46
Supplementary Materials
775
776
777
Fig. S1 SEM image of
13
C-labeled U-tube aragonite sample
s (a, b) and the samples post-
778
dissolution (c, d) (after 17 days in seawater of
Ω
=0.64, ~6% of the original samples were
779
dissolved). Samples are spherical aggregation of needles with hexagonal cross-sections.
780
781
47
782
Fig. S2 Relative peak intensity of calcite (104) and aragonite (111) XRD peaks vs. calcite
783
percentage. I
C
is the peak intensity of calcite (104) peak, I
A
is the peak intensity of aragonite
784
(111) peak. Blue circles are standards with different ratios of calcite and aragonite. Green
785
diamonds are sediment trap samples. A set of 6 standards (blue circles) was prepared by mixing
786
different weight % of calcite and aragonite. A standard curve (blue dotted line) of the relative
787
peak intensity vs. weight % calcite was generated. Calcite percentages in the sediment trap
788
samples (green diamonds) were estimated by fitting the data points in the standard curve.
789
790
791
48
792
Fig. S3 Analysis of aragonite percentages in suspended carbonate. Aragonite percentages
793
calculated based on counts and area of calcite/aragonite on the filters generally agree, except for
794
several filters that captured large aragonite or calcite particles. The data points above the 1:1 line
795
in this plot indicate filters that include large
aragonite fragments, wherea
s the data points below
796
the 1:1 line indicate filters that include large
calcite fragments. The inclusion of single large
797
particle of either mineral phase is random and not related to depth.
798
799
49
800
Table S1 A comparison of
Ω
values determined by USC (lab method in this paper) and USF
801
(field method in this paper) by measuring th
e same seawater from SPOT (San Pedro Ocean
802
Time-Series)
803
Depth (m)
USC
USF
DIC
(
μ
mol/kg)
Alkalinity
(
μ
mol/kg)
Ω
pH
Total
Alkalinity
(
μ
mol/kg)
Ω
250 2250.6 2271.6 1.12 7.4097 2273.6 1.17
500 2308.9 2303.6 0.88 7.3306 2303.0 0.91
750 2350.1 2342.1 0.82 7.3117 2344.6 0.83
* Alkalinity was measured at 21°C; pH was measured at 25°C
804
805
50
806
Table S2 Aragonite dissolution experimental conditions and rates
807
In situ
dissolution in the North Pacific
Station #
Depth (m) Temperature
(
°C
)
Ω
aragonite
Dissolution rate
(
×
10
-3
g g
-1
day
-1
)
Rate error
(
×
10
-3
g g
-1
day
-1
)
Station 2
700
5.433
0.557
3.86
0.35
710 5.329 0.540
4.02
0.35
2020 2.092 0.571
5.26
1.47
Station 3
500
6.138
0.804
1.60
0.08
575 5.190 0.671
2.07
0.11
600 4.983 0.638
1.79
0.14
650 4.694 0.552
7.39
0.18
700 4.421 0.452
4.53
0.22
730 4.281 0.488
6.52
0.08
740 4.232 0.486
5.24
0.27
Station 4
350
6.913
0.965
0.99
0.15
400 6.114 0.799
1.17
0.26
425 5.687 0.767
1.73
0.12
450 5.387 0.721
2.48
0.12
500 4.995 0.642
3.55
0.21
Station 5
100
4.185
1.199
0.84
0.32
110 3.981 1.033
0.66
0.26
115 4.079 0.944
0.72
0.23
51
120 4.049 0.868
0.94
0.29
50 6.464 1.464 0.46
0.28
808
Laboratory dissolution
Expt. # Temperature
(
°C
)
Ω
aragonite
Ω
aragonite
error
Dissolution rate
(
×
10
-3
g g
-1
day
-1
)
Rate error
(
×
10
-3
g g
-1
day
-1
)
A3 21 0.867 0.029
1.78
0.07
A4 1.009
0.016 1.19 0.08
A5 0.828
0.019 3.01 0.08
A6 0.971
0.022 0.70 0.08
A7 0.878
0.007 1.71 0.05
A8 0.652
0.017 8.30 0.44
A9 0.558
0.010 13.83 0.53
A10 0.551
0.013 13.84 0.02
A11 0.515
0.006 16.68 0.07
A14 0.636
0.016 6.74 0.15
A17 0.710
0.017 4.82 0.15
A15 5 0.685 0.012
4.76
0.50
A18 0.672
0.023 2.48 0.07
A19 0.699
0.016 1.80 0.06
A20 0.539
0.012 10.07 0.59
A21 0.650
0.008 1.66 0.15
A22 0.818
0.020 1.78 0.07
52
A23 0.543 0.006 4.98 0.09
A24 0.642
0.010 2.61 0.09
A26 0.587
0.016 4.52 0.08
A27 0.743
0.017 3.14 0.09
809
810
53
Table S3 Carbonate percentages by count and by area on
in situ
pump filters
811
Filter ID
Depth (m)
Latitude
Calcite/CaCO
3
Note
By count
By area
S1-D1-1
4575
22°45’N
91%
63%
Large aragonite fragment
S1-D1-3 4575
41%
24%
S1-D2-1 3375
64%
81%
S1-D3-1 150
89%
91%
S2-D1-1 1100 27°45’N 51%
59%
S2-D2-1 620
84%
80%
S2-D3-1 450
91%
93%
S2-D4-1 150
100% 100%
S2-D4-2
150
90%
47%
Large aragonite fragment
S2-D6-1 5300
56%
56%
S2-D7-1 40
99% 100%
S3-D1-1 1000 35°16’N N.A.
N.A.
No CaCO
3
detected
S3-D2-1 400
100% 100%
S3-D3-1 250
91%
95%
S3-D4-1 150
99% 100%
S3-D5-1 5100
100% 100%
S3-D6-1 75
98% 100%
S3-D6-2 75
99% 99%
S4-D2-1 450 41°45’N 100% 100%
S4-D3-1
150
65%
14%
Large aragonite fragment
54
S4-D4-1 4700
99%
99%
S4-D5-1 35 49°50’N 92% 97%
S5-D1-1 500
75%
84%
S5-D2-1 200
94%
97%
S5-D3-1 100
90%
85%
S5-D5-1 4500
N.A.
N.A.
No CaCO
3
detected
* Filter ID were named after: Station # - Depth # - Triplicate #
812
813
55
Model of aragonite dissolution fluxes in the North Pacific water column
814
(1) Thermodynamically-driven (a
biotic) aragonite dissolution
815
We construct a box model of the water column to diagnose the sinking and dissolution of
816
CaCO
3
particles in the upper 2000 m. First, to estimate the dissolution flux due to abiotic
817
aragonite dissolution, sinking aragonite particles are considered to be exposed to dissolution
818
when the water column first reaches
Ω
< 1, and dissolution rates are determined as a function of
819
Ω
according to the relationship
shown in Fig. 2. The whole water column is separated into
820
multiple boxes (box height from 20 to 800 m depending on the depth of CTD deployment). The
821
amount of aragonite dissolution in each box depends on the aragonite flux that reaches the box,
822
the average saturation state of the box, and the ar
agonite particles’ reside
nce period in the box.
823
The sinking flux in the i
th
box
Flux
Zi
(mmol m
-2
day
-1
) and
in situ
dissolution rate in the i
th
box
In
824
Situ Rate
Zi
(
ߤ
mol kg
-1
yr
-1
) are calculated based on the following equations:
825
826
ݔݑ݈ܨ
ݔݑ݈ܨ =
ିଵ
ݔݑ݈ܨ−
ିଵ
݁݉݅ݐ∗݁ݐܴܽ ݊݅ݐݑ݈ݏݏ݅ܦ∗
827
ݔݑ݈ܨ=
ିଵ
ݔݑ݈ܨ−
ିଵ
∗
ሾ
0.013
(
1−Ω
)
ଵ.ଷ
ሿ
∗
ܼ(
ܼ−
ିଵ
)
ݓ
828
Eq. 1
829
݁ݐܴܽ ݑݐ݅ܵ ݊ܫ
=
ݔݑ݈ܨ
∗ܵ∗
ሾ
0.013
(
1−Ω
)
ଵ.ଷ
ሿ
∗
ܼ(
ܼ−
ିଵ
)
ݓ
ܼ(∗ܵ
ܼ−
ିଵ
ߩ∗)
830
=
ݔݑ݈ܨ
∗
ሾ
0.013
(
1−Ω
)
ଵ.ଷ
ሿ
ݓ∗ߩ
831
Eq. 2
832
833
56
where
Z
i
(m) is the depth of the i
th
box,
ݔݑ݈ܨ
(mmol m
-2
day
-1
) is the sinking flux of aragonite
834
at depth
Z
i
,
Ω
is the saturation state of water column at
Z
i
,
ݓ
(m day
-1
) is the sinking rate of
835
aragonite flux,
݁ݐܴܽ ݑݐ݅ܵ ݊ܫ
(
ߤ
mol kg
-1
yr
-1
) is the
in situ
dissolution rate of aragonite at depth
836
Z
i
,
S
(m
2
) is the area of the water-column cross section, and
ߩ
(1029 kg m
-3
) is the density of
837
seawater. In Eq. 1 and 2, aragonite dissolution rate is calculated as established by our dissolution
838
experiments: Rate (g g
-1
day
-1
) = 0.013*(1-
Ω)
1.37
.
839
840
To estimate the average aragonite dissolution fluxes in the North Pacific, water column
841
saturation is taken from measurements at Station 3 (35
°
N, 151
°
W); and an aragonite sinking flux
842
of 0.1 mmol m
-2
day
-1
is assumed at the saturation horizon (430 m). Values adopted in the model
843
are chosen to be generally representative of the N. Pacific transect.
844
845
(b) Respiration-driven or metazoan/zoopla
nkton consumption-driven PIC dissolution
846
For the shallow depth dissolution indicated by
PIC losses in the sediment trap samples, a
847
model is developed to simulate the process in
which sinking fluxes at 100 m are taken from
848
measurements using sediment traps, and a constant dissolution rate of 40% every 100 m is
849
assumed based on the calculated dissolution rate between 100 and 200 m (Fig. 7b). The sinking
850
flux (mmol m
-2
day
-1
) and the
in situ
dissolution rate (
ߤ
mol kg
-1
yr
-1
) are calculated based on the
851
following equations:
852
853
ݔݑ݈ܨ
ݔݑ݈ܨ=
ିଵ
ݔݑ݈ܨ−
ିଵ
∗
40%
100݉
ܼ(∗
ܼ−
ିଵ
)
854
Eq. 3
855
57
݁ݐܴܽ ݑݐ݅ܵ ݊ܫ
=
ݔݑ݈ܨ
∗ܵ∗
40%
100݉
ܼ(∗
ܼ−
ିଵ
)
ܼ(∗ܵ
ܼ−
ିଵ
ߩ∗)
=
ݔݑ݈ܨ
∗40%
ߩ∗݉100
856
Eq. 4
857
858
PIC, calcite and aragonite sinking fluxes at 100 m (
Flux
100m
) are 1.2 mmol m
-2
day
-1
, 0.8 mmol
859
m
-2
day
-1
, and 0.4 mmol m
-2
day
-1
, respectively.
860
861
862