isotope signature of benthic foraminifera on hard

- 1 -

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

19

- 2 -

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

25

1 Corresponding author ([email protected]) 26

27

Running title: Isotope signature of foraminifera on the hard substrates 28

29

30

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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

43

44

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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

- 5 -

[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

- 6 -

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

- 7 -

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

- 8 -

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

- 9 -

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

- 10 -

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

- 11 -

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

- 12 -

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

- 13 -

(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

- 14 -

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

- 15 -

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

- 16 -

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

- 17 -

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

- 18 -

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

- 19 -

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

- 20 -

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

- 21 -

“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

seasonal and annual Colorado River discharge. Geocheimica et Cosmochimica Acta. 68: 500

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1253–1263. 501

––––, 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

Cosmochimica Acta. 63: 1049–1057. 504

Erez, J., and B. Luz. 1983. Experimental paleotemperature equation for planktonic 505

foraminifera. Geochimica and Cosmochimica Acta. 47: 1025–1031. 506

Fujii, T. 1998. Relationship between internal oscillation and movement of anoxic water in a 507

connected brackish water region – Lake Nakaumi and the Ohashi River. Japanese Journal 508

of Limnology. 59: 1–12. 509

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aragonite: temperature effect. Chemical Geology (Isotope Geoscience Section). 59: 511

59–74. 512

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revision of the world’s most commonly misidentified foraminifera. Marine 515

Micropaleontology. 50: 237–271. 516

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synthetic carbonate. Geochimica et Cosmochimica Acta. 61: 3461–3475. 518

Kim, S.-T., J. R. O’Neil, C. Hillare-Marcel, and A. Mucci. 2007. Oxygen isotope 519

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fractionation between synthetic aragonite and water: Influence of temperature and Mg2+ 520

concentration. Geochimica et Cosmochimica Acta. 71: 4704–4715. 521

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and the life history of Trochammina hadai Uchio in Hamana Lake, Japan. In: C. 531

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Biostratigraphy, Paleoceanography and Taxonomy of Agglutinated Foraminifera, pp. 533

695–715Kluwer Academic Publishers, Netherlands,. 534

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divalent water carbonate. The Journal of Chemical Physics, 51:5547–5558. 536

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foraminifera in paleoceanography, p. 735–764 In C. Hillaire-Marcel and A. de Vernal 538

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[eds.], Proxies in Late Cenozoic Paleoceanography. Elsevier. 539

Sampei, Y., M. Matsumoto, D. L. Dettman, T. Tokuoka, and O. Abe. 2005. Paleosalinity in a 540

brackish lake during the Holocene based on stable oxygen and carbon isotopes of shell 541

carbonate in Nakaumi Lagoon, southwestern Japan. Palaeogeography, Palaeoclimatology, 542

Palaeoecology. 224: 352–366. 543

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Research. 4: 217-223. 545

Seto, K., G. Tanaka, and K. Yamaguchi. 1999. Capacity of carbonate shell animals for 546

distribution in Lake Nakaumi, Shimane Prefecture, Southwestern Japan. LAGUNA. 6: 547

247-260 (in Japanese with English Abstract). 548

Takata, H., D., L. Dettman, K. Seto, K. Kurata, J. Hiratsuka, and B.-K. Khim. 2009a. Novel 549

habitat preference of Ammonia “beccarii” forma 1 in macrobenthos community on hard 550

substrates in the Ohashi River, southwest Japan. Journal of Foraminiferal Research. 39: 551

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178: 81-88. 559

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during the Pliocene warm period not supported by coral evidence. Nature, 471:209-211, 562

doi:10.1038/nature09777. 563

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


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




2010/10/1 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



2010/10/13 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


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


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


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


(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


Temperature

Salinity


YearSampling datePeriod

YearSampling datePeriod

Temperature

Salinity


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


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


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


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


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)


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



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)


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


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.)


-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)


Δ δ13CDIC-foram = -5.28 to -5.12‰

Hii River

Matsue Bridge, 1m

Nakaumi Bridge, 1 m Nakaumi Bridge, 1 m

Okidomari


-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

isotope signature of benthic foraminifera on hard

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