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

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

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

Float technology, communications, and new sensors…  Low latitude profiling  A new type of float: SOLO-II  Communications: Iridium  Other sensors: O 2, nitrate, wind speed, rainfall, SST, SSS  Profiling under sea ice

Displacement volume (cm 3 ) necessary to profile to 2000 m for a float with the volume and mass of APEX 260 (  240 cm 3 usable). Note the lack of necessary displacement volume for profiles to 2000 m at low latitudes. There are now remedies for this problem. [ Note: problems within  13  of the Equator ]

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. An APEX N2 float…

N 2 APEX float showing the main piston and pump assembly and N 2 canister [ marginal cost $400] N 2 canister Main piston Cowling (bladder inside) [ see Argonautics No. 10 for more details ]

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

Solo-II Profiling Float Compact, lightweight, efficient. Reduced labor for assembly 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. SOLO-I and SOLO-II

SOLO-ISOLO-II # of dive cycles~180~200 Energy (kJ)/dive w/SBE-41cp Max depth (dBar)2300 Ocean Max depth~45%100% TelemetryARGOSIridium Surface time (hr) Mass (kg) Main pressure- case length (in)4126 Seek capabilityBidirectional SOLO Version Comparison SOLO-II internal view, SOLO-I in back

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

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

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 Year-long trajectory of float 0006 in the Bay of Bengal  h 2h2h  Wind speed and rainfall (PAL)… [ h  650 m ]

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]

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

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)  TRMM m SALINITYWIND SPEED RAIN RATE rivers/near coast rainfall effect SW monsoon (wet) NE monsoon (dry)

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)

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.

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 ✭ 1000 m parking depth [data from 1000 levels]

CTD and O 2 data from float 5209 in the Bay of Bengal

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

Aug 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 The data from these will yield new clues to the nature of ocean/atmosphere/ice interaction and climate change in the Antarctic. Polarstern 2/25/08

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.

Water properties in Oct Water properties in Feb Research questions: heat budget; fresh water budget; seasonal variability in the ice zone; oxygen uptake/production; nutrient (NO 3 ) variability; long-term changes?  

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 NO 3 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.

Profile 21, 3/10/08 [near Hawaii] T/ST/S T/O 2 T/NO 3 (WMO )

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.

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.

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.

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.