scholarly journals Impact of climate induced hypoxia on calcifying biota in the Arabian Sea : An evaluation from the micropaleontological records of the Indian margin

MAUSAM ◽  
2021 ◽  
Vol 62 (4) ◽  
pp. 647-652
Author(s):  
A.D. SINGH ◽  
S. DAS ◽  
K. VERMA
Keyword(s):  
Arabian Sea ◽  
Global Climate ◽  
Marine Ecosystem ◽  
Oxygen Depletion ◽  
Marine Biota ◽  
Low Oxygen ◽  
Hypoxic Environment ◽  
Minimum Zone ◽  
Abundance And Diversity ◽  
Poor Ventilation

High biological productivity combined with the poor ventilation produces severe oxygen depletion (hypoxia) in upper intermediate waters of the Arabian Sea. The naturally developed Arabian Sea oxygen minimum zone (OMZ) is one of the most pronounced low oxygen ocean environments known today. The OMZ impinges the Indian margin where oxygen concentration reaches values less than 0.05 ml/l leading denitrification. In recent studies, it has been observed that the OMZ strength has varied considerably in the past, in tune with the global climate change. But the effect of changes in natural mid-water hypoxic environment on the marine biota particularly of the eastern Arabian Sea is unknown. Here, we analyzed 30,000 yr record of temporal changes in two major groups of marine calcifying microfauna pteropods secreting aragonitic shells and foraminifera secreting calcitic shells in terms of abundance and diversity variations. This study will provide an insight into our understanding of potential impact of rising atmospheric CO2 on marine ecosystem.

scholarly journals In situ observations show vertical community structure of pelagic fauna in the eastern tropical North Atlantic off Cape Verde

2020 ◽  
Vol 10 (1) ◽  
Author(s):  
H. J. T. Hoving ◽  
P. Neitzel ◽  
H. Hauss ◽  
S. Christiansen ◽  
R. Kiko ◽  
...  
Keyword(s):  
Climate Change ◽  
North Atlantic ◽  
Global Climate ◽  
Distribution Patterns ◽  
Cape Verde ◽  
Distribution Data ◽  
Low Oxygen ◽  
Study Region ◽  
Tropical North Atlantic ◽  
Minimum Zone

AbstractDistribution patterns of fragile gelatinous fauna in the open ocean remain scarcely documented. Using epi-and mesopelagic video transects in the eastern tropical North Atlantic, which features a mild but intensifying midwater oxygen minimum zone (OMZ), we established one of the first regional observations of diversity and abundance of large gelatinous zooplankton. We quantified the day and night vertical distribution of 46 taxa in relation to environmental conditions. While distribution may be driven by multiple factors, abundance peaks of individual taxa were observed in the OMZ core, both above and below the OMZ, only above, or only below the OMZ whereas some taxa did not have an obvious distribution pattern. In the eastern eropical North Atlantic, OMZ expansion in the course of global climate change may detrimentally impact taxa that avoid low oxygen concentrations (Beroe, doliolids), but favour taxa that occur in the OMZ (Lilyopsis, phaeodarians, Cydippida, Colobonema, Haliscera conica and Halitrephes) as their habitat volume might increase. While future efforts need to focus on physiology and taxonomy of pelagic fauna in the study region, our study presents biodiversity and distribution data for the regional epi- and mesopelagic zones of Cape Verde providing a regional baseline to monitor how climate change may impact the largest habitat on the planet, the deep pelagic realm.

scholarly journals Uptake of phytodetritus by benthic foraminifera under oxygen depletion at the Indian Margin (Arabian Sea)

2013 ◽  
Vol 10 (9) ◽  
pp. 15305-15335 ◽  
Author(s):  
A. J. Enge ◽  
U. Witte ◽  
M. Kucera ◽  
P. Heinz
Keyword(s):  
Continental Slope ◽  
Benthic Foraminifera ◽  
Arabian Sea ◽  
Isotope Labeling ◽  
Oxygen Depletion ◽  
Food Delivery ◽  
Short Term ◽  
Important Species ◽  
Minimum Zone ◽  
Species Specific

Abstract. Benthic foraminifera in sediments on the Indian margin of the Arabian Sea where the oxygen minimum zone (OMZ) impinges on the continental slope are exposed to particularly severe levels of oxygen depletion. Food supply for the benthic community is high but delivered in distinct pulses during upwelling and water mixing events associated with summer and winter monsoon periods. In order to investigate the response by benthic foraminifera to such pulsed food delivery under oxygen concentrations of less than 0.1 mL L−1 (4.5 μmol L−1), an in situ isotope labeling experiment (13C, 15N) was performed at the western continental slope of India at 540 m water depth (OMZ core region). The assemblage of living foraminifera (>125 μm) in the uppermost centimeter at this depth is characterized by an unexpectedly high population density of 3982 ind. 10 cm−2 and a strong dominance by few calcareous species. For the experiment, we concentrated on the nine most abundant taxa, which constitute 93% of the entire foraminifera population at 0–1 cm sediment depth. Increased concentrations of 13C and 15N in the cytoplasm indicate that all investigated taxa took up the labeled phytodetritus during the 4 day experimental phase. In total, these nine species had assimilated 113.8 mg C m−2 (17.5% of the total added carbon). The uptake of nitrogen by the three most abundant taxa (Bolivina aff. B. dilatata, Cassidulina sp., Bulimina gibba) was 2.7 mg N m−2 (2% of the total added nitrogen) and showed the successful application of 15N as tracer in foraminiferal studies. The short-term response to the offered phytodetritus varied largely among foraminiferal species with Uvigerina schwageri being by far the most important species in short-term processing whereas the most abundant taxa Bolivina aff. B. dilatata and Cassidulina sp. showed comparably low uptake of the offered food. We suggest that the observed species-specific differences are related to individual biomass of species and to specific feeding preferences. The high numbers of living foraminifera and their rapid response to deposited fresh phytodetritus demonstrate the importance of foraminifera in short-term carbon cycling under oxygen-depleted conditions. We propose that foraminifera at the studied site benefit from unique adaptations in their metabolisms to nearly anoxic conditions as well as from the exclusion of macrofauna and the resulting relaxation of competition for food and low predation pressure.

scholarly journals Impacts of hypoxia on the structure and processes in the pelagic community (zooplankton, macro-invertebrates and fish)

2009 ◽  
Vol 6 (3) ◽  
pp. 5073-5144 ◽  
Author(s):  
W. Ekau ◽  
H. Auel ◽  
H.-O. Pörtner ◽  
D. Gilbert
Keyword(s):  
Oxygen Depletion ◽  
Hypoxia Tolerance ◽  
Low Oxygen ◽  
System Productivity ◽  
Deep Waters ◽  
Trophic Pathways ◽  
Adaptive Mechanisms ◽  
Minimum Zone ◽  
Migration Strategies

Abstract. Dissolved oxygen (DO) concentration in the water column is an environmental parameter that is crucial for the successful development of many pelagic organisms. Hypoxia tolerance and threshold values are species- and stage-specific and can vary enormously. While some fish species may suffer from oxygen values of less than 3 ml L−1 and show impact on growth, development and behaviour, other organisms such as euphausiids may survive DO levels as low as 0.1 ml L−1. A change in the average or the minimum or maximum DO in an area may have significant impacts on the survival of certain species and hence on the species composition in the ecosystem with consequent changes in trophic pathways and productivity. Evidence of the deleterious effects of oxygen depletion on species of the pelagic realm is scarce, particularly in terms of the effect of low oxygen on development, recruitment and patterns of migration and distribution. While planktonic organisms have to cope with different DOs and find adaptive mechanisms, nektonic species may avoid areas of inconvenient DO and develop adapted migrational strategies. Planktonic organisms may only be able to escape vertically, above or beneath the Oxygen Minimum Zone (OMZ). In shallow areas only the surface layer can serve as a refuge, in deep waters many organisms have developed vertical migration strategies to use, pass and cope with the OMZ. This paper elucidates the role of DO for different taxa in the pelagic realm and the consequences of low oxygen for foodweb structure and system productivity.

scholarly journals Impacts of hypoxia on the structure and processes in pelagic communities (zooplankton, macro-invertebrates and fish)

2010 ◽  
Vol 7 (5) ◽  
pp. 1669-1699 ◽  
Author(s):  
W. Ekau ◽  
H. Auel ◽  
H.-O. Pörtner ◽  
D. Gilbert
Keyword(s):  
Coastal Upwelling ◽  
Oxygen Depletion ◽  
Hypoxia Tolerance ◽  
Low Oxygen ◽  
System Productivity ◽  
Trophic Pathways ◽  
Benguela Current ◽  
Minimum Zone ◽  
Migration Strategies ◽  
Pass Through

Abstract. Dissolved oxygen (DO) concentration in the water column is an environmental parameter that is crucial for the successful development of many pelagic organisms. Hypoxia tolerance and threshold values are species- and stage-specific and can vary enormously. While some fish species may suffer from oxygen values of less than 3 mL O2 L−1 through impacted growth, development and behaviour, other organisms such as euphausiids may survive DO levels as low as 0.1 mL O2 L−1. A change in the average or the range of DO may have significant impacts on the survival of certain species and hence on the species composition in the ecosystem with consequent changes in trophic pathways and productivity. Evidence for the deleterious effects of oxygen depletion on pelagic species is scarce, particularly in terms of the effect of low oxygen on development, recruitment and patterns of migration and distribution. While planktonic organisms have to cope with variable DOs and exploit adaptive mechanisms, nektonic species may avoid areas of unfavourable DO and develop adapted migration strategies. Planktonic organisms may only be able to escape vertically, above or beneath the Oxygen Minimum Zone (OMZ). In shallow areas only the surface layer can serve as a refuge, but in deep waters many organisms have developed vertical migration strategies to use, pass through and cope with the OMZ. This paper elucidates the role of DO for different taxa in the pelagic realm and the consequences of low oxygen for foodweb structure and system productivity. We describe processes in two contrasting systems, the semi-enclosed Baltic Sea and the coastal upwelling system of the Benguela Current to demonstrate the consequences of increasing hypoxia on ecosystem functioning and services.

Temporally invariable bacterial community structure in the Arabian Sea oxygen minimum zone

2014 ◽  
Vol 73 (1) ◽  
pp. 51-67 ◽  
Author(s):  
A Jain ◽  
M Bandekar ◽  
J Gomes ◽  
D Shenoy ◽  
RM Meena ◽  
...  
Keyword(s):  
Community Structure ◽  
Bacterial Community ◽  
Bacterial Community Structure ◽  
Arabian Sea ◽  
Oxygen Minimum Zone ◽  
Minimum Zone ◽  
Oxygen Minimum

scholarly journals A MicroRNA Signature of Hypoxia

2006 ◽  
Vol 27 (5) ◽  
pp. 1859-1867 ◽  
Author(s):  
Ritu Kulshreshtha ◽  
Manuela Ferracin ◽  
Sylwia E. Wojcik ◽  
Ramiro Garzon ◽  
Hansjuerg Alder ◽  
...  
Keyword(s):  
Expression Profiles ◽  
Hypoxia Inducible Factor ◽  
Tumor Formation ◽  
Low Oxygen ◽  
Functional Link ◽  
Factors Affecting ◽  
Cellular Processes ◽  
Hypoxic Environment ◽  
Tumorigenic Transformation ◽  
First Time

ABSTRACT Recent research has identified critical roles for microRNAs in a large number of cellular processes, including tumorigenic transformation. While significant progress has been made towards understanding the mechanisms of gene regulation by microRNAs, much less is known about factors affecting the expression of these noncoding transcripts. Here, we demonstrate for the first time a functional link between hypoxia, a well-documented tumor microenvironment factor, and microRNA expression. Microarray-based expression profiles revealed that a specific spectrum of microRNAs (including miR-23, -24, -26, -27, -103, -107, -181, -210, and -213) is induced in response to low oxygen, at least some via a hypoxia-inducible-factor-dependent mechanism. Select members of this group (miR-26, -107, and -210) decrease proapoptotic signaling in a hypoxic environment, suggesting an impact of these transcripts on tumor formation. Interestingly, the vast majority of hypoxia-induced microRNAs are also overexpressed in a variety of human tumors.

Denitrification exceeds anammox as a nitrogen loss pathway in the Arabian Sea oxygen minimum zone

2010 ◽  
Vol 57 (3) ◽  
pp. 384-393 ◽  
Author(s):  
Silvia E. Bulow ◽  
Jeremy J. Rich ◽  
Hema S. Naik ◽  
Anil K. Pratihary ◽  
Bess B. Ward
Keyword(s):  
Arabian Sea ◽  
Nitrogen Loss ◽  
Oxygen Minimum Zone ◽  
Minimum Zone ◽  
Oxygen Minimum

scholarly journals Open ocean dead zones in the tropical North Atlantic Ocean

2015 ◽  
Vol 12 (8) ◽  
pp. 2597-2605 ◽  
Author(s):  
J. Karstensen ◽  
B. Fiedler ◽  
F. Schütte ◽  
P. Brandt ◽  
A. Körtzinger ◽  
...  
Keyword(s):  
North Atlantic ◽  
North Atlantic Ocean ◽  
Dead Zone ◽  
Marine Ecosystem ◽  
High Surface ◽  
Open Ocean ◽  
Depth Range ◽  
Low Oxygen ◽  
Dead Zones ◽  
Tropical North Atlantic

Abstract. Here we present first observations, from instrumentation installed on moorings and a float, of unexpectedly low (<2 μmol kg−1) oxygen environments in the open waters of the tropical North Atlantic, a region where oxygen concentration does normally not fall much below 40 μmol kg−1. The low-oxygen zones are created at shallow depth, just below the mixed layer, in the euphotic zone of cyclonic eddies and anticyclonic-modewater eddies. Both types of eddies are prone to high surface productivity. Net respiration rates for the eddies are found to be 3 to 5 times higher when compared with surrounding waters. Oxygen is lowest in the centre of the eddies, in a depth range where the swirl velocity, defining the transition between eddy and surroundings, has its maximum. It is assumed that the strong velocity at the outer rim of the eddies hampers the transport of properties across the eddies boundary and as such isolates their cores. This is supported by a remarkably stable hydrographic structure of the eddies core over periods of several months. The eddies propagate westward, at about 4 to 5 km day−1, from their generation region off the West African coast into the open ocean. High productivity and accompanying respiration, paired with sluggish exchange across the eddy boundary, create the "dead zone" inside the eddies, so far only reported for coastal areas or lakes. We observe a direct impact of the open ocean dead zones on the marine ecosystem as such that the diurnal vertical migration of zooplankton is suppressed inside the eddies.

scholarly journals Live (Rose Bengal stained) foraminiferal faunas from the northern Arabian Sea: faunal succession within and below the OMZ

2014 ◽  
Vol 11 (4) ◽  
pp. 1155-1175 ◽  
Author(s):  
C. Caulle ◽  
K. A. Koho ◽  
M. Mojtahid ◽  
G. J. Reichart ◽  
F. J. Jorissen
Keyword(s):  
Rose Bengal ◽  
Arabian Sea ◽  
Environmental Parameters ◽  
Low Oxygen ◽  
Organic Input ◽  
The Core ◽  
Northern Arabian Sea ◽  
Transitional Group ◽  
Faunal Succession ◽  
Epistominella Exigua

Abstract. Live (Rose Bengal stained) benthic foraminifera from the Murray Ridge, within and below the northern Arabian Sea oxygen minimum zone (OMZ), were studied in order to determine the relationship between faunal composition, bottom water oxygenation (BWO), pore water chemistry and organic matter (organic carbon and phytopigment) distribution. A series of multicores were recovered from a ten-station oxygen (BWO: 2–78 μM) and bathymetric (885–3010 m depth) transect during the winter monsoon in January 2009. Foraminifera were investigated from three different size fractions (63–125 μm, 125–150 μm and >150 μm). The larger foraminifera (>125 μm) were strongly dominated by agglutinated species (e.g. Reophax spp.). In contrast, in the 63–125 μm fraction, calcareous taxa were more abundant, especially in the core of the OMZ. On the basis of a principal components analysis, three foraminiferal groups were identified and correlated to the environmental parameters by canonical correspondence analysis. The faunas from the shallowest stations, in the core of the OMZ (BWO: 2 μM), were composed of "low oxygen" species, typical of the Arabian Sea OMZ (e.g. Rotaliatinopsis semiinvoluta, Praeglobobulimina sp., Bulimina exilis, Uvigerina peregrina type parva). These taxa are adapted to the very low BWO conditions and to high phytodetritus supplies. The transitional group, typical for the lower part of the OMZ (BWO: 5–16 μM), is composed of species that are tolerant as well to low-oxygen concentrations, but may be less critical with respect to organic supplies (e.g. Globocassidulina subglobosa, Ehrenbergina trigona). Below the OMZ (BWO: 26–78 μM), where food availability is more limited and becomes increasingly restricted to surficial sediments, cosmopolitan calcareous taxa were present, such as Bulimina aculeata, Melonis barleeanus, Uvigerina peregrina and Epistominella exigua. Miliolids were uniquely observed in this last zone, reflecting the higher BWO and/or lower organic input. At these deeper sites, the faunas exhibit a clear succession of superficial, intermediate and deep infaunal microhabitats, which can be linked to the deeper oxygen and nitrate penetration into the sediment.

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