SC/J09/JR34

Oceanographic conditions of the western north Pacificbased on oceanographic data during the JARPN II
Makoto Okazaki*, Denzo Inagake*, Masachika Masujima*, Hiroto Murase**,Hikaru Watanabe***, Shiroh Yonezaki**, Hiroshi Nagashima****, Koji Matsuoka**,
Hiroshi Kiwada** and Shigeyuki Kawahara****National Research Institute of Fisheries Science, 2-12-4 Fukuura, Kanazawa,

Yokohama, Kanagawa, 236-8648, Japan**The Institute of Cetacean Research, 4-5, Toyomi-cho, Chuo, Tokyo, 104-0055,
Japan***National Research Institute of Far Seas Fisheries, 5-7-1, Orido, Shimizu, Shizuoka,Shizuoka, 424-8633, Japan****Miyagi Prefecture Fisheries Technology Institute, 97-6 Sodenohama, Watanoha,Ishinomaki, Miyagi 986-2135, Japan
Contact e-mail: ina@affrc.go.jp
ABSTRACT
Oceanographic conditions in the offshore and the coastal components of JARPN II (offKushiro) were examined using output from an operational ocean prediction system(FRA-JCOPE). Oceanographic observations with CTD and XCTD were conducted in thecetacean prey surveys in JARPN II. These observations were incorporated into theprediction system. The survey covered from subarctic area to the adjacent area of thesubtropical area where common minke, Bryde’s and sei whales were found. The survey
area was located between the Kuroshio Extension and the Subarctic Front, where thewater mass was characterized by the subarctic water, subtropical water and mixed water.

INTRODUCTION
Full scale JARPN II has been conducted since 2002.

JARPN II has three components(three regional survey areas) namely off Sanriku, off Kushiro and offshore. Cetacean
prey species surveys were conducted in JARPN II.

Oceanographic observations havebeen conducted in the prey surveys. Data were collected by using CTD(Conductivity-Temperature-Depth profiler) and XCTD (expendable CTD) in JARPN II.
The purpose of the oceanographic observations is to obtain fundamental information ofthe ecosystem in the JARPAN II area.
There are a lot of water masses and fronts in the western North Pacific. TheOyashio flows southwestward along the Kuril Islands and turns eastward from the1northern coast of Japan.

The Kuroshio flows northward from the tropical area toTohoku area east of Japan.

The Kuroshio turns eastward from the eastern coast ofHonshu, Japan, and the strong eastward flow is called the Kuroshio Extension.

Bothmajor currents, the Kuroshio Extension and the Oyashio, form Kuroshio-Oyashio
Inter-frontal Zone.

Waters originated in the Kuroshio and the Oyashio are mixed eachother in this zone.

They interact with the atmosphere and form new water masses.

In the high sea of the North Pacific Ocean, there are Subarctic Front and theSubarctic Boundary with a weak eastward flow.

The Subarctic Front is south limit of

the subarctic water and the Subarctic Boundary is north limit of the tropical water.
The area between these fronts is called the Transition Domain (Favorite et al. 1976).
Each oceanic area in the western North Pacific, like Kuroshio, Oyashio, warm-core
ring, etc, has unique oceanic environment and ecosystem.

Because distribution ofcetaceans as well as their preys is associated with the oceanographic conditions,realization of the oceanographic conditions is important.

In this paper, distributions ofwater masses and fronts in the survey area (offshore and off Kushiro) were described tomake clear the environment.

Though oceanographic observations were also conducted

off Sanriku, they were not considered in this paper.
MATERIALS AND METHODS
Hydrographic observations were carried out in the JARPN II area from 2002 to 2007 on
board R/Vs Shunyo-Maru, Kaiko-Maru, Kyoushin-Maru No. 2, and Kaiyou-Maru
No. 7 (Table 1).

Oceanographic data were collected by either CTD (SBE 19, SBE 19plus

or SBE 911plus) or XCTD profiles.

Figure 1 showed station maps in the survey area.

In the offshore component, CTD and XCTD casts were conducted at 160 and 16 stations,respectively.
stations.

In the coastal component off Kushiro, CTD casts were conducted at 156

Note that salinity correction using water sampling data was still not donewith the CTD data reported in this paper.
The output from FRA-JCOPE (Fisheries Research Agency - Japan Coastal Ocean
Predictability Experiment) were used to analyze the oceanographic conditions in
JARPN II area from 2002 to 2006.
system.

FRA-JCOPE is an operational ocean forecast

The observation data collected during JARPN II as well as GTSPP (GlobalTemperature and Salinity Profile Program) data were incorporated into FRA-JCOPE.
Indices for the oceanic fronts are used here to classify the water masses in the survey
area (Table 2).

Since the sea surface temperature distributions are obscure in this area,

the indices are usually defined by subsurface temperature.

The Kuroshio Extension isdefined by the 14℃ isotherm at the depth of 200m (Kawai, 1969).

The warm water

spread from Kuroshio Extension is defied by temperature more than 10℃ at the depthof 100 m .

The first and the second Oyashio Intrusions are defined by temperature lassthan 5℃ at the depth of 100 m (Murakami, 1994).

Subarctic front and the Subarctic

Boundary is defined by 4℃ temperature contour at the depth of 100 m and sea surface2

34.0psu salinity contour, respectively (Favorite et al. 1976).

We use these indices todepict the distribution of water mass in the survey area.
RESULTS AND DISCUSSION
Oceanographic conditions in the offshore survey region
The offshore region around 164º-166ºE, 156º-159ºE and 145º-151ºE was observed byusing CTD and XCTD in 2002-2005 and 2007 (upper panel of Fig. 1).
Figure 2 shows the meridional temperature, salinity and density sections along 165ºE
in August 15 by using FRA-JCOPE output.

Two major front systems are found in thesubarctic gyre region of the North Pacific. The northern one is called the subarctic
front as indicated by a drop of 4ºC contour in the temperature section (Favorite et al.,1976).

The front shows the southern boundary of the region characterized by thenear-surface temperature minimum and the strong halocline. The southern one is called
the subarctic boundary that marks the southern boundary of the subarctic low saline
surface water. The subarctic boundary is indicated by a drop of 34.0 psu contour to300m in the salinity section (Favorite et al., 1976).

The subarctic front occurred near

46ºN in 2003 and 2004, near 48ºN in 2004, 2005 and 2006.

The subsurface

temperature minimum layer is clearly formed in the area north of the subarctic front.
The temperature below 3ºC was detected. The subarctic boundary clearly occurred near
41ºN.
Figure 3 shows the meridional temperature, salinity and density sections along 157ºEin August 15.

The subarctic front occurred near 42 ºN in 2006, 43 ºN in 2003, 2004,2005, 44ºN in 2002.

The subarctic boundary occurred near 40ºN in all of 2002- 2006.

Figure 4 shows the horizontal temperature distributions at 100m overlapping over14ºC region at 200m to detect the Kuroshio region (striped area in Fig. 4).

Northernside of the 5ºC contour line in the 100m temperature indicates the subarctic water(gray-shaded area in Fig. 4).

These figure shows that observation was carried out fromthe subarctic region to the Kuroshio region.
Oceanographic conditions in the survey area southeast of HokkaidoThe area south of Hokkaido was observed by using CTD in 2002 and 2004-2007 (lowerpanel of Fig. 1).
Figure 5 shows meridional temperature, salinity and density sections along 144º12’E.
The temperature minimum layers below 2ºC, which is original Oyashio water, wasobserved southeast of Hokkaido every year.

Surface salinity at Hokkaido coastal

region was below 32 psu in 2002, 2003 and 2006.
Figure 6 shows temperature distributions at 100m and surface current in September
15 from 2002 to 2006.

Warm water mass from the Tsugaru warm current occupied thearea west of 143ºE.

In the area east of 143ºE, the cold and low-saline Oyashio water

were occupied.

Fig. 6 shows that almost all of the observation points were in the3Oyashio area.
143º20’E.

In 2006, warm water mass from the Tsugaru warm current enlarged to

The warm water ring was observed in 2005 southeastern part of theobservation area.

The southern limit of the first Oyashio Intrusion generally moves

northward from April (38º30’N) to November (41º30’N).

The position of the firstOyashio Intrusion was at 40º10’N, 143º20’E and second Oyashio Intrusion was at 39ºN,
146 º E in September 2002.

It shows first Oyashio Intrusion was normal position but

second Oyashio Intrusion spread southward stronger than first Oyashio Intrusion.

In

2003, second Oyashio Intrusion was not clear but its position was 40ºN, 145ºE, and firstOyashio Intrusion spread strongly to the position of 39º20’N, 142º20’E, nearby thecoastal area off Tohoku.

In 2004, the Oyashio area was restricted in narrow two bands,and southern limit of first and second Oyashio Intrusion were at 41ºN, 142º40’E and40º20’N, 146ºE, respectively.

The Oyashio water widely distributed in 2005, but

southern limit of first and second Oyashio Intrusion did not show distinctive southernposition.

In 2006, the Oyashio water was spread through narrow area similar with

2004, however the first Oyashio Intrusion spread to southern area south of 39 ºN.
Year-to-year variation was dominant in the first Oyashio Intrusion during JARPN II
observation periods.

References
Favorite, F., A. J. Dodimead and K. Nasu (1976): Oceanography of the subarctic Pacificregion, 1960-71. Bull. International North Pacific Fisheries Commission, 33, 187
pp.
Kawai, H. (1969):

Statistical estimation of isotherms indicative of the Kuroshio axis,Deep-Sea Res., Suppl. to 16, 109-115.
Murakami, M. (1994): On long-term variations in hydrographic conditions in theTohoku area, Bull. Tohoku Natl. Fish. Res. Inst., No. 56, 47-56 (in Japanese withEnglish abstract).

4

SC/J09/JR34

Table 1.

Detail of observation data in JARPAN II area from 2001 to 2007.

VesselObservation periods

AreaShunyo -Maru

17 July – 9 Aug., 2002Offshore

Shunyo -Maru

15 June – 9 July, 2003

Offshore

Shunyo -Maru

15 - 19 Sep., 2004

Offshore

Shunyo -Maru

13 – 23 July, 2005

Offshore

Shunyo -Maru

30 July – 8 Aug., 2005

Offshore

Kaiko -Maru

24 Aug. – 4 Sep., 2007

Offshore

Kyoushin -Maru # 2

10 – 24 Sep., 2002

Off Kushiro

Shunyo -Maru

23 – 29 Sep., 2004

Off Kushiro

Kaiyou –Maru #7

11 – 25 Sep., 2005

Off Kushiro

Kaiko -Maru

12 – 26 Sep., 2006

Off Kushiro

Kaiko -Maru

9 Sep. – 6 Oct., 2007

Off Kushiro

Table 2.

Extraction method from temperature map to determine the position of eachwater mass.
Target characteristics

Extraction method

Kuroshio Extension Axis

14℃ isotherm at 200 m

Warm-core ringTemperature front at 200 m

Oyashio front

5 ℃ isotherm at 100 m

Oyashio water

Area with T<5 ℃ at 100 m

Cold water
Warm water
Subarctic Boundary

Area with 5℃<T<10 ℃ at 100 m
Area with T>10 ℃ at 100 m and T<14 ℃ at 200 m
Salinity front defined by 34.0 psu

Subarctic Front

Temperature front defined by 4℃5SC/J09/JR34

Fig. 1Station maps observed in the JARPN II area (offshore (upper panel) and off Kushiro (bottompanel)) from 2002 to 2007.

6

SC/J09/JR34

Fig. 2. Vertical sections of temperature (upper panel), salinity (middle panel) and density (lowerpanel) along 165ºE on August 15 from 2002 to 2006.

7

Fig. 3. Vertical sections of temperature (upper panel), salinity (middle panel) and density (lowerpanel) along 157ºE on August 15 from 2002 to 2006. .

8

Fig. 4. 100 m temperature maps in offshore area, on August 15 in 2002 (upper panel) and 2003 (lowerpanel) with positions of observation stations in JARPN II (white circle).

Northern dark area isOyashio region, white area is Cold region, dotted area is warm area, and vertically striped area
is Kuroshio region. Arrows denote the velocity vector at the sea surface.

9Fig. 4. (cont.) 2004 (upper panel) and 2005 (lower panel).

10Fig. 4. (cont.) 2006.

11

Fig. 5. Vertical sections of temperature (upper panel), salinity (middle panel) and density (lowerpanel) along 144º12’E on September 15 from 2002 to 2006.

12

Fig. 6. 100 m temperature maps in the survey area southeast of Hokkaido, on September 15 from2002 to 2006. White circles in the maps denote observation stations in JARPN II. Northerndark area is Oyashio region, white area is Cold region, and vertically striped area is theTsugaru warm current region.

Arrows denote the velocity vector at the sea surface.

13