scholarly journals Dynamics and distribution of natural and human-caused hypoxia

2010 ◽  
Vol 7 (2) ◽  
pp. 585-619 ◽  
Author(s):  
N. N. Rabalais ◽  
R. J. Díaz ◽  
L. A. Levin ◽  
R. E. Turner ◽  
D. Gilbert ◽  
...  
Keyword(s):  
Climate Change ◽  
Organic Carbon ◽  
Nutrient Loading ◽  
Global Climate ◽  
The Other ◽  
Nutrient Loads ◽  
Oxygen Minimum Zones ◽  
Natural Processes ◽  
Carbon Production ◽  
Oxygen Minimum

Abstract. Water masses can become undersaturated with oxygen when natural processes alone or in combination with anthropogenic processes produce enough organic carbon that is aerobically decomposed faster than the rate of oxygen re-aeration. The dominant natural processes usually involved are photosynthetic carbon production and microbial respiration. The re-supply rate is indirectly related to its isolation from the surface layer. Hypoxic water masses (<2 mg L−1, or approximately 30% saturation) can form, therefore, under "natural" conditions, and are more likely to occur in marine systems when the water residence time is extended, water exchange and ventilation are minimal, stratification occurs, and where carbon production and export to the bottom layer are relatively high. Hypoxia has occurred through geological time and naturally occurs in oxygen minimum zones, deep basins, eastern boundary upwelling systems, and fjords. Hypoxia development and continuation in many areas of the world's coastal ocean is accelerated by human activities, especially where nutrient loading increased in the Anthropocene. This higher loading set in motion a cascading set of events related to eutrophication. The formation of hypoxic areas has been exacerbated by any combination of interactions that increase primary production and accumulation of organic carbon leading to increased respiratory demand for oxygen below a seasonal or permanent pycnocline. Nutrient loading is likely to increase further as population growth and resource intensification rises, especially with increased dependency on crops using fertilizers, burning of fossil fuels, urbanization, and waste water generation. It is likely that the occurrence and persistence of hypoxia will be even more widespread and have more impacts than presently observed. Global climate change will further complicate the causative factors in both natural and human-caused hypoxia. The likelihood of strengthened stratification alone, from increased surface water temperature as the global climate warms, is sufficient to worsen hypoxia where it currently exists and facilitate its formation in additional waters. Increased precipitation that increases freshwater discharge and flux of nutrients will result in increased primary production in the receiving waters up to a point. The interplay of increased nutrients and stratification where they occur will aggravate and accelerate hypoxia. Changes in wind fields may expand oxygen minimum zones onto more continental shelf areas. On the other hand, not all regions will experience increased precipitation, some oceanic water temperatures may decrease as currents shift, and frequency and severity of tropical storms may increase and temporarily disrupt hypoxia more often. The consequences of global warming and climate change are effectively uncontrollable at least in the near term. On the other hand, the consequences of eutrophication-induced hypoxia can be reversed if long-term, broad-scale, and persistent efforts to reduce substantial nutrient loads are developed and implemented. In the face of globally expanding hypoxia, there is a need for water and resource managers to act now to reduce nutrient loads to maintain, at least, the current status.

scholarly journals Dynamics and distribution of natural and human-caused coastal hypoxia

2009 ◽  
Vol 6 (5) ◽  
pp. 9359-9453 ◽  
Author(s):  
N. N. Rabalais ◽  
R. J. Díaz ◽  
L. A. Levin ◽  
R. E. Turner ◽  
D. Gilbert ◽  
...  
Keyword(s):  
Nutrient Loading ◽  
Bottom Layer ◽  
Aeration Rate ◽  
Water Masses ◽  
Geological Time ◽  
Oxygen Minimum Zones ◽  
Natural Processes ◽  
Carbon Production ◽  
Causative Factors ◽  
Hypoxic Water

Abstract. Water masses can become undersaturated with oxygen when natural processes alone or in combination with anthropogenic processes create enough carbon that is aerobically decomposed faster than the rate of oxygen re-aeration. The dominant natural processes usually involved are photosynthetic carbon production and microbial respiration. The re-aeration rate is indirectly related to its isolation from the surface layer. Hypoxic water masses (<2 mg L−1, or approximately 30% saturation) can form, therefore, under "natural" conditions, and is more likely to occur in marine systems when the water residence time is extended, water exchange and ventilation is minimal, stratification occurs, and where carbon production and export to the bottom layer are relatively high. Hypoxia has occurred throughout geological time and naturally occurs in oxygen minimum zones, deep basins, eastern boundary upwelling systems and fjords. Hypoxia development and continuation in many areas of the world's coastal ocean is accelerated by human activities, especially where nutrient loading increased in the Anthropocene. This higher loading set in motion a cascading set of events related to eutrophication. Nutrient loading is likely to increase further as population growth and resource intensification rises, especially in developing countries dependent on crops using fertilizers, and it is likely that the occurrence and persistence of hypoxia will be even more widespread and have more impacts than presently observed. Climate change will further complicate the causative factors.

scholarly journals Toward a global calibration for quantifying past oxygenation in oxygen minimum zones using benthic Foraminifera

2021 ◽  
Author(s):  
Martin Tetard ◽  
Laetitia Licari ◽  
Kazuyo Tachikawa ◽  
Ekaterina Ovsepyan ◽  
Luc Beaufort
Keyword(s):  
North Pacific ◽  
Transfer Functions ◽  
Late Quaternary ◽  
Global Climate ◽  
Single Species ◽  
Pore Waters ◽  
Oxygen Minimum Zones ◽  
Global Calibration ◽  
Circularity Index ◽  
Oxygen Minimum

Abstract. Oxygen Minimum Zones (OMZs) are oceanic areas largely depleted in dissolved oxygen, nowadays considered in expansion in the face of global warming. Their ecological and economic consequences are being debated. The investigation of past OMZ conditions allows us to better understand biological and physical mechanisms responsible for their variability with regards to climate change, carbon pump and carbonate system. To investigate the relationship between OMZ expansion and global climate changes during the late Quaternary, quantitative oxygen reconstructions are needed, but are still in their early development. Here, past bottom water oxygenation (BWO) was quantitatively assessed through a new, fast, semi-automated, and taxonfree morphometric analysis of benthic foraminiferal tests, developed and calibrated using Eastern North Pacific (ENP) and the Eastern South Pacific (ESP) OMZs samples. This new approach is based on an average size and circularity index for each sample. This method, as well as two already published micropalaeontological approaches based on benthic foraminiferal assemblages variability and porosity investigation of a single species, were here calibrated based on availability of new data from 23 core tops recovered along an oxygen gradient (from 0.03 to 1.79 mL.L−1) from the ENP, ESP, AS (Arabian Sea) and WNP (Western North Pacific, including its marginal seas) OMZs. Global calibrated transfer functions are thus herein proposed for each of these methods. These micropalaeontological reconstruction approaches were then applied on a paleorecord from the ENP OMZ to examine the consistency and limits of these methods, as well as the relative influence of bottom and pore waters on these micropalaeontological tools. Both the assemblages and morphometric approaches (that is also ultimately based on the ecological response of the complete assemblage and faunal succession according to BWO) gave similar and consistent past BWO reconstructions, while the porosity approach (based on a single species and its unique response to a mixed signal of bottom and pore waters) shown ambiguous estimations.

Understanding Harmful Algal Bloom Dynamics in a Mediterranean Hypereutrophic Reservoir insights from a Bayesian Network and a Structural Equation Model

2020 ◽  
Author(s):  
Ibrahim Alameddine ◽  
Eliza Deutsch
Keyword(s):  
Bayesian Network ◽  
Structural Equation Model ◽  
Temperature Effects ◽  
Structural Equation ◽  
Nutrient Loading ◽  
Harmful Algal Bloom ◽  
Equation Model ◽  
The Other ◽  
Nutrient Loads ◽  
Bloom Formation

&lt;p&gt;Cyanobacteria blooms, especially those involving Microcystis, are an increasing problem facing many freshwater systems worldwide. In this study, a Bayesian Network (BN) along with a Structural Equation Model (SEM) were concurrently developed through data-driven learning and expert elicitation in order to better delineate the main pathways responsible for the Microcystis dominance in a Mediterranean semi-arid hypereutrophic reservoir. The resulting two model structures were then compared with regards to the pathways they identified between the physical lake conditions and the nutrient loads on one hand and Microcystis dominance on the other. The two models were also used to predict the probability of bloom formation under different scenarios of climate change and nutrient loading. Both models showed that, given the eutrophic status of the study reservoir, direct temperature effects appear to be the primary driving force behind the Microcystis growth and dominance. Indirect temperature effects, which modulated water column stratification and internal nutrient release, were also found to play an important role in bloom formation. On the other hand, both models revealed that the direct nutrient pathways were less important as compared to the temperature effects, with internal nutrient loads dominating over external loads due to the seasonal variability in river flows, typical of Mediterranean rivers. Nevertheless, the BN model was unable to capture the recursive relationships between Microcystis and its forcings.&lt;/p&gt;

scholarly journals Organic carbon, and not copper, controls denitrification in oxygen minimum zones of the ocean

2008 ◽  
Vol 55 (12) ◽  
pp. 1672-1683 ◽  
Author(s):  
Bess B. Ward ◽  
Caroline B. Tuit ◽  
Amal Jayakumar ◽  
Jeremy J. Rich ◽  
James Moffett ◽  
...  
Keyword(s):  
Organic Carbon ◽  
Oxygen Minimum Zones ◽  
Oxygen Minimum

scholarly journals Whole-soil warming alters microbial community, but not concentrations of plant-derived soil organic carbon in subsoil

2021 ◽  
Author(s):  
Cyrill Zosso ◽  
Nicholas O.E. Ofiti ◽  
Jennifer L. Soong ◽  
Emily F. Solly ◽  
Margaret S. Torn ◽  
...  
Keyword(s):  
Climate Change ◽  
Microbial Community ◽  
Organic Carbon ◽  
Soil Organic Carbon ◽  
Soil Depth ◽  
Global Climate ◽  
Plant Litter ◽  
Soil Warming ◽  
Four Seasons ◽  
Set Up

&lt;p&gt;Soils will warm in near synchrony with the air over the whole profiles following global climate change. It is largely unknown how subsoil (below 30 cm) microbial communities will respond to this warming and how plant-derived soil organic carbon (SOC) will be affected. Predictions how climate change will affect the large subsoil carbon pool (&gt;50 % of SOC is below 30 cm soil depth) remain uncertain.&lt;/p&gt;&lt;p&gt;At Blodgett forest (California, USA) a field warming experiment was set up in 2013 warming whole soil profiles to 100 cm soil depth by +4&amp;#176;C compared to control plots. We took samples in 2018, after 4.5 years of continuous warming and investigated how warming has affected the abundance and community structure of microoganisms (using phospholipid fatty acids, PLFAs), and plant litter (using cutin and suberin).&lt;/p&gt;&lt;p&gt;The warmed subsoil (below 30 cm) contained significantly less microbial biomass (28%) compared to control plots, whereas the topsoil remained unchanged. Additionally below 50 cm, the microbial community was different in warmed as compared to control plots. Actinobacteria were relatively more abundant and Gram+ bacteria adapted their cell-membrane structure to warming. The decrease in microbial abundance might be related to lower SOC concentrations in warmed compared to control subsoils. In contrast to smaller SOC concentrations and less fine root mass in the warmed plots, the concentrations of the plant polymers suberin and cutin did not change. Overall our results demonstrate that already four seasons of simulated whole-soil warming caused distinct depth-specific responses of soil biogeochemistry: warming altered the subsoil microbial community, but not concentrations of plant-derived soil organic carbon.&lt;/p&gt;

scholarly journals MÁS ALLÁ DEL CAMBIO CLIMÁTICO: IMPLICACIONES DE LA CONTAMINACIÓN MARINA POR AGROQUÍMICOS SOBRE LAS INTERACCIONES SIMBIÓTICAS Y EL ÉXITO ECOLÓGICO DE LOS CORALES

e-CUCBA ◽  
2021 ◽  
Vol 15 (8) ◽  
pp. 1-9
Author(s):  
HECTOR OCAMPO-ALVAREZ ◽  
FABIAN ALEJANDRO RODRÍGUEZ-ZARAGOZA
Keyword(s):  
Climate Change ◽  
Global Climate Change ◽  
Climate Changes ◽  
Marine Pollution ◽  
Global Climate ◽  
External Environment ◽  
The Other ◽  
Symbiotic Interactions ◽  
Coral Reef Ecosystems ◽  
The One

Coral reefs are highly productive marine ecosystems that harborahigh biodiversity. The forming organisms of these reefs are the scleractinian corals, which form symbiotic interactions with multiple microorganisms. One of the best known symbiotic interactions in these systems is the one established with the microalgae Symbiodinium. The microalgae produce through photosynthesis up to 90% of the energy required by the coral. On the other hand, Symbiodiniumreceives from the coral an appropriate niche, that protects Symbiodiniumfrom the external environment, from the competition with other organisms and predation; it also provides abundant nutrients produced by other coral symbiontshighlighting the bacteria. As well as this, multiple symbiotic interactions confer metabolic capabilities to corals, which have enabled their capacity to adapt to climate changes for millions of years. However, in recent decades coral reef ecosystems are being extensively decimated. Given the new characteristics of an environment with significant changes sometimes somewhat erratic, probably the interactions that initially provided ecological advantages to corals are no longer sufficient to overcome environmental adversities or that as a result of the changes generated in the environment. The diversity of microorganisms capable of interactions that can be formed with the few remaining microorganisms do not confer to the coral, sufficient adaptative advantages to face the challenge of climate change. In this essay, we argue about the possibility that a decrease in the stock of microorganisms capable of interacting with corals, as a result of marine pollution, is a cause of the loss of biological aptitude of corals to survive in the current global climate change.

scholarly journals Oxygen minimum zones in the tropical Pacific across CMIP5 models: mean state differences and climate change trends

2015 ◽  
Vol 12 (8) ◽  
pp. 6525-6587 ◽  
Author(s):  
A. Cabré ◽  
I. Marinov ◽  
R. Bernardello ◽  
D. Bianchi
Keyword(s):  
Climate Change ◽  
Tropical Pacific ◽  
Cmip5 Models ◽  
Upper Ocean ◽  
Intermediate Water ◽  
Climate Change Projections ◽  
Oxygen Minimum Zones ◽  
Mean State ◽  
Oxygen Minimum ◽  
The Tropical Pacific

Abstract. We analyze simulations of the Pacific Ocean oxygen minimum zones (OMZs) from 11 Earth System model contributions to the Coupled Model Intercomparison Project Phase 5, focusing on the mean state and climate change projections. The simulations tend to overestimate the volume of the OMZs, especially in the tropics and Southern Hemisphere. Compared to observations, five models introduce incorrect meridional asymmetries in the distribution of oxygen including larger southern OMZ and weaker northern OMZ, due to interhemispheric biases in intermediate water mass ventilation. Seven models show too deep an extent of the tropical hypoxia compared to observations, stemming from a deficient equatorial ventilation in the upper ocean combined with a too large biologically-driven downward flux of particulate organic carbon at depth, caused by too high particle export from the euphotic layer and too weak remineralization in the upper ocean. At interannual timescales, the dynamics of oxygen in the eastern tropical Pacific OMZ is dominated by biological consumption and linked to natural variability in the Walker circulation. However, under the climate change scenario RCP8.5, all simulations yield small and discrepant changes in oxygen concentration at mid depths in the tropical Pacific by the end of the 21st century due to an almost perfect compensation between warming-related decrease in oxygen saturation and decrease in biological oxygen utilization. Climate change projections are at odds with recent observations that show decreasing oxygen levels at mid depths in the tropical Pacific. Out of the OMZs, all the CMIP5 models predict a decrease of oxygen over most of the surface, deep and high latitudes ocean due to an overall slow-down of ventilation and increased temperature.

scholarly journals Only the Voice of the Other: Science, Power, and Diversity’s Revolt in the Museum—A Manifesto of Sorts

2014 ◽  
Vol 8 (1) ◽  
pp. 45-54
Author(s):  
W. Warner Wood
Keyword(s):  
Climate Change ◽  
Global Climate Change ◽  
Environmental Science ◽  
Global Climate ◽  
Environmental Issues ◽  
The Other ◽  
Natural History Museums ◽  
History Museums ◽  
Museum Professionals ◽  
The Voice

While the importance of including diverse perspectives in museum programming has received considerable attention in the cultural realm, the same cannot be said for environmental science topics. In science and natural history museums, exhibitions on issues such as global climate change and loss of biodiversity are frequently narrowly defined in relation to an equally narrow perception of what constitutes environmental science. Because the facts of science in museums are still largely told by science curators, the voices of non-scientists are largely absent on such issues. As museum professionals, we must work to ensure that a diversity of perspectives is represented on environmental issues in our museums and on the capacity of our publics to participate in the presentation of environmental topics. We must support the public’s collective “power-to” (as John Holloway has termed it) have a voice in environmental programming.

scholarly journals Records of past mid-depth ventilation: Cretaceous ocean anoxic event 2 vs. Recent oxygen minimum zones

2015 ◽  
Vol 12 (4) ◽  
pp. 1169-1189 ◽  
Author(s):  
J. Schönfeld ◽  
W. Kuhnt ◽  
Z. Erdem ◽  
S. Flögel ◽  
N. Glock ◽  
...  
Keyword(s):  
Organic Matter ◽  
Organic Carbon ◽  
Bottom Water ◽  
Carbon Accumulation ◽  
Marine Biota ◽  
Accumulation Rates ◽  
Oxygen Minimum Zones ◽  
Oxygen Levels ◽  
Water Oxygen ◽  
Oxygen Minimum

Abstract. Present day oceans are well ventilated, with the exception of mid-depth oxygen minimum zones (OMZs) under high surface water productivity, regions of sluggish circulation, and restricted marginal basins. In the Mesozoic, however, entire oceanic basins transiently became dysoxic or anoxic. The Cretaceous ocean anoxic events (OAEs) were characterised by laminated organic-carbon rich shales and low-oxygen indicating trace fossils preserved in the sedimentary record. Yet assessments of the intensity and extent of Cretaceous near-bottom water oxygenation have been hampered by deep or long-term diagenesis and the evolution of marine biota serving as oxygen indicators in today's ocean. Sedimentary features similar to those found in Cretaceous strata were observed in deposits underlying Recent OMZs, where bottom-water oxygen levels, the flux of organic matter, and benthic life have been studied thoroughly. Their implications for constraining past bottom-water oxygenation are addressed in this review. We compared OMZ sediments from the Peruvian upwelling with deposits of the late Cenomanian OAE 2 from the north-west African shelf. Holocene laminated sediments are encountered at bottom-water oxygen levels of < 7 μmol kg−1 under the Peruvian upwelling and < 5 μmol kg−1 in California Borderland basins and the Pakistan Margin. Seasonal to decadal changes of sediment input are necessary to create laminae of different composition. However, bottom currents may shape similar textures that are difficult to discern from primary seasonal laminae. The millimetre-sized trace fossil Chondrites was commonly found in Cretaceous strata and Recent oxygen-depleted environments where its diameter increased with oxygen levels from 5 to 45 μmol kg−1. Chondrites has not been reported in Peruvian sediments but centimetre-sized crab burrows appeared around 10 μmol kg−1, which may indicate a minimum oxygen value for bioturbated Cretaceous strata. Organic carbon accumulation rates ranged from 0.7 and 2.8 g C cm−2 kyr−1 in laminated OAE 2 sections in Tarfaya Basin, Morocco, matching late Holocene accumulation rates of laminated Peruvian sediments under Recent oxygen levels below 5 μmol kg−1. Sediments deposited at > 10 μmol kg−1 showed an inverse exponential relationship of bottom-water oxygen levels and organic carbon accumulation depicting enhanced bioirrigation and decomposition of organic matter with increased oxygen supply. In the absence of seasonal laminations and under conditions of low burial diagenesis, this relationship may facilitate quantitative estimates of palaeo-oxygenation. Similarities and differences between Cretaceous OAEs and late Quaternary OMZs have to be further explored to improve our understanding of sedimentary systems under hypoxic conditions.

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