Effect of Dissolved Organic Carbon and Alkalinity on the Density of
Aquat Geochem DOI 10.1007/s10498-010-9111-2 ORIGINAL PAPER
Effect of Dissolved Organic Carbon and Alkalinity on the Density of Arctic Ocean Waters Frank J. Millero • Fen Huang • Ryan J. Woosley • Robert T. Letscher Dennis A. Hansell
•
Received: 23 June 2010 / Accepted: 15 October 2010 Ó Springer Science+Business Media B.V. 2010
Abstract At constant temperature, the density of deep waters in the oceans is higher than that of surface waters due to the oxidation of plant material that adds NO3, PO4, and Si(OH)4, and the dissolution of CaCO3(s) that adds Ca2? and HCO3. These increases in the density have been used to estimate the absolute salinity of seawater that is needed to determine its thermodynamic properties. Density (q), total alkalinity (TA), and dissolved organic carbon (DOC) measurements were taken on waters collected in the eastern Arctic Ocean. The results were examined relative to the properties of North Atlantic Waters. The excess densities (Dq = qMeas - qCalc) in the surface Arctic waters were higher than expected (maximum of 0.008 kg m-3) when compared to Standard Seawater. This excess is due to the higher values of the normalized total alkalinity (NTA = TA * 35/S) (up to *2,650 lmol kg-1) and DOC (up to *130 lmol kg-1) resulting from river water input. New measurements are needed to determine how the DOC in the river waters contributes to the TA of the surface waters. The values of Dq in deep waters are slightly lower (-0.004 ± 0.002 kg m-3) than that in Standard Seawater. The deep waters in the Arctic Ocean, unlike the Atlantic, Pacific, Indian, and Southern Oceans, do not have significant concentrations of silicate (maximum *15 lmol kg-1) and that can affect the densities. Since the NTA of the deep Arctic waters (2,305 ± 6 lmol kg-1) is the same as Standard Seawater (2,306 ± 3 lmol kg-1), the decrease in the density may be caused by the lower concentrations of DOC in the deep waters (44–50 lmol kg-1 compared to the Standard Seawater value of 57 ± 2 lmol kg-1). The relative deficit of DOC (7–13 lmol kg-1) in the deep Arctic waters appears to cause the lower densities (-0.004 kg m-3) and Absolute Salinities (SA, -0.004 g kg-1). The effect of increases or decreases in Dq and dSA due to DOC in other deep ocean waters may be hidden in the correlations of the changes with silicate. Further work is needed to separate the effects of SiO2 and DOC on the density of deep waters of the world oceans. Keywords
Dissolved organic carbon DOC Alkalinity Density Arctic Ocean
F. J. Millero (&) F. Huang R. J. Woosley R. T. Letscher D. A. Hansell Rosenstiel School of Marine and Atmospheric Science, University of Miami, Miami, FL 33149, USA e-mail: [email protected]
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1 Introduction Although the composition of the major constituents of surface seawaters is relatively constant, the composition of deep waters can differ due to the oxidation of plant material adding NO3, PO4, and Si(OH)4 and the dissolution of CaCO3(s) increasing Ca2? and HCO3-. Brewer and Bradshaw (1975) and Millero (2000) have shown that these composition differences can affect the relationship between the measured conductivity Practical Salinity (SP) and physical properties such as density (q). Many of the thermodynamic properties of seawater, as well as other natural waters (lakes and estuaries), have been shown to be a function of the Absolute Salinity (SA) rather than the Practical Salinity (Millero 1974; Millero et al. 1976b). The physical chemical properties of natural waters are directly related to the composition of the major components, but not the salinity determined by conductivity. Non-electrolytes like Si(OH)4 and dissolved organic carbon (DOC), for example, do not have a large conductivity signal but can affect the physical properties of seawater. For this reason, the new Gibbs function for the thermodynamic properties of seawater (IAPWS 2008; Feistel 2008) is expressed as a function of Absolute Salinity rather than the Practical Salinity. The seawater used to determine the density (Millero and Poisson 1981), as well as other properties of seawater, was Atlantic surface waters of known Chlorinity. These Atlantic waters have low concentrations of nutrients and nearly constant total alkalinity (TA), total dissolved CO2 (TCO2) and dissolved organic carbon (DOC). Millero et al. (1998, 2008b) examined the composition of the North Atlantic surface waters used to calibrate salinometers (Standard Seawater) and to measure most of the physical chemical properties of seawater. They used the composition to determine the Reference Salinity (SR). For the range of salinities where Practical Salinities are defined ð2\SP \42Þ; SR is related to the Practical Salinity (SP) by SR ¼ ð35:16504=35ÞSP ; g kg1
ð1Þ
Within the accuracy of present measurements, this reference composition is identical to that of Standard Seawater collected in a specific region of the North Atlantic. Millero et al. (2008b) estimated that the absolute uncertainty of SR is ±0.007 g kg-1. The difference between SR and SP (0.165 g kg-1) is much larger than the at-sea precision of measurements of SP (*0.003). This difference is related to the loss of boric acid and volatile salts during evaporation at 450°C (Millero 2006). The relationship of Practical Salinity Scale to Chlorinity (Cl) was defined by (Millero 2006) SP ¼ 1:80655 Cl
ð2Þ
This equation gives a value of SP = 35.000 when Cl = 19.374, the value for Standard Seawater used in many of the early physical chemical studies (Millero 2010). The Absolute Salinity of other waters in the oceans is related to the SR by SA ¼ SR þ dSA
ð3Þ
The correction dSA to the Reference Salinity SR is the sum of all the masses of the dissolved material added to deep waters (Millero et al. 2008b). Density measurements of seawaters by Millero et al. (1976a, b, 1978, 2008a, 2009; Millero 2000) were used to estimate the values of dSA for samples of seawater collected in the major oceans. The measured Practical Salinity SP and the differences in the density of seawater and pure water were measured on each sample at 25°C and atmospheric pressure (0 bars). The differences
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Aquat Geochem
in the measured and calculated densities from the equation of state of Millero and Poisson (1981) (Dq) were used to estimate the values of dSA dSA = g kg1 ¼ ðSA SR Þ= g kg1 ¼ Dq= kg m3 =0:7518 ð4Þ The 0.7518 kg m-3/(g kg-1) factor is determined from the partial derivative qq/qSA at 25°C and 1 atmosphere. Density measurements reported by Millero et al. (1976a, b, 1978, 2008a, 2009) indicated that the values of Dq and dSA were linear functions of the concentrations of Si(OH)4. Although changes in other nutrients and TA also showed a linear behavior, silicate was used because it displayed the best correlations, it is related to the other variables, it accounts for a significant fraction of the added material, and it is 90% non-ionic, thus having little effect on conductivity. McDougall et al. (2009) summarized all of the present 811 measurements and derived the equation for the world oceans ð5Þ dSA = g kg1 ¼ ðSA SR Þ= g kg1 ¼ 9:824 105 SiðOHÞ4 = lmol kg1 The standard error of the fit is 0.0054 g kg-1. This relationship was combined with global Si(OH)4 data to derive a relationship that can be used to estimate SA for many locations in the ocean (McDougall et al. 2009). It is assumed that these equations will be improved as more density measurements are made in other parts of the ocean. In the present paper, we present new density measurements made on waters collected in the Eastern Arctic Ocean. The effect of TA and DOC on the excess densities is examined.
2 Experimental Methods Samples were collected aboard the German icebreaker FS Polarstern during cruise ARKXXIII/3 (12 Aug. to 17 Oct., 2008). The cruise track circumnavigated the Arctic with extensive occupation of the western Chukchi/East Siberian Sea shelf break and adjacent Mendeleyev Ridge region. In addition, a transect crossing the Canada, Makarov, and Eurasian Basins at *80°N was occupied. Sea ice-free conditions were generally present south of 80°N in the study region with heavy ice conditions present to the north. Sampling was carried out through the ship’s hull-mounted seawater intake line at a depth of *10 m. Samples for TA, salinity, and density determinations were collected in 125-cm3 HDPE (high density polyethylene) bottles and sealed with parafilm until analyzed in the laboratory. Waters for DOC analysis were filtered inline between the Niskin bottles and 60-ml HDPE bottles and then stored frozen until analysis in the shore laboratory. Practical Salinities were measured with a Guildline Portasal salinometer calibrated with Standard Seawater (batch P31). It should be pointed out that the addition of Ca2? from the dissolution of CaCO3(s) causes very small changes in the measured Practical Salinity, SP. The densities were measured on a Paar 500 densimeter at 25.000 ± 0.003°C. Although the salinity was measured at sea, it was remeasured ashore at the same time as the densities were measured to account for any evaporation that may have occurred after collection. The relative density (q - q0) measurements of Standard Seawater were reproducible and agreed with those calculated from the equation of state (Millero and Poisson 1981) to r = 0.002 kg m-3. All of the measurements were taken relative to the density of pure water (q0) based on the equations of Kell (1975) and adjusted to the 1990 temperature scale (Spieweck and Bettin 1992). The densities for pure water from this equation are embedded
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Aquat Geochem
in the hardware of the Paar 500 densimeter. These relative densities are not strongly affected by changes in the temperature scale or the absolute value for the density of pure water used to calibrate the densimeter. Measurements taken on Standard Seawater (P146) of known Practical Salinity yielded densities at 25°C that agreed with the equation of state to within r = 0.003 kg m-3, which is the precision of the measurements. The excess densities (Dq = qMeas - qCalc) were determined by comparing the measured values to those determined from the equation of state of seawater (Millero and Poisson 1981). TA measurements were taken using methods developed by Millero et al. (1993). The titration system was calibrated using seawater of known TA (provided by Dr. Andrew G. Dickson, UCSD-SIO-Marine Physical Laboratory) and had a precision of ±2 lmol kg-1. DOC measurements were taken by high-temperature combustion using the methods of Farmer and Hansell (2007), with a precision of 2 lmol kg-1. DOC in Standard Seawater collected in the North Atlantic was 57.2 ± 2 lmol kg-1 and NTA was 2,306 ± 3 lmol kg-1. The surface layer data considered here exhibited little dilution by sea ice melt, as assessed by d18O measurements and as reported by Letscher et al. (2010).
3 Results Salinity (SP), TA, DOC, and excess density (Dq = qMeas - qCalc) were determined for all the Arctic seawaters returned to the laboratory. The hydrographic data and the laboratory measurements, as a function of location and depth, are tabulated in Table 1, and the surface values are compiled in Table 2. NTA results are shown as a function of depth in Fig. 1. All of the deep waters have NTA of 2,305 ± 6 lmol kg-1, similar to the values for Standard Seawater of 2,306 ± 3 lmol kg-1 collected in the North Atlantic. The surface values increase to concentrations as high as 2,650 lmol kg-1. Dissolved organic carbon (DOC) concentrations are shown as a function of depth in Fig. 2. The deep waters below 150 m have values between 44 (the deep Arctic basin waters) and 51 lM (the Atlantic water layer), which are lower by 6–13 lmol kg-1 than the values in North Atlantic Standard Seawater (57.2 ± 2 lmol kg-1). The surface water DOC concentrations are as high as 130 lmol kg-1, much higher than surface waters in other oceans (commonly \80 lmol kg-1; Hansell et al. 2009). The surface distributions of NTA and DOC at 10 m depth are shown in Figs. 3 and 4. The high values of NTA and DOC originate from Arctic rivers (Anderson et al. 2004; Letscher et al. 2010). The measured excess densities Dq/(kg m-3) = qmeas - qcalc are shown as a function of depth in Fig. 5. The deep waters have values of Dq = -0.004 ± 0.002 kg m-3, while the surface waters have values as high as Dq = 0.008 ± 0.002 kg m-3.
4 Discussion Unlike other oceans, the deep waters of the Arctic have values of Dq that are negative. Most deep ocean waters have positive values of Dq due to the addition of nutrients and calcium carbonate. Determinations of nutrients in Arctic deep water are sparse and concentrations are very low compared with most other deep ocean waters. The silicate concentrations, for example, have maximum values in deep water of *15 lmol kg-1 (Middag et al. 2009). Based upon our work in other oceans, this Si concentration will increase the
123
Aquat Geochem Table 1 Measurements of alkalinity, dissolved organic carbon, and excess density for waters in the Arctic Ocean as a function of depth LAT. o N
LONG. E
o
Depth dbar
Temp C
o
TA lmol kg-1
SP
NTA lmol kg-1
DOC lmol kg-1
Dq kg m-3
80.46
-158.68
3.6
-1.617
2,104
30.208
2,437
67.7
0.000
80.46
-158.68
30.1
-1.504
2,218
31.810
2,440
66.8
0.000
80.46
-158.68
80.46
-158.68
-1.611
2,213
31.992
2,421
66.2
0.002
101
49.8
-1.561
2,244
32.591
2,410
61.0
-0.005
80.46
-158.68
201.7
-0.909
2,271
34.346
2,314
58.5
-0.006
80.46
-158.68
303.2
0.468
2,282
34.756
2,298
53.7
-0.005
80.46
-158.68
506
80.46
-158.68
1,013.8
0.792
2,293
34.864
2,302
49.6
-0.006
-0.049
2,297
34.932
2,302
48.4
-0.004
80.46
-158.68
2,031.4
-0.408
2,300
34.950
2,304
43.6
-0.006
80.46
-158.68
3,054
-0.329
2,306
34.955
2,309
43.2
-0.002
80.58
-162.40
3.5
-1.611
2,118
30.338
2,443
66.6
0.006
80.58
-162.40
10.1
-1.613
2,119
30.446
2,436
66.2
0.002
80.58
-162.40
50.5
-1.611
2,216
32.081
2,418
63.4
0.004
80.58
-162.40
101.4
-1.617
2,231
32.668
2,391
60.5
0.001
80.58
-162.40
202.4
-0.880
2,276
34.345
2,319
58.4
-0.005
80.58
-162.40
303.3
0.402
2,279
34.730
2,296
50.6
-0.006 -0.006
80.58
-162.40
506
0.544
2,284
34.865
2,293
48.3
80.58
-162.40
1,013.2
-0.126
2,290
34.894
2,297
48.8
-0.005
80.58
-162.40
2,031.3
-0.416
2,293
34.951
2,297
44.0
-0.006
2,592.7
-0.005
80.58
-162.40
-0.365
2,298
34.960
2,301
43.9
80.55
-174.69
4
-1.639
2,123
30.633
2,425
67.9
0.001
80.55
-174.69
29.9
-1.544
2,229
32.149
2,426
68.5
0.000
80.55
-174.69
50.4
-1.653
2,222
32.332
2,405
65.2
0.000
80.55
-174.69
99.8
-1.484
2,246
33.055
2,379
61.5
0.000
80.55
-174.69
202.2
-0.460
2,284
34.490
2,318
56.6
-0.002
80.55
-174.69
303.6
0.685
2,294
34.807
2,306
51.0
-0.004
80.55
-174.69
505.8
0.710
2,289
34.862
2,298
52.6
-0.006
80.55
-174.69
1,013.2
-0.122
2,289
34.880
2,297
46.8
-0.007
80.55
-174.69
2,031.2
-0.411
2,295
34.965
2,297
40.8
-0.001
80.55
-174.69
2,553.4
-0.368
2,310
35.000
2,310
40.8
-0.004
80.39
178.71
9.8
-1.597
2,091
30.249
2,420
69.8
-0.001
80.39
178.71
40.4
-1.642
2,237
32.412
2,415
64.6
-0.002
80.39
178.71
101.1
-1.362
2,250
33.586
2,345
63.5
-0.004
80.39
178.71
202.2
-0.231
2,277
34.535
2,308
57.1
-0.002
80.39
178.71
303.6
0.965
2,283
34.811
2,295
52.3
-0.005
80.39
178.71
405
0.909
2,292
34.836
2,303
51.4
-0.005
80.39
178.71
506.3
0.781
2,300
34.850
2,310
51.8
-0.005
80.39
178.71
759.4
0.261
2,292
34.861
2,301
50.6
-0.004
80.39
178.71
1,012.9
-0.105
2,291
34.869
2,300
50.7
-0.001
80.56
175.74
3.5
-1.521
1,957
28.102
2,437
76.0
0.000
80.56
175.74
29.5
-1.308
2,176
31.472
2,420
71.1
0.005
80.56
175.74
50.2
-1.551
2,222
32.818
2,369
64.9
0.003
123
Aquat Geochem Table 1 continued LAT. o N
LONG. E
o
Depth dbar
Temp C
TA lmol kg-1
SP
NTA lmol kg-1
o
DOC lmol kg-1
Dq kg m-3
80.56
175.74
100.9
-1.330
2,281
34.140
2,338
63.1
0.002
80.56
175.74
202.3
0.326
2,282
34.643
2,306
53.7
0.002
80.56
175.74
303.3
0.950
2,293
34.824
2,305
51.0
0.001
80.56
175.74
555.8
0.611
2,290
34.869
2,298
50.0
-0.004
80.56
175.74
1,013.6
-0.148
2,299
34.870
2,308
51.3
-0.005
80.56
175.74
2,031.6
-0.410
2,294
34.954
2,297
42.8
-0.005
80.56
175.74
2,530.6
-0.369
2,308
34.966
2,310
40.0
-0.003
81.00
164.87
3.7
-1.490
1,966
27.601
2,494
111.0
0.002
81.00
164.87
10.1
-1.487
1,967
27.702
2,485
105.8
0.002
81.00
164.87
50.5
-1.550
2,247
33.605
2,340
72.4
0.001
81.00
164.87
101.3
-1.169
2,287
34.318
2,332
61.7
-0.001
81.00
164.87
202.7
0.684
2,294
34.743
2,311
51.5
-0.003
81.00
164.87
304.3
1.008
2,290
34.846
2,301
50.7
-0.004
81.00
164.87
507.2
0.619
2,295
34.867
2,303
50.6
-0.002
81.00
164.87
1,015.8
-0.221
2,297
34.881
2,305
50.3
-0.005
81.00
164.87
2,031.5
-0.408
2,308
34.945
2,312
42.5
-0.003
81.00
164.87
2,742.3
-0.353
2,303
34.959
2,306
42.2
-0.001
81.02
145.04
3.5
-1.737
2,172
31.848
2,387
81.02
145.04
10.3
-1.738
2,186
31.903
2,399
89.1
0.001 -0.001
0.002
81.02
145.04
50.5
-1.643
2,270
33.966
2,339
69.1
81.02
145.04
101.5
-1.009
2,290
34.447
2,326
61.1
0.000
81.02
145.04
152.3
-0.198
2,282
34.638
2,306
57.7
-0.004
81.02
145.04
303.8
0.972
2,298
34.848
2,308
53.6
-0.004
81.02
145.04
760.2
-0.029
2,299
34.869
2,308
51.0
-0.005
81.02
145.04
1,522.2
-0.467
2,285
34.915
2,291
46.7
-0.003
80.97
142.08
10.4
-1.750
2,171
32.013
2,374
88.5
-0.001
80.97
142.08
50.7
-1.597
2,265
33.739
2,350
70.5
-0.001
80.97
142.08
101.4
-1.042
2,281
34.430
2,318
58.3
-0.004
80.97
142.08
202.6
0.804
2,290
34.781
2,305
52.2
-0.004
80.97
142.08
407.6
0.884
2,288
34.883
2,296
51.8
-0.005
80.97
142.08
1,012.4
-0.247
2,292
34.888
2,299
47.0
-0.004 -0.004
80.97
142.08
1,584.8
-0.435
2,299
34.998
2,299
43.2
80.98
139.01
10.3
-1.750
2,195
32.138
2,391
85.0
0.001
80.98
139.01
50.8
-1.664
2,276
33.958
2,346
65.8
-0.004
80.98
139.01
101.3
-0.859
2,280
34.488
2,314
56.3
-0.004
80.98
139.01
253.1
1.236
2,295
34.871
2,304
51.8
-0.005
80.98
139.01
505.6
0.514
2,291
34.879
2,299
51.8
-0.003
80.98
139.01
1,013.4
-0.232
2,299
34.888
2,306
52.4
-0.005
80.98
139.01
1,667.8
-0.533
2,309
34.946
2,313
44.6
-0.004
81.01
136.11
3.7
-1.742
2,196
32.138
2,392
92.0
0.002
81.01
136.11
10.1
-1.745
2,205
32.144
2,401
91.7
0.000
81.01
136.11
49.1
-1.704
2,264
33.674
2,353
71.2
-0.001
123
Aquat Geochem Table 1 continued LAT. o N
LONG. E
o
Depth dbar
Temp C
TA lmol kg-1
o
SP
NTA lmol kg-1
DOC lmol kg-1
Dq kg m-3
81.01
136.11
101.3
-0.902
2,300
34.472
2,335
56.5
-0.005
81.01
136.11
202.3
1.519
2,297
34.860
2,306
49.3
-0.005
81.01
136.11
404.8
1.300
2,312
34.911
2,318
48.0
-0.004
81.01
136.11
1,013.1
-0.265
2,304
34.907
2,310
48.6
-0.002
81.01
136.11
2,541.8
-0.768
2,307
34.932
2,311
44.1
-0.003
81.24
121.27
3.4
-1.778
2,231
32.992
2,367
79.0
0.000
81.24
121.27
10.3
-1.780
2,241
33.088
2,371
77.1
0.001
81.24
121.27
50.4
-1.757
2,284
33.824
2,364
74.0
0.003
81.24
121.27
101.1
-0.602
2,277
34.377
2,319
57.5
-0.001
81.24
121.27
202.4
1.707
2,296
34.882
2,304
49.9
-0.002
81.24
121.27
303.2
1.424
2,295
34.891
2,302
48.7
-0.002
81.24
121.27
505.9
0.835
2,296
34.906
2,303
47.6
-0.003
81.24
121.27
1,013.1
-0.326
2,296
34.907
2,302
48.4
-0.001
81.24
121.27
2,031.5
-0.760
2,308
34.929
2,312
45.0
-0.002
81.24
121.27
3,054.1
-0.760
2,301
34.944
2,305
43.8
-0.003
81.24
121.27
4,260.4
-0.640
2,307
34.948
2,310
43.0
-0.002
Table 2 Measurements of alkalinity, dissolved organic carbon, and excess density for surface water (*10 m) in the Arctic Ocean LAT. o N
LONG. o E
Temp C
o
SP
TA lmol/kg
NTA lmol/kg
DOC lmol/kg
Dq kg m-3
74.92
-127.00
-1.28
27.601
1,941.3
2,461.8
60.5
0.002
74.86
-128.38
-1.01
27.425
1,929.6
2,462.6
60.7
-0.003
74.81
-129.76
-1.01
27.057
1,911.5
2,472.7
61.5
0.004
74.78
-129.39
-0.94
26.656
1,887.7
2,478.6
63.9
0.005
74.80
-130.67
-0.93
26.261
1,868.7
2,490.5
64.9
0.006
74.82
-131.25
-0.91
24.448
1,769.0
2,532.5
64.7
0.005
69.50
-136.01
6.07
24.237
1,750.7
2,528.1
89.4
0.007
73.34
-141.23
4.64
22.886
1,681.6
2,571.7
61.9
0.006
74.49
-147.17
3.11
22.891
1,670.4
2,554.0
60.6
0.004
75.17
-151.39
3.67
22.859
1,673.4
2,562.2
61.8
0.003
75.87
-155.32
1.92
24.227
1,761.2
2,544.3
61.4
0.003
76.93
-162.98
-0.83
24.340
1,766.9
2,540.7
59.6
0.004
77.09
-163.86
-0.73
24.771
1,785.0
2,522.1
59.1
0.003
77.47
-165.31
-0.83
26.129
1,867.8
2,501.9
59.5
0.002
77.95
-169.77
-1.04
26.220
1,858.8
2,481.3
58.3
0.004
78.00
-170.09
-1.19
26.143
1,858.2
2,487.7
59.6
0.002
78.11
-173.04
-1.02
28.947
2,029.2
2,453.5
62.8
0.003
78.23
-178.68
-1.55
29.137
2,029.2
2,437.5
61.6
0.002
78.23
179.17
-1.59
30.544
2,122.2
2,431.8
67.1
0.002
78.07
178.47
-1.62
30.541
2,117.9
2,427.2
64.6
-0.004
123
Aquat Geochem Table 2 continued LAT. o N
LONG. E
o
Temp C
o
SP
TA lmol/kg
NTA lmol/kg
DOC lmol/kg
Dq kg m-3 -0.001
78.15
177.47
-1.61
30.549
2,090.0
2,394.5
66.1
78.41
173.93
-1.55
30.586
2,117.8
2,423.4
64.1
0.003
78.47
173.00
-1.52
30.592
2,117.1
2,422.1
64.3
-0.002
78.19
172.73
-1.6
29.834
2,065.3
2,422.9
67.8
0.001
77.97
173.05
-1.65
30.430
2,099.9
2,415.2
66.9
0.002
77.60
177.07
-1.29
30.847
2,124.2
2,410.2
65.3
0.001
77.60
179.66
-1.27
30.185
2,081.2
2,413.1
67.5
0.001
77.60
-177.77
-1.36
30.084
2,077.2
2,416.7
64.8
0.003
77.59
-172.16
-0.88
30.101
2,079.1
2,417.5
63.7
0.001
77.59
-171.34
-0.99
30.343
2,097.0
2,418.9
65.0
-0.002
77.58
-170.48
-0.87
28.773
2,027.1
2,465.8
75.1
-0.001
77.59
-170.46
-0.86
28.801
2,015.4
2,449.2
66.1
0.003
77.62
-175.86
-0.98
28.830
2,008.8
2,438.8
68.4
0.004
77.60
-176.66
-0.98
28.800
2,018.4
2,452.9
62.3
0.001
77.51
-178.68
-1.22
30.214
2,090.1
2,421.2
70.5
0.001 -0.004
77.24
178.58
-0.84
30.161
2,090.8
2,426.2
70.1
77.31
179.05
-0.76
30.163
2,085.7
2,420.2
67.8
0.001
77.61
174.54
-1.41
30.236
2,088.6
2,417.7
68.6
0.000
77.34
174.14
-0.91
30.829
2,123.5
2,410.8
67.5
0.002
77.06
173.71
-0.85
30.840
2,126.2
2,413.0
70.0
-0.003
76.78
173.29
-1.02
30.471
2,103.4
2,416.0
72.8
0.000
76.47
172.85
-0.74
30.476
2,103.3
2,415.5
71.5
0.001
76.23
172.51
-0.65
30.486
2,107.1
2,419.1
73.3
0.001
75.98
172.16
-1.12
30.488
2,103.4
2,414.7
73.5
0.001
75.72
171.80
-1.44
30.422
2,093.9
2,409.0
73.5
0.000
75.51
171.50
-1.49
30.373
2,093.0
2,411.8
67.5
-0.002
75.25
170.98
-1.27
30.200
2,076.2
2,406.2
63.9
0.001
74.72
170.94
-1.28
29.383
2,032.8
2,421.4
71.2
0.005
74.79
171.57
-1.18
29.377
2,030.0
2,418.5
70.2
0.002
74.86
172.18
-0.88
29.391
2,028.4
2,415.6
67.5
0.002
74.92
172.83
-0.8
29.414
2,027.9
2,413.0
68.1
0.004
75.05
173.33
-0.36
30.138
2,081.2
2,417.0
67.3
0.003
75.05
173.99
-0.27
30.208
2,082.0
2,412.2
64.1
0.002
75.36
177.20
0.05
30.278
2,088.0
2,413.6
62.6
0.002
75.42
177.81
0.02
30.099
2,090.6
2,431.0
68.3
0.004
75.49
178.46
0.13
30.135
2,100.8
2,439.9
70.9
0.003
75.55
179.09
-0.37
30.112
2,095.0
2,435.1
67.1
0.001
75.61
179.72
-0.51
28.934
2,030.4
2,456.1
66.1
0.001
75.67
-178.33
-0.68
28.349
1,998.8
2,467.8
67.1
0.005
75.74
-177.02
-0.75
28.296
2,004.0
2,478.8
66.8
0.003
75.80
-177.63
-0.9
28.256
1,994.0
2,469.9
66.2
0.001
76.13
-174.87
-1.04
27.507
1,945.5
2,475.4
62.5
0.007
123
Aquat Geochem Table 2 continued LAT. o N
LONG. E
o
Temp C
o
SP
TA lmol/kg
NTA lmol/kg
DOC lmol/kg
Dq kg m-3
76.18
-173.56
-0.9
27.381
1,929.3
2,466.1
64.3
0.004
76.28
-172.13
-1.05
27.411
1,939.0
2,475.8
63.6
0.001
76.29
-172.83
-0.85
27.402
1,939.8
2,477.6
63.3
0.001
76.35
-171.49
-0.86
27.412
1,939.8
2,476.8
62.4
0.002
76.40
-170.14
-0.74
27.374
1,939.7
2,480.0
63.4
0.004
76.34
-170.78
-0.68
26.687
1,896.5
2,487.3
64.3
0.002
76.32
-169.40
-0.68
26.541
1,890.2
2,492.6
63.2
0.001
76.28
-165.15
1.07
26.195
1,856.8
2,481.0
60.1
0.003
75.98
-165.76
3.01
25.655
1,829.0
2,495.2
60.6
0.001
75.86
-165.83
2.99
25.663
1,832.4
2,499.0
60.7
0.001
75.72
-165.73
2.82
25.621
1,830.8
2,501.0
62.0
0.002
75.54
-165.71
2.8
25.623
1,831.7
2,502.0
63.6
0.002
74.57
-165.60
2.66
25.965
1,864.5
2,513.3
67.7
0.005
74.26
-165.56
3.04
25.756
1,843.1
2,504.6
68.6
0.005
73.93
-165.53
2.49
25.752
1,843.2
2,505.1
68.8
0.006
73.63
-165.49
0.28
25.764
1,842.3
2,502.8
67.5
0.005
73.85
-165.17
2.93
26.602
1,852.4
2,437.2
66.3
0.005
74.65
-167.69
2.65
26.365
1,853.4
2,460.4
63.5
0.005
74.84
-167.32
1.48
25.937
1,843.5
2,487.6
70.7
0.006
75.05
-168.93
1.92
25.959
1,863.6
2,512.7
67.8
0.005
75.04
-168.84
1.85
26.215
1,878.5
2,508.0
64.6
0.005
75.24
-168.55
1.39
26.207
1,863.0
2,488.0
64.6
0.006
75.39
-168.05
0.39
25.997
1,855.5
2,498.0
64.0
0.005
75.59
-169.82
26.044
1,863.5
2,504.4
62.6
0.005
-0.5
76.39
-171.81
-0.76
25.479
1,825.1
2,507.2
60.1
0.006
76.45
-172.71
-1.07
26.047
1,844.3
2,478.3
60.5
0.005
76.50
-173.84
-0.95
27.161
1,921.7
2,476.3
63.1
0.002
76.45
-174.62
-1.03
27.137
1,919.0
2,475.0
64.0
0.003
76.42
-175.48
-0.93
27.012
1,921.2
2,489.3
62.1
0.005
76.46
178.13
-0.08
29.733
2,073.2
2,440.5
68.1
0.006
75.33
174.75
-0.07
30.186
2,090.2
2,423.5
68.6
0.000
75.13
175.35
0.24
29.852
2,067.4
2,423.9
69.3
0.001
75.11
175.36
0.17
29.439
2,048.1
2,435.0
68.6
0.001
75.31
176.25
0.13
29.727
2,068.5
2,435.4
65.1
0.004
75.44
176.85
0.13
29.979
2,082.9
2,431.7
67.4
0.000
75.57
177.48
-0.16
28.948
2,029.7
2,454.0
65.0
0.002
75.84
178.76
0.01
29.602
2,064.5
2,440.9
66.4
0.001
76.15
-178.07
-0.18
29.207
2,049.8
2,456.4
67.6
0.002
76.48
-178.52
-0.14
29.456
2,056.2
2,443.3
67.1
0.002
76.75
-178.91
-0.21
29.769
2,073.9
2,438.3
66.9
0.001
77.05
-177.36
-0.23
29.475
2,058.9
2,444.8
66.9
0.002
77.01
-173.64
-0.66
28.893
2,034.9
2,465.0
66.2
0.004
123
Aquat Geochem Table 2 continued LAT. o N
LONG. E
o
Temp C
o
SP
TA lmol/kg
NTA lmol/kg
DOC lmol/kg
Dq kg m-3
77.06
-172.69
-0.72
28.629
2,009.0
2,456.0
65.0
0.004
77.06
-171.91
-1.02
27.004
1,930.1
2,501.6
54.4
0.003
77.16
-170.78
-0.99
26.646
1,890.2
2,482.8
62.5
0.002
77.63
-170.47
-1.04
27.673
1,955.6
2,473.4
64.0
0.006
79.20
-165.45
-1.46
29.331
2,051.3
2,447.7
65.5
0.002
79.51
-163.24
-1.49
29.281
2,045.7
2,445.2
66.3
0.003
79.76
-162.89
-1.55
29.457
2,057.2
2,444.3
64.2
0.004
80.09
-160.81
-1.61
30.090
2,097.9
2,440.2
69.0
0.003
80.29
-159.99
-1.57
30.162
2,103.7
2,441.2
71.3
0.002
80.60
-156.76
-1.56
29.956
2,088.5
2,440.2
64.7
0.000
80.72
-154.50
-1.5
29.900
2,086.0
2,441.8
63.5
0.002
80.57
-162.38
-1.58
30.213
2,103.0
2,436.2
65.0
0.004
80.64
-165.29
-1.45
30.380
2,084.2
2,401.1
64.8
0.003
80.62
-167.92
-1.57
30.303
2,107.1
2,433.7
63.6
0.004
80.59
-168.69
-1.45
30.267
2,107.6
2,437.1
73.5
0.000
80.62
-168.15
-1.51
30.425
2,118.1
2,436.6
55.9
0.001
80.69
-170.45
-1.61
30.346
1,937.6
2,463.0
72.5
0.002
80.56
-171.21
-1.61
30.356
2,108.7
2,431.2
70.6
0.004
80.38
-176.65
-1.59
30.657
2,123.9
2,424.8
71.0
0.004
80.32
-177.35
-1.58
30.640
2,122.6
2,424.6
70.0
-0.001
80.31
-177.45
80.39
178.69
-1.65
30.746
2,127.8
2,422.2
71.3
0.002
-1.6
29.973
2,076.2
2,424.4
70.7
0.000 -0.001
80.51
176.70
-1.46
28.482
1,982.4
2,436.0
80.2
80.54
173.77
-1.53
28.252
19,76.8
2,448.9
77.1
0.000
80.59
172.10
-1.51
28.210
1,968.5
2,442.3
79.8
-0.001
80.37
172.13
-1.5
28.270
1,969.9
2,438.9
79.8
0.002
80.87
167.62
-1.47
27.528
1,976.4
2,512.8
117.5
0.001
80.94
166.13
-1.49
27.482
1,967.5
2,505.7
118.9
0.000
81.00
158.73
-1.49
27.608
1,990.5
2,523.5
129.4
0.002
81.00
157.06
-1.44
26.586
1,925.2
2,534.5
124.0
0.002
81.00
155.42
-1.5
27.672
1,980.1
2,504.5
120.2
0.000
81.00
153.87
-1.53
28.319
2,015.8
2,491.4
119.1
0.003
81.00
151.97
-1.56
28.792
2,049.8
2,491.7
120.4
0.007
80.98
148.00
-1.74
32.298
2,220.0
2,405.7
91.6
0.004
80.99
146.47
-1.7
32.091
2,188.1
2,386.4
85.6
-0.002
81.05
140.57
-1.65
31.939
2,179.6
2,388.4
86.6
-0.003
80.98
137.54
-1.72
32.006
2,207.6
2,414.1
94.8
-0.003 -0.003
81.01
136.09
-1.7
32.135
2,212.5
2,409.8
91.5
81.17
128.79
-1.53
31.444
2,166.9
2,411.9
101.5
0.005
81.16
127.93
-1.42
31.371
2,167.9
2,418.6
100.9
0.005
81.10
126.61
-1.62
31.359
2,167.2
2,418.8
101.1
0.002
81.12
124.42
-1.57
31.464
2,165.7
2,409.1
98.8
0.001
123
Aquat Geochem Table 2 continued LAT. o N
LONG. E
Temp C
o
TA lmol/kg
SP
o
NTA lmol/kg
Dq kg m-3
DOC lmol/kg
81.16
123.10
-1.66
32.040
2,191.3
2,393.8
90.7
0.001
81.24
121.22
-1.79
32.968
2,229.3
2,366.7
78.6
0.000
80.48
121.48
-1.68
32.852
2,220.2
2,365.3
76.0
0.000
80.22
120.86
-1.73
32.951
2,219.2
2,357.2
73.6
-0.003
79.95
119.95
-1.74
33.040
2,220.7
2,352.4
71.0
-0.002
79.65
118.87
-1.69
32.623
2,192.0
2,351.8
70.1
-0.003
79.46
118.55
-1.69
32.214
2,181.3
2,370.0
77.6
-0.003
79.24
118.11
-1.69
32.258
2,181.4
2,366.8
79.8
-0.002
78.54
117.77
-1.65
31.284
2,130.9
2,384.0
91.4
-0.002
78.21
117.30
-1.64
30.251
2,072.7
2,398.0
95.6
-0.001
77.95
116.64
-1.57
29.899
2,067.7
2,420.5
98.8
0.001
77.92
115.22
-1.48
29.844
2,077.0
2,435.8
102.6
0.003
77.91
114.00
-1.59
29.769
2,083.5
2,449.6
105.8
0.001
NTA , μmol kg-1 2200 0
2300
2400
2500
2600
2700
1000
Depth, db
2000
3000
4000
5000
Fig. 1 Normalized total alkalinity (NTA = 35 TA/S) as a function of depth in the Arctic Ocean
123
Aquat Geochem
DOC, μmol kg-1 20 0
40
60
80
100
120
140
1000
Depth, db
2000
3000
4000
5000
Fig. 2 Dissolved organic carbon (DOC) as a function of depth in the Arctic Ocean
Fig. 3 Distribution of normalized total alkalinity (NTA, lmol/kg) for surface waters in the Arctic Ocean
density by 0.001 kg m-3, which is within the experimental error of our measurements. Since the values of NTA are the same as Standard Seawater, the decrease cannot be attributed to lower TA values. It appears that the decrease in density of the deep Arctic may be caused by the slightly lower DOC concentrations (44–51 lmol kg-1) below 150 m
123
Aquat Geochem
Fig. 4 Distribution of dissolved organic carbon (DOC, lmol/kg) for surface waters in the Arctic Ocean
Δ ρ, kg m -0.008 0
-0.006
-0.004
-0.002
0.000
-3
0.002
0.004
0.006
0.008
Depth, db
1000
2000
3000
4000
5000
Fig. 5 Values of (q - q0) as a function of depth in the Arctic Ocean
compared with the Standard Seawater value of 57 ± 2 lmol kg-1. Since the maximum changes in DOC concentration from the surface to depth in the open ocean are *30 lmol kg-1 (Hansell et al. 2009), one might estimate that the effect of DOC in the
123
Aquat Geochem 2800 Eastern Basin Western Basin
NTA, μmol kg
-1
2700 2600 2500 2400 2300 2200 24
26
28
30
32
34
Practical Salinity, SP Fig. 6 NTA as a function of the salinity for surface waters in the eastern and western Arctic Ocean
140 Eastern Basin Western Basin
DOC, μmol kg-1
120
100
80
60
40 26
27
28
29
30
31
32
33
34
Salinity Fig. 7 DOC as a function of salinity for surface waters in the eastern and western Arctic Ocean
world ocean waters could be as much 0.012 kg m-3. This is unfortunately very difficult to prove at the present time. The Dq values for most of the surface waters have positive values. These elevated densities can be attributed to the higher concentrations of NTA and DOC from the input of river waters to the Arctic (Anderson et al. 2004; Hansell et al. 2004). Evidence for this is shown in plots of all measured surface NTA as a function of salinity in Fig. 6. As shown elsewhere (Amon 2004; Letscher et al. 2010), DOC displays a linear behavior as a function of salinity near the major river inputs (Fig. 7). Figures 6 and 7 also give previously reported values of NTA (Bates et al. 2009) and DOC (Hansell et al. 2004) for surface waters in the western Arctic Ocean. At a given salinity, the values of NTA are lower and DOC is higher in the eastern sector of the Arctic compared with the western sector. The differences in NTA are due to the differences in NTA concentrations between eastern and western Arctic rivers (Cooper et al. 2008), while the differences in DOC are due to both differences in riverine concentrations (Cooper et al. 2008) and in the greater DOC removal
123
Aquat Geochem 140 Eastern Basin Western Basin
DOC, μmol kg
-1
120
100
80
60
40 2300
2350
2400
2450
2500
2550
2600
2650
-1
NTA, μmol kg
Fig. 8 Correlation of the values of DOC and NTA for waters in the eastern and western Arctic Ocean
in the western sector (Hansell et al. 2004; Letscher et al. 2010). As shown in Fig. 8, the values of DOC and NTA in this region correlate very well with one another. At an NTA around 2,300 lmol kg-1, the values of DOC are near 60 lmol kg-1, similar to Standard Seawater from the North Atlantic. At the present time, it is not possible to determine how much of the NTA from the rivers is due to organic compounds that can accept a proton. An over determination of pCO2 or pH with TA and TCO2 in Arctic estuaries may allow one to estimate the contribution of increases in TA due to organic compounds. This is also true of other estuarine systems that contribute alkalinity to the world oceans. Acknowledgments The authors wish to acknowledge the Ocean Sciences section of the US National Science Foundations for supporting our studies. FJM also wishes to acknowledge the support of the National Oceanic and Atmospheric Administration. DAH and RL were supported by NSF OPP-0822429 and NSF OPP-0732082. FJM is saddened by the sudden death of Dr. John Morse. He has been a longtime scientific and personal colleague that will be missed by all of the scientific community.
References Amon RMW (2004) The role of dissolved organic matter for the organic carbon cycle in the Arctic Ocean. In: Stein R, Macdonald RW (eds) The organic carbon cycle in the Arctic Ocean. Springer, Berlin, pp 83–99 Anderson LG, Jutterstro¨m S, Kaltin S (2004) Variability in river runoff distribution in the Eurasian Basin of the Arctic Ocean. J Geophys Res 109:C01016. doi:10.1029/2003JC001773 Bates NR, Mathis JT, Cooper LW (2009) Ocean acidification and biologically induced seasonality of carbonate mineral saturation states in the western Arctic Ocean. J Geophys Res 114:C11007. doi: 10.1029/2008JC004862 Brewer PG, Bradshaw A (1975) The effect of non-ideal composition of seawater on salinity and density. J Mar Res 33:157–175 Cooper LW, McCelland JW, Holmes RM, Raymond PA, Gibson JJ, Guay CK, Peterson BJ (2008) Flow-weighted values of runoff tracers (d18 O, DOC, Ba alkalinity) from the six largest Arctic rivers.Geophys Res Letts 35:L18606. doi:10.1029/2008GL035007 Farmer C, Hansell DA (2007) Determination of dissolved organic carbon and total dissolved nitrogen in sea water. In: Dickson AG, Sabine CL, Christian JR (eds) Guide to best practices for ocean CO2 measurements. PICES Special Publication 3, p 191 Feistel R (2008) A Gibbs function for seawater thermodynamics for -6 to 80°C and salinity up to 120 g kg–1. Deep Sea Res I 55:1639–1671
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Aquat Geochem Hansell DA, Kadko D, Bates NR (2004) Degradation of terrigenous dissolved organic carbon in the western Arctic Ocean. Science 304:858–861 Hansell DA, Carlson CA, Repeta DJ, Schlitzer R (2009) Dissolved organic matter in the ocean: new insights stimulated by a controversy. Oceanography 22:52–61 IAPWS (2008) Release on the IAPWS formulation 2008 for the thermodynamic properties of seawater. The International Association for the Properties of Water and Steam, Berlin. Available from www.iapws.org. This Release is referred to in the text as IAPWS-2008 Kell GS (1975) The density, thermal expansivity and compressibility of liquid water from 0 to 150°C: correlations and tables for atmospheric pressure and saturation reviewed and expressed on the 1968 temperature scale. J Chem Eng Data 20:97–105 Letscher RT, Hansell DA, Kadko D (2010) Rapid removal of terrigenous dissolved organic carbon over the Eurasian shelves of the Arctic Ocean. Mar Chem (in press) McDougall TJ, Jackett DR, Millero FJ (2009) An algorithm for estimating absolute salinity in the global ocean. Ocean Sci Discuss 6:215–242 Middag A, de Baar HJW, Laan P, Bakker K (2009) Dissolved aluminium and the silicon cycle in the Arctic Ocean. Mar Chem 115:176–195 Millero FJ (1974) Seawater as a multicomponent electrolyte solution. In: Goldberg ED (ed) The sea, Vol 5. Wiley, New York, pp 3–80 Millero FJ (2000) Effect of changes in the composition of seawater on the density-salinity relationship. Deep Sea Res I 47:1583–1590 Millero FJ (2006) Chemical oceanography, 3rd edn. CRC Press, New York Millero FJ (2010) History of the equation of state of seawater. Oceanography 23(3):18–33 Millero FJ, Poisson A (1981) International one atmosphere equation of state of seawater. Deep Sea Res 28:625–629 Millero FJ, Gonzalez A, Ward GK (1976a) The density of seawater solutions at one atmosphere as a function of temperature and salinity. J Mar Res 34:61–93 Millero FJ, Gonzalez A, Brewer PG, Bradshaw A (1976b) The density of North Atlantic and North Pacific deep waters. Earth Planet Sci Lett 32:468–472 Millero FJ, Forsht D, Means D, Giekes J, Kenyon K (1978) The density of North Pacific Ocean waters. J Geophys Res 83:2359–2364 Millero FJ, Lee K, Roche MP (1998) Distribution of alkalinity in the surface waters of the major oceans. Mar Chem 60:111–130 Millero FJ, Waters J, Woosley R, Huang F, Chanson M (2008a) The effect of composition of the density of Indian Ocean waters. Deep Sea Res I 55:470–960 Millero FJ, Feistel R, Wright DG, McDougall TJ (2008b) The standard seawater and the definition of a reference-composition salinity scale. Deep Sea Res I 55:50–72 Millero FJ, Huang F, Williams N, Waters J, Woosley R (2009) The effect of composition on the density of South Pacific Ocean waters. Mar Chem 114:56–62 Spieweck F, Bettin H (1992) Review: solid and liquid density determination. Technisches Messen 59:285–292
123
Effect of Dissolved Organic Carbon and Alkalinity on the Density of Arctic Ocean Waters Frank J. Millero • Fen Huang • Ryan J. Woosley • Robert T. Letscher Dennis A. Hansell
•
Received: 23 June 2010 / Accepted: 15 October 2010 Ó Springer Science+Business Media B.V. 2010
Abstract At constant temperature, the density of deep waters in the oceans is higher than that of surface waters due to the oxidation of plant material that adds NO3, PO4, and Si(OH)4, and the dissolution of CaCO3(s) that adds Ca2? and HCO3. These increases in the density have been used to estimate the absolute salinity of seawater that is needed to determine its thermodynamic properties. Density (q), total alkalinity (TA), and dissolved organic carbon (DOC) measurements were taken on waters collected in the eastern Arctic Ocean. The results were examined relative to the properties of North Atlantic Waters. The excess densities (Dq = qMeas - qCalc) in the surface Arctic waters were higher than expected (maximum of 0.008 kg m-3) when compared to Standard Seawater. This excess is due to the higher values of the normalized total alkalinity (NTA = TA * 35/S) (up to *2,650 lmol kg-1) and DOC (up to *130 lmol kg-1) resulting from river water input. New measurements are needed to determine how the DOC in the river waters contributes to the TA of the surface waters. The values of Dq in deep waters are slightly lower (-0.004 ± 0.002 kg m-3) than that in Standard Seawater. The deep waters in the Arctic Ocean, unlike the Atlantic, Pacific, Indian, and Southern Oceans, do not have significant concentrations of silicate (maximum *15 lmol kg-1) and that can affect the densities. Since the NTA of the deep Arctic waters (2,305 ± 6 lmol kg-1) is the same as Standard Seawater (2,306 ± 3 lmol kg-1), the decrease in the density may be caused by the lower concentrations of DOC in the deep waters (44–50 lmol kg-1 compared to the Standard Seawater value of 57 ± 2 lmol kg-1). The relative deficit of DOC (7–13 lmol kg-1) in the deep Arctic waters appears to cause the lower densities (-0.004 kg m-3) and Absolute Salinities (SA, -0.004 g kg-1). The effect of increases or decreases in Dq and dSA due to DOC in other deep ocean waters may be hidden in the correlations of the changes with silicate. Further work is needed to separate the effects of SiO2 and DOC on the density of deep waters of the world oceans. Keywords
Dissolved organic carbon DOC Alkalinity Density Arctic Ocean
F. J. Millero (&) F. Huang R. J. Woosley R. T. Letscher D. A. Hansell Rosenstiel School of Marine and Atmospheric Science, University of Miami, Miami, FL 33149, USA e-mail: [email protected]
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1 Introduction Although the composition of the major constituents of surface seawaters is relatively constant, the composition of deep waters can differ due to the oxidation of plant material adding NO3, PO4, and Si(OH)4 and the dissolution of CaCO3(s) increasing Ca2? and HCO3-. Brewer and Bradshaw (1975) and Millero (2000) have shown that these composition differences can affect the relationship between the measured conductivity Practical Salinity (SP) and physical properties such as density (q). Many of the thermodynamic properties of seawater, as well as other natural waters (lakes and estuaries), have been shown to be a function of the Absolute Salinity (SA) rather than the Practical Salinity (Millero 1974; Millero et al. 1976b). The physical chemical properties of natural waters are directly related to the composition of the major components, but not the salinity determined by conductivity. Non-electrolytes like Si(OH)4 and dissolved organic carbon (DOC), for example, do not have a large conductivity signal but can affect the physical properties of seawater. For this reason, the new Gibbs function for the thermodynamic properties of seawater (IAPWS 2008; Feistel 2008) is expressed as a function of Absolute Salinity rather than the Practical Salinity. The seawater used to determine the density (Millero and Poisson 1981), as well as other properties of seawater, was Atlantic surface waters of known Chlorinity. These Atlantic waters have low concentrations of nutrients and nearly constant total alkalinity (TA), total dissolved CO2 (TCO2) and dissolved organic carbon (DOC). Millero et al. (1998, 2008b) examined the composition of the North Atlantic surface waters used to calibrate salinometers (Standard Seawater) and to measure most of the physical chemical properties of seawater. They used the composition to determine the Reference Salinity (SR). For the range of salinities where Practical Salinities are defined ð2\SP \42Þ; SR is related to the Practical Salinity (SP) by SR ¼ ð35:16504=35ÞSP ; g kg1
ð1Þ
Within the accuracy of present measurements, this reference composition is identical to that of Standard Seawater collected in a specific region of the North Atlantic. Millero et al. (2008b) estimated that the absolute uncertainty of SR is ±0.007 g kg-1. The difference between SR and SP (0.165 g kg-1) is much larger than the at-sea precision of measurements of SP (*0.003). This difference is related to the loss of boric acid and volatile salts during evaporation at 450°C (Millero 2006). The relationship of Practical Salinity Scale to Chlorinity (Cl) was defined by (Millero 2006) SP ¼ 1:80655 Cl
ð2Þ
This equation gives a value of SP = 35.000 when Cl = 19.374, the value for Standard Seawater used in many of the early physical chemical studies (Millero 2010). The Absolute Salinity of other waters in the oceans is related to the SR by SA ¼ SR þ dSA
ð3Þ
The correction dSA to the Reference Salinity SR is the sum of all the masses of the dissolved material added to deep waters (Millero et al. 2008b). Density measurements of seawaters by Millero et al. (1976a, b, 1978, 2008a, 2009; Millero 2000) were used to estimate the values of dSA for samples of seawater collected in the major oceans. The measured Practical Salinity SP and the differences in the density of seawater and pure water were measured on each sample at 25°C and atmospheric pressure (0 bars). The differences
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in the measured and calculated densities from the equation of state of Millero and Poisson (1981) (Dq) were used to estimate the values of dSA dSA = g kg1 ¼ ðSA SR Þ= g kg1 ¼ Dq= kg m3 =0:7518 ð4Þ The 0.7518 kg m-3/(g kg-1) factor is determined from the partial derivative qq/qSA at 25°C and 1 atmosphere. Density measurements reported by Millero et al. (1976a, b, 1978, 2008a, 2009) indicated that the values of Dq and dSA were linear functions of the concentrations of Si(OH)4. Although changes in other nutrients and TA also showed a linear behavior, silicate was used because it displayed the best correlations, it is related to the other variables, it accounts for a significant fraction of the added material, and it is 90% non-ionic, thus having little effect on conductivity. McDougall et al. (2009) summarized all of the present 811 measurements and derived the equation for the world oceans ð5Þ dSA = g kg1 ¼ ðSA SR Þ= g kg1 ¼ 9:824 105 SiðOHÞ4 = lmol kg1 The standard error of the fit is 0.0054 g kg-1. This relationship was combined with global Si(OH)4 data to derive a relationship that can be used to estimate SA for many locations in the ocean (McDougall et al. 2009). It is assumed that these equations will be improved as more density measurements are made in other parts of the ocean. In the present paper, we present new density measurements made on waters collected in the Eastern Arctic Ocean. The effect of TA and DOC on the excess densities is examined.
2 Experimental Methods Samples were collected aboard the German icebreaker FS Polarstern during cruise ARKXXIII/3 (12 Aug. to 17 Oct., 2008). The cruise track circumnavigated the Arctic with extensive occupation of the western Chukchi/East Siberian Sea shelf break and adjacent Mendeleyev Ridge region. In addition, a transect crossing the Canada, Makarov, and Eurasian Basins at *80°N was occupied. Sea ice-free conditions were generally present south of 80°N in the study region with heavy ice conditions present to the north. Sampling was carried out through the ship’s hull-mounted seawater intake line at a depth of *10 m. Samples for TA, salinity, and density determinations were collected in 125-cm3 HDPE (high density polyethylene) bottles and sealed with parafilm until analyzed in the laboratory. Waters for DOC analysis were filtered inline between the Niskin bottles and 60-ml HDPE bottles and then stored frozen until analysis in the shore laboratory. Practical Salinities were measured with a Guildline Portasal salinometer calibrated with Standard Seawater (batch P31). It should be pointed out that the addition of Ca2? from the dissolution of CaCO3(s) causes very small changes in the measured Practical Salinity, SP. The densities were measured on a Paar 500 densimeter at 25.000 ± 0.003°C. Although the salinity was measured at sea, it was remeasured ashore at the same time as the densities were measured to account for any evaporation that may have occurred after collection. The relative density (q - q0) measurements of Standard Seawater were reproducible and agreed with those calculated from the equation of state (Millero and Poisson 1981) to r = 0.002 kg m-3. All of the measurements were taken relative to the density of pure water (q0) based on the equations of Kell (1975) and adjusted to the 1990 temperature scale (Spieweck and Bettin 1992). The densities for pure water from this equation are embedded
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in the hardware of the Paar 500 densimeter. These relative densities are not strongly affected by changes in the temperature scale or the absolute value for the density of pure water used to calibrate the densimeter. Measurements taken on Standard Seawater (P146) of known Practical Salinity yielded densities at 25°C that agreed with the equation of state to within r = 0.003 kg m-3, which is the precision of the measurements. The excess densities (Dq = qMeas - qCalc) were determined by comparing the measured values to those determined from the equation of state of seawater (Millero and Poisson 1981). TA measurements were taken using methods developed by Millero et al. (1993). The titration system was calibrated using seawater of known TA (provided by Dr. Andrew G. Dickson, UCSD-SIO-Marine Physical Laboratory) and had a precision of ±2 lmol kg-1. DOC measurements were taken by high-temperature combustion using the methods of Farmer and Hansell (2007), with a precision of 2 lmol kg-1. DOC in Standard Seawater collected in the North Atlantic was 57.2 ± 2 lmol kg-1 and NTA was 2,306 ± 3 lmol kg-1. The surface layer data considered here exhibited little dilution by sea ice melt, as assessed by d18O measurements and as reported by Letscher et al. (2010).
3 Results Salinity (SP), TA, DOC, and excess density (Dq = qMeas - qCalc) were determined for all the Arctic seawaters returned to the laboratory. The hydrographic data and the laboratory measurements, as a function of location and depth, are tabulated in Table 1, and the surface values are compiled in Table 2. NTA results are shown as a function of depth in Fig. 1. All of the deep waters have NTA of 2,305 ± 6 lmol kg-1, similar to the values for Standard Seawater of 2,306 ± 3 lmol kg-1 collected in the North Atlantic. The surface values increase to concentrations as high as 2,650 lmol kg-1. Dissolved organic carbon (DOC) concentrations are shown as a function of depth in Fig. 2. The deep waters below 150 m have values between 44 (the deep Arctic basin waters) and 51 lM (the Atlantic water layer), which are lower by 6–13 lmol kg-1 than the values in North Atlantic Standard Seawater (57.2 ± 2 lmol kg-1). The surface water DOC concentrations are as high as 130 lmol kg-1, much higher than surface waters in other oceans (commonly \80 lmol kg-1; Hansell et al. 2009). The surface distributions of NTA and DOC at 10 m depth are shown in Figs. 3 and 4. The high values of NTA and DOC originate from Arctic rivers (Anderson et al. 2004; Letscher et al. 2010). The measured excess densities Dq/(kg m-3) = qmeas - qcalc are shown as a function of depth in Fig. 5. The deep waters have values of Dq = -0.004 ± 0.002 kg m-3, while the surface waters have values as high as Dq = 0.008 ± 0.002 kg m-3.
4 Discussion Unlike other oceans, the deep waters of the Arctic have values of Dq that are negative. Most deep ocean waters have positive values of Dq due to the addition of nutrients and calcium carbonate. Determinations of nutrients in Arctic deep water are sparse and concentrations are very low compared with most other deep ocean waters. The silicate concentrations, for example, have maximum values in deep water of *15 lmol kg-1 (Middag et al. 2009). Based upon our work in other oceans, this Si concentration will increase the
123
Aquat Geochem Table 1 Measurements of alkalinity, dissolved organic carbon, and excess density for waters in the Arctic Ocean as a function of depth LAT. o N
LONG. E
o
Depth dbar
Temp C
o
TA lmol kg-1
SP
NTA lmol kg-1
DOC lmol kg-1
Dq kg m-3
80.46
-158.68
3.6
-1.617
2,104
30.208
2,437
67.7
0.000
80.46
-158.68
30.1
-1.504
2,218
31.810
2,440
66.8
0.000
80.46
-158.68
80.46
-158.68
-1.611
2,213
31.992
2,421
66.2
0.002
101
49.8
-1.561
2,244
32.591
2,410
61.0
-0.005
80.46
-158.68
201.7
-0.909
2,271
34.346
2,314
58.5
-0.006
80.46
-158.68
303.2
0.468
2,282
34.756
2,298
53.7
-0.005
80.46
-158.68
506
80.46
-158.68
1,013.8
0.792
2,293
34.864
2,302
49.6
-0.006
-0.049
2,297
34.932
2,302
48.4
-0.004
80.46
-158.68
2,031.4
-0.408
2,300
34.950
2,304
43.6
-0.006
80.46
-158.68
3,054
-0.329
2,306
34.955
2,309
43.2
-0.002
80.58
-162.40
3.5
-1.611
2,118
30.338
2,443
66.6
0.006
80.58
-162.40
10.1
-1.613
2,119
30.446
2,436
66.2
0.002
80.58
-162.40
50.5
-1.611
2,216
32.081
2,418
63.4
0.004
80.58
-162.40
101.4
-1.617
2,231
32.668
2,391
60.5
0.001
80.58
-162.40
202.4
-0.880
2,276
34.345
2,319
58.4
-0.005
80.58
-162.40
303.3
0.402
2,279
34.730
2,296
50.6
-0.006 -0.006
80.58
-162.40
506
0.544
2,284
34.865
2,293
48.3
80.58
-162.40
1,013.2
-0.126
2,290
34.894
2,297
48.8
-0.005
80.58
-162.40
2,031.3
-0.416
2,293
34.951
2,297
44.0
-0.006
2,592.7
-0.005
80.58
-162.40
-0.365
2,298
34.960
2,301
43.9
80.55
-174.69
4
-1.639
2,123
30.633
2,425
67.9
0.001
80.55
-174.69
29.9
-1.544
2,229
32.149
2,426
68.5
0.000
80.55
-174.69
50.4
-1.653
2,222
32.332
2,405
65.2
0.000
80.55
-174.69
99.8
-1.484
2,246
33.055
2,379
61.5
0.000
80.55
-174.69
202.2
-0.460
2,284
34.490
2,318
56.6
-0.002
80.55
-174.69
303.6
0.685
2,294
34.807
2,306
51.0
-0.004
80.55
-174.69
505.8
0.710
2,289
34.862
2,298
52.6
-0.006
80.55
-174.69
1,013.2
-0.122
2,289
34.880
2,297
46.8
-0.007
80.55
-174.69
2,031.2
-0.411
2,295
34.965
2,297
40.8
-0.001
80.55
-174.69
2,553.4
-0.368
2,310
35.000
2,310
40.8
-0.004
80.39
178.71
9.8
-1.597
2,091
30.249
2,420
69.8
-0.001
80.39
178.71
40.4
-1.642
2,237
32.412
2,415
64.6
-0.002
80.39
178.71
101.1
-1.362
2,250
33.586
2,345
63.5
-0.004
80.39
178.71
202.2
-0.231
2,277
34.535
2,308
57.1
-0.002
80.39
178.71
303.6
0.965
2,283
34.811
2,295
52.3
-0.005
80.39
178.71
405
0.909
2,292
34.836
2,303
51.4
-0.005
80.39
178.71
506.3
0.781
2,300
34.850
2,310
51.8
-0.005
80.39
178.71
759.4
0.261
2,292
34.861
2,301
50.6
-0.004
80.39
178.71
1,012.9
-0.105
2,291
34.869
2,300
50.7
-0.001
80.56
175.74
3.5
-1.521
1,957
28.102
2,437
76.0
0.000
80.56
175.74
29.5
-1.308
2,176
31.472
2,420
71.1
0.005
80.56
175.74
50.2
-1.551
2,222
32.818
2,369
64.9
0.003
123
Aquat Geochem Table 1 continued LAT. o N
LONG. E
o
Depth dbar
Temp C
TA lmol kg-1
SP
NTA lmol kg-1
o
DOC lmol kg-1
Dq kg m-3
80.56
175.74
100.9
-1.330
2,281
34.140
2,338
63.1
0.002
80.56
175.74
202.3
0.326
2,282
34.643
2,306
53.7
0.002
80.56
175.74
303.3
0.950
2,293
34.824
2,305
51.0
0.001
80.56
175.74
555.8
0.611
2,290
34.869
2,298
50.0
-0.004
80.56
175.74
1,013.6
-0.148
2,299
34.870
2,308
51.3
-0.005
80.56
175.74
2,031.6
-0.410
2,294
34.954
2,297
42.8
-0.005
80.56
175.74
2,530.6
-0.369
2,308
34.966
2,310
40.0
-0.003
81.00
164.87
3.7
-1.490
1,966
27.601
2,494
111.0
0.002
81.00
164.87
10.1
-1.487
1,967
27.702
2,485
105.8
0.002
81.00
164.87
50.5
-1.550
2,247
33.605
2,340
72.4
0.001
81.00
164.87
101.3
-1.169
2,287
34.318
2,332
61.7
-0.001
81.00
164.87
202.7
0.684
2,294
34.743
2,311
51.5
-0.003
81.00
164.87
304.3
1.008
2,290
34.846
2,301
50.7
-0.004
81.00
164.87
507.2
0.619
2,295
34.867
2,303
50.6
-0.002
81.00
164.87
1,015.8
-0.221
2,297
34.881
2,305
50.3
-0.005
81.00
164.87
2,031.5
-0.408
2,308
34.945
2,312
42.5
-0.003
81.00
164.87
2,742.3
-0.353
2,303
34.959
2,306
42.2
-0.001
81.02
145.04
3.5
-1.737
2,172
31.848
2,387
81.02
145.04
10.3
-1.738
2,186
31.903
2,399
89.1
0.001 -0.001
0.002
81.02
145.04
50.5
-1.643
2,270
33.966
2,339
69.1
81.02
145.04
101.5
-1.009
2,290
34.447
2,326
61.1
0.000
81.02
145.04
152.3
-0.198
2,282
34.638
2,306
57.7
-0.004
81.02
145.04
303.8
0.972
2,298
34.848
2,308
53.6
-0.004
81.02
145.04
760.2
-0.029
2,299
34.869
2,308
51.0
-0.005
81.02
145.04
1,522.2
-0.467
2,285
34.915
2,291
46.7
-0.003
80.97
142.08
10.4
-1.750
2,171
32.013
2,374
88.5
-0.001
80.97
142.08
50.7
-1.597
2,265
33.739
2,350
70.5
-0.001
80.97
142.08
101.4
-1.042
2,281
34.430
2,318
58.3
-0.004
80.97
142.08
202.6
0.804
2,290
34.781
2,305
52.2
-0.004
80.97
142.08
407.6
0.884
2,288
34.883
2,296
51.8
-0.005
80.97
142.08
1,012.4
-0.247
2,292
34.888
2,299
47.0
-0.004 -0.004
80.97
142.08
1,584.8
-0.435
2,299
34.998
2,299
43.2
80.98
139.01
10.3
-1.750
2,195
32.138
2,391
85.0
0.001
80.98
139.01
50.8
-1.664
2,276
33.958
2,346
65.8
-0.004
80.98
139.01
101.3
-0.859
2,280
34.488
2,314
56.3
-0.004
80.98
139.01
253.1
1.236
2,295
34.871
2,304
51.8
-0.005
80.98
139.01
505.6
0.514
2,291
34.879
2,299
51.8
-0.003
80.98
139.01
1,013.4
-0.232
2,299
34.888
2,306
52.4
-0.005
80.98
139.01
1,667.8
-0.533
2,309
34.946
2,313
44.6
-0.004
81.01
136.11
3.7
-1.742
2,196
32.138
2,392
92.0
0.002
81.01
136.11
10.1
-1.745
2,205
32.144
2,401
91.7
0.000
81.01
136.11
49.1
-1.704
2,264
33.674
2,353
71.2
-0.001
123
Aquat Geochem Table 1 continued LAT. o N
LONG. E
o
Depth dbar
Temp C
TA lmol kg-1
o
SP
NTA lmol kg-1
DOC lmol kg-1
Dq kg m-3
81.01
136.11
101.3
-0.902
2,300
34.472
2,335
56.5
-0.005
81.01
136.11
202.3
1.519
2,297
34.860
2,306
49.3
-0.005
81.01
136.11
404.8
1.300
2,312
34.911
2,318
48.0
-0.004
81.01
136.11
1,013.1
-0.265
2,304
34.907
2,310
48.6
-0.002
81.01
136.11
2,541.8
-0.768
2,307
34.932
2,311
44.1
-0.003
81.24
121.27
3.4
-1.778
2,231
32.992
2,367
79.0
0.000
81.24
121.27
10.3
-1.780
2,241
33.088
2,371
77.1
0.001
81.24
121.27
50.4
-1.757
2,284
33.824
2,364
74.0
0.003
81.24
121.27
101.1
-0.602
2,277
34.377
2,319
57.5
-0.001
81.24
121.27
202.4
1.707
2,296
34.882
2,304
49.9
-0.002
81.24
121.27
303.2
1.424
2,295
34.891
2,302
48.7
-0.002
81.24
121.27
505.9
0.835
2,296
34.906
2,303
47.6
-0.003
81.24
121.27
1,013.1
-0.326
2,296
34.907
2,302
48.4
-0.001
81.24
121.27
2,031.5
-0.760
2,308
34.929
2,312
45.0
-0.002
81.24
121.27
3,054.1
-0.760
2,301
34.944
2,305
43.8
-0.003
81.24
121.27
4,260.4
-0.640
2,307
34.948
2,310
43.0
-0.002
Table 2 Measurements of alkalinity, dissolved organic carbon, and excess density for surface water (*10 m) in the Arctic Ocean LAT. o N
LONG. o E
Temp C
o
SP
TA lmol/kg
NTA lmol/kg
DOC lmol/kg
Dq kg m-3
74.92
-127.00
-1.28
27.601
1,941.3
2,461.8
60.5
0.002
74.86
-128.38
-1.01
27.425
1,929.6
2,462.6
60.7
-0.003
74.81
-129.76
-1.01
27.057
1,911.5
2,472.7
61.5
0.004
74.78
-129.39
-0.94
26.656
1,887.7
2,478.6
63.9
0.005
74.80
-130.67
-0.93
26.261
1,868.7
2,490.5
64.9
0.006
74.82
-131.25
-0.91
24.448
1,769.0
2,532.5
64.7
0.005
69.50
-136.01
6.07
24.237
1,750.7
2,528.1
89.4
0.007
73.34
-141.23
4.64
22.886
1,681.6
2,571.7
61.9
0.006
74.49
-147.17
3.11
22.891
1,670.4
2,554.0
60.6
0.004
75.17
-151.39
3.67
22.859
1,673.4
2,562.2
61.8
0.003
75.87
-155.32
1.92
24.227
1,761.2
2,544.3
61.4
0.003
76.93
-162.98
-0.83
24.340
1,766.9
2,540.7
59.6
0.004
77.09
-163.86
-0.73
24.771
1,785.0
2,522.1
59.1
0.003
77.47
-165.31
-0.83
26.129
1,867.8
2,501.9
59.5
0.002
77.95
-169.77
-1.04
26.220
1,858.8
2,481.3
58.3
0.004
78.00
-170.09
-1.19
26.143
1,858.2
2,487.7
59.6
0.002
78.11
-173.04
-1.02
28.947
2,029.2
2,453.5
62.8
0.003
78.23
-178.68
-1.55
29.137
2,029.2
2,437.5
61.6
0.002
78.23
179.17
-1.59
30.544
2,122.2
2,431.8
67.1
0.002
78.07
178.47
-1.62
30.541
2,117.9
2,427.2
64.6
-0.004
123
Aquat Geochem Table 2 continued LAT. o N
LONG. E
o
Temp C
o
SP
TA lmol/kg
NTA lmol/kg
DOC lmol/kg
Dq kg m-3 -0.001
78.15
177.47
-1.61
30.549
2,090.0
2,394.5
66.1
78.41
173.93
-1.55
30.586
2,117.8
2,423.4
64.1
0.003
78.47
173.00
-1.52
30.592
2,117.1
2,422.1
64.3
-0.002
78.19
172.73
-1.6
29.834
2,065.3
2,422.9
67.8
0.001
77.97
173.05
-1.65
30.430
2,099.9
2,415.2
66.9
0.002
77.60
177.07
-1.29
30.847
2,124.2
2,410.2
65.3
0.001
77.60
179.66
-1.27
30.185
2,081.2
2,413.1
67.5
0.001
77.60
-177.77
-1.36
30.084
2,077.2
2,416.7
64.8
0.003
77.59
-172.16
-0.88
30.101
2,079.1
2,417.5
63.7
0.001
77.59
-171.34
-0.99
30.343
2,097.0
2,418.9
65.0
-0.002
77.58
-170.48
-0.87
28.773
2,027.1
2,465.8
75.1
-0.001
77.59
-170.46
-0.86
28.801
2,015.4
2,449.2
66.1
0.003
77.62
-175.86
-0.98
28.830
2,008.8
2,438.8
68.4
0.004
77.60
-176.66
-0.98
28.800
2,018.4
2,452.9
62.3
0.001
77.51
-178.68
-1.22
30.214
2,090.1
2,421.2
70.5
0.001 -0.004
77.24
178.58
-0.84
30.161
2,090.8
2,426.2
70.1
77.31
179.05
-0.76
30.163
2,085.7
2,420.2
67.8
0.001
77.61
174.54
-1.41
30.236
2,088.6
2,417.7
68.6
0.000
77.34
174.14
-0.91
30.829
2,123.5
2,410.8
67.5
0.002
77.06
173.71
-0.85
30.840
2,126.2
2,413.0
70.0
-0.003
76.78
173.29
-1.02
30.471
2,103.4
2,416.0
72.8
0.000
76.47
172.85
-0.74
30.476
2,103.3
2,415.5
71.5
0.001
76.23
172.51
-0.65
30.486
2,107.1
2,419.1
73.3
0.001
75.98
172.16
-1.12
30.488
2,103.4
2,414.7
73.5
0.001
75.72
171.80
-1.44
30.422
2,093.9
2,409.0
73.5
0.000
75.51
171.50
-1.49
30.373
2,093.0
2,411.8
67.5
-0.002
75.25
170.98
-1.27
30.200
2,076.2
2,406.2
63.9
0.001
74.72
170.94
-1.28
29.383
2,032.8
2,421.4
71.2
0.005
74.79
171.57
-1.18
29.377
2,030.0
2,418.5
70.2
0.002
74.86
172.18
-0.88
29.391
2,028.4
2,415.6
67.5
0.002
74.92
172.83
-0.8
29.414
2,027.9
2,413.0
68.1
0.004
75.05
173.33
-0.36
30.138
2,081.2
2,417.0
67.3
0.003
75.05
173.99
-0.27
30.208
2,082.0
2,412.2
64.1
0.002
75.36
177.20
0.05
30.278
2,088.0
2,413.6
62.6
0.002
75.42
177.81
0.02
30.099
2,090.6
2,431.0
68.3
0.004
75.49
178.46
0.13
30.135
2,100.8
2,439.9
70.9
0.003
75.55
179.09
-0.37
30.112
2,095.0
2,435.1
67.1
0.001
75.61
179.72
-0.51
28.934
2,030.4
2,456.1
66.1
0.001
75.67
-178.33
-0.68
28.349
1,998.8
2,467.8
67.1
0.005
75.74
-177.02
-0.75
28.296
2,004.0
2,478.8
66.8
0.003
75.80
-177.63
-0.9
28.256
1,994.0
2,469.9
66.2
0.001
76.13
-174.87
-1.04
27.507
1,945.5
2,475.4
62.5
0.007
123
Aquat Geochem Table 2 continued LAT. o N
LONG. E
o
Temp C
o
SP
TA lmol/kg
NTA lmol/kg
DOC lmol/kg
Dq kg m-3
76.18
-173.56
-0.9
27.381
1,929.3
2,466.1
64.3
0.004
76.28
-172.13
-1.05
27.411
1,939.0
2,475.8
63.6
0.001
76.29
-172.83
-0.85
27.402
1,939.8
2,477.6
63.3
0.001
76.35
-171.49
-0.86
27.412
1,939.8
2,476.8
62.4
0.002
76.40
-170.14
-0.74
27.374
1,939.7
2,480.0
63.4
0.004
76.34
-170.78
-0.68
26.687
1,896.5
2,487.3
64.3
0.002
76.32
-169.40
-0.68
26.541
1,890.2
2,492.6
63.2
0.001
76.28
-165.15
1.07
26.195
1,856.8
2,481.0
60.1
0.003
75.98
-165.76
3.01
25.655
1,829.0
2,495.2
60.6
0.001
75.86
-165.83
2.99
25.663
1,832.4
2,499.0
60.7
0.001
75.72
-165.73
2.82
25.621
1,830.8
2,501.0
62.0
0.002
75.54
-165.71
2.8
25.623
1,831.7
2,502.0
63.6
0.002
74.57
-165.60
2.66
25.965
1,864.5
2,513.3
67.7
0.005
74.26
-165.56
3.04
25.756
1,843.1
2,504.6
68.6
0.005
73.93
-165.53
2.49
25.752
1,843.2
2,505.1
68.8
0.006
73.63
-165.49
0.28
25.764
1,842.3
2,502.8
67.5
0.005
73.85
-165.17
2.93
26.602
1,852.4
2,437.2
66.3
0.005
74.65
-167.69
2.65
26.365
1,853.4
2,460.4
63.5
0.005
74.84
-167.32
1.48
25.937
1,843.5
2,487.6
70.7
0.006
75.05
-168.93
1.92
25.959
1,863.6
2,512.7
67.8
0.005
75.04
-168.84
1.85
26.215
1,878.5
2,508.0
64.6
0.005
75.24
-168.55
1.39
26.207
1,863.0
2,488.0
64.6
0.006
75.39
-168.05
0.39
25.997
1,855.5
2,498.0
64.0
0.005
75.59
-169.82
26.044
1,863.5
2,504.4
62.6
0.005
-0.5
76.39
-171.81
-0.76
25.479
1,825.1
2,507.2
60.1
0.006
76.45
-172.71
-1.07
26.047
1,844.3
2,478.3
60.5
0.005
76.50
-173.84
-0.95
27.161
1,921.7
2,476.3
63.1
0.002
76.45
-174.62
-1.03
27.137
1,919.0
2,475.0
64.0
0.003
76.42
-175.48
-0.93
27.012
1,921.2
2,489.3
62.1
0.005
76.46
178.13
-0.08
29.733
2,073.2
2,440.5
68.1
0.006
75.33
174.75
-0.07
30.186
2,090.2
2,423.5
68.6
0.000
75.13
175.35
0.24
29.852
2,067.4
2,423.9
69.3
0.001
75.11
175.36
0.17
29.439
2,048.1
2,435.0
68.6
0.001
75.31
176.25
0.13
29.727
2,068.5
2,435.4
65.1
0.004
75.44
176.85
0.13
29.979
2,082.9
2,431.7
67.4
0.000
75.57
177.48
-0.16
28.948
2,029.7
2,454.0
65.0
0.002
75.84
178.76
0.01
29.602
2,064.5
2,440.9
66.4
0.001
76.15
-178.07
-0.18
29.207
2,049.8
2,456.4
67.6
0.002
76.48
-178.52
-0.14
29.456
2,056.2
2,443.3
67.1
0.002
76.75
-178.91
-0.21
29.769
2,073.9
2,438.3
66.9
0.001
77.05
-177.36
-0.23
29.475
2,058.9
2,444.8
66.9
0.002
77.01
-173.64
-0.66
28.893
2,034.9
2,465.0
66.2
0.004
123
Aquat Geochem Table 2 continued LAT. o N
LONG. E
o
Temp C
o
SP
TA lmol/kg
NTA lmol/kg
DOC lmol/kg
Dq kg m-3
77.06
-172.69
-0.72
28.629
2,009.0
2,456.0
65.0
0.004
77.06
-171.91
-1.02
27.004
1,930.1
2,501.6
54.4
0.003
77.16
-170.78
-0.99
26.646
1,890.2
2,482.8
62.5
0.002
77.63
-170.47
-1.04
27.673
1,955.6
2,473.4
64.0
0.006
79.20
-165.45
-1.46
29.331
2,051.3
2,447.7
65.5
0.002
79.51
-163.24
-1.49
29.281
2,045.7
2,445.2
66.3
0.003
79.76
-162.89
-1.55
29.457
2,057.2
2,444.3
64.2
0.004
80.09
-160.81
-1.61
30.090
2,097.9
2,440.2
69.0
0.003
80.29
-159.99
-1.57
30.162
2,103.7
2,441.2
71.3
0.002
80.60
-156.76
-1.56
29.956
2,088.5
2,440.2
64.7
0.000
80.72
-154.50
-1.5
29.900
2,086.0
2,441.8
63.5
0.002
80.57
-162.38
-1.58
30.213
2,103.0
2,436.2
65.0
0.004
80.64
-165.29
-1.45
30.380
2,084.2
2,401.1
64.8
0.003
80.62
-167.92
-1.57
30.303
2,107.1
2,433.7
63.6
0.004
80.59
-168.69
-1.45
30.267
2,107.6
2,437.1
73.5
0.000
80.62
-168.15
-1.51
30.425
2,118.1
2,436.6
55.9
0.001
80.69
-170.45
-1.61
30.346
1,937.6
2,463.0
72.5
0.002
80.56
-171.21
-1.61
30.356
2,108.7
2,431.2
70.6
0.004
80.38
-176.65
-1.59
30.657
2,123.9
2,424.8
71.0
0.004
80.32
-177.35
-1.58
30.640
2,122.6
2,424.6
70.0
-0.001
80.31
-177.45
80.39
178.69
-1.65
30.746
2,127.8
2,422.2
71.3
0.002
-1.6
29.973
2,076.2
2,424.4
70.7
0.000 -0.001
80.51
176.70
-1.46
28.482
1,982.4
2,436.0
80.2
80.54
173.77
-1.53
28.252
19,76.8
2,448.9
77.1
0.000
80.59
172.10
-1.51
28.210
1,968.5
2,442.3
79.8
-0.001
80.37
172.13
-1.5
28.270
1,969.9
2,438.9
79.8
0.002
80.87
167.62
-1.47
27.528
1,976.4
2,512.8
117.5
0.001
80.94
166.13
-1.49
27.482
1,967.5
2,505.7
118.9
0.000
81.00
158.73
-1.49
27.608
1,990.5
2,523.5
129.4
0.002
81.00
157.06
-1.44
26.586
1,925.2
2,534.5
124.0
0.002
81.00
155.42
-1.5
27.672
1,980.1
2,504.5
120.2
0.000
81.00
153.87
-1.53
28.319
2,015.8
2,491.4
119.1
0.003
81.00
151.97
-1.56
28.792
2,049.8
2,491.7
120.4
0.007
80.98
148.00
-1.74
32.298
2,220.0
2,405.7
91.6
0.004
80.99
146.47
-1.7
32.091
2,188.1
2,386.4
85.6
-0.002
81.05
140.57
-1.65
31.939
2,179.6
2,388.4
86.6
-0.003
80.98
137.54
-1.72
32.006
2,207.6
2,414.1
94.8
-0.003 -0.003
81.01
136.09
-1.7
32.135
2,212.5
2,409.8
91.5
81.17
128.79
-1.53
31.444
2,166.9
2,411.9
101.5
0.005
81.16
127.93
-1.42
31.371
2,167.9
2,418.6
100.9
0.005
81.10
126.61
-1.62
31.359
2,167.2
2,418.8
101.1
0.002
81.12
124.42
-1.57
31.464
2,165.7
2,409.1
98.8
0.001
123
Aquat Geochem Table 2 continued LAT. o N
LONG. E
Temp C
o
TA lmol/kg
SP
o
NTA lmol/kg
Dq kg m-3
DOC lmol/kg
81.16
123.10
-1.66
32.040
2,191.3
2,393.8
90.7
0.001
81.24
121.22
-1.79
32.968
2,229.3
2,366.7
78.6
0.000
80.48
121.48
-1.68
32.852
2,220.2
2,365.3
76.0
0.000
80.22
120.86
-1.73
32.951
2,219.2
2,357.2
73.6
-0.003
79.95
119.95
-1.74
33.040
2,220.7
2,352.4
71.0
-0.002
79.65
118.87
-1.69
32.623
2,192.0
2,351.8
70.1
-0.003
79.46
118.55
-1.69
32.214
2,181.3
2,370.0
77.6
-0.003
79.24
118.11
-1.69
32.258
2,181.4
2,366.8
79.8
-0.002
78.54
117.77
-1.65
31.284
2,130.9
2,384.0
91.4
-0.002
78.21
117.30
-1.64
30.251
2,072.7
2,398.0
95.6
-0.001
77.95
116.64
-1.57
29.899
2,067.7
2,420.5
98.8
0.001
77.92
115.22
-1.48
29.844
2,077.0
2,435.8
102.6
0.003
77.91
114.00
-1.59
29.769
2,083.5
2,449.6
105.8
0.001
NTA , μmol kg-1 2200 0
2300
2400
2500
2600
2700
1000
Depth, db
2000
3000
4000
5000
Fig. 1 Normalized total alkalinity (NTA = 35 TA/S) as a function of depth in the Arctic Ocean
123
Aquat Geochem
DOC, μmol kg-1 20 0
40
60
80
100
120
140
1000
Depth, db
2000
3000
4000
5000
Fig. 2 Dissolved organic carbon (DOC) as a function of depth in the Arctic Ocean
Fig. 3 Distribution of normalized total alkalinity (NTA, lmol/kg) for surface waters in the Arctic Ocean
density by 0.001 kg m-3, which is within the experimental error of our measurements. Since the values of NTA are the same as Standard Seawater, the decrease cannot be attributed to lower TA values. It appears that the decrease in density of the deep Arctic may be caused by the slightly lower DOC concentrations (44–51 lmol kg-1) below 150 m
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Aquat Geochem
Fig. 4 Distribution of dissolved organic carbon (DOC, lmol/kg) for surface waters in the Arctic Ocean
Δ ρ, kg m -0.008 0
-0.006
-0.004
-0.002
0.000
-3
0.002
0.004
0.006
0.008
Depth, db
1000
2000
3000
4000
5000
Fig. 5 Values of (q - q0) as a function of depth in the Arctic Ocean
compared with the Standard Seawater value of 57 ± 2 lmol kg-1. Since the maximum changes in DOC concentration from the surface to depth in the open ocean are *30 lmol kg-1 (Hansell et al. 2009), one might estimate that the effect of DOC in the
123
Aquat Geochem 2800 Eastern Basin Western Basin
NTA, μmol kg
-1
2700 2600 2500 2400 2300 2200 24
26
28
30
32
34
Practical Salinity, SP Fig. 6 NTA as a function of the salinity for surface waters in the eastern and western Arctic Ocean
140 Eastern Basin Western Basin
DOC, μmol kg-1
120
100
80
60
40 26
27
28
29
30
31
32
33
34
Salinity Fig. 7 DOC as a function of salinity for surface waters in the eastern and western Arctic Ocean
world ocean waters could be as much 0.012 kg m-3. This is unfortunately very difficult to prove at the present time. The Dq values for most of the surface waters have positive values. These elevated densities can be attributed to the higher concentrations of NTA and DOC from the input of river waters to the Arctic (Anderson et al. 2004; Hansell et al. 2004). Evidence for this is shown in plots of all measured surface NTA as a function of salinity in Fig. 6. As shown elsewhere (Amon 2004; Letscher et al. 2010), DOC displays a linear behavior as a function of salinity near the major river inputs (Fig. 7). Figures 6 and 7 also give previously reported values of NTA (Bates et al. 2009) and DOC (Hansell et al. 2004) for surface waters in the western Arctic Ocean. At a given salinity, the values of NTA are lower and DOC is higher in the eastern sector of the Arctic compared with the western sector. The differences in NTA are due to the differences in NTA concentrations between eastern and western Arctic rivers (Cooper et al. 2008), while the differences in DOC are due to both differences in riverine concentrations (Cooper et al. 2008) and in the greater DOC removal
123
Aquat Geochem 140 Eastern Basin Western Basin
DOC, μmol kg
-1
120
100
80
60
40 2300
2350
2400
2450
2500
2550
2600
2650
-1
NTA, μmol kg
Fig. 8 Correlation of the values of DOC and NTA for waters in the eastern and western Arctic Ocean
in the western sector (Hansell et al. 2004; Letscher et al. 2010). As shown in Fig. 8, the values of DOC and NTA in this region correlate very well with one another. At an NTA around 2,300 lmol kg-1, the values of DOC are near 60 lmol kg-1, similar to Standard Seawater from the North Atlantic. At the present time, it is not possible to determine how much of the NTA from the rivers is due to organic compounds that can accept a proton. An over determination of pCO2 or pH with TA and TCO2 in Arctic estuaries may allow one to estimate the contribution of increases in TA due to organic compounds. This is also true of other estuarine systems that contribute alkalinity to the world oceans. Acknowledgments The authors wish to acknowledge the Ocean Sciences section of the US National Science Foundations for supporting our studies. FJM also wishes to acknowledge the support of the National Oceanic and Atmospheric Administration. DAH and RL were supported by NSF OPP-0822429 and NSF OPP-0732082. FJM is saddened by the sudden death of Dr. John Morse. He has been a longtime scientific and personal colleague that will be missed by all of the scientific community.
References Amon RMW (2004) The role of dissolved organic matter for the organic carbon cycle in the Arctic Ocean. In: Stein R, Macdonald RW (eds) The organic carbon cycle in the Arctic Ocean. Springer, Berlin, pp 83–99 Anderson LG, Jutterstro¨m S, Kaltin S (2004) Variability in river runoff distribution in the Eurasian Basin of the Arctic Ocean. J Geophys Res 109:C01016. doi:10.1029/2003JC001773 Bates NR, Mathis JT, Cooper LW (2009) Ocean acidification and biologically induced seasonality of carbonate mineral saturation states in the western Arctic Ocean. J Geophys Res 114:C11007. doi: 10.1029/2008JC004862 Brewer PG, Bradshaw A (1975) The effect of non-ideal composition of seawater on salinity and density. J Mar Res 33:157–175 Cooper LW, McCelland JW, Holmes RM, Raymond PA, Gibson JJ, Guay CK, Peterson BJ (2008) Flow-weighted values of runoff tracers (d18 O, DOC, Ba alkalinity) from the six largest Arctic rivers.Geophys Res Letts 35:L18606. doi:10.1029/2008GL035007 Farmer C, Hansell DA (2007) Determination of dissolved organic carbon and total dissolved nitrogen in sea water. In: Dickson AG, Sabine CL, Christian JR (eds) Guide to best practices for ocean CO2 measurements. PICES Special Publication 3, p 191 Feistel R (2008) A Gibbs function for seawater thermodynamics for -6 to 80°C and salinity up to 120 g kg–1. Deep Sea Res I 55:1639–1671
123
Aquat Geochem Hansell DA, Kadko D, Bates NR (2004) Degradation of terrigenous dissolved organic carbon in the western Arctic Ocean. Science 304:858–861 Hansell DA, Carlson CA, Repeta DJ, Schlitzer R (2009) Dissolved organic matter in the ocean: new insights stimulated by a controversy. Oceanography 22:52–61 IAPWS (2008) Release on the IAPWS formulation 2008 for the thermodynamic properties of seawater. The International Association for the Properties of Water and Steam, Berlin. Available from www.iapws.org. This Release is referred to in the text as IAPWS-2008 Kell GS (1975) The density, thermal expansivity and compressibility of liquid water from 0 to 150°C: correlations and tables for atmospheric pressure and saturation reviewed and expressed on the 1968 temperature scale. J Chem Eng Data 20:97–105 Letscher RT, Hansell DA, Kadko D (2010) Rapid removal of terrigenous dissolved organic carbon over the Eurasian shelves of the Arctic Ocean. Mar Chem (in press) McDougall TJ, Jackett DR, Millero FJ (2009) An algorithm for estimating absolute salinity in the global ocean. Ocean Sci Discuss 6:215–242 Middag A, de Baar HJW, Laan P, Bakker K (2009) Dissolved aluminium and the silicon cycle in the Arctic Ocean. Mar Chem 115:176–195 Millero FJ (1974) Seawater as a multicomponent electrolyte solution. In: Goldberg ED (ed) The sea, Vol 5. Wiley, New York, pp 3–80 Millero FJ (2000) Effect of changes in the composition of seawater on the density-salinity relationship. Deep Sea Res I 47:1583–1590 Millero FJ (2006) Chemical oceanography, 3rd edn. CRC Press, New York Millero FJ (2010) History of the equation of state of seawater. Oceanography 23(3):18–33 Millero FJ, Poisson A (1981) International one atmosphere equation of state of seawater. Deep Sea Res 28:625–629 Millero FJ, Gonzalez A, Ward GK (1976a) The density of seawater solutions at one atmosphere as a function of temperature and salinity. J Mar Res 34:61–93 Millero FJ, Gonzalez A, Brewer PG, Bradshaw A (1976b) The density of North Atlantic and North Pacific deep waters. Earth Planet Sci Lett 32:468–472 Millero FJ, Forsht D, Means D, Giekes J, Kenyon K (1978) The density of North Pacific Ocean waters. J Geophys Res 83:2359–2364 Millero FJ, Lee K, Roche MP (1998) Distribution of alkalinity in the surface waters of the major oceans. Mar Chem 60:111–130 Millero FJ, Waters J, Woosley R, Huang F, Chanson M (2008a) The effect of composition of the density of Indian Ocean waters. Deep Sea Res I 55:470–960 Millero FJ, Feistel R, Wright DG, McDougall TJ (2008b) The standard seawater and the definition of a reference-composition salinity scale. Deep Sea Res I 55:50–72 Millero FJ, Huang F, Williams N, Waters J, Woosley R (2009) The effect of composition on the density of South Pacific Ocean waters. Mar Chem 114:56–62 Spieweck F, Bettin H (1992) Review: solid and liquid density determination. Technisches Messen 59:285–292
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