New observations of late summer bio-physical sea-ice and snow conditions in the northwestern Weddell Sea

PS1

18-20190321_14 PS1

18-20190322_15 PS1

18-20190316_13 PS1

18-20190316_13* PS1

18-20190315_12 PS1

18_20190222_1 PS1

18-20190314_11 PS1

18-20190313_10 PS1

18-20190313_10* PS1

18-20190312_9 PS1

18_20190223_2 PS1

18_20190224_3 PS1

18_20190307_8 PS1

18_20190304_7 PS1

18_20190301_5 PS1

18_20190226_4 PS1

18_20190302_6

µg chla L-1

0 20 40 60 80

PS1

18-20190321_14 PS1

18-20190322_15 PS1

18-20190316_13 PS1

18-20190315_12 PS1

18_20190222_1 PS1

18-20190314_11 PS1

18-20190313_10 PS1

18-20190312_9 PS1

18_20190223_2 PS1

18_20190224_3 PS1

18_20190307_8 PS1

18_20190304_7 PS1

18_20190301_5 PS1

18_20190226_4 PS1

18_20190302_6

µg chla L-1

0 1 2 3 4 5

Christian Haas ¹ , Stefanie Arndt ¹ , Ilka Peeken ¹

BREMERHAVEN Am Handelshafen 12 27570 Bremerhaven Telefon 0471 4831-0 www.awi.de

WedIce stations during PS118 Ice station

Buoy deployment EM-Bird survey

1

Alfred-Wegener-Institut Helmholtz-Zentrum für Polar- und Meeresforschung

New observations of late summer bio-physical sea-ice and snow conditions in the northwestern Weddell Sea

Introduction: WedIce Project (2019)

Acknowledgements:

We gratefully acknowledge the support of the cruise leader Boris Dorschel and the captain and crew of R/V Polarstern during expedition PS118 (Larsen 2019). Especially, we thank Erika Allhusen and Kerstin Jerosch for supporting the entire sea-ice work on the ice, in the lab as well as in all needed preparations.

Contact:

Christian.Haas@awi.de Stefanie.Arndt@awi.de Ilka.Peeken@awi.de

§ High concentrations of ice algae biomass dominated by large species with maxima in various core sections

(gp: gap, bt: bottom, md: middle)

§ Latitudinal gradient in flagellate

dominated gap water communities

§ Small algae also dominate the low under ice water biomass

md md bt bt bt md bt bt bt bt bt bt bt bt gp bt

Int ice

PS118-20190321_14 PS118-20190322_15

PS118-20190316_13 PS118-20190316_13*

PS118-20190315_12 PS1

18_20190222_1 PS118-20190314_11

PS118-20190313_10 PS118-20190313_10*

PS118-20190312_9 PS1

18_20190223_2 PS1

18_20190224_3 PS1

18_20190307_8 PS1

18_20190304_7 PS1

18_20190301_5 PS1

18_20190226_4 PS1

18_20190302_6

chla mg m-2

0 5 10 15 20 25 30

PS118-20190321_14 PS118-20190322_15

PS118-20190316_13 PS118-20190316_13*

PS118-20190315_12

PS118_20190222_1PS118-20190314_11 PS118-20190313_10

PS118-20190313_10* PS118-20190312_9

PS118_20190223_2PS118_20190224_3PS118_20190307_8PS118_20190304_7PS118_20190301_5PS118_20190226_4PS118_20190302_6

Core length (m)

0,0 0,5 1,0 1,5 2,0 2,5 3,0 3,5

Integrated Ice Chl a

Core length Chl a Under Ice Water Chl a GAP Water Chl a ICE Max.

N S

Sea-ice biology

20190322 20190313

20190307

Composition of sampled snowpack

_§ The late-summer snowpack in the northwestern Weddell Sea is clearly dominated by melt forms

Superimposed ice

§ The thickness of superimposed ice was derived from ice-core texture (thick sections, TEX) and salinity profiles (salt-free sea ice, SAL):

TEX – 12 ± 6 cm / SAL – 16 ± 13 cm

§ Assuming sea-ice and snow densities of ~900 kg m^-3 and 300 kg m^-3,

36/ 48 cm of the seasonal snow are transformed into superimposed ice

§ The study region was characterized by the presence of at least three different ice regimes:

I. Heavily deformed ice near the coast and A68

II. A band of younger, thinner, less deformed ice originating from the Ronne Ice Shelf east of (I)

III. Older, strongly deformed, thick ice originating from the southeastern Weddell Sea in the very east

II I

III

Ice thickness distribution of the four most- southern ice-thickness survey flights close to the iceberg A68. Background of the map shows the Sentinel-1 image of March 07, 2019.

Our helicopter-borne frequency-domain electromagnetic induction (HEM) sounding system Rosie to measure the total sea-ice thickness (ice thickness plus snow depth).

Ice thickness distributions of all flights, from the south (bottom) to the north (top).

Snow depth distribution for all ice stations measured with the MagnaProbe.

Ground-based snow and sea-ice thickness

Overall ice thickness distributions from all ground-based (GEM, blue) and helicopter-based (HEM, red) surveys.

Here we present results of the interdisciplinary Weddell Sea Ice (WedIce) project carried out in the northwestern Weddell Sea on board the German icebreaker R/V Polarstern in February and March 2019, i.e. at the end of the summer ablation period. This is the region of the thickest, oldest ice in the Weddell Sea, at the outflow of the Weddell Gyre.

Within the WedIce project, the following measurements were carried out:

§ 10 airborne ice thickness surveys

§ 15 ice stations working on …

… sea-ice and snow thickness transects

… snow characteristics

… sea-ice coring for physical and biological analysis

§ 3 deployments of drift arrays containing 17 surface velocity profiler (not presented here)

Example of an ice core for station PS118_20190226_4.

While the ice-core texture is visually analyzed from the thick sections (left), salinity is measured from the melted ice core sections.

Snow and the underlying superimposed ice

Sea-ice thickness in the western Weddell Sea

Key points

§ Sea ice conditions in the northwestern Weddell Sea are still severe and have not changed significantly since the last observations carried out in 2004/2006

§ Observed snow depth was comparably low as a consequence of summer’s thaw and therefore its significant transition into superimposed ice

→ The presence of relatively thin, icy snow has strong implications for the sea-ice mass balance, for freshwater oceanography, and for the application of remote sensing methods

§ Standing stocks of integrated sea ice algae biomass are among the highest observed in Antarctica with a slight “seasonal” trend

→ Higher trophic levels in the Western Weddell Seas can be related to concentrated food source from the ice

82A3176 (49)