Heat flow measurement in shallow seas through long-term temperature monitoring

　　　　　 Hamamoto Hideki (Earthquake Research Institute,Univ. of Tokyo)

　　　 Yamano Makoto (Earthquake Research Institute,Univ. of Tokyo)

　　　 Goto Shusaku (Aso volcanological laboratory, Kyoto Univ.)

Research purpose

To obtain heat flow data in shallow sea areas.

Remove influence of bottom water temperature variation using results of long-term temperature monitoring

dz

dTkQ

Conventional measurement method in deep-sea areas

k　 ： Thermal conductivity

　　　　　　　　

：　 Temperature gradient　　

Q　　： Terrestrial heat flow 　　　

dz

dT

i

ii

iP

tcosAT)t,(T 2

0 0

2

2

z

T

t

T

κ ： Thermal diffusivity

zPP

tz

PAzGTtzT

ii

iiii

2cosexp),( 0

Amplitude decay Phase shift

Thermal diffusion

equation

Propagation of bottom water temperature variation

T（ 0,t）

T(z,t)

20m

　　

Pop-up heat flow instrument

er

recorder

picture

Measurement station

A

D

BC

Kumano area

Eurasian plate

Philippine Sea plate

Pacific

plate

Sub-bottom temperature data

CH1

CH2

CH3

CH4

Station B (water depth: 2055m)

1.70

1.75

1.80

1.85

1.90

1.95

0 50 100 150 200 250 300

CH1CH2CH3CH4

Temperature(

)℃

Time(days)

Heat transfer between CH1 and CH2

CH1

CH2

CH３

CH４-0.15

-0.10

-0.05

0.00

0.05

0.10

0 50 100 150 200 250 300

CH1 observedCH2 observedCH2 calculated

Rel

ativ

e T

empe

ratu

re (

K)

Time (days)

Correction for the effects of bottom water temperature variation

1.70

1.75

1.80

1.85

1.90

1.95

0 50 100 150 200 250 300

CH2CH3CH4

Temperature(

)℃

Time(days)

Temperature gradient

Temperature gradient

= 58 mK/m

Heat flow

c.a 60 mW/m2

Thermal conductivity 1 W/m/K

1.84 1.85 1.86 1.87 1.88 1.89 1.90 1.91 1.92

0.4

0.6

0.8

1.0

1.2

1.4

1.6

Temperature ( )℃

Rel

ativ

e de

pth

(m)

A

D

BC

Kumano area

Eurasian plate

Philippine Sea plate

Pacific

plate

Measurement station

A (water depth 1040m)

Time(days)

After correction

Raw dataT

empe

ratu

re　

（℃

）3.0

3.1

3.2

3.3

3.4

3.5

0 50 100 150 200 250 300

CH2CH3CH4CH5CH6CH7

3.0

3.1

3.2

3.3

3.4

3.5

0 50 100 150 200 250 300

Time(days)

Tem

pera

ture

　（

℃）

C(water depth 2008m)

1.75

1.80

1.85

1.90

1.95

0 50 100 150 200 250 300

CH2CH3CH4CH5CH6

1.75

1.80

1.85

1.90

1.95

0 50 100 150 200 250 300

After correction

Raw data

Time(days)

Tem

pera

ture

　（

℃）

1.901.921.941.961.982.002.022.04

0 50 100 150 200 250 300

D(water depth 2070m)

1.901.921.941.961.982.002.022.04

0 50 100 150 200 250 300

CH6CH4CH3CH1

After correction

Raw data

Heat flow cross section

0

20

40

60

80

100

120

140

160

-40 -20 0 20 40 60 80 100 120

HFPop-up heat flow instrumentBSR

Hea

t flo

w (

mW

/m2 )

Distance from trench axis (km)

Conventional prove

Estimated from BSR

Monitoring of sea-bottom water temperature

1. Estimation of appropriate monitoring period and probe length

2. Determination of heat flow in combination with ordinary probe measurements

Purposes

Measurement stations in Kumano

Sediment temperature

Bottom water temperature

Bottom water temperature

(in progress)

Sediment temperature

(in progress)

Bottom-water temperature records

2001/6 2001/12 2002/6 2002/12 2003/6 2003/12 2004/61.5

2.0

2.5

3.0

3.5

4.0

Date

1979m 1965m

2027m

2055m

2005m

2085m2081m

1795m

2073m

2534m

0.5K

Rel

ativ

e te

mpe

ratu

re (

K)

Temperature record for two years

1.80

1.85

1.90

1.95

2.00

2.05

2.10

2.15

2002/3 2002/7 2002/11 2003/3 2003/7 2003/11 2004/3

Tem

pera

ture (

)℃

Date

Spectrum analysis

0

0.01

0.02

0.03

0.04

0 100 200 300 400 500 600 700 800

振幅

( )時間 日Period 　(days)

Am

plitu

de　

Summary

1. Long-term temperature data over 220 days were obtained with pop-up heat flow instruments.

2. Heat flow values can be obtained by removing the influence of 　　 bottom water temperature variation.

Long-term temperature monitoring may be a useful method 　　 for heat flow determination in shallow sea areas.

Summary

3. Dominant periods of bottom-water temperature variations are 150 　 　　 to 200 days.

Heat flow can be determined well from 250 to 300 days temperature records.

BSR (Bottom Simulating Reflector) BSR

Station A

2.5

3.0

3.5

4.0

0 100 200 300 400 500 600Time(days)

Tem

pera

ture

(℃

)

0.00

0.02

0.04

0.06

0.08

0.10

0 100 200 300 400 500 600

Temperature(

)℃

Time(days)

Station A (water depth1040m) Spectrum

　A

mpl

itud

e

Thermal diffusivity

1 10-7 1.5 10-7 2 10-7 2.5 10-7 3 10-70.0

0.5

1.0

1.5

2.0

thermal diffusivity(mm2/s)

Relative depth(m)

CH1

CH2

CH3

CH4

Thermal conductivity

21.016k+3.67k5.79k

=κ- (Hyndman’s equation)

0.0 0.5 1.0 1.50.0

0.5

1.0

1.5

2.0

Thermal conductivity(W/m/K)

Depth(m)

Thermal conductivity of sediment sample

The sample was obtained near the station B (about 15miles away).

0.4 0.6 0.8 1 1.2 1.4 1.6 1.8 20

100

200

300

400

500

600

700

800

KH01-02-KMP2_QTM

Thermal conductivityDepth from Top(cm)

0

1

2

3

4

5

6

7

8

9

10

1.96 1.965 1.97 1.975 1.98 1.985 1.99 1.995

Disturbance from sea-bottom water temperature variation

Dep

th(m

)0.01K

Temperature

Example of temperature profiles

0.0 0.1 0.2 0.30

1

2

3

4

5

Relative temperature(K)

Relative depth(m)

Deep sea Shallow sea

0.0 0.1 0.2 0.30

1

2

3

4

5

Relative temperature(K)

Relative depth(m)

Temperature

Temperature

Time

Sea-bottom

Sub-bottom

Example of thermal diffusion

Amplitude decays Phase delays

水温変動が海底下の温度分布に与える影響を計算

複数の地点で長期間の海底水温データが得られた

海底水温が温度勾配に与える影響

通常の方法による測定が可能かどうかを検討

1.5m

2.5m

-10

10

30

50

70

90

0 50 100 150 200 250

(mK/m)

温度

勾配

時間（日）

(± 5% )許容範囲 以内

D 地点 ( 水深 1040m)

海底水温が温度勾配に与える影響

　G=50mK/m

κ＝ 2.4×10-7m2/s

2.5m

4.5m

-10

10

30

50

70

90

0 50 100 150 200 250

1.5-2.5m2.5-4.5m

(mK/m)

温度

勾配

時間（日）

(± 5% )許容範囲 以内

B 地点 ( 水深 2026m)

海底水温が温度勾配に与える影響

1.5m

2.5m2.5m

4.5m

　G=50mK/m

κ＝ 2.4×10-7m2/s

* 　 D 地点（水深 1040m ）では，温度勾配は通常の方法では測　　定できない

* 　 A ～ C 地点（水深 1230 ～ 2026m ）でも , プローブが４～５ m の　　深さまで貫入しなければ温度勾配を求めることが困難

長期観測が必要

海底下の温度データから水温変動の影響を取り除いて熱流量を求める

ここまでの結果

（プローブを 4 ～ 5 ｍ貫入させることは難しい場合が多い）

0.0 0.50 1.0 1.5 2.0 2.5 3.0 3.5 4.00.0

0.5

1.0

1.5

2.0

× 10-7(m熱拡散率 2/s)

(m)

相対的

深さ

CH2

CH3

CH4

CH5

CH6

CH7

CH1

1.47

1.75

1.99

2.16

2.23

2.29

Thermal 　 diffusivity 　　（ ×10-7 ）（ m2/ ｓ）

CH1 と各センサー間の熱拡散率

CH2

CH3

CH4

CH5

CH6

CH7

CH1

1.47

2.05

2.42

2.70

2.48

2.99

thermal diffusivity （ ×10-7m2/s ）0.0 0.50 1.0 1.5 2.0 2.5 3.0 3.5 4.0

0.0

0.5

1.0

1.5

2.0

(m熱拡散率 2/s)

(m)

相対的

深さ

× 10-7

隣り合った各センサー間の熱拡散率

-0.10

-0.05

0.00

0.05

0.10

0 5 10 15 20 25 30 35

A 1230 CH1-CH3地点（水深 ｍ）

計算値CH1CH3

温度（℃）

時間（日）

A 地点における計算値と実測値

計算値と実測値が一致しない

0.50 0.75 1.0 1.3 1.5

0.0

0.5

1.0

1.5

2.0

(W/m/K)熱伝導率(m)

相対

的深さ

各センサー間の熱伝導率

(Hyndman の経験式 )

21.016k+3.67k5.79k

=κ-

W/m/K610 - /sm 2

k: 熱伝導率

κ：熱拡散率

1.7

1.8

1.9

2.0

2.1

0 20 40 60 80 100

CH2CH3CH4CH5CH6CH7CH8CH9

Temperature(

)℃

Time(days)

C 地点の海底下の温度データ

1.5 2.0 2.5 3.0 3.5 4.0 4.5

0

1

2

3

4

5

6

7

Temperature( )℃Depth(m)

1K振幅 3× 10熱拡散率 -7ｍ2/ｓ 50mK/m温度勾配

3表面平均温度 ℃

1.5 2.0 2.5 3.0 3.5 4.0 4.5

0

1

2

3

4

5

6

7

Temperature( )℃

Depth(m)

1K振幅 3× 10熱拡散率 -7ｍ2/ｓ 50mK/m温度勾配

3表面平均温度 ℃

日変化 年変化

日変化と年変化の温度プロファイ

Long-term temperature monitoring

Long-term temperature monitoring system has been deployed with submersibles.

＊ Few chances for deployment and recovery .

＊ Submersibles can handle short probes only. (max. 1m)

We have developed Pop-up temperature monitoring system which can be deployed from surface vessels.

Demerits