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How fast are the oceans warming?

Abstract.

"Climate change from human activities mainly results from the energy imbalance in Earth's climate system caused by rising concentrations of heat-trapping gases. About 93% of the energy imbalance accumulates in the ocean as increased ocean heat content (OHC). The ocean record of this imbalance is much less affected by internal variability and is thus better suited for detecting and attributing human influences than more commonly used surface temperature records. Recent observation-based estimates show rapid warming of Earth's oceans over the past few decades (see the figure). [...]"

Source: Science
Authors: Lijing Cheng et al
DOI: 10.1126/science.aav7619

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Deglacial to Holocene Ocean Temperatures in the Humboldt Current System as Indicated by Alkenone Paleothermometry

Abstract.

"The response of the Humboldt Current System to future global warming is uncertain. Here we reconstruct alkenone‐derived near‐surface temperatures from multiple cores along the Peruvian coast to infer the driving mechanisms of upwelling changes for the last 20 kyr. Our records show a deglacial warming consistent with Antarctic ice‐core temperatures and a Mid‐Holocene cooling, which, in combination with other paleoceanographic records, suggest a strengthening of upwelling conditions. [...]"

Source: Geophysical Research Letters
Authors: Renato Salvatteci et al.
DOI: 10.1029/2018GL080634

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Ocean deoxygenation and zooplankton: Very small oxygen differences matter

Abstract.

"Oxygen minimum zones (OMZs), large midwater regions of very low oxygen, are expected to expand as a result of climate change. While oxygen is known to be important in structuring midwater ecosystems, a precise and mechanistic understanding of the effects of oxygen on zooplankton is lacking. Zooplankton are important components of midwater food webs and biogeochemical cycles. Here, we show that, in the eastern tropical North Pacific OMZ, previously undescribed submesoscale oxygen variability has a direct effect on the distribution of many major zooplankton groups. Despite extraordinary hypoxia tolerance, many zooplankton live near their physiological limits and respond to slight (≤1%) changes in oxygen. [...]"

Source: Science Advances
Authors: K. F. Wishner et al.
DOI: 10.1126/sciadv.aau5180

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Temperature-dependent hypoxia explains biogeography and severity of end-Permian marine mass extinction

Abstract.

"Climate change triggered by volcanic greenhouse gases is hypothesized to have caused the largest mass extinction in Earth’s history at the end of the Permian Period (~252 million years ago). Geochemical evidence provides strong support for rapid global warming and accompanying ocean oxygen (O2) loss, but a quantitative link among climate, species’ traits, and extinction is lacking. To test whether warming and O2 loss can mechanistically account for the marine mass extinction, we combined climate model simulations with an established ecophysiological framework to predict the biogeographic patterns and severity of extinction. Those predictions were confirmed by a spatially explicit analysis of the marine fossil record. [...]"

Source: Science
Authors: Justin L. Penn et al.
DOI: 10.1126/science.aat1327

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Distribution of Meiofauna in Bathyal Sediments Influenced by the Oxygen Minimum Zone Off Costa Rica

Abstract.

"Ocean deoxygenation has become a topic of increasing concern because of its potential impacts on marine ecosystems, including oxygen minimum zone (OMZ) expansion and subsequent benthic effects. We investigated the influence of oxygen concentration and organic matter (OM) availability on metazoan meiofauna within and below an OMZ in bathyal sediments off Costa Rica, testing the hypothesis that oxygen and OM levels are reflected in meiofaunal community structures and distribution. Mean total densities in our sampling cores (400–1800 m water depth) were highest with 3688 ind. 10 cm−2 at the OMZ core at 400 m water depth, decreasing rapidly downslope. [...]"

Source: Frontiers in Marine Science
Authors: Carlos Neira et al.
DOI: 10.3389/fmars.2018.00448

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Finding forced trends in oceanic oxygen

Abstract.

"Anthropogenically forced trends in oceanic dissolved oxygen are evaluated in Earth system models in the context of natural variability. A large ensemble of a single Earth system model is used to clearly identify the forced component of change in interior oxygen distributions and to evaluate the magnitude of this signal relative to noise generated by internal climate variability. The time of emergence of forced trends is quantified on the basis of anomalies in oxygen concentrations and trends. [...]"

Source: Global Biogeochemical Cycles
Authors: Matthew C. Long, Curtis Deutsch and Taka Ito
DOI: 10.1002/2015GB005310 

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Pacific Decadal Oscillation and recent oxygen decline in the eastern tropical Pacific Ocean

Abstract.

"The impact of the positive and negative phases of the Pacific Decadal Oscillation (PDO) on the extension of the poorly oxygenated regions of the eastern Pacific Ocean was assessed using a coupled ocean circulation–biogeochemical model. We show that during a “typical” PDO-positive phase the volume of the suboxic regions expands by 7 % over 50 years due to a slowdown of the large-scale circulation related to the decrease in the intensity of the trade winds. Changes in oxygen levels are mostly controlled by advective processes between 10∘ N and 10∘ S, whereas diffusive processes are dominant poleward of 10∘: in a “typical” PDO-positive phase the sluggish equatorial current system provides less oxygen to the eastern equatorial part of the basin while the oxygen transport by diffusive processes significantly decreases south of 10∘ S. [...]"

Source: Biogeosciences
Authors: Olaf Duteil, Andreas Oschlies, and Claus W. Böning
DOI: 10.5194/bg-15-7111-2018

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The case of the missing oxygen: Foster Scholar Kate Hewett studies hypoxia in national marine sanctuaries

"Not every marine scientist has the same origin story. Some are instantly enthralled by the ocean and its many inhabitants at a ripe young age. For others, a lightbulb goes off while sitting in an undergraduate class. Dr. Nancy Foster Scholar Kate Hewett grew up on the islands of Micronesia, but did not consider a career in marine sciences until graduate school. While working as an environmental engineer in Boston, Massachusetts, she decided to go back to school to develop a deeper understanding of the environmental problems she encountered at work. In her classes, the complicated physics associated with coastal zones pulled at Hewett’s engineering heartstrings. [...]"

Source: NOAA

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Tool to Capture Marine Biological Activity Gets Coastal Upgrade

"Upwelling hinders an efficient method to estimate a key measure of biological productivity in coastal waters, but accounting for surface temperatures could boost accuracy.

 

Although coastal waters make up only about 10% of the surface area of the ocean, they harbor most of its life. Measuring biological activity in these regions can reveal their impact on fisheries, low-oxygen dead zones, and the global carbon cycle, but coastal zones remain understudied. Now new research by Teeter et al. suggests how to improve the accuracy of a method that uses oxygen and argon measurements to quickly estimate marine biological activity. [...]"

Source: EOS

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Thallium isotopes reveal protracted anoxia during the Toarcian (Early Jurassic) associated with volcanism, carbon burial, and mass extinction

Abstract.

"For this study, we generated thallium (Tl) isotope records from two anoxic basins to track the earliest changes in global bottom water oxygen contents over the Toarcian Oceanic Anoxic Event (T-OAE; ∼183 Ma) of the Early Jurassic. The T-OAE, like other Mesozoic OAEs, has been interpreted as an expansion of marine oxygen depletion based on indirect methods such as organic-rich facies, carbon isotope excursions, and biological turnover. Our Tl isotope data, however, reveal explicit evidence for earlier global marine deoxygenation of ocean water, some 600 ka before the classically defined T-OAE. "

Source: PNAS
Authors: Theodore R. Them et al.
DOI: 10.1073/pnas.1803478115

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