Archive for calcite

What really controls deep-seafloor calcite dissolution?

Posted by mmaheigan 
· Monday, December 16th, 2019 

On time scales of tens to millions of years, seawater acidity is primarily controlled by biogenic calcite (CaCO3) dissolution on the seafloor. Our quantitative understanding of future oceanic pH and carbonate system chemistry requires knowledge of what controls this dissolution. Past experiments on the dissolution rate of suspended calcite grains have consistently suggested a high-order, nonlinear dependence on undersaturation that is independent of fluid flow rate. This form of kinetics has been extensively adopted in models of deep-sea calcite dissolution and pH of benthic sediments. However, stirred-chamber and rotating-disc dissolution experiments have consistently demonstrated linear kinetics of dissolution and a strong dependence on fluid flow velocity. This experimental discrepancy surrounding the kinetic control of seafloor calcite dissolution precludes robust predictions of oceanic response to anthropogenic acidification.

In a recent study published in Geochimica et Cosmochimica Acta, authors have reconciled these divergent experimental results through an equation for the mass balance of the carbonate ion at the sediment-water interface (SWI), which equates the rate of production of that ion via dissolution and its diffusion in sediment porewaters to the transport across the diffusive sublayer (DBL) at the SWI. If the rate constant derived from suspended-grain experiments is inserted into this balance equation, the rate of carbonate ion supply to the SWI from the sediment (sediment-side control) is much greater in the oceans than the rate of transfer across the DBL (water-side control). Thus, calcite dissolution at the seafloor, while technically under mixed control, is strongly water-side dominated. Consequently, a model that neglects boundary-layer transport (sediment-side control alone) invariably predicts CaCO3-versus-depth profiles that are too shallow compared to available data (Figure 1). These new findings will inform future attempts to model the ocean’s response to acidification.

Figure 1: Plots of the calcite (CaCO3) content of deep-sea sediments as a function of oceanic depth. Left panel: data from the Northwestern Atlantic Ocean. Right panel: data from the Southwest Pacific Ocean. The blue line represents predicted CaCO3 content assuming no boundary-layer effects (pure sediment-side control). The red line is the prediction that includes both sediment and water effects (mixed control), and the green line is the prediction with pure water-side control. The agreement between the red and green lines signifies that calcite dissolution is essentially water-side controlled at the seafloor. These results are duplicated for all tested regions of the oceans.

Authors:
Bernard P. Boudreau (Dalhousie University)
Olivier Sulpis (University of Utrecht)
Alfonso Mucci (McGill University)

Microbes: Gatekeepers of earth’s deep carbon?

Posted by mmaheigan 
· Tuesday, May 14th, 2019 

In 2017, an interdisciplinary group of early career scientists, the Biology Meets Subduction team, visited Costa Rica’s subduction zone, where the ocean floor sinks beneath the continent, to find out if subterranean microbes affect geological processes that move carbon from Earth’s surface into the deep interior.

Using carbon and helium isotope measurements of water and nearby sediments from geothermal springs in northern and central Costa Rica, the study published recently in Nature demonstrated that microbes consume and trap a small but measurable amount of the carbon sinking into the trench off Costa Rica’s Pacific coast. The microbes may also be involved in chemical processes that pull out even more carbon, leaving cement-like veins of calcite in the crust.

Figure 1: Schematic of deep carbon cycle subduction at the forearc region and into the mantle.

The team discovered that low temperatures in the forearc support microbial life and water-rock interactions that divert the down-going carbon from the subducting slab and trap it in the crust. The study estimates that about 94 percent of that redirected carbon transforms into calcite minerals and microbial biomass.

Figure 2: Biofilm in a natural seep in Costa Rica. Credit: Peter Barry.

These unexpected findings have important implications for how much carbon moves from Earth’s surface into the interior, especially over geological timescales. If these biological and geochemical processes occur worldwide, they would translate to 19% less carbon entering the deep mantle than previously estimated.

Authors:
PH Barry
JM de Moor
D Giovannelli
M Schrenk
D Hummer
T Lopez
CA Pratt
Y Alpízar Segura
A Battaglia
P Beaudry
G Bini
M Cascante
G d’Errico

M di Carl
D Fattorini
K Fullerton
E Gazel
G González
SA Halldórsson
K Iacovino
JT Kulongoski
E Manini
M Martínez
H Miller
M Nakagawa
S Ono

S Patwardhan
CJ Ramírez
F Regoli
F Smedile
S Turner
C Vetriani
M Yücel
CJ Ballentine
TP Fischer
DR Hilton
KG Lloyd

Filter by Keyword

abundance acidification africa air-sea interactions alkalinity allometry ammonium AMOC anoxia anoxic Antarctic anthropogenic carbon aragonite saturation arctic arsenic Atlantic Atlantic modeling atmospheric CO2 atmospheric nitrogen deposition authigenic carbonates autonomous platforms bacteria BATS benthic bgc argo bioavailability biogeochemical cycles biogeochemical models biogeochemistry biological pump biological uptake biophysics bloom blooms blue carbon bottom water boundary layer buffer capacity CaCO3 calcification calcite carbon-climate feedback carbon-sulfur coupling carbon cycle carbon dioxide carbon sequestration Caribbean CCA CCS changing marine ecosystems changing ocean chemistry chemoautotroph chesapeake bay chl a chlorophyll circulation climate change CO2 coastal darkening coastal ocean cobalt Coccolithophores community composition conservation cooling effect copepod coral reefs currents cyclone DCM decomposers decomposition deep convection deep ocean deep sea coral deoxygenation depth diagenesis diatoms DIC diel migration dimethylsulfide dinoflagellate dissolved inorganic carbon dissolved organic carbon DOC DOM domoic acid dust DVM earth system models ecosystem state eddy Education Ekman transport emissions ENSO enzyme equatorial regions error ESM estuarine and coastal carbon fluxes estuary euphotic zone eutrophication evolution export EXPORTS extreme events extreme weather events faecal pellets filter feeders filtration rates fire fish Fish carbon fisheries floats fluid dynamics fluorescence food webs forams freshening freshwater frontal zone functional role future oceans geochemistry geoengineering GEOTRACES glaciers gliders global carbon budget global warming go-ship grazing greenhouse gas Greenland groundwater Gulf of Maine Gulf of Mexico Gulf Stream gyre harmful algal bloom high latitude human food human impact hurricane hydrothermal hypoxia ice age ice cores ice cover industrial onset inverse circulation iron iron fertilization isotopes jellies katabatic winds kelvin waves krill kuroshio land-ocean continuum larvaceans lateral transport LGM lidar ligands light light attenuation mangroves marine heatwave marine snowfall marshes Mediterranean meltwater mesopelagic mesoscale metagenome metals methane microbes microlayer microorganisms microscale microzooplankton midwater mixed layer mixed layers mixotrophy modeling mode water molecular diffusion MPT multi-decade NASA NCP net community production new technology nitrate nitrogen nitrogen fixation nitrous oxide north atlantic north pacific nutricline nutrient budget nutrient cycling nutrient limitation nutrients OA ocean-atmosphere ocean acidification ocean carbon uptake and storage ocean color ocean observatories ODZ oligotrophic omics OMZ open ocean optics organic particles overturning circulation oxygen pacific paleoceanography particle flux pCO2 PDO peat pelagic pH phenology phosphorus photosynthesis physical processes physiology phytoplankton plankton POC polar regions pollutants prediction primary productivity Prochlorococcus proteins pteropods pycnocline radioisotopes remineralization remote sensing residence time resource management respiration resuspension rivers rocky shore Rossby waves Ross Sea ROV salinity salt marsh satell satellite scale seafloor seagrass sea ice sea level rise seasonal patterns sea spray seaweed sediments sensors shelf system shells ship-based observations shorelines silicate sinking particles size SOCCOM soil carbon southern ocean south pacific spatial covariations speciation SST subduction submesoscale subpolar subtropical sulfate surface surface ocean Synechococcus teleconnections temperate temperature temporal covariations thermocline thermohaline thorium tidal time-series time of emergence top predators total alkalinity trace elements trace metals trait-based transfer efficiency transient features trophic transfer tropical turbulence twilight zone upper ocean upper water column upwelling US CLIVAR validation velocity gradient ventilation vertical flux vertical migration vertical transport volcano water clarity water quality western boundary currents wetlands winter mixing zooplankton

Copyright © 2021 - OCB Project Office, Woods Hole Oceanographic Institution, 266 Woods Hole Rd, MS #25, Woods Hole, MA 02543 USA Phone: 508-289-2838  •  Fax: 508-457-2193  •  Email: ocb_news@us-ocb.org

link to nsflink to noaalink to WHOI

Funding for the Ocean Carbon & Biogeochemistry Project Office is provided by the National Science Foundation (NSF) and the National Aeronautics and Space Administration (NASA). The OCB Project Office is housed at the Woods Hole Oceanographic Institution.