Biogeochemistry & Ecophysiology at Duke University
We are seeking motivated scientists to join our lab. Please contact Nicolas Cassar for available positions.
A list of funding support (Duke and external) for graduate and postdoctoral studies can be found here. See also the database provided by the Institute for Broadening Participation (IBP).
ECE researchers Jason J Amsden, Rafael Bento Serpa, and Jeffrey T Glass, along with Nicolas Cassar from Duke University Nicholas School of the Environment are developing an underwater mass spectrometer that can detect dissolved methane and other gases in the ocean. The mass spectrometer is needed to help understand what happens when frozen methane hydrates at the seafloor begin to melt.
Recently, the team ruggedized and packaged the instrument for real-world use and validated it at depths down to 125 meters aboard the UNOLS vessel R/V Hugh Sharp. After 15 years of iterating, this marks the first field deployment of one of their mass spectrometers.
Two Cassar Lab projects highlighted in the Nicholas School of the Environment’s Polar Research Spotlight, showcasing research spanning Arctic tundra ecosystems and Southern Ocean biodiversity.
Excited to share a recent article in The Conversation by PhD student, Katryna Niva: “The ocean is fighting climate change and we’re trying to help it – here’s how.”
Drawing on fieldwork in Halifax Harbour, the piece offers a vivid look at how scientists are exploring marine carbon dioxide removal (mCDR), approaches that build on the ocean’s natural ability to absorb and store carbon. From improvised lab setups on a dive boat to cutting-edge instruments measuring invisible changes in seawater chemistry, the article captures both the ingenuity and the urgency of this work.
You can read the full article here: https://theconversation.com/the-ocean-is-fighting-climate-change-and-were-trying-to-help-it-heres-how-271554
Katryna Niva sailing through Halifax Harbour, investigating the effects of enhancing ocean carbon storage.
Postdoc Ali Merikhi working on the development of a new instrument for measurements of photosynthesis in the ocean.
See Duke Nicholas School Press release
In a new Nature Communications study, we present a comprehensive gene catalog from 218 metagenomes collected during the Antarctic Circumnavigation Expedition, providing one of the most extensive genomic surveys of the Southern Ocean (SO) to date.
We find that the SO harbors a highly distinct and largely uncharacterized genetic repertoire: most genes are absent from functional databases, and a significant fraction lack homologs in existing marine gene catalogs, defining a singular polar genetic seascape.
Southern Ocean are strongly structured by water masses at the scale of the SO, highlighting the role of ocean circulation in shaping microbial function.
We further identify genomic markers linked to key ecological processes, including DMSP cleavage by polar-adapted bacteria, organic matter degradation in the Mertz polynya bloom, and polar adaptations in Pelagibacter.
This work provides a new foundation for understanding Southern Ocean plankton ecology and and how it is changing over time.
Zhang, Y. & Cassar, N. 2025. Contemporary trends in planetary photosynthetic productivity. Nature Climate Change, https://www.nature.com/articles/s41558-025-02390-2.
Zhang, Y., Li, W., Sun, G., Mao, J., Danneberg, M., Xiao, J., Li, Z., Zhao, H., Hu, S., Conghe, S., Cassar, N. 2025. Contrasting biological production trends over land and ocean. Nature Climate Change, https://www.nature.com/articles/s41558-025-02375-1 .
Terrestrial and marine photosynthetic productions are typically studied separately, leaving major gaps in our understanding of planetary carbon uptake and biosphere health. Here, we jointly explored annual dynamics in land and ocean net primary production (NPP) from 2003 to 2021. Using multiple satellite-derived products, we identified an overall planetary NPP increase of 0.11 ± 0.13 PgC/yr (P = 0.05), driven by a significant terrestrial enhancement of 0.20 ± 0.07 PgC/yr (P < 0.001) and partially offset by an oceanic decline of –0.12 ± 0.12 PgC/yr (P = 0.07). These contrasting NPP trends between land and ocean likely reflect their differential sensitivity to climate warming, especially in tropical regions. While land contributes to the strong upward NPP trend, the inter-annual variability in global NPP is predominantly driven by the ocean. Our findings highlight the resilience and potential vulnerability of biospheric carbon productivity in a warming climate, calling for integrated land–ocean monitoring and assessment to support climate mitigation initiatives.
Although the global greening associated with climate change is well documented on land, similar trends in the ocean have not been thoroughly identified. Using satellite observations of ocean chlorophyll a (Chl) concentration, we show that the surface ocean experienced a poleward greening from 2003 to 2022. Contemporaneously, the subtropical regions of the Northern Hemisphere experienced a decrease in Chl. As such, the latitudinal disparity in Chl, as documented by an inequality index, has been increasing over the past two decades, particularly in the Northern Hemisphere. Rising water temperatures may primarily influence the Chl trends. The increasing Chl inequality—marked by “greener green and bluer blue” waters—has the potential to cascade to higher trophic levels, with implications for the fisheries and economies of coastal nations.
See https://www.science.org/doi/10.1126/science.adr9715
Poem by Prof. Sam Illingworth inspired by our research:
The edge extends
past grey-rims
drawn through
old plankton maps.
Where blue thins,
a green-thick seam
unspools,
threading north
with nothing
to net.
Each swell carries
a drift-line echo:
hunger’s anchor,
drifter’s bloom.
No signal,
just a reshaping –
shoal-quiet,
current-bent,
a pattern slipped
from one hinge
to another.
And further down,
the fish-shadows
turn,
but not back –
never back.
See Press coverage:
Biological nitrogen fixation is an important source of new nitrogen, influencing ocean fertility and carbon uptake. While recently documented in Arctic waters, its role in the Southern Ocean remains uncertain. We measured nitrogen fixation along the Western Antarctic Peninsula and at Palmer Station over two austral summer months. Rates from 15N2 assay were below conservative detection limits but detectable under less stringent detection thresholds. Continuous acetylene reduction assay provided further support. nifH gene sequencing identified Gammaproteobacteria as the dominating identified diazotrophs, while Epsilonproteobacteria contributed disproportionally to nifH expression when putative nitrogen fixation was highest. Combined with environmental observations, we hypothesize that vertical water mixing resuspended sediments into the water column and contributed to the limited nitrogen fixation. Given the sporadic and low rates, further research is needed to determine whether nitrogen fixation plays a minor role or represents an overlooked process with biogeochemical significance in the Southern Ocean.
Gittings, J. A., Dall’Olmo, Tang, W., G., Llort, J., Jebri, F., Livanou, E., Nencioli, F., Darmaraki, S., Theodorou, I., Brewin, R. J., Srokoz, M., Cassar, N., Raitsos, D. 2024. An exceptional phytoplankton bloom in the Southeast Magascar Sea driven by African dust deposition. PNAS Nexus, https://doi.org/10.1093/pnasnexus/pgae386.
© 2026 Cassar Lab
Theme by Anders Noren — Up ↑
You must be logged in to post a comment.