SC/62/IA4

January sea ice trends during the period of three IWC
IDCR/SOWER circumpolar surveys (1978-2004)
HIROTO MURASE
The Institute of Cetacean Research, 4-5 Toyomi-cho, Chuo-ku, Tokyo, 104-0055, Japan
ABSTRACT
Trends of sea ice in the period of IWC IDCR/SOWER circumpolar surveys from CPI to
CPIII (1978-2004) are fundamental information to understand the year-to-year sea ice
variability. The trends of sea-ice-extent (sea-ice-field) in the IWC management areas were
estimated by Murase and Shimada (2004) but the temporal coverage was limited to 2002.
Rest of two years (2003 and 2004) are included in this paper. In addition, trends of sea-icearea-in-the-sea-ice-field and open-sea-area-in-the-sea-ice-field are also considered in thispaper. The trends in each IWC management area, western and eastern half of each IWC
management area (e.g. Area I West and East) and each 10° degree longitudinal sector are
investigated in this paper. Region specific year-to-year sea ice variabilities were detected.
The variabilities were not consistent even in same management area. For example,
differences of open-sea-area-in-the-sea-ice-field in two 10° degree longitudinal sectors in
Area V (170°E-180° and 180°-170°W) between CPII and CPIII were large in comparison
with rest of Area V. Open-sea-area-in-the-sea-ice-field in these sectors in CPIII were larger
than CPII. Number of Antarctic minke whales in sea-ice-field is expected to be large if
open-sea-area-in-the-sea-ice-field is large. Region specific investigation is required tounderstand the effect of sea ice on abundance estimation of Antarctic minke whales.

INTRODUCTION
The International Whaling Commission (IWC) has conducted the Antarctic minke whale(Balaenoptera bonaerensis) abundance assessment cruises since 1978/79 in the Antarctic in australsummer. The names of the cruises were firstly the International Decade of Cetacean Research
programme (IDCR, from 1978/79 to 1995/96) and then the Southern Ocean Whale and Ecosystem
Research programme (SOWER, from 1996/97 to 2009/2010). Matsuoka, et al. (2003) presented an
extensive review of these cruises. These cruises covered three circumpolar surveys for the purposeof comprehensive assessments: 1978/79-1983/84 (first circumpolar, CPI), 1984/85-1990/91 (second
circumpolar, CPII) and 1991/92-2003/04 (third circumpolar, CPIII). A noticeable abundance
decline from CPII to the CPIII using the IWC standard abundance estimation method (Branch,2006) has raised questions whether the decline is true or apparent. Discussion on reasons for thedifference between the estimates between CPII and CPIII is ongoing in the Scientific Committee of
IWC (IWC/SC). One of the reasons identified in IWC/SC is change in the location of the ice-edge
and the proportion of animals south of the ice-edge (IWC, 2003a).
Several studies suggested that area of sea ice in the Antarctic showed area specific year-toyear variations (Zwally, et al., 2002; Cavalieri, et al., 2003; Cavalieri and Parkinson, 2008).
Understanding of the sea ice variability specific to each IWC management area is fundamental
information to see the effect of it on abundance estimation of Antarctic minke whales. IWC
established six areas in the Antarctic for management of large whales: Area I (120°W-60°W), Area
II (60°W-0°), Area III (0°-70°E), Area IV (70°E-130°E), Area V (130°E-170°W) and Area VI(170°W-120°W) (Donovan, 1991). Although Murase and Shimada (2004) investigated the January
yearly trend of sea ice extent in each IWC management area, their analysis was limited to 2002.
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Moreover, they only used sea-ice-extent (sea-ice-field). Recent discussion in IWC/SC more focusedon sea ice and abundance of Antarctic minke whales at regional scale (e.g. each 10 longitudinal
sector). In addition, it was acknowledged that open-sea-area-in-the-sea-ice-field is important toestimate abundance of Antarctic minke whales. This paper presents the results of investigation on
January sea ice trends during the period of three IWC IDCR/SOWER circumpolar surveys (19782004). Trends of sea-ice-extent (sea-ice-field), sea-ice-area-in-the-sea-ice-field and open-sea-areain-the-sea-ice-field in each IWC management area, western and eastern half of each IWC
management area (e.g. Area I West and East) and each 10° degree longitudinal sector are
investigated in this paper. .

MATERIALS AND METHODS
Satellite derived daily sea ice data, Bootstrap Sea Ice Concentrations from Nimbus-7 SMMR andDMSP SSM/I (Comiso, 1999) from 1978 to 2004 was used in the analysis. The data was provided
by the National Snow and Ice Data Center (NSIDC, US). Sea ice observation using the satellitepassive microwave sensors was started with the launch of Scanning Multichannel Microwave
Radiometer (SMMR) on Nimbus-7 in 1978. The sensor was changed to Special Sensor
Microwave/Imager (SSM/I) in 1987 and the data collection is still on going. The data werecollected every other day for the SMMR whereas those were collected every day for the SSM/I. Sea
ice concentration is expressed as percentage of area covered by sea ice in every 25km2 × 25 km2
grid cell. Sea ice concentrations more than 15% was commonly used in the sea ice trend analysis(Bjøgo, et al., 1997; Hanna, 2001; Zwally, et al., 2002). Therefore, grid cells with more than 15%
sea ice concentrations were used in this analysis. The original data was in the NSIDC polarstereographic projection and it was converted to the polar stereographic Zenithal equal area
projection. Monthly mean data in January were calculated by using daily data for each year. January
anomalies of sea-ice-extent (sea-ice-field), sea-ice-area-in-the-sea-ice-field and open-sea-area-inthe-sea-ice-field was calculated. Their anomalies were calculated as average values from 1978 to
2004 minus observed values for each year. Definitions of sea-ice-extent (sea-ice-field), sea-icearea-in-the-sea-ice-field and open-sea-area-in-the-sea-ice-field are summarized in Fig. 1. Polynya
is not considered in this paper because automatic detection of polynya is technically difficult. The
anomalies were calculated in each IWC management area, western and eastern half of each IWC
management area (e.g. Area I West and East) and each 10° degree longitudinal sector.

RESULTS AND DISCUSSIONAs an example of yearly variations of sea ice, anomalies of open-sea-area-in-the-sea-ice-field in the
IWC management areas in January are shown in Fig. 2. Each management area showed area
specific yearly variation. Large difference of open-sea-area-in-the-sea-ice-field between CPII and
CPIII was observed in Area V (130°E-170°W). The difference was pronounced in East (165°E170°W) in comparison with West (130°E-165°E) (Fig. 3). Sea ice conditions in East affected thechange in open-sea-area-in-the-sea-ice-field in Area V. Likewise, contribution of some 10° degree
longitudinal sectors affected the trends in West/East of Area V (Fig. 4). Differences of open-seaarea-in-the-sea-ice-field between CPII and CPIII in two 10° degree longitudinal sectors in Area V(170°E-180° and 180°-170°W) were large. Open-sea-area-in-the-sea-ice-field in these sectors in
CPIII were larger than CPII. Number of Antarctic minke whales in sea-ice-field is expected to belarge if open-sea-area-in-the-sea-ice-field is large. It was demonstrated that abundance of Antarctic
minke whales in Area V was low when sea-ice-extent (sea-ice-field) was large (Matsuoka et al.,2009). Number of Antarctic minke whales in sea-ice-field could relate to open-sea-area-in-the-seaice-field. Region specific year-to-year sea ice variabilities were also detected in other management
areas (see Figs. in Appendix). The results of this paper suggested that region specific investigation2

is required to understand the effect of sea ice on abundance estimation of Antarctic minke whales.
Development of such database is critically important to account the effect. Polynya (number of gridcells containing less than 15 % sea ice concentrations in the south of sea ice edge observed by
IDCR/SOWER vessels) was not considered in this analysis because automatic detection of polynya
is technically difficult. However, polynya is considered as one of the important habitat of Antarctic
minke whales, area of polynya should be calculated in each surveyed year in addition to open-seaarea-in-the-sea-ice-field.

REFERENCES
Bjøgo, E., Johannessen, O. M. and Miles, M. W. 1997. Analysis of merged SMMR&#8208;SSMI
time series of Arctic and Antarctic sea ice parameters 1978&#8211;1995. Geophys. Res.
Lett. 24: 413-416.
Branch, T. A. 2006. Abundance estimates for Antarctic minke whales from three completed
circumpolar sets of survey, 1978/79 to 2003/04. Paper SC/58/IA18, presented to the 58th
IWC Scientific Committee, May 2006 (unpublished). 28pp.
Cavalieri, D. J., Parkinson, C. L. and Vinnikov, K. Y. 2003. 30-Year satellite record reveals
contrasting Arctic and Antarctic decadal sea ice variability. Geophys. Res. Lett. 30.
Cavalieri, D. J. and Parkinson, C. L. 2008. Antarctic sea ice variability and trends, 1979-2006. J.
Geophys. Res.-Oceans. 113.
Donovan, G. P. 1991. A Review of Iwc Stock Boundaries. Rep. Int. Whal. Commn. Special Issue
13: 39-68.
Hanna, E. 2001. Anomalous peak in Antarctic sea-ice area, winter 1998, coincident with ENSO.
Geophys. Res. Lett. 28: 1595-1598.
IWC 2003a. Hypotheses that may explain why the estimates of abundance for the third circumpolar
set of survey (CP) using „the standard methods‟ are appreciably lower than estimates for thesecond CP. J. Cetacean Res. Manage. 5 (suppl.): 286-290.
IWC 2003b. Report of Scientific Committee, Annex G. J. Cetacean Res. Manage. (Suppl.) 5: 248268.
Matsuoka, K., Ensor, P., Hakamada, T., Shimada, H., Nishiwaki, S., Kasamatsu, F. and Kato, H.
2003. Overview of minke whale sightings surveys conducted on IWC/IDCR SOWER
Antarctic cruises from 1978/79 to 2000/01. J. Cetacean Res. Manage. 5: 173-201.
Matsuoka, K., Hakamada, T., Kimura, K. and Okada, Y. 2009. Influence of sea ice concentration on
Antarctic minke whale abundance estimation in the Ross Sea. Paper SC/61/IA16 presented
to the 61st IWC Scientific Committee, May 2009 (unpublished). 7pp.
Murase, H. and Shimada, H. 2004. Possible impact due to variability of sea ice condition on
Antarctic minke whale abundance estimation in the Antarctic from 1978 to 2002. Paper
SC/56/IA10, presented to the 56th IWC Scientific Committee, June 2004 (unpublished).
15pp.
Zwally, H. J., Comiso, J. C., Parkinson, C. L., Cavalieri, D. J. and Gloersen, P. 2002. Variability of
Antarctic sea ice 1979-1998. J. Geophys. Res.-Oceans. 107.

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25 km

25 km

15 %

50 %

80 %

Fig. 1. Schematic diagram of relationship between sea-ice-concentration, sea-ice-extent (sea-icefield), sea-ice-area-in-the-sea-ice-field and open-sea-area-in-the-sea-ice-field. Grey area shows sea
ice concentrations in 25 ×25 km grid cells. Spatial resolution of satellite data “Bootstrap Sea Ice
Concentrations from Nimbus-7 SMMR and DMSP SSM/I” is 25 ×25 km grid cell. Definitions of
sea-ice-concentration, sea-ice-extent (sea-ice-field), sea-ice-area-in-the-sea-ice-field and open-seaarea-in-the-sea-ice-field are as follows.
Sea-ice-concentration
Sea ice concentration in each 25×25 km grid cell (625km2) in %. In the diagram, the sea ice
concentrations are 15, 50 and 80 % from left to right.
Sea-ice-extent (sea-ice-field)
Number of grid cells containing more than 15 % sea ice concentrations. In the diagram, the sea ice
extent is 625km2 × 3. Sea-ice-field is used as an alternative definition of sea-ice-extent in this paper.
Sea-ice-area-in-the-sea-ice-field
Area covered by sea ice in each 25 ×25 km grid cell in sea-ice-field (grey area in the diagram). In
the diagram, the sea ice extent is 625km2×0.15+625km2×0. 5+625km2×0.8.
Open-sea-area-in-the-sea-ice-field
Sea ice free area in each 25 ×25 km grid cell (white area in the diagram). In the diagram, the sea ice
free area in the sea ice field is 625km2×0.85+625km2×0. 5+ 625km2×0.2.
Polynya
Number of grid cells containing less than 15 % sea ice concentrations in the south of sea ice edge.
The ice edge is defined by a level of ice cover that prevents the survey from being conducted at
normal survey speed (11.5 knots) (IWC, 2003b). Because automatic detection of polynya istechnically difficult, polynya is not considered in this paper.

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Fig. 2. Anomaly of open-sea-area-in-the-sea-ice-field in January from 1978 to 2004 in each IWC
management area (I-VI).

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Fig. 3. Anomaly of open-sea-area-in-the-sea-ice-field in January from 1978 to 2004 in West(130°E-165°E) and East (165°E-170°W) of Area V.

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Fig. 4. Anomaly of open-sea-area-in-the-sea-ice-field in January from 1978 to 2004 in each 10ºlongitudinal sector in Area V.

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APPENDIX
Fig. E-1 ~ 9. Anomaly of sea-ice-extent (sea-ice-field) in January from 1978 to 2004 in each IWC
management area, western and eastern half of each IWC management area and each 10° degree
longitudinal sector.
Fig. A-1 ~ 9. Anomaly of sea-ice-area-in-the-sea-ice-field in January from 1978 to 2004 in each
IWC management area, western and eastern half of each IWC management area and each 10°
degree longitudinal sector.
Fig. O-1 ~ 9. Anomaly of open-sea-area-in-the-sea-ice-field in January from 1978 to 2004 in each
IWC management area, western and eastern half of each IWC management area and each 10°
degree longitudinal sector.

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Fig. E-1. Anomaly of sea-ice-extent (sea-ice-field) in January from 1978 to 2004 in each IWC
management area (I-VI).

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Fig. E-2. Anomaly of sea-ice-extent (sea-ice-field) in January from 1978 to 2004 in each IWC
management area (I-III). Each area is divided into two: West (W) and East (E).

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Fig. E-3. Anomaly of sea-ice-extent (sea-ice-field) in January from 1978 to 2004 in each IWC
management area (IV-VI). Each area is divided into two: West (W) and East (E).

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Fig. E-4. Anomaly of sea-ice-extent (sea-ice-field) in January from 1978 to 2004 in each 10ºlongitudinal sector in Area I.

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Fig. E-5. Anomaly of sea-ice-extent (sea-ice-field) in January from 1978 to 2004 in each 10ºlongitudinal sector in Area II.

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Fig. E-6. Anomaly of sea-ice-extent (sea-ice-field) in January from 1978 to 2004 in each 10ºlongitudinal sector in Area III.
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Fig. E-7. Anomaly of sea-ice-extent (sea-ice-field) in January from 1978 to 2004 in each 10ºlongitudinal sector in Area IV.

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Fig. E-8. Anomaly of sea-ice-extent (sea-ice-field) in January from 1978 to 2004 in each 10ºlongitudinal sector in Area V.

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Fig. E-9. Anomaly of sea-ice-extent (sea-ice-field) in January from 1978 to 2004 in each 10ºlongitudinal sector in Area VI.

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Fig. A-1. Anomaly of sea-ice-area-in-the-sea-ice-field in January from 1978 to 2004 in each IWC
management area (I-VI).

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Fig. A-2. Anomaly of sea-ice-area-in-the-sea-ice-field in January from 1978 to 2004 in each IWC
management area (I-III). Each area is divided into two: West (W) and East (E).

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Fig. A-3. Anomaly of sea-ice-area-in-the-sea-ice-field in January from 1978 to 2004 in each IWC
management area (IV-VI). Each area is divided into two: West (W) and East (E).

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Fig. A-4. Anomaly of sea-ice-area-in-the-sea-ice-field in January from 1978 to 2004 in ach 10ºlongitudinal sector in Area I.

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Fig. A-5. Anomaly of sea-ice-area-in-the-sea-ice-field in January from 1978 to 2004 in each 10ºlongitudinal sector in Area II.

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Fig. A-6. Anomaly of sea-ice-area-in-the-sea-ice-field in January from 1978 to 2004 in each 10ºlongitudinal sector in Area III.
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Fig. A-7. Anomaly of sea-ice-area-in-the-sea-ice-field in January from 1978 to 2004 in each 10ºlongitudinal sector in Area IV.

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Fig. A-8. Anomaly of sea-ice-area-in-the-sea-ice-field in January from 1978 to 2004 in each 10ºlongitudinal sector in Area V.

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Fig. A-9. Anomaly of sea-ice-area-in-the-sea-ice-field in January from 1978 to 2004 in each 10ºlongitudinal sector in Area VI.

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Fig. O-1. Anomaly of open-sea-area-in-the-sea-ice-field in January from 1978 to 2004 in each 10ºlongitudinal sector in each IWC management area (I-VI).

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Fig. O-2. Anomaly of open-sea-area-in-the-sea-ice-field in January from 1978 to 2004 in each IWC
management area (I-III). Each area is divided into two: West (W) and East (E).

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Fig. O-3. Anomaly of open-sea-area-in-the-sea-ice-field in January from 1978 to 2004 in each IWC
management area (IV-VI). Each area is divided into two: West (W) and East (E).

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Fig. O-4. Anomaly of open-sea-area-in-the-sea-ice-field in January from 1978 to 2004 in each 10ºlongitudinal sector in Area I.

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Fig. O-5. Anomaly of open-sea-area-in-the-sea-ice-field in January from 1978 to 2004 in each 10ºlongitudinal sector in Area II.

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Fig. O-6. Anomaly of open-sea-area-in-the-sea-ice-field in January from 1978 to 2004 in each 10ºlongitudinal sector in Area III.
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Fig. O-7. Anomaly of open-sea-area-in-the-sea-ice-field in January from 1978 to 2004 in each 10ºlongitudinal sector in Area IV.

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Fig. O-8. Anomaly of open-sea-area-in-the-sea-ice-field in January from 1978 to 2004 in each 10ºlongitudinal sector in Area V.

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Fig. O-9. Anomaly of open-sea-area-in-the-sea-ice-field in January from 1978 to 2004 in each 10ºlongitudinal sector in Area VI.

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