Tuchen et al. 
850 m. In Uncertainty Assessment, we use these overlapping 
velocity time series to assess the uncertainty of the current 
velocity measurements. 
The same steps of filtering and interpolation have been 
applied to current meter data from the PIRATA moored 
surface buoy located at 10 or 12 m from 2005 to the present. 
Like the shallow PIRATA ADCP data, these data provide a 
valuable contribution to filling the data gap near the surface 
where upward-looking ADCP measurements are corrupted due 
to the strong surface reflection. 
MMP Measurements 
At 0°N/23°W, the deep ocean is covered by vertical profiles of the 
McLane moored profiler (MMP). The MMP was first deployed in 
June 2006 and forms an integral part of the KPO moorings ever since. 
However, no MMP was installed during mooring deployment KPO- 
1023 and, unfortunately, during mooring deployment KPO-1063 the 
instrument failed. Apart from that, the MMP provides an overall 
good data coverage and improved full-depth coverage in comparison 
[oO current meter data as installed before 2006 (see Figure 1). 
In general, the MMPs are equipped with an acoustic current 
meter (ACM) and a conductivity-temperature-depth (CTD) sonde 
‚Doherty et al., 1999). From June 2006 to September 2016, the MMP 
was installed to measure current velocities between about 1000 to 
3500 m. It was then moved up to cover the water column between 
850 and 3350 m and to further close the gap between ADCP and 
Moored Velocity Observations at 0°N, 23°W 
MMP measurements. The MMPs were programmed to provide one 
pair of up- and down-profile every 3 to 6 days depending on the 
length of the mooring deployment due to battery consumption. 
With a vertical speed of about 0.20 to 0.25 m s”*, an average profile 
covering the full range of 2500 m takes about 3 to 4 hours. 
Considering the sampling frequency of 3 to 4 measurements per 
second (for CTD and ACM, respectively), the vertical resolution is 
comparably fine and is averaged onto a 1-dbar vertical grid during 
processing. After each pair of profiles, the MMP rests for 3 to 6 days. 
Hence, the temporal resolution is considerably lower when 
compared to velocity data from moored ADCPs and current 
meters (see also Combining Current Velocity Measurements). 
The processing of the MMP current velocities includes a 
correction for high-frequency horizontal velocity fluctuations 
due to instrument vibrations during the up- and downcasts, as 
well as a correction for the horizontal movement of the 
instrument during the up- and downcasts that is due to the tilt 
of the mooring cable that is generally <0.01 m s**. 
LADCP Measurements 
The final data product is complemented by 10 full-depth vertical 
profiles of LADCP measurements carried out during the subsurface 
mooring service cruises (see Table 1) and another 10 deep LADCP 
profiles carried out during the annual service cruises of the moored 
surface buoy (PIRATA-FR-22 to PIRATA-FR-31). LADCP profiles 
were recorded as part of the CTD casts by attaching an upward- 
Iry, 
_ 
500m 
1000m 
{500m 
In 
N 
Ks 
OO” 
ADCPs: 
1 hour / 8-16 m 
Current Meters: 
1-2 hours / 
single depth 
vl 
INA 
MMP: 
3-6 days /1m 
Er 
DNAArn 
3500 
1000 
[Orr rt. aan RRERRAAKHAREFARRURKKRAKARRENUERRFEARKERERARRRAUPKAUKANERAREERARERKUREREAEURRKAKEEKEREAEERMUAREKKREERERAUNDG 
| WE STE a 
2001 2002 2003 2004 2005 2006 2007 2008 2009 2010 2011 2012 2013 2014 2015 2016 2017 2018 2019 2020 2021 2022 
{7 
<-0.3 
a 
Current Meters: 
1-2 hours / 
single depth 
FIGURE 1 | Zonal current velocity time series from the moored observatory at 0°N, 23°W. For reference, the original temporal and vertical resolutions of the differen:? 
‚nstrument types are indicated on the right side. Current meter data below the ADCP range are stretched +15 m about the nominal depth of the instrument. Note 
that the color bar is limited to velocities of up to +0.3 m s”' in order to visualize the deep equatorial circulation. The Equatorial Undercurrent (EUC)} in the upper 
200 m generally exceeds eastward velocities of 0.8 m s”. Also shown are the vertical mean profiles of zonal (u) and meridional (v} velocity {in m s”’} in the inset (thick 
lines) and their standard deviation (shaded envelopes). Please note the different axes for zonal velocity (black: top axis) and meridional velocity (areen: bottom axis) 
The dashen lines indicate the water denth at the maarinag lacatian at anpraoximatel 39230 m 
Zrontiers in Marine Science | www. frontiersin or 
une 2022 | Valume 9 | Article 91097