Potential impact of changes in river nutrient supply on global ocean biogeochemistry

As one of the major carbon sinks in the global ocean, the North Atlantic is a key player in mediating and ameliorating the ongoing global warming. Projections of the North Atlantic carbon sink in a high-CO2 future vary greatly among models, with some showing that a slowdown in carbon uptake has already begun and others predicting that this slowdown will not occur until nearly 2100.Discrepancies among models largely originate because of differences in the efficiency of the high-latitude transport of carbon from the surface to the deep ocean. This transport occurs through biological production, deep convection and subsequent transport via the deep western boundary current. For an ensemble of 11 CMIP5-models, we studied the efficiency of this transport and identified two indicators of contemporary model behavior that are highly correlated with a model&#180;s projected future carbon-uptake. The first indicator is the high latitude summer pCO2sea-anomaly of a model, which is tightly linked to winter mixing and nutrient supply, but also to deep convection. The second indicator is the fraction of the anthropogenic carbon-inventory stored below 1000-m depth, indicating how efficient carbon is transported into the deep ocean. By comparing to the observational database, these indicators allow us to better constrain the model ensemble, and demonstrate that the models with more efficient surface to deep transport are best aligned with current observations. These models also show the largest future North Atlantic carbon uptake, which we then conclude is the more plausible future evolution. We further study if the high correlations between our contemporary indicators and a model&#180;s future North Atlantic carbon uptake is also upheld for the next model generation, CMIP6. We hypothesize that this is the case and that our indicators can not only help us to constrain the CMIP6 model ensemble but also inform us about progress made between CMIP5 and CMIP6 in terms of North Atlantic carbon uptake, winter mixing, nutrient supply, deep convection and transport of carbon into the deep ocean.

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Development and Assessment of NEMO(v3.6)-TOPAZ(v2), a Coupled Global Ocean Biogeochemistry Model

Asia-Pacific Journal of Atmospheric Sciences ◽

10.1007/s13143-019-00147-4 ◽

2019 ◽

Vol 56 (3) ◽

pp. 411-428

Author(s):

Hyun-Chae Jung ◽

Byung-Kwon Moon ◽

Hyomee Lee ◽

Jin-Ho Choi ◽

Han-Kyoung Kim ◽

...

Keyword(s):

Global Ocean ◽

Ocean Biogeochemistry

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

Biogeosciences ◽

10.5194/bg-6-2333-2009 ◽

2009 ◽

Vol 6 (11) ◽

pp. 2333-2353 ◽

Cited By ~ 30

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.

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The ECCO‐Darwin Data‐Assimilative Global Ocean Biogeochemistry Model: Estimates of Seasonal to Multidecadal Surface Ocean p CO 2 and Air‐Sea CO 2 Flux

Journal of Advances in Modeling Earth Systems ◽

10.1029/2019ms001888 ◽

2020 ◽

Vol 12 (10) ◽

Author(s):

D. Carroll ◽

D. Menemenlis ◽

J. F. Adkins ◽

K. W. Bowman ◽

H. Brix ◽

...

Keyword(s):

Global Ocean ◽

Surface Ocean ◽

Ocean Biogeochemistry

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Biogeochemical versus ecological consequences of modeled ocean physics

Biogeosciences ◽

10.5194/bg-14-2877-2017 ◽

2017 ◽

Vol 14 (11) ◽

pp. 2877-2889 ◽

Cited By ~ 8

Author(s):

Sophie Clayton ◽

Stephanie Dutkiewicz ◽

Oliver Jahn ◽

Christopher Hill ◽

Patrick Heimbach ◽

...

Keyword(s):

Primary Production ◽

Ocean Circulation ◽

Mixed Layer ◽

Phytoplankton Biomass ◽

Phytoplankton Community ◽

Resource Competition ◽

Nutrient Supply ◽

Zooplankton Biomass ◽

Global Ocean ◽

Competition Theory

Abstract. We present a systematic study of the differences generated by coupling the same ecological–biogeochemical model to a 1°, coarse-resolution, and 1∕6°, eddy-permitting, global ocean circulation model to (a) biogeochemistry (e.g., primary production) and (b) phytoplankton community structure. Surprisingly, we find that the modeled phytoplankton community is largely unchanged, with the same phenotypes dominating in both cases. Conversely, there are large regional and seasonal variations in primary production, phytoplankton and zooplankton biomass. In the subtropics, mixed layer depths (MLDs) are, on average, deeper in the eddy-permitting model, resulting in higher nutrient supply driving increases in primary production and phytoplankton biomass. In the higher latitudes, differences in winter mixed layer depths, the timing of the onset of the spring bloom and vertical nutrient supply result in lower primary production in the eddy-permitting model. Counterintuitively, this does not drive a decrease in phytoplankton biomass but results in lower zooplankton biomass. We explain these similarities and differences in the model using the framework of resource competition theory, and find that they are the consequence of changes in the regional and seasonal nutrient supply and light environment, mediated by differences in the modeled mixed layer depths. Although previous work has suggested that complex models may respond chaotically and unpredictably to changes in forcing, we find that our model responds in a predictable way to different ocean circulation forcing, despite its complexity. The use of frameworks, such as resource competition theory, provides a tractable way to explore the differences and similarities that occur. As this model has many similarities to other widely used biogeochemical models that also resolve multiple phytoplankton phenotypes, this study provides important insights into how the results of running these models under different physical conditions might be more easily understood.

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

Biogeosciences Discussions ◽

10.5194/bgd-6-3511-2009 ◽

2009 ◽

Vol 6 (2) ◽

pp. 3511-3562 ◽

Cited By ~ 3

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.

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