Fragilariopsis kerguelensis

Fragilariopsis kerguelensis, is a pennate diatom native to the Southern Ocean. It has been characterized as "the most abundant diatom in the Antarctic Seas".

Description
Fragilariopsis kerguelensis is a unicellular, phototrophic, microalga with a range in size of 10 - 80 μm. It is encased in a heavily silicified cell wall, called the frustule, and is identified by its unique theca, raphe and striations, which distinguish it from other diatoms. They are native to pelagic environments of the Southern Ocean within a temperature range of -1° to 18° C. F. kerguelensis is known to form community chains that consist of 20-100 cells and can be up to 300 μm long.

Use as a paleoceanographic proxy
Fragilariopsis kerguelensis is well preserved in the fossil record and commonly referenced as a paleoceanographic or paleoclimatic proxy. F. kerguelensis comprises the largest deposit of biogenic silica in the world (~75%) despite only accounting for 20% of global production. It is an open water species and is found in its highest abundance between the Antarctic Circumpolar Current and the Subtropical Front. This, along with its tendency to increase valve size near polar fronts, makes F. kerguelensis an ideal indicator of paleoclimate polar front or low-carbon, high-silica exporting regimes. Modern assemblages with F. kerguelensis can be used to calculate past sea surface temperature through the use of transfer functions.