The Pacific-Atlantic connection: biogeochemical signals in the southern end of the Argentine shelf

GARZON CARDONA, J.E; MARTINEZ, A.M.; BARRERA, F.; PFAFF, F.; KOCH, B.P.; FREIJE,R.H; GOMEZ, E.A.; LARA, R.J.

JOURNAL OF MARINE SYSTEMS

ELSEVIER SCIENCE BV

Lugar: Amsterdam; Año: 2016

0924-7963

The Cape Horn current transports low-salinity waters from the SE Pacific Ocean into the Atlantic, which are transported further north by the Malvinas current. Biogeochemical signals of this connection were studied by the determination of dissolved organic carbon (DOC), fluorescent dissolved organic matter (FDOMc), DOM humification index (HIX), inorganic nutrients, salinity, temperature, stable isotopic composition of particulate organic nitrogen (δ15N) and chlorophyll ?a? (Chl a) in the southern end of the Argentine shelf in March 2012. Three zones were characterized: waters of the Beagle Channel (BCW), coastal waters (CW) and oceanic waters (OW). Highest values of ammonium, DOC, FDOMc and HIX were found in BCW, the lowest in OW, suggesting that terrestrial input is a main source of ammonium and refractory carbon, which is supported by a highly significant inverse correlation of these parameters with salinity. In turn, lowest concentrations of nitrate, silicate and phosphate were found in BCW and CW, and highest in OW, with highly significant correlations of these nutrients with salinity, indicating the contribution of the saltier, nutrient-rich Antarctic Circumpolar Current to the Pacific-Atlantic connection system. There was an inverse distribution pattern of nitrate, silicate and phosphate and Chl a, which showed highest values in the internal part of BCW. This suggests a role of ammonium and organic ligands in DOM and related iron availability in BCW, in contrast with the low-silicate, high-nutrient, low-chlorophyll frame of the OW and the Subantarctic waters north of the Polar Front. δ15N values were positive in the study region, and same as ammonium reached a maximum in the inner part of the BCW, declining towards OW. This does not support a previous assumption that rainfall on the SE Pacific could be the source of ammonium and hence explain negative δ15N values previously found in the northern Drake Passage. The highly significant inverse correlations of ammonium, FDOMc, HIX, DOC with salinity suggest that continental runoff rather than wet deposition is an important source of ammonium and DOM in the Pacific-Atlantic connection.