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The biennial Ocean Optics Conference is one of the major international meetings devoted to the optics of inland, coastal and ocean waters, bringing together researchers working in ocean colour, remote sensing, phytoplankton ecology, bio-optics, radiative transfer and global change. The 2026 meeting featured more than 270 poster presentations alongside plenary and oral sessions.

 

The PHOTOCLIM team presented four posters covering complementary aspects of the project’s central research themes: understanding and modelling marine photosynthesis, improving the use of observations and satellite data, quantifying uncertainty in primary-production estimates, and investigating how climate-driven environmental variability can affect marine primary production.

 

 

Building a global database for photosynthesis modelling

 

Žarko Kovač presented “Analysis ready photosynthesis parameters data”, a study focused on developing and expanding datasets needed for the development and evaluation of marine primary-production models. The work builds on the global compilation of 6,084 in situ primary-production profiles assembled by Mattei & Scardi (2021), together with existing compilations of photosynthesis–irradiance parameters. The dataset contains 37,722 paired measurements of chlorophyll concentration and primary production, covering observations from 1958 to 2017. 

 

The research uses inverse modelling to derive photosynthesis parameters directly from measured vertical production profiles. It also demonstrated the approach using the long-term Hawaii Ocean Time Series (HOT) and Bermuda Atlantic Time-series Study (BATS), both of which provide more than three decades of observations. These long records allow the seasonal behaviour of photosynthesis parameters to be examined and provide an important basis for testing different approaches to assigning photosynthesis parameters in primary-production models. 

 

This work directly supports PHOTOCLIM's objective of understanding the sensitivity and changing behaviour of marine photosynthesis under environmental change. Reliable, analysis-ready observations and better parameter estimates are essential for determining how photosynthetic performance varies in space and time and for improving the models used to project changes in marine primary production.

 

 

Bringing uncertainty into estimates of marine primary production

 

Marija Bačeković Koloper presented a second study, “Bayesian Estimation of P–I Parameters with Uncertainty Propagation into Watercolumn Primary Production”. The work introduces a hierarchical Bayesian approach to estimating photosynthesis–irradiance (P–I) parameters from replicated 14C incubation measurements.

 

Rather than producing only a single best-fit set of parameters, the Bayesian approach provides full posterior distributions for the parameters describing low-light efficiency, light-saturated photosynthesis, dark respiration and photoinhibition. These parameter distributions are then propagated through the underwater light field and integrated over depth and daylight to obtain a corresponding probability distribution for daily watercolumn primary production. 

 

Using historical observations from Bedford Basin, Nova Scotia, the study demonstrates how uncertainty in individual photosynthesis parameters translates into uncertainty in production profiles and integrated watercolumn production. The analysis therefore provides not only an estimate of primary production, but also a quantitative measure of how certain that estimate is. 

This is particularly relevant to PHOTOCLIM because understanding the fragility of photosynthesis requires distinguishing genuine changes in biological processes from uncertainty associated with observations, parameter estimation and model formulation. Explicit propagation of uncertainty provides a framework for assessing how robust predicted changes in marine primary production are.

 

 

Reconstructing the vertical structure of chlorophyll from satellite observations

 

Frano Matić presented “Optically-enhanced Chlorophyll a profile gap-filling”. The study addresses an important limitation of ocean-colour observations: satellites provide valuable information about surface and near-surface chlorophyll, but cannot directly observe the complete vertical structure of the water column.

 

The research combined long-term in situ chlorophyll-a profiles from the BATS, HOT and CARIACO ocean time-series stations with daily ESA Ocean Colour Climate Change Initiative (OC-CCI) satellite observations of chlorophyll-a and diffuse attenuation coefficient.

 

The analysis first investigated how deeply satellite-derived chlorophyll information is related to the observed vertical profiles. The relationship decreases with depth, and the study found substantial station-to-station differences in the depth to which the satellite signal remains informative. The research then tested machine-learning and statistical approaches for reconstructing complete vertical chlorophyll profiles from satellite information.

 

The results show that satellite chlorophyll contains substantial information about the upper part of the water column, while reconstruction skill decreases toward deeper layers. The study also highlights that overall model performance can conceal substantial depth-dependent errors. 

 

For PHOTOCLIM, this represents an important connection between ocean-colour remote sensing and the vertical processes controlling photosynthesis. Filling gaps in vertical chlorophyll observations can help provide the vertical information on biomass required by primary-production models, while also allowing long-term satellite records to be better connected with in situ observations.

 

 

Investigating the role of temperature variability and noise

 

Marin Vojković presented “The effect of noise in sea surface temperature on marine primary production”. This work examines a less commonly considered aspect of environmental variability: not only the mean temperature and its long-term trend, but also the short-term variability or noise around the seasonal cycle.

 

The study uses a thermal performance function describing the dependence of phytoplankton growth on temperature. By averaging this function over normally distributed temperature fluctuations, the research shows that temperature variability can modify the mean growth rate. In particular, the effect of noise depends on where the environmental temperature lies relative to the optimal and critical temperatures of the organism.

 

Global sea-surface-temperature observations were then separated into their mean, trend, seasonal cycle and residual variability. The residual component was used to quantify the intensity of SST noise at different locations. The poster also examined long-term changes in SST variability at several ocean time-series stations, including HOT, BATS and CARIACO. 

 

Finally, the effect of this variability was explored with a simple stochastic phytoplankton growth model. Simulations with and without SST noise produced different temporal dynamics, illustrating that environmental variability itself can influence the dynamics of marine phytoplankton populations. 

 

The study connects directly to the climate-change dimension of PHOTOCLIM. Climate change does not only alter the mean environmental conditions experienced by phytoplankton; it can also alter the variability around those conditions. Understanding how this variability propagates through the temperature dependence of biological processes is therefore important for assessing the resilience and potential fragility of marine photosynthesis.

 

 

Connecting observations, remote sensing and climate change

 

Together, the four contributions presented at Ocean Optics XXVII illustrate several complementary components of PHOTOCLIM's research programme. The work spans the chain from observations and data preparation, through photosynthesis parameter estimation and uncertainty quantification, to satellite-based reconstruction of biological structure and the investigation of environmental variability and its effects on phytoplankton dynamics.

 

Participation in Ocean Optics XXVII also provided an opportunity to present PHOTOCLIM's research to the wider international ocean-optics community and to exchange ideas with researchers working at the interface of ocean colour, remote sensing, marine ecology and global change: fields that are central to developing a better understanding of how marine photosynthesis may respond to a changing climate.

 

Presented posters can be downloaded below.