Phytoplankton Nitrogen Nutrition in the Western Indian Ocean: Ecophysiological Adaptations of Neritic and Oceanic Assemblages to Ammonium Supply

Comparative simulations of dissolved organic matter cycling in idealized oceanic, coastal, and estuarine surface waters

“…The strong bottom-up control, and the importance of the microbial loop, in this simulation are consistent with some well recognized concepts of the nutrient cycling (e.g., lots of recycling, little new input) and the food web dynamics in oligotrophic oceanic waters that lack nitrogen fixers and are not subjected to frequent environmental perturbations (Azam et al, 1983;Clark et al, 2008;Fenchel, 2008;Kirchman, 2000;Mengesha et al, 1999;Sanders et al, 1992;Varela et al, 2005). Although there is still an ongoing debate about the importance of top-down versus bottom-up control in oligotrophic waters, which suggest that under some conditions top-down control may be more important than in our model (Banse, 1995;Marañón et al, 2000Marañón et al, , 2003Sherr and Sherr, 2009), the results of this simulation are likely valid in many oligotrophic regions.…”

“…3) and the primary factor limiting primary production (see Supplemental for calculations of light versus DIN limitation). The low ammonium and nitrate concentrations in the oceanic simulation were similar to concentrations that are typically observed (Table 4) in oligotrophic oceanic surface waters around the world Karl et al, 2001;Lipschultz, 2001;Mengesha et al, 1999;Metzler et al, 1997). In temperate coastal and estuarine surface waters a very wide range of inorganic nitrogen concentrations have been observed (Fisher et al, 1988;Harding, 1994;Thompson et al, 2009;Wafar et al, 2004) making it difficult to evaluate our idealized coastal and estuarine simulations.…”

“…b Glibert et al (1991) for the Western N. Atlantic coast, Metzler et al (1997) for the Western S. Atlantic (coastal stations. 1, 61, & 39), and Mengesha et al (1999) for the Western Indian Ocean coast. c Summer observations from Fisher et al (1988) and Malone et al (1996) for the Chesapeake estuary and Gameiro et al (2007) for the Targus estuary.…”

“…Sub-Tropical Gyre, Metzler et al (1997) for the Western S. Atlantic (oceanic stations. 11 & 23), Mengesha et al (1999) for the Western Indian Ocean (oceanic stations, intermonsoon period), Karl et al (2001) for station ALOHA in the Pacific, and Lipschultz (2001) at BATS. b Glibert et al (1991) for the Western N. Atlantic coast, Metzler et al (1997) for the Western S. Atlantic (coastal stations.…”

Variation in upwelling intensity along the NorthWest Iberian Peninsula (Galicia)

“…If this is the case, water depletion occurs in the upper layers, and a lower sea level sets in, forcing water from below to move upward and replenish the space vacated by the offshore drift. The major upwelling regions of the world in terms of primary production are the Canary Current System (Pelegri et al 2005), the California Current System (Di Lorenzo 2003), the Benguela Current (Fennel 1999, Monteiro andLargier 1999), the Peru-Humboldt Current (Nixon andThomas 2001, Mesias et al 2003) and the Somalia Current (Mengesha et al 1999). These upwelling processes tend to trigger intense phytoplankton blooms since they are responsible for a major injection of new nutrients into the euphotic layer.…”