Dry atmospheric deposition and diazotrophy as sources of new nitrogen to northwestern Mediterranean oligotrophic surface waters - Université Pierre et Marie Curie Accéder directement au contenu
Article Dans Une Revue Deep Sea Research Part I: Oceanographic Research Papers Année : 2007

Dry atmospheric deposition and diazotrophy as sources of new nitrogen to northwestern Mediterranean oligotrophic surface waters

Résumé

Atmospheric dry deposition of nitrogen (N) and dinitrogen (N-2) fixation rates were assessed in 2004 at the time-series DYFAMED station (northwestern Mediterranean, 43 degrees 25'N, 7 degrees 52'E). The atmospheric input was monitored over the whole year. Dinitrogen fixation was measured during different seasonal trophic states (from mesotrophy to oligotrophy) sampled during nine cruises. The bioavailability of atmospherically deposited nutrients was estimated by apparent solubility after 96h. The solubility of dry atmospheric N deposition was highly variable (from similar to 18% to more than 96% of total N). New N supplied to surface waters by the dry atmospheric deposition was mainly nitrate (NO3-) (similar to 57% of total N, compared to similar to 6% released as ammonium (NH4+)). The mean bioavailable dry flux of total N was estimated to be similar to 112 mu mol m(-2) d(-1) over the whole year. The NO3- contribution (70 mu mol NO3- m(-2) d(-1)) was much higher than the NH4+ contribution (1.2 mu mol NH4+ m(-2) d(-1)). The N:P ratios in the bioavailable fraction of atmospheric inputs (122.5-1340) were always much higher than the Redfield N: P ratio (16). Insoluble N in atmospheric dry deposition (referred to as ``organic'' and believed to be strongly related to anthropogenic emissions) was similar to 40 mu mol m(-2) d(-1). N-2 fixation rates ranged from 2 to 7.5 nmol L-1 d(-1). The highest values were found in August, during the oligotrophic period (7.5 nmol L-1 at 10 in depth), and in April, during the productive period (4 nmol L-1 d(-1) at 10 m depth). Daily integrated values of N-2 fixation ranged from 22 to 100 mu mol N m(-2) d(-1), with a maximum of 245 mu mol N m(-2) d(-1) in August. No relationship was found between the availability of phosphorus or iron and the observed temporal variability of N-2 fixation rates. The atmospheric dry deposition and N-2 fixation represented 0.5-6% and 1-20% of the total biological nitrogen demand, respectively. Their contribution to new production was more significant: 1-28% and 2-55% for atmospheric dry deposition and N-2 fixation, respectively. The dry atmospheric input was particularly significant in conditions of water column stratification (16-28% of new production), while N2 fixation reached its highest values in June (46% of new production) and in August (55%). (C) 2007 Elsevier Ltd. All rights reserved.

Domaines

Océanographie

Dates et versions

hal-03504930 , version 1 (30-12-2021)

Identifiants

Citer

V. Sandroni, P. Raimbault, Christophe Migon, N. Garcia, E. Gouze. Dry atmospheric deposition and diazotrophy as sources of new nitrogen to northwestern Mediterranean oligotrophic surface waters. Deep Sea Research Part I: Oceanographic Research Papers, 2007, 54 (11), pp.1859-1870. ⟨10.1016/j.dsr.2007.08.004⟩. ⟨hal-03504930⟩
6 Consultations
0 Téléchargements

Altmetric

Partager

Gmail Facebook X LinkedIn More