scholarly journals Oxygen and Nutrient Trapping in the Southern Benguela Upwelling System

2021 ◽  
Vol 8 ◽  
Author(s):  
Tim Rixen ◽  
Niko Lahajnar ◽  
Tarron Lamont ◽  
Rolf Koppelmann ◽  
Bettina Martin ◽  
...  
Keyword(s):  
Global Warming ◽  
Global Change ◽  
Trapping Efficiency ◽  
Nutrient Concentrations ◽  
Ecosystem Structure ◽  
Austral Spring ◽  
Critical Feature ◽  
Upwelling System ◽  
Benguela Upwelling ◽  
The Impact

The Benguela Upwelling System in the southeast Atlantic Ocean is of crucial socio-economic importance due to its high productivity. However, predicting its response to global change and understanding past changes are still great challenges. Here, we compile data obtained from a research cruise and an oceanographic mooring to demonstrate that a topographically steered nutrient trapping zone develops in a narrow belt along the coast during the main upwelling season in austral spring and summer in the southern Benguela Upwelling System. High nutrient concentrations within this zone increase the impact of upwelling on the productivity of the southern Benguela Upwelling System, but the efficient nutrient trapping operates at the expense of decreasing oxygen concentrations. This enhances the probability of anoxic events emerging toward the end of the upwelling season. However, at the end of the upwelling season, the front that separates the coastally trapped waters from open shelf waters weakens or even collapses due to upwelling cessation and the reversing current regime. This, in addition to a stronger vertical mixing caused by winter cooling, fosters the ventilation of the nutrient trapping zone, which reestablishes during the following upwelling season. The postulated intensification of upwelling and changes in the ecosystem structure in response to global warming seem to reduce the nutrient trapping efficiency by increasing offshore advection of surface waters and plankton blooms. The intensified upwelling and resulting lower biological oxygen consumption appears to mask the expected impacts of global warming on the oxygen minimum zone (OMZ) in the southern Benguela Upwelling System. In contrast to other OMZs, including those in northern Benguela Upwelling Systems, the OMZ in the southern Benguela Upwelling System reveals so far no detectable long-term decrease in oxygen. Thus, the nutrient trapping efficiency seems to be a critical feature mitigating global change impacts on the southern Benguela Upwelling System. Since it is topographically steered, regional impacts on the nutrient trapping efficiency appear also to explain varying responses of upwelling systems to global change as the comparison between southern and northern Benguela Upwelling System shows. This emphasizes the need for further and more comparable studies in order to better understand the response of Eastern Boundary Upwelling Systems and their ecosystem services to global change.

scholarly journals Spatio-temporal patterns of C : N : P ratios in the northern Benguela upwelling system

2014 ◽  
Vol 11 (3) ◽  
pp. 885-897 ◽  
Author(s):  
A. Flohr ◽  
A. K. van der Plas ◽  
K.-C. Emeis ◽  
V. Mohrholz ◽  
T. Rixen
Keyword(s):  
N2 Fixation ◽  
South Atlantic ◽  
Subtropical Gyre ◽  
Total Alkalinity ◽  
Nutrient Concentrations ◽  
The South ◽  
Upwelling System ◽  
Benguela Upwelling ◽  
Bottom Waters ◽  
The Impact

Abstract. On a global scale the ratio of fixed nitrogen (N) and phosphate (P) is characterized by a deficit of N with regard to the classical Redfield ratio of N : P = 16 : 1 reflecting the impact of N loss occurring in the oceanic oxygen minimum zones. The northern Benguela upwelling system (NBUS) is known for losses of N and the accumulation of P in sub- and anoxic bottom waters and sediments of the Namibian shelf resulting in low N : P ratios in the water column. To study the impact of the N : P anomalies on the regional carbon cycle and their consequences for the export of nutrients from the NBUS into the oligotrophic subtropical gyre of the South Atlantic, we measured dissolved inorganic carbon (CT), total alkalinity (AT), oxygen (O2) and nutrient concentrations in February 2011. The results indicate increased P concentrations over the Namibian shelf due to P efflux from sediments resulting in a C : N : P : -O2 ratio of 106 : 16 : 1.6 : 138. N reduction further increase C : N and reduce N : P ratios in those regions where O2 concentrations in bottom waters are < 20 μmol kg−1. However, off the shelf along the continental margin, the mean C : N : P : -O2 ratio is again close to the Redfield stoichiometry. Additional nutrient data measured during two cruises in 2008 and 2009 imply that the amount of excess P, which is created in the bottom waters on the shelf, and its export into the subtropical gyre after upwelling varies through time. The results further reveal an inter-annual variability of excess N within the South Atlantic Central Water (SACW) that flows from the north into the NBUS, with highest N values observed in 2008. It is postulated that the N excess in SACW occurred due to the impact of remineralized organic matter produced by N2 fixation and that the magnitude of excess P formation and its export is governed by inputs of excess N along with SACW flowing into the NBUS. Factors controlling N2 fixation north of the BUS need to be addressed in future studies to better understand the role of the NBUS as a P source and N sink in the coupled C : N : P cycles.

scholarly journals The Impact of Agulhas Leakage on the Central Water Masses in the Benguela Upwelling System From A High‐Resolution Ocean Simulation

2018 ◽  
Vol 123 (12) ◽  
pp. 9416-9428 ◽  
Author(s):  
Nele Tim ◽  
Eduardo Zorita ◽  
Franziska U. Schwarzkopf ◽  
Siren Rühs ◽  
Kay‐Christian Emeis ◽  
...  
Keyword(s):  
High Resolution ◽  
Water Masses ◽  
Upwelling System ◽  
Benguela Upwelling ◽  
The Impact ◽  
Ocean Simulation

An Appraisal of the Stoichiometry of Dissolved Oxygen/Nutrient Inter-Relationships in the Upwelling System Off Northern Chile

1998 ◽  
Vol 78 (3) ◽  
pp. 697-706 ◽  
Author(s):  
Anthony G. Davies ◽  
Carmen E. Morales
Keyword(s):  
Carbon Dioxide ◽  
Dissolved Oxygen ◽  
Molar Ratio ◽  
Nutrient Concentrations ◽  
Northern Chile ◽  
Oxygen Production ◽  
Shore Zone ◽  
Austral Spring ◽  
Upwelling System ◽  
Near Shore

Using vertical profile data from the upwelling system off northern Chile, the slopes of dissolved oxygen/nutrient concentration regressions have been analysed, in conjunction with a value of 1·4 for the molar ratio of net community oxygen production to nitrate-driven carbon dioxide assimilation, to investigate the stoichiometric inter-relationships between photosynthetic oxygen production and carbon dioxide and nutrient consumption. There was little interseasonal variation in ΔCO2/ΔDIN (nitrate+nitrite) molar ratios, ranging from 10·3 to 11·6 in the near-shore zone of active upwelling and 6·7 to 9·0 in mid-water, between 25 and 50 m depth offshore. Although the former range exceeded the value expected from Redfield-Richards stoichiometry (6·6) by more than 50%, it was in line with published ratios for phytoplankton blooms in coastal and oceanic waters. Mean ΔDIN/ΔPO4 ratios were similar for the near-shore stations and the mid-water, ranging respectively from 7·0 to 10·7 and 8·4 to 11·5, these subRedfield-Richards values mirroring the ratios of the nutrient concentrations in the water and probably implying ‘luxury’ consumption of phosphate. Seasonal variations in the ΔO2/ΔPO4 ratios for the near-shore zone are shown to be consistent with the view that, in the austral spring and summer when upwelling is strongest in the area, the main source of the water coming to the surface is the Peru-Chile Undercurrent, whereas in the autumn, it could be of subantarctic origin.

Coupled benthic cycling of iron, phosphorus and sulfur in the Benguela upwelling system

2020 ◽  
Author(s):  
Kristin Anna Ungerhofer ◽  
Gert-Jan Reichart ◽  
Peter Kraal
Keyword(s):  
Water Column ◽  
Bottom Water ◽  
Solid Phase ◽  
Oxygen Depletion ◽  
Biogeochemical Cycles ◽  
Sediment Surface ◽  
Upwelling System ◽  
Benguela Upwelling ◽  
Bottom Waters ◽  
The Impact

&lt;p&gt;The Benguela upwelling system (BUS) offshore Namibia is among the most productive ocean regions worldwide and is a globally important reservoir of biodiversity and biomass. The forcing of cold, nutrient-rich deep waters up the coastal shelf leads to high rates of primary productivity in surface waters, intense carbon remineralization and consequently to (bottom water) oxygen depletion on the shelf that varies temporally and spatially with the intensity of the upwelling.&lt;br&gt;Recurring events of deoxygenation have a severe impact on marine ecosystems, for instance increased mortality and altered biogeochemical cycles of key elements such as carbon (C), iron (Fe), phosphorus (P) and sulfur (S). Therefore, it is crucial that we establish a clear mechanistic framework of the impact of oxygen depletion on (global) biogeochemical cycles, not only to allow for the reconstruction of climate-ocean feedbacks in upwelling regions in the past, but to enable predictions of future behavior.&lt;br&gt;During an expedition with &lt;em&gt;RV Pelagia&lt;/em&gt; in February of 2019, we collected water column and sediment samples from the shelf and slope off Namibia (100 to 1517 m water depth, bottom water O&lt;sub&gt;2&lt;/sub&gt; between 0.5 and 175 &amp;#181;mol L&lt;sup&gt;-1&lt;/sup&gt;) and measured nutrient fluxes in on-board sediment incubations to understand the early diagenetic behavior of those key elements and trace metals underlying the (periodically) oxygen-depleted waters of the BUS.&lt;br&gt;We analyzed dissolved concentrations as well as solid-phase speciation of key elements such as iron (Fe), manganese (Mn), phosphorus (P) and sulfur (S) to understand the chemical and physical processes controlling their distribution along the depth/redox-transect.&lt;br&gt;Our results show intense P cycling on the shelf, as evidenced by very high pore-water P concentrations, an enhanced efflux of PO&lt;sub&gt;4&lt;/sub&gt; to suboxic bottom waters and indications of phosphorite formation at depth in the sediment. N/P ratios well below Redfield indicate N depletion and (relative) P accumulation in the water column, a shift in nutrient stoichiometry that can impact the composition of microbial communities in such waters. Meanwhile, the slope sediments are overlain by oxic bottom waters, retain P more efficiently and exhibit N/P ratios close to Redfield stoichiometry.&lt;br&gt;The capacity of the sediment to buffer toxic sulfide and prevent its release to the water column was dependent on the abundance of sulfide oxidizers at the sediment surface. Furthermore, the variable accumulation of sulfide affected Fe speciation and sedimentary P retention.&lt;br&gt;Overall, we show an intimate coupling between sedimentary cycles of essential elements in the Benguela upwelling system, a stark contrast between shelf and slope environments that is further enhanced by local variation of oxygen depletion and a very strong role of microbes in driving the cycles.&lt;/p&gt;

scholarly journals Relation between Upwelling Intensity and the Variability of Physical and Chemical Parameters in the Southern Benguela Upwelling System

2015 ◽  
Vol 2015 ◽  
pp. 1-8 ◽  
Author(s):  
Hassan Ebrahiem Ismail ◽  
Johannes Jacobus Agenbag ◽  
Stephanie de Villiers ◽  
Bhekumusa Jabulani Ximba
Keyword(s):  
Temperature Gradient ◽  
Vertical Mixing ◽  
Surface Heating ◽  
Nutrient Concentrations ◽  
Upper Ocean ◽  
Ocean Temperature ◽  
Upwelling System ◽  
Benguela Upwelling ◽  
Upwelling Intensity ◽  
Upwelling Index

The extent to which wind-driven seasonal upwelling cycles manifest in surface ocean temperature and nutrient variability along a monitoring line in the Southern Benguela upwelling system was investigated. Monitoring conducted monthly over a six-year period shows that surface temperature and nutrient concentrations exhibit very poor seasonality and weak correlation with the upwelling index. This is, despite clear evidence for spatial inshore-offshore gradients in temperature, nutrients, and chlorophyll, consistent with an upwelling regime. The upper ocean temperature gradient shows a much better correspondence to the upwelling index but at the same time demonstrates that surface heating, and not vertical mixing related to upwelling, controls the upper ocean temperature gradient. The results suggest that remote sensing techniques would be inadequate tools to monitor upwelling events in the Southern Benguela. Also, the incidence of phytoplankton blooms is more likely triggered by stratified conditions associated with surface heating than relaxation of upwelling winds.

IMPACT ASSESSMENT ON STORM SURGE RISKS TO CONTAINERS CONSIDERING GLOBAL WARMING

2017 ◽  
Author(s):  
Rikito Hisamatsu ◽  
Rikito Hisamatsu ◽  
Kei Horie ◽  
Kei Horie
Keyword(s):  
Risk Assessment ◽  
Global Warming ◽  
Storm Surge ◽  
Storm Surges ◽  
Assessment Tools ◽  
Inundation Depth ◽  
Risk Assessment Tools ◽  
Risk Maps ◽  
The Impact ◽  
Vulnerability Functions

Container yards tend to be located along waterfronts that are exposed to high risk of storm surges. However, risk assessment tools such as vulnerability functions and risk maps for containers have not been sufficiently developed. In addition, damage due to storm surges is expected to increase owing to global warming. This paper aims to assess storm surge impact due to global warming for containers located at three major bays in Japan. First, we developed vulnerability functions for containers against storm surges using an engineering approach. Second, we simulated storm surges at three major bays using the SuWAT model and taking global warming into account. Finally, we developed storm surge risk maps for containers based on current and future situations using the vulnerability function and simulated inundation depth. As a result, we revealed the impact of global warming on storm surge risks for containers quantitatively.

Development of a water temperature-ecological model to stimulate global warming effects on lake ecosystem

1996 ◽  
Vol 34 (7-8) ◽  
pp. 237-244 ◽  
Author(s):  
Masaaki Hosomi ◽  
Tetsu Saigusa ◽  
Kenichi Yabunaka ◽  
Takuya Okubo ◽  
Akihiko Murakami
Keyword(s):  
Global Warming ◽  
Water Temperature ◽  
Thermal Stratification ◽  
Ecological Model ◽  
Nutrient Release ◽  
Eddy Diffusion ◽  
Nutrient Concentrations ◽  
Lake Ecosystem ◽  
Phytoplankton Species ◽  
Freezing And Thawing

This paper describes a newly developed combined water temperature-ecological (WT-ECO) model which is employed to simulate the effects of global warming on lake and reservoir ecosystems. The WT model includes (i) variations in the eddy diffusion coefficient based on the degree of thermal stratification and the velocity of wind, and (ii) a sub-model for simulating the freezing and thawing processes of surface water, water temperatures, and the mixing rates between two adjacent layers of water. The ECO model then uses these results to calculate the resultant effect on a lake's ecological dynamics, e.g., composition of phytoplankton species, their respective concentrations, and nutrient concentrations. When the model was benchmarked against Lake Yunoko, a dimictic lake, fairly good agreement was obtained over a 4-yr period; thereby indicating it is suitably calibrated. In addition, to assess the effects of global warming on a lake ecosystem, changes in Lake Yunoko's water temperature/quality were simulated in response to an increase in air temperature of 2 - 4°C. Results indicate that such an increase will (i) increase thermal stratification in summer, which increases the nutrient concentrations in bottom water due to nutrient release from bottom sediment, (ii) increase the concentration of phytoplankton at the beginning of the autumn circulation period, and (iii) change the composition of phytoplankton species.

scholarly journals Case study of a water bioengineering construction site in Austria. Ecological aspects and application of an environmental life cycle assessment model

2021 ◽  
Author(s):  
M. von der Thannen ◽  
S. Hoerbinger ◽  
C. Muellebner ◽  
H. Biber ◽  
H. P. Rauch
Keyword(s):  
Global Warming ◽  
Life Cycle Assessment ◽  
Life Cycle ◽  
Energy Demand ◽  
Assessment Model ◽  
Construction Site ◽  
Negative Effects ◽  
Environmental Life Cycle Assessment ◽  
The Impact ◽  
Soil And Water

AbstractRecently, applications of soil and water bioengineering constructions using living plants and supplementary materials have become increasingly popular. Besides technical effects, soil and water bioengineering has the advantage of additionally taking into consideration ecological values and the values of landscape aesthetics. When implementing soil and water bioengineering structures, suitable plants must be selected, and the structures must be given a dimension taking into account potential impact loads. A consideration of energy flows and the potential negative impact of construction in terms of energy and greenhouse gas balance has been neglected until now. The current study closes this gap of knowledge by introducing a method for detecting the possible negative effects of installing soil and water bioengineering measures. For this purpose, an environmental life cycle assessment model has been applied. The impact categories global warming potential and cumulative energy demand are used in this paper to describe the type of impacts which a bioengineering construction site causes. Additionally, the water bioengineering measure is contrasted with a conventional civil engineering structure. The results determine that the bioengineering alternative performs slightly better, in terms of energy demand and global warming potential, than the conventional measure. The most relevant factor is shown to be the impact of the running machines at the water bioengineering construction site. Finally, an integral ecological assessment model for applications of soil and water bioengineering structures should point out the potential negative effects caused during installation and, furthermore, integrate the assessment of potential positive effects due to the development of living plants in the use stage of the structures.

scholarly journals Life Cycle Assessment of Households in Santiago, Chile: Environmental Hotspots and Policy Analysis

2021 ◽  
Vol 13 (5) ◽  
pp. 2525
Author(s):  
Camila López-Eccher ◽  
Elizabeth Garrido-Ramírez ◽  
Iván Franchi-Arzola ◽  
Edmundo Muñoz
Keyword(s):  
Global Warming ◽  
Life Cycle Assessment ◽  
Life Cycle ◽  
Environmental Impacts ◽  
Food Consumption ◽  
Household Income ◽  
Resource Scarcity ◽  
Life Cycles ◽  
The Impact ◽  
Freshwater Eutrophication

The aim of this study is to assess the environmental impacts of household life cycles in Santiago, Chile, by household income level. The assessment considered scenarios associated with environmental policies. The life cycle assessment was cradle-to-grave, and the functional unit considered all the materials and energy required to meet an inhabitant’s needs for one year (1 inh/year). Using SimaPro 9.1 software, the Recipe Midpoint (H) methodology was used. The impact categories selected were global warming, fine particulate matter formation, terrestrial acidification, freshwater eutrophication, freshwater ecotoxicity, mineral resource scarcity, and fossil resource scarcity. The inventory was carried out through the application of 300 household surveys and secondary information. The main environmental sources of households were determined to be food consumption, transport, and electricity. Food consumption is the main source, responsible for 33% of the environmental impacts on global warming, 69% on terrestrial acidification, and 29% on freshwater eutrophication. The second most crucial environmental hotspot is private transport, whose contribution to environmental impact increases as household income rises, while public transport impact increases in the opposite direction. In this sense, both positive and negative environmental effects can be generated by policies. Therefore, life-cycle environmental impacts, the synergy between policies, and households’ socio-economic characteristics must be considered in public policy planning and consumer decisions.

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