Phosphorus

• The Great Southern Australian Coastal Upwelling System is an upward current of water over vast distances along Australia’s southern coast.
• This nutrient-rich water supports a rich ecosystem that attracts iconic species like the southern bluefin tuna (Thunnus maccoyii) and blue whale (Balaenoptera musculus brevicauda).
• This year marks the 20th anniversary of a research publication that revealed the existence of the large seasonal upwelling system along Australia’s southern coastal shelves.

Where do the nutrients come from?

• Only the upper 50 metres of the water column receives enough light to support the microscopic phytoplankton – single-celled organisms that depend on photosynthesis.
• This is the process of using light energy to make a simple sugar, which phytoplankton and plants use as their food.
• As well as light, the process requires a suite of nutrients including nitrogen and phosphorus.

What causes the upwelling?

• These winds force near-surface water offshore, which draws up deeper, nutrient-enriched water to replace it in the sunlight zone.
• The summer winds also produce a swift coastal current, called an upwelling jet.
• Coastal upwelling driven by southerly winds also forms occasionally along Tasmania’s west coast.

• Recent research suggests the overall upwelling intensity has not dramatically changed in the past 20 years.
• The findings indicate global climate changes of the past 20 years had little or no impact on the ecosystem functioning.

What are the links between upwelling, tuna and whales?

• They are the Australian sardine (Sardinops sagax) and the Australian krill (Nyctiphanes australis), a small, shrimp-like creature that’s common in the seas around Tasmania.
• Sardines are the key diet of larger fish, including the southern bluefin tuna, and various marine mammals including the Australian sea lion (Neophoca cinerea).
• Nonetheless, their timing and location appear to fit perfectly into the annual migration patterns of southern bluefin tuna and blue whales, creating a natural wonder in the southern hemisphere.

Jochen Kaempf does not work for, consult, own shares in or receive funding from any company or organisation that would benefit from this article, and has disclosed no relevant affiliations beyond their academic appointment.