scholarly journals Riverine nitrogen supply to the global ocean and its limited impact on global marine primary production: a feedback study using an Earth system model

2021 ◽  
Vol 18 (19) ◽  
pp. 5327-5350
Author(s):  
Miriam Tivig ◽  
David P. Keller ◽  
Andreas Oschlies
Keyword(s):  
River Discharge ◽  
Nitrogen Loss ◽  
Nitrogen Supply ◽  
Open Ocean ◽  
Global Ocean ◽  
Positive Feedbacks ◽  
Nitrogen Input ◽  
Ocean Biogeochemistry ◽  
Marine Productivity ◽  
The Impact

Abstract. A common notion is that negative feedbacks stabilize the natural marine nitrogen inventory. Recent modeling studies have shown, however, some potential for localized positive feedbacks leading to substantial nitrogen losses in regions where nitrogen fixation and denitrification occur in proximity to each other. Here we include dissolved nitrogen from river discharge in a global 3-D ocean biogeochemistry model and study the effects on near-coastal and remote-open-ocean biogeochemistry. We find that at a steady state the biogeochemical feedbacks in the marine nitrogen cycle, nitrogen input from biological N2 fixation, and nitrogen loss via denitrification mostly compensate for the imposed yearly addition of 22.8 to 45.6 Tg of riverine nitrogen and limit the impact on global marine productivity to < 2 %. Global experiments that regionally isolate river nutrient input show that the sign and strength of the feedbacks depend on the location of the river discharge and the oxygen status of the receiving marine environment. Marine productivity generally increases in proximity to the nitrogen input, but we also find a decline in productivity in the modeled Bay of Bengal and near the mouth of the Amazon River. While most of the changes are located in shelf and near-coastal oceans, nitrogen supply from the rivers can impact the open ocean, due to feedbacks or knock-on effects.

scholarly journals Riverine nitrogen supply to the global ocean and its limited impact on global marine primary production: a feedback study using an Earth System Model

2021 ◽  
Author(s):  
Miriam Tivig ◽  
David Peter Keller ◽  
Andreas Oschlies
Keyword(s):  
River Discharge ◽  
Nitrogen Loss ◽  
Nitrogen Supply ◽  
Open Ocean ◽  
Global Ocean ◽  
Positive Feedbacks ◽  
Nitrogen Input ◽  
Ocean Biogeochemistry ◽  
Marine Productivity ◽  
The Impact

Abstract. A common notion is that negative feedbacks stabilize the marine nitrogen inventory. Recent modeling studies have shown, however, some potential for localized positive feedbacks leading to substantial nitrogen losses, in regions where nitrogen fixation and denitrification occur in proximity to each other. Here we include dissolved nitrogen from river discharge in a global 3-D ocean biogeochemistry model and study the effects on near-coastal and remote open ocean biogeochemistry. We find that at steady state the biogeochemical feedbacks in the marine nitrogen cycle, nitrogen input from biological N2 fixation, and nitrogen loss via denitrification, mostly compensate for the yearly addition of 22.8 to 45.6 Tg of riverine nitrogen and limit the impact on global marine productivity to < 2 %. Global experiments that regionally isolate river nutrient input show that sign and strength of the feedbacks depend on the location of the river discharge and the oxygen status of the receiving marine environment. Marine productivity generally increases in proximity to the nitrogen input, but we also find a decline in productivity in the Bay of Bengal and near the mouth of the Amazon River. While most of the changes are located in shelf and near coastal oceans, nitrogen supply from the rivers can impact the open ocean, due to feedbacks or knock-on effects.

Modeling the physical drivers of the decadal variability of the Southern Ocean carbon uptake

2021 ◽  
Author(s):  
Lavinia Patara ◽  
Torge Martin ◽  
Ivy Frenger ◽  
Jan Klaus Rieck ◽  
Chia-Te Chien
Keyword(s):  
Southern Ocean ◽  
Decadal Variability ◽  
Open Ocean ◽  
Global Ocean ◽  
Carbon Uptake ◽  
Positive Trend ◽  
The Past ◽  
Rate Of Increase ◽  
Ocean Biogeochemistry ◽  
Ocean Carbon

&lt;p&gt;Observational estimates point to pronounced changes of the Southern Ocean carbon uptake in the past decades, but the mechanisms are still not fully understood. In this study we assess physical drivers of the Southern Ocean carbon uptake variability in a suite of global ocean biogeochemistry models with 0.5&amp;#186;, 0.25&amp;#186; and 0.1&amp;#186; horizontal resolution as well as in a 3-member ensemble performed with an Earth System Model (ESM) sharing the same ocean biogeochemistry model. The ocean models show a positive trend of the Southern Ocean CO&lt;sub&gt;2&lt;/sub&gt; uptake in the past decades, with a weakening of its rate of increase in the 1990s. The 0.1&amp;#186; model exhibits the strongest trend in the Southern Ocean carbon uptake.&amp;#160;&lt;span&gt;Different physical drivers of the carbon up&lt;/span&gt;take variability and of its trends (such as changes in stratification, ventilation, overturning circulation, and SST) are analyzed. A particular focus of this study is to assess the role of open-ocean polynyas in driving Southern Ocean carbon uptake. Open-ocean polynyas in the Southern Ocean have pronounced climate fingerprints, such as reduced sea-ice coverage, heat loss by the ocean and enhanced bottom water formation, but their role for the Southern Ocean carbon uptake has been as yet little studied. To this end we analyze conjunctly ESM simulations and an ocean-only sensitivity experiment where open-ocean polynyas are artificially created by perturbing the Antarctic freshwater runoff. We find that enhanced CO&lt;sub&gt;2&lt;/sub&gt; outgassing takes place during the polynya opening, because old carbon-rich waters come in contact with the atmosphere. The concomitant increased uptake of anthropogenic CO&lt;sub&gt;2&lt;/sub&gt; partially compensates the CO&lt;sub&gt;2&lt;/sub&gt; outgassing. When the polynya closes, the ocean CO&lt;sub&gt;2&lt;/sub&gt; uptake increases significantly, possibly fueled by abundant nutrients and higher alkalinity brought to the surface during the previous convective phase. Our results suggest that open-ocean polynyas could have a significant impact on the Southern Ocean CO&lt;sub&gt;2&lt;/sub&gt; uptake and could thus modulate its decadal variability.&lt;/p&gt;&lt;p&gt;&amp;#160;&lt;/p&gt;

scholarly journals An explicit estimate of the atmospheric nutrient impact on global oceanic productivity

2020 ◽  
Author(s):  
Stelios Myriokefalitakis ◽  
Matthias Gröger ◽  
Jenny Hieronymus ◽  
Ralf Döscher
Keyword(s):  
Primary Production ◽  
Global Scale ◽  
Global Ocean ◽  
Deposition Fluxes ◽  
Nutrient Deposition ◽  
Atmospheric Processing ◽  
Atmospheric Forcings ◽  
Marine Productivity ◽  
Atmospheric Inputs ◽  
The Impact

Abstract. State-of-the-art global nutrient deposition fields are here coupled to the biogeochemistry model PISCES to investigate the effect on ocean biogeochemistry in the context of atmospheric forcings for preindustrial, present, and future periods. Present-day atmospheric deposition fluxes of inorganic N, Fe, and P over the global ocean are accounted equal to ~40 Tg-N yr−1, ~0.28 Tg-Fe yr−1 and ~0.10 Tg-P yr−1. The resulting globally integrated primary production of roughly 47 Pg-C yr−1 is well within the range of satellite-based estimates and other modeling predictions. Preindustrial atmospheric nutrient deposition fluxes are lower compared to present-day (~51 %, ~36 %, and ~40 % for N, Fe, and P, respectively), resulting here in a lower marine primary production by ~3 % globally. Future changes in air pollutants under the RCP8.5 scenario result in a modest decrease of the bioaccessible nutrients input into the global ocean compared to present-day (~13 %, ~14 % and ~20 % for N, Fe and P, respectively), without significantly affecting the projected primary production in the model. The global mean nitrogen-fixation rates changed only marginally from preindustrial to future conditions (111 ± 0.6 Tg-N yr−1). With regard to the atmospheric inputs to the ocean, sensitivity model simulations indicate that the contribution of nutrients' organic fraction results in an increase in primary production by about 2.4 %. This estimate is almost equal to the effect of emissions and atmospheric processing on the oceanic biogeochemistry since preindustrial times in the model when only the inorganic fraction of the nutrients is considered. Although the impact of the atmospheric organic nutrients may imply a relatively weak response of marine productivity on a global scale, stronger regional effects up to ~20 % are calculated in the oligotrophic subtropical gyres. Overall, this work provides a first explicit assessment of the contribution of the organic forms of atmospheric nutrients, highlighting the importance of their representation in biogeochemistry models and thus the oceanic productivity estimates.

scholarly journals Strong sensitivity of Southern Ocean carbon uptake and nutrient cycling to wind stirring

2013 ◽  
Vol 10 (9) ◽  
pp. 15033-15076 ◽  
Author(s):  
K. B. Rodgers ◽  
O. Aumont ◽  
S. E. Mikaloff Fletcher ◽  
Y. Plancherel ◽  
L. Bopp ◽  
...  
Keyword(s):  
Carbon Cycle ◽  
Southern Ocean ◽  
Ad Hoc ◽  
Global Ocean ◽  
Nutrient Concentrations ◽  
Carbon Uptake ◽  
Carbon Cycle Model ◽  
Ocean Biogeochemistry ◽  
Ocean Carbon ◽  
The Impact

Abstract. Here we test the hypothesis that winds have an important role in determining the rate of exchange of CO2 between the atmosphere and ocean through wind stirring over the Southern Ocean. This is tested with a sensitivity study using an ad hoc parameterization of wind stirring in an ocean carbon cycle model. The objective is to identify the way in which perturbations to the vertical density structure of the planetary boundary in the ocean impacts the carbon cycle and ocean biogeochemistry. Wind stirring leads to reduced uptake of CO2 by the Southern Ocean over the period 2000–2006, with differences of order 0.9 Pg C yr−1 over the region south of 45° S. Wind stirring impacts not only the mean carbon uptake, but also the phasing of the seasonal cycle of carbon and other species associated with ocean biogeochemistry. Enhanced wind stirring delays the seasonal onset of stratification, and this has large impacts on both entrainment and the biological pump. It is also found that there is a strong sensitivity of nutrient concentrations exported in Subantarctic Mode Water (SAMW) to wind stirring. This finds expression not only locally over the Southern Ocean, but also over larger scales through the impact on advected nutrients. In summary, the large sensitivity identified with the ad hoc wind stirring parameterization offers support for the importance of wind stirring for global ocean biogeochemistry, through its impact over the Southern Ocean.

A state-of-the-art parameterization of atmospheric nutrient deposition fluxes in the global ocean

2020 ◽  
Author(s):  
Stelios Myriokefalitakis ◽  
Matthias Gröger ◽  
Jenny Hieronymus ◽  
Ralf Döscher
Keyword(s):  
Atmospheric Deposition ◽  
State Of The Art ◽  
Marine Ecosystem ◽  
Open Ocean ◽  
Marine Phytoplankton ◽  
Global Ocean ◽  
Model Calculations ◽  
Deposition Fluxes ◽  
Atmospheric Processing ◽  
The Impact

&lt;p&gt;Atmospheric deposition of trace constituents of natural and anthropogenic origin act as a nutrient source into the open ocean, affecting the marine ecosystem functioning and subsequently the exchange of CO&lt;sub&gt;2&lt;/sub&gt; between the atmosphere and the global ocean. Among other species that are deposited into the open ocean, nitrogen (N), iron (Fe), and phosphorus (P) are considered as highly significant nutrients that can limit marine phytoplankton growth and thus directly impact on ocean carbon fluxes in the ocean, particularly where the nutrient availability is the limiting factor for productivity. For this work, we take into account the up-to-date understanding of the effects of air quality on the atmospheric aerosol cycles to investigate the potential ocean biogeochemistry perturbations via the atmospheric input with the European Community Earth System Model EC-Earth (http://www.ec-earth.org/), which is jointly developed by several European institutes. In more detail, state-of-the-art N, Fe, and P atmospheric deposition fields are coupled to the embedded marine biogeochemistry model and the response of oceanic biogeochemistry to natural and anthropogenic atmospheric aerosols deposition changes is demonstrated and quantified. Model calculations show that compared to the present day, the preindustrial atmospheric deposition fluxes are calculated lower (~1.7, ~1.5, and ~1.4 times for N, Fe, and P, respectively) corresponding to a respective lower marine primary production. On the other hand, future changes in air pollutants under the RCP8.5 scenario result in a modest decrease of the bioaccessible nutrients input into the global ocean (~ -15%, ~ -16% and ~ -22% for N, Fe and P, respectively) and overall to a slightly lower projected export production compared to present day. Although the impact of atmospheric processing on atmospheric inputs to the ocean results in a relatively weak response in total global-scale simulated marine productivity estimates, strong regional changes up to 40-60% are calculated in the subtropical gyres. Overall, this study indicates that both the atmospheric processing and the speciation of the atmospheric nutrients deposited in the ocean should be considered in detail in carbon-cycling studies, since they may significantly affect the marine ecosystems and thus the current estimates of the carbon cycle feedbacks to climate.&lt;/p&gt;&lt;p&gt;This work has been financed by the National Observatory of Athens internal grant (number 5065), the &amp;#8220;Atmospheric deposition impacts on the ocean system&amp;#8221;, and the European Commission's Horizon 2020 Framework Programme, under Grant Agreement number 641816, the &quot;Coordinated Research in Earth Systems and Climate: Experiments, kNowledge, Dissemination, and Outreach (CRESCENDO)&quot;.&lt;/p&gt;

scholarly journals Strong sensitivity of Southern Ocean carbon uptake and nutrient cycling to wind stirring

2014 ◽  
Vol 11 (15) ◽  
pp. 4077-4098 ◽  
Author(s):  
K. B. Rodgers ◽  
O. Aumont ◽  
S. E. Mikaloff Fletcher ◽  
Y. Plancherel ◽  
L. Bopp ◽  
...  
Keyword(s):  
Carbon Cycle ◽  
Southern Ocean ◽  
Ad Hoc ◽  
Global Ocean ◽  
Relative Reduction ◽  
Carbon Uptake ◽  
Carbon Cycle Model ◽  
Ocean Biogeochemistry ◽  
Ocean Carbon ◽  
The Impact

Abstract. Here we test the hypothesis that winds have an important role in determining the rate of exchange of CO2 between the atmosphere and ocean through wind stirring over the Southern Ocean. This is tested with a sensitivity study using an ad hoc parameterization of wind stirring in an ocean carbon cycle model, where the objective is to identify the way in which perturbations to the vertical density structure of the planetary boundary in the ocean impacts the carbon cycle and ocean biogeochemistry. Wind stirring leads to reduced uptake of CO2 by the Southern Ocean over the period 2000–2006, with a relative reduction with wind stirring on the order of 0.9 Pg C yr−1 over the region south of 45° S. This impacts not only the mean carbon uptake, but also the phasing of the seasonal cycle of carbon and other ocean biogeochemical tracers. Enhanced wind stirring delays the seasonal onset of stratification, and this has large impacts on both entrainment and the biological pump. It is also found that there is a strong reduction on the order of 25–30% in the concentrations of NO3 exported in Subantarctic Mode Water (SAMW) to wind stirring. This finds expression not only locally over the Southern Ocean, but also over larger scales through the impact on advected nutrients. In summary, the large sensitivity identified with the ad hoc wind stirring parameterization offers support for the importance of wind stirring for global ocean biogeochemistry through its impact over the Southern Ocean.

On the impact of sea ice in a global ocean circulation model

1997 ◽  
Vol 25 ◽  
pp. 111-115 ◽  
Author(s):  
Achim Stössel
Keyword(s):  
Southern Ocean ◽  
Sea Ice ◽  
Ocean Circulation ◽  
General Circulation ◽  
Thermohaline Circulation ◽  
Circulation Model ◽  
Deep Ocean ◽  
Global Ocean ◽  
Convective Activity ◽  
The Impact

This paper investigates the long-term impact of sea ice on global climate using a global sea-ice–ocean general circulation model (OGCM). The sea-ice component involves state-of-the-art dynamics; the ocean component consists of a 3.5° × 3.5° × 11 layer primitive-equation model. Depending on the physical description of sea ice, significant changes are detected in the convective activity, in the hydrographic properties and in the thermohaline circulation of the ocean model. Most of these changes originate in the Southern Ocean, emphasizing the crucial role of sea ice in this marginally stably stratified region of the world's oceans. Specifically, if the effect of brine release is neglected, the deep layers of the Southern Ocean warm up considerably; this is associated with a weakening of the Southern Hemisphere overturning cell. The removal of the commonly used “salinity enhancement” leads to a similar effect. The deep-ocean salinity is almost unaffected in both experiments. Introducing explicit new-ice thickness growth in partially ice-covered gridcells leads to a substantial increase in convective activity, especially in the Southern Ocean, with a concomitant significant cooling and salinification of the deep ocean. Possible mechanisms for the resulting interactions between sea-ice processes and deep-ocean characteristics are suggested.

The impact of glaciation, river-discharge and sea-level change on Late Quaternary environments in the southwestern Kara Sea

2000 ◽  
Vol 89 (3) ◽  
pp. 550-562 ◽  
Author(s):  
Leonid Polyak ◽  
Mikhail Levitan ◽  
Valery Gataullin ◽  
Tatiana Khusid ◽  
Valery Mikhailov ◽  
...  
Keyword(s):  
Sea Level ◽  
River Discharge ◽  
Late Quaternary ◽  
Sea Level Change ◽  
Kara Sea ◽  
Level Change ◽  
The Impact ◽  
And Sea Level

Improving SAR Altimeter processing over the coastal zone and inland waters - the ESA HYDROCOASTAL project

2021 ◽  
Author(s):  
David Cotton ◽  
Keyword(s):  
Coastal Zone ◽  
Test Data ◽  
River Discharge ◽  
Altimeter Data ◽  
Inland Waters ◽  
Data Sets ◽  
Data Set ◽  
Discharge Data ◽  
Processing Algorithms ◽  
The Impact

&lt;p&gt;&lt;strong&gt;Introduction&lt;/strong&gt;&lt;/p&gt;&lt;p&gt;HYDROCOASTAL is a two year project funded by ESA, with the objective to maximise exploitation of SAR and SARin altimeter measurements in the coastal zone and inland waters, by evaluating and implementing new approaches to process SAR and SARin data from CryoSat-2, and SAR altimeter data from Sentinel-3A and Sentinel-3B. Optical data from Sentinel-2 MSI and Sentinel-3 OLCI instruments will also be used in generating River Discharge products.&lt;/p&gt;&lt;p&gt;New SAR and SARin processing algorithms for the coastal zone and inland waters will be developed and implemented and evaluated through an initial Test Data Set for selected regions. From the results of this evaluation a processing scheme will be implemented to generate global coastal zone and river discharge data sets.&lt;/p&gt;&lt;p&gt;A series of case studies will assess these products in terms of their scientific impacts.&lt;/p&gt;&lt;p&gt;All the produced data sets will be available on request to external researchers, and full descriptions of the processing algorithms will be provided&lt;/p&gt;&lt;p&gt;&amp;#160;&lt;/p&gt;&lt;p&gt;&lt;strong&gt;Objectives&lt;/strong&gt;&lt;/p&gt;&lt;p&gt;The scientific objectives of HYDROCOASTAL are to enhance our understanding&amp;#160; of interactions between the inland water and coastal zone, between the coastal zone and the open ocean, and the small scale processes that govern these interactions. Also the project aims to improve our capability to characterize the variation at different time scales of inland water storage, exchanges with the ocean and the impact on regional sea-level changes&lt;/p&gt;&lt;p&gt;The technical objectives are to develop and evaluate&amp;#160; new SAR&amp;#160; and SARin altimetry processing techniques in support of the scientific objectives, including stack processing, and filtering, and retracking. Also an improved Wet Troposphere Correction will be developed and evaluated.&lt;/p&gt;&lt;p&gt;&lt;strong&gt;Project&amp;#160; Outline&lt;/strong&gt;&lt;/p&gt;&lt;p&gt;There are four tasks to the project&lt;/p&gt;&lt;ul&gt;&lt;li&gt;Scientific Review and Requirements Consolidation: Review the current state of the art in SAR and SARin altimeter data processing as applied to the coastal zone and to inland waters&lt;/li&gt; &lt;li&gt;Implementation and Validation: New processing algorithms with be implemented to generate a Test Data sets, which will be validated against models, in-situ data, and other satellite data sets. Selected algorithms will then be used to generate global coastal zone and river discharge data sets&lt;/li&gt; &lt;li&gt;Impacts Assessment: The impact of these global products will be assess in a series of Case Studies&lt;/li&gt; &lt;li&gt;Outreach and Roadmap: Outreach material will be prepared and distributed to engage with the wider scientific community and provide recommendations for development of future missions and future research.&lt;/li&gt; &lt;/ul&gt;&lt;p&gt;&amp;#160;&lt;/p&gt;&lt;p&gt;&lt;strong&gt;Presentation&lt;/strong&gt;&lt;/p&gt;&lt;p&gt;The presentation will provide an overview to the project, present the different SAR altimeter processing algorithms that are being evaluated in the first phase of the project, and early results from the evaluation of the initial test data set.&lt;/p&gt;&lt;p&gt;&amp;#160;&lt;/p&gt;

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