The table below provides basic information about the float, including primary sensors, mission parameters and current status of profiles.
Institute | CSIRO |
Principal Investigator | Susan Wijffels |
Pressure Sensor | Druck (serial number=10273) |
CTD Sensor | APEX-SBE-41 (serial number=2902) |
CTD Sampling Mode | Burst Sampler |
Controller Board | APF 8 |
Additional Sensors/Software | None |
Park Depth | 1000 m |
Profile Depth | 2000 m |
Launch Date | 26-04-2007 |
Number of D-moded Profiles | 130 |
Calibration Date | 06-05-2012 |
Pressure Drift | Surface Pressure Offset corrected |
Salinity Drift | No salinity drift detected |
This float was deployed by the MV Wellington Express in the southwest Pacific at 29.02 °S, 160.2°E on the 26th April 2007. Since its deployment the float has followed a large anti-clockwise path over the topographically shallow, undersea ridge known as the Lord Howe Seamount Chain. The float’s drift depth was 2000 m and it grounded on numerous profiles over the shallower parts of the ridge. The New Caledonia Basin (greater than 3500m) flanks the ridge on the east while in the west water depths are greater than 4500m in the northern part of the Tasman Abyssal Plain. The float has grounded on the Australian continental shelf and is moving south with the EAC.
The surface pressure for this float is shown in the plot below.
Potential Temperature-Salinity (a), Location (b, Max Temperature (c) and Sea Surface Salinity (d) plots located below.
Surface temperatures generally varied between 19 and 25 ºC and surface salinities from 35.3 to 35.9.
The three plots below highlight an unusual profile in the series (pf 45). The top left plot is salinity versus depth with pf 45 highlighted in red, the top right plot is the TS plot from gilson for profiles 1 to 45 (with pf 45 in red). The bottom plot is the TS plot for profiles 1 to 63 with early profiles (1 to 45 in blue to green to yellow), profile 45 in black and profiles 46 to 63 in orange red.
The last profile in our series available for delayed mode processing, (profile 45) exhibited a sudden and large, step-wise jump in salinity, just above the salinity minimum in Antarctic Intermediate Water (AAIW) present at around 800 to 1000m. The AAIW suddenly became significantly colder (0.017) and fresher (0.06) between 800 and 750 m depth. At first glance, a sudden jump like this would tend to indicate sensor drift caused by instrument damage or bio-fouling. However, the shape of the profile was also significantly different at the surface, with much fresher and warmer waters than previous profiles. Inspection of subsequent, real-time profiles, (profiles 46 to 63) revealed two distinct clusters of profiles distinguished by different AAIW salinity signatures. This clearly showed that the observed drift is real and caused by the float traversing a water mass boundary during its upward ascent into a water mass with markedly different AAIW properties.
The two plots below show a). the location of this float (black circles) in relation to the position of other nearby argo floats (coloured circles) and b). The potential-temperature/salinity curve for this float (in black) compared to nearby argo floats (coloured).
The plot below shows the potential-temperature/salinity relationship for the deepest theta levels where the relationship between the two parameters should show the least variation (left). The potential-temperature/salinity relation for the deepest theta levels for this float (in black) and nearby argo floats (coloured) is displayed below (right).
The deep profiles at depth for this float are obviously divided into two separate clusters sampling different water masses. Nearby Argo floats show that there is a large spread in the data at depth (0.02) and that this separation is due to the float sampling different water masses in different basins separated by a ridge.
There were inversions in profiles; 26,34,79. These were not significant and were not flagged.
Salt hooks were located in profiles; 9,10,11,12,13,15,16,31,32,33,34,35,36,37,38,39,61,62,64,65,66,67,68,71,77,78,79,80,81,82,83,84,85,,86,87,89,92,93,96,100,101,102. These were flagged as QC 4 for both T & S.
The float grounded on multiple profiles; 1, 2, 3, 4, 5, 6, 7, 8, 14, 17, 18 to 33, 43 to 45. Some of the grounded profiles exhibited strange values at the bottom of the profiles, these were QC'd as 4 for both T & S.
A section plot of salinity over time clearly illustrates the abrupt change in water mass properties that occurred at profile 45. AAIW is typically centred at around 1000 m with a distinct salinity minimum. This water mass was markedly fresher over the western and north-western parts of the ridge (profiles 46 to 63) and to a lesser extent in profiles 1 to 3, compared to the AAIW encountered over profiles 4 to 44 over the south-eastern parts of the float trajectory. The isopycnals are displaced upwards over the ridge by the shallowing topography, moving colder, fresher AAIW about 200m up into the water column. The convoluted topography in the region may restrict mixing between basins and create complex pathways of flow resulting in the large observed variability in AAIW water mass properties.
The plot below shows the analysis of salinity drift using the WJO/OW software.
The four plots below show the salinity anomalies on theta surfaces compared to (a) the Gouretski and Kolterman climatology, (b) the CARS (CSIRO Atlas of Regional Seas)/WOA (World Ocean Atlas) climatology, (c) the anomalies within the float series itself, (i.e. the salinity anomaly of each profile from the mean profile average for the float and (d) the raw float salinity compared to the CARS and G&K climatological salinity on a deep theta surface.
The float is very close to the climatologies.
The plots below show the raw float salinity data (solid blue line) compared to neighbouring argo floats (coloured symbols) on a deep potential temperature surface. The locality map shows the location of the profiles for this float and for neighbouring floats.
The float has distinctly crossed a water mass boundary at profile 45. There is a 0.02 to 0.03 spread in the data on a deep theta level. The float is in the middle of the argo envelope.
This float required no salinity drift correction.
The plot below summarises the QC flags and salinity differences for the raw and adjusted salinity fields in the final delayed mode files submitted to the GDAC.
Created 06-05-2012