Ice condition in the subarea 48.6, Southern OceanIn RB5, the SICs in Feb. 2021 were the highest and the SSTs were the lowest for
the years 2016-2021. In March 2021, the highest SICs decreased to nearly the longterm
average while the SST increased accordingly. In the same year, the SICs and
SSTs had two peaks in Feb. and March respectively. In RB4, the SICs during Jan.-
Feb (Austral summer) in 2021 were also the highest since 2016. The sharp spikes of
SST (rapid increasing SST) had become smaller year by year from 2017 to 2021, which
indicates that the SSTs had a cooling phase in 5-6 year periodical cycles corresponding
to an increasing trend in SICs.
Spatial dynamics of SICs with SSTs contour of -1.8°C and -0.8°C were analyzed. It
was found that the ice edges are at approximately -1.8°C and partially broken ices exist
between -1.8°C and -0.8°C when comparing imagery by GIBS and SICs distribution by
AMSRs with SSTs by NOAA.
Daily wind stick plots indicate that the eastward winds could encourage the off-shore
Ekman transport at the end of Feb. and the beginning of Mar. which resulted in late
(slow) ice retrieval in 2021

Ichii, T

Namba, T

Okuda, T

Pompert, J

Sarralde-Vizuete, R. (Roberto)

Somhlaba, S

English

Ice condition in the subarea 48.6, Southern OceanIn RB5, the SICs in Feb. 2021 were the highest and the SSTs were the lowest for
the years 2016-2021. In March 2021, the highest SICs decreased to nearly the longterm
average while the SST increased accordingly. In the same year, the SICs and
SSTs had two peaks in Feb. and March respectively. In RB4, the SICs during Jan.-
Feb (Austral summer) in 2021 were also the highest since 2016. The sharp spikes of
SST (rapid increasing SST) had become smaller year by year from 2017 to 2021, which
indicates that the SSTs had a cooling phase in 5-6 year periodical cycles corresponding
to an increasing trend in SICs.
Spatial dynamics of SICs with SSTs contour of -1.8°C and -0.8°C were analyzed. It
was found that the ice edges are at approximately -1.8°C and partially broken ices exist
between -1.8°C and -0.8°C when comparing imagery by GIBS and SICs distribution by
AMSRs with SSTs by NOAA.
Daily wind stick plots indicate that the eastward winds could encourage the off-shore
Ekman transport at the end of Feb. and the beginning of Mar. which resulted in late
(slow) ice retrieval in 2021.ATLANSUREstudio de los recursos marinos vivos del Atlántico Sur, Océano Austral, Índico y Pacífico

Namba, T.

Sarralde-Vizuete, Roberto

Ichii, Taro

Okuda, Takehiro

Somhlaba, S.

Digital.CSIC

2021 updated analysis of the sea ice concentration (SIC) in research blocks 4 (RB4), and 5 (RB5) of Subarea 48.6 with sea surface temperature (SST) and winds

Ichii, T. (Taro)

Okuda, T. (Takehiro)

Pompert, J.

Repositorio Institucional Digital del IEO

WG-SAMThis paper is presented for consideration by CCAMLR and may contain unpublished data, analyses, and/or conclusions subject to change. Data in this paper shall not be cited or used for purposes other than the work of the CAMLR Commission, Scientific Committee or their subsidiary bodies without the permission of the originators and/or owners of the data.Commission for the Conservation of Antarctic Marine Living ResourcesCommission pour la conservation de la faune et la flore marines de l’AntarctiqueКомиссия по cохранению морских живых pесурсов АнтарктикиComisión para la Conservación de los Recursos Vivos Marinos AntárticosWG-SAM-2021/2111 June 2021Original: English2021 updated analysis of the sea ice concentration (SIC) in researchblocks 4 (RB4), and 5 (RB5) of Subarea 48.6 with sea surfacetemperature (SST) and windsT. Namba, R. Sarralde, T. Ichii, T. Okuda, S. Somhlaba and J. Pompert2021 updated analysis of the sea ice concentration(SIC) in research blocks 4(RB4), and 5(RB5) of Subarea 48.6 with sea surface temperature(SST) and windsT. Namba, R. Sarralde, T. Ichii, T. Okuda, S. Somhlaba and J. PompertAbstractIn RB5, the SICs in Feb. 2021 were the highest and the SSTs were the lowest for the years 2016-2021. In March 2021, the highest SICs decreased to nearly the long-term average while the SST increased accordingly. In the same year, the SICs and SSTs had two peaks in Feb. and March respectively. In RB4, the SICs during Jan.-Feb (Austral summer) in 2021 were also the highest since 2016. The sharp spikes of SST (rapid increasing SST) had become smaller year by year from 2017 to 2021, which indicates that the SSTs had a cooling phase in 5-6 year periodical cycles corresponding to an increasing trend in SICs.Spatial dynamics of SICs with SSTs contour of -1.8°C and -0.8°C were analyzed. Itwas found that the ice edges are at approximately -1.8°C and partially broken ices existbetween -1.8°C and -0.8°C when comparing imagery by GIBS and SICs distribution byAMSRs with SSTs by NOAA.Daily wind stick plots indicate that the eastward winds could encourage the off-shore Ekman transport at the end of Feb. and the beginning of Mar. which resulted in late (slow) ice retrieval in 2021.Results1. Research blocks of Subarea of 48.6 exploratory fisheries (Figure 1)There are four research blocks 2,3,4 and 5 in Subarea of 48.6. Research block 2 islocated north of 60°S and the other blocks are located south of 60°S. In general,research blocks 4 and 5 are covered by ice spatially at almost 100% concentration,except for 4 months from December to March. The SICs of RB4 and RB5 starts todecrease at the beginning of November and then reach their minimum in the middleof February. Then, the SICs starts to increase again and reaches almost 100% spatialcoverage in Apr. and remains at 100% coverage from Apr. through to Oct. (Figure 2).2. Data sources of sea ice concentration (SIC) and sea surface temperature (SST)anomalyThe SIC provided by the University of Bremen (https://seaice.uni-bremen.de/sea-ice-concentration/) based on the Advanced Microwave Scanning Radiome-ter 2 (AMSR2), the photo of Global Imagery Browse Services (GIBS) by NOAA(https://developer.earthdata.nasa.gov/gibs/gibs-api-for-developers,https://worldview.earthdata.nasa.gov) and SIC provided by HYCOM areanalyzed. The resolutions of the ice concentration of the AMSR2 are 3125m and6250m/grid and that of GIBS is 250m/grid (https://seaice.uni-bremen.de/data/amsr2/asi_daygrid_swath/s6250/2019/apr/Antarctic/,https://seaice.uni-bremen.de/data/amsr2/asi_daygrid_swath/s3125/2019/apr/Antarctic3125/). (http://map1.vis.earthdata.nasa.gov/wmts-geo/MODIS_Terra_CorrectedReflectance_TrueColor/default/2019-02-15/EPSG4326_250m). Inaddition, sea surface temperature (SST) is obtained from the ERDDAP of NOAA(https://coastwatch.pfeg.noaa.gov/erddap/index.html).Evaluation of the data for the analysis of the SIC in the subarea 48.6 by three datasources above had been conducted carefully.3. Daily plots of SICs in RB4 and RB5 for 6 years in 2016-2021 (Figure 2).In RB5, the SICs in 2021 were the highest almost over the summer season. Unlikein 2016- 2020, the SICs both in RB4 and RB5 in 2021 had rather peculiar seasonaldynamics as the highest SICs in the beginning and middle of Feb. and then decreaseddynamically at the end of Feb. and in the beginning of Mar., and remained at theaverage in the middle of Mar.4. 4. Four-year comparison of SICs spatial distribution of 15th Jan. and 15th Mar.respectively ( Figure3 & 4) for 2018 - 2021 in RB4 and RB5The spatial coverage of SICs in RB5 in Jan. 2021 was the highest for the period ,but then in Mar. reached the lowest for 2018-2021. However, as the color of SICsindicate, the density of SICs in Jan. 2021 was the second highest with 2019 thehighest. The rather dense ice in 2021 had less spatial coverage.5. Four-year comparison of the SST contours of -1.8 °C (red) and -0.8 °C (black) withSICs chart of 15th Jan. and Mar. (respectively Figure 5 & 6) from 2018 - 2021 inRB4 and RB5, based on ERDDAP of NOAA.-1.8 °C of SST is considered the border between sea ice and water. There are partiallybroken ices located between -1.8 and -0.8°C. In Jan. 2021, both the contours of -1.8°C (red) and -0.8°C (black) were located further north than in 2018-2020, whichindicates that the SST in 2021 was the lowest and the SICs was highest for four years(2018-2021). The color of SICs, indicating the intensity of SICs, corresponds well tothe SST contours. In Mar. 2021, the contours were located almost the same as in2019 and 2020 (not further north) unlike the contours in Jan. 2021.6. Daily SST plot in 2021(top) in RB4 and RB5, 6 years daily plot (middle) and for 20years from 2002-2021 (lower) (Figure 7)SSTs in RB5 in Jan.-Mar. in 2021 (top) indicate that there were two peaks in SSTs,which coincidence with the two peaks of SICs in Jan. and Mar.. The six yearplot(upper) indicates that the SST spikes (sharp increase) became smaller year byyear since 2018 in RB5 and since 2019 in RB4 respectively. The 20 years plot(lower)indicate that there are 5-6 year periodical cycle of SSTs spikes (sharp increase) for20 years in 2002-2021. Higher SST spikes in RB5 occurred in 2003, 2005-2006, 2011,2017 and 2018 and the lower spikes occurred in 2007-2009, 2012-2016 and 2021.7. Seasonal changes in SST anomaly for 6 years in RB5 (lower) with 20 years daily plotof SST (upper) (Figure 8)Dashed red line indicates the daily SST anomaly in 2021, which is the lowest since2016. The SST anomaly in Feb. 2021 was the lowest overall which correspond to thesmallest spikes in 20 years daily SST. The SST anomalies also show the two peaks inJan. and Mar. but not as clear as in Figure 7. The SST plots for 20 years in 2002-2021 (upper) indicates that higher SST spikes in RB5 occurred in 2003, 2005-2006,2011 and 2017-2018 and the lower spikes occurred in 2007-2009, 2012-2016 and 2021.8. Five-year comparison of SICs spatial distribution for Subarea 48.6 by month (Dec.- Mar.), 2016/2017 to 2020/2021 (upper) with year-to-year plots of SST anomalies(lower) (Figure 9)These ice chart cover the whole Subarea 48.6 (called middle scale chart), as thecharts in Figure 3 and 4 cover only the southern part of Subarea 48.6(called smallscale chart).As the SST spike has decreased since 2018, the SICs especially in 15 Feb has increased.The SICs in 15 Dec 2020 was the highest for 2016-2021 then in January, the SICshad decreased dynamically more. However, in Jan. and Feb. 2021, the SICs werestill the highest.Even though the SIC in Dec. was the lowest, the SICs in Mar. was the highest.The SICs in Dec. 2019 was the lowest for 2017-2021 and then dropped down rapidlythrough Jan.-Feb. 2020 and in Mar. the SICs became the highest for 2017-2021.9. Daily stick plots of the south-north(left) and west-east component (right) of wind inRB5, 6years for 2016- 2021 (Figure 10).(https://coastwatch.pfeg.noaa.gov/erddap/griddap/erdQMekm1day)The daily stick plot of the south-north component of wind indicates that there seemsto have been more dominant northwardly wind in Feb. -Mar. 2021, in which thenorth- ward(red) wind could bring the sea ice northward toward off the coast. Theeastward wind at the end of Feb. and the beginning of Mar. 2021 also were rathermore dominant than in 2018, 2019 and 2020 The dominant eastward wind along theAntarctic continent could strengthen the Ekman off-shore transport. Theoretically,the eastward winds in Subarea 48.6 can be propelled by higher air pressure on theAntarctic continent which results in decreasing cloud coverage and increases sunlight.According to the images by GIBS, there was a lot of cloud coverage from Jan. to Feb.2021 so that less sunlight could prevent the surface from heating. The relationshipbetween SICs and winds (or air pressure) is complicated in physics. However inrespect of physical oceanography, so further study and atmospheric analysis of windsand air pressure should be developed with a parameter of cloud albedo.Conclusions1. In RB5 and RB4, the SICs in 2021 had exceptional dynamics and unlike 2016-2020.The SICs dynamics in 2021 had two peaks in Feb. and Mar. which increased andremained higher in Feb and then started to decrease in the end of Feb. and remainedrather low approximately for two weeks. It is rare that the SICs started to increasein early or middle of Feb. which was much earlier than in 2017-2020.2. In RB5 the sharp SSTs spike in 2021 is the smallest for the 6 years 2016-2021 whichis the lowest SST and corresponds to the highest SICs.3. SST of -1.8 °C is the ice edge based on the ice images (GIBS) and SSTs(NOAA).Between -1.8 and -0.8°C, there are partially broken ices which could provide theuseful information on fishable area in RB5 and RB4.4. Dominant eastward winds in the end of Feb. and the beginning of Mar. in 2021 couldencourage the ices to leave off shores which resulted in late ice retrieval. South-northword winds must also have the influence on the ice extension.Related documents• T. Namba, K. Taki and T. Ichii, 2016, Analysis of sea-ice concentration of 48.6_4 and _5 withremote sensing data during the latest four seasons, WG-SAM-16/42 Rev. 1• T. Namba, T. Ichii and T. Okuda, 2017, Update of analysis on sea-ice concentration of southernpart of 48.6 and 58.4.2 for the new research block on expected spawning ground of TOA,WG-FSA-17/10.• T. Namba, T. Ichii and T. Okuda, 2017, Correlation of sea-surface temperature in Ross Sea, WeddellSea and the sea off Peru for the ice analysis,WGFSA-17/08• T. Okuda, T. Namba and T Ichii1, 2018, hypothesis in region for 48.6, 58.4.2, and 58.4.1,WS-DmPH-18/06• H. Pehlke, K. Teschke and T. Brey, 2018, Predicting fishing ground accessibility in the AntarcticWeddell Sea, WG-SAM-18/01• T. Namba, R. Sarralde, S. Somhlaba and J. Pompert, Possibility of predicting sea-ice concentration(SIC) in research block (RB) 48.6-5 (Southern part of Subarea 48.6) using sea surface temperature(SST) in RB 48.6-2 (Northern part of 48.6)WG-FSA-2019/49-20˚-10˚ 0˚ 10˚ 20˚-70˚-60˚-50˚-1000-2000-2000-2000-3000-3000-3000-3000-3000-3000-3000-3000-3000 -3000-3000-3000-3000-3000-3000-3000-3000-3000-3000-1500 48.6_448.6_548.6_348.6_2100020003000400050006000(m)Figure 1 Location and topography of Subarea 48.6. There are four research blocks2,3,4 and 5 in 48.6 where the research block 2 is located north of 60°S with otherblocks south of 60°S.Figure 2. Daily plots of SICs for 6 years in 2016-2021in RB4(lower) and RB5 (upper). (https://seaice.uni-bremen.de/sea-ice-concentration/)  2021 May 04 18:58:47  −10˚−10˚0˚0˚10˚10˚−72˚−72˚−70˚−70˚−68˚−68˚−66˚−66˚−64˚−64˚2020 01 15  2021 May 04 19:01:31  −10˚−10˚0˚0˚10˚10˚−72˚−72˚−70˚−70˚−68˚−68˚−66˚−66˚−64˚−64˚2021 01 15  2021 May 04 18:53:09  −10˚−10˚0˚0˚10˚10˚−72˚−72˚−70˚−70˚−68˚−68˚−66˚−66˚−64˚−64˚2018 01 15  2021 May 04 18:56:01  −10˚−10˚0˚0˚10˚10˚−72˚−72˚−70˚−70˚−68˚−68˚−66˚−66˚−64˚−64˚2019 01 15Figure 3. Four-year comparison of SICs distribution of 15th Jan., in 2018 - 2021 in RB4 and RB5 of souther part of Subarea 48.6 based on AMSR2.  2021 May 04 19:57:22  −10˚−10˚0˚0˚10˚10˚−72˚−72˚−70˚−70˚−68˚−68˚−66˚−66˚−64˚−64˚2020 03 15  2021 May 04 20:00:11  −10˚−10˚0˚0˚10˚10˚−72˚−72˚−70˚−70˚−68˚−68˚−66˚−66˚−64˚−64˚2021 03 15  2021 May 04 19:51:46  −10˚−10˚0˚0˚10˚10˚−72˚−72˚−70˚−70˚−68˚−68˚−66˚−66˚−64˚−64˚2018 03 15  2021 May 04 19:54:35  −10˚−10˚0˚0˚10˚10˚−72˚−72˚−70˚−70˚−68˚−68˚−66˚−66˚−64˚−64˚2019 03 15Figure 4. Four-year comparison of SICs distribution of 15th Mar., in 2018 - 2021 in RB4 and RB5 of souther part of Subarea 48.6 based on AMSR2.  2021 May 10 00:32:16  −10˚−10˚0˚0˚10˚10˚−72˚−72˚−70˚−70˚−68˚−68˚−66˚−66˚−64˚−64˚−0.8−0.8−1.7−1.72020 01 15  2021 May 10 00:44:19  −10˚−10˚0˚0˚10˚10˚−72˚−72˚−70˚−70˚−68˚−68˚−66˚−66˚−64˚−64˚−0.8−0.8−1.7−1.72021 01 150 20 40 60 80 100 %  2021 May 10 00:06:59  −10˚−10˚0˚0˚10˚10˚−72˚−72˚−70˚−70˚−68˚−68˚−66˚−66˚−64˚−64˚−0.8−0.82018 01 15  2021 May 10 00:19:34  −10˚−10˚0˚0˚10˚10˚−72˚−72˚−70˚−70˚−68˚−68˚−66˚−66˚−64˚−64˚−0.8−0.8−1.7−1.72019 01 15Figure 5 Four-year comparison of SICs (based on SSTs(NOAA)) distribution of 15th Jan., in 2018 - 2021 in RB4 and RB5 of the Southern part of Subarea 48.6 based on ERDDAP of NOAA.  2021 May 09 23:50:20  −10˚−10˚0˚0˚10˚10˚−72˚−72˚−70˚−70˚−68˚−68˚−66˚−66˚−64˚−64˚−0.8−0.8−0.8−1.72020 03 15  2021 May 09 23:51:04  −10˚−10˚0˚0˚10˚10˚−72˚−72˚−70˚−70˚−68˚−68˚−66˚−66˚−64˚−64˚−0.8−0.8 −1.7−1.72021 03 150 20 40 60 80 100 %  2021 May 09 23:37:14  −10˚−10˚0˚0˚10˚10˚−72˚−72˚−70˚−70˚−68˚−68˚−66˚−66˚−64˚−64˚−0.8−0.8−0.82018 03 15  2021 May 09 23:38:06  −10˚−10˚0˚0˚10˚10˚−72˚−72˚−70˚−70˚−68˚−68˚−66˚−66˚−64˚−64˚−0.8−0.8−1.7−1.72019 03 15Figure 6. Four-year comparison of SICs (based on SSTs(NOAA)) distribution of 15th Mar., in 2018 - 2021 in RB4 and RB5 of the souther part of Subarea 48.6 based on ERDDAP of NOAA.−2.0−1.5−1.001 15 29 01 15 01 15 29 01 15 292021 JAN 2021 FEB 2021 MAR 2021 APRBlock_4 Block_5Two PeaksBlock_4&5 in 2021−2−1012J A J O J A J O J A J O J A J O J A J O J A J O2016 2017 2018 2019 2020 2021Block_4−2−1012J A J O J A J O J A J O J A J O J A J O J A J O2016 2017 2018 2019 2020 2021Block_5−2020JAN MAY SEP JAN MAY SEP JAN MAY SEP JAN MAY SEP JAN MAY SEP JAN MAY SEP JAN MAY SEP JAN MAY SEP JAN MAY SEP JAN MAY SEP JAN MAY SEP JAN MAY SEP JAN MAY SEP JAN MAY SEP JAN MAY SEP JAN MAY SEP JAN MAY SEP JAN MAY SEP JAN MAY SEP JAN MAY SEP2004 2008 2012 2016 2020Block_5SST realFigure 7. Daily plots of SICs for 6 years in 2016-2021.(https://seaice.uni-bremen.de/sea-ice-concentration/)−2−1012JAN FEB MAR APR MAY JUN JUL AUG SEP OCT NOV DEC The flat means it is covered by ice 100%.2021 Because the SST of 100% can not be detected .2021(dashed)20202019201820172016201720182016201920202021486 block 5SST Anomaly Timeseries of−202JAN MAY SEP JAN MAY SEP JAN MAY SEP JAN MAY SEP JAN MAY SEP JAN MAY SEP JAN MAY SEP JAN MAY SEP JAN MAY SEP JAN MAY SEP JAN MAY SEP JAN MAY SEP JAN MAY SEP JAN MAY SEP JAN MAY SEP JAN MAY SEP JAN MAY SEP JAN MAY SEP JAN MAY SEP JAN MAY SEP2002 2004 2006 2008 2010 2012 2014 2016 2018 2020Block_5SST realFigure 8. Seasonal change in SST for 6 years in RB5 (lower) with 20 years daily plot of SST (upper) (Figure 8)...2016/17 2017/18 2018/19 2019/20 2020/21Dec_15 Dec_15 Dec_15 Ded_15 Dec_15Jan_15 Jan_15 Jan_15 Jan_15 Jan_15Feb_15 Feb_15 Feb_15 Feb_15 Feb_15Mar_15 Mar_15 Mar_15 Mar_15 Mar_15Figure 9. Five-year comparison of SICs distribution for Subarea 48.6 by month (December - March), 2016/2017 to 2020/2021 (upper) with daily plots (red) of SSTs for 6 years in 2016-2021 (lower).South-North component0 0NOV DEC JAN FEB MARNOV DEC JAN FEB MARdominant wind201620172018201920202021NWest-East component00NOVDECJANFEBMARNOVDECJANFEBMARdominant wind201620172018201920202021NFigure 10. Wind stick plots of the south-north(left) and west_east component (right) of wind in RB5, 6years for 2016-2021.

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2021 updated analysis of the sea ice concentration (SIC) in research blocks 4 (RB4), and 5 (RB5) of Subarea 48.6 with sea surface temperature (SST) and winds

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