Variabilidade do carbono orgânico dissolvido no estreito de Bransfield, Norte da Península Antártica, entre os anos de 2015 e 2016

Abstract

The marine reservoir of dissolved organic carbon (DOC) is equivalent to the atmospheric carbon reservoir and represents the largest reduced carbon stock in the ocean. However, the role of DOC in the global carbon cycle is not fully understood. This study analyzed the distribution of DOC in the water column of the Bransfield Strait, Northern Antarctic Peninsula, in February 2015 and 2016. Data were collected during two summer oceanographic cruises of the NAUTILUS project conducted by the Brazilian High Latitude Oceanography Group. The DOC samples were determined using the “non-purgable organic carbon” method and the results were correlated with hydrographic data such as temperature, salinity and dissolved oxygen. Concentrations of DOC ranged from 40.70 to 122.82 μmol kg−1 in 2015 and from 33.12 to 112.20 μmol kg−1 in 2016. The analyzes showed that the vertical distribution of DOC in the Bransfield Strait can be controlled by a combination of vertical stratification of the water column, vertical export of organic matter and biological activity in the upper mixing layer during the summer. The significant interannual differences observed between DOC concentrations and most of the physicochemical parameters can be related to the El Niño - South Oscillation (ENSO) and Southern Annular Mode (SAM) climate modes. The highest concentrations of DOC, observed in February 2015, were associated with a layer of warm and stratified surface water. The ENSO and SAM climate modes showed positive and weak intensity in 2015, favoring water intrusions from the Antarctic Circumpolar Current. In contrast, the February 2016 campaign was characterized by positive ENSO and SAM events of record intensity. The intensification of the Weddell Gyre induced by these climatic modes, promoted the advection of cold waters, more oxygenated and recently formed from the shelf to the Bransfield Strait, which may have contributed to the lower concentrations of DOC in the water column. This study contributes to a better understanding of the role of DOC in the global carbon cycle in a region of complex circulation and oceanic mix and sensitive to global climate change