SC/D06/J30

Results of oceanographic analyses conducted under JARPA andpossible evidence of environmental changes.
Tomowo Watanabe*, Takashi Yabuki**, Toshio Suga**, Kimio Hanawa**,Koji Matsuoka*** and Hiroshi Kiwada****National Research Institute of Far Seas Fisheries** Tohoku University*** Institute of Cetacean Research

ABSTRACT
Oceanographic observation data obtained by JARPA were analyzed to clarify physicaloceanographic conditions in the JARPA area as a basis for understanding of habitat environment ofwhales.

Accumulated XBT, XCTD and CTD data were stored in the HydroBase format andutilized to describe the oceanographic feature of JARPA area.

The Southern Boundary (SB) of theAntarctic Circumpolar Current was clearly observed as a 0ºC temperature contour line on the 27.6σθ
isopycnal surface.

It is evident that the position of SB is controlled by major features of bottom

topography such as the Kerguelen Plateau the Pacific-Antarctic ridge.

The analyses presented

several evidences for year-to-year variations in oceanographic conditions, including large
year-to-year meridional shift of the SB found east of the Kerguelen plateau. Although the global
warming is important forcing for the Southern Ocean, the influence is not clear in the JARPA region
unlike the Antarctic Peninsula region. Comparison between the JARPA data and satellite-derived
Chlorophyll distribution indicates that the intensity of the wintertime cooling determines the primary
productivity south of SB in the following seasons.

JARPA data also provided a new evidence ofAntarctic Bottom Water formation in the Prydz Bay region.

INTRODUCTION
Oceanographic observation has been included in JARPA and many data were corrected from JARPA
area (Pacific and Indian sector of the Southern Ocean, poleward of 60S) for 18 years period
87/88-04/05.

The purpose of the oceanographic observations is to obtain fundamental informationof the ecosystem in the JARPA area and to investigate the relationship between the oceanographic
conditions and whales.
The repeat observation conducted in the JARPA is also important from the oceanographical view
point as the southern ocean plays key roles in the global thermohaline circulation. The North
Atlantic Deep Water (NADW) formed in the northern North Atlantic flows into the Southern Ocean
and lifted up to subsurface depth.

The Antarctic Bottom Water (AABW) which occupies thebottom layer of the world ocean is formed in the coastal area of the Antarctic continent by mixing-1-cold and dense shelf water with the NADW (Schmitz, 1996).
The Antarctic Circumpolar Currents (ACC) is major feature of the Southern Ocean and the spatial
water mass distribution of the area is characterized by the zonal structure reach to the deeper layer.
The oceanographic conditions of the JARPA area are also under the strong influence of the ACC.
The Southern Boundary (SB) of the ACC is thought to be most important oceanographic componentof the JARPA area. The upwelling of the NADW around the SB is enriching the nutrient in the upperlayer and is sustaining the rich ecosystem in the Southern Ocean.
Matsuoka et. al. (2003) investigated the relationship between oceanographic fronts and distributionof the large whale species. They showed that the humpback whale gathered in the sea area aroundSB east of the Keruguelen Plateau in Area IV.

Nicol et al. (2000) indicated the results of theBROKE (baseline research on oceanography, krill and the environment) in the area from 80E-150E
conducted in 1996.

They showed that the ecosystem in the region south of the SB of the ACC isrich and the SB determines the spatial structure.
As a first step of the oceanographic analysis of JARPA data from the view point of ecosystem, we
made climatological pictures of the various physical parameters by using the JARPA data toinvestigate the large scale feature of the oceanographic structure.

The information about theyear-to-year variability is also provided by using the satellite observed data.

DATA
Vertical oceanographic structures were observed by using XBT (eXpendable Bathy Thermograph),
CTD (Conductivity-Temperature-Depth profiler) and XCTD (eXpendable CTD). XBT was mainly
used in the first stage of JARPA (87/88-96/97).
instrument in the late 1990’s.
0m to 1000m by XCTD.
ocean currents.

XCTD is a newly developed oceanographic

We can get temperature and salinity profile for the depth range fromIn the Southern Ocean, salinity is important factor for the dynamics ofSo XCTD was promptly introduced instead of XBT in the second stage of JARPA(97/98- presents).

CTD(SBE19 SEACAT profiler) was also introduced after 98/99 JARPA.

These

data were combined and stored in the HydroBase format (Macdonald et al., 2001). Figure 1 shows
oceanographic observation stations of JAPRA.

In our analysis, we mainly used the data obtained

after 97/98 JARPA when salinity data available and the water mass analysis are possible.

915

XCTD stations and 499 CTD stations were occupied during 8 JARPA cruises. CTD sensors werecalibrated every year and no significant error was reported.

XCTD data was checked by using

climatology of the World Ocean Atlas (WOA 2001) and the systematic positive bias found in salinity
data in JARPA 97/98 was corrected. XCTD data was also checked statistically to exclude suspicious
data from analysis.

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RESULTS
Large scale oceanographic conditions of JARPA area
By using all the temperature profile data, the temperature section along the Date Line is constructed.
The mean temperature section and standard deviation section are shown in Figures 2.

Thedichothermal structure (temperature minimum) is observed in the upper layer of poleward region of64S.

This structure is remainder of the mixing of upper water in former winter. The SB of the ACC

coincides with the northern limit of 0ºC water.

In the subsurface layer, relatively warm deep water

exists under the dichothermal layer indicating the upwelling of the upper Circumpolar Deep Water(UCDW).

Large standard deviation found in the surface layer around 63S reflects the year-to-year

variation of the SB.
Front systems of the ACC are important for the marine ecology of the Southern Ocean.

The SB is asouthernmost front of the ACC and is recognized as an important oceanographic feature for large
whale in the JARPA area.

To detect the SB in the JARPA area, we construct the spatial temperatureand salinity map on 27.6σθ isopycnal surface.
contour on temperature map (Fig. 3).

Frontal structure is clearly observed along the 0ºC

The contour line shows the southern limit of UCDW andindicates the southern boundary of ACC (Orsi et al., 1995).
bottom topography (Fig. 4).

The path of the SB closely follows theThe ACC strongly influenced by the bottom topography deep structureof the ACC.
Ice edge is another important boundary which restricts movement of whale. Relationship between
the SB of the ACC and seasonal variation of ice edge position was analyzed. Figure 5 shows
seasonally changing ice edge positions in the summer season with the SB position. Seasonalvariation is larger in the regions west of the Kergualen Plateau and east of 160E.

As to the region

east of 160E, it is obvious that wide area without ice appears south of the SB in months from Januaryto March.

The figure is also suggesting that there is some delay in time when ice edge reaches theSB position in the Ross sea region compared with other region.
Detailed structure of the SB in Area IV and V
The SB of ACC for 8 JARPA cruises (Fig. 6) in the Area IV and Area V.

The position of the SB isdefined as the positions of 0ºC temperature contour on 27.6σθ isopycnal surface. Figure 7 shows theobservation line and the position of the SB.

In Area IV, the meandering path east of the Kergualen

Plateau was observed in all four years. The year-to-year variation of the meridional position of theSB was obviously indicated. The dichothermal structure developed in the south of the SB, and its
temperature and thickness change each year.

In AREA V, the SB approaches the continent west of150E and is left offshore east of 150E and it clear that the SB runs along the Pacific-Antarctic ridgein the east of 160E. These maps show the stable structure of SB in Area V.
SB detection by satellite altimeter data
The position of SB detected by oceanographic data of JARPA was compared with the dynamic-3-

topography at the sea surface relative to 2000dbar derived from satellite altimeter data andhydrographic climatology.
SB position.

It was shown that the contour line of 0.815m is good indicator for theBy using the relationship, we made a data set of the SB position for the period from1993 to 2005 when the satellite altimeter is available. Figure 8 shows all the data for JARPA area
and the probability distribution of the SB.

It is indicated that the SB position in Area V is stable asobserved by analysis of the JARPA oceanographic data.
highly variable in the east of the Kerguelen Plateau.

On the other hand, the SB position isStandard deviation is 0.4 degree in Area V andis 0.8 degree or more between the Kerguelen Plateau and 110E.
each area is shown in Figure 9.
and V.

Year-to-year variability of SB in

Temporal variation with 5-6 year periodicity is obvious in Area IV

In Area III-east and Area VI, northward shift of SB was also found after 2000.

Year-to-year variation of Chlorophyll fields in the JARPA area derived from the satellite
observation
Chlorophyll distribution observed by satellite ocean color sensor SeaWiFs was compared with theoceanographic conditions in Area IV.
(Fig. 10-1-A).

The chlorophyll-a concentration was low in January 1998

The hydrographic section shows dichothernal water was weak during JARPA 97/98,indicating weak wintertime cooling in the previous winter (Fig.10-1-B).
chlorophyll-a concentration was high in January 2000 (Fig. 10-2-A).

On the other hand, theThe dichothermal water wasintense during JARPA 99/00, indicating intense wintertime cooling in the previous winter (Fig.
10-2-B).

These observations suggest that the wintertime cooling affects the primary productivity inthe following seasons.

The chlorophyll-a concentration in January 2002 was high (Fig.10-3-A),

which is consistent with the intense dichothermal water (Fig.10-3-B).

The high concentration area

was confined near the coast, which is possibly related to the SB approaching the coast during JARPA
01/02 (Fig. 7).
Year-to-year variation of SST in the JARPA area
Time series of Sea surface Temperature (SST) along the circle of latitude at 62S were analyzed.
Year-to-year variations of March SST in Area IV are characterized by warming after 2001 andextraordinary high SST in 1988 and low in 2000 (Fig. 11).
March SST is larger than Area IV (Fig. 12).

In Area V, year-to-year variation ofWarm SST in the eastern part of Area V is related to El

Nino 1982/83, 1986/87, 1991-93 and 1997/98 (Kwok and Comiso, 2002).
significant long-term trend is observed for the period 1982-2004.

In both areas, noOn the other hand, the SST timeseries around the Antarctic Peninsula include warming trend of about 0.02 degree C/year for 23
years period from 1982 to 2004 (not shown). This trend is related to remarkable warming observedin the Antarctic Peninsula where the influence of global warming has appeared notably.
Oceanographic structure of the Prydz Bay region
While the major formation sites of AABW are located in the Weddell Sea and the Ross Sea, recent
studies suggested a few other sites including the Prydz Bay region (Orsi et al. 1999).

Thehydrographic data in the Prydz Bay region during the JARPA 99/00 and 01/02 were analyzed to seek-4-

an evidence for the AABW formation (Fig. 13).

One of the essential elements for the AABW

formation is high salinity shelf water (HSSW), which is cold and saline (S>34.6) shelf water.
HSSW was observed near the shelf break in the Bay at the station JARPA99/00-113 (Fig. 14), which
is a clear additional evidence for the AABW formation in the Prydz Bay region

SUMMARY AND REMARKS
Basic oceanographic structure of JARPA area was realized by the JARPA oceanographic data.

Theposition of the SB of ACC is mainly determined by bottom topography such as the Kerguelen
Plateau the Pacific-Antarctic ridge.

The JARPA area is also characterized as upwelling area ofCircumpolar Deep Water, which provides nutrients to support high primary productivity. Largeinterannual variations in the meridional position of SB of ACC in the east of the Kerguelen plateau
are revealed. By using the chlorophyll data, we made several map and compare the chlorophyll
distribution with the oceanographic structure in area IV. In the area south of the SB, low chlorophyll
concentration in 97/98 season was related to weak dichothermal structure and relatively highchlorophyll concentration in 99/00 and 01/02 season were related to colder and thick dichothermal
structure. The relationship suggested that wintertime mixing of surface layer affect the production inthe summer season.

Influence of El Nino on SST in area V –VI is also suggested. Although theglobal warming is also important forcing for the Southern Ocean, it is not clear that the JARPA
region is affected like the Antarctic Peninsula region does. By water mass analysis of JARPA
oceanographic data, it is suggested that the Prydz Bay region can be one of the formation area of theAABW.
The most important aspect of JARPA is that observation is repeated in the same area in the sameseason. Useful marine environment information is beginning to be extracted from JARPA data. We
regard JARPA as one of the important monitoring platform of the marine environment in theSouthern Ocean.

Sufficient consideration based on the experience of JARPA 1987/88-2004/05 isneeded to get an efficient future observation plan for the JARPA area. It is also important to make
JARPA oceanographic observation link with the monitoring by other in-situ observation projects(Argo, IPY, etc.) and satellite observations.

The fundamental information about physicaloceanographic environment in the JAPPA area has been accumulated for 18 years, which will befully utilized to investigate the relation among physical environment, biochemical environment andhabitat environment of the whale in the future stage of JARPA.

ACKNOWLEDGMENT

The authors are grateful to the captains, crew, scientists and other staff of the JARPA
cruises for their support for the hydrographic observations.

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REFERENCES
Kwok, R. and Comiso, J. C. 2002. Southern Ocean climate and sea ice anomalies associated with theSouthern Oscillation. J. Climate, 15, 487-501
Macdonald, A. M., T. Suga, and Curry, R. G. 2001. An isopycnally averaged North PacificClimatology. J. Atmosph. and Oceanic Tech, 18(3), 394-420 (2001).
Matsuoka K., Watanabe, T., Ichii, T., Shimada, H. and Nishiwaki, S. 2003. Large whale distributions(south of 60S, 35 E-130 E) in relation to the southern boundary of the ACC. Antarctic Biology in a
Global Context, pp26-30. Edited by A. H. L. Huiske, W. W. C. Gieskes, J. Rozema, R. M. L. Schrno,S, M, van der Vies & W. J. Wolff. Backhuys Publishers, Leiden, The Netherlands
Nicol S., T. Pauly, Bindof, N. L., Wright, S., Thiele, D., Hosie, G. W., Strutton, P. G. and Woehler, E.
2000. Ocean circulation off east Antarctica affects ecosystem structure and sea-ice extent. Nature,406: 504-507.
Orsi, A. H., Whitworth III, T.and Nowlin Jr., W. D. 1995. On the meridional extent and fronts of theAntarctic Circumpolar Current, Deep Sea Res., Part I, 42, 641-673.
Orsi, A. H., Johnson, G. C. andBullister, J. L. 1999. Circulation, mixing, and production ofAntarctic Bottom Water. Prog. in Oceanogr., 43, 55-109.
Schmitz, W. J.,1996, On the World Ocean Circulation : Volume II. The Pacific and Indian Oceans/ A
Global Update. Woods Hole Oceanographic Institution, Technical Report WHOI-96-08, 241pp-6-.

Fig.1. Oceanographic observation in the JARPA.

Fig. 2. Long-term mean meridional

Fig. 3. Temperature (top panel) and salinity

temperature section (left) and standard(bottom panel) distribution on 27.6σθ

deviation (right) along the date line.

isopycnal surface.

-7-Fig. 4. Relationship between SB of ACC and bottom topography. Red curves indicate
temperature contours on 27.6σθ isopycnal surface. Thick line is 0ºC contour.

Blackcurves are 3000m depth contour.

Relationship between SB position and seasonal movement of Ice Edge
50.0

55.0
SB of ACC
OCTNOVDECJAN
FEB
MAR

Latitude

60.0

65.0

70.0

75.0

80.0
030

6090

120
Longitude150

180210240

Fig. 5. Relationship between SB of ACC and ice edge for months, October – March.

-8-Fig. 6.

Oceanographic stations of JARPA from 97/98 to 04/05. Closed circle and open circle

indicate XCTD and CTD stations, respectively.

The region shallower than 3000m is shaded.

Fig. 7. SB of ACC detected by the XCTD and CTD data of JARPA-97/98 – 04/05 Cruise. Red line
shows position of SB.

-9-Fig. 8.

(a) The map of the Southern Boundary of the Antarctic Circumpolar Current estimated fromsea surface height. Average position is indicated by dashed line.

(b) The map of probability

density of SB.

Figure 9.

Upper: Time-longitude diagram of interannual variation of SB position. Positive value

indicate northward shift. Lower: Interannual variation of SB position of each JARPA Area.

- 10 -1-B

1-C

1-A

2-B

2-A

2-C

3-B

3-A

3-C

4-B

4-A

4-C

Fig.10. 1-A: Distribution of Chl-a in January 1998. 1-B and 1-C are temperature and salinity
composited section of area IV for 1997/98 JARPA respectively. Horizontal axis of 1-B and 1-Cis distance from the SB and vertical axis is depth.

2-A is for January 2000 and 2-B,C are for1999/2000 JARPA. 3-A is for January 2002 and 3-B,C are for 2001/2002 JARPA. 4-A is forJanuary 2004 and 4-B and C are for 2003/2004 JARPA.
- 11 -1.50
1.00
60-70
70-80
80-90
90-100100-110110-120120-130

0.50
0.00
-0.50
-1.00
-1.50
1982

19841986

1988

1990

1992

19941996

1998

2000

2002

2004

Fig. 11. Year-to-year variations of March SST for area IV

1.50
1.00
130-140140-150
150-160
160-170
170-180
180-170

0.50
0.00
-0.50
-1.00
-1.50
1982 1984 1986 1988 1990 1992 1994 1996 1998 2000 2002 2004

Fig. 12. Year-to-year variations of March SST for area V- 12 -Fig. 13. Observation points in the Pridz Bay region, 1999/00 and 2001/02 JARPA Cruise.

Fig. 14. XCTD sections in the Prydz Bay- 13 -