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

2021 ◽  
Vol 18 (9) ◽  
pp. 2827-2841
Author(s):  
Martin Tetard ◽  
Laetitia Licari ◽  
Ekaterina Ovsepyan ◽  
Kazuyo Tachikawa ◽  
Luc Beaufort
Keyword(s):  
North Pacific ◽  
Transfer Functions ◽  
Late Quaternary ◽  
Global Climate ◽  
Single Species ◽  
Shape Index ◽  
Pore Waters ◽  
Oxygen Minimum Zones ◽  
Global Calibration ◽  
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. 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 taxon-independent morphometric analysis of benthic foraminiferal tests, developed and calibrated using WNP (western North Pacific, including its marginal seas), ENP (eastern North Pacific), and ESP (eastern South Pacific) OMZ samples. This new approach is based on an average size and shape index for each sample. This method, as well as two already published micropalaeontological techniques based on benthic foraminiferal assemblages' variability and porosity investigation of a single species, was calibrated here based on availability of new data from 45 core tops recovered along an oxygen gradient (from 0.03 to 2.88 mL L−1) from the WNP, ENP, EEP (eastern Equatorial Pacific), ESP, SWACM (southwest African continental margin), and AS (Arabian Sea) OMZs. Global calibrated transfer functions are herein proposed for these methods. These micropalaeontological reconstruction approaches were then applied to a palaeorecord 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 assemblage and morphometric approaches (which are 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) showed ambiguous estimations.

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.

Expansion of the eastern North Pacific OMZ and the associated denitrification regime

2020 ◽  
Author(s):  
Allan Devol ◽  
Wendi Ruef
Keyword(s):  
Pacific Decadal Oscillation ◽  
North Pacific ◽  
Arabian Sea ◽  
Thermocline Depth ◽  
Fixed Nitrogen ◽  
Potential Density ◽  
Hurricane Intensity ◽  
Oxygen Minimum Zones ◽  
Marine Areas ◽  
Oxygen Minimum

<p> </p><p>At this point ocean deoxygenation is well documented, including in oxygen minimum zones (OMZs).  Within the large OMZs of the Arabian Sea and eastern Pacific are imbedded areas where oxygen concentrations are so low that they are undetectable by routine CTD sensors (oxygen deficient zones, ODZs).  How do we determine if these ODZ are losing O<sub>2</sub>?  Furthermore, denitrification occurs in oxygen minimum zones (OMZs) so one might hypothesize that denitrification is likewise expanding if oxygen is decreasing.  This is important because the ocean's fixed nitrogen inventory limits the productivity over large marine areas.</p><p>We have investigated these questions in the largest OMZ, the eastern tropical North Pacific (ETNP) through an analysis of  6 repeats of a 1000 km transect along 110<sup>o</sup> West in the heart of the ETNP ODZ between 1971-2019.  We use N*, a stoichiometric parameter calculated from nitrate and phosphate, as our indicator of denitrification. The more Negative N* the more denitrification has occurred. After secondary QC the values of O<sub>2</sub> concentration between potential density 24.75 and 1000m along with N* were integrated across the transect and over the depth of the ODZ.  </p><p>The results show a clear decrease in oxygen inventory along with an increase in N*, suggesting deoxygenation and intensification of denitrification over during the 50 year period. We discuss potential mechanisms for denitrification signal increase including ENSO, Pacific Decadal Oscillation, tropical hurricane intensity, and variations in thermocline depth.</p>

scholarly journals Genome-resolved viral ecology in a marine oxygen minimum zone (OMZ)

2020 ◽  
Author(s):  
Dean Vik ◽  
Maria Consuelo Gazitúa ◽  
Christine L. Sun ◽  
Montserrat Aldunate ◽  
Margaret R. Mulholland ◽  
...  
Keyword(s):  
Community Structure ◽  
Global Climate ◽  
South Pacific ◽  
Ecological Change ◽  
Alpha And Beta Diversity ◽  
Oxygen Minimum Zones ◽  
Anoxic Waters ◽  
Viral Community ◽  
Viral Communities ◽  
Oxygen Minimum

SummaryOxygen minimum zones (OMZs) are critical to marine nitrogen cycling and global climate change. While OMZ microbial communities are relatively well-studied, little is known about their viruses. Here we assess the viral community ecology of 22 deeply sequenced viral metagenomes along a gradient of surface oxygenated to anoxic waters (< 0.02 μmol/L O2) in the Eastern Tropical South Pacific (ETSP) OMZ. We identified 46,127 viral populations (>5 kb), which augments the known viruses at this site by 10-fold. ETSP viral communities clustered into 6 groups that correspond to oceanographic features, with 3 clusters representing samples from suboxic to anoxic waters. Oxygen concentration was the predominant environmental feature driving viral community structure. Alpha and beta diversity of viral communities in the anoxic zone were lower than in surface waters, which parallels the low microbial diversity seen in other studies. Viruses were largely endemic as few (6% of viruses from this study) were found in at least another marine metagenome, and of those, most (77%) were restricted to other OMZs. Together these findings provide an ecological baseline for viral community structure, drivers and population variability in OMZs that will help future studies assess the role of viruses in these climate-critical environments.Originality-Significance StatementMarine oxygen minimum zones (OMZs) are unique and important ocean ecosystems where microbes drive climate-altering nutrient transformations. This study provides a baseline, deeply sequenced viral metagenomic dataset and reference viral genomes to assess ecological change and drivers across the oxygenated surface to de-oxygenated deep waters of the Eastern Tropical South Pacific (ETSP) OMZ. Community ecological assessment of the ETSP viromes reveals a relatively low diversity viral community with a high degree of endemic populations in the OMZ waters.

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.

Centennial changes in North Pacific anoxia linked to tropical trade winds

Science ◽  
2014 ◽  
Vol 345 (6197) ◽  
pp. 665-668 ◽  
Author(s):  
Curtis Deutsch ◽  
William Berelson ◽  
Robert Thunell ◽  
Thomas Weber ◽  
Caitlin Tems ◽  
...  
Keyword(s):  
Climate Warming ◽  
North Pacific ◽  
Sediment Cores ◽  
Equatorial Pacific ◽  
Biological Productivity ◽  
Anoxic Zone ◽  
Trade Winds ◽  
Oxygen Minimum Zones ◽  
Oxygen Minimum ◽  
The Tropical Pacific

Climate warming is expected to reduce oxygen (O2) supply to the ocean and expand its oxygen minimum zones (OMZs). We reconstructed variations in the extent of North Pacific anoxia since 1850 using a geochemical proxy for denitrification (δ15N) from multiple sediment cores. Increasing δ15N since ~1990 records an expansion of anoxia, consistent with observed O2 trends. However, this was preceded by a longer declining δ15N trend that implies that the anoxic zone was shrinking for most of the 20th century. Both periods can be explained by changes in winds over the tropical Pacific that drive upwelling, biological productivity, and O2 demand within the OMZ. If equatorial Pacific winds resume their predicted weakening trend, the ocean’s largest anoxic zone will contract despite a global O2 decline.

scholarly journals The evolving response of mesopelagic fishes to declining midwater oxygen concentrations in the southern and central California Current

2018 ◽  
Vol 76 (3) ◽  
pp. 626-638 ◽  
Author(s):  
J Anthony Koslow ◽  
Pete Davison ◽  
Erica Ferrer ◽  
S Patricia A Jiménez Rosenberg ◽  
Gerardo Aceves-Medina ◽  
...  
Keyword(s):  
Baja California ◽  
Southern Oscillation ◽  
Global Climate ◽  
California Current ◽  
Deep Ocean ◽  
Near Surface ◽  
Oxygen Minimum Zones ◽  
The North ◽  
The Pacific ◽  
Oxygen Concentrations

Abstract Declining oxygen concentrations in the deep ocean, particularly in areas with pronounced oxygen minimum zones (OMZs), are a growing global concern related to global climate change. Its potential impacts on marine life remain poorly understood. A previous study suggested that the abundance of a diverse suite of mesopelagic fishes off southern California was closely linked to trends in midwater oxygen concentration. This study expands the spatial and temporal scale of that analysis to examine how mesopelagic fishes are responding to declining oxygen levels in the California Current (CC) off central, southern, and Baja California. Several warm-water mesopelagic species, apparently adapted to the shallower, more intense OMZ off Baja California, are shown to be increasing despite declining midwater oxygen concentrations and becoming increasingly dominant, initially off Baja California and subsequently in the CC region to the north. Their increased abundance is associated with warming near-surface ocean temperature, the warm phase of the Pacific Decadal oscillation and Multivariate El Niño-Southern Oscillation Index, and the increased flux of Pacific Equatorial Water into the southern CC.

Quaternary Mammal Communities: Relevance of the Individualistic Response and Non-Analogue Faunas

2005 ◽  
Vol 11 ◽  
pp. 141-158 ◽  
Author(s):  
Russell W. Graham
Keyword(s):  
Climate Change ◽  
Global Climate Change ◽  
Natural Experiment ◽  
Late Quaternary ◽  
Global Climate ◽  
Land Use Management ◽  
Change Analysis ◽  
Climate Fluctuations ◽  
Core Species ◽  
Mammal Communities

Frequent and repeated climate fluctuations of the late Quaternary serve as a “natural experiment” for the response of species to environmental change. Analysis of the FAUNMAP database documents individualistic shifts in the geographic distributions for late Quaternary mammals. However, because the individualistic response is not necessarily random and because many species share similar niche parameters, it is possible that some species appear to form coherent groups of core species. In reality their dispersals are individualistic with regard to rate and timing. The individualistic response of mammals, as well as that of other organisms, has created late Quaternary communities without modern analogues. This concept has profound implications for the design of biological reserves and for land use management with respect to future global climate change. However, the relevance of non-analogue mammal communities has been challenged by Alroy (1999), who claims that non-analogue associations were not common in the Quaternary and that they appeared to occur in both the Pleistocene and Holocene. Reexamination of his analysis shows that he employed a different definition for non-analogue faunas and that his methods of analyses created artificially low counts of non-analogue communities and consequently an underestimate of their importance.

scholarly journals In situ quantification of ultra‐low O 2 concentrations in oxygen minimum zones: Application of novel optodes

2016 ◽  
Vol 14 (12) ◽  
pp. 784-800 ◽  
Author(s):  
Morten Larsen ◽  
Philipp Lehner ◽  
Sergey M. Borisov ◽  
Ingo Klimant ◽  
Jan P. Fischer ◽  
...  
Keyword(s):  
Oxygen Minimum Zones ◽  
Oxygen Minimum
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