Identifying oxygen minimum zone-type biogeochemical cycling in Earth history using inorganic geochemical proxies
"Because of anthropogenic global warming, the world ocean is currently losing oxygen. This trend called ocean deoxygenation is particularly pronounced in low-latitude upwelling-related oxygen minimum zones (OMZs). In these areas, the temperature-related oxygen drawdown is additionally modulated by biogeochemical feedback mechanisms between sedimentary iron (Fe) and phosphorus release, water column nitrogen cycling and primary productivity. Similar feedbacks were likely active during past periods of global warming and oceandeoxygenation. However, their integrated role in amplifying or mitigating climate change-driven ocean anoxia has not been evaluated in a systematic fashion. [...]"
Source: Earth-Science Reviews
Author: Florian Scholz
Modulation of the vertical particle transfer efficiency in the oxygen minimum zone off Peru
"The fate of the organic matter (OM) produced by marine life controls the major biogeochemical cycles of the Earth's system. The OM produced through photosynthesis is either preserved, exported towards sediments or degraded through remineralisation in the water column. The productive eastern boundary upwelling systems (EBUSs) associated with oxygen minimum zones (OMZs) would be expected to foster OM preservation due to low O2 conditions. But their intense and diverse microbial activity should enhance OM degradation. To investigate this contradiction, sediment traps were deployed near the oxycline and in the OMZ core on an instrumented moored line off Peru. [...]"
Authors: Marine Bretagnon et al.
Hydrochemical properties and chemocline of the Sansha Yongle Blue Hole in the South China Sea
"Blue holes can provide valuable information regarding paleoclimate, climate change, karst processes, marine ecology, and carbonate geochemistry. The Sansha Yongle Blue Hole, located on Yongle Atoll in the Paracel Islands in the South China Sea, is the deepest blue hole in the world. A comprehensive investigation of the blue hole was conducted to determine the hydrochemical properties and associated redox processes active in the water column. Results indicate the presence of two thermoclines, one at 13–20 m and a second at 70–150 m, dividing the water column into five stratified water layers. [...]"
Source: Science of the Total Environment
Authors: Linping Xie et al.
H2S events in the Peruvian oxygen minimum zone facilitate enhanced dissolved Fe concentrations
"Dissolved iron (DFe) concentrations in oxygen minimum zones (OMZs) of Eastern Boundary Upwelling Systems are enhanced as a result of high supply rates from anoxic sediments. However, pronounced variations in DFe concentrations in anoxic coastal waters of the Peruvian OMZ indicate that there are factors in addition to dissolved oxygen concentrations (O2) that control Fe cycling. [...]"
Source: Scientific Reports
Authors: Christian Schlosser et al.
Large-scale ocean deoxygenation during the Paleocene-Eocene Thermal Maximum
"The consequences of global warming for fisheries are not well understood, but the geological record demonstrates that carbon cycle perturbations are frequently associated with ocean deoxygenation. Of particular interest is the Paleocene-Eocene Thermal Maximum (PETM), where the carbon dioxide input into the atmosphere was similar to the IPCC RCP8.5 emission scenario. Here we present sulfur-isotope data that record a positive 1 per mil excursion during the PETM. Modeling suggests that large parts of the ocean must have become sulfidic. [...]"
Authors: Weiqi Yao, Adina Paytan, Ulrich G. Wortmann
Decomposing the effects of ocean environments on predator–prey body-size relationships in food webs
"Body-size relationships between predators and their prey are important in ecological studies because they reflect the structure and function of food webs. Inspired by studies on the impact of global warming on food webs, the effects of temperature on body-size relationships have been widely investigated; however, the impact of environmental factors on body-size relationships has not been fully evaluated because climate warming affects various ocean environments. Thus, here, we comprehensively investigated the effects of ocean environments and predator–prey body-size relationships by integrating a large-scale dataset of predator–prey body-size relationships in marine food webs with global oceanographic data. We showed that various oceanographic parameters influence prey size selection. [...]"
Source: Royal Society Open Science
Authors: Tomoya Dobashi, Midori Iida, Kazuhiro Takemoto
Acid coastal seas off US putting common fish species at risk
Scientists have recently discovered that marine creatures can be adversely affected by hypercapnia, a condition of too much dissolved CO2 in seawater (CO2 partial pressure, or pCO2). When this level rises above 1000 micro atmospheres (1000 μatm), some fish species suffer cognitive problems and disorientation, such as losing their way or even swimming towards predators. Surface ocean CO2 partial pressures tend to be around 400 μatm, so until now scientists have thought that hypercapnia was a problem which would only become apparent over time in subsurface waters. [...]"
Sedimentary molybdenum cycling in the aftermath of seawater inflow to the intermittently euxinic Gotland Deep, Central Baltic Sea
"Molybdenum (Mo) concentrations and isotope compositions in sediments and shalesare commonly used as proxies for anoxic and sulfidic (i.e., euxinic) conditions in the water column of paleo-marine systems. A basic assumption underlying this practice is that the proxy signal extracted from the geological record is controlled by long-term (order of decades to millennia) Mo scavenging in the euxinic water column rather than Mo deposition during brief episodes or events (order of weeks to months). [...]"
Source: Chemical Geology
Authors: Florian Scholz et al.
Autonomous biogeochemical floats detect significant carbon dioxide outgassing in the high‐latitude Southern Ocean
"Although the Southern Ocean is thought to account for a significant portion of the contemporary oceanic uptake of carbon dioxide (CO2), flux estimates in this region are based on sparse observations that are strongly biased towards summer. Here we present new estimates of Southern Ocean air‐sea CO2 fluxes calculated with measurements from biogeochemical profiling floats deployed by the Southern Ocean Carbon and Climate Observations and Modeling (SOCCOM) project during 2014‐2017. Compared to ship‐based CO2 flux estimates, the float‐based fluxes find significantly stronger outgassing in the zone around Antarctica where carbon‐rich deep waters upwell to the surface ocean. [...]"
Source: Geophysical Research Letters
Authors: Alison R. Gray et al.
Transport, properties, and life cycles of mesoscale eddies in the eastern tropical South Pacific
"The influence of mesoscale eddies on the flow field and the water masses, especially the oxygen distribution of the eastern tropical South Pacific, is investigated from a mooring, float, and satellite data set. Two anticyclonic (ACE1/2), one mode-water (MWE), and one cyclonic eddy (CE) are identified and followed in detail with satellite data on their westward transition with velocities of 3.2 to 6.0cms−1 from their generation region, the shelf of the Peruvian and Chilean upwelling regime, across the Stratus Ocean Reference Station (ORS; ∼ 20°S, 85°W) to their decaying region far west in the oligotrophic open ocean. [...]"
Source: Ocean Science
Authors: Rena Czeschel et al.
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