Argo Floats as a Novel Part of the Monitoring the Hydrography of the Bothnian Sea

Abstract

We made an assessment of the hydrography in the Bothnian Sea based on data collected by the Argo floats during the first 6 years of operation in the Bothnian Sea (2012)(2013)(2014)(2015)(2016)(2017). We evaluated the added value of Argo data related to the pre-existing monitoring data. The optimal usage and profiling frequency of Argo floats was also evaluated and the horizontal and vertical coverage of the profiles were assessed. For now we lose 4 m of data from the surface due to sensor design and some meters from the bottom because of the low resolution of available bathymetry data that is used to avoid bottom collisions. Mean monthly temperature and salinity close to surface and below halocline from the float data were within the boundaries given in literature, although some variation was lost due to scarcity of winter profiles. The temporal coverage of the Argo data is much better than that of ship monitoring, but some spatial variability is lost since the floats are confined in the over 100 m deep area of the Bothnian Sea. The possibility to adjust the float profiling frequency according to weather forecasts was successfully demonstrated and found a feasible way to get measurements from storms and other short term phenomena unreachable with research vessels. First 6 years of operation have shown that Argo floats can be successfully operated in the challenging conditions of the Bothnian Sea and they are shown to be an excellent addition to the monitoring network there. With multiple floats spread in the basin we can increase our general knowledge of the hydrographic conditions and occasionally get interesting data related to intrusions and mixing during high wind events and other synoptic scale events.

Applying area-locked, shallow water Argo floats in Baltic Sea monitoring

“…One drawback in our Argo data is the loss of the topmost metres of the surface layer. The algorithm that protects the SBE CTD sensor of our APEX floats shuts down the measurements well before the sensors reach the surface (Haavisto et al 2018).…”

“…Other basins with similar characteristics should be considered for further float deployments. Another larger area is operated in the Gulf of Bothnia (Haavisto et al 2018;Roiha et al 2018). Other interesting areas for deployment in the Baltic Sea include Bay of Bothnia, Gulf of Gdansk, Bornholm Basin (IOPAN 2018) and Western Gotland Basin.…”

Estimating Currents From Argo Trajectories in the Bothnian Sea, Baltic Sea

“…In winter the upper and deep layers are separated by a weak halocline, which also is a pycnocline, at somewhere between 70 and 90 m depths. The winter time convection reaches this pycnocline as interpreted from Argo data in the Bothnian Sea (Haavisto et al, 2018) and data from fixed oceanographic station at Utö (Haapala and Alenius, 1994).…”

“…Diving pressures were chosen so, that the estimated distance from bottom remained roughly 30 m in the first two missions A (6901901) and B (6902013) (Figure 1) and 10 m in the rest of the missions, based on known topography. For further description of the bottom distance see (Haavisto et al, 2018). The shortest cycles are used when the float has been deployed and recovered to ensure that the float can receive commands via satellite.…”

Baltic Sea Operational Oceanography—A Stimulant for Regional Earth System Research

“…Most of the operational observations cover the coastal water, only a few moorings, Argo profiler and ship stations cover the open Baltic Sea. In recent years, the shallow water Argo profiler has been demonstrated as an efficient tool for monitoring hydrographic conditions in operational mode (Haavisto et al, 2018). There is also a potential to derive the currents from the shallow water Argo profilers (Roiha et al, 2018).…”