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
Rising water temperatures endanger health of coastal ecosystems, study finds
"Increasing water temperatures are responsible for the accumulation of a chemical called nitrite in marine environments throughout the world, a symptom of broader changes in normal ocean biochemical pathways that could ultimately disrupt ocean food webs, according to new research from the University of Georgia. "
Temperature Decouples Ammonium and Nitrite Oxidation in Coastal Waters
"Nitrification is a two-step process linking the reduced and oxidized sides of the nitrogen cycle. These steps are typically tightly coupled with the primary intermediate, nitrite, rarely accumulating in coastal environments. Nitrite concentrations can exceed 10 μM during summer in estuarine waters adjacent to Sapelo Island, Georgia, U.S.A. Similar peaks at other locations have been attributed to decoupling of the two steps of nitrification by hypoxia; however, the waters around Sapelo Island are aerobic and well-mixed. Experiments examining the response to temperature shifts of a nitrifying assemblage composed of the same organisms found in the field indicate that ammonia- and nitrite-oxidation become uncoupled between 20 and 30 °C, leading to nitrite accumulation. [...]"
Source: Environmental Science & Technology
Authors: Sylvia C. Schaefer, James T. Hollibaugh
Decadal dynamics and predictability of oxygen and subsurface tracers in the California Current System
"The oxygen of the source waters that feed the upwelling in the California Current System show prominent multi-decadal fluctuations that are not significantly correlated with the dominant modes of Pacific climate variability. By combining observations and ocean reanalysis products between 1950-2010, we show that decadal changes in oxygen are linked to subsurface salinity variability and primarily controlled by ocean circulation dynamics. We find that subsurface anomalies in the core of the North Pacific Current propagate the oxygen signal downstream into the coastal upwelling system following the path of the mean gyre circulation with a timescale of 10-years. [...]"
Source: Geophysical Reasearch Letters
Authors: Mercedes Pozo Buil, Emanuele Di Lorenzo
Effects of low oxygen concentrations on aerobic methane oxidation in seasonally hypoxic coastal waters
"Coastal seas may account for more than 75 % of global oceanic methane emissions. There, methane is mainly produced microbially in anoxic sediments from which it can escape to the overlying water column. Aerobic methane oxidation (MOx) in the water column acts as a biological filter, reducing the amount of methane that eventually evades to the atmosphere. The efficiency of the MOx filter is potentially controlled by the availability of dissolved methane and oxygen, as well as temperature, salinity, and hydrographic dynamics, and all of these factors undergo strong temporal fluctuations in coastal ecosystems. [...]"
Source: Biogeosciences 14
Authors: Lea Steinle et al.
Tropical dead zones and mass mortalities on coral reefs
"Oxygen-starved coastal waters are rapidly increasing in prevalence worldwide. However, little is known about the impacts of these “dead zones” in tropical ecosystems or their potential threat to coral reefs. We document the deleterious effects of such an anoxic event on coral habitat and biodiversity, and show that the risk of dead-zone events to reefs worldwide likely has been seriously underestimated. Awareness of, and research on, reef hypoxia is needed to address the threat posed by dead zones to coral reefs."
Source: Proceedings of the National Academy of Sciences of the United Stated of America (PNAS)
Authors: Andrew H. Altieri et al.