Antarctica iron limitation

The southern flank of the upwelling CDW sinks around the continent of Antarctica to become AABW The northern flank of upwelling CDW is transported by surface currents, first into the polar frontal zone (PFZ) where AAIW forms, and then into the subantarctic zone (SAZ ) where SAMW forms. At these latitudes, dust deposition is high enough to reduce iron limitation of the diatoms. As the surfece waters move northward. 

Table 1 The pigment composition of Phaeocystis antarctica for chlorophyll a (n = 3) (average values s.d.) iron-limited and iron-replete cells, expressed as ratios to ...

Vaillancourt RD, Sambrotto RN, Green S, Matsuda A (2003) Phytoplankotn biomass and photosynthetic competency in the summertime Metz Glacier Region of East Antarctica. Deep-Sea Res II 50 1415-1440 van Leeuwe MA, De Baar HJW (2000) Photoacclimation by the Antarctic flagellate Pyramimonas sp. (Prasin-ophyceae) in response to iron limitation. Eur J Phyol 35 295-303... 

Sedwick PN, DiTullio GR, Mackey DJ (2000) Iron and manganese in the Ross Sea, Antarctica seasonal iron limitation in Antarctic shelf waters. J Geophys Res 105(C5) 11321-11336... 

Blooms of P. antarctica occur in regions where trace metals, notably iron, are limiting phytoplankton growth (Martin et al. 1990 Coale et al. 2003, Schoemann et al. 2005). The effect of iron limitation on the overflow production by P. antarctica is largely unknown. Since iron limitation directly affects the photosynthetic process (Geider and La Roche 1994) the production of carbohydrates is likely to be hampered,... 

Our experimental estimates of growth rate as a function of iron concentration yielded a half-saturation constant for growth of 0.45 nM dissolved Fe for colonial P. antarctica at an irradiance of -20 m 2 s 1 (Sedwick et al., this issue). These results imply that at this relatively low irradiance, colonial P. antarctica was iron-limited (sensu Morel et al. 1991) at ambient dissolved Fe concentrations < 0.45 nM (Fuco -Hex < 0.035), and was still significantly iron-stressed (sensu Morel et al. 1991) at dissolved iron concentrations of 1-2 nM (Fuco Hex -0.075-0.15). Thus, the mean Fuco Hex ratio of 0.076 measured in subsurface, P. antarctica-dominated... 

So far there has been only limited research addressing the iron requirements of colonial P. antarctica. Sedwick et al. (2000) performed a shipboard iron-addition experiment with a... 

Solomon CM, Lessard EJ, Keil RG, Foy MS (2003) Characterization of extracellular polymers of Phaeocystis glob-osa and P. antarctica. Mar Ecol Prog Ser 250 81-89 Sugimura Y, Suzuki Y (1988) A high temperature catalytic oxidation method for the determination of non-volatile dissolved organic carbon in seawater by direct injection of a liquid sample. Mar Chem 24 105-131 Sunda WG, Huntsman SA (1995) Iron uptake and growth limitation in oceanic and coastal phytoplankton. Mar Chem 50 189-206... 

Iron is a nutritive trace element whose role as a limiting agent for algal growth has been demonstrated in areas where certain Phaeocystis species (e.g., P. antarctica) are also commonly found. Viral lysis will affect the absolute concentration of iron that is potentially available for biological requirement, but may also directly affect the spe-ciation and bioavailability as iron is mostly com-plexed with organic ligands and colloids. 

Annual patterns of P. antarctica in the Southern Ocean may thus be determined by the interplay between variable micronutrient concentrations and irradiance availability. In contrast, patterns in high latitudes in the northern hemisphere, where iron is not typically limiting, are primarily determined by nutrient conditions and large-scale hydrographical phenomena. 

Thus there is a need for further experimental work to assess the relationship between the pigment composition of P. antarctica and dissolved iron concentrations as a function of irradiance. To this end, we are currently undertaking the analysis of pigment samples from iron-addition culture experiments conducted at irradiances > 20 nE m 2 s In addition, there are other factors that may limit the utility of pigment ratios such as Fuco Hex in assessing the physiological status and/or ambient growth conditions of... 

P. antarctica in Antarctic waters. These factors include growth limitation/co-limitation by other resources, such as zinc (Coale et al. 2003) or vitamin B12 (Bertrand et al. in press) luxury uptake of iron integrated effects of prior changes in availability of iron and/or light physiological... 

Recently, studies have been conducted in which iron was added to surface waters of the southern ocean near Antarctica to study its effect on phytoplankton. Adding iron resulted in a substantial buildup in the amount of phytoplankton and at least a short-term drop in the amount of carbon dioxide in the air immediately above them. These results were consistent with similar experiments performed earlier in the equatorial Pacific Ocean, confirming the hypothesis that iron is the limiting nutrient of these microoiganisms in much of the ocean. However, there was no increase in the amount of microbes sinking out of the top layer of ocean water. Thus, this procedure may be of no use for the long-term reduction of atmospheric carbon dioxide. 

---