TY - JOUR
T1 - Modeling the effect of nitrogen fixation on carbon and nitrogen fluxes at BATS
AU - Hood, Raleigh R.
AU - Bates, Nicholas R.
AU - Capone, Douglas G.
AU - Olson, Donald B.
PY - 2001/5/24
Y1 - 2001/5/24
N2 - Recent geochemical estimates of N2-fixation in the North Atlantic ocean indicate rates that are significantly higher than those derived from direct observations. In this paper different N2-fixation rate scenarios are explored using a one-dimensional, biogeochemical model that includes an explicit representation of Trichodesmium. This model reproduces most of the observed interannual variability in phytoplankton production and generates seasonal Trichodesmium biomass and N2-fixation cycles similar to those observed at BATS. Two solutions are presented, one where the N2-fixation rate is increased enough to reproduce the observed summertime drawdown of DIC, and a second where it is tuned to reproduce the observed sediment trap fluxes. The high N2-fixation solution reproduces the seasonal and interannual variability in DIC concentrations quite accurately and generates N2-fixation rates that agree with direct rate measurements from 1990 and recent geochemical estimates. However, this solution generates export fluxes that are more than 4 times higher than those observed, and predicts the development of DON and DOC anomalies in late summer/early fall that have not been observed. In contrast, the low N2-fixation solution generates trap fluxes that are approximately correct, but overestimates the summertime DIC concentrations by 20-30 μmol/kg-1. Both solutions indicate that there is significant interannual variability in N2-fixation at BATS and that the rates were much lower in 1995-1996 than in the previous six years. It is suggested that this variability is linked to decadal-scale fluctuations in the North Atlantic climate.
AB - Recent geochemical estimates of N2-fixation in the North Atlantic ocean indicate rates that are significantly higher than those derived from direct observations. In this paper different N2-fixation rate scenarios are explored using a one-dimensional, biogeochemical model that includes an explicit representation of Trichodesmium. This model reproduces most of the observed interannual variability in phytoplankton production and generates seasonal Trichodesmium biomass and N2-fixation cycles similar to those observed at BATS. Two solutions are presented, one where the N2-fixation rate is increased enough to reproduce the observed summertime drawdown of DIC, and a second where it is tuned to reproduce the observed sediment trap fluxes. The high N2-fixation solution reproduces the seasonal and interannual variability in DIC concentrations quite accurately and generates N2-fixation rates that agree with direct rate measurements from 1990 and recent geochemical estimates. However, this solution generates export fluxes that are more than 4 times higher than those observed, and predicts the development of DON and DOC anomalies in late summer/early fall that have not been observed. In contrast, the low N2-fixation solution generates trap fluxes that are approximately correct, but overestimates the summertime DIC concentrations by 20-30 μmol/kg-1. Both solutions indicate that there is significant interannual variability in N2-fixation at BATS and that the rates were much lower in 1995-1996 than in the previous six years. It is suggested that this variability is linked to decadal-scale fluctuations in the North Atlantic climate.
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U2 - 10.1016/S0967-0645(00)00160-0
DO - 10.1016/S0967-0645(00)00160-0
M3 - Article
AN - SCOPUS:0035041549
VL - 48
SP - 1609
EP - 1648
JO - Deep-Sea Research Part II: Topical Studies in Oceanography
JF - Deep-Sea Research Part II: Topical Studies in Oceanography
SN - 0967-0645
IS - 8-9
ER -