Most of the ocean is deeper than 2000m; its average depth is 4267m. Yet the global array of Argo floats measures only the top 2000m. This means that our knowledge of the deep ocean is based on sparse data from research ships and moorings. To remedy this scientists have been developing floats capable of collecting data down to 4000 m.
Developing new deep floats
The Deep-Arvor floats developed at Ifremer in France have been designed to collect up up to 150 profiles to a depth of about 4000m. To operate at these depths the floats must withstand pressures of more than 400 times those found at the sea surface.
T, S and O2 profiles from a deep Argo float
Testing of the new floats started in May 2013 in the North Atlantic. A further two floats will be tested in the Canary basin during 2015. The tests were successful; the first two floats collected 180 cycles to a depth of 3500m and two other floats reached 100 cycles down to 4000m.
Why we need deep Argo floats
There are many reasons why we need better measurements of variability and change in the deep ocean. Among the most important is the need for better understanding and predictions of climate change and its impacts.
Climate variability and changes in the deep ocean
The deep ocean plays an import role in Earth's climate system. Some 90% of the heat absorbed by the ocean in the last 40 years is now in the deep ocean.
The information we have indicates that climate variability can quickly affect deep ocean currents. Together with deep-reaching ocean eddies these contribute to the global redistribution of temperature, salinity, nutrients, oxygen, and carbon.
Predicting sea level rise
Warming and freshening seawater expands and leads to rising sea level. A significant contribution to mean sea level rise comes from warming of the ocean below 2000 m. If we want to understand and predict sea level rise, we therefore need to measure temperature and salinity in the whole ocean, not just the top half.