Confidential manuscript submitted to
Journal of Geophysical Research
Supporting Information for
“Controls on Wintertime Ventilation in Southern Drake Passage”
Lilian A. Dove*
1
, Giuliana A. Viglione*
1
,
2
, Andrew F. Thompson
1
, M. Mar Flexas
1
, Taylor R.
Cason
3
, Janet Sprintall
4
1
Environmental Science and Engineering, California Institute of Technology, Pasadena, California
2
Carbon Brief
, London, United Kingdom
3
University of California Los Angeles, Los Angeles, California
4
Scripps Institution of Oceanography, University of California San Diego, La Jolla, California
Contents
1. Text S1: Processing of Seaglider data
2. Figures S1 to S4
Text S1: Processing of Seaglider data
Seaglider measurements of salinity, temperature, pressure, and dissolved oxygen were col-
lected down to 1000 m depth. Salinity, temperature, and pressure were collected at a vertical res-
olution of approximately 1 m, while dissolved oxygen and optical backscatter data were collected
with a vertical resolution of 2–3 m. 500 dives were performed, each with an upcast and a down-
cast. The raw glider data were processed using the GliderTools toolbox (
Gregor et al.
[2019]).
The data were then mapped onto a regular grid with 5 m vertical spacing and 2.5 km horizon-
tal spacing, which corresponds to a temporal scale of approximately 2.4 hours following the Glid-
erTools routine. With this gridding, each 5 meter depth bin holds approximately 10-15 measure-
ments made by the glider. When transformed into neutral density bins, there are approximately
20 glider measurements in near-surface density bins and up to 100 glider measurements in deep
density bins. The interpolation uses a Gaussian weighting function with vertical and horizon-
tal scales of 10 m and 4 km, respectively.
Optical backscatter data on the gliders was measured 532 nm. Backscatter data was only
collected to 300 m depth, and only in the first third of the deployment. Raw sensor counts were
calibrated using the manufacturer-supplied scale factor and dark counts. The resulting volume
Corresponding author: Lilian A. Dove,
dove@caltech.edu
–1–
Confidential manuscript submitted to
Journal of Geophysical Research
scattering function includes scattering signal from pure seawater and particulate scattering (
Zhang
et al.
[2009];
Vaillancourt et al.
[2004]). The scattering by seawater was calculated using a func-
tion described in
Zhang et al.
[2009] and subtracted from the volume scattering function. The
resulting particulate volume scattering function was converted into particulate optical backscat-
tering coefficient, bbp (
Bol et al.
[2018];
Briggs et al.
[2011]). Finally, following
Briggs et al.
[2011], the backscatter data were filtered using a seven-point minimum filter followed by a seven-
point maximum filter in order to remove spikes, which often occur in profiles of bbp due to ag-
gregate material.
Supplemental Figures
Figure 1.
Temperature-Salinity diagrams for the June northward transect by the second Seaglider. Points
are colored by the latitude at which they were collected. (a) shows data for the entire transect; (b) shows data
only in the region immediately surrounding the PF (approximately 1 degree of latitude). The core of the PF
was located at approximately 58.5
°
S.
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Confidential manuscript submitted to
Journal of Geophysical Research
SACCF
PF
SAF
SACCF
PF
SAF
Figure 2.
Glider track with various definitions of the Polar Front in (a) June and (b) July. Gradient of Abso-
lute Dynamic Topography [ADT] on the date of the PF crossing is shown in color with ADT definitions of the
major fronts of the ACC by
Kim and Orsi
[2014] in black dashed contours. Glider transects are shown in light
red with the location of the PF crossing based on hydrographic definitions by
Orsi et al.
[1995] at the red star.
SACCF = South ACC Front. PF = Polar Front. SAF = Subantarctic Front.
References
Bol, R., S. A. Henson, A. Rumyantseva, and N. Briggs (2018), High-Frequency Variability
of Small-Particle Carbon Export Flux in the Northeast Atlantic,
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–3–
Confidential manuscript submitted to
Journal of Geophysical Research
(b)
(c)
Figure 3.
Surface forcing over Drake Passage over the deployment, from ECMWF ERA5 reanalysis. Drake
Passage is taken as the box bounded by 55
°
S, 65
°
S and 60
°
W, 70
°
W. (a) Histogram of wind directions. The
winds are primarily westerly and south-westerly , as is typical of Drake Passage. (b) Surface heat flux, with
the diurnal cycle removed. The dotted black line denotes zero surface heat flux. (c) 10-meter wind stress. In
(b) and (c), the dashed blue and red lines indicate the start and end, respectively, of the glider deployment.
Monterey, G. I., and S. Levitus (1997),
Seasonal variability of mixed layer depth for the
world ocean
, US Department of Commerce, National Oceanic and Atmospheric Adminis-
tration, National Environmental Satellite, Data, and Information Service.
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the Antarctic Circumpolar Current,
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(5), 641–673.
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backscattering properties of marine phytoplankton: relationships to cell size, chem-
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(2), 191–212, doi:
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–4–
Confidential manuscript submitted to
Journal of Geophysical Research
Figure 4.
Histogram of mixed layer depths from glider data, using the criterion of
Δ
휎
0
=
0
.
125 kg m
−
3
from the surface [
Monterey and Levitus
, 1997].
–5–