EXPANDING THE CAPABILITIES OF ARGO-TYPE FLOATS Stephen C. Riser University of Washington

1. EXPANDING THE CAPABILITIES OF ARGO-TYPE FLOATS Stephen C. Riser University of Washington Seattle, Washington USA riser@ocean.washington.edu

2. Longevity of US Argo floats as a function of deployment year; the US longevity is consistently  5-10% higher than for non-US float programs

3. Presently: 2 types of US Argo floats Argos antenna SeaBird CTD unit SOLO (SIO; WHOI) APEX (UW; PMEL) Configuration: T, S, p sensors ARGOS 70 samples, 0-2000 m Up to 275 profiles 10-day sampling Cowling (air and oil bladders inside) Air bladder outside, oil bladder inside

4. Float technology, communications, and new sensors… • Low latitude profiling • A new type of float: SOLO-II • Communications: Iridium • Other sensors: O2 , nitrate, wind speed, rainfall, SST, SSS • Profiling under sea ice

5. [ Note: problems within 13 of the Equator ] Displacement volume (cm3)necessary to profile to 2000 m for a float with the volume and mass of APEX 260 ( 240 cm3 usable). Note the lack of necessary displacement volume for profiles to 2000 m at low latitudes. There are now remedies for this problem.

6. An APEX N2 float… For N2 floats, the additional oil and piston connected to the gas canister provide a means to store energy as the gas is compressed during the float descent and recover this energy and use it to increase the float’s buoyancy during the ascent phase.

7. N2 APEX float showing the main piston and pump assembly and N2 canister [ marginal cost $400] N2 canister Main piston Cowling (bladder inside) [ see Argonautics No. 10 for more details ]

8. 2000 m profiles…. t = 20.76   [data from 71 levels]

9. Solo-II Profiling Float SOLO-I and SOLO-II • Compact, lightweight, efficient. • Reduced labor for assembly. • 2000 m profiles anywhere. • Long life (~6 years). • No air bladder. • Reciprocating pump (same as Spray glider) • Scalable (in length, batteries, sensors). • Pumping system adaptable for deep-ocean profiling. Prototype SOLO-2 floats are now undergoing lab-testing; deployments soon.

10. SOLO Version Comparison SOLO-II internal view, SOLO-I in back

11. Dissolved oxygen measurements from profiling floats 2 types of O2 sensors: SBE and Aanderaa Optode UW float 894, with SBE O2 sensor, operated for more than 3 years in the N. Pacific and showed evidence of blooms and net O2 production (Riser and Johnson, Nature, 2008; Martz et al., L-O, in press).

12. Float 894 8/02 – 7/05 99 profiles The first SBE O2 sensor worked well for nearly 3 years, showing only small instrument drift over that time. [ now more than 150 floats with O2 deployed in Argo; 2 types of sensors; see O2 White Paper for details ]

13. Wind speed and rainfall (PAL)… 2h  Profiling float end cap with PAL hydrophone added that can be used to make acoustic measurements of wind speed and rainfall, as on UW float 0006 h  [ h 650 m ] Year-long trajectory of float 0006 in the Bay of Bengal

14. The wind speed from the float and from QwikScat agree well at speeds below about 10 m/sec. [similar good comparisons between float/PAL and TRMM rainfall]

15. Surface salinity in the Bay of Bengal can be very low due to rain events and large river input

16. WIND SPEED 5 m SALINITY  TRMM RAIN RATE rainfalleffect SW monsoon (wet) NE monsoon (dry) SW monsoon (wet) rivers/near coast 2004 2005 Surface salinity in the Bay of Bengal is correlated to both position of the float in the basin and rain input events (Riser et al., L-O, in press)

17. Faster communications: IRIDIUM • 2-way communication with floats (mission changeable after deployment; many downloadable commands: profile depth, interval between profiles, sampling interval, etc.) • Fast communication compared to ARGOS ( 180 byte/sec compared to < 1 byte/sec) • Short times on the surface (  6 minutes for a 55 KB, high resolution deep profile, compared to 9 hours for a low resolution 0.8 KB profile with ARGOS) • Use of new sensors and high-resolution experiments become possible • Cost per profile greater than ARGOS; cost per byte << ARGOS (in the US only)

18. Iridium floats (approximately 150 deployed): An antenna suitable for both Iridium and GPS communications is required for Iridium floats, as well as numerous changes to internal electronics.

19. 1000 m parking depth ✭ [data from 1000 levels] CTD data from UW Iridium float 5037, showing high resolution T and S data (p = 2 dbar) over a 2000 m profile (1000 T/S/p samples); surface time  6 minutes

20. CTD and O2 data from float 5209 in the Bay of Bengal

21. Uses of Iridium….  Applications requiring 2-way communication  More complex sensors that require shore-based processing • Drift-phase sampling  Operation under sea-ice

22. Polarstern 2/25/08 Aug 1 2007 Antarctic sea ice cover: recent seasonal extremes There are now over 75 UW Argo floats in the Antarctic ice zone, with more to be deployed late in 2008. The data from these will yield new clues to the nature of ocean/atmosphere/ice interaction and climate change in the Antarctic.

23. Argo float positions in and around the seasonal ice zone in the Antarctic. For the first time, large amounts of data can be collected under the Antarctic ice in winter. These floats store profile data internally while under ice and transmit the saved profiles during ice-free periods. The floats are programmed with an ice-avoidance algorithm.

24. Water properties in Oct. 2007 Research questions: heat budget; fresh water budget; seasonal variability in the ice zone; oxygen uptake/production; nutrient (NO3) variability; long-term changes?  Water properties in Feb. 2008 

25. 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.

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

27. To examine the relationship between the near surface (5 m) salinity and the true sea surface salinity, 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.

28. 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.

29. This is an example of typical temperature and salinity profiles from the STS sensors. Note that the measurments continue to be collected until the float breaks the sea surface during its ascent.

30. SUMMARY: There are a number of new technical developments taking place with profiling floats, including new float designs, new sensors, and faster communications. Some of these new features are already commercially available. When planning for the observing system of the future, the utility of these developments should be taken into consideration, both globally and regionally.