scholarly journals Iron colloids dominate sedimentary supply to the ocean interior

2021 ◽  
Vol 118 (13) ◽  
pp. e2016078118
Author(s):  
William B. Homoky ◽  
Tim M. Conway ◽  
Seth G. John ◽  
Daniela König ◽  
FeiFei Deng ◽  
...  
Keyword(s):  
Continental Margins ◽  
Iron Isotopes ◽  
Low Oxygen ◽  
Ocean Carbon Cycle ◽  
Dissolved Iron ◽  
Iron Supply ◽  
Ocean Sediment ◽  
Sediment Porewaters ◽  
Ocean Models ◽  
Ocean Carbon

Dissolution of marine sediment is a key source of dissolved iron (Fe) that regulates the ocean carbon cycle. Currently, our prevailing understanding, encapsulated in ocean models, focuses on low-oxygen reductive supply mechanisms and neglects the emerging evidence from iron isotopes in seawater and sediment porewaters for additional nonreductive dissolution processes. Here, we combine measurements of Fe colloids and dissolved δ56Fe in shallow porewaters spanning the full depth of the South Atlantic Ocean to demonstrate that it is lithogenic colloid production that fuels sedimentary iron supply away from low-oxygen systems. Iron colloids are ubiquitous in these oxic ocean sediment porewaters and account for the lithogenic isotope signature of dissolved Fe (δ56Fe = +0.07 ± 0.07‰) within and between ocean basins. Isotope model experiments demonstrate that only lithogenic weathering in both oxic and nitrogenous zones, rather than precipitation or ligand complexation of reduced Fe species, can account for the production of these porewater Fe colloids. The broader covariance between colloidal Fe and organic carbon (OC) abundance suggests that sorption of OC may control the nanoscale stability of Fe minerals by inhibiting the loss of Fe(oxyhydr)oxides to more crystalline minerals in the sediment. Oxic ocean sediments can therefore generate a large exchangeable reservoir of organo-mineral Fe colloids at the sediment water interface (a “rusty source”) that dominates the benthic supply of dissolved Fe to the ocean interior, alongside reductive supply pathways from shallower continental margins.

scholarly journals Changes in the Arctic Ocean carbon cycle with diminishing ice cover

2020 ◽  
Author(s):  
Michael D. DeGrandpre ◽  
Wiley Evans ◽  
Mary-Louise Timmermans ◽  
Richard A. Krishfield ◽  
William J Williams ◽  
...  
Keyword(s):  
Carbon Cycle ◽  
Arctic Ocean ◽  
Ice Cover ◽  
The Arctic ◽  
Ocean Carbon Cycle ◽  
The Arctic Ocean ◽  
Ocean Carbon

scholarly journals Imprint of a dissolved cobalt basaltic source on the Kerguelen Plateau

2012 ◽  
Vol 9 (12) ◽  
pp. 5279-5290 ◽  
Author(s):  
J. Bown ◽  
M. Boye ◽  
P. Laan ◽  
A. R. Bowie ◽  
Y.-H. Park ◽  
...  
Keyword(s):  
Surface Waters ◽  
External Input ◽  
Eastern Slope ◽  
Kerguelen Plateau ◽  
Dissolved Iron ◽  
Deep Waters ◽  
Iron Supply ◽  
Natural Iron ◽  
Shelf Sediments ◽  
Lateral Advection

Abstract. Processes of cobalt (Co) entrainment from shelf sediments over the Kerguelen Plateau were studied during the KEOPS (Kerguelen Ocean Plateau compared Study) in order to explain the exceptionally high dissolved cobalt concentrations that have been measured in the surface waters above the Kerguelen Plateau, and in intermediate and deep waters above its eastern slope. Lateral advection and dissolution of Co contained in basalt sediments around Heard Island, a main source of lithogenic Co in the study area, were shown to imprint the process of surface enrichment over the plateau. Dissolved Co enrichment was strongest at the intercept of the eastern slope with intermediate and deep waters, probably due to more efficient mobilisation of the sediments in the slope current, in addition to advection of Co-enriched and low-oxygenated ocean water masses. In surface waters, the strong sedimentary Co inputs were estimated to be much higher than biological Co uptake in phytoplankton blooms, underlining the potential use of dissolved cobalt as tracer of the natural iron fertilization above the Kerguelen Plateau. Based on a simple steady-state balance equation of the external input of dissolved iron over the plateau, the fertilization of iron inferred by using dissolved Co as a tracer of basalt sources is estimated to be 28 × 102 ± 21 × 102 t yr−1 in surface waters of the Kerguelen Plateau. This estimate is consistent with preceding ones (Zhang et al., 2008; Chever et al., 2010), and the calculated iron supply matches with the phytoplankton demand (Sarthou et al., 2008).

scholarly journals A fishy tale: A missing part of the inorganic ocean carbon cycle

2011 ◽  
Vol 33 (3) ◽  
pp. 30-34
Author(s):  
Rod W. Wilson ◽  
Erin E. Reardon ◽  
Christopher T. Perry
Keyword(s):  
Carbon Cycle ◽  
Ocean Acidification ◽  
Fossil Fuels ◽  
Sea Water ◽  
Atmospheric Co2 ◽  
Co2 Production ◽  
Ph Change ◽  
Ocean Carbon Cycle ◽  
Sea Levels ◽  
Ocean Carbon

Human activities, such as burning fossil fuels, are playing an important role in the rising levels of carbon dioxide (CO2) in the Earth's atmosphere1. The oceans may store a large portion of CO2 that we are releasing into the atmosphere, with up to 40% already taken up by the oceans. Although this absorption helps to offset some of the greenhouse effect of atmospheric CO2, it also contributes to ocean acidification, or a fall in the pH of sea water. The historical global mean pH of oceanic sea water is about 8.2, and this has already declined by 0.1 pH units (a 30% increase in H+ concentration) and is predicted to reach pH ~7.7 by the end of the century if current rates of fossil fuel use continue, leading to an atmospheric CO2 level of 800 p.p.m.1,2. Even this extreme potential fall in pH would still leave seawater above the neutral point (pH 7.0), so technically it is more accurate to say that the ocean is becoming less alkaline, rather than truly acidic (i.e. below pH 7.0). However, the magnitude is perhaps less important than the speed of pH change which is occurring faster than at any time during the previous 20 million years. Over this time, the average ocean pH has probably never fallen below pH 8.02,3. It is only during the last decade that the importance of ocean acidification has come to the forefront of concerns for scientists1,2. Consequences of these changes in global CO2 production are predicted to include elevated global temperatures, rising sea levels, more unpredictable and extreme weather patterns, and shifts in ecosystems1. In order to more fully understand the implications of ocean acidification, teams of researchers, including fisheries scientists, physiologists, geologists, oceanographers, chemists and climate modellers, are working to refine current understanding of the ocean carbon cycle.

Coccolith chemistry reveals secular variations in the global ocean carbon cycle?

2007 ◽  
Vol 253 (1-2) ◽  
pp. 83-95 ◽  
Author(s):  
R.E.M. Rickaby ◽  
E. Bard ◽  
C. Sonzogni ◽  
F. Rostek ◽  
L. Beaufort ◽  
...  
Keyword(s):  
Carbon Cycle ◽  
Global Ocean ◽  
Ocean Carbon Cycle ◽  
Secular Variations ◽  
Ocean Carbon

scholarly journals Ocean Carbon Cycle Feedbacks Under Negative Emissions

2018 ◽  
Vol 45 (10) ◽  
pp. 5062-5070 ◽  
Author(s):  
Jörg Schwinger ◽  
Jerry Tjiputra
Keyword(s):  
Carbon Cycle ◽  
Ocean Carbon Cycle ◽  
Negative Emissions ◽  
Ocean Carbon

scholarly journals Temperature effects on carbon-specific respiration rate and sinking velocity of diatom aggregates – potential implications for deep ocean export processes

2013 ◽  
Vol 10 (6) ◽  
pp. 4073-4085 ◽  
Author(s):  
M. H. Iversen ◽  
H. Ploug
Keyword(s):  
Respiration Rate ◽  
Deep Ocean ◽  
Sediment Traps ◽  
Average Particle ◽  
Data Set ◽  
Direct Measurements ◽  
Ocean Sediment ◽  
Influence Of Temperature On ◽  
Ocean Carbon ◽  
Sinking Velocity

Abstract. Most deep ocean carbon flux profiles show low and almost constant fluxes of particulate organic carbon (POC) in the deep ocean. However, the reason for the non-changing POC fluxes at depths is unknown. This study presents direct measurements of formation, degradation, and sinking velocity of diatom aggregates from laboratory studies performed at 15 °C and 4 °C during a three-week experiment. The average carbon-specific respiration rate during the experiment was 0.12 ± 0.03 at 15 °C, and decreased 3.5-fold when the temperature was lowered to 4 °C. No direct influence of temperature on aggregate sinking speed was observed. Using the remineralisation rate measured at 4 °C and an average particle sinking speed of 150 m d−1, calculated carbon fluxes were similar to those collected in deep ocean sediment traps from a global data set, indicating that temperature plays a major role for deep ocean fluxes of POC.

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