The Atlantic Water pathways in the Nordic Seas observed by Argo floats (2012)

 

Walczowski W., Goszczko I. and Cisek M. (1)

Corresponding author : Waldemar Walczowski

(1) : Institute of Oceanology Polish Academy of Sciences (IOPAS), Sopot, Poland

Motivation

The Argo Poland program is led by the Institute of Oceanology, Polish Academy of Sciences (IOPAS), which has long and extensive experience in the field measurements performed in the Nordic (Norwegian, Greenland and western Barents) Seas. The warm and salt Atlantic Water (AW) is here a particular medium transporting huge amount of salt and heat into the Arctic Ocean. Properties, variability and transformation of that water mass has been investigated during hydrographical experiments done along the West Spitsbergen Current (WSC) system since the late 1990s. Nevertheless, all of these measurements were collected only during two months of the summer cruise. Last years, this broad data sets of CTD and ADCP measurements could be enhanced in the results gained by means of ARGO floats, also deployed in the mentioned area. This lets to understand and draw more complete pattern of the WSC structure.

Data

Till now all in all 9 floats were deployed by IOPAS from the board of R/V Oceania during three (2009, 2010 and 2012) summer cruises to the Nordic Seas. The localization of deployment has been chosen basing on the measurements conducted in the previous years. Floats were deployed at several places along two sections perpendicular to the boundary current (between 75 and 76°N), north of the Bear Island. 5 of them were launched in the frame of the Argo Poland (Figure 1, Table 1), 4 others were owned by the Alfred Wegener Institute (AWI), Bremerhaven.

All floats were innovative NEMO floats, provided by German OPTIMARE company and were equipped with RAFOS technology as well as Argos or Iridium modems for communication and data transfer. They have been programmed to sample every 3 or 6 hours at the parking level, the cycle time was equal to 3 days. The parking level was set at 500 or 1000 dbar while the profiling level has been as deep as 2000 dbar.

No

Date of Deployment

WMO #

Latitude N

Longitude E

Good Profiles

Days

Until

1

26 June 2009

6900808

75°06.000'

15°01.560'

46

242

11 Feb.2010

2

28 June 2009

6900809

74°59.940'

07°46.560'

0

0

-

3

27 June 2010

6901388

75°00.078'

07°41.340'

1

11

7 July 2010

4

29 June 2010

6901387

75°00.018'

14°57.552'

111

333

28 May 2011

5

02 July 2012

6901902

75°53.174'

11°29.782'

1

5

active

Table 1 : Argo Poland deployments

Figure 1. Locations of floats deployments from Argo Poland done in 2009, 2010 and 2012.

Results

Only 2 of 5 floats were active longer than couple of days. First of them, with WMO#6900808 collected 242 profiles from late June 2009 till February 2010. Second, with WMO#6901387 worked until 28 May 2011, and did 111 good profiles during 333 days. At the beginning, the float circulated in the area of its launching and headed north with the WSC (Figure 2). The changing direction of the drifting float over the Knipovich Ridge was controlled by bathymetry. Recorded decrease of the temperature and salinity values indicates that float left warm and salty AW and flowed into the region dominated by the Arctic type water in the Boreal and Greenland Basins (Figure 3). The mean velocity of the northward advection of the float was about 1.4 cms-1.

Data collected by Argo floats give a possibility of analyzing the hydrographical situation in the mentioned area all year round. Most of the floats are located in area of the Greenland and Lofoten Basins. Although, warmer and more saline Atlantic Water may be observed as northward flow of WSC. Furthermore, combination of Argo data from July 2009 and CTD collected during the summer cruise gave an image more accurately identifying the structure of the WSC over the shallow shelf edge/slope region.

Obtained results have been be also used during the other studies. Some of them investigate changes in the climate of the European Arctic, others allow to validate and evaluate high resolution (2 km) numerical model of the circulation in the Nordic Seas and the Arctic Ocean (Figure 4).

Figure 2. Trajectory of NEMO float WMO#6901387 deployed aboard R/V Oceania in June 2010. Numbers show following positions from 1 to 111 with some incorrect excluded.

Figure 3. Profiles of temperature (upper panel) and salinity (lower panel) collected by NEMO float WMO#6901387 deployed aboard R/V Oceania in June 2010.

Figure 4. Results from the 2 km model and path (green lines) of NEMO float WMO#6900808 deployed aboard R/V Oceania in June 2009. Two main ocean currents are visible: the West Spitsbergen Current (WSC) on the east and the East Greenland Current (EGC) on the west.

References
  • Cisek M., Walczowski W., Wieczorek P. : “Observations of Atlantic Water pathways and velocities in the Nordic Seas”, 3rd Euro-Argo User Workshop, 17-18 June, 2010, Paris, France, poster presentation.
  • Osinski R., Maslowski W., Jakacki J. : “Eddy-resolving ocean modeling of the pan-arctic region”, AWAKE workshop “Ocean influence on climate and cryosphere in the Arctic”, 28-30 November 2011, IOPAS, Sopot, Poland, oral presentation.
  • Goszczko I., Cisek M., Walczowski W. : “Properties and pathways of the Atlantic Water in the Greenland Sea observed with Argo floats”, 4th Argo Science Workshop, 26-28, September 2012, Venice-Lido, Italy, poster presentation.