News

Effect of oxygen minimum zone formation on communities of marine protists

Abstract.

"Changes in ocean temperature and circulation patterns compounded by human activities are leading to oxygen minimum zone (OMZ) expansion with concomitant alteration in nutrient and climate active trace gas cycling. Here, we report the response of microbial eukaryote populations to seasonal changes in water column oxygen-deficiency using Saanich Inlet, a seasonally anoxic fjord on the coast of Vancouver Island British Columbia, as a model ecosystem. [...]"

Source: The ISME Journal 6
Authors: William Orsi et al.
DOI: 10.1038/ismej.2012.7

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West Maui shoreline water quality to be documented in huge collection program

"A groundbreaking scientific data collection program to expand the measuring of water quality off 18 West Maui shoreline sites has been forged between the state Department of Health and Maui community groups involved in the protection of the island’s nearshore waters. [...]"

Source: The Maui News

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Positive Indian Ocean Dipole events prevent anoxia off the west coast of India

Abstract.

"The seasonal upwelling along the west coast of India (WCI) brings nutrient-rich, oxygen-poor subsurface waters to the continental shelf, favoring very low oxygen concentrations in the surface waters during late boreal summer and fall. This yearly-recurring coastal hypoxia is more severe during some years, leading to coastal anoxia that has strong impacts on the living resources. In the present study, we analyze a 1/4◦ resolution coupled physical–biogeochemical regional oceanic simulation over the 1960–2012 period to investigate the physical processes influencing the oxycline interannual variability off the WCI, that being a proxy for the variability on the shelf in our model. [...]" 

Source: Bioggeosciences 14
Authors: Parvathi Vallivattathillam et al.
DOI: 10.5194/bg-14-1541-2017

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The influence of oxygen exposure time on the composition of macromolecular organic matter as revealed by surface sediments on the Murray Ridge

Abstract.

"The Arabian Sea represents a prime example of an open ocean extended oxygen minimum zone (OMZ) with low oxygen concentrations (down to less than 2 mM) between 200 and 1000 m water depth. The OMZ impinges on the ocean floor, affect ingorganic matter (OM) mineralization. We investigated impact of oxygen depletion on the composition of macromolecularOM (MOM) along a transect through the OMZ on the slopes of the Murray Ridge. This sub-marine high in the northern Arabian Sea, with the top at approximately 500 m below sea surface (mbss), intersects the OMZ. We analyzed sediments deposited in the core of OMZ (suboxic conditions) [...]"

Source: Geochimica et Cosmochimica Acta 206
Authors: Nierop, K.G.J.; Reichart, G.-J.; Veld, H.; Sinninghe Damsté, J.S
DOI: dx.doi.org/10.1016/j.gca.2017.02.032

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Remineralization of particulate organic carbon in an ocean oxygen minimum zone

Abstract.

"Biological oceanic processes, principally the surface production, sinking and interior remineralization of organic particles, keep atmospheric CO2 lower than if the ocean was abiotic. The remineralization length scale (RLS, the vertical distance over which organic particle flux declines by 63%, affected by particle respiration, fragmentation and sinking rates) controls the size of this effect and is anomalously high in oxygen minimum zones (OMZ). Here we show in the Eastern Tropical North Pacific OMZ 70% of POC remineralization is due to microbial respiration, indicating that the high RLS is the result of lower particle fragmentation by zooplankton, likely due to the almost complete absence of zooplankton particle interactions in OMZ waters. [...]"

Source: Nature Communications 8
Authors: E. L. Cavan, M. Trimmer, F. Shelley & R. Sanders
DOI: 10.1038/ncomms14847

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Tropical dead zones and mass mortalities on coral reefs

Description

"Oxygen-starved coastal waters are rapidly increasing in prevalence worldwide. However, little is known about the impacts of these “dead zones” in tropical ecosystems or their potential threat to coral reefs. We document the deleterious effects of such an anoxic event on coral habitat and biodiversity, and show that the risk of dead-zone events to reefs worldwide likely has been seriously underestimated. Awareness of, and research on, reef hypoxia is needed to address the threat posed by dead zones to coral reefs."

 

Source: Proceedings of the National Academy of Sciences of the United Stated of America (PNAS)
Authors: Andrew H. Altieri et al.
DOI: 10.1073/pnas.1621517114

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Buoyancy-driven coastal current blocks ventilation of an anoxic fjord on the Pacific coast of Canada

Abstract. 

"Shallow sills restrict the ventilation of deep coastal fjords. Dense oceanic water seaward of the sill and lower density water within the receiving basin are generally required for oxygenated water to cross the sill and descend deep into the fjord. Here, we use concurrent 10-year time series from current meters in the fjord and on the continental shelf to examine ventilation of the 120-m deep, anoxic inner basin of Effingham Inlet on the west coast of Vancouver Island. Whereas density currents traverse the 40 m-deep sill and flow into the inner basin at mid-depth at quasi-fortnightly tidal intervals, only five current intrusions descended to the bottom of the basin over the decade-long measurement period. [...]"

Source: Journal of Geophysical Research (JGR)
Authors: Richard E. Thomson et al.
DOI: 10.1002/2016JC012512

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Declining oxygen – is Humboldt’s nutrient boost at risk?

Experiment with the KOSMOS mesocosms in Peru

"If less and less oxygen is available in the ocean as a result of climate change, this also affects highly productive regions such as the waters off the coast of Peru – an area strongly influenced by the nutrient-rich Humboldt Current. An international team led by GEOMAR Helmholtz Center for Ocean Research Kiel now investigates the impact of declining oxygen on the productivity of the Peruvian upwelling system employing the KOSMOS mesocosm facility. [...]"

Source: GEOMAR
Contact: Maike Nicolai

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The geologic history of seawater pH

Abstract.  

"Although pH is a fundamental property of Earth’s oceans, critical to our understanding of seawater biogeochemistry, its long-timescale geologic history is poorly constrained. We constrain seawater pH through time by accounting for the cycles of the major components of seawater. We infer an increase from early Archean pH values between ~6.5 and 7.0 and Phanerozoic values between ~7.5 and 9.0, which was caused by a gradual decrease in atmospheric pCO2 in response to solar brightening, alongside a decrease in hydrothermal exchange between seawater and the ocean crust. [...]"

Source: Science Vol. 355
Authors: I. Halevy, A. Bachan
DOI: 10.1126/science.aal4151

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A significant net sink for CO2 in Tokyo Bay

Abstract.

"Most estuaries and inland waters are significant source for atmospheric CO2 because of input of terrestrial inorganic carbon and mineralization of terrestrially supplied organic carbon. In contrast to most coastal waters, some estuaries with small freshwater discharge are weak source or sometimes sink for CO2. Extensive surveys of pCO2 in Tokyo Bay showed that the overall bay acts as a strong net sink for atmospheric CO2. Although small area was a consistent source for CO2, active photosynthesis driven by nutrient loading from the land overwhelmed the CO2 budget in the bay. [...]"

Source: Scientific Reports Vol. 7
Authors: Atsushi Kubo, Yosaku Maeda & Jota Kanda
DOI: 10.1038/srep44355

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