Floats

Nordic Seas

Float deployments in the Nordic Seas

In summer 2004 and 2005 all together 25 ARGO (2 equipped with an additional oxygen sensor) floats were deployed in the different basins of the Nordic Seas. They were partly financed by mersea, partly by the german project SFB 512 – E2.

In summer 2007 12 floats are still transmitting data.

Red: Greenland Sea

Blue: Lofoten Basin

Cyan: Islandic Sea

Yellow: Norwegian Basin

Green: south of the Greenland-Scottland-Ridge

Background

During winter the heat loss from the ocean to the atmosphere over the Nordic Seas is very high. The near-surface waters cool and in the Greenland Sea gyre get dense enough to sink to intermediate or large depth. Trough exchange with the boundary currents this newly formed water reaches the East Greenland Current and contributes to the overflow from the Nordic Seas into the Atlantic. The overflow itself is an important driver of the Atlantic Meridional Overturning Circulation.

With the ARGO float data we would like to analyse seasonal to interannual variability of water mass transformation in the deep basins of the Nordic Seas and estimate their importance for the variability of the overflow, which itself vary the Overturning Circulation in the Atlantic.

Dataset

In summer 2004 and 2005 25 ARGO floats were deployed in the Nordic Seas, transmitting more than 1600 profiles in the period September 2004 to May 2007.

Their profile depth is 2000 dbar, except for the 3 Island Sea floats which have profile depths of 1300 dbar.

More than a third of this profiles are from the Greenland Sea, so we decided to start with the delayed mode quality control there.

Greenland Sea Basin

In this area intermediate and deep convection produces the most dense water masses of the whole Nordic Seas. Nevertheless if and how much these water masses contribute to the deep overflow of the Nordic Seas is unclear.

To answer this questions and analyse the seasonal cycle of hydrography we start our work with the float data from this area.

Delayed mode quality control

For the dmqc the software package developed by Lars Böhme (Böhme and Send, 2004) is used. This quality control system has been set up to identify and correct salinity sensor drifts by using historical hydrographic data. An objective mapping method is adapted, which takes special account of the spatial and temporal variations in water mass properties in the specific area. The result is a set of calibrated salinity data with corresponding uncertainties. For implementing this method to the Greenland Sea we add a lot of recent hydrographic data to the reference dataset. From 8 quality controlled floats only two show a clear error and need a correction. The raw salinity data of the other 6 floats were correct within the ARGO-accepted range. In the next step the delayed mode quality control will be applied to the data of the other areas.

Seasonal cycle of hydrography in the Greenland Sea

The mean hydrographic conditions, derived from all float profiles within the Greenland Sea, are dominated by the seasonal cycle of cooling and warming / of freshwater supply from the East Greenland Current. In the winter 2001/2002 and 2006/2007 layers down to 1000 dbar are affected by convection and mixing, whereas during the winters in between a maximum depth of 500 dbar is reached.

Time series of mean temperature, salinity and density Greenland Sea Basin for 0 to 1500m depths.

Float activities within MerSea