Biodiversity response to natural gradients of multiple stressors on continental margins
"Sharp increases in atmospheric CO2 are resulting in ocean warming, acidification and deoxygenation that threaten marine organisms on continental margins and their ecological functions and resulting ecosystem services. The relative influence of these stressors on biodiversity remains unclear, as well as the threshold levels for change and when secondary stressors become important. [...]"
Source: Proceedings of the Royal Society B
Authors: Erik A. Sperling, Christina A. Frieder, Lisa A. Levin
Meat industry blamed for largest-ever 'dead zone' in Gulf of Mexico
"The global meat industry, already implicated in driving global warming and deforestation, has now been blamed for fueling what is expected to be the worst “dead zone” on record in the Gulf of Mexico.
Toxins from manure and fertiliser pouring into waterways are exacerbating huge, harmful algal blooms that create oxygen-deprived stretches of the gulf, the Great Lakes and Chesapeake Bay, according to a new report by Mighty, an environmental group chaired by former congressman Henry Waxman. [...]"
Source: The Guardian
Gulf of Mexico ‘dead zone’ is the largest ever measured
"Scientists have determined this year’s Gulf of Mexico “dead zone,” an area of low oxygen that can kill fish and marine life, is 8,776 square miles, an area about the size of New Jersey. It is the largest measured since dead zone mapping began there in 1985."
Source: National Oceanic and Atmospheric Administration (NOAA)
Ensemble modeling informs hypoxia management in the northern Gulf of Mexico
"A large region of low-dissolved-oxygen bottom waters (hypoxia) forms nearly every summer in the northern Gulf of Mexico because of nutrient inputs from the Mississippi River Basin and water column stratification. Policymakers developed goals to reduce the area of hypoxic extent because of its ecological, economic, and commercial fisheries impacts. However, the goals remain elusive after 30 y of research and monitoring and 15 y of goal-setting and assessment because there has been little change in river nitrogen concentrations. [...]"
Source: Proceeding of the National Academy of Sciences of the United States of America (PNAS)
Authors: Donald Scavia et al.
Historical records of coastal eutrophication-induced hypoxia
"Under certain conditions, sediment cores from coastal settings subject to hypoxia can yield records of environmental changes over time scales ranging from decades to millennia, sometimes with a resolution of as little as a few years. A variety of biological and geochemical indicators (proxies) derived from such cores have been used to reconstruct the development of eutrophication and hypoxic conditions over time. [...]"
Authors: A. J. Gooday 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
Eutrophication-Driven Deoxygenation in the Coastal Ocean
"Human activities, especially increased nutrient loads that set in motion a cascading chain of events related to eutrophication, accelerate development of hypoxia (lower oxygen concentration) in many areas of the world’s coastal ocean. Climate changes and extreme weather events may modify hypoxia. Organismal and fisheries effects are at the heart of the coastal hypoxia issue, but more subtle regime shifts and trophic interactions are also cause for concern. The chemical milieu associated with declining dissolved oxygen concentrations affects the biogeochemical cycling of oxygen, carbon, nitrogen, phosphorus, silica, trace metals, and sulfide as observed in water column processes, shifts in sediment biogeochemistry, and increases in carbon, nitrogen, and sulfur, as well as shifts in their stable isotopes, in recently accumulated sediments."
Source: Oceanography Volume 27 (2014)
Authors: Nancy N. Rabalais et al.
An oceanographic, meteorological, and biological ‘perfect storm’ yields a massive fish kill
"Mass mortality events are ephemeral phenomena in marine ecosystems resulting from anthropogenically enhanced and natural processes. A fish kill in King Harbor, Redondo Beach, California, USA, in March 2011 killed ~1.54 × 105 kg of fish and garnered international attention as a marine system out of balance. Here, we present data collected prior to, during, and following the event that describe the oceanographic conditions preceding the event, spatial extent of hypoxia (dissolved oxygen < 1.4 ml l−1), and subsequent recovery of the harbor. In situ sensors within the harbor revealed rapid decreases in dissolved oxygen in surface waters from 7 to 9 March 2011, coincident with the mortality event on 8 March. [...]"
Source: Marine Eco Progress Series
Authors: Beth A. Stauffer et al.
Hypoxic induced decrease in oxygen consumption in cuttlefish (Sepia officinalis) is associated with minor increases in mantle octopine [...]
"The common cuttlefish (Sepia officinalis), a dominant species in the north-east Atlantic ocean and Mediterranean Sea, is potentially subject to hypoxic conditions due to eutrophication of coastal waters and intensive aquaculture. Here we initiate studies on the biochemical response to an anticipated level of hypoxia. Cuttlefish challenged for one hour at an oxygen level of 50% dissolved oxygen saturation showed a decrease in oxygen consumption of 37% associated with an 85% increase in ventilation rate. [...]"
Source: Frontiers in Marine Physiology
Authors: Juan C. Capaz et al.
Oregon Shelf Hypoxia Modeling
"Bottom hypoxia on the shelf in the Northeast Pacific is caused by different processes than coastal hypoxia related to riverine inputs. Hypoxia off the coast of Oregon is a naturally occurring process as opposed to the anthropogenically forced hypoxia found in many coastal environments (e.g., Gulf of Mexico shelf, Chesapeake Bay). Off Oregon, bottom hypoxia occurs in summers that have large upwelling-driven near-bottom transport of high nitrate, low dissolved oxygen (DO) waters onto the shelf. The combination of low DO and high nitrate provides initially low (but not hypoxic) DO conditions near the bottom, and nitrate fertilization of shelf surface waters, leading to substantial phytoplankton production. [...]"
Source: Modeling Coastal Hypoxia (pp 215-238)
Authors: Andrey O. Koch, Yvette H. Spitz, Harold P. Batchelder