Cruise News

Crozet Cruising – Coming Home!

It has been a long cruise, but finally the science is over (more or less) and we are on our way back to Cape Town. The final days were spent working around the Crozet Islands, collecting water and particulate material for the measurement of iron, the fertiliser of the Southern Oceans! In one of the first blogs from the ship, the role of iron in fertilising the phytoplankton bloom to the north of the Crozet Islands was mentioned – but one question is are the Islands (or more properly the seamount) themselves a source of iron? They are volcanic in nature and should be rich in iron, but much of that is likely to locked up in crystalline minerals and is not readily available. The forms of iron that are likely to be important for the oceans include non-crystalline so-called “colloidal” oxide and hydroxide minerals that are more reactive than their crystalline counterparts. Weathered material from land is one possible source of such material, and there is certainly weathering going on at the Crozet Islands.

“Fresh water from the island is likely to supply some colloidal iron to surface water!”

Large volume stand alone pumps that are used to collect particulate material for the analysis of iron

However, this is likely to be a very minor source the surface waters; more likely sources of iron are from deep water, which rises to the surface (upwells) to the north of the islands, or possibly continental dust blown from the South African desert regions by the prevailing winds. The dust has to be transported a long way, but remember washing your cars after the rather frequent Saharan dust falls (red rain) in the UK. The way in which iron, which is a very insoluble element in its stable form in sea water, becomes available to phytoplankton is something of a conundrum and another story which is the subject of great debate in modern oceanography.