Key Expoitable Results (KERs)

As the volume of accessible marine pelagic observations increases exponentially, incorporating diverse data types such as metagenomics and quantitative imaging, the need for standardized modelling frameworks becomes critical to predict biogeographic patterns in space and time and across the diverse range of emergent sampling methods. In response, we introduce CEPHALOPOD (Comprehensive Ensemble Pipeline for Habitat modelling Across Large-scale Ocean Pelagic Observation Datasets), a standardized, highly automated and flexible framework designed to integrate and analyse heterogeneous marine data for multi-species habitat modelling following best practices in the field. CEPHALOPOD is built on observational data from federating initiatives such as AtlantECO, OBIS, GBIF, associated with already existing statistical and machine learning methods that enable to extract and model information from heterogeneous, scarce and biased field observations. It is highly automated and follows explicit quality checks informing the user of the predictive accuracy and interpretability of the results. Here, we document our statistical ensemble modelling approach and then assess its strengths and limitations with a virtual ecologist approach. We show how our framework performs in reproducing a range of distributions from biased field samples. Our modelling framework serves as a foundation for the consistent generation of Essential Biodiversity and Ocean Variables (EBVs and EOVs) and carries the potential to significantly advance our comprehension of biodiversity and marine ecosystem functioning. Finally, it provides an unprecedented opportunity to foster collaborations in the field of marine science, sustainable ecological practices, and ultimately contribute to the preservation of global marine biodiversity.

Marine species are increasingly threatened by extreme and compound events, as warming, deoxygenation, and acidification unfold. Yet, the surface and especially the subsurface distribution and evolution of such compound events remain poorly understood. We present the current and projected distributions of compound marine heatwave (MHW), low oxygen (LOX), and high acidity (OAX) events throughout the water column, using observation-based data from 2004 to 2019 and large ensemble Earth system model simulations from 1890 to 2100. Our findings reveal that compound MHW-OAX and OAX-LOX events are prevalent in the low to mid latitudes at the ocean surface. At 200 and 600 m, MHW-OAX and MHW-LOX events are frequent in the high latitudes and parts of the tropics, while OAX-LOX events occur globally. Subsurface compound events are often associated with vertical displacements of water masses, with the climatological vertical gradients of ecosystem stressors typically explaining their occurrence patterns. Projections show a strong rise in compound event frequency over the historical period and under continued global warming, primarily driven by shifts in mean oceanic conditions. The portion of the top 2,000 m affected by extreme or compound events rises from 20 to 98 under 2°C of global warming in a high emissions scenario using a preindustrial baseline, and to 30 using a shifting-mean baseline. However, physical and biogeochemical changes may also lead to regional decreases in subsurface events, highlighting complexities in how warming, deoxygenation, and acidification unfold in the ocean interior. Increasing compound event frequency poses a major threat to marine ecosystems, potentially disrupting food webs and biodiversity.

The contribution of the ocean biological carbon pump to the export of organic carbon at depth has predominantly been assessed by considering sinking particulate matter and vertically migrating organisms. Despite growing recognition of the importance of dynamical pathways that export carbon through upper-ocean mixing and advection, observation-based estimates of their global impact are still lacking. Here, we quantify the values and uncertainties of the export driven by the physical injection pump (PIP) and its interannual variability by leveraging a 4D data-driven time series (1997-2018) of particulate organic carbon concentration (POC) and ocean circulation, as well as 3D fields of climatological dissolved organic carbon (DOC). Vertical diffusion dominates our POC export estimates, but remains the most uncertain process. Assuming maximal diffusivity estimates that are consistent with observations, POC and DOC export amount to 0.37 Pg C yr−1 and 0.48 Pg C yr−1, respectively. The contribution from entrainment and advection is strongly modulated by the POC annual cycle, revealing the critical coupling between biological production and upper-layer mixing in driving the net annual export. Observed interannual signals correlate with a linear combination of El Niño–Southern Oscillation and Southern Annular Mode indices, suggesting that the PIP is connected to intermediate- and mode-water formation dynamics in the Southern Ocean.