isotope signature of benthic foraminifera on hard
TRANSCRIPT
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Isotope signature of benthic foraminifera on hard substrates in the Ohashi River, 1
southwest Japan 2
3
Hiroyuki Takata 1 4
Research Center for Coastal Lagoon Environments, Shimane University, 1060 Nishikawatasu, 5
Matsue 690-8504, Japan; Marine Research Institute, 2 Busandaehaku-ro, 63 beon-gil, 6
Geumjeong-gu, Busan 609-735, Korea 7
8
David L. Dettman 9
Geosciences Department, University of Arizona, 1040 E. Fourth Street, Tucson, AZ 85721, 10
USA 11
12
Koji Seto and Kengo Kurata 13
Research Center for Coastal Lagoon Environments, Shimane University, 1060 Nishikawatasu, 14
Matsue 690-8504, Japan 15
16
Jun’ichi Hiratsuka 17
Shimane Research Group of Wildlife, 802-3 Saiwaicho, Matsue 690-0041, Japan 18
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Boo-Keun Khim 20
Department of Oceanography, Division of Earth Environmental System, Pusan National 21
University, 2 Busandaehaku-ro, 63 beon-gil, Geumjeong-gu, Busan 609-735, Korea 22
23
–––––––– 24
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1 Corresponding author ([email protected]) 26
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Running title: Isotope signature of foraminifera on the hard substrates 28
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Acknowledgements 31
We thank Mr. Sadao Matsumoto and Mr. Seiji Miyawaki (Shimane University), Dr. Kota 32
Katsuki (Korea Institute of Geoscience and Mineral Resources) and Mr. Kouki Noda and Mr. 33
Hiroki Ogusa (Shimane University) for their assistance during the field surveys. We are also 34
indebted to Dr. Saburo Sakai (JAMSTEC) and Dr. Shuji Ohtani (Shimane University) for 35
benefit to use water samplers and water profiler for field surveys. We appreciate Dr. C. J. 36
Eastoe (Univ. of Arizona) for stable isotope analyses of water samples. We also thank the 37
Inland Water Fisheries and Coastal Fisheries Division, Shimane Prefectural Fisheries 38
Technology Center and the Izumo River Office, Minister of Land, Infrastructure, Transport 39
and Tourism to provide us high-resolution data of water properties at the observatories in the 40
Lake Sinji – Nakaumi system. This study was partly supported by grants of the Research 41
Project Promotion Institute, Shimane University and Pro Natura Fund. 42
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Abstract 45
In this study, we investigated isotope signatures of Ammonia “beccarii” forma 1 (Rhizaria) 46
on the hard substrates in the Lake Shinji–Nakaumi system, southwestern Japan, in order to 47
learn the isotope signatures of carbonate tests of benthic foraminifera in brackish-water 48
system. There was a generally positive relationship between stable oxygen isotope ratio of 49
bridge pier A. “beccarii” forma 1 (δ18Oforam) and salinity of the waters in the Ohashi River. 50
However, the relationship did not show a linear trend in the low salinity regime (lower than a 51
salinity of 15). We compared these the oxygen isotope ratio of equilibrium calcite (δ18Oeq. cal.) 52
values to δ18Oforam. The δ18Oeq. cal. was more consistent with the δ18Oforam if the average value 53
of the highest 5% of salinity each day was adopted, rather than that of the simple average 54
salinity. Thus, it is highly probable that bridge pier A. “beccarii” forma 1 probably biases 55
production of calcareous hard tissues toward higher salinities, whereas it seems to cease 56
calcite precipitation under in low salinities. There was large offset between the stable carbon 57
isotope ratio of DIC of the water (δ13CDIC) and bridge pier A. “beccarii” forma 1 (δ13Cforam), 58
ranging between -5.28‰ and -5.12‰. This difference is considerably large offset compared 59
to that of mollucan tests. A. “beccarii” forma 1 seems to make carbonate shells, not only 60
using [CO32-] of the ambient waters, but also [CO3
2-] derived from food. 61
62
63
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[Text] 64
65
Stable oxygen and carbon isotope ratios of calcareous hard tissue of aquatic biota are an 66
excellent tool for understanding modern and past aquatic environments: mullusca (e.g., 67
Dettman et al., 1999; 2004); Coral (e.g., Watanabe, 2011). Stable oxygen and carbon isotope 68
signatures of benthic foraminifera (Rhizaria) have also been utilized as powerful tool in order 69
to investigate paleoenvironmental changes also not only in pelagic setting but also in the 70
neritic environments. Stable oxygen isotope ratio of hard-tissue carbonate is affected by both 71
water temperature and stable isotope of the water, whereas the stable carbon isotope ratio is 72
influenced by uptaking 12C of primary production of phytoplankton and oxidation of old 73
organic matter (e.g., Ravelo and Hillaire-Marcel, 2007). In addition, the environmental 74
conditions of neritic environments are usually variable in terms of both seasonal and/or 75
occasional fluctuations. Nevertheless, stable isotope signatures of carbonate hard tissues have 76
great potential for quantitative paleoenvironmental reconstructions, based on careful 77
discussion. 78
Sampei et al. (2005) investigated stable oxygen and carbon isotope ratios of the water and 79
molluscan shells in the Lake Shinji–Nakaumi system, southwestern Japan. They revealed 80
macro-scale correlations of stable oxygen and carbon isotope ratios of biogenic carbonate to 81
salinity of the waters. They showed potential of stable oxygen and carbon isotope data for the 82
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paleo-salinity reconstruction in the Holocene using molluscan fossils of a sediment core. In 83
contrast, Sampei et al. (2005) also pointed out a few remarks on application to 84
paleoenvironmental studies. Firstly, they mentioned possible variations in stable oxygen 85
isotope ratio of the riverine waters compared to that of seawater that may arise an uncertainty 86
for paleoenvironmental reconstruction. Next, they also argued different tendency of stable 87
carbon isotope to salinity between DIC of the waters and molluscan shells. The former trend 88
was logarithmic, whereas the latter was linear. They implied a possibility that food-derived 89
[CO32-] has contribution for calcification of molluscan shells as other source, in addition to 90
[CO32-] of DIC of the ambient water. 91
In this study, we investigated isotope signatures of Ammonia “beccarii” forma 1 (benthic 92
foraminifera) on the hard substrates in the Lake Shinji–Nakaumi system, for better 93
understanding of isotope signatures of biogenic carbonate in the brackish-water system. 94
Firstly, (a) we conducted multi-year evaluations of stable oxygen and carbon isotope ratios 95
from 2006 to 2010, in order to cover possible annual variations of the stable isotope ratio of 96
the riverine waters. Next, (b) because most benthic foraminifera make calcite hard tissues, 97
isotope study of benthic foraminifera provides nice opportunity to learn isotope signature of 98
calcite producer in the brackish-water system, comparing it to those of aragonite producers 99
(mollusca) in the same study area. Thirdly, (c) because we focused on isotope signature of a 100
single species, we may predict that the possible problem of inter-species difference will be 101
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avoided. Additionally, (d) we investigated the stable isotope signature of attached individuals 102
of A. “beccarii” forma 1 on hard substrates. Ammonia “beccarii” forma 1 usually lives in the 103
surface sediment (Matsushita and Kitazato, 1990; Kitazato, 1994). We reported occurrence of 104
this species within macrobenthos colonies on hard substrate at a bridge pier in the Ohashi 105
River (southwest Japan) (Takata et al., 2009). Stable isotope study of such individuals may 106
lead us opportunity to avoid the influence of pore water of the surface sediment, especially 107
stable carbon isotope ratio. Hence, it is expected that attached individuals reflect isotope 108
signature of the water column well, compared with the individuals in the surface sediment. 109
Our approaches may lead us to a better understanding of the detailed relationship between 110
isotope signatures of the ambient waters and calcareous hard tissues in the brackish-water 111
system. It is also expected that our results may clarify characteristic of isotope signatures of 112
benthic foraminifera, comparing to those of other biota, such as mollusca. Such results may 113
contribute more detail paleoenvironmental reconstructions in brackish-water system that is 114
generally characterized by seasonal and/or occasional environmental fluctuations. 115
116
Materials and Methods 117
Study area 118
The Ohashi River is located between Lake Shinji and Lake Nakaumi in the southwest Japan 119
(Figure 1). The length of river is approximately 7.6 km, and the maximum width and water 120
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depth are approximately 200 m and 7 m, respectively. Maximum tidal range is approximately 121
20 cm. Saline water comes from the Sea of Japan (East Sea) through the Sakai Channel and 122
Lake Nakaumi by tides or winds. River water is often density-stratified (e.g., Fujii 1998). 123
Water temperature and salinity of river water in the Ohashi River are shown in Figure 2. The 124
surface layer remains typically oligohaline due to Lake Shinji, whereas the bottom layer is 125
characterized by the mesohaline and often oxygen-depleted water of Lake Nakaumi. 126
We studied benthic foraminifera at concrete piers of the Matsue and Nakaumi Bridges in 127
the upper and lowermost reaches of the Ohashi River (Figure 1), respectively. The latter site 128
is the same as that of Takata et al. (2009; 2010). Water depths at these sites are approximately 129
5 and 3 m, respectively. Hydrozoa, Musculista senhousia (Bivalvia, Mytilidae), Crassostrea 130
gigas (Bivalvia, Oystreidae) and barnacles are common components of the macrobenthos 131
attached to the bridge piers (Seto et al. 1999; Takata et al., 2009). At the Nakaumi 132
Observatory Station (6 m water depth) (Figure 1) that was our supplementary study sites, 133
attached macrobenthos was different from those of the Matsue and Nakaumi Bridges, such as 134
abundant mytilids. 135
136
Stable isotope analyses for the water 137
The water samples were collected in October 2007, 2008, 2009 and 2010 at 1 m, 3 m and 138
4.4 m water depths of the Matsue Bridge, at 1 m and 2 m water depths of the Nakaumi Bridge, 139
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and at 1 m, 3 m and 5 m water depths of the Nakaumi Observatory (Figure 1), using a 140
Niskin-type water sampler. In addition, the water samples were also collected at the Hii River, 141
Ihnashi River and the Sea of Japan (East Sea) using a bucket. The water samples were sealed 142
into a 100 ml glass vial bottle, poisoning by a few drops of mercury chloride solution. Water 143
temperature, salinity and dissolved oxygen content of the water were measured using a 144
Hydrolab Quanta Multiparameter Sonde, Hydrolab Inc. 145
Additional water sampling to investigate stable carbon isotope signature of DIC of the 146
waters more detail was carried out at the Matsue Port (Figure 1) twice per one week during 147
September to October 2010. The water samples were collected at 0 m and 3 m water depths as 148
same manner. Alkalinity of the same water sample was analyzed by the titrimetry, using 149
0.02N sulfuric acid solution, within several hours after sampling, and pH of the waters was 150
measured by a handy pH meter (Horiba, Inc.). 151
Stable oxygen isotope ratio of the water and stable carbon isotope ratio of dissolved 152
inorganic carbon (DIC) in the water were analyzed at the Environmental Isotope Laboratory, 153
the University of Arizona. (*** protocol about stable isotope measurement) 154
155
Stable isotope analyses for bridge pier foraminifera and fine detritus 156
Samples of benthic foraminifera from the bridge piers were collected in October 2007, 2008, 157
2009 and 2010 by SCUBA diving. Samples of attached macrobenthos on the bridge-pier were 158
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collected at 1 m, 3 m and 4.4 m water depth at the Matsue Bridge and 1 m and 2 m water 159
depth at the Nakaumi Bridge, respectively, (Figure 1) by scraping with a spatula and plastic 160
container (8 cm diameter). Three replicate samples were taken at all depth levels. 161
Macrobenthos samples were fixed with a 70% ethanol–seawater mixture. Samples were 162
separated into the coarse and fine fractions using a five mesh (4 mm opening) sieve. The fine 163
fraction was used for foraminiferal and organic detritus analyses. In addition, attached 164
macrobenthos samples on the one of five pillars were collected at 1 m, 3 m and 5 m at the 165
Nakaumi Observatory (water depth approximately 6 m) in a similar way in October, 2008, 166
2009 and 2010 (Figure 1). 167
The <4 mm size-fraction sample for foraminiferal analysis were washed on a 250 mesh (63 168
µm opening) sieve. The fraction of <63µm size of the 2010 samples was collected into plastic 169
container and filtered by a GF/F glass microfiber filter that was used for stable carbon isotope 170
ratio of organic matter. Residues (>63 µm) were stained with 0.5% rose Bengal solution for 171
twenty-four hours. The residues were washed with warm water (<50°C) to remove excess dye 172
and dried at 50°C. Living (stained) specimens of Ammonia “beccarii” forma 1 were picked 173
from the residues under a stereo-binocular microscope based on the presence of staining. 174
Maximum test diameter of A. “beccarii” forma 1 specimens was measured under 175
stereo-binocular microscope. 176
Stable oxygen and carbon isotope ratios of living (stained) individuals of A. “beccarii” 177
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forma 1 in 230–250 µm maximum test diameter from the bridge-pier were analyzed using an 178
automated carbonate preparation device (KIEL-III) coupled to a gas-ratio mass spectrometer 179
(Finnigan MAT 252). Powdered samples were reacted with dehydrated phosphoric acid under 180
vacuum at 70°C. The isotope ratio measurement is calibrated based on repeated 181
measurements of NBS-19 and NBS-18 and precision (1σ) is ±0.1‰ for δ18O and ±0.06‰ for 182
δ13C. The stable oxygen and carbon isotope data of bridge pier A. “beccarii” forma 1 in 2006 183
were referred from Takata et al. (2009). 184
Stable carbon isotope analysis of detritus within macrobenthos on the hard substrate in 2010 185
were carried our at the Environmental Isotope Laboratory, the University of Arizona. (*** 186
protocol about stable isotope measurement) 187
188
Calculations on stable oxygen isotope ratios of equilibrium calcite 189
We estimated stable oxygen isotope ratio of equilibrium calcite (δ18Oeq. cal.) in order to 190
compare it to observed stable oxygen isotope ratio of bridge pier foraminifera. The δ18Oeq. cal. 191
was calculated by the averages of water temperature and stable oxygen isotope ratio of the 192
ambient water, using the equation of O’Neil et al. (1969). Stable oxygen isotope ratio of the 193
water was obtained by entering salinity of the water into the equation (see next chapter) 194
between stable oxygen isotope ratio and salinity of the water. We supposed the two months 195
prior to sampling time as the growth duration of the studied size class of bridge pier 196
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foraminifera. This duration correspond to the expected one that A. “beccarii” forma 1 grew 197
the size of 230–250 µm, according to previous our study (Takata et al., 2009) that referred to 198
Brashaw (1957). Additionally, we also calculated the δ18Oeq. cal., using the averages of water 199
temperature and salinity during one month prior to the sampling dates for evaluation of the 200
shorter growth period. 201
In order to estimate the average values of water temperature and salinity of the ambient 202
water, we calculated average values using high-resolution water profile data that were 203
provided by the Inland Water Fisheries and Coastal Fisheries Division, Shimane Prefectural 204
Fisheries Technology Center and the Izumo River Office, the Ministry of Land, Infrastructure, 205
Transport and Tourism. The data were recorded every 20 minutes or every one hour. With 206
respect to calculation of the average salinity, we also conducted the average of the highest 5% 207
salinity each day in addition to simple average salinity, covering the highest range of salinity 208
variations in the study area. In contrast, we only adopted the simple average temperature, 209
because there was no marked difference between the simple average and the average of the 210
highest 5% each day. 211
212
Results 213
Stable oxygen isotope ratio of the waters in the Lake Shinji – Nakaumi system 214
Stable oxygen isotope ratio of the water (δ18Owater) ranged between -8.3 to 0.3 ‰ VSMOW 215
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(Table 1). The δ18Owater was more negative at the river mouths of the Hii and Ihnashi Rivers 216
(approximately -8‰ VSMOW), whereas that of the seawater was more positive at Okidomari 217
(Sea of Japan (East Sea)) (approximately 0‰ VSMOW). The δ18Owater in each year showed 218
linear trend with salinity of the waters (Figure 4). Based on linear regression, the equation 219
between the δ18Owater and salinity of the waters in each year was as follows: (2007) δ18Owater 220
(‰ VSMOW) = 0.18 * salinity - 6.77; (2008) δ18Owater (‰ VSMOW) = 0.22 * salinity - 7.83; 221
(2009) δ18Owater (‰ VSMOW) = 0.23 * salinity – 8.13; (2010) δ18Owater (‰ VSMOW) = 0.23 222
* salinity – 7.58. The equations were slightly variable among the years. The slopes of our 223
equations were also similar to that of Sampei et al. (2005) (δ18Owater (‰ VSMOW) = 0.22 * 224
salinity – 7.79). The δ18Owater of the river waters (approximately -8‰ VSMOW) was slightly 225
lower than the expected value as shown by the intercept of the above regression line (i.e., 226
expected value at zero salinity) in each year (approximately -7‰ VSMOW) (Figure 4). 227
228
Stable carbon isotope ratio of DIC in the waters in the Lake Shinji – Nakaumi system 229
Stable carbon isotope ratio of DIC of the water (δ13CDIC) ranged between -10.9 and 2.5 (‰ 230
VPDB) (Table 1). The δ13CDIC was more negative at the river mouths of the Hii and Ihnashi 231
Rivers (approximately -11 to -8‰ VPDB), whereas that of the seawater was more positive at 232
Okidomari (Sea of Japan (East Sea)) (approximately 2‰ VPDB). The δ13CDIC of the Ihnashi 233
River in 2010 was especially more negative value. The δ13CDIC in each year showed 234
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logarithmic trend with salinity of the waters (Figure 5). The tendencies were variable among 235
the years. There was (A) positive relationship between δ13CDIC and salinity of the waters in 236
2010. Similar trend were also recognized in the data of 2007 to 2009. In contrast, two other 237
different trends were observed in 2010. Firstly, (B) there was more positive shift of the 238
δ13CDIC under low salinity regime (Figure 5), whereas (C) more negative shift of δ13CDIC was 239
observed in the samples of hypolimnetic water commonly with low oxygen concentration (< 240
2mg/l) around at the sampling time (e.g., 5 m water depth at the Nakaumi Observatory) 241
(Figure 5). 242
243
Stable oxygen and carbon isotope ratios of bridge pier foraminifera in the Lake Shinji – 244
Nakaumi system 245
Ammonia “beccarii” forma 1 was present almost at the all samples of the Matsue and 246
Nakaumi Bridges, whereas it occurred only at 5 m water depth of the Nakaumi Observatory 247
Station. Stable oxygen isotope ratio of bridge-pier A. “beccarii” forma 1 (δ18Oforam) ranged 248
between -7.4 to -2.0 (‰ VPDB) (Tables 3 and 4; Figure 6). The δ18Oforam was more negative 249
at 1 m water depth of the Matsue Bridge (approximately -7‰ PDB), whereas it was more 250
positive at 5 m water depth at Nakaumi Observatory Station (approximately -3‰ VPDB). The 251
δ18Oforam generally increased with water depth (Figure 6; Tables 3 and 4). The vertical profiles 252
were slightly variable among the years. 253
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Stable carbon isotope ratio of bridge-pier A. “beccarii” forma 1 (δ13Cforam) ranged between 254
-6.74 to -2.37‰ VPDB (Table 2; Figure 7). The δ13Cforam was more negative at 1 m water 255
depth of the Matsue Bridge (approximately -6‰ PDB), whereas it was more positive at 2 m 256
water depth at Nakaumi Bridge (approximately -3‰ VPDB). The vertical profiles were 257
considerably variable among the years, particularly the cases of 2010 (Figure 7). The δ13Cforam 258
generally increased with water depth (Figure 7; Tables 3 and 4). In addition, the δ13Cforam 259
occasionally showed an inverse trend with water depth (e.g. at Nakaumi Bridge on October 19, 260
2006). 261
262
Stable carbon isotope ratio of organic detritus with macrobenthos community on hard 263
Stable carbon isotope ratio of fine detritus (<63 µm) within macrobenthos on the hard 264
substrate (δ13Corg) ranged between -22.7 to -21.0 (‰ VPDB) (Table 5). The δ13Corg did not 265
show marked variation among the water depths or the stations. Variations in the δ13Corg were 266
almost constant compared to those of the δ13CDIC and the δ13Cforam. 267
268
Discussion 269
Stable oxygen and carbon isotope ratios of the waters in the Lake Shinji – Nakaumi system 270
Lake Shinji – Nakaumi system is basically characterized by lateral salinity gradient from 271
east to west (*** references). Fresh water is mainly discharged from the Hii River (Figure 1), 272
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whereas saline water comes from the Sea of Japan (East Sea) through the Sakai Channel by 273
tides or winds. The typically oligohaline water from Lake Shinji and the mesohaline and often 274
oxygen-depleted water from Lake Nakaumi meet in the Ohashi River. As a result, isotope 275
signature of the water is mainly resulted from the mixing between the riverine water from the 276
Hii River and the seawater from the Sea of Japan (East Sea) (e.g., Sampei et al., 2005). Our 277
results of δ18Owater also showed the linear mixing trend between riverine water and seawater 278
distinctly in the Lake Shinji–Nakaumi system (Figure 4). Thus, we concluded that the isotope 279
signature of stable oxygen isotope ratio in the Lake Shinji–Nakaumi system is mainly 280
controlled by mixing trend of riverine and seawater. 281
The δ18Owater was almost constant around at -0.5‰ VSMOW among the year, whereas those 282
of the riverine water showed some variations (-8.3 to -7.9‰ VSMOW). The δ18Owater of the 283
waters at the river mouths of the Hii and Ihnashi Rivers is lower than the expected value as 284
shown by the intercept of the regression line between the δ18Owater and salinity in each year 285
(approximately -1‰ VSMOW) (Figure 4). There are two possible explanations for the offset, 286
as follows: (1) variation of stable oxygen isotope of the riverine water among the sampling 287
times and (2) more positive shift of the δ18Owater of the water with evaporation from the river 288
mouths of the Hii River to the Ohashi River through Lake Shinji. According to our 289
unpublished data, the δ18Owater of the Hii River ranged between -8 and -10 and its variation 290
was variable, as Sampei et al. (2005) noted. Because the data of our study were the snapshot 291
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data, the δ18Owater offset may be explained by the difference of the δ18Owater of the Hii River. 292
In terms of a possibility of evaporation between the river mouth of the Hii River and Ohashi 293
River, our water samples were mainly collected in October of every year that was after 294
summer high temperature condition (more than 30 °C) (e.g., Figure 2). Thus, we judged that 295
the evaporation of the surface water in the Lake Shinji is also one possible explanation. 296
Because of these possibilities, we excluded the data of the water at the river mouths of the 297
Hii River and Ihnashi River from the equations between δ18Owater and salinity of the waters of 298
the former chapter. If we exclude the data of the river water from the regression lines, the 299
equation between the δ18Owater and salinity of the water in each year was as follows: (2008) 300
δ18Owater (‰ VSMOW) = 0.18 * salinity – 6.76; (2009) δ18Owater (‰ VSMOW) = 0.20 * 301
salinity – 7.33; (2010) δ18Owater (‰ VSMOW) = 0.18 * salinity – 6.45. After this treatment, 302
both the slope and intercept of the regression line were closer to each other among the years 303
than those of the non-treated ones. We adopted these equations for the further discussion in 304
this paper. 305
The δ13CDIC also showed the mixing trend between riverine water and seawater (Figure 5), 306
as Sampei et al. (2005) reported. The δ13CDIC of the seawaters was almost constant around at 307
2‰ VPDB among the years, whereas those of the riverine waters ranged between -11 and 308
-8‰ VPDB. The relationship between the δ13CDIC and salinity of the waters had 309
approximately linear-like trend in more than 10 salinity, but these showed logarithmic trend in 310
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less than 10 salinity. 311
According to the 2010 dataset of he δ13CDIC (Figure 5), three trends were recognized, as 312
follows: (A) positive relationship between the δ13CDIC and salinity of the waters, (B) more 313
positive shift of δ13CDIC under low salinity regime, and (C) more negative shift of the δ13CDIC 314
was observed in the samples of the hypolimnionic water commonly with low oxygen 315
concentration (< 2 mg/l in this study) in Lake Nakaumi. In terms of the more positive shift of 316
the δ13CDIC (the trend [B]), this kind of trend has been commonly reported by 12C uptaking by 317
phytoplaktons (e.g., Ravelo and Hillaire-Marcel, 2007). Lake Shinji is characterized by 318
eutrophic condition by abundant phytoplanktons (*** reference). Hence, it is reasonable to 319
suppose that the trend of more positive shift of the δ13C under low salinity regime was 320
influenced by selective removal of 12C from DIC of the water by phytoplanktons. Similar 321
phenomenon was likely observed at 3 m water depth of Lake Nakaumi that corresponded to 322
picnocline with high production of phytoplanktons. In terms of more negative shift of the 323
δ13CDIC (trend [C]), it is reasonable to suppose that the δ13CDIC is also altered to more negative 324
value by oxidation of old organic carbon that provides more 12C to DIC of the ambient water 325
(e.g., Ravelo and Hillaire-Marcel, 2007), because the hypolimnionic water of Lake Nakaumi 326
was characterized by oxygen depleted condition in the summer and fall seasons (*** 327
references). 328
In summary, the isotope signature of the δ13CDIC in the Lake Shinji–Nakaumi system is 329
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mainly influenced by the mixing trend of riverine water and seawater. In addition, the 330
selective removal of 12C from DIC of the waters by phytoplanktons in the epilimnetic water in 331
Lake Shinji (and partly 3 m water depth of Lake Nakaumi), whereas providing 12C to DIC of 332
the ambient water due to oxidation of old organic carbon also affects the δ13CDIC under the 333
oxygen depleted hypolimnetic water of Lake Nakaumi. Thus, the isotope signature of the 334
δ13CDIC is more complicate than that of the δ18Owater. 335
336
Stable oxygen isotope ratio of bridge pier foraminifera in the Lake Shinji – Nakaumi system 337
The relationship between stable oxygen isotope ratio of bridge pier Ammonia “beccarii” 338
forma 1 and salinity of the waters at each depth levels were shown in Figure 8. There were 339
basically positive relationship between the δ18Oforam and salinity of the waters in the Lake 340
Shinji–Nakaumi system. However, the relationship was not linear in the low salinity regime 341
(lower than 15 salinity) (Figure 8). This is marked difference compared to the relationship 342
between oxygen isotope signatures and salinity both of the waters (Sampei et al., 2005; this 343
study) and molluscan shells (Sampei et al., 2005) in the Lake Shinji–Nakaumi system. In 344
addition, approximately -0.9‰ offset between calcite of foraminifera and aragonite of 345
mollusca must be expected, whereas there was no clear difference in the low salinity regime 346
in Figure 8 (a) (***Takata: at first, to state a possibility of temperature influence, 347
disequilibrium and so on?) These discrepancies imply possible influence of “vital effect” that 348
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the timing of test formation in bridge pier A. “beccarii” forma 1 may not reflect the average 349
of salinity of the waters simply. 350
With respect to the possible “vital effect”, it is probable that temporal cease of carbonate 351
precipitation under low salinity condition is a possible candidate, because Bradshaw (1961) 352
reported that Ammonia tepida did not grow under lower than 8 salinity by culture experiment. 353
According to this knowledge, it is reasonable to suppose that bridge pier A. “beccarii” forma 354
1 did not always secrete test carbonate (calcite). We set one working hypothesis that A. 355
“beccarii” forma 1 did not secrete calcite under low salinity regime and made the test 356
carbonate only in higher salinity timings. 357
We argued this hypothesis based on comparison of stable oxygen isotope ratios between 358
benthic foraminifera and equilibrium calcite (δ18Oforam and δ18Oeq. cal., respectively). The 359
comparison between the δ18Oforam and the δ18Oeq. cal. were shown in Figure 6 and Table 6. 360
There was always negative offset ranging between -3 and -2‰, between δ18Oforam and δ18Oeq. 361
cal. using simple average salinity. Thus, we confirmed that the δ18Oforam of the bridge pier A. 362
“beccarii” forma 1 could not be explained by calcite precipitation under the average salinity 363
during the two month. We also compared the δ18Oforam and the δ18Oeq. cal. using the average of 364
the highest 5% salinity each day that represents the higher salinity condition each day. The 365
δ18Oeq. cal. using the average of the highest 5% salinity each day was more consistent to those 366
of the δ18Oforam. Thus, it is highly probable that the oxygen isotope signature of bridge pier A. 367
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“beccarii” forma 1 tests in the Lake Shinji–Nakaumi system is explained by the average of 368
the highest 5% salinity each day rather than by simple average salinity. Although it is 369
necessary to argue what means biologically the average of the highest 5% salinity each day, it 370
is suggested that A. “beccarii” forma 1 likely produced test carbonate under during higher 371
salinity timings. 372
When we adopted the average of the highest 5% salinity each day during the two months, 373
there was still approximately -0.5‰ offset between the δ18Oforam and the δ18Oeq. cal. (Figure 9). 374
The δ18Oeq. cal. using the highest 5% salinity each day during the one month was more 375
consistent to those of the δ18Oforam than those of the two months (Figure 9). We implied that 376
the large amount of calcite of the foraminiferal tests seemed to be produced in the late growth 377
stage due to increasing body size of this species, even though the growth period is the two 378
months prior to the sampling time. (*** knowledge about growth rate based on culture 379
experiments) 380
Figure 8 (b) is the cross plot between salinity of the waters and the δ18Oforam, adopting the 381
average of the highest 5% salinity each day. Both the problems with respect to (1) non-linear 382
trend based on δ18Oforam and salinity of the waters under low salinity regime and (2) no offset 383
between mollusca (aragonite) and benthic foraminifera (calcite) were likely solved, adopting 384
the average of the highest 5% salinity each day. The stable oxygen isotope signature of A. 385
“beccarii” forma 1 seemed to indicate the upper range of paleo-salinity variation even under 386
- 22 -
salinity variable setting. Combining (paleo-)salinity estimations using mullucan shell and 387
foraminiferal test may have a potential to know different kind of salinity information (the 388
mean and the upper range of salinity variations, respectively). Furthermore, it is suggested 389
that the stable oxygen isotope signature of A. “beccarii” forma 1 may be useful for 390
reconstructing paleo-salinity even under the frequent salinity variable condition. 391
*** comparison to ecological knowledge about culture experiments (not only isotope study, 392
tolerance experiment for growth is enough) 393
394
Stable carbon isotope ratio of bridge pier foraminifera among the water depths and sites 395
Figure 10 shows the relationship between salinity of the waters and δ13Cforam of A. 396
“beccarii” forma 1. According to the inference based on the aforementioned discussion of 397
stable oxygen isotope ratio, we only adopted the average of the highest 5% salinity each day. 398
This generally showed linear trend, except for the data of the oxygen-poor hypolimnetic 399
waters in Lake Nakaumi (Figure 10). The δ13Cforam had no marked difference with that of 400
mollucan shells (Sampei et al., 2005), except for the 2010 data. Thus, the relationship 401
between salinity of the waters and the δ13Cforam seemed to be simple, compared to that of the 402
δ18Oforam. 403
Sampei et al. (2005) pointed out different trend of the δ13C between DIC of the waters and 404
molluscan shells that were logarithmic and linear trends, respectively. They implied a possible 405
- 23 -
influence of food-derived (metabolic) [CO32-] for calcification, in addition to [CO3
2-] of the 406
ambient water. Because Sampei et al. (2005) dealt with several molluscan species for 407
discussing stable carbon isotope, different “vital effect” among several species may be 408
involved. It is expected that our approach dealing with single species (A. “beccarii” forma 1) 409
can avoid such inter-species difference for evaluation of the sources between [CO32-] of the 410
ambient waters and food. 411
Figure 11 showed the relationship of salinity of the water to the 13CDIC and the δ13Cforam, to 412
the average of the highest 5% salinity each day in 2010. We obtained the regression lines both 413
for the δ13CDIC–salinity and the δ13Cforam–salinity on the 2010 data. The linear regression line 414
on the δ13CDIC–salinity was δ13CDIC = -7.30 + 0.36*salinity, based on the data except for the 415
trends (B) and (C), riverine waters and seawaters. Although the regression line must have 416
logarithmic trend betweenδ13CDIC and salinity of the water, the approximation using the linier 417
regression line seemed to arise no marked problem in the salinity range between 17 and 23 418
(Figure 11). The regression line on the δ13Cforam–salinity was obtained as δ13Cforam = -13.28 + 419
0.40*salinity. According to the linear regression lines in the salinity range between 17.61 and 420
21.42, the δ13CDIC ranged between -0.96‰ and 0.41‰, whereas the δ13Cforam ranged between 421
-6.24‰ and -4.71‰. There was offset between the δ13CDIC and the δ13Cforam, ranging -5.28 to 422
-5.12‰ between salinity of 17.61 and 21.42 (Figure 11). 423
This offset is considerably large, compared to that of molluca (Sampei et al., 2005). This 424
- 24 -
suggests the influence of other [CO32-] source having more negative δ13C, in addition to 425
[CO32-] of DIC of the waters in order to explain such large offset between the δ13CDIC and the 426
δ13Cforam. We regarded δ13Corg of the detritus samples of macrobenthos colonies as food for 427
foraminifera. Because the δ13Corg of the detritus was around -22‰ (Table 5), food derived 428
[CO32-] appears to be reasonable candidate that accounts for [CO3
2-] source having more 429
negative δ13C. Therefore, we concluded that A. “beccarii” forma 1 seemed to make carbonate 430
tests, not only using [CO32-] of the ambient waters, but also [CO3
2-] derived from food. This 431
might be nice adaptation for calcification of foraminiferal shells under low salinity regime 432
(i.e., low DIC concentration). 433
Given that the end-members of δ13CDIC (-0.96‰ and 0.41‰) and δ13Corg (-22‰) and no 434
large isotopic fractionation to calcification of the calcite, the contributions of [CO32-] of DIC 435
of the waters and [CO32-] of food were estimated as ~75% and ~25%, respectively at salinity 436
17.61 and ~77% and ~23%, respectively at salinity 21.42. (*** Takata: I remember you told 437
me +1‰ isotopic fractionation to calcite precipitation. Could you send me the reference? In 438
addition, is there consensus about isotopic fractionation through the process of 439
remineralization of organic matter to DIC? I think this would be no so small.) 440
441
Stable carbon isotope ratio of bridge pier foraminifera among the four years 442
The δ13Cforam of bridge pier A. “beccarii” forma 1 showed relatively wide variation among 443
- 25 -
the four years, especially in the data of 2010 (Figure 7). We calculated the difference of stable 444
carbon isotope ratio from the 2010 data to that of each year (Δδ13C). The Δδ13Cforam at the 445
Matsue and Nakaumi Bridges was calculated based on subtraction of the δ13Cforam of each year 446
from the estimated one of 2010 using the same salinity value and the regression line of the 447
δ13Cforam–salinity, because there is difference in salinity of the waters in the observed δ13C 448
among the years. The Δδ13CDIC at the Matsue and Nakaumi Bridges was calculated in the 449
same manner. In contrast, the Δδ13CDIC of the waters of the Hii River and Okidomari (Sea of 450
Japan (East Sea)) was calculated based on simple subtraction from the 2010 data to that of 451
each year, because of the negligible difference of salinity. 452
There was large annual variation between the Δδ13CDIC and the Δδ13Cforam at the Mastue 453
and Nakaumi Bridges (Figure 12). In contrast, there was little difference on Δδ13CDIC in the 454
Hii River and the Sea of Japan among the years (Figure 12). It is suggested that stable carbon 455
isotope signature in the Lake Shinji–Nakaumi system is affected by alteration of δ13CDIC by 456
biological processes as shown by the trends (B) ad (C) in our study in Lakes Shinji and 457
Nakaumi rather than by possible variations in the end-member values of the riverine waters 458
and the seawater (Figure 12). This implied that careful evaluation of the stable carbon isotope 459
signature is necessary for paleo-salinity reconstruction using fossil samples through 460
crosschecking with the stable oxygen isotope signature, because variation in stable carbon 461
isotope ratio might be susceptible to influences of phytoplankton bloom or oxidation of 462
- 26 -
organic matter. 463
464
Conclusions 465
Our study about stable oxygen and carbon isotope ratios of the waters and Ammonia 466
“beccarii” forma 1 (benthic foraminifera) on the hard substrate in the Ohashi River, 467
southwestern Japan led following conclusions: 468
(1) Stable oxygen isotope ratio of the water in the Lake Shinji–Nakaumi system had positive 469
correlation with salinity of the waters. By contrast, stable carbon isotope ratio of dissolved 470
inorganic carbon (DIC) of the water generally showed (A) positive relationship to salinity of 471
the water, but there were also (B) more positive shift without salinity variation under low 472
salinity regime due to uptaking 12C by phytoplanktons in Lake Shinji and (C) more negative 473
shift under high salinity regime due to oxidation of old organic carbon with oxygen deficiency 474
in the hypolimnetic water of Lake Nakaumi. 475
(2) Stable oxygen isotope ratio of bridge pier A. “beccarii” forma 1 showed positive 476
relationship to average salinity of the waters. Expected stable oxygen isotope ratio of 477
equilibrium calcite of the ambient water during the two months was considerably more 478
negative (about 3‰) than the stable oxygen isotope ratio of bridge pier A. “beccarii” forma 1. 479
This implied that tests of bridge pier A. “beccarii” forma 1 did not record the average of 480
salinity simply. If the average of the highest 5% salinity each day during the two months was 481
- 27 -
adopted, the stable oxygen isotope ratio of equilibrium calcite was more similar to the stable 482
oxygen isotope ratio of bridge pier A. “beccarii” forma 1. Therefore, bridge pier A. 483
“beccarii” forma 1 probably produces calcareous test under relatively high salinity timing 484
and ceased calcite precipitation under low salinity circumstance. 485
(3) Stable carbon isotope ratio of bridge pier A. “beccarii” forma 1 showed small variation 486
vertically, whereas there was relatively wide variation among the three study locations. There 487
was large offset between the δ13CDIC and the δ13Cforam, ranging -5.28‰ to -5.12‰. Ammonia 488
“beccarii” forma 1 seemed to make carbonate tests, not only using [CO32-] of the ambient 489
waters, but also using [CO32-] derived from food that has the more negative stable carbon 490
isotope ratio. 491
492
References 493
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beccarii (Linné) var. tepida (Cushman).” Journal of Paleontology. 31:1168–1147. 495
––––, 1961. Laboratory experiments on the ecology of foraminifera. Contributions from the 496
Cushman Foundation for Foraminiferal Research, 12:87–106. 497
Dettman, D. L., K. W. Flessa, P. D. Roopnarine, Schöne, and D. H. Goodwin. 2003. The use 498
of oxygen isotope variations in shells of estuarine mollusks as a quantitative record of 499
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––––, A. K. Reische, and K. C. Lohmann. 1999. Controls on the stable isotope composition of 502
seasonal growth bands in aragonitic fresh-water bivalves (unionidea). Geocheimica et 503
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Erez, J., and B. Luz. 1983. Experimental paleotemperature equation for planktonic 505
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fractionation between synthetic aragonite and water: Influence of temperature and Mg2+ 520
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[eds.], Proxies in Late Cenozoic Paleoceanography. Elsevier. 539
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during the Pliocene warm period not supported by coral evidence. Nature, 471:209-211, 562
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564
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Table legends 565
566
Table 1. Stable oxygen isotope ratio of the waters (δ18Owater) and stable carbon isotope ratio of 567
dissolved inorganic carbon (DIC) in the waters (δ13CDIC) in the Lake Shinji – Nakaumi 568
system from 2006 to 2009 569
570
Table 2. Stable oxygen isotope ratio of the waters (δ18Owater) and stable carbon isotope ratio of 571
dissolved inorganic carbon (DIC) in the waters (δ13CDIC) in the Lake Shinji – Nakaumi 572
system in 2010. Water properties in the Lake Shinaji – Nkauami system in 2010 were also 573
shown. 574
575
Table 3. Stable carbon and oxygen isotope ratios of Ammonia “beccarii” forma 1 tests 576
(δ18Oforam and δ13Cforam, respectively) 577
578
Table 4. Average values of water temperature and salinity of the waters during the two 579
months prior to the sampling (data referred from the Inland Water Fisheries and Coastal 580
Fisheries Division, Shimane Prefectural Fisheries Technology Center and the Izumo River 581
Office, Minister of Land, Infrastructure, Transport and Tourism, pers comm.) and mean 582
value and standard deviation of each depth level of stable carbon and oxygen isotope 583
- 33 -
ratios of Ammonia “beccarii” forma 1 tests (δ18Oforam and δ13Cforam, respectively) in the 584
Lake Shinji – Nakaumi system 585
586
Table 5. Stable carbon isotope ratio of organic matter in the fine detritus (<63 µm) (δ13Corg) 587
within the attached macrobenthos on the concrete piers of the Matsue and Nakaumi 588
Bridges in the Ohashi River and the Nakaumi Observatory Station in Lake Nakaumi 589
590
Table 6. Inferred stable oxygen isotope ratio of equilibrium calcite (δ18Oeq. cal.) at the Matsue 591
Bridge, Nakaumi Bridge and Nakaumi Observatory Station, based on the average values 592
of water temperature and salinity of the ambient waters (data referred from the Inland 593
Water Fisheries and Coastal Fisheries Division, Shimane Prefectural Fisheries 594
Technology Center and the Izumo River Office, Minister of Land, Infrastructure, 595
Transport and Tourism, pers comm.); the tables (a) and (b) were based on the simple 596
average salinity and the average of the highest 5% salinity each day, respectively; stable 597
oxygen isotope ratio of the ambient water was estimated equations of this study 598
599
600
- 34 -
Figure legends 601
602
Fig. 1. Locality maps (a-c) of the study area. 603
604
Fig. 2. Time series changes of water temperature, dissolved oxygen content, salinity and 605
alkalinity and stable oxygen isotope ratio and stable carbon isotope ratio of dissolved 606
inorganic carbon (DIC) of the waters (δ18Owater and δ13CDIC) at the Matsue Port and Matsue 607
Bridge in September to October, 2010. 608
609
Fig. 3. (a) Relationship between salinity and alkalinity and (b) relationship between salinity 610
and ΣCO2 in the Lake Shinji – Nakaumi system. 611
612
Fig. 4. Relationship between stable oxygen isotope ratio (δ18Owate) and salinity of the waters 613
in the Lake Shinji – Nakaumi system: (a) 2006 to 2007, (b) 2008, (c) 2009 and (d) 2010. 614
615
Fig. 5. Relationship between stable carbon isotope ratio of dissolved inorganic carbon (DIC) 616
of the waters (δ13CDIC) and salinity of the waters in the Lake Shinji – Nakaumi system: (a) 617
2006 to 2007, (b) 2008, (c) 2009 and (d) 2010. The three trends (A), (B) and (C) in the 618
panel (d) correspond to the explanations in the text. 619
- 35 -
620
Fig. 6. Depth profiles of stable oxygen isotope ratio of bridge-pier Ammonia “beccarii” 621
forma 1 (δ18Oforam) at the Matsue and Nakaumi Bridges. Inferred stable oxygen isotope ratio 622
of equilibrium calcite from the ambient water (see Table 6) was shown in the panels. 623
624
Fig. 7. Depth profiles of stable carbon isotope ratio of bridge-pier Ammonia “beccarii” forma 625
1 (δ13Cforam) at the Matsue and Nakaumi Bridges. 626
627
Fig. 8. Relationship between salinity and stable oxygen ratio of bridge-pier Ammonia 628
“beccarii” forma 1 (δ13Cforam) at the Mastue and Nakaumi Bridges, and the Nakaumi 629
Observatory Station (salinity data referred from the Izumo River Office, Minister of Land, 630
Infrastructure, Transport and Tourism, pers comm.). Regression line was taken from Sampei 631
et al. (2005); salinity in the panel (a) was the simple average values during two months, 632
whereas those in the panel (b) was the average of the 5% salinity each day in the same 633
period. 634
635
Fig. 9. Comparison of stable oxygen isotope ratios between bridge-pier Ammonia “beccarii” 636
forma 1 and the equilibrium calcite (δ18Oforam and δ18Oeq. cal., respectively) at the Mastue and 637
Nakaumi Bridges, and the Nakaumi Observatory Station: (a) δ18Oeq. cal., based on the 638
- 36 -
average salinities during the two month average and (b) δ18Oeq. cal., based on the average 639
salinities during the one month. 640
641
Fig. 10. Relationship between salinity and stable carbon ratio of bridge-pier Ammonia 642
“beccarii” forma 1 at the Mastue and Nakaumi Bridges, and the Nakaumi Observatory 643
Station (salinity data referred from the Izumo River Office, Minister of Land, Infrastructure, 644
Transport and Tourism, pers comm.). Regression line was taken from Sampei et al. (2005); 645
salinity in the panel was the average of the 5% salinity each day in the same period. 646
647
Fig. 11. Comparison between salinity of the waters (derived from the average of the highest 648
5% salinity each day) and stable carbon isotope ratios between the DIC of the waters in the 649
Lake Sinji–Nakaumi system and bridge-pier Ammonia “beccarii” forma 1 (δ13CDIC and 650
δ13Cforam, respectively) at the Mastue and Nakaumi Bridges in 2010 (salinity data referred 651
from the Izumo River Office, Minister of Land, Infrastructure, Transport and Tourism, pers 652
comm.). The three trend (A), (B) and (C) with respect to the δ13CDIC correspond to the 653
explanations in the text. The regression lines on the δ13CDIC–salinity and the 654
δ13Cforam–salinity were δ13CDIC = -7.30 + 0.36*salinity and δ13Cforam = -13.28 + 0.40*salinity, 655
respectively. 656
657
- 37 -
Fig. 12. Annual variations on the difference from 2010 to each year in the stable carbon 658
isotope ratio of dissolved inorganic carbon (DIC) of the water (Δδ13CDIC) and bridge pier 659
Ammonia “beccarii” forma 1 (Δδ13Cforam) at the Hii River, 1 m water depth of the Matsue 660
Bridge, 1 m water depth of the Nakaumi Bridge, and Okidomari (Sea of Japan (East Sea)). 661
662
Table1_takataDouble-column width
Date Locality Water depth(m) Salinity Salinity (in
Lab)δ18Owater (‰VSMOW)
δ13CDIC (‰VPDB)
2006/10/20 Nakaumi Bridge 0.0 16 15.5 -4.04 0.722007/10/11 Matsue Bridge 0.0 4.5 -6.04 -3.332007/10/11 Matsue Bridge above 50 cm 4.5 -6.00 -4.062007/10/11 Nakaumi Bridge 0.0 9 -4.97 -2.232007/10/11 Nakaumi Bridge 2.5 15 -4.12 -1.102008/10/6 Hii River 0.0 0.06 1 -8.28 -9.722008/10/6 Matsue Bridge 1.0 7.22 8 -5.43 -0.952008/10/6 Matsue Bridge 3.0 14.56 10.5 -4.70 0.772008/10/6 Nakaumi Bridge 1.0 19.26 20 -3.21 1.542008/10/6 Nakaumi Observatory 1.0 20.14 18.5 -3.44 -0.532008/10/6 Nakaumi Observatory 5.0 28.74 28 -1.85 0.002008/10/6 Okidomari (Sea of Japan) 0.0 33.93 33.5 -0.61 1.942009/10/6 Hii River 0.0 0.04 1 -7.85 -8.702009/10/6 Ihnashi River 0.0 0.06 1 -8.06 -8.332009/10/9 Matsue Bridge 1.0 6.86 12.5 -4.97 -2.262009/10/9 Matsue Bridge 3.0 16.9 17 -3.44 1.212009/10/9 Nakaumi Bridge 1.0 21.52 21 -2.98 -0.222009/10/9 Nakaumi Observatory 1.0 20.21 20.5 -3.42 0.172009/10/9 Nakaumi Observatory 5.0 26.95 27 -1.78 -0.412009/10/6 Okidomari (Sea of Japan) 0.0 33.41 34 -0.37 1.90
Table2_takataDouble-column width
Date Locality Waterdepth (m) Time Water
temperatureDisslved oxygen
contentSalinity Salinity (in
Lab)Alkalin
ity pH ΣCO2δ18Owater (‰VSMOW)
δ13CDIC (‰VPDB)
2010/9/11 Matsue Port 0.2 11:55 30.14 8.45 6.12 6 -5.77 -2.04Matsue Port 3.0 11:55 29.45 2.62 23.61 23 -2.28 -1.36Hii River 0.0 9:30 27.31 8.20 0.06 0 -7.96 -9.30Ihnashi River 0.0 10:45 27.50 9.45 0.05 0 -8.10 -9.33Okidomoari 0.0 12:55 28.72 6.44 32.09 32 -0.59 3.17
2010/9/14 Matsue Port 0.2 11:38 27.67 8.06 6.41 7 0.84 8.31 0.85 -5.52 -2.89Matsue Port 3.0 11:38 29.11 1.35 24.02 25 1.76 7.76 1.84 -2.21 -2.13
2010/9/17 Matsue Port 0.2 9:55 26.71 8.66 6.62 7 0.85 8.63 0.84 -5.45 -0.99Matsue Port 3.0 9:55 28.18 5.30 22.02 22 1.60 8.17 1.62 -2.62 0.45
2010/9/21 Matsue Port 0.2 12:32 28.21 8.64 7.13 7 0.85 8.80 0.83 -5.22 -1.25Matsue Port 3.0 12:32 28.57 0.43 25.42 25 1.78 7.49 1.92 -2.06 -1.71
2010/9/24 Matsue Port 0.2 9:29 24.01 7.45 5.16 5 0.80 8.64 0.79 -5.66 -5.35Matsue Port 3.0 9:29 24.05 7.61 5.19 5 0.79 8.68 0.78 -5.65 -5.02
2010/9/28 Matsue Port 0.2 9:00 23.70 6.54 19.56 19 1.40 8.12 1.42 -3.14 -0.43Matsue Port 3.0 9:00 23.67 6.56 19.56 20 1.43 8.16 1.44 -3.06 -0.95
2010/10/1 Matsue Port 0.2 8:47 22.05 7.53 15.01 16 1.21 8.28 1.21 -3.82 -1.27Matsue Port 3.0 8:47 23.71 8.16 20.93 21 1.48 8.34 1.48 -2.78 0.03
2010/10/4 Matsue Port 0.2 9:07 22.74 8.25 8.75 10 0.96 8.37 0.96 -5.16 -3.73Matsue Port 3.0 9:07 23.72 4.80 22.03 17 1.32 8.15 1.33 -3.48 -1.51
2010/10/8 Matsue Port 0.2 8:50 21.92 6.48 6.68 6 0.77 8.04 0.79 -5.37 -5.74Matsue Port 3.0 8:50 22.04 6.40 6.84 7 0.84 8.06 0.86 -5.30 -5.05
2010/10/13 Matsue Bridge 1.0 10:20 21.95 10.19 6.34 5 0.76 8.85 0.74 -5.61 -2.40Matsue Bridge 3.0 10:20 23.22 3.75 20.78 7 0.88 8.55 0.87 -5.04 -2.43Matsue Bridge 4.4 10:20 23.33 3.75 22.02 21 1.52 7.93 1.56Nakaumi Bridge 1.0 10:55 23.06 6.77 20.15 18 1.39 8.18 1.40 -3.16 -1.11Nakaumi Bridge 2.0 10:55 23.15 6.51 20.71 20 1.40 8.16 1.41Nakaumi Observatory 1.0 11:40 23.48 10.16 20.37 21 1.48 8.54 1.47 -2.78 1.71Nakaumi Observatory 3.0 11:40 23.39 4.17 23.42 22 1.60 8.42 1.59 -2.58 2.74Nakaumi Observatory 5.0 11:40 23.78 1.61 26.81 26 1.75 7.92 1.80 -1.86 -0.66
2010/10/14 Okidomoari 0.0 12:50 24.50 7.80 33.14 33 1.98 8.28 1.99 -0.28 2.52Hii River 0.0 14:30 24.24 9.05 0.06 0 0.48 8.13 0.49 -7.97 -8.28Ihnashi River 0.0 16:00 23.04 9.72 0.05 0 0.32 8.31 0.32 -7.96 -10.94
Table3_takataDouble-column width
Date LocalityWater depth
(m)δ18Oforam
(‰VPDB)δ13Cforam
(‰VPDB)SAMPLE ID
2006/10/2 Nakaumi Bridge 1.0 -5.68 -3.46 Nakaumi 100cm/Takata/DD./Nakaumi Bridge 1.0 -5.57 -3.22 Nakaumi 100cm/DD/Takata/Nakaumi Bridge 1.0 -5.51 -3.29 Nakaumi 100cm/DD/Takata/Nakaumi Bridge 2.0 -5.31 -3.51 Nakaumi 200cmA/Takata/DD./Nakaumi Bridge 2.0 -5.36 -3.43 Nakaumi 200cmA/DD/Takata/Nakaumi Bridge 2.0 -5.45 -3.34 8 TEST 200CM/NAKAUMI FORAM/DD
2007/10/2 Matsue Bridge 1.0 -7.37 -5.15 1M-1 MATSUE BR/OCT07 TAKATA/K254Matsue Bridge 1.0 -7.03 -5.04 1M-3 MATSUE BR/OCT07 TAKATA/K254Matsue Bridge 3.0 -6.66 -4.85 3M-3 MATSUE BR/OCT07 TAKATA/K254Matsue Bridge 3.0 -6.80 -5.01 3M-3 MATSUE BR/OCT07 TAKATA/K254Matsue Bridge 3.0 -6.72 -4.71 3M-3 MATSUE BR/OCT07 TAKATA/K254Matsue Bridge 3.0 -6.24 -4.29 3m-3 M.BR/TAKATA/K254Matsue Bridge 3.0 -6.12 -4.54 3m-3 M.Br/TAKATA/K254Matsue Bridge 4.4 -7.17 -5.01 4.4M-3 MATSUE B/OCT07 TAKATA/K254Matsue Bridge 4.4 -6.43 -4.12 4.4M-3 MATSUE B/OCT07 TAKATA/K254Matsue Bridge 4.4 -6.40 -4.52 4.4M-3 MATSUE B/OCT07 TAKATA/K254Matsue Bridge 4.4 -6.43 -4.63 4.4m-3/TAKATA/K254Matsue Bridge 4.4 -6.02 -4.26 4.4m-3/TAKATA/K254Matsue Bridge 4.4 -6.25 -4.29 4.4m-3/TAKATA/K254Nakaumi Bridge 1.0 -5.45 -3.37 100CM-1 NAKAUMI/OCT07 TAKATA/K254Nakaumi Bridge 1.0 -5.64 -3.63 100CM-1 NAKAUMI/OCT07 TAKATA/K254Nakaumi Bridge 1.0 -5.86 -4.05 100CM-1 NAKAUMI/OCT07 TAKATA/K254Nakaumi Bridge 1.0 -5.70 -4.09 100 cm-1/TAKATA/K254Nakaumi Bridge 1.0 -5.39 -3.55 100 cm-1/TAKATA/K254Nakaumi Bridge 1.0 -5.37 -3.72 100 cm-1/TAKATA/K254Nakaumi Bridge 2.0 -5.09 -3.35 200CM-1 NAKAUMI/OCT07 TAKATA/K254Nakaumi Bridge 2.0 -5.21 -3.50 200CM-1 NAKAUMI/OCT07 TAKATA/K254Nakaumi Bridge 2.0 -5.44 -3.71 200CM-1 NAKAUMI/OCT07 TAKATA/K254Nakaumi Bridge 2.0 -5.22 -3.53 200 cm/TAKATA/K254Nakaumi Bridge 2.0 -5.50 -3.45 200 cm/TAKATA/K254Nakaumi Bridge 2.0 -5.21 -3.43 200 cm/TAKATA/K254
2008/10/8 Matsue Bridge 1.0 -5.83 -3.93 MATBRID1.0-H1a/HIROYUKI/K341Matsue Bridge 1.0 -6.07 -4.36 MB-1.0M-A/TAKATA/k395Matsue Bridge 1.0 -6.49 -4.43 MB-1.0M-B/TAKATA/K395Matsue Bridge 1.0 -6.44 -4.05 MB-1.0M-C/TAKATA/K395Matsue Bridge 1.0 -6.48 -4.47 MB-1.0M-C/TAKATA/K395Matsue Bridge 3.0 -6.18 -4.02 MB-3.0M-A/TAKATA/k395Matsue Bridge 3.0 -6.17 -4.15 MB3m-a/TAKATA/K395Matsue Bridge 3.0 -6.47 -4.30 MB-3.0M-C/TAKATA/K395Matsue Bridge 3.0 -5.99 -4.00 MB3m-b/TAKATA/K395Matsue Bridge 3.0 -5.93 -3.68 MB-3m-C/TAKATA/K395Matsue Bridge 4.4 -6.24 -4.03 MATBRID4.4-HOL1/HIROYUKI/K341Matsue Bridge 4.4 -5.84 -3.69 MATBRID4.4-H1a/HIROYUKI/K341Matsue Bridge 4.4 -5.88 -3.82 MATBRID4.4-H1b/HIROYUKI/K341Matsue Bridge 4.4 -6.02 -3.82 MATBRID4.4-H2a/HIROYUKI/K341Matsue Bridge 4.4 -6.30 -3.85 MATBRID4.4-H2c/HIROYUKI/K341Matsue Bridge 4.4 -3.19 -2.93 MB-4.4M-B/TAKATA/K395Matsue Bridge 4.4 -5.74 -3.72 MB-4.4M-C/TAKATA/K395Nakaumi Bridge 1.0 -5.20 -3.33 NB-1.0M-A/TAKATA/K395Nakaumi Bridge 1.0 -5.08 -3.25 NB-1.0M-B/TAKATA/K395Nakaumi Bridge 2.0 -4.87 -2.99 NB-2.0M-B/TAKATA/K395Nakaumi Bridge 2.0 -5.23 -3.57 NB-2.0M-C/TAKATA/K395Nakaumi Bridge 2.0 -5.31 -3.47 NB-2m-C/TAKATA/K395Nakaumi Obserbatory 5.0 -3.00 -2.57 MATBRID5.0-H3a/HIROYUKI/K341Nakaumi Obserbatory 5.0 -3.14 -2.37 MATBRID5.0-H1b/HIROYUKI/K341Nakaumi Obserbatory 5.0 -3.15 -2.85 NO-5.0M-A/TAKATA/K395Nakaumi Obserbatory 5.0 -3.00 -2.58 NO-5.0M-B/TAKATA/K395Nakaumi Obserbatory 5.0 -3.10 -2.67 NO-5.0M-A'/TAKATA/K395Nakaumi Obserbatory 5.0 -3.30 -2.58 NO-5.0M-B'/TAKATA/K395
2009/10/12 Matsue Bridge 1.0 -6.22 -4.53 1M MATSUE BR 09/TAKATA/K453Matsue Bridge 1.0 -6.04 -4.32 1M 2009/MATSUEBR TAKATA/K453Matsue Bridge 1.0 -6.13 -4.34 MATS BR 1M/9OCT09 TAKATA/K481Matsue Bridge 3.0 -5.82 -4.17 3M MATSUE BR 09/TAKATA/K453Matsue Bridge 3.0 -6.15 -4.35 3M 2009/MATSUEBR TAKATA/K453Matsue Bridge 3.0 -5.98 -4.38 MATS BR 3M/9OCT09 TAKATA/K481Matsue Bridge 4.4 -6.04 -4.10 4.4M 2009/MATSUEBR TAKATA/K453Matsue Bridge 4.4 -5.69 -3.68 4.4M 2009/MATSUEBR TAKATA/K453Matsue Bridge 4.4 -5.54 -4.03 MATS BR 4.4M/9OCT09 TAKATA/K481
2010/10/12 Matsue Bridge 1.0 -6.39 -5.97 MATS BR 1M/12OCT10 TAKATA/K481Matsue Bridge 1.0 -6.21 -6.03 MATS BR 1M/12OCT10 TAKATA/K481Matsue Bridge 1.0 -6.65 -6.74 MATS BR 1M/12OCT10 TAKATA/K481Matsue Bridge 1.0 -6.63 -6.55 M BRIDGE 1M/OCT10 TAKATA /K481Matsue Bridge 3.0 -6.21 -5.92 MATS BR 3M/12OCT10 TAKATA/K481Matsue Bridge 3.0 -6.10 -5.93 MATS BR 3M/12OCT10 TAKATA/K481Matsue Bridge 3.0 -6.13 -5.96 MATS BR 3M/12OCT10 TAKATA/K481Matsue Bridge 3.0 -6.00 -5.68 M BRIDGE 3M/OCT10 TAKATA /K481Matsue Bridge 3.0 -6.17 -5.77 M BRIDGE 3M/OCT10 TAKATA /K481 Matsue Bridge 4.4 -6.02 -6.00 MATS BR 4.4M/12OCT10 TAKATA/K481Matsue Bridge 4.4 -6.42 -6.18 MATS BR 4.4M/12OCT10 TAKATA/K481Matsue Bridge 4.4 -5.97 -5.29 MATS BR 4.4M/12OCT10 TAKATA/K481Matsue Bridge 4.4 -6.12 -6.14 M BRIDGE 4.4M/OCT10 TAKATA /K481 Matsue Bridge 4.4 -5.91 -5.64 M BRIDGE 4.4M/OCT10 TAKATA /K481 Nakaumi Bridge 1.0 -5.17 -4.39 NAKA BR 1M/12OCT10 TAKATA/K481Nakaumi Bridge 1.0 -5.22 -4.65 NAKA BR 1M/12OCT10 TAKATA/K481Nakaumi Bridge 1.0 -5.55 -4.88 NAKA BR 1M/12OCT10 TAKATA/K481Nakaumi Bridge 1.0 -5.31 -4.66 N BRIDGE 1M/OCT10 TAKATA /K481 Nakaumi Bridge 1.0 -5.29 -4.50 N BRIDGE 1M/TAKATA /K481Nakaumi Bridge 1.0 -5.42 -4.69 N BRIDGE 1M/TAKATA /K481Nakaumi Bridge 2.0 -4.69 -3.93 NAKA BR 2M/12OCT10 TAKATA/K481Nakaumi Bridge 2.0 -5.15 -4.30 NAKA BR 2M/12OCT10 TAKATA/K481Nakaumi Bridge 2.0 -4.77 -4.19 NAKA BR 2M/12OCT10 TAKATA/K481Nakaumi Bridge 2.0 -4.97 -4.38 N BRIDGE 2M/OCT10 TAKATA /K481 Nakaumi Bridge 2.0 -4.99 -4.23 N BRIDGE 2M/OCT10 TAKATA /K481 Nakaumi Obserbatory 5.0 -3.73 -3.62 NAKA OBS 5M/12OCT10 TAKATA/K481
Table4_takataDouble-column width
Date LocalityWater
depth (m)Average
temperatureAverage salinity
(simple)Average salinity(daily minmum)
Average salinity(daily maximum)
Average salinity(highest 5%)
δ18Oforam (‰VPDB) (mean)
δ18Oforam (‰VPDB) (St
dev.)
δ13Cforam (‰VPDB) (mean)
δ13Cforam (‰VPDB) (St
dev.)2006/10/2 Nakaumi Bridge 1.0 24.90 10.76 3.77 15.99 15.64 -5.59 0.09 -3.32 0.122006/10/2 Nakaumi Bridge 2.0 24.95 12.44 4.69 17.45 17.10 -5.37 0.07 -3.43 0.092007/10/2 Matsue Bridge 1.0 27.63 6.82 4.35 11.69 11.33 -7.20 -5.092007/10/2 Matsue Bridge 3.0 27.75 8.34 4.49 13.99 13.80 -6.51 0.31 -4.68 0.282007/10/2 Matsue Bridge 4.4 27.52 8.81 4.65 14.34 14.14 -6.45 0.39 -4.47 0.322007/10/2 Nakaumi Bridge 1.0 27.58 12.18 5.89 16.92 16.67 -5.57 0.20 -3.73 0.282007/10/2 Nakaumi Bridge 2.0 27.59 12.85 6.35 17.56 17.30 -5.28 0.16 -3.49 0.122008/10/8 Matsue Bridge 1.0 26.82 8.50 6.24 13.20 12.92 -6.26 0.30 -4.25 0.252008/10/8 Matsue Bridge 3.0 26.94 10.20 6.65 15.20 15.01 -6.15 0.21 -4.03 0.232008/10/8 Matsue Bridge 4.4 26.85 11.00 6.96 16.00 15.86 -6.00 0.23 -3.82 0.122008/10/8 Nakaumi Bridge 1.0 27.01 14.84 8.41 19.76 19.43 -5.14 -3.292008/10/8 Nakaumi Bridge 2.0 27.09 16.52 9.15 21.04 20.91 -5.14 0.23 -3.34 0.312008/10/8 Nakaumi Obserbatory 5.0 26.07 27.37 25.88 28.37 -3.11 0.11 -2.60 0.15
2009/10/12 Matsue Bridge 1.0 25.00 5.95 3.37 11.35 11.04 -6.13 0.09 -4.40 0.122009/10/12 Matsue Bridge 3.0 25.20 7.69 3.65 13.86 13.71 -5.98 0.17 -4.30 0.112009/10/12 Matsue Bridge 4.4 25.10 8.08 3.68 13.96 13.85 -5.76 0.26 -3.94 0.222010/10/12 Matsue Bridge 1.0 27.99 9.54 4.35 17.16 17.16 -6.47 0.21 -6.32 0.382010/10/12 Matsue Bridge 3.0 27.99 10.73 4.44 18.01 17.87 -6.12 0.08 -5.85 0.122010/10/12 Matsue Bridge 4.4 27.99 11.67 4.69 18.13 18.06 -6.09 0.20 -5.85 0.382010/10/12 Nakaumi Bridge 1.0 28.01 15.20 6.36 20.72 20.54 -5.33 0.14 -4.63 0.172010/10/12 Nakaumi Bridge 2.0 28.06 16.22 7.51 21.54 21.42 -4.91 0.18 -4.21 0.172010/10/12 Nakaumi Obserbatory 5.0 26.37 27.91 -3.73 -3.62
Table5_takataDouble-column width
Date Locality Waterdepth (m)
δ13Corg (‰VPDB)
-21.52010/10/12 Matsue Bridge 1.0 -21.9
-21.6-21.8
2010/10/12 Matsue Bridge 3.0 -21.9-21.1-21.8
2010/10/12 Matsue Bridge 4.4 -22.1-22.6-22.0
2010/10/12 Nakaumi Bridge 1.0 -22.4-22.4-22.5
2010/10/12 Nakaumi Bridge 2.0 -22.4-22.6-21.5
2010/10/12 Nakaumi Observatory 1.0 -21.0-21.8-21.4
2010/10/12 Nakaumi Observatory 3.0 -21.4-21.8-22.7
2010/10/12 Nakaumi Observatory 5.0 -22.4-22.1
Table6_takataDouble-column width
(a) simple average salinity 2006 2007 2008 2009 2010
Oct 19 Oct 11 Oct 6 Oct 12 Oct 12Aug 20 - Oct 19 Aug 11 - Oct 10 Aug 6 - Oct 5 Aug 12 - Oct 11 Aug 10 - Oct 11
Matsue Bridge1.0 m 27.63 26.82 25.00 27.993.0 m 27.75 26.94 25.20 27.994.4 m 27.52 26.85 25.10 27.991.0 m 6.82 8.50 5.95 9.543.0 m 8.34 10.20 7.69 10.734.4 m 8.81 11.00 8.08 11.671.0 m -8.13 -7.76 -8.40 -7.393.0 m -7.88 -7.49 -8.06 -7.174.4 m -7.75 -7.33 -7.95 -7.00
Nakaumi Bridge1.0 m 24.90 27.58 27.01 28.012.0 m 24.95 27.59 27.09 28.061.0 m 10.76 12.18 14.84 15.202.0 m 12.44 12.85 16.52 16.221.0 m -6.86 -7.16 -6.67 -6.512.0 m -6.57 -7.04 -6.39 -6.34
Nakaumi ObsavatoryTemperature 5.0 m 26.07 26.37Salinity 5.0 m 27.37 27.91δ18Oeq. cal. (‰VPDB)5.0 m -4.23 -4.05
(b) average of the highest 5% salinity each day2006 2007 2008 2009 2010
Oct 19 Oct 11 Oct 6 Oct 12 Oct 12Aug 20 - Oct 19 Aug 11 - Oct 10 Aug 6 - Oct 5 Aug 12 - Oct 11 Aug 10 - Oct 11
Matsue Bridge1.0 m 27.63 26.82 25.00 27.993.0 m 27.75 26.94 25.20 27.994.4 m 27.52 26.85 25.10 27.991.0 m 11.33 12.92 11.04 17.163.0 m 13.80 15.01 13.71 17.874.4 m 14.14 15.86 13.85 18.061.0 m -7.26 -6.92 -7.21 -6.023.0 m -6.87 -6.60 -6.70 -5.864.4 m -6.76 -6.43 -6.66 -5.84
Nakaumi Bridge1.0 m 24.90 27.58 27.01 28.012.0 m 24.95 27.59 27.09 28.061.0 m 15.64 16.67 19.43 20.542.0 m 17.10 17.30 20.91 21.421.0 m -5.94 -6.31 -5.79 -5.522.0 m -5.67 -6.19 -5.58 -5.38
Nakaumi ObsavatoryTemperature 5.0 m 26.07Salinity 5.0 m 28.37δ18Oeq. cal. (‰VPDB)5.0 m -3.90
Temperature
Salinity
δ18Oeq. cal. (‰VPDB)
Temperature
Salinity
δ18Oeq. cal. (‰VPDB)
Temperature
Salinity
δ18Oeq. cal. (‰VPDB)
YearSampling datePeriod
YearSampling datePeriod
Temperature
Salinity
δ18Oeq. cal. (‰VPDB)
Sea ofJapan
(East Sea)
NWPacific
(b)
Tokyo
(a) 145°45°
Figure1_takataDouble-column width
133°00' 10' 20'
35°30'
25'
Lake Nakaumi
Sakai ChannelSea of Japan(East Sea)
HiiRiver
Lake Shinji
(c)
(b)Nakaumi Observatory Station
-2.5 mLakeShinji
LakeNakaumi
-5 m
Ohashi River
AsakumiRiver
500 m
(c) N
MatsueBridge
NakaumiBridge
Observatoryst. (lower)
Observatoryst. (Matsue)
Observatory st. (Matsue B.)
Matsue Port
Temp
DO
Salinity
Salinity (in lab.)
Alkalinity
d13C
0 m3 m
Salinity (laboraory)
Alkalinity(meq l-1)
Dissolvedoxygen(mg l-1)
Salinity (field)
Temperature(ºC)
OctoberSeptember
sampling
20
24
28
32
Temp
0
4
8
12
DO
0
10
20
30
Salinity
0
10
20
30
Salinity (in lab.)
0.5
1
1.5
2
Alkalinity
-6
-5
-4
-3
-2
d18O (vsmow)
-6
-4
-2
0
2
Figure2_takataDouble-column width
δ13CDIC (‰VPDB)
δ18Owater (‰VSMOW)
0
0.5
1
1.5
2
2.5
0 5 10 15 20 25 30 35
y = 0.48 + 0.050x r = 0.99
0
0.5
1
1.5
2
2.5
0 5 10 15 20 25 30 35
y = 0.49 + 0.048x r = 0.99
Salinity
Alk
alin
ity(m
eq l-1
)Σ
CO
2(m
mol
l-1)
Salinity
Figure3_takataSingle-column width
Figure4_takataSingle-column width
Salinity
δ18O
wat
er (‰
VS
MO
W)
δ18O
wat
er (‰
VS
MO
W)
riverine waters
seawaters
-10
-8
-6
-4
-2
0
0 5 10 15 20 25 30 35-10
-8
-6
-4
-2
0
0 5 10 15 20 25 30 35
-10
-8
-6
-4
-2
0
0 5 10 15 20 25 30 35-10
-8
-6
-4
-2
0
0 5 10 15 20 25 30 35
0-1 m3-5 m
Salinity
riverine waters
seawaters
riverine waters
seawaters
(a) 2006-2007 (b) 2008
(c) 2009 (d) 2010
Figure5_takataSingle-column width
δ13C
DIC
(‰V
PD
B)
AC
Boxygen-poor hypolimnetic waters of Lake Nakaumi
δ13C
DIC
(‰V
PD
B)
riverine waters
seawaters
-12
-10
-8
-6
-4
-2
0
2
4
0 5 10 15 20 25 30 35-12
-10
-8
-6
-4
-2
0
2
4
0 5 10 15 20 25 30 35
-12
-10
-8
-6
-4
-2
0
2
4
0 5 10 15 20 25 30 35-12
-10
-8
-6
-4
-2
0
2
4
0 5 10 15 20 25 30 35
riverine waters
seawater
oxygen-poor hypolimnetic waters of Lake Nakaumi
riverine water
seawater
oxygen-poor hypolimnetic waters of Lake Nakaumi
Salinity Salinity
(a) 2006-2007 (b) 2008
(c) 2009 (d) 2010
Figure6_takataDouble-column width
0
1
2
3
4
5
-9 -8 -7 -6 -5 -4
0
1
2
3-9 -8 -7 -6 -5 -4 -9 -8 -7 -6 -5 -4
-9 -8 -7 -6 -5 -4-9 -8 -7 -6 -5 -4
2006 2007 2008
Dep
th (m
)
-9 -8 -7 -6 -5 -4-9 -8 -7 -6 -5 -4
-9 -8 -7 -6 -5 -4
20102009
δ18Oforam (‰VPDB)
Dep
th (m
)
simple average
average of the highest
5% each day
Mat
sue
Brid
geN
akau
mi B
ridge
δ18Oforam (‰VPDB)
Figure7_takataDouble-column width
2006 2007 2008 20102009
0
1
2
3
4
5
-6 -5 -4 -3 -2 -6 -5 -4 -3 -2
0
1
2
3-6 -5 -4 -3 -2 -6 -5 -4 -3 -2 -6 -5 -4 -3 -2
-7 -6 -5 -4 -3 -7 -6 -5 -4 -3
-7 -6 -5 -4 -3
Dep
th (m
)
δ13Cforam (‰VPDB)
Dep
th (m
)
Mat
sue
Brid
geN
akau
mi B
ridge
δ13Cforam (‰VPDB)
Figure8_takataSingle-column width
Salinity (simple average)
δ18O
fora
m ,δ
18O
mol
lusc
a (‰
VP
DB
) (a)
Salinity (average of the highest 5% each day)
(b)
δ18O
fora
m, δ
18O
mol
lusc
a (‰
VP
DB
)
-10
-8
-6
-4
-2
0
0 5 10 15 20 25 30 35
-10
-8
-6
-4
-2
0
0 5 10 15 20 25 30 35
Ammonia “beccarii” forma 1 (this study)Mollusca (Sampei et al., 2005)
δ18O
eq. c
al. (
‰V
PD
B)
average salinityaverage of the highest 5% salinity each day
δ18Oforam (‰ VPDB)
Figure9_takataSingle-column width
δ18O
eq. c
al. (
‰V
PD
B)
(a)
(b)
-9
-8
-7
-6
-5
-4
-3
-2
-9 -8 -7 -6 -5 -4 -3 -2
-9
-8
-7
-6
-5
-4
-3
-2
-9 -8 -7 -6 -5 -4 -3 -2
Figure10_takataSingle-column width
Salinity (average of the highest 5% each day)
δ13C
fora
m, δ
13C
mol
lusc
a (‰
VP
DB
)
-8
-6
-4
-2
0
2
0 5 10 15 20 25 30 35
Ammonia “beccarii” forma 1 (this study)Mollusca (Sampei et al., 2005)
AC
B
Salinity(average of the highest 5% each day)
δ13C
DIC
, δ13
, Cfo
ram (‰
VP
DB
)
δ13CDIC: -0.96 to -0.41 (‰VPDB)
δ13Corg: ca. -22 (‰VPDB)
δ13Cforam: -6.24 to -4.71 (‰VPDB)
(water)
(food)
(foram.)
Figure11_takataSingle-column width
-12
-10
-8
-6
-4
-2
0
2
4
0 5 10 15 20 25 30 35
δ13CDIC: 0-1 m (‰VPDB)
δ13CDIC: 3-5 m (‰VPDB)
δ13Cforam (‰VPDB)
Δ δ13CDIC-foram = -5.28 to -5.12‰
Hii River
Matsue Bridge, 1m
Nakaumi Bridge, 1 m Nakaumi Bridge, 1 m
Okidomari
Figure12_takataDouble-column width
-101234
-101234
-3-2-1012
-3-2-1012
2007 2008 2009 2010
2007 2008 2009 2010
Δ δ
13C
DIC
(‰V
PD
B)
Δ δ
13C
fora
m (‰
VP
DB
)
012345
012345
Matsue Bridge, 1 m