令和 5 年度

神戸大学大学院海事科学研究科国際交流基金援助金申請書（３ 国際学術交流のための教職員海外派遣事業）
2024 年

神戸大学大学院海事科学研究科長

3月29 日殿申請者氏名林美鶴

所属・職名

海洋基礎科学講座・准教授

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記
渡航者

3．開催地

氏名（所属・職名）林美鶴（海洋基礎科学領域・准教授）
都市名：カーン
1．学会名

国名：フランス

COAST CAEN 2023

2．開催日時 10 月 24～27 日（公式行事 10 月 22～28 日）
渡 国際学術航 講演会等

Distribution of CO2 and N2O concentrations in surface
講演題目

seawater measured in the Seto Inland Sea and Shikoku southern
offing

目
講演者

的4．規模

参加 300 名

林美鶴
8 セッション、120 講演、30 ポスター、6．関わり 講演者
渡航期間2023 年 10 月 20 日～2023 年 10 月 28 日

（9 日間）

5．発表要旨深江丸の瀬戸内海航海において、1990～2004 年に大気・海水中 CO2、N2O 濃度を測定した。両者を同時に測定した 2008 年 3 月、9 月、2009 年 3 月、9 月、2010 年 3 月の 5 航海の結果を比較した。船底（水深 3m）から取水し、CO2 濃度は 15 分ごと、N2O 濃度は 1 時間ごとに、バブリング法により測定した。3 月の CO2 濃度は 3 年間ほぼ同じであった。9 月の CO2 濃度は 2 年の濃度レベルが異なるが、空間変動の傾向は一致していた。3 月の N2O 濃度は、海水密度が高い年ほど高くなる傾向があったが、9 月には有意な傾向は見られなかった。CO2 および N2O 濃度と塩分、水温、溶存酸素濃度との相関は、CO2 については各年で異なる傾向を示し、CO2 濃度に生化学的な影響が大きいことが示唆された。N2O の相関は各年で類似の分布形状を示し、年によって全体がシフトした。このことは、N2O 濃度に対する物理的影響が大きいことを示唆している。

発表論文の写し：Springer Nature から書籍として出版する講演論文集の編纂中のため、プレゼンテーションファイルを添付する。

Distribution of CO2 and N2O concentrations
in surface seawater measured in the Seto Inland Sea
and Shikoku southern offing
HAYASHI Mitsuru (Kobe Univ.) & YAMASHITA Eiji (Okayama Univ.)
Objective# To crafty the distribution ofCO2 & N2O concentrationsin the seawaterin the Seto Inland Sea& around area.
# To understand the factors
contributing tospatial distribution of N2O.

BisanHiroshima

KanmonConcentration Life Time Radiative Forcing GWP(ppb)(year)(W/m²/ppb)(100 year)
379,000
51
CO2
1.4×10-5
319
114
310
N2 O
3.0×10-3
Gas

Bingo
HiuchiAki
Kurushima

Additionally,
N2O was measured on two cruises.

Track chart

June 2010
Aug. 2010

Observations were Height of inlet
conductedof5 theaironis 12m.
The in-situ on
data obtained incruses
T/S# March
Fukae
maru
and
September in 2009

Kitan
NarutoKii
Channel# March,June and August in 2010
(KobeUniversity)
Length: 49.95 m
Gross tonnage: 449 tonNavigation speed : 12.5 knot

SuoIyoHoyo

Bungo
Channel# Almost 3,000 islands are located,and it is formed by a chain ofmajor 9 bays and 7 straits.

Both CO2 & N2O
were measured
on these five cruises.

Laboratory

Seawater was pumped
from a depth of 3m.

Pacific Ocean# It connects to the Pacific Ocean through the Bungo and Kii Channels.

Spatial Variation

Equilibration
CylinderDryer

PC
Carrier Gas Mixer

N2O Analyzer

Filter

WaterPump

Flow meter# Water temperature# Salinity# Dissolved Oxygen# pH# Meteorology

AirPump

Difference between carrier gas
and exchanged gas (ppb)

Measuring system
Measurement System of N2O(IPCC)# The ocean is a large N2O source to the atmosphereaccounting for 10–33% of the global source (Jiang et al., 2007),and coastal sea account for 35–60% of that (Bange et al., 1998).
# We measured seawater and atmospheric concentrations ofCO2 from 1994-2010 and N2O from 2008-2010.

The Seto Inland Sea# The length from east to west is 450km, # The Yodo Riverand from south to north varies
has a wide basin area
Kyoto
from 15 to 55km. and flows into Osaka Bay# The water depth is shallow in most places,
through major cities. YodoRiv.
Akashithe average depth is 38 m
Osaka Osakaand the greatest depth is 105m.
HarimaHibikiBackground# CO2 & N2O (Nitrous Oxide) are the greenhouse effect gas.
# N2O has low concentration in the atmosphere of 1/1000 of CO2,
however a life time of over 100 years.

N2O

CO2
Calibration lineMar.

Concentration in seawater
Concentration of carrier gas (ppb)# The bubbling method was used for gas exchange.
# The gas concentration was measured
using the principle of infrared absorption.
# The concentration in the seawater
was quantified by calibration line.
# CO2 was also measured by the same method.

CO2: Yamashita et. al.(1993), N2O: Sakamoto et.al. (2013)

LowSep.

◇ △ ‘08□ ○ ‘09×‘10

CO2# in Mar.
Nearly consistentfor three years# in Sep.
Concentration levels varyfrom year to year,
howeverHigh
trends in spatial variability
are generally consistent.
N2 O# Characteristics ofspatial variability are unclear,
except for Osaka Bay,

Spatial Variation
N2O

CO2Mar.

Correlation between N2O and T, S, DO
The correlations show
similar trends in both seasons.
It's just a shift,
no seasonal differences.

OpenOcean

T-S diagram
The plots arelinearly distributed
between two watermasses
Estuary

N2 O - TLow

StraitHigh

N2O is produced # AOU(Apparent Oxygen Utilization)by nitrification.
= O2 saturation- observed DO > 0means O2 consumption# ΔN2O= observed N2O
ΔN2O-AOU- N2O solubility > 0distributionmeans N2O production

River waterSep.

The source of N2O
to the sea surface
N2 O - S◇ △ ‘08□ ○ ‘09

Bottomwater

N2O - DON2O-S correlation× factors‘10
The contributing
to spatial distribution of each region
were investigated on each cruises.

（T.Yoshinari,1976, Walter, 2006）

Akashi Striate ~ Osaka Bay in June 2010
# N2O was highest
linearOsaka Bayin the inner partof Osaka Bayand decreased
toward the west.
AkashiT-S diagram
Striate# Plots of T-S
was linearly distributed
in Osaka Bay.
N2O-S correlation# In the inner part
Salinity is lower& N2O is higher
compare to the west.
# Slightly higher N2O
N2O would have been& Higher S, lower T
supplied at the inner partin Akashi Strait
and spread to the west,compared to Osaka Bay.
and from the bottom layer in Akashi Strait.

N2O concentration in Yodo River Estuary# N2O in the surface water,
was highest at the river mouth.
Based on the nitrogen budget,
Muko Riv.
it was presumed
Kanzaki Riv.
to be produced by nitrification.
# High concentrations
also appear in the bottom layer,
E D
which would be
Depth: 2mSewage
denitrification in the sediment.
Disposal
F:6

In the surface water

Spatial distributions of N2O

Observed in June and July in 2004
Kobe University

RokkoIsland4Km

Depth (m) C:16

B:14

CB

Harima-nada

The source of N2O
at the inner part of Osaka Bay
not only river water,
but also nitrificationand denitrification in the estuary.

A

Depth – Time Distribution

Bisan-seto in June 2010
Spatial distributions of N2O

ΔN2O-AOU distribution

linearPlant

A:12

Harima-nada ~ Akashi Striate in June 2010
Spatial distributions of N2O

Method of investigation# In the T-S diagram
the seawater is exchange horizontally
between the water masses.
# The N2O-S correlation was used to determine
fluvial effects (low S & High N2O)
and vertical mixing (High S & High N2O).

Almost linear in W

HighestNitrification

ΔN2O-AOU distribution

Nitrification

HarimaEW

Akashi
StriateDecreased
toward the both side.

T-S diagram
N2O-S correlation

N2O would have been supplied
from the bottom layerin Akashi Strait
and spread to Harima-nada,
and produced by nitrification in Harima-nada.

# N2O decreased
toward Harimafrom Akashi.
# Plots of T-S was linearly.
# Slightly higher N2O & S
in Akashi Strait.
# Nitrification
was occurring.

T-S diagramof Bisan

N2O-S correlation

備讃瀬戸
広島湾
安芸灘

燧灘

播磨灘

大阪湾

紀伊水道

周防灘
伊予灘
豊後水道

Major river

N2O would have been
supplied from the rivers,
andproduced by nitrification
mainly in the central partof Bisan-seto.

Summary of June 2010 River W. & The source of N2O would be# River water
Production
to Osaka Bay & Bisan-seto# Nitrification & Denitrification
River W. &in the estuary
Nitrificationof the inner part of Osaka Bay# Nitrificationin Bisan-seto & Harima-nada# Bottom waterin Akashi & Kurushima Striate
Then, N2O spread from these sources
Kurushima
AkashiAki
Bingo BisanHarima
Osakaby horizontal mixing.
These are schematically drawn
Vertical Mixing
N

March 2008

Summary of the contributing factors

September 2008

No production
by nitrification.
March 2009

March 2010

Results ofeach
observation

NN

There is production
Nby nitrification.
The influenceof factors
September 2009NN
other thanNNseawaterexchangeon the spatialDistribution
August 2010
in Sept.
Nwill be greaterthan in March.

Bottom W.

N

1

Sep. N
2008

Unclear Horizontal exchange
Small variation

Summary of the contributing factors
123 45 67 8

9 10 11 12 13Mar.
2008
Sep. N2008

NNMar.
2009
Sep.
2009

NN

N

NMar.
2010
N N

June
2010
Aug.
2010

Vertical Mixing
Horizontal exchange
Unclear Horizontal exchange

N45 632

N:
Nitrification
Smallvariation

79 108 111213

1# N2O supply
from the bottom layer
was not observed in Bisan Seto,a vertically mixed area.
# In the central par of the sea,
N2O were producedby nitrification in summer,
however, not enoughto be a source to the around area,
and it is difficult to explain
the spatial distribution byhorizontal seawater exchange.

3 4

N:Nitrification
Concentration gradient5678Sep.
2009

NN

NMar.
2010
N NJune2010
Vertical Mixing
Horizontal exchange
Unclear Horizontal exchange

NHorizontal exchange
Unclear Horizontal exchange
Small variation

9 10 11 12 13

45 6
3
2

NN

Mar.
2009

Aug.
2010

Vertical Mixing

2NMar.
2008

N:Nitrification
Horizontal exchange

Bottom W.

Aki-nada ~ Kurushima Striate ~ Hiuchi&Bingo-nada in June 2010
# N2O was almost constantAdjacent toin Bingo&Hiuchi-nada
Kurushima& high in Aki-nada
Bingo
Striateadjacent&Hiuchia
to Kurushima Striate.
-nada# Plots of T-S was linearly.
T-S diagram Aki-nada# The salinity in Aki-nada
was lower
N2O-S correlationin the adjacent area
to Kurushima Strait.
N2O may have been
suppliedfrom the bottom layer
in the Kurushima Strait& spreadto the Aki-nada side.
Spatial distributions of N2O

79 108 111213

1# The main regions of N2O source
were the straits
and the inner part of Osaka BayNin all observations.
# The contributionof horizontal seawater exchange
to the spatial distributionof N2O
is large form Kurushima
N:and Akashi Strait
Nitrification
to the open ocean.
Smallvariation

Conclusion
CO2 and N2O concentrations in surface seawater
were measured in the Seto Inland Sea and Shikoku southern offing.
# It was characteristic both CO2 and N2O concentrations in Osaka Bay.
# The main regions of N2O source were the inner part of Osaka Bay & the straits.
# The contribution of horizontal seawater exchange to the spatial distribution ofN2O is large expect the central par of the Seto Inland Sea.
To quantify & clarify the spatial distribution & it’s variation of concentrationof N2O in seawater in the Seto Inland Sea,
it is necessary to correctly estimate
the horizontal and vertical advection of seawater.