https://doi.org/10.20575/00000053
Polar Data Journal, Vol. 8, 23–33, April 2024
Ⓒ 2024 National Institute of Polar Research. This work is distributed
under the Creative Commons Attribution 4.0 International license.

Marine ecosystem monitoring in the sea-ice region of Lützow-Holm
Bay, off Syowa Station, during the icebreaker Shirase cruise of the58th Japanese Antarctic Research Expedition
Kunio T. TAKAHASHI1, 2*, Ryosuke MAKABE1, 2, 3,
Shintaro TAKAO1, 2** and Tsuneo ODATE1,2 (Deceased)

1

National Institute of Polar Research, Research Organization of Information and Systems,
10-3 Midori-cho, Tachikawa, Tokyo 190-8518.

2

Polar Science Program, The Graduate University for Advanced Studies (SOKENDAI), 10-3,
Midori-cho, Tachikawa, Tokyo 190-8518.

3Tokyo University of Marine Science and Technology, 4-5-7 Konan, Minato, Tokyo 108-8477.
*Corresponding author. E-mail: takahashi.kunio@nipr.ac.jp**Current affiliation. National Institute for Environmental Studies, 16-2, Onogawa,
Tsukuba 305-8506.
(Received February 7, 2024; Accepted April 1, 2024)

Abstract: As part of the monitoring program of the Japanese Antarctic Research Expedition(JARE), marine ecological monitoring in the sea-ice region of Lützow-Holm Bay, off Syowa Station,
has been routinely carried out since JARE-52 (2010/11 season) to investigate biological production
and mechanisms in relation to sea-ice. Water temperature, salinity, chlorophyll-a concentration,
macro-nutrients (nitrate, nitrite, phosphate, and silicate), and zooplankton data were collected at six
stations in various sea-ice environments: fast-ice, pack-ice, and ice-free open ocean. The use of an“ice-fence” protected observation equipment (e.g., plankton nets and CTDs) from damage due tosea-ice. This report provides the data obtained during the icebreaker Shirase cruise of the 58th
Japanese Antarctic Research Expedition in the 2016/17 season.

1. Background and Summary
The Southern Ocean marine ecosystems have been changing dramatically due to the effects ofglobal climate change. Among the most obvious physical changes are the regionally contrasting
variations in the extent and seasonality of sea-ice1. The Antarctic sea-ice zone is an ecologicallyimportant region of the Southern Ocean. The seasonal fluctuation of sea-ice formation and melting

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K. T. Takahashi, R. Makabe, S. Takao and T. Odate

events has a significant effect on the life cycle of many organisms living in this region. However,since it is difficult to access by existence of sea-ice in these areas, the accumulation of biologicalknowledge is extremely poor compared to the open ocean region until now. The powerful icebreaking capability of the current Japanese icebreaker Shirase (Japan Maritime Self-Defense Force)raises the possibility of marine observations in the fast-ice and/or permanent ice zone. The shipbased marine ecological monitoring program for the sea-ice region of Lützow-Holm Bay, off Syowa
Station, East Antarctica, began with the 52nd Japanese Antarctic Research Expedition (JARE-52)
during 2010/11 season2. The aim of this program is to investigate biological production andmechanisms in relation to sea-ice.
This report presents the water temperature, salinity, macro-nutrients, phytoplankton
chlorophyll-a concentrations, and zooplankton monitoring data obtained during a cruise by theicebreaker Shirase as part of the JARE-58 (February 2017). Similar datasets collected previously by
JARE have been published in JARE Data Reports 2, 3, 4, 5, 6, 7, 8, 9, 10, 11.

2. Sampling Location
Seawater and plankton samples were collected at six monitoring stations (A, B, C, D, E, andBP) in Lützow-Holm Bay in various sea-ice environments: fast-ice, pack-ice, and ice-free open
ocean (Fig. 1 and Table 1). At the time of sampling, Station A was in the multi-year fast-ice zone,
Station B was in the first-year fast-ice zone, Stations C and D were in the pack-ice zone, andStations E and BP were in the open-ocean zone.

3. Methods
3.1. Protection of the observation equipment
Oceanographic observations in sea-ice areas have the problem that the existence of sea-ice
makes it difficult to use conventional equipment such as plankton net. We devised the “ice-fence”
which guards observation equipment from sea-ice (Fig. 2)12. Lützow-Holm Bay is a region where
fast-ice cover persists during summer and heavy sea-ice states continue. Therefore, we modified theice-fence several time in order to carry out observation under heavy sea-ice conditions andsucceeded in protecting equipment from the damage by sea-ice13.
3.2. Temperature and salinity
Vertical profiles of temperature and salinity were determined at six stations using a
conductivity-temperature-depth (CTD) memory probe (SBE19 plus, Sea-Bird Scientific) attached toa water sampler with six 4-L bottles (SBE 55 ECO, Sea-Bird Scientific). The data were downloaded
from the CTD to a laptop computer immediately after each cast. The CTD sensor was calibrated by
Sea-Bird Scientific during the last boreal summer. The salinity data in this report were not correctedby the bottle salinity data by the salinometer.

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3.3. Chlorophyll a
Vertical water samples were collected over the upper 100 m of the water column using six
Niskin bottles attached to the water sampler, and surface water was collected using a plastic bucket.
Samples for chlorophyll a measurement were collected in two dark bottles (ca. 300 mL) for bulk
measurements using glass-fiber filter (Whatman, GF/F) and size-fractionated measurements todetermine the phytoplankton size composition using Whatman nuclepore membrane filter (pore size:
10 and 2 μm) and a Whatman GF/F. The filters were immediately soaked in N, Ndimethylformamide14, and the pigments were extracted for more than 24 hours. The samples werestored (–18ºC) until onboard analysis. Concentrations of chlorophyll-a were determined
fluorometrically15 with an onboard fluorometer (10-AU; Turner Design, Sunnyvale, CA, USA). The
fluorometer was calibrated against a chlorophyll-a standard (Fujifilm Wako Pure Chemical Corp.,
Osaka, Japan) at a laboratory on-land before the cruise, using a spectrophotometer and the specificabsorption coefficient of chlorophyll-a16. For a fluorometer calibration result, see Shimada et al.
(2020)17.
3.4. Macro-nutrients
Seawater to determine macro-nutrient contents was collected at the time when seawater was
sampled for chlorophyll-a. The sampled water was stored (–18ºC) until analysis in a land laboratory.
The analytical method after melting the frozen samples was performed according to Makabe et al.
(2020)18. The coefficients of variation calculated from five replicates of nitrate, nitrite, silicate, andphosphate were 0.18%, 0.29%, 0.16%, and 0.13%, respectively.
3.5. Zooplankton sampling
Zooplankton samples are collected using a closing net (mouth diameter 0.75 m, mesh size 100μm). To prevent sea-ice from entering the net, an “ice-fence” is employed and the net was closed as
it reaches the surface12. The net was equipped with a flow-meter to estimate the volume of water
filtered, and was hauled vertically from a depth of 150 m to the surface at stations where the bottom
is deeper than 150 m, or from 5 m above the bottom to the surface at stations where the bottom isshallower than 150 m. All samples are fixed immediately in seawater with 5% buffered formalin.

4. Data Records
4.1. Temperature, salinity, macro-nutrients, and chlorophyll-a concentration
All measurements are presented in two data files, named “JARE58_Sea-ice_CTD”, and“JARE58_Chl&Nuts”. The fields in the datasheets in the two files are:
CTDPRS – the pressure (dbar) of the data collected
CTDTMP – the temperature (degree C)
CTDCND – the conductivity (s/m)

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K. T. Takahashi, R. Makabe, S. Takao and T. Odate

CTDSAL – the salinity
THETA – the potential temperature (degree C)
SIGT – the sigma-t (kg m-3)
CRUISE – the cruise code of the vessel
SHIP – the name of the ship on which the sampling was conducted
STNNBR – the name of the station on which the sampling was conducted
DATE – the sampling date (DD/MM/YYYY)TIME – the sampling time (UTC)LATITUDE – the decimal latitude of the sampling station (negative value for South)
LONGITUDE – the decimal longitude of the sampling station (positive value for East)
DEPTH – the sampling depth (m)SIG0 – the sigma-θ (kg m-3)
CHL BULK – total chlorophyll-a concentration (µg l-1)
CHL 10UM – composition of chlorophyll-a in >10 µm fraction (%)
CHL 2UM – composition of chlorophyll-a in 2 – 10 µm fraction (%)
CHL GF/F – composition of chlorophyll-a in <2 µm fraction (%)
NITRAT – concentration of nitrate (µmol l-1 or µmol kg-1)
NITRIT – concentration of nitrite (µmol l-1 or µmol kg-1)
SILCAT – concentration of silicic acid (µmol l-1 or µmol kg-1)
PHSPHT – concentration of phosphate (µmol l-1 or µmol kg-1)
4.2. Zooplankton dataset
Zooplankton monitoring datasets are presented at data file named “JARE58_Seaice_Zooplankton” in three data sheets, species/taxa list, abundance data and wet weight data. The
fields in the dataset are:
JARE number – the JARE number of this sampling season
Ship name – the name of the ship on which the sampling was conducted
Station number – the name of the station on which the sampling was conducted
Latitude – the decimal latitude of the sampling station (negative value for South)
Longitude – the decimal longitude of the sampling station (positive value for East)
Sampling season – two-year Antarctic season based around the austral summer, e.g. “2016-2017”
runs from December 2016 to March 2017
Sampling year – the sampling date year
Sampling month – the sampling date monthSampling day – the sampling date day
Sampling time – the sampling date time (UTC)Sampling depth – the depth of sampling tow
Mesh size – the mesh size of plankton net

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Estimated volume of water filtered – the estimated volume of water filtered using a flow-meter
Abundance – the abundance of each species/taxa
Total abundance – total abundance of all zooplankton in a sample
Number of species/taxa – the number of species/taxa in a sample
Wet weight – the wet weight of each category
Total wet weight - total wet weight of all zooplankton in a sample
5. Technical Validation
5.1. Zooplankton identification
Zooplankton were identified to lowest practical taxonomic level, generally to species or genus,
using a stereo-microscope. Copepodite stages of copepod species, calyptopis stages and furcilia
stages of euphausiid species were subdivided from the adults. The nauplius stages of Rhincalanus
gigas (Copepoda: Calanoida) were distinguished from other calanoid nauplii by their large size andmorphology. Zooplankton abundance was converted to individuals per cubic meter.
The species list for this dataset was checked using the Taxon Match of the World Register ofMarine Species (WoRMS: http://www.marinespecies.org/index.php) name validation tool. WoRMS
is an open-access inventory of all marine species, being >90% complete19. The tool performs across-check of the spelling and taxonomic status of species against the WoRMS database; it returns
standard taxonomic information with valid names.
5.2. Wet weight measurement
Processing of samples was carried out according to the four-step procedure outlined below andshown in Fig. 3.
Step 1: the large-sized zooplankton (more than 10 mm in size) were sorted for the wholesample in the laboratory. Zooplankton were classified into seven categories, and counting number ofindividuals and measured the wet weight each category using an electronic balance (Sartorius
Quintix124-1SJP, readability 0.1 mg).
Step 2: all other species (<10 mm in size) were counted from 1/2 to 1/32 aliquots of the wholesample, and identified to the lowest taxonomic level, generally species or genus, level, using astereo-microscope. We used a Motoda box-type plankton sample splitter to subdivide a sample.
While sorting and counting this size fraction, the wet weight of zooplankton typically reached morethan 10 mg per aliquot.
Step 3: given that the wet weight of zooplankton of 1 mm size or less were hard to sort, thisfraction was estimated by using conversion factors listed in Table 2.
Step 4: the weights obtained in steps 1–3 were summed to give a total wet weight. Zooplankton
abundance was converted to mg m-3. For a detailed description of zooplankton processing for wetweight measurements, see Ukai et al. (2014)28.

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K. T. Takahashi, R. Makabe, S. Takao and T. Odate

6. Figures

20ºS
JARE-58 (Shirase)
30ºS
66ºS

40ºS

BP
E

67ºS

68ºS

50ºS

D
C
B

69ºS

60ºS

70ºS

70ºS

A

36ºE 38ºE 40ºE 42ºE

Syowa Station
40ºE

60ºE

80ºE

100ºE

120ºE

Fig. 1. Location of the sampling sites at Lützow-Holm Bay in February 2017.

Fig. 2. CTD with a water sampler (left) and closing net (right) used in the monitoring program in
the sea-ice region. We used the “ice-fence” which guards observation equipment from sea-ice.

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Fig. 3. Four-step procedure used to measure and to estimate the wet weight of closing net samples.

7. Tables
Table 1. Sampling information of CTD cast and closing net at six stations.

CTD cast
Station

Date
(UTC)

Closing net samplingTime

LatitudeLongitude

Time

LatitudeLongitude

(UTC)

(ºS)

(ºE)

(UTC)

(ºS)

(ºE)

B

14/02/2017

13:44-68.94284

38.92443

14:02-68.94280

38.92432A

15/02/2017

07:24-68.99854

39.18048

07:39-69.00147

39.16450C

15/02/2017

10:51-68.59259

38.72969

11:21-68.59124

38.73656D

16/02/2017

04:19-68.26821

38.49425

04:45-68.26872

38.48760E

16/02/2017

10:50-67.28377

38.16855

11:22-67.29079

38.14853

BP

16/02/2017

13:44-66.83733

37.84389

14:15-66.84676

37.82601

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30

Ikeda (1970)21. [5]: The Oceanographic Society of Japan (1986)22. [6]: Uye et al. (1996)23. [7]: Sato et al. (2001)24. [8]: Ikeda (1990)25. [9]: Ikeda and Imamura (1996)26. [10]: Iguchi et al. (1999)27.

[1]: Wet weight was calculated from the volume of the ellipsoid body (Specific gravity = 1). [2]: Wet weight was calculated from the volume of the cone (Specific gravity = 1). [3]: Beers (1966)20. [4]:Shell length (SL), Trunk length (TL) and Body width (BW) used in this study.

Table 2. Conversion factors between Carbon weight (CW), Dry weight (DW), Wet weight (WW), Body length (L), Bell height (BH), Bell diameter (BD),

K. T. Takahashi, R. Makabe, S. Takao and T. Odate

Polar Data Journal, Vol. 8, 23–33, April 2024

Author contributions
K.T. Takahashi performed the processing of zooplankton samples and writing of the manuscript.
T. Odate directed the JARE-58 monitoring program. R. Makabe and S. Takao carried out thenutrient analysis in the land laboratory and analyzed the sensor data.

Acknowledgments
The authors thank Mr. Tomohide Noguchi, Marine Works Japan Ltd., for collecting samples onboard the icebreaker Shirase. We express our heartfelt appreciation to all members of JARE-58 fortheir support. We also thank the officers and crew of the icebreaker Shirase.

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Data Citations
Takahashi, K. T., Makabe, R., Takao, S., and Odate, T. (Deceased). Marine ecosystem monitoring in thesea-ice region of Lützow-Holm Bay, off Syowa Station, during the icebreaker Shirase cruise of the 58th
Japanese Antarctic Research Expedition. 1.00, Japan, Arctic Data archive System (ADS), 2024.
https://doi.org/10.17592/001.2024011202.

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