Biogeochemical role of subsurface coherent eddies in the ocean: Tracer cannonballs, hypoxic storms, and microbial stewpots?


"Subsurface coherent eddies are well-known features of ocean circulation, but the sparsity of observations prevents an assessment of their importance for biogeochemistry. Here, we use a global eddying (0.1° ) ocean-biogeochemical model to carry out a census of subsurface coherent eddies originating from eastern boundary upwelling systems (EBUS), and quantify their biogeochemical effects as they propagate westward into the subtropical gyres.  [...]"

Source: Global Biogeochemical Cycles
Authors: Ivy Frenge et al.
DOI: 10.1002/2017GB005743

Glacial–interglacial changes and Holocene variations in Arabian Sea denitrification


"At present, the Arabian Sea has a permanent oxygen minimum zone (OMZ) at water depths between about 100 and 1200 m. Active denitrification in the upper part of the OMZ is recorded by enhanced δ15N values in the sediments. Sediment cores show a δ15N increase during the middle and late Holocene, which is contrary to the trend in the other two regions of water column denitrification in the eastern tropical North and South Pacific.  [...]"

Source: Biogeosciences
Authors: Birgit Gaye et al.
DOI: 10.5194/bg-15-507-2018

Read the full article here.

New measurement technology helps to determine NO concentrations in the ocean

"Nitrogen monoxide (NO) belongs to the group of nitrogen oxides which are infamous as toxic emissions in urban agglomerations. But NO is also produced in nature and plays a role in the nitrogen cycle. However, from earth's largest ecosystem, the ocean, we have hardly any NO measurements."

Source: Science Daily

Read the full article here.

Nitric oxide (NO) in the oxygen minimum zone off Peru


"Nitric oxide (NO) is a short-lived compound of the marine nitrogen cycle. However, measurements of NO in seawater are analytically challenging and our knowledge about its oceanic distribution is, therefore, rudimentary. NO was measured in the oxygen minimum zone (OMZ) of the eastern tropical South Pacific Ocean (ETSP) off Peru during R/V Meteor cruise M93 in February/March 2013. [...]"

Source: Deep Sea Research Part II: Topical Studies in Oceanography
Authors: Hannah E. Lutterbeck et al.
DOI: 10.1016/j.dsr2.2017.12.023

Read the full article here.

Insights into the metabolic functioning of a multipartner ciliate symbiosis from oxygen-depleted sediments


"Symbioses between anaerobic or microaerophilic protists and prokaryotes are common in anoxic and oxygen-depleted habitats ranging from marine sediments to gastrointestinal tracts. Nevertheless, little is known about the mechanisms of metabolic interaction between partners. In these putatively syntrophic associations, consumption of fermentative end products (e.g., hydrogen) by the prokaryotic symbionts is thought to facilitate protistan anaerobic metabolism.  [...]"

Source: Molecular Ecology
Authors: R. A. Beinart et al.
DOI: 10.1111/mec.14465

Read the full article here.

Mn∕Ca intra- and inter-test variability in the benthic foraminifer Ammonia tepida


"The adaptation of some benthic foraminiferal species to low-oxygen conditions provides the prospect of using the chemical composition of their tests as proxies for bottom water oxygenation. Manganese may be particularly suitable as such a geochemical proxy because this redox element is soluble in reduced form (Mn2+) and hence can be incorporated into benthic foraminiferal tests under low-oxygen conditions. [...]"

Source: Biogeosciences
Authors: Jassin Petersen et al.
DOI: 10.5194/bg-15-331-2018

Read the full article here.

Ocean Deoxygenation – Another Global Challenge

"The ocean is facing unprecedented pressures that are causing massive ecosystem and nutrient cycle disruption the result of industrial-scale depletion of ocean wildlife and destabilization of steady-state ecosystems. This occurs not only on the seafloor by trawling, dredging, drilling, and mining but also in the water column with nets, long lines, fish aggregating devices and other techniques; methods introduced in recent decades to extract with unprecedented speed and scale from ecosystems hundreds of millions of years in the making.  [...]"

Source: GIS and Science
Author: Matt Artz

Read the full article here.


Tropical Atlantic climate and ecosystem regime shifts during the Paleocene–Eocene Thermal Maximum


"The Paleocene–Eocene Thermal Maximum (PETM, 56 Ma) was a phase of rapid global warming associated with massive carbon input into the ocean–atmosphere system from a C-depleted reservoir. Many midlatitude and high-latitude sections have been studied and document changes in salinity, hydrology and sedimentation, deoxygenation, biotic overturning, and migrations, but detailed records from tropical regions are lacking. [...]"

Source: Climate of the Past
Authors: Joost Frieling et al.
DOI: 10.5194/cp-14-39-2018

Read the full article here.

Oxygen loss strains marine ecosystems

A new review highlights the impact of declining oxygen levels in the open ocean and coastal waters due to increasing temperatures and nutrient discharge.


"Half of the world’s oxygen originates from the ocean. Yet, worldwide, the amount of open ocean without any oxygen has quadrupled over the past 50 years. Oxygen-minimum zones have expanded by several million square kilometres, increasing by more than 10-fold since 1950.  [...]"

Source: nature Middle East
Author: Lakshini Mendis
DOI: 10.1038/nmiddleeast.2018.2

Read the full article here.

Intensification and deepening of the Arabian Sea oxygen minimum zone in response to increase in Indian monsoon wind intensity


"The decline in oxygen supply to the ocean associated with global warming is expected to expand oxygen minimum zones (OMZs). This global trend can be attenuated or amplified by regional processes. In the Arabian Sea, the world's thickest OMZ is highly vulnerable to changes in the Indian monsoon wind. Evidence from paleo-records and future climate projections indicates strong variations of the Indian monsoon wind intensity over climatic timescales. [...]"

Source: Biogeosciences
Authors: Zouhair Lachkar, Marina Lévy, and Shafer Smith
DOI: 10.5194/bg-15-159-2018

Read the full article here.

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