role ◽  
Centre Of Gravity ◽  
Gravity Centre ◽  
Global Mean

<p>An approach is here investigated that uses the depth of the centre of gravity as a central ocean property, thought to give a clear and practical indicator on the state of the general ocean circulation. The depth of the gravity centre can be directly linked to the volume-integral of potential energy, or of dynamic enthalpy when making the Boussinesq approximation, and therefore to the strength of the global mean stratification. Because the stratification is directly linked to the global overturning circulation, it is hypothesized that the depth of the centre of gravity can be used to assess the state of global circulation. In order to test this hypothesis, the depth of the centre of gravity is diagnosed in an ocean model simulation for an idealized square basin configuration with the NEMO model. The centre of gravity is compared to the value it would have if the ocean was perfectly well mixed, giving a state of maximum potential energy. We find in our idealized simulation that the centre of gravity is lowered by only 22 cm compared to the reference well-mixed state, reflecting the potential energy that would be required to destroy the ocean stratification. The smallness of that number highlights the inefficiency of the ocean engine. Furthermore, the dynamic balance setting the depth of the gravity centre is investigated, diagnosing separately the tendency terms on the equation of conservation of potential energy. A positive change (sinking) of the centre of gravity indicates an input of high density water into lower levels or low density water in upper levels, essentially enhancing the global mean stratification, while for a negative change (lifting) it is reversed. The goal is to compare the relative role of the wind stress, surface buoyancy forcing and internal mixing in setting the general circulation.</p>

scholarly journals SPEAD 1.0 – A model for Simulating Plankton Evolution with Adaptive Dynamics in a two-trait continuous fitness landscape applied to the Sargasso Sea

2020 ◽  
Author(s):  
Guillaume Le Gland ◽  
Sergio M. Vallina ◽  
S. Lan Smith ◽  
Pedro Cermeño
Keyword(s):  
General Circulation ◽  
Environmental Changes ◽  
Adaptive Dynamics ◽  
Computational Cost ◽  
Circulation Model ◽  
Global Ocean ◽  
Mutation Rates ◽  
Sargasso Sea ◽  
Continuous Trait ◽  
Trait Diversity

Abstract. Diversity plays a key role in the adaptive capacities of marine ecosystems to environmental changes. However, modeling phytoplankton trait diversity remains challenging due to the strength of the competitive exclusion of sub-optimal phenotypes. Trait diffusion (TD) is a recently developed approach to sustain diversity in plankton models by allowing the evolution of functional traits at ecological timescales. In this study, we present a model for Simulating Plankton Evolution with Adaptive Dynamics (SPEAD), where phytoplankton phenotypes characterized by two traits, nitrogen half-saturation constant and optimal temperature, can mutate at each generation using the TD mechanism. SPEAD does not resolve the different phenotypes as discrete entities, computing instead six aggregate properties: total phytoplankton biomass, mean value of each trait, trait variances, and inter-trait covariance of a single population in a continuous trait space. Therefore SPEAD resolves the dynamics of the population's continuous trait distribution by solving its statistical moments, where the variances of trait values represent the diversity of ecotypes. The ecological model is coupled to a vertically-resolved (1D) physical environment, and therefore the adaptive dynamics of the simulated phytoplankton population are driven by seasonal variations in vertical mixing, nutrient concentration, water temperature, and solar irradiance. The simulated bulk properties are validated by observations from BATS in the Sargasso Sea. We find that moderate mutation rates sustain trait diversity at decadal timescales and soften the almost total inter-trait correlation induced by the environment alone, without reducing the annual primary production or promoting permanently maladapted phenotypes, as occur with high mutation rates. As a way to evaluate the performance of the continuous-trait approximation, we also compare the solutions of SPEAD to the solutions of a classical discrete entities approach, both approaches including TD as a mechanism to sustain trait variance. We only find minor discrepancies between the continuous model SPEAD and the discrete model, the computational cost of SPEAD being lower by two orders of magnitude. Therefore SPEAD should be an ideal eco-evolutionary plankton model to be coupled to a general circulation model (GCM) at the global ocean.

scholarly journals A near-global eddy-resolving OGCM for climate studies

2016 ◽  
Author(s):  
X. Zhang ◽  
P. R. Oke ◽  
M. Feng ◽  
M. A. Chamberlain ◽  
J. A. Church ◽  
...  
Keyword(s):  
Ocean Circulation ◽  
General Circulation ◽  
Heat Content ◽  
Circulation Model ◽  
Surface Heat ◽  
Global Ocean ◽  
Biogeochemical Model ◽  
Relaxation Rates ◽  
Ocean Forecasting ◽  
Climate Studies

Abstract. Eddy-resolving global ocean models are highly desired for spatially-improved climate studies, but this is challenging because they require careful configuration and substantial computational resources. Model drift, partially related to insufficient model spin-up, imperfect model physics or bias in surface forcing, can be problematic, leading to contamination of climate change signals. In this study, we adapt a near-global eddy-resolving ocean general circulation model, originally developed for short-range ocean forecasting, for climate studies. The Ocean Forecasting Australia Model version 3 (OFAM3) is spun up for 20 years, with repeated year 1979 forcing and adaptive relaxation (Newtonian nudging) of temperature and salinity in the deep ocean to an observation-based climatology. In addition, surface heat fluxes from the JRA-55 atmospheric reanalysis are adjusted during the spin-up experiment to minimise excessive net heat uptake in the ocean. In the historical experiment, spanning 1979–2014, a non-adaptive relaxation is applied by repeating the same relaxation rates derived from the last five years of the spin-up experiment, and the surface heat flux adjustment diagnosed during the spinup experiment is also maintained. We demonstrate that the historical experiment driven by the JRA-55 reanalysis does not have significant drifts (e.g., as shown by simulated global ocean heat content), and also provides an eddy-resolving simulation of the global ocean circulation over the period 1979–2014. Decadal changes, such as the strengthening of the subtropical gyre circulation, are also reasonably simulated. A biogeochemical model is coupled with OFAM3 to produce patterns of primary productivity and carbon fluxes that are consistent with observations. Experiences gained from our numerical experiments will be helpful to other modelling groups who are interested in running global eddy-resolving OGCMs for climate studies.

scholarly journals Marine productivity response to Heinrich events: a model-data comparison

2012 ◽  
Vol 8 (1) ◽  
pp. 557-594 ◽  
Author(s):  
V. Mariotti ◽  
L. Bopp ◽  
A. Tagliabue ◽  
M. Kageyama ◽  
D. Swingedouw
Keyword(s):  
North Atlantic ◽  
General Circulation ◽  
Circulation Model ◽  
Global Ocean ◽  
Biogeochemical Model ◽  
Heinrich Events ◽  
The North ◽  
Heinrich Event ◽  
The North Atlantic ◽  
Marine Productivity

Abstract. Marine sediments records suggest large changes in marine productivity during glacial periods, with abrupt variations especially during the Heinrich events. Here, we study the response of marine biogeochemistry to such an event by using a biogeochemical model of the global ocean (PISCES) coupled to an ocean-atmosphere general circulation model (IPSL-CM4). We conduct a 400-yr-long transient simulation under glacial climate conditions with a freshwater forcing of 0.1 Sv applied to the North Atlantic to mimic a Heinrich event, alongside a glacial control simulation. To evaluate our numerical results, we have compiled the available marine productivity records covering Heinrich events. We find that simulated primary productivity and organic carbon export decrease globally (16% for both) during a Heinrich event, albeit with large regional variations. In our experiments, the North Atlantic displays a significant decrease, whereas the Southern Ocean shows an increase, in agreement with paleo-productivity reconstructions. In the Equatorial Pacific, the model simulates an increase in organic matter export production but decreased biogenic silica export. This opposite behaviour results from changes in relative uptake of carbon and silicic acid by diatoms. Reasonable agreement between model and data for the large-scale response to Heinrich events gives confidence in models used to predict future centennial changes in marine production. In addition, our model enables to decipher the mechanisms behind the observed changes in the response to Heinrich events.

scholarly journals Assessment of the sea-ice carbon pump: Insights from a three-dimensional ocean-sea-ice biogeochemical model (NEMO-LIM-PISCES)

Elem Sci Anth ◽  
2016 ◽  
Vol 4 ◽  
Author(s):  
Sébastien Moreau ◽  
Martin Vancoppenolle ◽  
Laurent Bopp ◽  
Oliver Aumont ◽  
Gurvan Madec ◽  
...  
Keyword(s):  
Carbon Cycle ◽  
Sea Ice ◽  
General Circulation ◽  
Circulation Model ◽  
Total Alkalinity ◽  
The Arctic ◽  
Global Ocean ◽  
Biogeochemical Model ◽  
Co2 Fluxes ◽  
Ice Growth

Abstract The role of sea ice in the carbon cycle is minimally represented in current Earth System Models (ESMs). Among potentially important flaws, mentioned by several authors and generally overlooked during ESM design, is the link between sea-ice growth and melt and oceanic dissolved inorganic carbon (DIC) and total alkalinity (TA). Here we investigate whether this link is indeed an important feature of the marine carbon cycle misrepresented in ESMs. We use an ocean general circulation model (NEMO-LIM-PISCES) with sea-ice and marine carbon cycle components, forced by atmospheric reanalyses, adding a first-order representation of DIC and TA storage and release in/from sea ice. Our results suggest that DIC rejection during sea-ice growth releases several hundred Tg C yr−1 to the surface ocean, of which < 2% is exported to depth, leading to a notable but weak redistribution of DIC towards deep polar basins. Active carbon processes (mainly CaCO3 precipitation but also ice-atmosphere CO2 fluxes and net community production) increasing the TA/DIC ratio in sea-ice modified ocean-atmosphere CO2 fluxes by a few Tg C yr−1 in the sea-ice zone, with specific hemispheric effects: DIC content of the Arctic basin decreased but DIC content of the Southern Ocean increased. For the global ocean, DIC content increased by 4 Tg C yr−1 or 2 Pg C after 500 years of model run. The simulated numbers are generally small compared to the present-day global ocean annual CO2 sink (2.6 ± 0.5 Pg C yr−1). However, sea-ice carbon processes seem important at regional scales as they act significantly on DIC redistribution within and outside polar basins. The efficiency of carbon export to depth depends on the representation of surface-subsurface exchanges and their relationship with sea ice, and could differ substantially if a higher resolution or different ocean model were used.

scholarly journals A Last Glacial Maximum world-ocean simulation at eddy-permitting resolution – Part 1: Experimental design and basic evaluation

2013 ◽  
Vol 9 (1) ◽  
pp. 297-328 ◽  
Author(s):  
M. Ballarotta ◽  
L. Brodeau ◽  
J. Brandefelt ◽  
P. Lundberg ◽  
K. Döös
Keyword(s):  
Last Glacial Maximum ◽  
General Circulation ◽  
Climate Model ◽  
Model Simulation ◽  
Spatial Scales ◽  
World Ocean ◽  
Glacial Maximum ◽  
Global Ocean ◽  
Last Glacial ◽  
Climate Model Simulation

Abstract. Most state-of-the-art climate models include a coarsely resolved oceanic component, which has difficulties in capturing detailed dynamics, and therefore eddy-permitting/eddy-resolving simulations have been developed to reproduce the observed World Ocean. In this study, an eddy-permitting numerical experiment is conducted to simulate the global ocean state for a period of the Last Glacial Maximum (LGM, ~ 26 500 to 19 000 yr ago) and to investigate the improvements due to taking into account these higher spatial scales. The ocean general circulation model is forced by a 49-yr sample of LGM atmospheric fields constructed from a quasi-equilibrated climate-model simulation. The initial state and the bottom boundary condition conform to the Paleoclimate Modelling Intercomparison Project (PMIP) recommendations. Before evaluating the model efficiency in representing the paleo-proxy reconstruction of the surface state, the LGM experiment is in this first part of the investigation, compared with a present-day eddy-permitting hindcast simulation as well as with the available PMIP results. It is shown that the LGM eddy-permitting simulation is consistent with the quasi-equilibrated climate-model simulation, but large discrepancies are found with the PMIP model analyses, probably due to the different equilibration states. The strongest meridional gradients of the sea-surface temperature are located near 40° N and S, this due to particularly large North-Atlantic and Southern-Ocean sea-ice covers. These also modify the locations of the convection sites (where deep-water forms) and most of the LGM Conveyor Belt circulation consequently takes place in a thinner layer than today. Despite some discrepancies with other LGM simulations, a glacial state is captured and the eddy-permitting simulation undertaken here yielded a useful set of data for comparisons with paleo-proxy reconstructions.

scholarly journals Projections of oceanic N<sub>2</sub>O emissions in the 21st century using the IPSL Earth system model

2015 ◽  
Vol 12 (13) ◽  
pp. 4133-4148 ◽  
Author(s):  
J. Martinez-Rey ◽  
L. Bopp ◽  
M. Gehlen ◽  
A. Tagliabue ◽  
N. Gruber
Keyword(s):  
21St Century ◽  
Climate Model ◽  
Model Simulation ◽  
Global Ocean ◽  
Biogeochemical Model ◽  
N2o Emissions ◽  
Earth System ◽  
Low Oxygen ◽  
N2o Production ◽  
The Future

Abstract. The ocean is a substantial source of nitrous oxide (N2O) to the atmosphere, but little is known about how this flux might change in the future. Here, we investigate the potential evolution of marine N2O emissions in the 21st century in response to anthropogenic climate change using the global ocean biogeochemical model NEMO-PISCES. Assuming nitrification as the dominant N2O formation pathway, we implemented two different parameterizations of N2O production which differ primarily under low-oxygen (O2) conditions. When forced with output from a climate model simulation run under the business-as-usual high-CO2 concentration scenario (RCP8.5), our simulations suggest a decrease of 4 to 12 % in N2O emissions from 2005 to 2100, i.e., a reduction from 4.03/3.71 to 3.54/3.56 TgN yr−1 depending on the parameterization. The emissions decrease strongly in the western basins of the Pacific and Atlantic oceans, while they tend to increase above the oxygen minimum zones (OMZs), i.e., in the eastern tropical Pacific and in the northern Indian Ocean. The reduction in N2O emissions is caused on the one hand by weakened nitrification as a consequence of reduced primary and export production, and on the other hand by stronger vertical stratification, which reduces the transport of N2O from the ocean interior to the ocean surface. The higher emissions over the OMZ are linked to an expansion of these zones under global warming, which leads to increased N2O production, associated primarily with denitrification. While there are many uncertainties in the relative contribution and changes in the N2O production pathways, the increasing storage seems unequivocal and determines largely the decrease in N2O emissions in the future. From the perspective of a global climate system, the averaged feedback strength associated with the projected decrease in oceanic N2O emissions amounts to around −0.009 W m−2 K−1, which is comparable to the potential increase from terrestrial N2O sources. However, the assessment for a potential balance between the terrestrial and marine feedbacks calls for an improved representation of N2O production terms in fully coupled next-generation Earth system models.

Sign in / Sign up

Export Citation Format

Share Document