BONUS - GOODHOPE
The oceanic area located South of South Africa is important in various respects:
- It is a critical crossroad for the global thermohaline circulation as it provides an inter-ocean communication route for heat and freshwater anomalies (Sloyan & Rintoul, 2001), and for chemical elements, notably through Mesoscale transports.
- As a part of the Southern Ocean, it is also a key area for the global carbon cycle. The outcropping of deep water masses allows for the exchange of gases such as CO2 between the deep sea and the atmosphere, while the incomplete utilization of nutrients by marine phytoplankton allows the concentration of CO2 in the atmosphere to be substantially greater than would be the case if these nutrients were used efficiently.
- Transport processes in this area could transfer significant amount of terrigeneous matter form the African area southwards into the Antarctic Circumpolar Current.
The scarcity of direct observations has greatly hampered our understanding of this physical, biological and chemical environment.
At the 5 super stations, iron isotopes have been measured in both the dissolved and particulate phases. These data are the first iron isotope data ever measured in a HNLC area. Iron concentrations in both phases have also been measured, which is also quiet rare (for the particulate phase). One profile is shown in Fig. 3, at station S4.
Fig.3 Isotopic composition and conentration of dissloved (DFe) and particulate (PFe) Fe, and dissolved O2 concentration at station S4.
The remarkable "light" iron (negative isotopic composition) signal observed in the core of the Upper Circumpolar Deep Water (UCDW) characterized by a vertical minimum in dissolved O2 concentration suggests a relation between the iron isotope cycle and either the oxygen cycle or the remineralization of organic matter. Compared to the monotonously increasing Fe concentrations, the data clearly illustrate that Fe isotopes provide unique information, invisible from Fe concentrations data. This work is submitted [Abadie et al, Sub.].
The chemical composition of many elements have been measured in the suspended particles at the 5 super stations, notably, Al, Ca, Mn, Fe, Co, Ni, Cu, Sr, Cd, Ba, REE, Th. These kind of data are very rare for most of these elements. They provide diverse information (micronuient cyclings, dissolved particles interactions, land to ocean fluxes etc…). Some have been published (Fe, Co, REE, Ba, Th [Bown et al., 2011; Garcia-Solsona et al., 2014; Abadie et al. Sub.]) other remain to be published.
Participants: F. Lacan, C. Jeandel, C. Pradoux, C. Abadie, E. Garcia-Solsona, M. Labatut, A. Radic
Partners: LEGOS; LEMAR; LPO; VUB (Belgium), LSCE
Fundings: INSU, IPEV, ANR, IFREMER