Global niche of marine anaerobic metabolisms expanded by particle microenvironments

Importance of Cadmium Sulfides for Biogeochemical Cycling of Cd and Its Isotopes in Oxygen Deficient Zones—A Case Study of the Angola Basin

“…Seawater Cd isotope data in oceanic oxygen deficient zones (ODZs), however, indicate that cadmium sulfide (CdS hereafter) precipitation within sinking biogenic particles may constitute an important mechanism for removal of Cd from the water column (Conway & John, ; D. J. Janssen et al, ; R. C. Xie et al, ) in agreement with modeling studies (D. Bianchi et al, ). The possible occurrence of CdS was first described in the Mauritanian ODZ based on a combination of (1) depletion of dissolved Cd, (2) enrichment of particulate Cd relative to PO 4 and (3) a shift of dissolved δ 114 Cd toward heavier values (Conway & John, ; D. J. Janssen et al, ).…”

“…The Cd isotope fractionation factor determined experimentally during CdS precipitation in synthetic seawater is α 114/110 Cdsol‐CdS = 1.00032 (D. Guinoiseau et al, ) and is in agreement with field observations of a seawater Cd isotope shift, as well as with ab initio models (J. Yang et al, ). Furthermore, the size‐resolved particle model recently developed by Bianchi et al () predicts that microbial sulfate reduction can occur in coarse particle aggregates (>1 mm) at the upper boundary of ODZs (100–200 m depth), thereby releasing H 2 S into solution and thus promoting local CdS precipitation. The model results of Bianchi et al () agree well with measured Cd and Cd/PO 4 profiles in the particulate phase of the Mauritanian ODZ.…”

“…Furthermore, the size‐resolved particle model recently developed by Bianchi et al () predicts that microbial sulfate reduction can occur in coarse particle aggregates (>1 mm) at the upper boundary of ODZs (100–200 m depth), thereby releasing H 2 S into solution and thus promoting local CdS precipitation. The model results of Bianchi et al () agree well with measured Cd and Cd/PO 4 profiles in the particulate phase of the Mauritanian ODZ. Such an active cryptic sulfur cycle has also been proposed in the Chilean (D. E. Canfield et al, ), Arabian (B. M. Fuchs et al, ), North Pacific (Beman & Carolan, ; M. T. Carolan et al, ) and Peruvian ODZs (R. C. Xie et al, ), based on the identification of sulfide oxidizers and sulfate reducing species in picoplankton and bacterial communities.…”

Remote Western Arctic Nutrients Fuel Remineralization in Deep Baffin Bay

“…In this regard, the Barents Sea halocline branch upstream in the Canada Basin does not show an analogous signal of denitrification in the dissolved NO 3 ‐ pool (Granger et al, ). While significant denitrification associated with water column particles has been observed in ODZs (Ganesh et al, ), we deem this scenario unlikely in deep Baffin Bay, given the relatively elevated O 2 concentration in the deep basin, as well as the decreasing size of particles with depth, likely resulting in a diffusive O 2 flux to particles that exceeds the associated oxidant demand (Bianchi et al, ). If the denitrification signal (e.g., N* minimum and 15 N‐enrichment) originates from brine‐enriched waters accumulating at the bottom of the shelf in NS, this signal would need to be significantly higher than the signal we see in deep Baffin Bay to withstand dilution and mixing during its slow descent toward the bottom (Bourke & Paquette, ).…”

Assessing Marine Nitrogen Cycle Rates and Process Sensitivities With a Global 3‐D Inverse Model

“…There has been some debate in the literature over what these threshold O 2 concentrations are, ranging from nanomolar levels of O 2 to upward of 20 to 25 μM O 2 (Dalsgaard et al, ; Jensen et al, ; Kalvelage et al, ; Kuypers et al, ). For our standard model optimizations, we chose moderate thresholds to allow for the potential of anaerobic microsites in particles (Bianchi et al, ), as well as the overall increase in the lowest O 2 concentrations that occurs due to binning over O 2 gradients when interpolating the World Ocean Atlas O 2 product to the model grid (i.e., there end up being almost no “zero” O 2 concentrations due to averaging). The initial O 2 threshold for NO 3 − reduction (O 2 NAR , 7 μM O 2 ) was chosen to be higher than that of NO 2 − reduction (O 2 NIR , 5 μM O 2 ) since it is thought to be less sensitive to O 2 (Bonin et al, ).…”