The production of Antarctic Bottom Water (AABW) plays a major role in determining the strength of the global Meridional Overturning circulation and, therefore, is an important element in the ocean’s contribution to global climate. The total production rate of AABW is estimated at about 8 Sv with about 50% coming from the Weddell Sea and 25% from the Ross Sea. Recent observations along the Antarctic continental shelves, while discontinuous and sparse, show that AABW has declined in salinity in recent decades, highlighting the importance of continuously monitoring the regions of major AABW outflows.
In the frame of different national research programs the Italian PNRA (Programma Nazionale di Ricerche in Antartide – National Program for Antarctic Research, www.pnra.it) has deployed since 1994 a number of oceanographic moorings in the Ross Sea to monitor the oceanographic condition of the shelf waters, which are precursor of AABW, and to study the biogeochemical cycling in the water column of the largest continental shelf sea and most biologically productive region of Antarctica. This mooring network was modified over the years with changes in scientific focus of the funded projects, and today comprises 4 moorings located in the western part of the Ross Sea (Figure 1, red dots).
Figure 1: The Italian oceanographic mooring network in the Ross Sea deployed in the framework of the Italian PNRA from 1994 to 2014. Red dots indicate moorings active in 2014.
Since 2009, all the moorings were brought together under a single 5-year monitoring program “MORSea - Marine Observatory in the Ross Sea” (http://morsea.uniparthenope.it/) coordinated by the University of Naples "Parthenope", which takes care of the logistics management and the science tasks together with the Italian CNR (Consiglio Nazionale delle Ricerche – National Research Council).
Specifically, the current Italian mooring network comprises:
During the last expedition of the Italian PNRA in the Ross Sea (2013-14) on board of R/V “Italica”, all the mooring of the MORSea project were recovered and redeployed, improving the thermohaline, current and geochemical time series in the Ross Sea. The next maintenance is scheduled for the austral summer 2015-16.
Data and samples are currently distributed according to Italian PNRA policies; for information contact the scientific coordinators (giancarlo.spezie AT uniparthenope.it; and Giorgio Budillon)
Figure 2: Bottom temperature time series at mooring “B” (Joides Basin) from 1995 to 2010 (see figure 1 for the mooring location). The bottom layer, in this area o by the presence of HSSW, show a clear interannual variability with a warmer period during 1996-2001 and a colder years in 2004-2007 (from Ravaioli M., Giglio F., Langone L., Capotondi L., Bergami C., Chiarini F., Dunbar RB, Aliani S., Paschini E., Meloni R., Focaccia P., 2012. Stazioni di ricerca in Antartide - Mooring B. In: (a cura di R. Bertoni, La rete italiana per la ricerca ecologica a lungo termine (LTER-Italia) - Situazione e prospettive dopo un quinquennio di attività (2006-2011), Aracne ed., 216-218, in Italian).
Figure 3: Mooring “D” at Terra Nova Bay polynya (see figure 1 for the mooring location), time series of temperature and salinity acquired by SeaCat SBE16 from February 1996 to December 2000 in the sub-surface layer. Instruments depths and acquisition year are also shown (from Rusciano, E. ,et al., Evidence of atmosphere – sea ice – ocean coupling in the Terra Nova Bay polynya (Ross Sea— Antarctica). Continental Shelf Research (2013), http://dx.doi.org/10.1016/j.csr.2013.04.002i
Figure 4: Salinity record in the benthic layer (about 15 m above the sea bottom) at mooring “G” in the northern Drygalski Trough (see figure 1 for the mooring location). Hourly (thin line) and low-pass filtered (bold line, cut off of 15 days) time series are shown. The higher salinity values indicate a benthic layer occupied by High Salinity Shelf Water, while the fresher values indicate warm intrusions of Modified Circumpolar Deep Water flowing southward into the Drygalski Through providing a crucial source of heat and salt for the Ross Sea (from Budillon, G. et al. Thermohaline variability and Antarctic bottom water formation at the Ross Sea shelf break, Deep Sea Research Part I: Oceanographic Research Papers, Volume 58, Issue 10, October 2011, Pages 1002-1018, ISSN 0967-0637, http://dx.doi.org/10.1016/j.dsr.2011.07.002.).