北海道地質研究報告書第86号

Size: px

Start display at page:

Download "北海道地質研究報告書第86号"

よいかずふじした
7 years ago
Views:

1 Hydrographic Conditions in the Pacific Ocean off the Southern Hokkaido observed by a ferryboat Kazuo Kido, Masato Osawa and Naoyuki Higaki Abstract For the better understanding about the oceanographic condition around Hokkaido and contribution to Maritime weather forecasting in the future which means numerical prediction of the oceanographic condition, we developed a monitoring system of temperature, salinity and fluorescence intensity attached to the cooling pipe system of the ferryboat SUISEN of Shin Nihonkai Ferry Corporation. Using this system, we conducted, from 2003 through 2012, a continual and daily observation on temperature, salinity and fluorescence intensity of the surface layer along the course of the ferryboat from Tomakomai on the Pacific coast of Hokkaido to Tsuruga on the Japan Sea coast of Honshu. In this report, we described year to year changes of the oceanographic conditions along a part of the course off the southern Hokkaido, accompaniedwiththeseasonalalternationofthreewatermasseswitheachother.afterthepaststudiesontheoceanographic conditions in Funka Bay and its adjacent waters including our study area, the three water masses concerned are ; Coastal Oyashio Water which is Oyashio Water transformed by ice melted water in Okhotsk Sea, and Oyashio Upper Water, from late winter through summer ; Tsugaru Warm Water originated from Kuroshio, from mid summer through winter. Furthermore we showed some newly observed phenomena as follows. 1 Although these waters appear in the waters in turns basically, Tsugaru Warm Water appears unexpectedly in a season of the other water mass in some years. 2 From the late in spring through summer, these water masses and those diluted by riverine water appear simultaneously in confused patchy shape, especially in salinity distribution. We call this term of confusion state as confusion term. 3 In the summers of 2009 and 2010, waters of salinity lower than 32 expanded long and widely. These waters were Coastal Oyashio Water diluted in the waters off the eastern Hokkaido, the upper stream of Coastal Oyashio. 4 Tsugaru Warm Water did not appear in the winter of , different from the other winters. 5 Fluorescence intensity as an index of chlorophyll concentration increases in March and/or April for the phytoplankton bloom. The bloom happens sharp and clearly in years when Coastal Oyashio Water is predominant, and gently and unclearly when Oyashio Upper Water is predominant and Tsugaru Warm Water intrudes unexpectedly in the season of cold water masses. The results stated above are based on the data of the surface layer observed with our monitoring system, and so, verifications by the data of vertical sections obtained by research vessels should be carried out. Key words : Maritime meteorological observatory, ferryboat, monitoring, hydrography of the Pacific Ocean off the southern Hokkaido, temperature, salinity, fluorescence intensity, Tsugaru Warm Water, Oyashio

system of temperature, salinity and fluorescence intensity attached to the cooling pipe system of the ferryboat SUISEN of Shin Nihonkai Ferry Corporation.

2 km JCOPE Japan Coastal Ocean Prediction ExperimentJCOPE2 http : // jp/frcgc/jcope FRA ROMS http : //fm.dc.affrc.go.jp/fra roms /index.html

JCOPE Japan Coastal Ocean Prediction ExperimentJCOPE2 http : //www.

3 , ms d e f d e f ab c JFE ACL μg /L Compact CT km km

4 Fig. 1 a bc The monitoring system attached to a pipe of cooling system of the ferryboat SUISEN of the Shin Nihonkai Ferry Company. Left a : fluorometer, b : conductivity and temperature sensors, c : connecting flange, those are operated at every ten minutes. Right Arrangement of the system, d, e and f : the valves controlling the sea water flow. The positions of observation are recorded by a GPS settled in the bridge of the ferryboat. Fig. 2 AB A A : The current system around Japan, and the cruising course of the ferryboat SUISEN. B : The observation lines referred to in this report bold lines and the main rivers flowing into the Pacific Ocean off Hokkaido. A line is that operated by the Fisheries Research Agency. GPS Wintec GPS WBT GPS 10 http : //kaiho.mlit.go.jp/kan1/kaisyou/sokuho.htm A

Right Arrangement of the system, d, e and f : the valves controlling the sea water flow. The positions of observation are recorded by a GPS settled in the bridge of the ferryboat. Fig.

5 XBT A :XBT B C XBT 0 m 1 m Fig. 3 A Vertical temperature profile measured by a XBT, B and C Relationships between the temperature measured by the monitoring system and those by XBT at 0 m, and at 1 m respectively. Although the relationship at 0 m is not so good relative to that at 1 m because of time shortage for equilibrating with water temperature, we conclude that the monitoring system measures well the temperature in surface layer. http : //tnfri.fra.affrc.go.jp/seika/a line/a line_index.html http : //rose.hucc.hokudai.ac.jp/~a20011/salino_top.html NOAA http : //odyssey.fish.hokudai.ac.jp/avhrr/ http : // Voluntary Observation Ship : VOS Expendable Bathythermograph : XBT 3A XBT 2030 m 0 m B 1m C 0 m XBT XBT T S

Although the relationship at 0 m is not so good relative to that at 1 m because of time shortage for equilibrating with water temperature, we conclude that the monitoring system measures well the

6 Fig. 4 T S The characteristics of the water masses concerned with our study on the Temperature Salinity diagram, after Ohtani 1971 in modified form

0 1972 8 18 33.0 10 33.0 33.5 11 33.5 1971 5 8 1 2004 20045 1 4 33.0 33.5 2 33.0 5 20055 3 433.

7 Fig. 5 Time cross sections of temperature upper and salinity lower for each year along the ferry course for Notice is taken of the seasonal change of water mass revealed especially in salinity distribution ; Oyashio Upper Water of , or Oyashio Coastal Water lower than 33.0 from the late in winter through spring, and Tsugaru Warm Water higher than 33.5 from mid summer through winter. From the late in spring through summer, these waters and diluted ones exist simultaneously in confused patchy shape, and we call the term of this confused state as confusion term.

5, or Oyashio Coastal Water lower than 33.0 from the late in winter through spring, and Tsugaru Warm Water higher than 33.

8 Fig Same as Fig. 5 except for The water of salinity in January and February 2007 is considered to be not Oyashio Upper Water, but a little diluted Tsugaru Warm Water differing from the other years, in consequence of referring the temperature distributions shown in Fig. 9.

5 in January and February 2007 is considered to be not Oyashio Upper Water,

9 Fig Same as Fig. 5 except for The waters of salinity lower than 32.0, spreading long and widely in the summers of 2009 and 2010, are Coastal Oyashio Water diluted by the riverine water mainly from Tokachigawa as described in Fig. 13. It flows into the waters off the eastern Hokkaido, the upper stream of Coastal Oyashio, and its surface layer shallower than 30 m is stratified strongly as shown in Fig. 14. The diluted water flows along the coast of the eastern Hokkaido and, as shown in Fig. 12, it spread off the coast to the west of Cape Erimo. Tsugaru Warm Water appears merely in a short term from late November to early December 2009, and does not appear regularly in the winter of

It flows into the waters off the eastern Hokkaido, the upper stream of Coastal Oyashio, and its surface layer shallower than 30 m is stratified strongly as shown in Fig. 14.

10 Fig Same as Fig.5 except for Tsugaru Warm Water intrudes into the predominant Coastal Oyashio Water unexpectedly in April, shown by the salinity higher than NOAA 30 km Fig Sea surface temperature around Hokkaido from Dec through Mar modified from the Quick Bulletin of Ocean Conditions of Hydrographic and Oceanographic Department, 1 st Regional Coast Guard Headquarters. The 5 C isotherms are emphasized for convenience as a border between the cold water masses Coastal Oyashio Water and Oyashio Upper Water and the warm water masses Tsugaru Warm Water and the warm water cut off from Kuroshio. The warm water along the coasts of the southern Hokkaido and Honshu is Tsugaru Warm Water. From January through February, Tsugaru Warm Water occupies the waters off the southern coast of Hokkaido, and Coastal Oyashio Water reveals in March, 1 2 months later than the other years.

2007 modified from the Quick Bulletin of Ocean Conditions of Hydrographic and Oceanographic Department, 1 st Regional Coast Guard Headquarters.

11 NOAA 1011 μg/l μg/l μg/l

12 Fig Time cross sections of fluorescence intensity calibrated with sodium fluorescein concentration in the unit of μg/l, along the ferry course for The lines at the bottom of figure for each year indicate the predominant water mass and the confusion term. The spring phytoplankton bloom happens sharp and clearly in years when Coastal Oyashio Water is predominant, and gently and unclearly when Oyashio Upper Water is predominant and Tsugaru Warm Water intrudes unexpectedly in the season of cold water masses.

The lines at the bottom of figure for each year indicate the predominant water mass and the confusion term.

13 Fig. 11 Same as Fig.10, except for

14 Fig Monthly discharges of the main rivers shown in Figure 2 from June through August in Water Information System, Ministry of Land, Infrastructure and Transport, Japan. Large discharges of Tokachigawa in 2009 and 2010 are thought to contribute to the formation of the salinity lower than 32.0 revealed in Fig. 7. Fig. 12 Salinity profiles around Hokkaido in June July and September 2009, observed by T/S Ushio maru, Hokkaido University. The profile in September shows that the waters of low salinity spreads off the coast to the west of Cape Erimo A m A Fig. 14 Vertical sections of temperature and salinity in July of 2009 and 2010, along the A line observed by Fisheries Research Agency. In both years, waters shallower than 50 m are strongly stratified at this section, the upper stream of Coastal Oyashio. The low salinity waters shown in Fig. 7 are thought to have spread in these surface waters

7. Fig. 12 Salinity profiles around Hokkaido in June July and September 2009, observed by T/S Ushio maru, Hokkaido University.

15 Fig Sea surface temperature around Hokkaido from June through December 2009 modified from the Quick Bulletin of Ocean Conditions, Hydrographic and Oceanographic Department, 1st Regional Coast Guard Headquarters. As same as in Fig. 9, some isotherms are emphasized for convenience as the border between Coastal Oyashio Water and the warm water masses, Tsugaru Warm Water and warm water mass cut off from Kuroshio. In all months, Tsugaru Warm Water flows along Honshu and does not enter the waters off the southern Hokkaido Conlon, 1982 Conlon,

9, some isotherms are emphasized for convenience as the border between Coastal Oyashio Water and the warm water masses, Tsugaru Warm Water and

16 p p p p p p p XBT Conlon, D. M : On the Outflow Modes of the Tsugaru Warm Current. La mer, 20,

1996 6 471p 1968 612p. 2001 29 2 3. 2004 93. XBT Conlon, D. M.

LAGUNA LAGUNA 8 p Saline wedge at River Gonokawa, Shimane Pref., Japan Saline water intrusion at estuary r

LAGUNA LAGUNA 8 p Saline wedge at River Gonokawa, Shimane Pref., Japan Saline water intrusion at estuary r LAGUNA8 67 78 2001 3 LAGUNA 8 p.67 78 2001 1 1 2 3 4 5 6 7 8 Saline wedge at River Gonokawa, Shimane Pref., Japan Saline water intrusion at estuary river and its relation to the underground water Observation