NOVEMBER 2020 
LIN ET AL. 
30737 
Ger 
Ti) 
* CTD stations 
*  Along-track ADT 
— | Atrabjarg line N 
IA: 
5697 
55° 
x 
64° 
g Fra 
40° TA 
ww 35°7 
30°W 
EFF 
95°W 
0°W 
FIG. 2. Locations of the hydrographic and satellite measurements used in the study. The red 
Jdots are the CTD stations. There are a total of 122 CTD sections (many of them overlap, 
nence the dense clustering of red dots). The Lätrabjarg transect from Mastropole et al. (2017) 
s the black line. The blue dots are the absolute dynamic topography (ADT) altimeter 
neasurements. 
investigated by Moritz et al. (2019). While these measure- 
ments have enhanced our understanding of the flow com- 
ponents in Denmark Strait, they are limited in cross-strait 
coverage and only have near-bottom temperature and 
salinity information. 
In this study we analyze the updated collection of shipboard 
occupations of the Lätrabjarg line (Fig. 1). The number of 
occupations is now 122, and, importantly, 22 of them contain 
direct velocity measurements. This provides the first-ever ro- 
vust view of the two-dimensional velocity structure across the 
strait. It enables us to determine the fate of the three above- 
nentioned pathways of overflow water into Denmark Strait, 
including the water masses they advect and their relationship 
iO the NIIC. We are also able to investigate dynamical aspects 
of the overflow. The paper is organized as follows. We begin 
with a presentation of the data. This is followed by a descerip- 
jon of the mean hydrographic and velocity structure and the 
sartitioning of the overflow transport by water masses and 
currents. We then characterize the dominant mode of vari- 
ability and its relationship to local wind forcing. Finally, we 
address the hydraulic criticality of the overflow, along with 
the occurrence of symmetric instability and implications 
for mixing. 
J).001°C and 0.002, respectively. A detailed description of the 
process used for constructing the gridded sections is found in 
Mastropole et al. (2017). Briefly, each occupation is projected 
anto the standard Lätrabjarg line (black line in Fig. 2), and 
vertical sections of the hydrographic variables are con- 
structed with a grid spacing of 2.5km X 10m. We followed 
‚he same procedure for the 11 additional occupations con- 
sidered here, which are listed in Table 1. We also use direct 
velocity information obtained on 22 of the sections (Table 1; 
Fig. 3). This consisted of vessel-mounted acoustic Doppler 
zurrent profiler (ADCP) data (15 of the occupations) and 
‚owered ADCP data (7 of the occupations). Our study fo- 
zuses primarily on the 22 occupations with velocity data, 
sxcept for section 5 where the full historical hydrographic 
dataset is used. 
Absolute geostrophic velocity sections were constructed 
asing the gridded hydrographic sections in conjunction with 
zridded sections of the cross-track ADCP velocities, follow- 
ng the same procedure as in Pickart et al. (2016). Errors in the 
volume transport estimates are associated with the instrument 
ıncertainty, the gridding process, and the inability to measure 
‘he flow in the bottom triangles (the area beneath the deepest 
common level of adjacent stations). Because of the generally 
small station spacing of the sections, the latter effect is taken to 
Je negligible. The instrument uncertainties of both the vessel- 
nounted ADCP and lowered ADCP are taken as 0.02 ms”! 
‚Pickart et al. 2016, 2017). The gridding error was obtained by 
calculating the differences between the vertically averaged 
velocity measurement at each station versus the same quantity 
determined using the gridded values closest to the station 
‚Nikolopoulos et al. 2009), and was found to be on average 
).008 m s 7! (with little variation from section to section). The 
inal error is taken to be the root of the sum of the squares 
af the instrument and gridding errors, 0.022 ms*, and is ap- 
alied over the area of the section where the transport is 
being calculated. Since this does not assume that the errors 
2. Data and methods 
a. Lätrabjarg sections 
We use 122 occupations of the Lätrabjarg conductivity- 
(emperature-depth (CTD) transect across Denmark Strait 
:aken between 1990 and 2018 (Fig. 2). This is an updated 
version of the dataset used by Mastropole et al. (2017), who 
analyzed 111 of the sections (1990-2012; see Table 1 in 
Mastropole et al. 2017). As noted in Mastropole et al. (2017), 
the contributing institutions each applied their own calibration 
procedures and processing steps. The accuracy of the temper- 
ature and salinity measurements are generally deemed to be 
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