We are pleased to announce an upcoming 4D-BGC webinar on Thursday, December 4th, at 11:00 EST / 16:00 UTC. Gian Giacomo Navarra from Princeton University will present Causality Analysis of Positive Trend in Southern Ocean Chlorophyll-a. More information below:
Thursday, 4 December 2025, at 11:00 EST / 16:00 UTC
Registration Link: https://washington.zoom.us/meeting/register/sRsVP45gSHGdr7z-aRIwnw
Meeting ID: 991 9491 3012 ● Passcode: 088600
Find your local number: https://us06web.zoom.us/u/kdy6pLJAeC
SCOR Working Group 168 Webinar #6
Title: Causality Analysis of Positive Trend in Southern Ocean Chlorophyll-a
Presenter:
Gian Giacomo Navarra
Princeton University
The positive trend in Southern Ocean chlorophyll-a (Chl-a) concentrations remains a central and unresolved question in ocean biogeochemistry and climate research. Satellite records have suggested regional increases in surface Chl-a, yet the underlying drivers remain debated due to sparse in situ observations and the complex interplay of physical and biogeochemical processes. Here we have used satellite observations with a data-assimilating biogeochemical state estimate (B-SOSE) to investigate the mechanisms shaping the observed positive trend in Southern Ocean Chl-a over the past decade. We perform a suite of diagnostics, including trend analyses, iron budget decomposition, and causality analyses to separate the roles of physical forcing (e.g., freshwater fluxes, mixed layer depth, mesoscale diffusion, and advection) and ecosystem processes (light and iron limitation). Our results highlight a latitudinal difference in terms of what originates the Chl-a trend. In the ACC region, enhanced mixing leading to changes in mixed layer depths and changes in wind stress amplitude are the main causes of the Chl-a increase. In the low-latitude Pacific and near the Antarctica Coast, reduction in light limitation is the main driver.
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4D-BGC seminars are recorded, and previous presentations can be found at https://www.youtube.com/@4D-BGC