Different Behaviours of the Ross and Weddell Seas Surface Heat Fluxes in the Period 1972–2015

Abstract

Abstract:Operational analyses and re-analyses, provided by ECMWF for the period 1972-2015, were used to investigate the behaviour of the surface heat fluxes between ocean and atmosphere, estimated via empirical formulae, over the Ross and Weddell Seas. The presence and thickness of sea ice cover, which strongly affects ocean-atmosphere interactions, was estimated through Special Sensor Microwave Imager and Special Sensor Microwave Imager Sounder brightness temperatures. Because of the lack of ice information before 1992, daily averaged ice and snow thickness obtained from the 1992-2012 dataset has been used as a 'climatological year' for the 1972-2015 period. The heat loss in the Ross Sea reached its maximum in 2008 (−98 W·m −2 ) and its minimum (−58 W·m −2 ) in 1980, while in the Weddell Sea, it ranged between −65 W·m −2 (1999) and −99 W·m −2 (2015). Results showed that the surface heat fluxes behaviour in the two seas moved from opposite to synchronous during the study period. The wavelet analysis was applied to evaluate if this result might be linked to the signature of global climate variability expressed by El Niño Southern Oscillation (ENSO) and Southern Annular Mode (SAM). The synchronous behaviour of the surface heat fluxes in the Ross and Weddell seas, observed since 2001, coincides with a change in the energy peak associated to the time scale of the SAM variability, which moved from 32 to 64 months during 1990s. This change generates a common energy peak for the SAM and ENSO with a lagged in phase relationship between the signals, possibly influencing the behaviour of the surface heat fluxes.

Analysis of Physical and Biogeochemical Control Mechanisms on Summertime Surface Carbonate System Variability in the Western Ross Sea (Antarctica) Using In Situ and Satellite Data

“…Amplified effects on both physical and biological water column properties can be observed when SAM+ coincides with La Niña [57], as occurred in 2012. Thus, the later spring sea ice retreat observed in 2012 was likely linked to the different interactions and effects of the two climate modes on the Ross Sea area [25,26,55]. Consequently, the addition of melting freshwater in 2012 resulted in a dilution of A T and C T .…”

Sea surface salinity and temperature in the southern Atlantic Ocean from South African icebreakers, 2010–2017

“…The measuring system is similar on both vessels, with the water inlet sitting at about 5.0 m below the waterline. The nominal accuracy of Sea-Bird TSG SSS is better than 0.01 on the practical salinity scale (PSS), while the resolution is close to 0.001 (www.seabird.com, last access: 29 May 2018); these values are largely sufficient to capture the surface variability (Gaillard et al, 2015). These sensors are regularly calibrated and continuously monitored in-between cruises, and no appreciable sensor drift emerged in the study period.…”

“…These values can be slightly different because of heat exchanges along the seawater path to reach the TSG. Exchanges depend on the flow rate, the volume of water in the circuit, and on the temperature difference between the seawater and the ambient temperature (Gaillard et al, 2015).…”

“…Then, following the World Ocean Circulation Experiment (WOCE) principles and NOAA National Center for Environmental Information (NCEI) database requirements, quality flags (good, suspicious, bad, harbour, icefield) were attributed to the data based on the analysis of several factors, i.e., the detection of insufficient seawater flow, the contamination by air bubbles, and the presence of sea ice (QC-2). The episodic reductions in seawater flow were identified on the basis of a large and increasing difference between SST and SSTH, while SSS remains nearly constant; a threshold difference of 0.2 • C was used for recognizing bad data (Gaillard et al, 2015). The analysis of the conductivity measurements pointed out the presence of episodic quick decreases to underestimated, and often unreliable, values; of course, this is also reflected in SSS, with variations that range between a few decimal places and several units on the PSS.…”

“…In particular, improving the knowledge of sea surface thermohaline features is one of the most important results to be achieved for advancing studies focusing on climate variability in the Southern Hemisphere. Although the Southern Ocean is a key place for atmosphere-ocean interactions at different spatial and temporal scales (Cerrone et al, 2017a, b;Buongiorno Nardelli et al, 2017;Fusco et al, 2018), mesoscale and submesoscale processes acting in the Atlantic sector are still poorly known because of the limited number of available G. Aulicino et al: 2010 south Atlantic sea surface salinity in situ measurements and the coarse accuracy/resolution of the available SSS satellite observations (Boutin et al, 2016). That is particularly true of the ACC region and its fronts, which are characterized by complex dynamics and intense eddy activity (Cotroneo et al, 2013;Frenger et al, 2015).…”