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

GARZÓN CARDONA JOHN EDISON; MARTÍNEZ ANA MARIA; BARRERA FACUNDO; PFAFF FLORIAN; BORIS P. KOCH; FREIJE RUBEN HUGO; GÓMEZ EDUARDO; LARA RUBEN JOSE

JOURNAL OF MARINE SYSTEMS

ELSEVIER SCIENCE BV

Lugar: Amsterdam; Año: 2016 p. 95 - 101

0924-7963

The Cape Horn Current transports low-salinity waters from the SE Pacific Ocean into the Atlantic, which aretransported further north by the Malvinas current. Biogeochemical signals of this connection were studied bycharacterization of dissolved organicmatter (DOM) by determination of dissolved organic carbon (DOC), fluorescentdissolved organic matter (FDOMc), and DOMhumification index (HIX). Further, inorganic nutrients, salinity,temperature, stable isotopic composition of particulate organic nitrogen (δ15N) and chlorophyll a (Chla) weremeasured in the southern end of the Argentine shelf inMarch 2012. Three water types were characterized: watersof 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 inOW, suggesting that terrigenous input is a main source ofammoniumand refractory carbon, which is supported by a highly significant inverse correlation of these parameterswith salinity. In turn, lowest concentrations of nitrate, silicate and phosphate were found in BCWand CW,and highest in OW, with highly significant correlations of these nutrients with salinity, indicating the contributionof the saltier, nutrient-rich Antarctic Circumpolar Current (ACC) to the Pacific-Atlantic connection system.In general there was an inverse distribution pattern between Chla and those nutrients contributed by the ACC,which is consistent with the transition from coastal waters to the low-silicate, high-nitrate, low-chlorophyll,iron-limited setting of the Subantarctic oceanic waters north of the Polar Front. In contrast, in the low-salinity,internal BCW, high values of ammonium, DOC, HIX and FDOM indicate continental inputs, likely including ironcomplexes, which could have led to the observed high Chla values. δ15N valueswere positive in the study region,and same as ammonium, reached a maximumin the inner part of the BCW, declining towardsOW. This does notsupport a previous assumption that rainfall on the SE Pacific could be the source of ammoniumand hence explainnegative δ15N values previously found in the northern Drake Passage. The highly significant inverse correlationsof ammonium, FDOMc, HIX, and DOC with salinity suggest that continental runoff rather than wet deposition isan important source of ammonium and DOM in the Pacific-Atlantic connection.