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Float activities within MerSea

Why Float Observations? How does it work? Deployment and Scientific results 1- Nordic Seas. 2- Atlantic Ocean 3- Southern Ocean . Apex Float equipped with a Seabird salinity sensor

Southern Ocean

The Southern Ocean contributes significantly to the variability of the climate system through atmosphere-ice-ocean interaction processes. The Weddell Sea in particular is a key source for deep and bottom water of the world oceans. ARGO floats in interior Weddell Sea provide for the first time a means to investigate and monitor processes responsible for the formation of deep and bottom water on a weekly resolution over decadal scales. These data and results will enable modelling applications to properly capture the impact transient fluctuations in the driving forces such as the wind field or the influx from the Antarctic Circumpolar Current
 

A total of 27 ARGO Floats were deployed throughout the austral season 2006/7 during legs 6, 7 and 9 of Polarstern cruise ANT-XXIII, with MERSEA funded deployments occurring during legs 6 (3 floats) and 9 (8 floats). These deployments conclude the float deployments under the MERSEA programme in this ocean region.

Float deployments during RV Polarstern cruise ANT-XXIII. Deployments during legs 6, 7 and 9 are marked red, yellow and black, respectively. Symbols indicate float types: NEMO (+), Apex (*).

 Technical results

Since this (2006/2007) season, all float deployments comply with the ARGO standard of 2000m profiling depth. ISA (Ice Sensing Algorithm) was introduced in 2002 and implemented on all floats deployed since. ISA improved float endurance in ice-covered seas significantly from less than 40% to 80% percent. In particulars, the first generation of ISA equipped floats has now completed its 5th summer season and hence meets the 5-year endurance design criterion originally established for ice-free oceans.

Endurance of floats deployed in the Weddell sea. Each dot represents a float surfacing. Color indicates the remotely sensed, average ice-density at the surfacing site (blue = open water, red = 100% ice coverage). Black dots represent hydrographic profiles collected under ice and transmitted by the iStore (interim storage) algorithm during the subsequent austral summer.

NEMO (Navigating European Marine Observer) floats being prepared onboard Research Vessel
Polarstern for deployment in the Southern Ocean.

 

Scientific results

Of particular interest are the wintertime profiles of temperature and salinity obtained via iStore. These profiles show rapid cooling in fall, with heat flux exceeding 60 Wm-2 for more than a month, before sea-ice formation commences. A detailed analysis of these heat fluxes is in progress.

Temperature and salinity profiles of an iStore equipped float while drifting in the central Weddell Sea. Wintertime profiles terminate at about 20m depth, when the float’s logic decides not to attempt surfacing due to a high likeliness of sea-ice.