scholarly journals Marine denitrification rates determined from a global 3-dimensional inverse model

2012 ◽  
Vol 9 (10) ◽  
pp. 14013-14052 ◽  
Author(s):  
T. DeVries ◽  
C. Deutsch ◽  
P. A. Rafter ◽  
F. Primeau
Keyword(s):  
Ocean Circulation ◽  
Isotopic Ratio ◽  
Circulation Model ◽  
Simple Relationship ◽  
N Losses ◽  
3 Dimensional ◽  
Global Rate ◽  
Nitrate Consumption ◽  
The Difference

Abstract. A major impediment to understanding long-term changes in the marine nitrogen (N) cycle is the persistent uncertainty about the rates, distribution, and sensitivity of its largest fluxes in the modern ocean. We use a global 3-dimensional ocean circulation model to obtain the first estimate of marine denitrification rates that is maximally consistent with available observations of nitrate deficits and the nitrogen isotopic ratio of ocean nitrate. We find a global rate of marine denitrification in suboxic waters and sediments of 120–240 Tg N yr−1, which is lower than most other recent estimates. The difference stems from the ability to represent the 3-D spatial structure of suboxic zones, where denitrification rates of 50–77 Tg N yr−1 result in up to 50% depletion of nitrate. This depletion reduces the effect of local isotopic enrichment on the rest of the ocean, allowing the N isotope ratio of oceanic nitrate to be achieved with a sedimentary denitrification rate about 1.3–2.3 times that of suboxic zones. This balance of N losses between sediments and suboxic zones is shown to obey a simple relationship between isotope fractionation and the degree of nitrate consumption in the core of the suboxic zones. The global denitrification rates derived here suggest that the marine nitrogen budget is likely close to balanced.

scholarly journals Marine denitrification rates determined from a global 3-D inverse model

2013 ◽  
Vol 10 (4) ◽  
pp. 2481-2496 ◽  
Author(s):  
T. DeVries ◽  
C. Deutsch ◽  
P. A. Rafter ◽  
F. Primeau
Keyword(s):  
Ocean Circulation ◽  
Isotopic Ratio ◽  
Circulation Model ◽  
Global Ocean ◽  
Simple Relationship ◽  
N Losses ◽  
Global Rate ◽  
Nitrate Consumption ◽  
The Difference ◽  
Global Ocean Circulation

Abstract. A major impediment to understanding long-term changes in the marine nitrogen (N) cycle is the persistent uncertainty about the rates, distribution, and sensitivity of its largest fluxes in the modern ocean. We use a global ocean circulation model to obtain the first 3-D estimate of marine denitrification rates that is maximally consistent with available observations of nitrate deficits and the nitrogen isotopic ratio of oceanic nitrate. We find a global rate of marine denitrification in suboxic waters and sediments of 120–240 Tg N yr−1, which is lower than many other recent estimates. The difference stems from the ability to represent the 3-D spatial structure of suboxic zones, where denitrification rates of 50–77 Tg N yr−1 result in up to 50% depletion of nitrate. This depletion reduces the effect of local isotopic enrichment on the rest of the ocean, allowing the N isotope ratio of oceanic nitrate to be achieved with a sedimentary denitrification rate about 1.3–2.3 times that of suboxic zones. This balance of N losses between sediments and suboxic zones is shown to obey a simple relationship between isotope fractionation and the degree of nitrate consumption in the core of the suboxic zones. The global denitrification rates derived here suggest that the marine nitrogen budget is likely close to balanced.

scholarly journals Overlooked runaway feedback in the marine nitrogen cycle: the vicious cycle

2012 ◽  
Vol 9 (7) ◽  
pp. 8905-8930
Author(s):  
A. Landolfi ◽  
H. Dietze ◽  
W. Koeve ◽  
A. Oschlies
Keyword(s):  
Ocean Circulation ◽  
Nitrogen Loss ◽  
Spatial Association ◽  
Circulation Model ◽  
Spatial Proximity ◽  
N Losses ◽  
Sources And Sinks ◽  
Close Spatial Proximity ◽  
Individual Rate ◽  
Apparent Stability

Abstract. The marine nitrogen (N) inventory is controlled by the interplay of nitrogen loss processes, here referred to as denitrification, and nitrogen source processes, primarily nitrogen fixation. The apparent stability of the marine N inventory on time scales longer than the estimated N residence time, suggests some intimate balance between N sinks and sources. Such a balance may be perceived easier to achieve when N sinks and sources occur in close spatial proximity, and some studies have interpreted observational evidence for such a proximity as indication for a stabilizing feedback processes. Using a biogeochemical ocean circulation model, we here show instead that a close spatial association of N2 fixation and denitrification can, in fact, trigger destabilizing feedbacks on the N inventory and, because of stoichiometric constrains, lead to net N losses. Contrary to current notion, a balanced N inventory requires a regional separation of N sources and sinks. This can be brought about by factors that reduce the growth of diazotrophs, such as iron, or by factors that affect the fate of the fixed nitrogen remineralization, such as dissolved organic matter dynamics. In light of our findings we suggest that spatial arrangements of N sinks and sources have to be accounted for in addition to individual rate estimates for reconstructing past, evaluating present and predicting future marine N inventory imbalances.

scholarly journals A simple nutrient-dependence mechanism for predicting the stoichiometry of marine ecosystems

2015 ◽  
Vol 112 (27) ◽  
pp. 8199-8204 ◽  
Author(s):  
Eric D. Galbraith ◽  
Adam C. Martiny
Keyword(s):  
Ocean Circulation ◽  
Large Scale ◽  
Phytoplankton Community ◽  
Simple Relationship ◽  
Low Latitude ◽  
Average Composition ◽  
Biogeochemical Models ◽  
The Relationship ◽  
Globally Distributed

It is widely recognized that the stoichiometry of nutrient elements in phytoplankton varies within the ocean. However, there are many conflicting mechanistic explanations for this variability, and it is often ignored in global biogeochemical models and carbon cycle simulations. Here we show that globally distributed particulate P:C varies as a linear function of ambient phosphate concentrations, whereas the N:C varies with ambient nitrate concentrations, but only when nitrate is most scarce. This observation is consistent with the adjustment of the phytoplankton community to local nutrient availability, with greater flexibility of phytoplankton P:C because P is a less abundant cellular component than N. This simple relationship is shown to predict the large-scale, long-term average composition of surface particles throughout large parts of the ocean remarkably well. The relationship implies that most of the observed variation in N:P actually arises from a greater plasticity in the cellular P:C content, relative to N:C, such that as overall macronutrient concentrations decrease, N:P rises. Although other mechanisms are certainly also relevant, this simple relationship can be applied as a first-order basis for predicting organic matter stoichiometry in large-scale biogeochemical models, as illustrated using a simple box model. The results show that including variable P:C makes atmospheric CO2 more sensitive to changes in low latitude export and ocean circulation than a fixed-stoichiometry model. In addition, variable P:C weakens the relationship between preformed phosphate and atmospheric CO2 while implying a more important role for the nitrogen cycle.

scholarly journals Effects of long-term protein excess or deficiency on whole-body protein turnover in sheep nourished by intragastric infusion of nutrients

1995 ◽  
Vol 73 (6) ◽  
pp. 829-839 ◽  
Author(s):  
S. M. Liu ◽  
G. E. Lobley ◽  
N. A. Macleod ◽  
D. J. Kyle ◽  
X.B. Chen ◽  
...  
Keyword(s):  
Dietary Protein ◽  
Protein Turnover ◽  
Protein Intake ◽  
Volatile Fatty Acids ◽  
Whole Body ◽  
N Losses ◽  
Body Protein ◽  
Fractional Rate ◽  
The Difference

The effect of long-term dietary protein excess and deficit on whole-body protein-N turnover (WBPNT) was examined in lambs nourished by intragastric infusions of nutrients. Ten sheep were given 500 mg N/kg metabolic weight (W0.75) per d from casein for 2 weeks and then either 50 (L), 500 (M) or 1500 (H) mg N/kgW0.75per d for 6 weeks. Volatile fatty acids were infused at 500 kJ/kgW0.75per d. Daily WBPNT was measured by continuous intravenous infusion of [l-13C]leucine 3 d before, and on days 2, 21 and 42 after the alteration in protein intake. Whole-body protein-N synthesis (WBPNS) was calculated as the difference between WBPNT and the protein-N losses as urinary NH3and urea. Whole-body protein-N degradation (WBPNS) was then estimated from WBPNS minus protein gain determined from N balance. Fractional rates of WBPNS and WBPND were calculated against fleece-free body N content. WBPNS rates at the L, M and H intakes were respectively 35·1, 41·5 amd 6·37 g/d (P< 0.001) on average over the 6 weeks and WBPND rates were 39·5, 41·1 and 56·8 g/d (P< 0.001). The fractional rates of WBPNS were 5·01, 6·37 and 7·73% per d (P< 0.001) while those of WBPND were 5·64, 6·29 and 6·81% per d (P< 0.005) respectively. On days 2, 21 and 42, WBPNS rates at intake H were 54·0, 61·8 and 75·4 g/d (P= 0·03) respectively, and WBPND rates were 43·2, 56·4 and 70·9 g/d (P= 0.03); at intake L the amounts were 38·2, 34·2 and 32·8 g/d for WBPNS (P= 0.003) and for WBPND were 43·4, 38·0 and 36·9 g/d (P= 0·016) respectively. There were no significant (P> 0·05) differences in fractional rates of WBPNS and WBPND with time at either the L or H intake. We concluded that absolute protein turnover was affected both by dietary protein intake and by body condition while the fractional rate of turnover was predominantly influenced by intake.

Local egg production and larval losses to advection contribute to interannual and long-term variability of American lobster (Homarus americanus) settlement intensity

2019 ◽  
Vol 76 (3) ◽  
pp. 350-363
Author(s):  
Louise Gendron ◽  
Denis Lefaivre ◽  
Bernard Sainte-Marie
Keyword(s):  
Ocean Circulation ◽  
Egg Production ◽  
Size Structure ◽  
Growth Models ◽  
Larval Growth ◽  
Circulation Model ◽  
Homarus Americanus ◽  
American Lobster ◽  
Positive Trend

American lobster (Homarus americanus) egg production and settlement intensity were examined over a 19-year period (1995–2013) in the Gulf of St. Lawrence at the Magdalen Islands (MI), where the population is spatially isolated during the benthic phase. Settlement and hatch dates by year were back-calculated from observed young-of-the-year size structure and juvenile and larval growth models. Drift of locally released larvae, from stage I to the end of stage III, was simulated using an ocean circulation model. Settlement intensity was related positively to egg production and negatively to drift distance. There was a strong positive trend in settlement intensity explained largely by increasing egg production, as well as by declining larval duration and drift distance. In the last years of the study, settlement intensity may have been limited by nursery saturation. The results suggest that demographic connectivity through larval drift is highly dynamic in time and that it declined during our study period. The demographic dependence of the MI lobster population on other populations in the Gulf of St. Lawrence is probably low.

Model Study of the Water Exchange in a Shallow Bay

2013 ◽  
Vol 726-731 ◽  
pp. 3439-3442
Author(s):  
Hao Liu ◽  
Dan Luo ◽  
Hong Xuan Kang ◽  
Bao Shu Yin
Keyword(s):  
Water Exchange ◽  
Circulation Model ◽  
Tidal Prism ◽  
3 Dimensional ◽  
Model Study ◽  
Term Variation ◽  
Enclosed Bay ◽  
Coastal Circulation Model ◽  
Shallow Bay

Both the tidal prism and the water exchange duration can be used as the index of examining the residence time of the pollutants in a semi-enclosed bay, and it is significant to predict the long-term variation of water quality. A 3-dimensional coastal circulation model is used to reproduce the tidal regime in the Shenhu Bay. Simulated tidal currents are examined first, and the then the tidal prism is also compared to observations. Based on the validated simulations, the water exchange duration is further estimated by means of the numerical experiment. The simulations show that the half-exchange and 80%-exchange time are about 14 and 30 d, respectively.

scholarly journals How have both cultivation and warming influenced annual global isoprene and monoterpene emissions since the preindustrial era?

2012 ◽  
Vol 12 (20) ◽  
pp. 9703-9718 ◽  
Author(s):  
K. Tanaka ◽  
H.-J. Kim ◽  
K. Saito ◽  
H. G. Takahashi ◽  
M. Watanabe ◽  
...  
Keyword(s):  
Southeast Asia ◽  
Ocean Circulation ◽  
Circulation Model ◽  
Global Scale ◽  
The Other ◽  
Forest Conversion ◽  
Climate Data ◽  
Monthly Basis ◽  
Air Temperatures ◽  
The Difference

Abstract. To examine the influence of both crop cultivation and surface air temperatures (SATs) on annual global isoprene and monoterpene emissions, which can lead to the formation of secondary organic aerosols (SOAs), we simulated, on a monthly basis, the annual emissions of volatile organic compounds (VOCs) during the period 1854–2000. The model estimates were based on historical climate data such as SATs, and downward solar radiation (DSR) reproduced with an atmospheric-ocean circulation model, as well as a time series of the global distribution of cropland (to test the hypothesis that conversion of forests into croplands lowers emissions). The simulations demonstrated that global SAT, DSR, the combination of SAT and DSR, and the expansion of cropland all affected emissions. The effect of cropland expansion (i.e., forest conversion) on annual emissions during this period was larger for isoprene (~7% reduction on a global scale) than for monoterpenes (~2% reduction), mainly because of the reduction in broadleaf evergreen forests (BEFs) in Southeast Asia, which have the highest and most constant emissions of isoprene and where both temperature and radiation are high all year round. The reduction in the Amazon region and in parts of Africa, which are other primary sources of annual global isoprene emissions, but where the conversion of BEF to cropland has been much smaller than in Southeast Asia, was less remarkable, probably because the broadleaf deciduous forests and C4 grasslands in these areas have lower and seasonal emissions; hence, their conversion has less effect. On the other hand, the difference in the emission factors (ε) between cropland and the other vegetation types was much lower for monoterpenes than for isoprene, although the ε for cropland was generally the lowest for both compounds. Thus, the expansion of cropland also contributed to the reduction in monoterpene emissions to some degree, but had less effect. A ~5% increase in emissions due to rising SAT was more than offset by the decrease in isoprene emissions and a concurrent ~2% reduction caused by a decrease in DSR. Overall, annual global isoprene emissions in 2000 were lower than in 1854 by 13 TgC yr−1, whereas annual global monoterpene emissions were higher by 2.3 TgC yr−1.

scholarly journals Subthermocline Eddies in the Western Equatorial Pacific as Shown by an Eddy-Resolving OGCM*

2013 ◽  
Vol 43 (7) ◽  
pp. 1241-1253 ◽  
Author(s):  
Tzu-Ling Chiang ◽  
Tangdong Qu
Keyword(s):  
Ocean Circulation ◽  
Circulation Model ◽  
Propagation Speed ◽  
Guinea Coast ◽  
Ocean Circulation Model ◽  
South Pacific Ocean ◽  
Analysis Of Results ◽  
In Situ Observations

Abstract Sporadic in situ observations have shown evidence that subthermocline eddies exist off the Mindanao coast. These subthermocline eddies are believed to play an important role in the heat, freshwater, and other ocean property transports of the region, but their characteristics and in particular their pathway and source of energy are poorly explored because of the lack of long-term observations. Analysis of results from an eddy-resolving general ocean circulation model has revealed that most subthermocline eddies off the Mindanao coast originate from the equatorial South Pacific Ocean to the west of the Ninigo Group. These eddies propagate northward along the New Guinea coast, cross the equator in the far western Pacific, and reach the Mindanao coast at a typical propagation speed of ~0.12 m s−1. The dominant time scales of these eddies range between 50 and 60 days.

scholarly journals How have both cultivation and warming influenced annual global isoprene and monoterpene emissions since the preindustrial era?

2012 ◽  
Vol 12 (7) ◽  
pp. 16515-16555 ◽  
Author(s):  
K. Tanaka ◽  
H.-J. Kim ◽  
K. Saito ◽  
H. G. Takahashi ◽  
M. Watanabe ◽  
...  
Keyword(s):  
Southeast Asia ◽  
Ocean Circulation ◽  
Surface Air Temperature ◽  
Circulation Model ◽  
Global Scale ◽  
The Other ◽  
Primary Sources ◽  
Forest Conversion ◽  
Climate Data ◽  
The Difference

Abstract. To examine the influence of both crop cultivation and surface air temperature (SAT) on annual global isoprene and monoterpene emissions, which can lead to the formation of secondary organic aerosols (SOAs), we simulated the annual emissions of volatile organic compounds (VOCs) during the period 1854–2000. The model estimates were based on historical climate data such as SATs, and downward solar radiation (DSR) reproduced with an atmospheric-ocean circulation model, as well as a time series of the global distribution of cropland (to test the hypothesis that conversion of forests into croplands lowers emissions). The simulations demonstrated that global SAT, DSR, the combination of SAT and DSR, and the expansion of cropland all affected emissions. The effect of cropland expansion (i.e., forest conversion) on annual emissions during this period was larger for isoprene (~7% reduction on a global scale) than for monoterpenes (~2% reduction), mainly because of the reduction in broadleaf evergreen forests (BEFs) in Southeast Asia, which have the highest and most constant emissions of isoprene and where both temperature and radiation are high all year round. The reduction in the Amazon region and in parts of Africa, which are other primary sources of annual global isoprene emissions, but where the conversion of BEF to cropland has been much smaller than in Southeast Asia, was less remarkable, probably because the broadleaf deciduous forests and C4 grasslands in these areas have lower and seasonal emissions; hence, their conversion has less effect. On the other hand, the difference in the emission factors (ε) between cropland and the other vegetation types was much lower for monoterpenes than for isoprene, although the ε for cropland was generally the lowest for both emissions. Thus, the expansion of cropland also contributed to the reduction in monoterpene emissions to some degree, but had less effect. A ~5% increase in emissions due to rising SAT was more than offset by the decrease in isoprene emissions and a concurrent ~2% reduction caused by a decrease in DSR. Overall, annual global isoprene emissions in 2000 were lower than in 1854, whereas annual global monoterpene emissions were higher.

A Problem of Long - Term Digital Preservation: Difference in Humanities and Natural Sciences

2014 ◽  
Vol 3 ◽  
pp. 183-195
Author(s):  
Elena Macevičiūtė
Keyword(s):  
Social Sciences ◽  
Digital Preservation ◽  
Dynamic Activity ◽  
Private Companies ◽  
Time Line ◽  
Digital Documents ◽  
Whole Process ◽  
The Difference ◽  
Technological Science

The article deals with the requirements and needs for long-term digital preservation in different areas of scholarly work. The concept of long-term digital preservation is introduced by comparing it to digitization and archiving concepts and defined with the emphasis on dynamic activity within a certain time line. The structure of digital preservation is presented with regard to the elements of the activity as understood in Activity Theory. The life-cycle of digitization processes forms the basis of the main processing of preserved data in preservation archival system.The author draws on the differences between humanities and social sciences on one hand and natural and technological science on the other. The empirical data characterizing the needs for digital preservation within different areas of scholarship are presented and show the difference in approaches to long-term digital preservation, as well as differences in selecting the items and implementing the projects of digital preservation. Institutions and organizations can also develop different understanding of preservation requirements for digital documents and other objects.The final part of the paper is devoted to some general problems pertaining to the longterm digital preservation with the emphasis of the responsibility for the whole process of safe-guarding the cultural and scholarly heritage for the re-use of the posterior generations. It is suggested that the longevity of the libraries in comparison with much shorter life-span of private companies strengthens the claim of memory institutions to playing the central role in the long-term digital preservation.

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