Award: OCE-1735436

Biological, chemical, and physical processes work synergistically in the Southern Ocean. In other words, these processes are all connected, and changes to one process have a domino effect on others. Despite knowing that these processes are connected, we don't always know exactly HOW these processes are connected. Our research in the Pacific sector of the Southern Ocean revealed some novel insights into how major nutrients like nitrogen (N) and phosphorus (P) are connected to trace metal nutrients like zinc (Zn) and cadmium (Cd). Our recent expedition in 2021, supported by this project, confirmed trends found in previous studies. For example, dissolved Zn and silicic acid cycle together in the global oceans, based on the ratios found in surface waters that sink at the polar and subpolar fronts of the Southern Ocean. In another example, dissolved Cd and P are also closely related, showing a unique relationship that is mostly linear at higher concentrations of both elements, but changing to a flatter Cd/P ratio at lower concentrations. However, while our 2021 data confirmed these relationships, COVID-related interruptions guided us to reevaluate historic data sets, to investigate if and how these trends changed over time. We discovered that in samples collected during the CLIVAR P16S 2006 expedition, which surveyed the same region (20-60 S, 150 W) at about the same time of year (Jan-Mar), the Cd/P ratio "split" at higher concentrations into two distinct ratios with slightly different slopes. Digging deeper into this "bifurcation", we discovered that the Cd/P ratio of waters found south of the polar front (~55 S) had more Cd per P than in waters found further north (~20 S). While data sets from the Southern Ocean are somewhat limited, this bifurcation at higher Cd and P concentrations in the Pacific sector in 2006 are not observed in our 2021 data (this project) or in similar waters of the southern Indian Ocean (CLIVAR I8S 2007). These differences appear to be authentic and not analytical artifacts, and we continue to review historic and recent data sets for more details to explain these differences in major and trace nutrient relationships, and how they might affect or be affected by connected biological and physical cycles. Last Modified: 01/16/2024 Submitted by: PeterMorton