A Contribution to the Oceanology of the Prince Edward Islands

Nutrient dynamics in the vicinity of the Prince Edward Islands

“…Macronutrient concentrations in the ocean in the immediate vicinity of the islands are largely determined by the interaction between the oceanographic environment and the activity of seabirds and seals (Lindeboom 1984;Allanson et al 1985;Duncombe Rae 1989;Ismail 1990;Balarin 2000). In the shallow shelf waters between the two islands, concentrations of macronutrients, particularly reduced nitrogen (ammonia and urea) and phosphate are elevated compared to the open waters of the PFZ (Fig.…”

“…7.1) Pakhomov & Chown 2003). These elevated nutrient concentrations are largely derived from the guano of sea going animals, dung, urine and animal remains which are carried off the islands to the shelf waters via freshwater runoff (Allanson et al 1985;Duncombe Rae 1989). Indeed, good correlations are found between the concentrations of the nutrients between the two islands and water column stability generated by freshwater runoff from the islands (Allanson et al 1985;Duncombe Rae 1989).…”

“…These elevated nutrient concentrations are largely derived from the guano of sea going animals, dung, urine and animal remains which are carried off the islands to the shelf waters via freshwater runoff (Allanson et al 1985;Duncombe Rae 1989). Indeed, good correlations are found between the concentrations of the nutrients between the two islands and water column stability generated by freshwater runoff from the islands (Allanson et al 1985;Duncombe Rae 1989). Maximum concentrations of phosphate derived from the mineralization of feathers are recorded from April to May in the shallow shelf waters of the islands whereas the peak in guano production occurs from December to February .…”

“…By contrast, when the SAF lies in close proximity to the islands, advection forces prevail and a flow through-flow system is established between the islands (Perissinotto & Duncombe Rae 1990;Pakhomov et al 2000b). The retention of waters over the shallow island shelf when eddies are trapped between the islands contributes to the build-up of nutrient concentrations derived from the freshwater runoff from the islands within the inter-island region (Allanson et al 1985). These elevated nutrient concentrations coupled with the increased water column stability derived from the freshwater runoff from the islands generates periodic phytoplankton blooms between the two islands; a phenomenon known as the, "island mass effect" (Allanson et al 1985;Boden 1985;Perissinotto et al 1990a, ;Pakhomov & Chown 2003;McQuaid & Froneman 2004).…”

“…Surface concentrations of nitrate, silicate and phosphate range from 9.5 to 97.5, from 0.2 to 16.5 and from < 0.1 to 16.6 mmol m -3 , respectively (Allanson et al 1985;Duncombe Rae 1989;Ismail 1990;Balarin 2000). Changes in nutrient concentrations coincide with the intrusion of Antarctic surface water from the south and sub-Antarctic surface water from the north Froneman et al 1999).…”