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 m and 1200 m. Active denitrification in this OMZ is recorded by enhanced δ15N values in the sediments. Sediment cores show a δ15N increase from early to late Holocene which is contrary to the trend in other regions of water column denitrification. We calculated composite sea surface temperature (SST) and δ15N in time slices of 1000 years of the last 25 ka to better understand the reasons for the establishment of the Arabian Sea OMZ and its response to changes in the Asian monsoon system. [...]"
Source: Biogeosciences (under review)
Authors: Birgit Gaye et al.
Coastal hypoxia and sediment biogeochemistry
"The intensity, duration and frequency of coastal hypoxia (oxygen concentration <63 μM) are increasing due to human alteration of coastal ecosystems and changes in oceanographic conditions due to global warming. Here we provide a concise review of the consequences of coastal hypoxia for sediment biogeochemistry. Changes in bottom-water oxygen levels have consequences for early diagenetic pathways (more anaerobic at expense of aerobic pathways), the efficiency of re-oxidation of reduced metabolites and the nature, direction and magnitude of sediment-water exchange fluxes. Hypoxia may also lead to more organic matter accumulation and burial and the organic matter eventually buried is also of higher quality, i.e. less degraded. [...]"
Source: Biogeosciences (2009)
Authors: J. J. Middelburg and L. A. Levin
Massive Bloom Of Pickle-Shaped Sea Creatures Fills The Pacific
"Millions of tubular sea creatures called pyrosomes have taken over the Pacific Ocean in an unprecedented bloom that has scientists baffled.
These bumpy, translucent organisms look like sea cucumbers that range in size from six inches to more than two feet long. But they’re actually made up of hundreds of tiny animals knit together with tissue into a filter-feeding cylinder. [...]
No one knows what the effects of the bloom will be, but scientists worry that if all the creatures die off at once they could sink to the seafloor and suck up all the oxygen as they’re decomposing, creating a dead zone for marine life."
Ecological Energetic Perspectives on Responses of Nitrogen-Transforming Chemolithoautotrophic Microbiota to Changes in the Marine Environment
"Transformation and mobilization of bioessential elements in the biosphere, lithosphere, atmosphere and hydrosphere constitute the Earth's biogeochemical cycles, which are driven mainly by microorganisms through their energy and material metabolic processes. Without microbial energy harvesting from sources of light and inorganic chemical bonds for autotrophic fixation of inorganic carbon, there would not be sustainable ecosystems in the vast ocean. Although ecological energetics (eco-energetics) has been emphasized as a core aspect of ecosystem analyses and microorganisms largely control the flow of matter and energy in marine ecosystems, marine microbial communities are rarely studied from the eco-energetic perspective. [...]"
Source: Frontiers in Microbiology
Authors: Hongyue Dang and Chen-Tung A. Chen
Reminder: SFB 754 International Conference
The distribution of oxygen in the ocean is controlled by physical, biogeochemical and biological processes. Both the supply and consumption of oxygen are sensitive to climate change in ways that are not fully understood.
Recent observations suggest that the oxygen content of the ocean is declining (ocean deoxygenation) and that oxygen minimum zones and coastal hypoxia sites are expanding with tremendous effects on the ocean’s ecosystems and living organisms.
This conference will:
- focus on the past, present and future state of oxygen in the ocean on global, regional and local scales
- nalyse mechanisms and feedbacks critical to identify natural and anthropogenic causes of oxygen variability
- determine impacts on biogeochemical cycles and ecosystems
The call for submission opens December 2017.
NOAA, USGS and partners predict third largest Gulf of Mexico summer ‘dead zone’ ever
"Larger-than-average low and no oxygen area may affect the region’s shrimp fisheries
Federal scientists forecast that this summer’s Gulf of Mexico dead zone – an area of low to no oxygen that can kill fish and other marine life – will be approximately 8,185 square miles, or about the size of New Jersey.
This would be the third largest dead zone recorded since monitoring began 32 years ago – the average Gulf dead zone since then has been 5,309 square miles.
The Gulf’s hypoxic or low-oxygen zones are caused by excess nutrient pollution, primarily from human activities such as agriculture and wastewater treatment. The excess nutrients stimulate an overgrowth of algae, which then sinks and decomposes in the water. The resulting low oxygen levels are insufficient to support most marine life and habitats in near-bottom waters, threatening the Gulf’s fisheries. [...]"
Source: National Oceanic and Atmospheric Administration (NOAA)
Community composition of nitrous oxide consuming bacteria in the oxygen minimum zone of the Eastern Tropical South Pacific
"The ozone-depleting and greenhouse gas, nitrous oxide (N2O), is mainly consumed by the microbially mediated anaerobic process, denitrification. N2O consumption is the last step in canonical denitrification, and is also the least O2 tolerant step. Community composition of total and active N2O consuming bacteria was analyzed based on total (DNA) and transcriptionally active (RNA) nitrous oxide reductase (nosZ) genes using a functional gene microarray. The total and active nosZ communities were dominated by a limited number of nosZ archetypes, affiliated with bacteria from marine, soil and marsh environments. [...]"
Source: Frontiers in Microbiology
Authors: Xin Sun, Amal Jayakumar and Bess B. Ward
Sensitivity of Future Ocean Acidification to Carbon Climate Feedbacks
"Carbon-climate feedbacks have the potential to significantly impact the future climate by altering atmospheric CO2 concentrations (Zaehle et al., 2010). By modifying the future atmospheric CO2 concentrations, the carbon-climate feedbacks will also influence the future trajectory for ocean acidification. Here, we use the CO2 emissions scenarios from 4 Representative Concentration Pathways (RCPs) with an Earth System Model to project the future trajectories of ocean acidification with the inclusion of carbon-climate feedbacks. [...]"
Source: Biogeosciences (under review)
Authors: Richard J. Matear and Andrew Lenton
NOAA, USGS and partners predict larger summer ‘dead zone’ for the Chesapeake Bay
"Scientists expect this year’s summer Chesapeake Bay hypoxic or “dead zone” — an area of low to no oxygen that can kill fish and aquatic life — will be larger than average, approximately 1.89 cubic miles, or nearly the volume of 3.2 million Olympic-size swimming pools.
Measurements for the Bay’s dead zone go back to 1950, and the 30-year mean maximum dead zone volume is 1.74 cubic miles. [...]"
Source: U.S. Geological Survey
Stormy waters: the salmon farmer trying to limit fishing and save the ocean
In the 1980s, protests over the proposed Franklin River hydroelectric dam threw the Apple Isle’s conservation plight onto the national stage. This time, it is the state’s salmon farming industry that is under a cloud. The relatively young industry is worth over $700m a year and now outpaces all other farming activities on the island but environmental campaigners are worried about its impact on the region’s pristine waters. [...]"
Source: The Guardian