Present Status of APEX Float Technology S. Riser, University of Washington

1. Present Status of APEX Float Technology S. Riser, University of Washington • Lithium batteries. WRC continues to refuse to sell floats with Li batteries, so users must do their own replacement. Several groups have taken steps to change to Li batteries (China, India, Canada, UK). • APF9 controller will soon be discontinued, to be replaced by APF10. This is due to the fact that a number of components on the APF9 board are obsolete. The APF10 will have 2 additional serial ports and extra flash memory (64 Mb compared to 8 Mb for the APF9). • Pressure offset errors on APF8. This effect can now be assessed using data from APF9-equipped floats. The problem remains unfixed. • Bladder leaks. In late 2006 and early 2007 a number of floats with leaky air bladders were discovered by Webb, UW, and other labs. The problem was traced to a faulty weld on the air-bladder side of the bladder assembly. To remedy the problem, Webb added double-sided welds. This appeared to fix the problem, but recently a leaky bladder with a double-sided weld has been found. Webb has changed bladder vendors and hopes the problem is solved. For now, the air bladders on all UW-built APEX floats continue to be tested under pressure during construction, until it is clear that the problem has been solved.

2. APEX technology, continued: • Profiling to 2000 m anywhere in the world ocean. A growing number of APEX floats have been equipped with the N2 feature, an inexpensive internal gas canister that allows floats to profile to 2000 m anywhere in the world ocean, including near the Equator. While useful, use of this feature places some limitations on parking depth (ie, the float becomes unstable in some regions of the water column). In the past year we have altered the gas pressure in the canister so that floats can park at 1000 m and profile to 2000 m anywhere in the world ocean. • New sensors added to floats. (a) SeaBird Surface Temperature and Salinity (STS); (b) dissolved nitrate.

3. SeaBird STS assembly To examine the relationship between the near surface (5 m) values of T and S and the true sea surface values, we have recently deployed an Argo-type float with a 2nd CTD sensor that can continue to collect CTD data all the way to the sea surface, known as the STS (surface temperature/salinity) unit. This work as been funded by NASA in anticipation of the Aquarius program.

4. (WMO 5901469) (WMO 5901469) The first STS float was deployed at the HOT site in mid-December of 2007 and continues to operate normally.

5. The data stream from the STS float is designed to allow the STS sensor to be compared and recalibrated to the main SBE41CP CTD unit on each profile, thus insuring the specified accuracy. [note: Iridium required] (0.6 samples/sec)/(8 cm/sec) = 0.075 samples/cm 13 cm/sample

6. (WMO 5901469) This is an example of typical temperature and salinity profiles from the STS sensors. Note that the measurements continue to be collected until the float breaks the sea surface during its ascent.

7. T Temperature and salinity in the upper 3 meters of the water column as functions of time and depth, measured by the STS, sampled at intervals of 2 hours in order to examine diurnal effects. S

8. Nitrate Sensors on Profiling Floats: A collaboration between UW and MBARI Iridium antenna CTD unit Optode Carbon fiber hull ISUS Spectro- photometer UV light source ISUS electronics ISUS sensor ISUS electronics ISUS sensor Sensor guard The NO3 sensor (ISUS) consists of a spectrophotometer and a light source. With 3 Li battery packs, this float should be capable of about 275 profiles. If a good pH sensor was added, a nearly complete carbon budget could be constructed from a single float.

9. T/S T/NO3 Profile 21, 3/10/08 [near Hawaii] T/O2 (WMO 5901468)