Nong et al. 
Argo Data 1999-2019 
74). Draofile vertical resolution 
200 
400 
500 
800 
7 1000 
4 1200 
* 1400: 
L600 
L800 
2000 ' 
SD > un X 
S ® S 5 | 
„SS N SS N 
„SS 
x» S & WW A 
S SS Nö „SS „SS 
Time (vears} 
CE 
AR? NN 
ö © x SU 
DS N NO 
% 15000 
5 10000, 
2. 5000 
* On rn AL 
2001 2002 2003 2004 2005 2006 2007 2008 2009 2010 2011 2012 2013 2014 2015 2016 2017 2018 2019 
(c). Number of operational floats bv telecommunication: ARGOS and IRIDIUM 
. x. a > * rn 
{b). Average number of profiles per month 
NEE NA 
n 3000 F— ı __. 
& 2000 '— ARGOS 
2000 = IRIDIUM 
# 
0 
En LA LT NL u __ 
7001 2002 2003 2004 2005 2006 2007 2008 2009 2010 2011 2012 2013 2014 2015 2016 2017 2018 2019 
FIGURE 6 | (a) Changes in Argo CTD profile vertical resolution from year 2000 to 2019. The color bar indicates the number of measurements divided by the number 
of profiles in every 10-dbar bin and in every month, averaged over each year. (b) The average number of total Argo profiles per month. (e) The number of ARGOS and 
Iridium floats. Note that the increase in vertical resolution is due to the increase in Iridium floats 
are publicly available, an auxiliary directory has been established 
at the GDACSs to distribute data from experimental sensors (e.g., 
passive acoustic listeners). The format of the data in the auxiliary 
directory is determined and documented by the float provider. 
ARGO DATA DESCRIPTION 
CTD Profile Vertical Resolution, Pressure 
Ranges, and Geographical Coverage 
Vertical Resolution 
The Argo CTD profile vertical resolution has been changing 
slowly in the past 20 years as float-providing groups switched 
to using Iridium for data telemetry (Figure 6). In the early days 
when only ARGOS telemetry was available, data transmission 
was limited to about 256 bytes of data per ARGOS message, 
which in turn limited the number of P-T-S triplets that could be 
transmitted per profile. Due to this data transmission limitation, 
and also as a means to conserve battery energy, early APEX floats 
used the SBE-41, which operated in the spot-sampling mode and 
returned low-resolution vertical profiles that typically contained 
about 50 to 80 discrete samples per 2,000-dbar profile. Early 
SOLO and PROVOR floats used the SBE-41CP and operated 
in the continuous-profiling mode, but yielded roughly the same 
number of sampling levels as the SBE-41, as the continuous 
rontiers in Marine Science | www.frontiersin.orı 
data from the SBE-41CP were bin-averaged in coarse depth 
bins for ARGOS telemetry. With the transition to Iridium 
telemetry, continuous data from the SBE-41CP are averaged in 
smaller depth bins (typically 1-dbar or 2-dbar bins) to make 
good use of the increased data transmission capability, thus 
giving profiles with higher vertical resolutions. APEX floats 
subsequently switched to using the SBE-41CP as well. 
The SBE-41CP can operate in both the spot-sampling 
mode and the continuous-profiling mode. Some float operators 
prescribe a “mixed” vertical scheme that typically involves 
sampling the deeper (e.g., below 1,000 dbar), less variable part 
of the vertical profile in the low-resolution spot-sampling mode, 
and the shallower, more variable part of the vertical profile in the 
high-resolution CP mode. This “mixed” vertical sampling scheme 
is mainly used for the purpose of conserving the battery energy of 
the floats, especially those that are equipped with biogeochemical 
sensors (Riser et al., 2018). Table 1 gives an overview of the 
primary vertical sampling schemes used by the various float types 
in Argo as of 2019 
Pressure Ranges 
The distribution of pressure ranges of Argo floats has also 
been changing over the past 20 years following the increase 
in float capability to profile to greater depths (Figure 7). Most 
Qanteambear 2020 1 Valııme 7 | Article 701