| Autor: |
Xie, H., Bélanger, S., Song, G., Benner, R., Taalba, A., Blais, M., Lefouest, V., Tremblay, J.-É., Babin, M. |
| Předmět: |
|
| Zdroj: |
Biogeosciences Discussions; 2012, Vol. 9 Issue 4, p4441-4462, 46p, 6 Charts, 8 Graphs, 3 Maps |
| Abstrakt: |
Photochemistry of dissolved organic matter (DOM) plays an important role in marine biogeochemical cycles, including the regeneration of inorganic nutrients. DOM photochemistry affects nitrogen cycling by converting bio-refractory dissolved organic nitrogen to labile inorganic nitrogen, mainly ammonium Due to image rights restrictions, multiple line equation(s) cannot be graphically displayed.. During the August 2009 Mackenzie Light and Carbon (MALINA) Program, the absorbed photon-based efficiency spectra of Due to image rights restrictions, multiple line equation(s) cannot be graphically displayed. photoproduction (i.e. photoammonification) were determined using water samples from the SE Beaufort Sea, including the Mackenzie River estuary, shelf, and Canada Basin. The photoammonification efficiency decreased with increasing wavelength across the ultraviolet and visible regimes and was higher in offshore waters than in shelf and estuarine waters. The efficiency was positively correlated with the molar nitrogen : carbon ratio of DOM and negatively correlated with the absorption coefficient of chromophoric DOM (CDOM). Combined with collateral measurements of CO2 and CO photoproduction, this study revealed a stoichiometry of DOM photochemistry with a CO2 : CO : Due to image rights restrictions, multiple line equation(s) cannot be graphically displayed. molar ratio of 165 : 11 : 1 in the estuary, 60 : 3 : 1 on the shelf, and 18 : 2 : 1 in the Canada Basin. The Due to image rights restrictions, multiple line equation(s) cannot be graphically displayed. efficiency spectra, along with solar photon fluxes, CDOM absorption coefficients and sea ice concentrations, were used to model the monthly surface and depth-integrated photoammonification rates in 2009. The summertime (June-August) rates at the surface reached 6.6 nmoll-1 d-1 on the Mackenzie Shelf and 3.7 nmoll-1 d-1 further offshore; the depth-integrated rates were correspondingly 8.8 µmolm-2 d-1 and 11.3 µmolm-2 d-1. The offshore depth-integrated rate in August (8.0 µmolm-2 d-1) was comparable to the missing dissolved inorganic nitrogen (DIN) source required to support the observed primary production in the upper 10-m layer of that area. The yearly Due to image rights restrictions, multiple line equation(s) cannot be graphically displayed. photoproduction in the entire study area was estimated to be 1.4x108 moles, with 85% of it being generated in summer when riverine DIN input is low. Photoammonification could mineralize 4% of the annual dissolved organic nitrogen (DON) exported from the Mackenzie River and provide a DIN source corresponding to 7% of the riverine DIN discharge and 1400 times the riverine Due to image rights restrictions, multiple line equation(s) cannot be graphically displayed. flux. Under a climate warming-induced ice-free scenario, these quantities would increase correspondingly to 6 %, 11 %, and 2100 times. Photoammonification is thus a significant nitrogen cycling term and may fuel previously unrecognized autotrophic and heterotrophic production pathways in the surface SE Beaufort Sea. [ABSTRACT FROM AUTHOR] |
| Databáze: |
Complementary Index |
| Externí odkaz: |
|
