SC/F14/J21

Consideration of the Kerguelen-Davis Oscillation Index(KDOI) influencing variability on the environmental
ecosystem in the Prydz Bay Region, east Antarctic: data
exploration
MIKIO NAGANOBU1, KOJI MATSUOKA2 AND KUNIO KUTSUWADA3
1

National Research Institute of Far Seas Fisheries, 2-12-4 Fukuura, Yokohama, Kanagawa, 236-8648, Japan

2

The Institute of Cetacean Research, 4-5 Toyomi-cho, Chuo-ku, Tokyo 104-0055, Japan3

School of Marine Science and Technology, Tokai University, 3-20-1 Orido, Shimizu-ku, Shizuoka 424-8610, Japan

Contact e-mail:naganobu@affrc.go.jp
ABSTRACT
Significant changes in the environment (climate-sea ice-ocean) and the ecosystem of the Antarctic Ocean haveoccurred frequently in recent decades. A key factor that has brought about these changes in the environmental
ecosystem of the Antarctic Ocean seems to be a large change in the westerlies around the Antarctica analyzing
Southern Annular Mode (SAM), alias Antarctic Oscillation Index (AOI). On the other hand, JARPA I and II havevarious datasets on whales over two decades since 1989/90. From these aspects, we have hypothetically thought thatthe variability of in westerlies has influenced the ocean including sea ice, biological factors and the whale ecosystem
as upper predators. We therefore tried to search, arrange and analyze accessible relevant data in the complex
systems of climate-ocean-ecosystem as data exploration in stages. As a basic environmental regional climate index,
we made determinations from sea level pressure differences between the Kerguelen Islands and the Davis Station,
the east Antarctica (Kerguelen-Davis Oscillation Index; KDOI). KDOI during 2006 and 2013 showed the variabilityof an upward trend with approximately 2-year periodicity. Sea ice extent in austral summer from 1979 to 2011
showed the upward trend taking yearly variability suggesting some relationship with KDOI. In addition, the lower
abundance estimate of Antarctic minke whales coincided with the larger sea ice extent as in 1997/98 and 2007/08,
probably due to navigational limited survey by sea ice. Rapid southward shift of the Southern Boundary of the
Antarctic Circumpolar Current (SBACC) coincided with a rapid increase in humpback whales as in 1995/96 and2001/02, probably due to the Antarctic Circumpolar Water shifts southward. KDOI indicates the characteristic
variability and suggests the relationships to the regional environmental ecosystems such as sea ice, ocean andbiological ecosystem including whales with the coordinate environmental regional index as a future possibility.
KEY WORDS: EAST ANTARCTIC OCEAN, ENVIRONMENTAL ECOSYSTEM, KDOI, WESTERLIESVARIABILITY, WHALE
INTRODUCTION
Significant changes in the environment (climate-sea ice-ocean) and the ecosystem of the Antarctic Ocean frequently
have occurred in recent decades (as review, IPCC, 2001; IPCC, 2007; Turner et al., 2009; Rintoul et al., 2012). The
key factor that has brought about these changes in the environmental ecosystem of the Antarctic Ocean seems to bea large change in the westerlies around the Antarctica analyzing Southern Annular Mode (SAM), alias Antarctic
Oscillation Index (AOI) (Gong and Wang, 1999; Thompson and Solomon, 2002; Arblaster and Meehl, 2006;
Stammerjohn et al., 2008; Kang et al., 2011; Thompson et al., 2011; Villalba et al., 2012, Miles et al., 2013).
On the other hand, there are many reports on variability in the biological ecosystem (as review, Turner et al., 2009;
Rintoul et al., 2012). Especially, the abundance of Antarctic krill (Euphausia superba) , a key species of the
Antarctic Ocean ecosystem, has decreased in recent decades (Siegel and Loeb, 1995；Siegel et al., 1997; Loeb et al.,
1997；Naganobu et al., 1999; Atkinson et.al., 2004). It is often discussed that remarkable decreases in krill and its
predators such as penguins around the Antarctic Peninsula area depend on regional environmental changes due tothe entire climate change in the Antarctic/Southern Ocean (Loeb et al., 1997; Naganobu et al., et al., 1999; Loeb etal., 2009; Trivelpiece et al., 2011, Loeb et al., 2013). In these various phenomena, how can we take an approach to
examine the relationships between the climate and/or oceanic environmental variability and relevant issues of1

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JARPA I and II surveys (Pastene et al., 2014)? As these relationships are basically complex and controversial,
various approaches can be attempted. Here we try to apply an original climate regional index of westerlies
variability for the biological ecosystem around Prydz Bay relating the JARPA survey area as a hypothetical
approach.
.
Changes in the ocean and sea ice are closely related to SAM. However, SAM is a macro scale of the entire Southern
Ocean. The targeted ecosystem phenomena are on a regional scale. It is better to use an environmental index
corresponding to the regional scale of the targeted ecosystem phenomena. Then, we try to apply the proven approachon a climate oscillation index; Drake Passage Oscillation Index (DPOI) (Naganobu et al., 1999) in the Antarctic
Peninsula area, the west Antarctic Ocean, to the Prydz Bay region related to the JARPA area, the east Antarctic
Ocean. DPOI indicated high correlations with several factors such as krill recruitment, sea ice and chlorophyll-a(Naganobu et al., 1999). IPCC (2001) reviewed these results and had the interest in the long-term continuous trend
to DPOI. The continuous studies of DPOI have been indicating additional preliminary results using the long-term
period data for approximately 60 years since 1952 (Kondo, 2009; Naganobu et al., 2009; Yoda, 2011). Then, themethodology of DPOI in the west Antarctic Ocean is applied to the Prydz bay area, the east Antarctic Ocean (Fig.
1).
Although both east and west areas have common circumpolar structure, each area indicates the regional
characteristics of each region. The Prydz Bay area has the aspects of the typical east Antarctic Ocean ecosystem(Anonymous, 1985; Hosie et al., 2000; Nicol et al., 2000; Nicol and Meiners, 2010) including the traditional krill
fishing grounds (Naganobu et al., 2008) compared with the west Antarctic Ocean ecosystem (Hewitt et al., 2004;
Watkins et al., 2004). However, analysis on the time series of the environment and ecosystem is a complex subject
with limited datasets. Therefore, it first noticed the climatic variation of the complex subject. The same methodologyof DPOI was applied to the Prydz Bay area. Two climate observation stations to obtain each Sea Level Pressure(SLP) were selected; the north, Port-aux-francais, Kerguelen Islands in the Southern Ocean and the south, Davis
Station, Antarctica (Fig. 2). The differences in SLP between Kerguelen and Davis indicate strength of westerlies asgeostrophic wind. Fluctuations in the differences are hereinafter referred to as the Kerguelen-Davis Oscillation
Index (KDOI).
MATERIALS AND METHODSWe tried to search, arrange and analyze accessible relevant data in the complex systems of climate-ocean-ecosystem
as data exploration in stages.
First, we have assessed a climate environmental index, as a regional basic indictor, determined from sea levelpressure differences between Port-aux-francais (surface meteorological observation ID: 61998, location 49°-21’S70°-15’E), Kerguelen Islands as the northern station and Davis Station (ID: 89571, 68°-34’S, 77°-58’E) as thesouthern station from 2006 to 2013 (Fig. 3). KDOI can be obtained to calculate the differences in sea level pressure(SLP) between two meteorological stations crossing the westerlies zone.
KDOI=SLP (Kerguelen) －SLP (Davis)
SLP: sea level pressure (monthly), hPa
KDOI is understood as geostrophic wind. A higher KDOI means stronger westerlies. On the other hand, a weaker
KDOI means weaker westerlies. The northern station requires a suitable position in the Southern Ocean and thesouthern station on the Antarctic Continent. We considered some meteorological observation stations in the eastern
Antarctic Ocean. Finally, we adopted Port-aux-francais, Kerguelen Islands and Davis Station because of its suitable
position in the Prydz Bay region with regards to high productivity waters.
The SLP data at Kerguelen were acquired from the public web site of German Weather Service (The Global Climate
Observing System Surface Network Monitoring Centre data set, Deutscher Wetterdienst).
http://www.dwd.de/bvbw/appmanager/bvbw/dwdwwwDesktop?_nfpb=true&_windowLabel=dwdwww_main_book&T15806838371147176099165gsbDocumentPath=Content%2FOeffentlichkeit%2FKU%2FKU4%2FKU42%2FGS
NMC%2Fteaser__datensaetze.html&switchLang=en&_pageLabel=_dwdwww_klima_umwelt_datenzentren_gsnmc
The SLP data at Davis station were acquired from the public web site of the British Antarctic Survey.
http://www.antarctica.ac.uk/met/READER/surface/Davis.06.msl_pressure.html

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The period of the Kerguelen data that can be actually used is comparatively short from 2006 up to the present time.
On the other hand, the period of the Davis data that can be actually used is long from 1957 up to the present time.
Therefore, we calculated KDOI from January 2006 to May 2013 due to the availability of both data periods.
Second, the variability in the extent of sea ice enclosed within 60°S south and 70°E -90°E, from 1979 to 2011 was
examined. The data on sea ice concentration measured by the Advanced Microwave Scanning Radiometer for the
Earth Observing System (AMSR-E) sensor from the Japan Aerospace Exploration Agency (JAXA) satellite wasused. The geographical range of the analysis was enclosed within 70°E-90°E and 60°S- of the coast of Antarctica.
We calculated the monthly average of the sea ice area (more than 15% per a pixel (25×25km ) in December, January
and February (austral summer season) from 1979-2011.
Third, we used the estimates of abundance and distribution patterns of humpback whales (Megaptera novaeangliae)
and Antarctic minke whales (Balaenoptera bonaerensis) in Area IV from 1989/90 to 2007/08 based on JARPA and
JARPA II sighting survey data south of 60 °S (Hakamada and Matsuoka, 2014a, 2014b; Matsuoka and Hakamada,
2014; Murase et al., 2014) to examine relationships between KDOI, sea ice and the latitudinal variability of theSouthern Boundary of Antarctic Circumpolar Current in the existing paper.
RESULTS AND DISCUSSION
Time-series of KDOI showed the following results. (1) KDOI indicated that the available data of Kerguelen was
limited to the years since 2006 while the Davis’s data was spread over 56 years since 1957 (Fig. 4) Therefore, theanalytical period of KDOI was limited to seven and half years at this stage. (2) The monthly KDOI from 2006 to2013 showed the variability of an upward trend (Fig. 5a). The seasonal KDOI, 3-month running mean showednumerically higher values during austral summer and lower during winter with an upward trend (Fig. 5b). The
yearly KDOI, 12-month running mean showed approximately a 2-year periodicity with an upward trend (Fig. 5c).
The combined graph of the monthly with its liner approximation and yearly KDOI shows the trends moving upwardwith a 2-year periodicity, although the period from 2006 to 2013 was limited and short (Fig. 5d). Although thisavailable period of KDOI has difficulty examining minute relationships with whales, KDOI has a role as a
background environmental factor.
Time-series of sea ice suggested concurrent trends with abundance estimates of Antarctic minke whales (Fig. 6). Sea
ice extent in austral summer (December, January and February) from 1979 to 2011 showed the upward trend taking
yearly variability suggesting some relationship with KDOI. In addition, the lower abundance estimate of Antarctic
minke whales coincided with the larger sea ice extent as in 1997/98 and 2007/08, probably due to a navigational
survey limited by the hard conditions of sea ice.
Although we initially hypothesised the effect of KDOI with regards to the question on the recent rapid increase in
humpback whales in the JARPA area (Pastene et al., 2014), the available period of KDOI is too short to examine it.
On the other hand, we searched different ways using existing papers on the long-term oceanographic variability,
especially SBACC which might affect the biological ecosystem (Tynan, 1998; Matsuoka et al., 2003; Naganobu etal., 2010). We therefore found the coincidental phenomena between SBACC and whale as follows. Rapid southward
shift of SBACC (Yabuki, 2006) coincided with a rapid increase in humpback whales as in 1995/96 and 2001/02,
probably due to the Antarctic Circumpolar Water southward shift (Fig. 7). The variability of the Antarctic
Circumpolar Water is an important subject for the Antarctic Ocean ecosystem and a detailed analysis is encourage(Iida et al., 2013; Watanabe et al., 2014).
KDOI indicates the characteristic variability and suggests relationships with the regional environmental ecosystems
such as sea ice, ocean and biological ecosystem including whales. In addition, KDOI is just one regional climate
phenomena compared with the entire Southern Ocean scale such as SAM. The limited data made it difficult todepend to construct the process of the regional environmental ecosystem around whales as scientific results have todepend on the evidence data. Fig. 8 shows the comprehensive linkages of the periods of JARPA and KDOI with thevariability of SAM. During the period of JARPA, SAM showed large variability with an upward trend. SAM as theentire scale index and KDOI as the regional scale index must have some syncronisations. KDOI has potential as thecoordinate environmental index in the east Antarctic Ocean with the increasing SLP and relevant oceanic/biologicaldatasets.

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CONCLUSIONSKDOI from 2006 to 2013 showed the variability of an upward trend with approximately 2-year periodicity. Sea ice
extent in austral summer from 1979 to 2011 showed the upward trend taking yearly variability suggesting somerelationship with KDOI. In addition, the lower abundance estimate of Antarctic minke whales coincided with thelarger sea ice extent as in 1997/98 and 2007/08, probably due to a navigational survey limited by sea ice. Rapid
southward shift of SBACC coincided with the rapid increase in humpback whales as in 1995/96 and 2001/02,
probably due to the Antarctic Circumpolar Water southward shift. KDOI indicates the characteristic variability andsuggests relationships with the regional environmental ecosystems such as sea ice, ocean and biological ecosystem
including krill and whales with the coordinate climate index as a future possibility.
ACKNOWLEDGEMENTS
We would like to express our gratitude to N. Kokubun (NIPR), Y. Arai (RESTEC), T. Yabuki (JAFIC) and H.
Watanabe (NRIFSF) for their useful information/data and discussions for this paper.
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S
1<Figure 1-8 and captiions>Figure 1. Connectionaal image from DPOI to KD
DOI: (a) the sccientific geogrraphical distriibution of krilll (from Marr,,
1962) andd (b) the worlld fishing positions of krill with MTEM--200 (Mean TEMperatureTffrom 0 to 2000m) indicatingg
the locatiions of oceaniic fronts suchh as SBACC ((the Southern Boundary of the Antarcticc Circumpolarr Current) andd
others (mmodified from Orsi et al., 1995; Naganobbu et al., 2008
8). SBACC iss the key fronnt for krill andd its predatorsssuch as w
whales in the circumcAntarcttic Ocean ecoosystem.

Figure 2. KDOI (Kerguuelen-Davis OscillationO
Inddex: the differences in sea leevel pressuress between Kerrguelen andDavis staation) with thee main oceanicc study area arround Prydz Bay
B referring tot JARPA’s arrea, east Antarrctica.

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S
1

Figure 3. Data explorattion on Sea Leevel Pressure (monthly) at Port-Aux-Franncais (world ssurface meteo
orologicalstation ID
D: 61998), Kerrguelen Island
ds and Davis S
Station (ID: 1220515) for KD
DOI.

Figure 4. Comparison betweenbthe availableadata periods at Kerguelen and Davis.
D
The avaailable data off Kerguelen
was limitted to the yearrs from 2006 whilew
Davis’s data was overr 56 years sincce 1957.

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1

Figure 5aa. Time series of sea level pressure differeence between Kerguelen annd Davis Oscilillation Index (KDOI)),
monthly mmean from 20006 to 20013 showss
upwardd trend.

Figure 5bb. Time series of KDOI, 3-mmonth runningg mean from 20062
to 2013 showssnumeriically higher duringdaustralsummer aand lower durring winter.

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1

Figure 5cc. Time series of KDOI, 12--month runninng mean from 2006 to 2013 shows approxximately 2-yeear
periodicitty.

Figure 5dd. The combinned graph of th
he monthly, linner approximaation and yearrly KDOI. Varriability of KD
DOI from
2006 to 22013 shows uppward trend withw approximaately 2-year periodicity.

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S
1

Figure 6. (a) Abundancce estimate off Antarctic minnke whales inn Area IV fromm 1989/90 to 22007/08, JARP
PA (data fromm
Hakamadda and Matsuooka., 2014a) anda (b) sea icee extent in Deecember, Januuary and Febru
ruary in the reegion betweenn
70-90E ssouth of 60S, from 1978/79
9 to 2010/11.. The lower abundanceaesttimate coincidded with the larger sea icee
extent as in 1997/98 annd 2007/08.

Figure 7.. (a) Abundannce estimate ofo humpback whales in Arrea IV from 1989/90 to 20007/08, JARP
PA (data fromm
Hakamadda and Matsuuoka., 2014b)) and (b) zonnal average (black(
thick linelindicates 11-month ru
unning mean,,negative anomaly inddicates southw
ward shift) off SBACC (the Southern BoundaryBof tthe Antarctic Circumpolarr
Current) in the Indian sector from 19931
to 2005 (modified fro
om Yabuki, 2006). Rapid ssouthward shiift of SBACC
C
coincidedd with rapid inncrease of hum
mpback whalees as in 1995/9
96 and 2001/0
02.

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SC/F14/J21
S
1

Figure 8. Time series ofo the Decembber-May SAM
M (Southern AnnularAMode)) index (blackk thick line ind
dicates 5-yearr
moving) from 1963 to 2010 (modified from Miless et al., 2013)) with the avaiilable periods of JARPA an
nd KDOI data..
The SAMM trend shows upward moveement which mmeans a strengthening of th
he circumpolarar westerlies.

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