Abstract
AbstractIcebergs which calve from the Antarctic ice shelves and drift in the Southern Ocean deliver fresh water, dust and minerogenic particles to the surface ocean along the iceberg's path. Each of these components may have an effect on growth conditions for phytoplankton, as might the mechanical effects of the iceberg keel disturbing the water. Although anecdotal evidence and small-scale surveys suggest that drifting icebergs increase local primary production, no large-scale studies have reported on this possibility in detail. A combination of satellite and automated iceberg tracking data presented here shows that the probability of increased surface phytoplankton biomass was two-fold higher in the wake of a tracked iceberg compared to background biomass fluctuations. Only during the month of February were the effects of icebergs on surface biomass likely to be negative. These results confirm icebergs as a factor affecting phytoplankton in the Southern Ocean and highlight the need for detailed process studies so that responses to future changes in the Antarctic ice sheets may be predicted.
Highlights
Icebergs which calve from the Antarctic ice shelves and drift in the Southern Ocean deliver fresh water, dust and minerogenic particles to the surface ocean along the iceberg’s path
Whether cells are lost from the mixed layer would depend on the iceberg keel depth, which determines the degree of turbulent mixing relative to the mixed layer depth
The net effect of melt water on the water column structure depends on the volume of water melting, the strength of wind-mixing and on the ambient temperature and salinity structure: Unless the ambient temperature is close to freezing, the melt water will have a negative temperature-component of buoyancy, while the salinity-component will be positive, since fresh water is less dense than saline water
Summary
Icebergs which calve from the Antarctic ice shelves and drift in the Southern Ocean deliver fresh water, dust and minerogenic particles to the surface ocean along the iceberg’s path. Input of macro-nutrients (nitrate, phosphate, silicate) would be likely to have a positive impact on phytoplankton growth late in the summer season, when the surface waters are stratified, with a shallow pycnocline (30 to 50 m) in which iron and silicate, in particular, are depleted[7].
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