J A/J 05/J R15< Not to be cited without authors permittion>

Results of oceanogr aphic analyses conducted under J ARPAand possible evidence of environmental changes
Tomowo Watanabe1, Takashi Yabuki2, Toshio Suga2, Kimio Hanawa2, Koji Matsuoka3 and Hiroshi
Kiwada3
1

National Research Institute of Fisheries Science, 2-12-4 Fukuura, Kanazawa, Yokohama,
Kanagawa 236-8648, Japan
2
Tohoku University, 6-3 Aoba, Aramaki, Aoba-ku, Sendai, Miyagi 980-8578, Japan
3
Institute of Cetacean Research, 4-5 Toyomi, Chuo-ku, Tokyo 104-0055, Japan
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 of
whales. 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
the Antarctic Circumpolar Current was clearly observed as a 0ºC temperature contour line on the27.6 isopycnal surface. It is evident that the position of SB is controlled by major features ofbottom 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. The JARPA
data also provided a new evidence of Antarctic Bottom Water formation in the Prydz Bay region.
Comparison between the JARPA data and satellite-derived Chlorophyll distribution indicates thatthe intensity of the wintertime cooling determines the primary productivity south of SB in thefollowing seasons. These data provide to investigate the Antarctic marine ecosystem including therelation between environmental condition of the sea and distribution of whales.

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 17 years period
1987/88-2003/04. The purpose of the oceanographic observations is to obtain fundamental
information of the ecosystem in the JARPA area and to investigate the relationship between theoceanographic 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
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-1-

J A/J 05/J R15
upper layer 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 Kerguelen Plateau in Area IV. Nicol et al. (2000) indicated the results of the
BROKE (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 the
year-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). XCTD is a newly developed
oceanographic instrument in the late 1990’s. We can get temperature and salinity profile for thedepth range from 0m to 1000m by XCTD. In the Southern Ocean, salinity is important factor forthe dynamics of ocean currents. So XCTD was promptly introduced instead of XBT in the second
stage of JARPA (97/98-presents). CTD was also introduced after 98/99 JARPA. These data werecombined and stored in the HydroBase format (Curry, 1996). Figure 1 shows observation stations.
In our analysis, we mainly used the data obtained after 97/98 JARPA when salinity data available,
so the water mass analysis is possible.
RESULTS
Large scale oceanographic conditions of J ARPA 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 and 3,
respectively. The dichothermal structure (temperature minimum) is observed in the upper layer ofpoleward region of 64S. 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 theupper 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 isa southernmost 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
temperature and salinity map on 27.6 isopycnal surface. Frontal structure is clearly observed
along the 0ºC contour on temperature map (Fig. 4). The contour line shows the southern limit of
UCDW and indicates the southern boundary of ACC (Orsi et al., 1995). The path of the SB
closely follows the bottom topography (Fig. 5). The ACC strongly influenced by the bottom
topography deep structure of the ACC.
Detailed structure of the SB in Area V and IV
Detailed oceanographic structure in Area V was investigated by JARPA 01/02 data set. Figure 6
shows the observation line and the position of the SB as defined the 0ºC on 27.6 isopycnal
surface. The SB approaches the continent west the 150E and is left offshore east the 150E and it
clear that the SB runs along the Pacific-Antarctic ridge in the east of 160E.
-2-

J A/J 05/J R15
The SB of ACC in the Area IV was detected by using the JARPA 97/98, 99/00, 01/02 oceanographic
observation data (Fig. 7). The position of the SB is defined as the positions of 0ºC temperature
contour on 27.6 isopycnal surface. The meandering path east of the Kerguelen Plateau wasobserved in all three years. The year-to-year variation of the meridional position of the SB was
obviously indicated. The dichothermal structure developed in the south of the SB, and its
temperature and thickness change each year.
The position of SB detected above was compared with the dynamic topography at the sea surface
relative to 2000dbar derived from satellite altimeter data and hydrographic climatology (Fig. 8). It
was shown that the contour line of 0.82m is good indicator for the SB position.
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). The
hydrographic data in the Prydz Bay region during the JARPA 99/00 and 01/02 were analyzed toseek an evidence for the AABW formation (Fig. 9). 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. 10),which is a clear additional evidence for the AABW formation in the Prydz Bay region.
Year-to-year variation of Chlorophyll fields in the J ARPA area derived from the satellite
observation
Chlorophyll distribution observed by satellite ocean color sensor SeaWiFS was compared with theoceanographic conditions in Area IV. The chlorophyll-a concentration was low in January 1998
(Fig. 11). The hydrographic section shows dichothermal water was weak during JARPA 97/98,
indicating weak wintertime cooling in the previous winter (Fig. 12). On the other hand, thechlorophyll-a concentration was high in January 2000 (Fig. 13). The dichothermal water was
intense during JARPA 99/00, indicating intense wintertime cooling in the previous winter (Fig. 14).
These observations suggest that the wintertime cooling affects the primary productivity in thefollowing seasons. The chlorophyll-a concentration in January 2002 was high, which is consistent
with the intense dichothermal water (not shown). The high concentration area was confined near
the coast, which is possibly related to the SB approaching the coast during JARPA 01/02 (notshown).
Year-to-year variation of SST in the J ARPA area
Time series of SST along the circle of latitude at 62S were analyzed. Year-to-year variations ofMarch SST in Area IV are characterized by warming after 2001 (Fig. 15). No significant
long-term trend is observed for the period 1982-2004. SST was extraordinary high in 1988 andlow in 2000. Year-to-year variation of March SST in Area V is large (Fig. 16). Warm SST in theeastern part of Area V is related to El Nino 1982/83, 1986/87, 1991-93 and 1997/98 (Kwok andComiso, 2002).
SUMMARY AND REMARKS
Basic oceanographic structure of JARPA area was realized by the JARPA oceanographic data. The
position 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 of
Circumpolar Deep Water, which provides nutrients to support high primary productivity. An
evidence for the AABW formation in the Prydz Bay region was found. Large inter-annual
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-3-

J A/J 05/J R15
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 high chlorophyll
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 in thesummer season. Influence of El Nino on SST in Area V-VI is also suggested.
The most important aspect of JARPA is that observation is repeated in the same area in the same
season. 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 JARPA area has been accumulated for 17 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, researchers and other staff of the JARPA cruises fortheir support for the hydrographic observations.
REFERENCES
Curry, R. G. 1996. HydroBase –A Database of Hydrographic Stations and Tools for Climatological
Analysis, Woods Hole Oceanogr. Inst. Tech. Rept., WHOI-96-01, 44pp.
Kwok, R. and Comiso, J. C. 2002. Southern Ocean climate and sea ice anomalies associated with
the Southern Oscillation. J. Climate, 15, 487-501.
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 the
Antarctic Circumpolar Current, Deep Sea Res., Part I, 42, 641-673.
Orsi, A. H., Johnson, G. C. and Bullister, J. L. 1999. Circulation, mixing, and production of
Antarctic 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.

-4-

J A/J 05/J R15

Fig. 1. Oceanographic observation in the JARPA.

Fig. 2. Long-term mean meridional temperature section along the date line.

-5-

J A/J 05/J R15

Fig. 3. Standard deviation associated with the long-term mean meridional temperature section along
the date line shown in Fig. 1.

Fig. 4. Temperature (top panel) and salinity (bottom panel) distribution on 27.6
-6-

isopycnal surface.

J A/J 05/J R15

Fig. 5. Relationship between SB of ACC and bottom topography. Red curves indicate temperature
contours on 27.6 isopycnal surface. Thick line is 0ºC contour. Black curves are 3000m depth
contour.

SB

Fig. 6. SB of ACC detected by the XCTD and CTD data of JARPA-00/01 Cruise.

-7-

J A/J 05/J R15

Fig. 7. SB of ACC detected by the XCTD and CTD data of JARPA-97/98 (top), JARPA-99/00(middle) and JARPA-01/02 (bottom) cruises.

-8-

J A/J 05/J R15

Fig. 8. Comparison with Sea surface height field by using the “Mean Sea Level Anomaly (MSLA)”
data and mean field derived from WOA98.

Fig. 9. Observation points in the Prydz Bay region, 1999/00 and 2001/02 JARPA Cruise.

JARPA99/00-113

Fig. 10. XCTD sections in the Prydz Bay.
-9-

J A/J 05/J R15

Fig.11. Distribution of Chl-a in January 1998.

Fig. 12. Temperature and Salinity composited section of area IV for 1997/98 JARPA.

- 10 -J A/J 05/J R15

Fig. 13. Distribution of Chl-a in January 2000.

Fig. 14. Temperature and Salinity composited section of area IV for 1999/2000 JARPA.

- 11 -J A/J 05/J R15
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 1984 1986 1988 1990 1992 1994 1996 1998 2000 2002 2004

Fig. 15. 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. 16. Year-to-year variations of March SST for area V.

- 12 -