scholarly journals Impact of vertical and horizontal advection on nutrient distribution in the southeast Pacific

Ocean Science ◽  
2016 ◽  
Vol 12 (4) ◽  
pp. 1003-1011 ◽  
Author(s):  
Bàrbara Barceló-Llull ◽  
Evan Mason ◽  
Arthur Capet ◽  
Ananda Pascual
Keyword(s):  
Vertical Velocity ◽  
Nitrate Uptake ◽  
Austral Summer ◽  
Lagrangian Particle ◽  
Nutrient Distribution ◽  
Uptake Rates ◽  
Southeast Pacific ◽  
Omega Equation ◽  
The Impact ◽  
Initial Distributions

Abstract. An innovative approach is used to analyze the impact of vertical velocities associated with quasi-geostrophic (QG) dynamics on the redistribution and uptake of nitrate in the southeast Pacific (SEP). A total of 12 years of vertical and horizontal currents are derived from an observation-based estimate of the ocean state. Horizontal velocities are obtained through the application of thermal wind balance to weekly temperature and salinity fields. Vertical velocities are estimated by integration of the QG omega equation. Seasonal variability of the synthetic vertical velocity and kinetic energy associated with the horizontal currents is coincident, with peaks in austral summer (November–December) in accord with published observations. The impact of vertical velocity on SEP nitrate uptake rates is assessed by using two Lagrangian particle tracking experiments that differ according to vertical forcing (ω = ωQG vs. ω = 0). From identical initial distributions of nitrate-tagged particles, the Lagrangian results show that vertical motions induce local increases in nitrate uptake reaching up to 30 %. Such increases occur in low uptake regions with high mesoscale activity. Despite being weaker than horizontal currents by a factor of up to 10−4, vertical velocity associated with mesoscale activity is demonstrated to make an important contribution to nitrate uptake, hence productivity, in low uptake regions.

scholarly journals Impact of vertical and horizontal advection on nutrient distribution in the South East Pacific

2015 ◽  
Vol 12 (5) ◽  
pp. 2257-2281
Author(s):  
B. Barceló-Llull ◽  
E. Mason ◽  
A. Pascual
Keyword(s):  
Vertical Velocity ◽  
Austral Summer ◽  
The South ◽  
Lagrangian Particle ◽  
Nutrient Distribution ◽  
Horizontal Advection ◽  
East Pacific ◽  
Omega Equation ◽  
The Impact ◽  
Initial Distributions

Abstract. An innovative approach is used to analyse the impact of vertical velocities associated with quasi-geostrophic (QG) dynamics on the distribution of a passive nutrient tracer (nitrate) in the South East Pacific. Twelve years of vertical and horizontal currents are derived from an observation-based estimate of the ocean state. Horizontal velocities are obtained through application of thermal wind balance to weekly temperature and salinity fields. Vertical velocities are estimated by integration of the QG Omega equation. Seasonal variability of the synthetic vertical velocity and kinetic energy associated with the horizontal currents are coincident, with peaks in austral summer (November–December) in accord with published observations. Two ensembles of Lagrangian particle tracking experiments that differ according to vertical forcing (w = wQG vs. w = 0) enable a quantitative analysis of the impact of the vertical velocity. From identical initial distributions of nitrate-tagged particles, the Lagrangian results show that the impact of vertical advection on nutrient distribution is 30 % of the contribution of horizontal advection. Despite being weaker by a factor of up to 10−4 than the horizontal currents, vertical velocity is demonstrated to make an important contribution to nutrient distributions in the region of study.

scholarly journals A geographical and seasonal comparison of nitrogen uptake by phytoplankton in the Southern Ocean

2014 ◽  
Vol 11 (4) ◽  
pp. 1829-1869
Author(s):  
R. Philibert ◽  
H. Waldron ◽  
D. Clark
Keyword(s):  
Southern Ocean ◽  
Primary Production ◽  
Nitrogen Uptake ◽  
Uptake Rate ◽  
Nitrate Uptake ◽  
Day Length ◽  
Ammonium Uptake ◽  
Ammonium Concentration ◽  
Uptake Rates ◽  
The Impact

Abstract. Primary production in the Southern Ocean has been shown to be regulated by light and nutrients (such as silicate and iron) availability. However, the impact of these factors vary seasonally and differ from region to region. The seasonal cycle of primary production in this region is not fully resolved over an annual scale due to the lack of winter in situ measurements. In this study, nitrate and ammonium uptake rates were measured using 15N tracers during a winter cruise in July 2012 and a summer cruise in February/March 2013. In winter, nitrogen uptake rates were measured at 55% and 1% of the surface photosynthetically active radiation (sPAR). The summer uptake rates were measured at 4 light depths corresponding to 55, 30, 10 and 3% sPAR. The integrated nitrate uptake rates during the winter cruise ranged from 0.16–5.20 (average 1.14) mmol N m−2 d−1 while the ammonium uptake rates ranged from 0.6–32.8 (average 6.72) mmol N m−2 d−1. During the summer cruise, the mean integrated nitrate uptake rate was 0.34 mmol N m−2 d−1 with a range between 0.16–0.65 mmol N m−2 d−1. The integrated ammonium uptake rate averaged 5.61 mmol N m−2 d−1 and ranged from 1.44–11.28 mmol N m−2 d−1. The factors controlling primary production in winter and summer were investigated. During the winter cruise, it was found the different nitrogen uptake regimes were not separated by fronts. Light (in terms of day length) and ammonium concentration had the most influence on the nitrogen uptake regime. In the summer, increases in the mixed layer depth (MLD) resulted in increased nitrogen uptake rates. This suggests that the increases in the MLD could be alleviating nutrient limitations experienced by the phytoplankton at the end of summer.

scholarly journals The vertical structure of precipitation at two stations in East Antarctica derived from micro rain radars

2019 ◽  
Vol 13 (1) ◽  
pp. 247-264 ◽  
Author(s):  
Claudio Durán-Alarcón ◽  
Brice Boudevillain ◽  
Christophe Genthon ◽  
Jacopo Grazioli ◽  
Niels Souverijns ◽  
...  
Keyword(s):  
Vertical Velocity ◽  
Austral Summer ◽  
Extreme Environment ◽  
East Antarctica ◽  
Vertical Profiles ◽  
Atmospheric Conditions ◽  
Surface Mass ◽  
Surface Precipitation ◽  
Future Evolution ◽  
The Impact

Abstract. Precipitation over Antarctica is the main term in the surface mass balance of the Antarctic ice sheet, which is crucial for the future evolution of the sea level worldwide. Precipitation, however, remains poorly documented and understood mainly because of a lack of observations in this extreme environment. Two observatories dedicated to precipitation have been set up at the Belgian station Princess Elisabeth (PE) and at the French station Dumont d'Urville (DDU) in East Antarctica. Among other instruments, both sites have a vertically pointing micro rain radar (MRR) working at the K band. Measurements have been continuously collected at DDU since the austral summer of 2015–2016, while they have been collected mostly during summer seasons at PE since 2010, with a full year of observation during 2012. In this study, the statistics of the vertical profiles of reflectivity, vertical velocity, and spectral width are analyzed for all seasons. Vertical profiles were separated into surface precipitation and virga to evaluate the impact of virga on the structure of the vertical profiles. The climatology of the study area plays an important role in the structure of the precipitation: warmer and moister atmospheric conditions at DDU favor the occurrence of more intense precipitation compared with PE, with a difference of 8 dBZ between both stations. The strong katabatic winds blowing at DDU induce a decrease in reflectivity close to the ground due to the sublimation of the snowfall particles. The vertical profiles of precipitation velocity show significant differences between the two stations. In general, at DDU the vertical velocity increases as the height decreases, while at PE the vertical velocity decreases as the height decreases. These features of the vertical profiles of reflectivity and vertical velocity could be explained by the more frequent occurrence of aggregation and riming at DDU compared to PE because of the lower temperature and relative humidity at the latter, located further in the interior. Robust and reliable statistics about the vertical profile of precipitation in Antarctica, as derived from MRRs for instance, are necessary and valuable for the evaluation of precipitation estimates derived from satellite measurements and from numerical atmospheric models.

scholarly journals A geographical and seasonal comparison of nitrogen uptake by phytoplankton in the Southern Ocean

Ocean Science ◽  
2015 ◽  
Vol 11 (2) ◽  
pp. 251-267 ◽  
Author(s):  
R. Philibert ◽  
H. Waldron ◽  
D. Clark
Keyword(s):  
Southern Ocean ◽  
Nitrogen Uptake ◽  
Uptake Rate ◽  
Nitrate Uptake ◽  
Day Length ◽  
Ammonium Uptake ◽  
Ammonium Concentration ◽  
Atlantic Sector ◽  
Uptake Rates ◽  
The Impact

Abstract. The impact of light and nutrients (such as silicate and iron) availability on nitrogen uptake and primary production vary seasonally and regionally in the Southern Ocean. The seasonal cycle of nitrogen uptake by phytoplankton in the Southern Ocean is not fully resolved over an annual scale due to the lack of winter in situ measurements. In this study, nitrate and ammonium uptake rates were measured using 15N tracers during a winter cruise in July 2012 and a summer cruise in February–March 2013. The winter cruise consisted of two legs: leg 1 extended from Cape Town to the ice margin along the GoodHope line and leg 2 stretched from the ice margin to Marion Island. The summer cruise was mostly focused on the subantarctic zone of the Atlantic sector. In winter, nitrogen uptake rates were measured at 55 and 1% of the surface photosynthetically active radiation (sPAR). The summer uptake rates were measured at four light depths corresponding to 55, 30, 10 and 3% sPAR. The integrated nitrate uptake rates during the winter cruise ranged from 0.17 to 5.20 mmol N m−2 d−1 (average 1.14 mmol N m−2 d−1) while the ammonium uptake rates ranged from 0.60 to 32.86 mmol N m−2 d−1 (average 6.73 mmol N m−2 d−1). During the summer cruise, the mean-integrated nitrate uptake rate was 0.20 mmol N m−2 d−1 with a range between 0.10 and 0.38 mmol N m−2 d−1. The integrated ammonium uptake rate averaged 4.39 mmol N m−2 d−1 and ranged from 1.12 to 9.05 mmol N m−2 d−1. The factors controlling nitrogen uptake in winter and summer were investigated. During the winter cruise, it was found that the different nitrogen uptake regimes were not separated by the fronts of the Antarctic Circumpolar Current (ACC). Light (in terms of day length) and ammonium concentration had the most influence on the nitrogen uptake. In the summer, increases in the mixed layer depth (MLD) resulted in increased nitrogen uptake rates. This suggests that the increases in the MLD could be alleviating nutrient limitations experienced by the phytoplankton at the end of summer.

scholarly journals The vertical structure of precipitation at two stations in East Antarctica derived from micro rain radars

2018 ◽  
Author(s):  
Claudio Durán-Alarcón ◽  
Brice Boudevillain ◽  
Christophe Genthon ◽  
Jacopo Grazioli ◽  
Niels Souverijns ◽  
...  
Keyword(s):  
Vertical Velocity ◽  
Austral Summer ◽  
Extreme Environment ◽  
East Antarctica ◽  
Vertical Profiles ◽  
Atmospheric Conditions ◽  
Surface Mass ◽  
Surface Precipitation ◽  
Future Evolution ◽  
The Impact

Abstract. Precipitation over Antarctica is the main term in the surface mass balance of the Antarctic ice sheet, which is crucial for the future evolution of the sea level worldwide. Precipitation however remains poorly documented and understood mainly because of a lack of observations in this extreme environment. Two observatories dedicated to precipitation have been set up at the Belgian station Princess Elisabeth (PE) and at the French station Dumont d'Urville (DDU) in East Antarctica. Among other instruments, both sites have a vertically-pointing micro rain radar (MRR) working at the K-band. Measurements are continuously collected at DDU since the austral summer 2015–2016, while they have been collected mostly during summer seasons at PE since 2010, with a full year of observation during 2012. In this study, the statistics of the vertical profiles of reflectivity, vertical velocity and spectral width are analyzed for all seasons. Vertical profiles were separated into surface precipitation and virga to evaluate the impact of virga on the structure of the vertical profiles. The climatology of the study area plays an important role in the structure of the precipitation: warmer and moister atmospheric conditions at DDU favor the occurrence of more intense precipitation compared with PE, with a difference of 8 dBZ between both stations. The strong katabatic winds blowing at DDU induce a decrease of reflectivity close to the ground due to the sublimation of the snowfall particles. The vertical profiles of precipitation velocity show significant differences between the two stations. In general, at DDU the vertical velocity increases as the height decreases, while at PE the vertical velocity decreases as the height decrease. These features of the vertical profiles of reflectivity and vertical velocity could be explained by the more frequent occurrence of aggregation and riming at DDU compared to PE, because of the colder and drier conditions at the latter. Robust and reliable statistics about the vertical profile of precipitation in Antarctica, as derived from micro rain radars for instance, are necessary and valuable for the evaluation of precipitation estimates derived from satellite measurements and from numerical atmospheric models.

scholarly journals Characterization of the inter-annual, seasonal, and diurnal variations of condensation particle concentrations at Neumayer, Antarctica

2011 ◽  
Vol 11 (24) ◽  
pp. 13243-13257 ◽  
Author(s):  
R. Weller ◽  
A. Minikin ◽  
D. Wagenbach ◽  
V. Dreiling
Keyword(s):  
Ultrafine Particles ◽  
Particle Diameter ◽  
Austral Summer ◽  
Southern Annular Mode ◽  
Contamination Control ◽  
Atmospheric Circulation Indices ◽  
Seasonal And Diurnal Variations ◽  
Time Series Analyses ◽  
June July ◽  
The Impact

Abstract. Continuous condensation particle (CP) observations were conducted from 1984 through 2009 at Neumayer Station under stringent contamination control. During this period, the CP concentration (median 258 cm−3) showed no significant long term trend but exhibited a pronounced seasonality characterized by a stepwise increase starting in September and reaching its annual maximum of around 103 cm−3 in March. Minimum values below 102 cm–3 were observed during June/July. Dedicated time series analyses in the time and frequency domain revealed no significant correlations between inter-annual CP concentration variations and atmospheric circulation indices like Southern Annular Mode (SAM) or Southern Ocean Index (SOI). The impact of the Pinatubo volcanic eruption and strong El Niño events did not affect CP concentrations. From thermodenuder experiments we deduced that the portion of volatile (at 125 °C) and semi-volatile (at 250 °C) particles which could be both associated with biogenic sulfur aerosol, was maximum during austral summer, while during winter non-volatile sea salt particles dominated. During September through April we could frequently observe enhanced concentrations of ultrafine particles within the nucleation mode (between 3 nm and 7 nm particle diameter), preferentially in the afternoon.

Short-term effects of carbon source on the competition of polyphosphate accumulating organisms and glycogen accumulating organisms

2004 ◽  
Vol 50 (10) ◽  
pp. 139-144 ◽  
Author(s):  
A. Oehmen ◽  
Z. Yuan ◽  
L.L. Blackall ◽  
J. Keller
Keyword(s):  
Carbon Source ◽  
In Situ Hybridisation ◽  
Operating Conditions ◽  
Fluorescence In Situ Hybridisation ◽  
Biological Phosphorus Removal ◽  
Short Term ◽  
Uptake Rates ◽  
Polyphosphate Accumulating Organisms ◽  
The Impact ◽  
Short Term Effects

The effectiveness of enhanced biological phosphorus removal (EBPR) systems is directly affected by the competition of polyphosphate accumulating organisms (PAOs) and glycogen accumulating organisms (GAOs). This study investigated the short-term effects of carbon source on PAO and GAO performance. The tests were designed to clearly determine the impact of volatile fatty acid (VFA) composition on the performance of two types of biomass, one enriched for PAOs and the other for GAOs. The two populations were enriched in separate reactors using identical operating conditions and very similar influent compositions with acetate as the sole carbon source. The only difference was that a very low level of phosphorus was present in the influent to the GAO reactor. The abundance of PAOs and GAOs was quantified using fluorescence in-situ hybridisation. The results clearly show that there are some very distinctive differences between PAOs and GAOs in their ability to utilise different carbon substrates. While both are able to take up acetate rapidly and completely, the GAOs are far slower at consuming propionate than the PAOs during short-term substrate changes. This provides a potentially highly valuable avenue to influence the competition between PAOs and GAOs. Other VFAs studied seem to be less usable in the short term by both PAOs and GAOs, as indicated by their much lower uptake rates.

scholarly journals On the relationship between low cloud variability and lower tropospheric stability in the Southeast Pacific

2011 ◽  
Vol 11 (2) ◽  
pp. 3777-3811
Author(s):  
F. Sun ◽  
A. Hall ◽  
X. Qu
Keyword(s):  
Climate Change ◽  
Seasonal Cycle ◽  
Austral Summer ◽  
Cloud Amount ◽  
Anthropogenic Climate Change ◽  
Cloud Feedbacks ◽  
Southeast Pacific ◽  
Low Cloud ◽  
Lower Tropospheric Stability ◽  
The Relationship

Abstract. In this study, we examine observed marine low cloud variability in the southeast Pacific and its association with lower-tropospheric stability (LTS) across a spectrum of timescales. On both daily and interannual timescales, LTS and low cloud amount are very well correlated in austral summer (DJF). Meanwhile in winter (JJA), when ambient LTS increases, the LTS-low cloud relationship disintegrates. The DJF LTS-low cloud relationship also weakens in years with unusually large ambient LTS values. These are generally strong El Niño years, in which DJF LTS values are comparable to those typically found in JJA. Thus the LTS-low cloud relationship is strongly modulated by the seasonal cycle and the ENSO phenomenon. We also investigate the origin of LTS anomalies closely associated with low cloud variability during austral summer. We find that the ocean and atmosphere are independently involved in generating anomalies in LTS and hence variability in the southeast Pacific low cloud deck. This highlights the coupled nature of the climate system in this region, and raises the possibility of cloud feedbacks related to LTS. We conclude by addressing the implications of the observed LTS-low cloud relationship in the southeast Pacific for low cloud feedbacks in anthropogenic climate change.

scholarly journals Effect of incubation time and substrate concentration on N-uptake rates by phytoplankton in the Bay of Bengal

2005 ◽  
Vol 2 (5) ◽  
pp. 1331-1352
Author(s):  
S. Kumar ◽  
R. Ramesh ◽  
S. Sardesai ◽  
M. S. Sheshshayee
Keyword(s):  
Incubation Time ◽  
Uptake Rate ◽  
Nitrate Uptake ◽  
N Uptake ◽  
Marine Phytoplankton ◽  
Total Production ◽  
New Production ◽  
Urea Uptake ◽  
Uptake Rates

Abstract. We report here the results of three experiments, which are slight variations of the 15N method (JGOFS protocol) for determination of new production. The first two test the effect of (i) duration of incubation time and (ii) concentration of tracer added on the uptake rates of various N-species (nitrate, ammonium and urea) by marine phytoplankton; while the third compares in situ and deck incubations from dawn to dusk. Results indicate that nitrate uptake can be underestimated by experiments where incubation times shorter than 4h or when more than 10% of the ambient concentration of nitrate is added prior to incubation. The f-ratio increases from 0.28 to 0.42 when the incubation time increases from two to four hours. This may be due to the observed increase in the uptake rate of nitrate and decrease in the urea uptake rate. Unlike ammonium [y{=}2.07x{-}0.002\\, (r2=0.55)] and urea uptakes [y{=}1.88x{+}0.004 (r2=0.88)], the nitrate uptake decreases as the concentration of the substrate (x) increases, showing a negative correlation [y{=}-0.76x+0.05 (r2=0.86)], possibly due to production of glutamine, which might suppress nitrate uptake. This leads to decline in the f-ratio from 0.47 to 0.10, when concentration of tracer varies from 0.01 to 0.04μ M. The column integrated total productions are 519 mg C m-2 d-1 and 251 mg C m-2 d-1 for in situ and deck incubations, respectively. The 14C based production at the same location is ~200 mg C m-2 d-1, which is in closer agreement to the 15N based total production measured by deck incubation.

scholarly journals Effect of deep convection on the tropical tropopause layer composition over the southwest Indian Ocean during austral summer

2020 ◽  
Vol 20 (17) ◽  
pp. 10565-10586
Author(s):  
Stephanie Evan ◽  
Jerome Brioude ◽  
Karen Rosenlof ◽  
Sean M. Davis ◽  
Holger Vömel ◽  
...  
Keyword(s):  
Water Vapor ◽  
Indian Ocean ◽  
Tropical Cyclones ◽  
Austral Summer ◽  
Lagrangian Model ◽  
Southwest Indian Ocean ◽  
Tropical Tropopause Layer ◽  
Tropical Tropopause ◽  
Tropopause Region ◽  
The Impact

Abstract. Balloon-borne measurements of cryogenic frost-point hygrometer (CFH) water vapor, ozone and temperature and water vapor lidar measurements from the Maïdo Observatory on Réunion Island in the southwest Indian Ocean (SWIO) were used to study tropical cyclones' influence on tropical tropopause layer (TTL) composition. The balloon launches were specifically planned using a Lagrangian model and Meteosat-7 infrared images to sample the convective outflow from tropical storm (TS) Corentin on 25 January 2016 and tropical cyclone (TC) Enawo on 3 March 2017. Comparing the CFH profile to Aura's Microwave Limb Sounder's (MLS) monthly climatologies, water vapor anomalies were identified. Positive anomalies of water vapor and temperature, and negative anomalies of ozone between 12 and 15 km in altitude (247 to 121 hPa), originated from convectively active regions of TS Corentin and TC Enawo 1 d before the planned balloon launches according to the Lagrangian trajectories. Near the tropopause region, air masses on 25 January 2016 were anomalously dry around 100 hPa and were traced back to TS Corentin's active convective region where cirrus clouds and deep convective clouds may have dried the layer. An anomalously wet layer around 68 hPa was traced back to the southeast Indian Ocean where a monthly water vapor anomaly of 0.5 ppmv was observed. In contrast, no water vapor anomaly was found near or above the tropopause region on 3 March 2017 over Maïdo as the tropopause region was not downwind of TC Enawo. This study compares and contrasts the impact of two tropical cyclones on the humidification of the TTL over the SWIO. It also demonstrates the need for accurate balloon-borne measurements of water vapor, ozone and aerosols in regions where TTL in situ observations are sparse.

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