scholarly journals Evidences and drivers of ocean deoxygenation off Peru over recent past decades

2021 ◽  
Vol 11 (1) ◽  
Author(s):  
D. Espinoza-Morriberón ◽  
V. Echevin ◽  
D. Gutiérrez ◽  
J. Tam ◽  
M. Graco ◽  
...  
Keyword(s):  
Coupled Model ◽  
Wind Variability ◽  
Remote Forcing ◽  
Subsurface Waters ◽  
Huge Impact ◽  
Minimum Zone ◽  
In Situ Observations ◽  
Oxygen Minimum

AbstractDeoxygenation is a major threat to the coastal ocean health as it impacts marine life and key biogeochemical cycles. Understanding its drivers is crucial in the thriving and highly exploited Peru upwelling system, where naturally low-oxygenated subsurface waters form the so-called oxygen minimum zone (OMZ), and a slight vertical shift in its upper limit may have a huge impact. Here we investigate the long-term deoxygenation trends in the upper part of the nearshore OMZ off Peru over the period 1970–2008. We use a unique set of dissolved oxygen in situ observations and several high-resolution regional dynamical-biogeochemical coupled model simulations. Both observation and model present a nearshore deoxygenation above 150 m depth, with a maximum trend of – 10 µmol kg−1 decade1, and a shoaling of the oxycline depth (− 6.4 m decade−1). Model sensitivity analysis shows that the modeled oxycline depth presents a non-significant (+ 0.9 m decade−1) trend when remote forcing is suppressed, while a significant oxycline shoaling (− 3 m decade−1) is obtained when the wind variability is suppressed. This indicates that the nearshore deoxygenation can be attributed to the slowdown of the near-equatorial eastward currents, which transport oxygen-rich waters towards the Peruvian shores. The large uncertainties in the estimation of this ventilation flux and the consequences for more recent and future deoxygenation trends are discussed.

scholarly journals Evidences and drivers of ocean deoxygenation off Peru over recent past decades

2021 ◽  
Author(s):  
Dante Espinoza-Morriberón ◽  
Vincent Echevin ◽  
Dimitri Gutiérrez ◽  
Jorge Tam ◽  
Michelle Graco ◽  
...  
Keyword(s):  
Coupled Model ◽  
Oxygen Minimum Zone ◽  
Model Simulations ◽  
Subsurface Waters ◽  
Huge Impact ◽  
Minimum Zone ◽  
Northern Peru ◽  
Oxygen Minimum

Abstract Deoxygenation is a major threat to the coastal ocean health as it impacts marine life and key biogeochemical cycles. Understanding its drivers is crucial in the thriving and highly exploited Peru upwelling system, where naturally low-oxygenated subsurface waters form the so-called oxygen minimum zone, and a slight vertical shift in its upper limit may have a huge impact. Here we investigate the long-term deoxygenation trends in the upper part of the nearshore oxygen minimum zone off Peru over the period 1970-2008. We use a unique set of dissolved oxygen in situ observations and several high resolution regional dynamical-biogeochemical coupled model simulations. The upper part of the oxygen minimum zone appears to lose oxygen over the period, particularly off Northern Peru, a trend well reproduced by the model. Model simulations attribute the deoxygenation to the slowdown of the near-equatorial eastward currents, which transport oxygen toward the Peruvian shores. The large uncertainties in the estimation of this ventilation flux and the consequences for more recent and future deoxygenation trends are discussed.

scholarly journals ENSO-driven fluctuations in oxygen supply and vertical extent of oxygen-poor waters in the oxygen minimum zone of the Eastern Tropical South Pacific

2019 ◽  
Author(s):  
Yonss Saranga José ◽  
Lothar Stramma ◽  
Sunke Schmidtko ◽  
Andreas Oschlies
Keyword(s):  
El Niño ◽  
Oxygen Supply ◽  
El Nino ◽  
La Niña ◽  
Vertical Extent ◽  
La Nina ◽  
Minimum Zone ◽  
In Situ Observations ◽  
Oxygen Minimum

Abstract. The El Niño Southern Oscillation (ENSO) with its warm (El Niño) and cold (La Niña) phase has strong impacts on marine ecosystems off Peru. This influence extends from changes in nutrient availability to productivity and oxygen levels. While several studies have demonstrated the influence of ENSO events on biological productivity, less is known about their impact on oxygen concentrations. In situ observations along the Peruvian and Chilean coast have shown a strong water column oxygenation during the 1997/1998 strong El Niño event. These observations suggest a deepening of the oxygen minimum zone (OMZ) along the continental shelf. However, due to reduced spatial coverage of the existing in situ observations, no studies have yet demonstrated the OMZ response to El Niño events in the whole Eastern Tropical South Pacific (ETSP). Furthermore, most studies have focused on El Niño events. Much less attention was given to the oxygen dynamics under La Niña influence. Here, we provide a comprehensive analysis of the ENSO influence on OMZ dynamics. Interannual variability of the OMZ during the period 1990–2010 is derived from a regional coupled physical-biogeochemical model forced with realistic atmospheric and lateral boundary conditions. Our results show a reduction of the vertical extent and a deepening of suboxic waters (SW) during the El Niño phase. During the La Niña phase, there is a vertical expansion of SW. These fluctuations in OMZ extent are due to changes in oxygen supply into its core depth mainly from lateral margins. During the El Niño phase, the enhanced lateral oxygen supply from the subtropics is the main reason for the reduction of SW in both coastal and offshore regions. During the La Niña phase, the oxygenated subtropical waters are blocked by the poleward transport along the southern margin of the OMZ. Consequently, oxygen concentrations within the OMZ are reduced and suboxic conditions expand during La Niña. The detailed analysis of transport pathways presented here provides new insights into how ENSO variability affects the oxygen-sensitive marine biogeochemistry of the ETSP.

scholarly journals Prokaryotic picoplankton distribution within the oxygen minimum zone of the central Mexican Pacific across environmental gradients

2018 ◽  
Vol 66 (2) ◽  
pp. 157-171 ◽  
Author(s):  
Zuleima Santana-Vega ◽  
David Uriel Hernández-Becerril ◽  
Alejandro R. Morales-Blake ◽  
Francisco Varona-Cordero ◽  
Martín Merino-Ibarra
Keyword(s):  
Environmental Gradients ◽  
Wide Distribution ◽  
Oxygen Minimum Zone ◽  
Mexican Pacific ◽  
Subsurface Waters ◽  
Minimum Zone ◽  
Tropical Areas ◽  
Abundance And Distribution ◽  
Oxygen Minimum

Abstract Marine picophytoplankton has become an important issue to understand the global ecology of phototrophic forms, due to its wide distribution and contribution to biomass and productivity. We studied the abundance, distribution and signature pigments of the prokaryote picophytoplankters Prochlorococcus and Synechococcus during an oceanographic cruise (26 April to 7 May, 2011) in the central Mexican Pacific, a relatively poorly-known oxygen minimum zone (OMZ), and the effect of three environmental gradients. Prochlorococcus and Synechococcus abundances were comparable with those found in other tropical areas (0.17 to 30.37 X 104 cells mL-1, and 0.9 to 30.97 X 104 cells mL-1, respectively). Prochlorococcus abundances reached highest numbers in deeper waters, often coinciding with the second deep in situ fluorescence (and chlorophyll α) maxima, at oceanic stations, below the nitratecline, whereas Synechococcus abundances were higher at subsurface waters and its concentration maxima usually coincided with the subsurface in situ fluorescence maxima, with slightly higher abundances in coastal stations. Statistical analyses support significantly these results. Distribution of divinyl-chlorophyll α was erratic along the water column and occasionally coincided with the deep in situ fluorescence maxima, whereas the distribution of zeaxanthin usually followed that of chlorophyll α and the abundances of Synechococcus, and peaked together. These results are similar to those previously found in the study area and in more temperate zones, and also to the general trend in OMZ, but confirm that the second deep chlorophyll α maxima are attributed to high Prochlorococcus densities. We additionally found the abundance and distribution of Prochlorococcus and Synechococcus strongly driven by the environmental gradients observed.

scholarly journals Mediterranean Sea climatic indices: monitoring long term variability and climate changes

2018 ◽  
Author(s):  
Athanasia Iona ◽  
Athanasios Theodorou ◽  
Sarantis Sofianos ◽  
Sylvain Watelet ◽  
Charles Troupin ◽  
...  
Keyword(s):  
Climate Change ◽  
Time Series ◽  
Mediterranean Sea ◽  
Climate Changes ◽  
Salt Content ◽  
Climatic Indices ◽  
In Situ Observations ◽  
The Mediterranean

Abstract. We present a new product composed of a set of thermohaline climatic indices from 1950 to 2015 for the Mediterranean Sea such as decadal temperature and salinity anomalies, their mean values over selected depths, decadal ocean heat and salt content anomalies at selected depth layers as well as their long times series. It is produced from a new high-resolution climatology of temperature and salinity on a 1/8° regular grid based on historical high quality in situ observations. Ocean heat and salt content differences between 1980–2015 and 1950–1979 are compared for evaluation of the climate shift in the Mediterranean Sea. The spatial patterns of heat and salt content shifts demonstrate in greater detail than ever before that the climate changes differently in the several regions of the basin. Long time series of heat and salt content for the period 1950 to 2015 are also provided which indicate that in the Mediterranean Sea there is a net mean volume warming and salting since 1950 with acceleration during the last two decades. The time series also show that the ocean heat content seems to fluctuate on a cycle of about 40 years and seems to follow the Atlantic Multidecadal Oscillation climate cycle indicating that the natural large scale atmospheric variability could be superimposed on to the warming trend. This product is an observations-based estimation of the Mediterranean climatic indices. It relies solely on spatially interpolated data produced from in-situ observations averaged over decades in order to smooth the decadal variability and reveal the long term trends with more accuracy. It can provide a valuable contribution to the modellers' community, next to the satellite-based products and serve as a baseline for the evaluation of climate-change model simulations contributing thus to a better understanding of the complex response of the Mediterranean Sea to the ongoing global climate change. The product is available here: https://doi.org/10.5281/zenodo.1210100.

scholarly journals The control of hydrogen sulfide on benthic iron and cadmium fluxes in the oxygen minimum zone off Peru

2019 ◽  
Author(s):  
Anna Plass ◽  
Christian Schlosser ◽  
Stefan Sommer ◽  
Andrew W. Dale ◽  
Eric P. Achterberg ◽  
...  
Keyword(s):  
Hydrogen Sulfide ◽  
Trace Metals ◽  
Pore Water ◽  
Oxygen Minimum Zone ◽  
Benthic Fluxes ◽  
Benthic Chamber ◽  
Bottom Waters ◽  
Minimum Zone ◽  
Oxygen Minimum

Abstract. Sediments in oxygen-depleted marine environments can be an important sink or source of bio-essential trace metals in the ocean. However, the key mechanisms controlling the release from or burial of trace metals in sediments are not exactly understood. Here, we investigate the benthic biogeochemical cycling of Fe and Cd in the oxygen minimum zone off Peru. We combine bottom water profiles, pore water profiles, as well as benthic fluxes determined from pore water profiles and in-situ from benthic chamber incubations along a depth transect at 12° S. In agreement with previous studies, both concentration-depth profiles and in-situ benthic fluxes indicate a Fe release from sediments into bottom waters. Diffusive Fe fluxes and Fe fluxes from benthic chamber incubations are roughly consistent (0.3–17.1 mmol m−2 y−1), indicating that diffusion is the main transport mechanism of dissolved Fe across the sediment-water interface. The occurrence of mats of sulfur oxidizing bacteria on the seafloor represents an important control on the spatial distribution of Fe fluxes by regulating hydrogen sulfide (H2S) concentrations and, potentially, Fe sulfide precipitation within the surface sediment. Removal of dissolved Fe after its release to anoxic bottom waters is rapid in the first 4 m away from the seafloor (half-life

scholarly journals Uptake of algal carbon and the likely synthesis of an "essential" fatty acid by <i>Uvigerina</i> ex. gr. <i>semiornata</i> (Foraminifera) within the Pakistan margin oxygen minimum zone: evidence from fatty acid biomarker and <sup>13</sup>C tracer experiments

2014 ◽  
Vol 11 (14) ◽  
pp. 3729-3738 ◽  
Author(s):  
K. E. Larkin ◽  
A. J. Gooday ◽  
C. Woulds ◽  
R. M. Jeffreys ◽  
M. Schwartz ◽  
...  
Keyword(s):  
Fatty Acids ◽  
Fatty Acid ◽  
Food Source ◽  
Benthic Communities ◽  
Oxygen Minimum Zone ◽  
Monsoon Period ◽  
Minimum Zone ◽  
Oxygen Minimum ◽  
Tracer Experiments

Abstract. Foraminifera are an important component of benthic communities in oxygen-depleted settings, where they potentially play a significant role in the processing of organic matter. We tracked the uptake of a 13C-labelled algal food source into individual fatty acids in the benthic foraminiferal species Uvigerina ex. gr. semiornata from the Arabian Sea oxygen minimum zone (OMZ). The tracer experiments were conducted on the Pakistan margin during the late/post monsoon period (August–October 2003). A monoculture of the diatom Thalassiosira weisflogii was 13C-labelled and used to simulate a pulse of phytoplankton in two complementary experiments. A lander system was used for in situ incubations at 140 m water depth and for 2.5 days in duration. Shipboard laboratory incubations of cores collected at 140 m incorporated an oxystat system to maintain ambient dissolved oxygen concentrations and were terminated after 5 days. Uptake of diatoms was rapid, with a high incorporation of diatom fatty acids into foraminifera after ~ 2 days in both experiments. Ingestion of the diatom food source was indicated by the increase over time in the quantity of diatom biomarker fatty acids in the foraminifera and by the high percentage of 13C in many of the fatty acids present at the endpoint of both in situ and laboratory-based experiments. These results indicate that

Long-term in situ observations at the Athina mud volcano, Eastern Mediterranean: Taking the pulse of mud volcanism

2017 ◽  
Vol 721 ◽  
pp. 12-27 ◽  
Author(s):  
Walter Menapace ◽  
David Völker ◽  
Heiko Sahling ◽  
Christian Zoellner ◽  
Christian dos Santos Ferreira ◽  
...  
Keyword(s):  
Eastern Mediterranean ◽  
Mud Volcano ◽  
Mud Volcanism ◽  
In Situ Observations

scholarly journals An evaluation of ASCAT surface soil moisture products with in-situ observations in Southwestern France

2009 ◽  
Vol 13 (2) ◽  
pp. 115-124 ◽  
Author(s):  
C. Albergel ◽  
C. Rüdiger ◽  
D. Carrer ◽  
J.-C. Calvet ◽  
N. Fritz ◽  
...  
Keyword(s):  
Soil Moisture ◽  
Surface Soil ◽  
Mountainous Area ◽  
Surface Soil Moisture ◽  
Water Index ◽  
In Situ Observations ◽  
Weather Stations ◽  
Term Data

Abstract. A long term data acquisition effort of profile soil moisture is currently underway at 13 automatic weather stations located in Southwestern France. In this study, the soil moisture measured in-situ at 5 cm is used to evaluate the normalised surface soil moisture (SSM) estimates derived from coarse-resolution (25 km) active microwave data of the ASCAT scatterometer instrument (onboard METOP), issued by EUMETSAT for a period of 6 months (April–September) in 2007. The seasonal trend is removed from the satellite and in-situ time series by considering scaled anomalies. One station (Mouthoumet) of the ground network, located in a mountainous area, is removed from the analysis as very few ASCAT SSM estimates are available. No correlation is found for the station of Narbonne, which is close to the Mediterranean sea. On the other hand, nine stations present significant correlation levels. For two stations, a significant correlation is obtained when considering only part of the ASCAT data. The soil moisture measured in-situ at those stations, at 30 cm, is used to estimate the characteristic time length (T) of an exponential filter applied to the ASCAT product. The best correlation between a soil water index derived from ASCAT and the in-situ soil moisture observations at 30 cm is obtained with a T-value of 14 days.

scholarly journals Cryptic role of tetrathionate in the sulfur cycle: A study from Arabian Sea oxygen minimum zone sediments

2019 ◽  
Author(s):  
Subhrangshu Mandal ◽  
Sabyasachi Bhattacharya ◽  
Chayan Roy ◽  
Moidu Jameela Rameez ◽  
Jagannath Sarkar ◽  
...  
Keyword(s):  
Arabian Sea ◽  
Potential Role ◽  
Sediment Cores ◽  
Oxygen Minimum Zone ◽  
Sulfur Cycle ◽  
Metagenome Analysis ◽  
Minimum Zone ◽  
Oxygen Minimum

ABSTRACTTo explore the potential role of tetrathionate in the sulfur cycle of marine sediments, the population ecology of tetrathionate-forming, oxidizing, and respiring microorganisms was revealed at 15-30 cm resolution along two, ∼3-m-long, cores collected from 530- and 580-mbsl water-depths of Arabian Sea, off India’s west coast, within the oxygen minimum zone (OMZ). Metagenome analysis along the two sediment-cores revealed widespread occurrence of the structural genes that govern these metabolisms; high diversity and relative-abundance was also detected for the bacteria known to render these processes. Slurry-incubation of the sediment-samples, pure-culture isolation, and metatranscriptome analysis, corroborated thein situfunctionality of all the three metabolic-types. Geochemical analyses revealed thiosulfate (0-11.1 μM), pyrite (0.05-1.09 wt %), iron (9232-17234 ppm) and manganese (71-172 ppm) along the two sediment-cores. Pyrites (via abiotic reaction with MnO2) and thiosulfate (via oxidation by chemolithotrophic bacteria prevalentin situ) are apparently the main sources of tetrathionate in this ecosystem. Tetrathionate, in turn, can be either converted to sulfate (via oxidation by the chemolithotrophs present) or reduced back to thiosulfate (via respiration by native bacteria); 0-2.01 mM sulfide present in the sediment-cores may also reduce tetrathionate abiotically to thiosulfate and elemental sulfur. Notably tetrathionate was not detectedin situ- high microbiological and geochemical reactivity of this polythionate is apparently instrumental in the cryptic nature of its potential role as a central sulfur cycle intermediate. Biogeochemical roles of this polythionate, albeit revealed here in the context of OMZ sediments, may well extend to the sulfur cycles of other geomicrobiologically-distinct marine sediment horizons.

scholarly journals Traffic restrictions in Beijing during the Sino-African Summit 2006: aerosol size distribution and visibility compared to long-term in situ observations

2008 ◽  
Vol 8 (4) ◽  
pp. 12971-12998 ◽  
Author(s):  
Y. F. Cheng ◽  
J. Heintzenberg ◽  
B. Wehner ◽  
Z. J. Wu ◽  
M. Hu ◽  
...  
Keyword(s):  
Wind Speed ◽  
Fine Particles ◽  
Ultrafine Particle ◽  
Weather Conditions ◽  
Particle Formation ◽  
Control Measures ◽  
Aerosol Size Distribution ◽  
In Situ Observations

Abstract. Based on the long-term in-situ observations of aerosol particle number size distributions and meteorological parameters, the traffic restriction measures during the Sino-African Summit (4–6 November 2006) in Beijing, China have been found to be remarkably efficient in reducing the number concentration of aerosol particles, in particular Aitken and accumulation mode particles, and in improving the visibility. The influence of traffic restriction in Beijing on the particle concentrations differed for different particle sizes. More significant effects on fine particles with diameters ranging from 40 to 800 nm have been found. Based on statistical analysis of long-term observation, under comparable weather conditions, the source strength of the particles in Aitken and accumulation modes seemingly was reduced by 40–60% when the traffic restrictions were in place. It may be mainly due to the reduction of secondary particle formation. Our size-dependent aerosol data also indicate that measures led to reductions in particulate air pollution in the optically most important diameter range, whereas further vehicle control measures may lead to an increase in ultrafine particle formation from the gas phase if the condensational sink further decreased. Assuming that there were no traffic restrictions and with normal levels of the vehicle emissions, the visibilities during the Summit would have been lower by about 50%. The importance of the restrictions is highest when the wind speed is lower than 3 m s−1. The fact that over 95% cases with visual range lower than 5 km during 2004 to 2007 occurred when the local wind speed was lower than 3 m s−1 may suggest that future traffic restrictions will lead to significant improvements of visibility in Beijing.

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