NOVEMBER 2020 
{a} 
LIN ET AL. 
= ® 
z 
V 
wr 
5241 
| 
4 
PA 
AO 
&0 
— 
x ArOW 
a za a - 
338 34 34.2 344 346 34.8 35 3652 
Salinitv 
587” 
h) Aretie-oriain Overflow Water 
\%) 
— 100 
0 
100 
200 
be Es 
s 
3 400 
a 
500 
600 
{(c) Atlantie-arigin Overflow Water 
% vo 
00 
0 
3 300 
Ss 
Z 1 
5 400 
a 
500 
500 
700 
A420 
„an 
40 0 40 80 
Distance (km) 
(d) Polar Surface Water 
120 
700 
120 
19) 
40 
0 40 80 120 
Distance (km) 
'a) Irminoer Water 
Bd 
00 
% ang 
0 
100 
200 
_ 
E 300 
3 400 
300 
600 
700 
„420 
%) 
200 
> 
= 300 
Ss 
3 400 
500 
500 
30 
0 
“ 
SD 
-80 40 0 40 80 40 0 40 80 
Distance (km) Distance (km) 
FIG. 5. (a) Water mass end members identified by Mastropole et al. (2017) and used in this study (stars), including 
‘he uncertainty (boxes), plotted in the T-S plane. The contours are potential density (kg m). Atlantic-origin 
Dverflow Water (AtOW): 2.50° + 0.66°C, 34.98 + 0.05; Arctic-origin Overflow Water (ArOW): —0.63° + 0.66°C, 
34.92 + 0.01; Polar Surface Water (PSW): —1.42° + 0.18°C, 34.07 + 0.11; Irminger Water (IW): 6.97° + 0.18°C, 
35.07 + 0.05. (b)-(e) Mean vertical sections of percentage presence of (b) the ArOW end member, (c) the ArOW 
and member, (d) the PSW end member, and (e) the IW end member. The highlighted isopycnal of 27.8 kg m *isthe 
upper boundary of the overflow water. 
00 - 
120 
mnesoscale features, boluses, and pulses, are associated with 
a cyclonic and anticyclonic sense of rotation, respectively. 
Following the definitions in Mastropole et al. (2017), we 
identified eight instances of a bolus and nine instances of a 
zulse in our collection of sections (5 sections could not be 
classified as either type of feature). We found relatively little 
difference in the across-strait structure of the alongstream 
velocity field in these two scenarios. However, inspection of the 
individual sections revealed 15 cases characterized by a strong 
zyclonic structure centered in the trough. Figure 6 shows the 
composite mean of these realizations, compared to the com- 
»osite of the remaining seven sections (where again we have 
only plotted regions with at least five realizations). In the 
former case, which is referred to as the cyclonic state, both 
ihe northward-flowing NIIC near the Iceland shelf break 
and the southward-flowing merged NIJ-separated EGC on 
:he western flank of the trough are intensified, while the 
shelfbreak EGC is weakened. In the latter case. referred to 
as the noncyclonic state, the entire trough contains equa- 
corward flow, but it is weaker and more bottom-trapped. 
In addition, the NIIC is weaker but there is enhanced 
soleward flow over much of the Iceland shelf. (The data 
zoverage is insufficient to say anything about the shelfbreak 
GC in this state.) The hydrographic structure is not notice- 
ıbly different in the two states (not shown). The height of the 
overflow layer (ie., the height of the 27.8 kg m * isopycnal) is 
also similar in both composites, although the stronger flow in 
:he cyclonic composite results in a larger transport of DSOW. 
t is clear that these two states are not reflective of boluses and 
aulses, which, as noted above, correspond to large differences 
n overflow layer height. This begs the question: what is the 
nature of this dominant variability? We argue that it is related 
:O wind forcing. 
50 help demonstrate this, we first characterized the velocity 
structure in the center of each section by the lateral gradient of 
the depth-mean velocity across the trough. This is an effective 
Zroncht to van hy RBUNDFSAMT EUR SPFESCHIFET A HP" 
| Inauthenticataer | RDawnlaaden 01/12/72 05-47 
ARA TI}