News

Dissolved oxygen and pH criteria leave fisheries at risk

Abstract.

"Changes in human population centers and agricultural fertilizer use have accelerated delivery rates of nitrogen and phosphorus to coastal waters, often stimulating rapid accumulations of primary production (1). Whereas resulting eutrophication processes are of less environmental relevance in well-mixed, ocean ecosystems, when they occur in warm, stratified, and/or poorly mixed waters, they can result in hypoxia [depletion of dissolved oxygen (DO)] and acidification (decrease in pH), both of which individually can have adverse effects on aquatic life, affecting a suite of physiological processes and increasing mortality rates (23). [...]"

Source: Science
Authors: Stephen J. Tomasetti, Christopher J. Gobler
DOI: 10.1126/science.aba4896

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A revisit to the regulation of oxygen minimum zone in the Bay of Bengal

Abstract.

"Occurrence of intense oxygen minimum zone (OMZ) is known in the Bay of Bengal (BoB), but it has been recently reported to have become more acute and is at its tipping point. Here, we show that the intensification of OMZ to acute condition is a random and short-term rather than perennial phenomenon based on re-evaluation of old and recent information in the BoB. Short-term modifications in dissolved oxygen (DO) in the OMZ are caused by balance among physical forcings: salinity stratification, occurrence of cyclonic (CE), and anticyclonic eddies (ACE). [...]"

Source: Journal of Earth System Science
Authors: B Sridevi and V V S S Sarma
DOI: 10.1007/s12040-020-1376-2

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Ocean deoxygenation could be silently killing coral reefs, scientists say

"In March, Australia’s Great Barrier Reef suffered its most widespread bleaching event to date. Sixty percent of the reef underwent moderate to severe bleaching, and some corals may never recover.

The cause of this bleaching event was climate change, which brought unusually warm waters to the Great Barrier Reef in February, and disrupted the delicate, symbiotic relationship between the corals and their life-sustaining algae. In general, when sea temperatures rise, corals become stressed and expel algae from their tissues. Without this algae, the corals turn ghostly white and slowly starve. [...]"

Source: Mongabay

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Warm afterglow from the Toarcian Oceanic Anoxic Event drives the success of deep-adapted brachiopods

Abstract.

"Many aspects of the supposed hyperthermal Toarcian Oceanic Anoxic Event (T-OAE, Early Jurassic, c. 182 Ma) are well understood but a lack of robust palaeotemperature data severely limits reconstruction of the processes that drove the T-OAE and associated environmental and biotic changes. New oxygen isotope data from calcite shells of the benthic fauna suggest that bottom water temperatures in the western Tethys were elevated by c. 3.5 °C through the entire T-OAE. [...]"

Source: Scientific Reports
Auhtors: C. V. Ullmann et al.
DOI: 10.1038/s41598-020-63487-6

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Properties and dynamics of mesoscale-eddies in the Fram Strait from a comparison between two high-resolution ocean-sea ice models

Abstract.

"The Fram Strait, the deepest gateway to the Arctic Ocean, is strongly influenced by eddy dynamics. Here we analyse the output from two eddy-resolving models (ROMS and FESOM) with around 1 km mesh resolution in the Fram Strait, with focus on their representation of eddy properties and dynamics. A comparison with mooring observations shows that both models reasonably simulate hydrography and eddy kinetic energy. [...]"

Source: Ocean Science
Authors: Claudia Wekerle et al.
DOI: 10.5194/os-2020-24

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'A bad time to be alive': Study links ocean deoxygenation to ancient die-off

"In a new study, Stanford researchers have strongly bolstered the theory that a lack of oxygen in Earth's oceans contributed to a devastating die-off approximately 444 million years ago. The new results further indicate that these anoxic (little- to no-oxygen) conditions lasted over 3 million years—significantly longer than similar biodiversity-crushing spells in our planet's history. Beyond deepening understandings of ancient mass extinction events, the findings have relevance for today: Global climate change is contributing to declining oxygen levels in the open ocean and coastal waters, a process that likely spells doom for a variety of species. [...]"

Source: Phys.org

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High Resolution Osmium Data Record Three Distinct Pulses of Magmatic Activity During Cretaceous Oceanic Anoxic Event 2 (OAE-2)

Abstract.

"Oceanic anoxic Event 2 (OAE-2) occurred at the Cenomanian-Turonian boundary (∼94.1 Ma) and was a time of profound global changes in ocean chemistry and the carbon cycle. This event was characterized by a positive carbon isotope excursion (CIE) caused by massive organic carbon burial, global greenhouse temperatures, ocean deoxygenation, and changes in ocean life driven by large igneous province (LIP) activity. LIPS throughout the Phanerozoic have had dynamic magma flux, with episodes of major eruptions interspersed with periods of relatively less intense eruptions. [...]"

Source: Geochimica et Cosmochimica Acta
Authors: Daniel L. Sullivan et al.
DOI: 10.1016/j.gca.2020.04.002

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Is deoxygenation detectable before warming in the thermocline?

Abstract.

"Anthropogenic greenhouse gas emissions cause ocean warming and oxygen depletion, with adverse impacts on marine organisms and ecosystems. Warming is one of the main indicators of anthropogenic climate change, but, in the thermocline, changes in oxygen and other biogeochemical tracers may emerge from the bounds of natural variability prior to warming. Here, we assess the time of emergence (ToE) of anthropogenic change in thermocline temperature and thermocline oxygen within an ensemble of Earth system model simulations from the fifth phase of the Coupled Model Intercomparison Project. [...]"

Source: Biogeosciences
Authors: Angélique Hameau et al.
DOI: 10.5194/bg-17-1877-2020

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The simulated biological response to Southern Ocean eddies via biological rate modification and physical transport

Abstract.

"We examine the structure and drivers of anomalous phytoplankton biomass in Southern Ocean eddies tracked in a global, multi‐year, eddy‐resolving, 3‐D ocean simulation of the Community Earth System Model. We examine how simulated anticyclones and cyclones differentially modify phytoplankton biomass concentrations, growth rates, and physical transport. [...]"

Source: Global Biogeochemical Cycles
Authors: Tyler Rohr et al.
DOI: 10.1029/2019GB006385

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The coupling of Phanerozoic continental weathering and marine phosphorus cycle

Abstract.

"Organic matter production and decomposition primarily modulate the atmospheric O2 and CO2 levels. The long term marine primary productivity is controlled by the terrestrial input of phosphorus (P), while the marine P cycle would also affect organic matter production. In the past 540 million years, the evolution of terrestrial system, e.g. colonization of continents by vascular land plants in late Paleozoic, would certainly affect terrestrial P input into the ocean, which in turn might have impacted the marine primary productivity and organic carbon burial. [...]"

Source: Scientific Reports
Authors: Ruimin Wang et al.
DOI: 10.1038/s41598-020-62816-z

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