Physical controls on the distribution of phytoplankton round the Crozet Plateau, Southern Ocean

The spatial and temporal distribution of phytoplankton around the Crozet Plateau,<br/>Southern Ocean, is studied through a variety of satellite datasets and in situ cruise and<br/>Argo float measurements. Parts of the study area regularly contain phytoplankton<br/>concentrations significantly enhanced over the other parts, and over most of the rest of<br/>the Southern Ocean, due to natural iron fertilization from the Crozet Islands. Study is<br/>made of these contrasts in order to further understand the processes that limit<br/>phytoplankton over the mostly High Nutrient Low Chlorophyll (HNLC) Southern Ocean.<br/>The longer timescales, larger areas and regularity of naturally iron-fertilized<br/>phytoplankton blooms make them preferable to study compared to studies of the effects<br/>of iron released from a ship. Data from these experiments, and from other islands in the<br/>Southern Ocean, is investigated in the context of the results found around the Crozet<br/>Plateau.<br/>The circulation patterns around the Crozet Plateau are studied in detail, with particular<br/>emphasis on understanding where surface water that has passed close to the Crozet<br/>Islands flows, as this is a known source of iron to the surface water. The surface mixed<br/>layer depth and incoming irradiance are also studied so that the variation in light<br/>availability with time and latitude can be understood. The distribution of phytoplankton is<br/>studied through satellite chlorophyll-a images, with values adjusted to match those<br/>observed in situ during the research cruises.<br/>The initial development of the bloom is controlled by variations in light availability but<br/>the advection and lateral mixing of iron is sufficient to explain the spatial extent of the<br/>bloom and the variations in peak chlorophyll-a concentrations. The variability of the<br/>strength of the bloom is driven mostly by variations in the iron utilization by<br/>phytoplankton during the preceding winter and wind-driven variations in the circulation.

Name dc:type.qualificationname

Ph.D.

Level dc:type.qualificationlevel

doctoral

Grantor dc:publisher.institution

University of Southampton

Year dc:date.issued

2007

Author dc:creator

• Venables, Hugh James