Sources and distribution of dissolved organic matter and inorganic nitrogen in waters of the southern Patagonian shelf and northern Drake Passage (51–56°S, 64–69°W)

• Published in: Journal of marine systems 2024-01, Vol.241, p.103893, Article 103893
• Main Authors: Garzón-Cardona, John E., Martínez, Ana M., Koch, Boris P., Krock, Bernd, Palma, Elbio D., Kong, Xianyu, Lara, Rubén J.
• Format: Article
• Language: English
• Subjects: Dissolved organic carbon; Inorganic nitrogen; Southern Patagonian shelf
• ISSN: 0924-7963; 1879-1573
• DOI: 10.1016/j.jmarsys.2023.103893

Dissolved organic matter (DOM) plays a crucial role in the biogeochemistry of coastal ecosystems, particularly nutrient cycling and distribution. Little is known about these processes in the highly productive Southern Patagonian shelf. This study was conducted to better understand the sources, composition, and behavior of DOM and inorganic nutrients in the sector between 51 and 56°S and 64–69°W with particular emphasis on inorganic nitrogen and DOM fractions. Surface water samples taken during late austral summer from the Beagle Channel (BCW), Subantarctic (SAW), Subantarctic Shelf (SASW), Grande Bay (GBW) and Tierra del Fuego Waters (TFW) and were analyzed for properties of fluorescent DOM (FDOM), dissolved organic carbon (DOC) and inorganic nutrients. Data were related to hydrographic and plankton conditions. Highest values of ammonium, DOC, humic-like FDOM (FDOMC and FDOMM peaks) and humification index (HIX) were found in BCW, and the lowest in SAW, suggesting that terrigenous input is a main source of ammonium and refractory carbon in this region, which is supported by a highly significant inverse correlation of these parameters with salinity. In contrast, nitrate, phosphate, silicate and the fluorescence index (FI) were positively correlated with salinity, pointing to the contribution of autochthonous FDOM from the saltier and nutrient-rich Antarctic Circumpolar Current to the Southern Patagonian shelf. In TFW and GBW, high nitrite concentrations, accompanied by elevated values of BIX (biological activity index of DOM), circulation patterns and high particle residence times computed from model results suggest the occurrence of regeneration processes that deserve further investigation of the poorly known dynamics of the nitrogen-rich water in this region. •The Antarctic Circumpolar Current delivers nitrate to the Southern Patagonian Shelf.•Cape Horn Current and Fuegian freshwater sources supply ammonium to the shelf.•An anticyclonic cell and particle retention induce high nitrite in Fuegian seawater.•Fluorescence index point to peatland runoff as source of DOC and refractory humics.•Background DOC in the northern Drake Passage consists mainly of aliphatic compounds.