The Southern Ocean plays a key role in global biogeochemical cycles through the redistribution of nutrients and trace elements by large-scale circulation. Among these, cadmium (Cd) exhibits nutrient-type behaviour and is closely linked to phosphate, yet regional variability in its distribution and controlling processes remains insufficiently constrained.
Here, we investigate dissolved Cd distributions along the GEOTRACES I09S transect (IN2024_V01; ~115°E, 30–65°S) in the Australian sector of the Southern Ocean. Using high-resolution hydrographic and trace element observations obtained through trace metal clean sampling and ICP-MS analysis, we assess the influence of water mass structure, frontal systems, and biogeochemical processes on Cd distributions and Cd–PO₄ relationships.
Cd concentrations display a pronounced vertical gradient, with depleted surface waters and elevated concentrations in intermediate and deep waters. Variability across frontal zones reflects shifts in dominant water masses and mixing regimes. The Cd–PO₄ relationship shows a strong positive correlation consistent with nutrient-type behaviour, while regional differences in slope and scatter indicate variations in biological cycling and hydrographic structure. Deviations from the canonical Cd–PO₄ relationship, expressed as Cd* distributions show distinct north–south contrasts within both surface and intermediate waters, highlighting regional differences in biological utilisation, remineralisation, and water mass transport.
These results highlight the dominant role of hydrographic structure in shaping Cd distributions while demonstrating regional biogeochemical modification across the Australian sector of the Southern Ocean.

How much CO₂ do marine bacteria produce during respiration? Ocean carbon budgets assume the answer lies in the stoichiometry of organic matter, converting O₂ consumption to CO₂ fluxes using a fixed respiratory quotient (RQ, dimensionless number calculated as the ratio of CO₂ produced to O₂ consumed during cellular respiration). Here, we reveal for the first time that cellular metabolism itself can override this assumption. Using membrane inlet mass spectrometry and controlled bacterial cultures, we show that iron (Fe) limitation causes a fourfold collapse in RQ, from ~1.1 to ~0.3, independently of substrate stoichiometry. Mechanistically, cells adapt their metabolism to redirect carbon into biomass rather than release it as CO₂. These laboratory findings were validated in the Southern Ocean during the SWINGS expedition, combining conventional and isotopic approaches including ¹³C-stable isotope incubations and single-cell analyses. Accounting for variable bacterial RQ reveals systematic biases exceeding 20% in O₂-based estimates of net community production across HNLC regions and reframes the role of heterotrophic bacteria from remineralizers to “carbon storers”. At global scale, these findings establish partial carbon oxidation as a process that overrides the stoichiometric assumptions, one that must be explicitly represented in biogeochemical models.

The cold desert soils of Antarctica host unique microbial communities adapted to harsh environmental conditions. While much attention has focussed on climate change in the Antarctic Peninsula, far less consideration has been given to its effects on microbial communities across the ~40,000 km² of ice-free land in the rest of the continent. Here, rising wind speeds are expected to increase aridity with unknown consequences for regional microbial communities, many of which are already living at the edge of habitability. Using soil samples collected across Antarctica, we quantified rates of atmospheric trace gas oxidation (aerotrophy, a key energy metabolism) and carbon fixation (both light- and H₂-stimulated). Modelling these results against soil physicochemistry and landscape geomorphology variables revealed that soil total organic carbon (TOC) and moisture are key drivers of these fundamental ecosystem processes. Aerotrophy is a widespread process powering the generation of new organic carbon in these nutrient-depleted soils, thus any shift in these metabolic rates could have wide-ranging consequences for Antarctic soil ecosystems and biogeochemical cycling. This work provides critical baseline data to inform how projected climate futures will impact Antarctica’s unique cold desert microbial communities and regional carbon cycling.

Microbial life in the ocean drives global biogeochemical cycles, yet we still lack a quantitative understanding of how cellular molecular processes translate into ecosystem-scale outcomes. Molecular approaches such as genomics, transcriptomics, and proteomics have transformed microbial oceanography, whereas physiological research has stagnated. While 'omics has revealed patterns in marine microbial diversity and metabolic pathways, it largely provides only static snapshots of physiological potential, and biological rates and biogeochemical fluxes remain the main currencies in biogeochemistry models. This gap limits our ability to accurately model microbial contributions to ocean processes, particularly important to correctly assess the effects of global change.
This presentation provides an overview of the SCOR working group “Physiology and Rates in Microbial Oceanography” (PRIMO, primoscorwg.org), a collective of physiologists, molecular biologists, and modellers organised around a common aim: how do we translate the wealth of information on physiological potential from ‘omics-based studies to quantifiable physiological rates and, ultimately, to biogeochemical processes and their representation in Earth system models? At the halfway point of the working group’s mandate, we reflect on limitations and lessons learned to foster collective progress toward the development of a core suite of model-ready measurements that are harmonised, low-cost, and high throughput to promote co-measurement of ‘omics and rates.

Melting of the Antarctic cryosphere is increasingly recognised within the scientific community as a potential significant source of trace metals to sustain Antarctic coastal productivity. However, ice shelf-related biogeochemical (including trace metal) processes remain poorly constrained in both observational and modelling studies. During an austral autumn (March-April 2025) research voyage aboard RSV Nuyina, comprehensive and rare physical, biological, and chemical observations were collected near the Denman Glacier in East Antarctica. Concentrations of dissolved iron (dFe) combined with water mass fractions derived from stable oxygen isotopes provided insights into dFe inputs associated with the meltwater pump. We observed high subsurface (1.7-2.7nM, 250-400m) dFe concentrations in proximity to the ice shelf front, and dFe depleted Antarctic Surface Water (0.09-0.7nM, 0-250m). To investigate these processes leading to the high subsurface concentrations, we implemented Langrangian particles within a high-resolution ocean–sea ice–ice shelf model of the Denman region (MITgcm) to examine the pathways of Circumpolar Deep Water across the continental shelf, tracing its trajectory beneath the ice shelf and emergence as a freshwater buoyant plume. This estimates of potential glacier-derived iron provides a critical quantitative benchmark for future research focusing on integrating ice shelf processes into biogeochemical models.