Identification of Southern Ocean Upwelling From Biogeochemical-Argo Floats

Abstract

The Southern Ocean surrounds the continent of Antarctica, linking the southern regions of the Atlantic, Indian, and Pacific Oceans. It plays a fundamental role in the global overturning circulation, and is a location of intense upwelling of deep water. The deep water that upwells is rich in nutrients, depleted in oxygen (O₂), and enriched in carbon dioxide (CO₂). Southern Ocean upwelling is thus important to the global carbon cycle through its impact on global ocean productivity and through its influence on air-sea CO₂ exchange. However, because of its widespread nature in time and space, and its underpinning weak vertical flows, it is challenging to detect Southern Ocean upwelling from observations. In a novel approach, we utilize measurements from Biogeochemical-Argo floats deployed throughout the Southern Ocean by the Southern Ocean Carbon and Climate Observations and Modeling project, to identify Southern Ocean upwelling through its biogeochemical fingerprint. Our approach detects upwelling by examining surface carbon dioxide ([CO₂]) and oxygen ([O₂]) concentration Relative to Saturation (CORS). Differences between observed (calculated from pH for CO₂) and saturating gas concentrations are used to fingerprint upwelling. Spatial analysis of the identified upwelling reveals a latitudinal gradient in upwelling, with the maximum toward the south of the Antarctic Circumpolar Current. Furthermore, our observational diagnostics provides some support of previous model-based propositions of a focalization of Southern Ocean upwelling on hotspots of complex topography. Ongoing analysis with our approach can provide further insight into the nature and spatio-temporal variability of Southern Ocean upwelling.