Revisiting atmospheric dust export to the Southern Hemisphere ocean: Biogeochemical implications

Abstract

[1] Aerosol concentrations in the Southern Hemisphere are largely undersampled. This study presents a chemical and physical description of dust particles collected on board research vessels in the southeast Pacific (SEPS) and the Southern Ocean (SOKS). Concentrations of dust were 6.1 ± 2.4 ng m À3 for SEPS and 13.0 ± 6.3 ng m À3 for SOKS. Dust fluxes, derived from those concentrations, were 9.9 ± 3.7 mg m À2 d À1 for SEPS and 38 ± 14 mg m À2 d À1 for SOKS and are shown to be representative of actual fluxes in those areas. Dust and iron deposition are up to 2 orders of magnitude lower than former predictions. A map of dust deposition on the Southern Hemisphere is proposed by incorporating those in situ measurements into a dust model. This study confirms that dust deposition is not the dominant source of iron to the large high-nutrient low-chlorophyll Southern Ocean.

Heterotrophic organisms dominate nitrogen fixation in the South Pacific Gyre

“…Diazotrophs have higher requirements for iron than non-diazotrophic primary producers. Hence, the low iron inputs to the SPG, as a result of the remoteness of the SPG to any continents, may ultimately limit N 2 -fixation (Wagener et al, 2008). A recent study (Mohr et al, 2010) showed that the method used here would likely have underestimated N 2 -fixation rates in the SPG.…”

Diatom δ13C, δ15N, and C/N since the Last Glacial Maximum in the Southern Ocean: Potential impact of Species Composition

“…[26] The higher concentrations of chlorophyll are likely related to the input of dust from Patagonia into the Atlantic sector, especially in the west [Mahowald et al, 1999;Wagener et al, 2008], and thus of the often-limiting micronutrient, iron; large parts of the Pacific and Indian sectors, too distantly removed from any such dust source, are likely to be significantly more iron limited than the Atlantic sector. Iron enrichment experiments in the Southern Ocean indicate that inputs of iron to surface waters here shifts the structure of the phytoplankton community toward domination by large diatoms (Fragilariopsis, Thalassiothrix, and Odontella spp.…”

“…All three core positions are located south of the present-day Antarctic Polar Front (APF) and were chosen to represent different environmental conditions during both the Holocene and the last glacial, especially in term of sea ice coverage. The site from the Scotia Sea (Atlantic sector) is the site which is closest to the sea ice edge and currently has the highest amount of dust [Wagener et al, 2008] and chlorophyll ( Figure 2) compared to the sites from the Indian and Pacific sectors.…”

The influence of iron and light on net community production in the Subantarctic and Polar Frontal Zones

“…We calculate oxygen solubility from atmospheric pressure, temperature, and salinity measurements (Garcia and Gordon, 1992). The piston velocity for oxygen is estimated from the NCEP/NCAR windspeed reanalysis data product (Kalnay et al, 1996) and the parameterization of Wanninkhof (Wanninkhof, 1992). Piston velocity is weighted for windspeed history at the collection site (Reuer et al, 2007).…”

“…Atmospheric Fe deposition was estimated following a method recently described (Wagener et al, 2008). See for a description of the dissolved Fe budget, including the atmospheric Fe deposition measurements, during the SAZ Sense cruise.…”