Intense oceanic uptake of oxygen during 2014–2015 winter convection in the Labrador Sea
"Measurements of near-surface oxygen (O2) concentrations and mixed layer depth from the K1 mooring in the central Labrador Sea are used to calculate the change in column-integrated (0–1700 m) O2 content over the deep convection winter 2014/2015. During the mixed layer deepening period, November 2014 to April 2015, the oxygen content increased by 24.3 ± 3.4 mol m−2, 40% higher than previous results from winters with weaker convection. By estimating the contribution of respiration and lateral transport on the oxygen budget, the cumulative air-sea gas exchange is derived. [...]"
Source: Geophysical Research Letters
Authors: Jannes Koelling, Douglas W. R. Wallace, Uwe Send, Johannes Karstensen
Taking a deep breath? Scientists measure unusually high oxygen uptake in the Labrador Sea
"The Labrador Sea in the North Atlantic is one of the few areas in the world ocean where cold, saline seawater sinks to large depths and forms deep water. This convection process also transports oxygen into the deep sea. A team of scientists from Scripps Institution of Oceanography (San Diego, California), Dalhousie University (Halifax, Canada) and GEOMAR Helmholtz Centre for Ocean Research Kiel have now published the analysis of data obtained from the mooring K1 in the international scientific journal Geophysical Research Letters. [...]"
Role of zooplankton in determining the efficiency of the biological carbon pump
"The efficiency of the ocean's biological carbon pump (BCPeff – here the product of particle export and transfer efficiencies) plays a key role in the air–sea partitioning of CO2. Despite its importance in the global carbon cycle, the biological processes that control BCPeff are poorly known. We investigate the potential role that zooplankton play in the biological carbon pump using both in situ observations and model output. Observed and modelled estimates of fast, slow, and total sinking fluxes are presented from three oceanic sites: the Atlantic sector of the Southern Ocean, the temperate North Atlantic, and the equatorial Pacific oxygen minimum zone (OMZ)."
Authors: Emma L. Cavan et al.
Widespread seawater circulation in 18–22 Ma oceanic crust: Impact on heat flow and sediment geochemistry
"On the basis of heat-flow measurements, seismic mapping, and sediment pore-water analysis, we demonstrate widespread and efficient ventilation of the 18–22 Ma oceanic crust of the northeast equatorial Pacific Ocean. Recharge and discharge appear to be associated with basement outcrops, including seamounts and north-south–trending faults, along which sediment cover thins out and volcanic rocks are exposed. Low-temperature hydrothermal circulation through the volcanic crust leads to the reduction of heat flow through overlying sediments, with measured heat-flow values that are well below those expected from conductive cooling curves for lithosphere of this age. [...]"
Authors: Thomas Kuhn et al.
The onset of widespread marine red beds and the evolution of ferruginous oceans
"Banded iron formations were a prevalent feature of marine sedimentation ~3.8–1.8 billion years ago and they provide key evidence for ferruginous oceans. The disappearance of banded iron formations at ~1.8 billion years ago was traditionally taken as evidence for the demise of ferruginous oceans, but recent geochemical studies show that ferruginous conditions persisted throughout the later Precambrian, and were even a feature of Phanerozoic ocean anoxic events. [...]"
Source: Nature Communications
Authors: Haijun Song et al.
Acid zone in Chesapeake Bay identified
"Zone of water 30 feet below surface is increasing in acidity, threatening shellfish.
A research team, led by University of Delaware professor Wei-Jun Cai, has identified a zone of water that is increasing in acidity in the Chesapeake Bay.
The team analyzed little studied factors that play a role in ocean acidification (OA)--changes in water chemistry that threaten the ability of shellfish such as oysters, clams and scallops to create and maintain their shells, among other impacts."
Redox reactions and weak buffering capacity lead to acidification in the Chesapeake Bay
"The combined effects of anthropogenic and biological CO2 inputs may lead to more rapid acidification in coastal waters compared to the open ocean. It is less clear, however, how redox reactions would contribute to acidification. Here we report estuarine acidification dynamics based on oxygen, hydrogen sulfide (H2S), pH, dissolved inorganic carbon and total alkalinity data from the Chesapeake Bay, where anthropogenic nutrient inputs have led to eutrophication, hypoxia and anoxia, and low pH. [...]"
Source: Nature Communications
Authors: Wei-Jun Cai
The influence of variable slope-water characteristics on dissolved oxygen levels in the northern California Current System
"Observations have suggested a trend of decreasing dissolved oxygen (DO) and increasing spiciness in summertime mid-depth slope waters and bottom shelf waters along the United States west coast over the past 50 years, but they have also demonstrated a large amount of interannual and decadal variability. Shelf bottom water and slope water properties can be influenced by both local and remote effects, including changes in circulation or changes in the characteristics of the source waters supplying the region. [...]"
Authors: Scott M. Durski et al.
Uranium isotope evidence for an expansion of marine anoxia during the end-Triassic extinction
"The end-Triassic extinction coincided with an increase in marine black shale deposition and biomarkers for photic zone euxinia, suggesting that anoxia played a role in suppressing marine biodiversity. However, global changes in ocean anoxia are difficult to quantify using proxies for local anoxia. Uranium isotopes (δ238U) in CaCO3 sediments deposited under locally well-oxygenated bottom waters can passively track seawater δ238U, which is sensitive to the global areal extent of seafloor anoxia due to preferential reduction of 238U(VI) relative to 235U(VI) in anoxic marine sediments. [...]"
Source: Geochemistry, Geophysics, Geosystems
Authors: Adam B. Jost et al.
N2 production by the anammox reaction in the anoxic water column of Golfo Dulce, Costa Rica
"In oxygen-depleted zones of the open ocean, and in anoxic basins and fjords, denitrification (the bacterial reduction of nitrate to give N2) is recognized as the only significant process converting fixed nitrogen to gaseous N2. Primary production in the oceans is often limited by the availability of fixed nitrogen such as ammonium or nitrate, and nitrogen-removal processes consequently affect both ecosystem function and global biogeochemical cycles. [...]"
Source: Nature (2003)
Authors: Tage Dalsgaard et al.