Scholars@Duke
Nicolas Cassar

Nicolas Cassar

Lee Hill Snowdon Professor of Biogeochemistry
Earth and Climate Sciences
nicolas.cassar@duke.edu
Box 90328, Durham, NC 27708
Grainger Hall, 9 Circuit Drive (GH5119), Nicholas School of the Environment, Durham, NC 27708

Selected Publications

Evidence of limited N2 fixation in the Southern Ocean

Journal Article Communications Earth and Environment · December 1, 2025 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 Wester ... Full text Cite

Overview of BLOOFINZ/INDITUN investigations of the southern bluefin spawning region off northwest Australia, January–March 2022

Journal Article Deep Sea Research Part II Topical Studies in Oceanography · December 1, 2025 Southern Bluefin Tuna (SBT, Thunnus maccoyii) range broadly in rich feeding grounds of the Southern Hemisphere but spawn only in a small tropical region off northwestern Australia directly downstream of the Indonesian Throughflow. Here, we describe goals, ... Full text Cite

The overlooked contribution of the seasonal mixed layer pump to carbon export in low-latitude oceans.

Journal Article Nature communications · November 2025 The seasonal mixed layer pump (MLP) is an important pathway transporting organic carbon from the upper ocean to the ocean interior. While the MLP's export role has been well-studied in high latitudes, its contribution in low latitudes remains uncertain. He ... Full text Cite

Nitrogen fixation in Arctic lichens and mosses: A survey across circumpolar subzones.

Journal Article The Science of the total environment · October 2025 Nitrogen bioavailability frequently constrains primary production in the Arctic with tundra communities vulnerable to ecological and metabolic disruption from climate variability. Diazotrophs associated with lichens and mosses are the primary source of new ... Full text Cite

Thermodynamics and kinetics of the isotopic equilibration of nitrogen gas (N2) in water: Implications for biological N2 fixation experiments

Journal Article Limnology and Oceanography Methods · August 1, 2025 Better characterization of biological N2 fixation along with its controlling factors is needed for improved projections of the feedbacks between nitrogen cycling, ecosystems productivity, and climate dynamics. Building on an ongoing community ef ... Full text Cite

Contrasting biological production trends over land and ocean

Journal Article Nature Climate Change · August 1, 2025 Terrestrial and marine ecosystems constitute the primary components of the Earth’s biosphere, yet their photosynthetic productions are typically studied separately, which limits understanding of planetary carbon uptake and biosphere health. Here, using mul ... Full text Cite

An upper-mesopelagic-zone carbon budget for the subarctic North Pacific

Journal Article Biogeosciences · July 10, 2025 Mesopelagic zone (MZ) carbon budgets comparing supply with demand can be difficult to constrain due to the temporal and spatial offsets between key sources and sinks, their associated uncertainties, and potential sampling biases. To address these challenge ... Full text Cite

Control system for an underwater coded aperture miniature mass spectrometer

Journal Article Green Analytical Chemistry · June 1, 2025 In situ measurements of the spatiotemporal distribution of dissolved gases in the ocean are useful for a wide variety of applications including monitoring biogeochemical cycles (e.g., methane, oxygen, and carbon dioxide fluxes), detecting pollutants, study ... Full text Cite

Greener green and bluer blue: Ocean poleward greening over the past two decades.

Journal Article Science (New York, N.Y.) · June 2025 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 surfac ... Full text Cite

Emergent patterns of patchiness differ between physical and planktonic properties in the ocean.

Journal Article Nature communications · February 2025 While a rich history of patchiness research has explored spatial structure in the ocean, there is no consensus over the controls on biological patchiness and how physical-ecological-biogeochemical processes and patchiness relate. The prevailing thought is ... Full text Cite

Nitrogen concentration shapes the size structure and the functional diversity of phytoplankton communities in the southern Indian Ocean.

Journal Article ISME communications · January 2025 Phytoplankton are fundamental to marine ecosystems, biogeochemical cycling and climate regulation. Their community structure and productivity are shaped by biotic and abiotic factors, notably temperature and macronutrient concentrations. Climate change is ... Full text Cite

An exceptional phytoplankton bloom in the southeast Madagascar Sea driven by African dust deposition.

Journal Article PNAS nexus · October 2024 Rising surface temperatures are projected to cause more frequent and intense droughts in the world's drylands. This can lead to land degradation, mobilization of soil particles, and an increase in dust aerosol emissions from arid and semi-arid regions. Dus ... Full text Cite

The influence of phytoplankton size fractions on the carbon export ratio in the surface ocean

Journal Article Ecological Modelling · September 1, 2024 The fraction of primary production exported out of the surface ocean, also known as the carbon export ratio, is believed to be a function of phytoplankton size fractions. However, this relationship is often elusive in observations. Here, we explore this re ... Full text Cite

Size-Fractionated Primary Production Dynamics During the Decline Phase of the North Atlantic Spring Bloom

Journal Article Global Biogeochemical Cycles · July 1, 2024 The North Atlantic is a region of enhanced biogeochemical and climatological importance for the global ocean as it is the site of one of the largest seasonal phytoplankton blooms on the planet. However, there is a lack of understanding of how phytoplankton ... Full text Cite

Fronts divide diazotroph communities in the Southern Indian Ocean.

Journal Article FEMS microbiology ecology · July 2024 Dinitrogen (N2) fixation represents a key source of reactive nitrogen in marine ecosystems. While the process has been rather well-explored in low latitudes of the Atlantic and Pacific Oceans, other higher latitude regions and particularly the Indian Ocean ... Full text Cite

Evidence for Kilometer-Scale Biophysical Features at the Gulf Stream Front

Journal Article Journal of Geophysical Research Oceans · March 1, 2024 Understanding the interplay of ocean physics and biology at the submesoscale and below (<30 km) is an ongoing challenge in oceanography. While poorly constrained, these scales may be of critical importance for understanding how changing ocean dynamics will ... Full text Cite

Microbial respiration in contrasting ocean provinces via high-frequency optode assays

Journal Article Frontiers in Marine Science · January 1, 2024 Microbial respiration is a critical component of the marine carbon cycle, determining the proportion of fixed carbon that is subject to remineralization as opposed to being available for export to the ocean depths. Despite its importance, methodological co ... Full text Cite

Corrigendum: Data-driven modeling of dissolved iron in the global ocean (Front. Mar. Sci., (2022), 9, (837183), 10.3389/fmars.2022.837183)

Journal Article Frontiers in Marine Science · January 1, 2024 In the original article, there are two issues in Figure 4. First, cross “artifacts” appear at the longitude and latitude of 0 degrees in the panels showing the coefficient variability (C.V.) of the Support Vector Machine and Artificial Neural Network (ANN) ... Full text Cite

Global oceanic diazotroph database version 2 and elevated estimate of global oceanic N2 fixation

Journal Article Earth System Science Data · August 15, 2023 Marine diazotrophs convert dinitrogen (N2) gas into bioavailable nitrogen (N), supporting life in the global ocean. In 2012, the first version of the global oceanic diazotroph database (version 1) was published. Here, we present an updated versi ... Full text Cite

Evaluation of new and net community production estimates by multiple ship-based and autonomous observations in the Northeast Pacific Ocean

Journal Article Elementa · June 16, 2023 New production (NP) and net community production (NCP) measurements are often used as estimates of carbon export potential from the mixed layer of the ocean, an important process in the regulation of global climate. Diverse methods can be used to measure N ... Full text Cite

Open science resources from the Tara Pacific expedition across coral reef and surface ocean ecosystems.

Journal Article Scientific data · June 2023 The Tara Pacific expedition (2016-2018) sampled coral ecosystems around 32 islands in the Pacific Ocean and the ocean surface waters at 249 locations, resulting in the collection of nearly 58 000 samples. The expedition was designed to systematically study ... Full text Cite

Multiscale Temporal Variability of the Global Air-Sea CO2 Flux Anomaly

Journal Article Journal of Geophysical Research Biogeosciences · June 1, 2023 The global air-sea CO2 flux (F) impacts and is impacted by a plethora of climate-related processes operating at multiple time scales. In bulk mass transfer formulations, F is driven by physico- and bio-chemical factors such as the air-sea partia ... Full text Cite

Can We Estimate Air-Sea Flux of Biological O2 From Total Dissolved Oxygen?

Journal Article Global Biogeochemical Cycles · September 1, 2022 In this study, we compare mechanistic and empirical approaches to reconstruct the air-sea flux of biological oxygen ((Formula presented.)) by parameterizing the physical oxygen saturation anomaly (ΔO2[phy]) in order to separate the biological co ... Full text Cite

Phytoplankton size-class contributions to new and regenerated production during the EXPORTS Northeast Pacific Ocean field deployment

Journal Article Elementa · July 29, 2022 The NASA EXport Processes in the Ocean from RemoTe Sensing (EXPORTS) program was established to better quantify the pathways of the biological carbon pump in order to gain a more comprehensive understanding of global carbon export efficiency. The summer 20 ... Full text Cite

Data-Driven Modeling of Dissolved Iron in the Global Ocean

Journal Article Frontiers in Marine Science · May 19, 2022 The importance of dissolved Fe (dFe) in regulating ocean primary production and the carbon cycle is well established. However, the large-scale distribution and temporal dynamics of dFe remain poorly constrained in part due to incomplete observational cover ... Full text Cite

Exploring the coupled ocean and atmosphere system with a data science approach applied to observations from the Antarctic Circumnavigation Expedition

Journal Article Earth System Dynamics · November 30, 2021 The Southern Ocean is a critical component of Earth's climate system, but its remoteness makes it challenging to develop a holistic understanding of its processes from the small scale to the large scale. As a result, our knowledge of this vast region remai ... Full text Cite

Inorganic and organic carbon and nitrogen uptake strategies of picoplankton groups in the northwestern Atlantic Ocean

Journal Article Limnology and Oceanography · October 1, 2021 Picoplankton populations dominate the planktonic community in the surface oligotrophic ocean. Yet, their strategies in the acquisition and the partitioning of organic and inorganic sources of nitrogen (N) and carbon (C) are poorly described. Here, we measu ... Full text Cite

Linking Southern Ocean Mixed-Layer Dynamics to Net Community Production on Various Timescales

Journal Article Journal of Geophysical Research Oceans · October 1, 2021 Mixed-layer dynamics exert a first order control on nutrient and light availability for phytoplankton. In this study, we examine the influence of mixed-layer dynamics on net community production (NCP) in the Southern Ocean on intra-seasonal, seasonal, inte ... Full text Cite

Decomposing the Oxygen Signal in the Ocean Interior: Beyond Decomposing Organic Matter

Journal Article Geophysical Research Letters · September 28, 2021 In the subsurface ocean, O2 depleted because of organic matter remineralization is generally estimated based on apparent oxygen utilization (AOU). However, AOU is an imperfect measure of oxygen utilization because of O2 air-sea disequ ... Full text Cite

Widespread phytoplankton blooms triggered by 2019-2020 Australian wildfires.

Journal Article Nature · September 2021 Droughts and climate-change-driven warming are leading to more frequent and intense wildfires1-3, arguably contributing to the severe 2019-2020 Australian wildfires4. The environmental and ecological impacts of the fires include loss ... Full text Cite

Decline in plankton diversity and carbon flux with reduced sea ice extent along the Western Antarctic Peninsula.

Journal Article Nature communications · August 2021 Since the middle of the past century, the Western Antarctic Peninsula has warmed rapidly with a significant loss of sea ice but the impacts on plankton biodiversity and carbon cycling remain an open question. Here, using a 5-year dataset of eukaryotic plan ... Full text Cite

An operational overview of the EXport processes in the ocean from RemoTe sensing (EXPORTS) northeast pacific field deployment

Journal Article Elementa · July 7, 2021 The goal of the EXport Processes in the Ocean from RemoTe Sensing (EXPORTS) field campaign is to develop a predictive understanding of the export, fate, and carbon cycle impacts of global ocean net primary production. To accomplish this goal, observations ... Full text Cite

Low diversity of a key phytoplankton group along the West Antarctic Peninsula

Journal Article Limnology and Oceanography · June 1, 2021 The West Antarctic Peninsula (henceforth “Peninsula”) is experiencing rapid warming and melting that is impacting the regional marine food web. The primary phytoplankton groups along the Peninsula are diatoms and cryptophytes. Relative to diatoms, there ha ... Full text Cite

Mesoscale temporal wind variability biases global air-sea gas transfer velocity of CO2 and other slightly soluble gases

Journal Article Remote Sensing · April 1, 2021 The significance of the water-side gas transfer velocity for air-sea CO2 gas exchange (k) and its non-linear dependence on wind speed (U) is well accepted. What remains a subject of inquiry are biases associated with the form of the non-linear r ... Full text Cite

The Intensifying Role of High Wind Speeds on Air-Sea Carbon Dioxide Exchange

Journal Article Geophysical Research Letters · March 16, 2021 While it has been known that wave breaking and bubble generation at high wind speeds enhance air-sea carbon dioxide (CO2) exchange rates (F), quantification of their contribution at the global scale remains a formidable challenge. There is urgen ... Full text Cite

Investigating the microbial ecology of coastal hotspots of marine nitrogen fixation in the western North Atlantic.

Journal Article Scientific reports · March 2021 Variation in the microbial cycling of nutrients and carbon in the ocean is an emergent property of complex planktonic communities. While recent findings have considerably expanded our understanding of the diversity and distribution of nitrogen (N2 Full text Cite

Global Estimates of Marine Gross Primary Production Based on Machine Learning Upscaling of Field Observations

Journal Article Global Biogeochemical Cycles · March 1, 2021 Approximately half of global primary production occurs in the ocean. While the large-scale variability in net primary production (NPP) has been extensively studied, ocean gross primary production (GPP) has thus far received less attention. In this study, w ... Full text Cite

New insights into the distributions of nitrogen fixation and diazotrophs revealed by high-resolution sensing and sampling methods.

Journal Article The ISME journal · October 2020 Nitrogen availability limits marine productivity across large ocean regions. Diazotrophs can supply new nitrogen to the marine environment via nitrogen (N2) fixation, relieving nitrogen limitation. The distributions of diazotrophs and N2 Full text Cite

Using global reanalysis data to quantify and correct airflow distortion bias in shipborne wind speed measurements

Journal Article Atmospheric Measurement Techniques · June 30, 2020 At sea, wind forcing is responsible for the formation and development of surface waves and represents an important source of near-surface turbulence. Therefore, processes related to near-surface turbulence and wave breaking, such as sea spray emission and ... Full text Cite

Lagrangian Studies of Marine Production: A Multimethod Assessment of Productivity Relationships in the California Current Ecosystem Upwelling Region

Journal Article Journal of Geophysical Research Oceans · June 1, 2020 A multimethod process-oriented investigation of diverse productivity measures in the California Current Ecosystem (CCE) Long-Term Ecological Research study region, a complex physical environment, is presented. Seven multiday deployments covering a transiti ... Full text Cite

Lagrangian Studies of Net Community Production: The Effect of Diel and Multiday Nonsteady State Factors and Vertical Fluxes on O2/Ar in a Dynamic Upwelling Region

Journal Article Journal of Geophysical Research Biogeosciences · June 1, 2020 The ratio of dissolved oxygen to argon in seawater is frequently employed to estimate rates of net community production (NCP) in the oceanic mixed layer. The in situ O2/Ar-based method accounts for many physical factors that influence oxygen con ... Full text Cite

A call for refining the role of humic-like substances in the oceanic iron cycle.

Journal Article Scientific reports · April 2020 Primary production by phytoplankton represents a major pathway whereby atmospheric CO2 is sequestered in the ocean, but this requires iron, which is in scarce supply. As over 99% of iron is complexed to organic ligands, which increase iron solub ... Full text Cite

Trends in tuna carbon isotopes suggest global changes in pelagic phytoplankton communities.

Journal Article Global change biology · February 2020 Considerable uncertainty remains over how increasing atmospheric CO2 and anthropogenic climate changes are affecting open-ocean marine ecosystems from phytoplankton to top predators. Biological time series data are thus urgently needed for the w ... Full text Cite

Expanding Tara Oceans Protocols for Underway, Ecosystemic Sampling of the Ocean-Atmosphere Interface During Tara Pacific Expedition (2016–2018)

Journal Article Frontiers in Marine Science · December 11, 2019 Interactions between the ocean and the atmosphere occur at the air-sea interface through the transfer of momentum, heat, gases and particulate matter, and through the impact of the upper-ocean biology on the composition and radiative properties of this bou ... Full text Cite

Strategies among phytoplankton in response to alleviation of nutrient stress in a subtropical gyre.

Journal Article The ISME journal · December 2019 Despite generally low primary productivity and diatom abundances in oligotrophic subtropical gyres, the North Atlantic Subtropical Gyre (NASG) exhibits significant diatom-driven carbon export on an annual basis. Subsurface pulses of nutrients likely fuel b ... Full text Cite

Data-Driven Modeling of the Distribution of Diazotrophs in the Global Ocean

Journal Article Geophysical Research Letters · November 16, 2019 Diazotrophs play a critical role in the biogeochemical cycling of nitrogen, carbon, and other elements in the global ocean. Despite their well-recognized role, the diversity, abundance, and distribution of diazotrophs in the world's ocean remain poorly cha ... Full text Cite

The Tara Pacific expedition-A pan-ecosystemic approach of the "-omics" complexity of coral reef holobionts across the Pacific Ocean.

Journal Article PLoS biology · September 2019 Coral reefs are the most diverse habitats in the marine realm. Their productivity, structural complexity, and biodiversity critically depend on ecosystem services provided by corals that are threatened because of climate change effects-in particular, ocean ... Full text Cite

NanoSIMS single cell analyses reveal the contrasting nitrogen sources for small phytoplankton.

Journal Article The ISME journal · March 2019 Nitrogen (N) is a limiting nutrient in vast regions of the world's oceans, yet the sources of N available to various phytoplankton groups remain poorly understood. In this study, we investigated inorganic carbon (C) fixation rates and nitrate (NO3 Full text Cite

Towards Quantitative Microbiome Community Profiling Using Internal Standards.

Journal Article Applied and environmental microbiology · March 2019 An inherent issue in high-throughput rRNA gene tag sequencing microbiome surveys is that they provide compositional data in relative abundances. This often leads to spurious correlations, making the interpretation of relationships to biogeochemical rates c ... Full text Cite

Machine Learning Estimates of Global Marine Nitrogen Fixation

Journal Article Journal of Geophysical Research Biogeosciences · March 1, 2019 Marine nitrogen (N2) fixation supplies “new” nitrogen to the global ocean, supporting uptake and sequestration of carbon. Despite its central role, marine N2 fixation and its controlling factors remain elusive. In this study, we compi ... Full text Cite

Revisiting the distribution of oceanic N2 fixation and estimating diazotrophic contribution to marine production.

Journal Article Nature communications · February 2019 Marine N2 fixation supports a significant portion of oceanic primary production by making N2 bioavailable to planktonic communities, in the process influencing atmosphere-ocean carbon fluxes and our global climate. However, the geogra ... Full text Cite

Theoretical Considerations on Factors Confounding the Interpretation of the Oceanic Carbon Export Ratio

Journal Article Global Biogeochemical Cycles · November 1, 2018 The fraction of primary production exported out of the surface ocean, known as the export ratio (ef ratio), is often used to assess how various factors, including temperature, primary production, phytoplankton size, and community structure, affect the expo ... Full text Cite

Net Community Production in the Southern Ocean: Insights From Comparing Atmospheric Potential Oxygen to Satellite Ocean Color Algorithms and Ocean Models

Journal Article Geophysical Research Letters · October 16, 2018 The contribution of oceanic net community production (NCP) to the observed seasonal cycle in atmospheric potential oxygen (APO) is estimated at Cape Grim, Tasmania. The resulting APONCP signal is compared to satellite and ocean model-based estim ... Full text Cite

Spring-summer net community production, new production, particle export and related water column biogeochemical processes in the marginal sea ice zone of the Western Antarctic Peninsula 2012-2014.

Journal Article Philosophical transactions. Series A, Mathematical, physical, and engineering sciences · June 2018 New production (New P, the rate of net primary production (NPP) supported by exogenously supplied limiting nutrients) and net community production (NCP, gross primary production not consumed by community respiration) are closely related but mechanistically ... Full text Cite

Linking patterns of net community production and marine microbial community structure in the western North Atlantic.

Journal Article The ISME journal · May 2018 Marine net community production (NCP) tracks uptake of carbon by plankton communities and its potential transport to depth. Relationships between marine microbial community composition and NCP currently remain unclear despite their importance for assessing ... Full text Cite

Examination of gene repertoires and physiological responses to iron and light limitation in Southern Ocean diatoms

Journal Article Polar Biology · April 1, 2018 Diatoms play a fundamental role at the base of the polar marine food web. In the Southern Ocean, low iron concentrations and light levels control diatom abundance and distribution. Diatoms must therefore employ strategies that allow them to cope when iron ... Full text Cite

Method for High Frequency Underway N2 Fixation Measurements: Flow-Through Incubation Acetylene Reduction Assays by Cavity Ring Down Laser Absorption Spectroscopy (FARACAS).

Journal Article Analytical chemistry · February 2018 Because of the difficulty in resolving the large variability of N2 fixation with current methods which rely on discrete sampling, the development of new methods for high-resolution measurements is highly desirable. We present a new method for hi ... Full text Cite

Plant and Microbial Responses to Repeated Cu(OH)2 Nanopesticide Exposures Under Different Fertilization Levels in an Agro-Ecosystem.

Journal Article Frontiers in microbiology · January 2018 The environmental fate and potential impacts of nanopesticides on agroecosystems under realistic agricultural conditions are poorly understood. As a result, the benefits and risks of these novel formulations compared to the conventional products are curren ... Full text Cite

A mechanistic model of an upper bound on oceanic carbon export as a function of mixed layer depth and temperature

Journal Article Biogeosciences · November 14, 2017 Export production reflects the amount of organic matter transferred from the ocean surface to depth through biological processes. This export is in large part controlled by nutrient and light availability, which are conditioned by mixed layer depth (MLD). ... Full text Cite

Specific eukaryotic plankton are good predictors of net community production in the Western Antarctic Peninsula.

Journal Article Scientific reports · November 2017 Despite our current realization of the tremendous diversity that exists in plankton communities, we have little understanding of how this biodiversity influences the biological carbon pump other than broad paradigms such as diatoms contributing disproporti ... Full text Cite

Ice melt influence on summertime net community production along the Western Antarctic Peninsula

Journal Article Deep Sea Research Part II Topical Studies in Oceanography · May 1, 2017 The Western Antarctic Peninsula (WAP) is a highly productive marine environment that is undergoing rapid change, with consequences for productivity and total ecosystem carbon cycling. We present continuous underway O2/Ar estimates of net communi ... Full text Cite

An advective mechanism for deep chlorophyll maxima formation in southern Drake Passage

Journal Article Geophysical Research Letters · October 28, 2016 We observe surface and subsurface fluorescence-derived chlorophyll maxima in southern Drake Passage during austral summer. Backscatter measurements indicate that the deep chlorophyll maxima (DCMs) are also deep biomass maxima, and euphotic depth estimates ... Full text Cite

Interannual variability in net community production at the Western Antarctic Peninsula region (1997–2014)

Journal Article Journal of Geophysical Research Oceans · July 1, 2016 In this study, we examined the interannual variability of net community production (NCP) in the Western Antarctic Peninsula (WAP) using in situ O2/Ar-NCP estimates (2008–2014) and satellite data (SeaWiFS and MODIS-Aqua) from 1997 to 2014. We fou ... Full text Cite

Ocean productivity south of Australia during spring and summer

Journal Article Deep Sea Research Part I Oceanographic Research Papers · June 1, 2016 We estimated mixed layer gross and net community production on a total of 20 crossings in the Australian sector of the Southern Ocean during the summer half-years (October-March) of 2007-2010. These estimates were calculated from measurements of O2 Full text Cite

Satellite estimates of net community production based on O2/Ar observations and comparison to other estimates

Journal Article Global Biogeochemical Cycles · May 1, 2016 We present two statistical algorithms for predicting global oceanic net community production (NCP) from satellite observations. To calibrate these two algorithms, we compiled a large data set of in situ O2/Ar-NCP and remotely sensed observations ... Full text Cite

Physical-biogeochemical coupling in the southern ocean

Conference Eos United States · December 1, 2015 Full text Cite

An Ultrahigh Precision, High-Frequency Dissolved Inorganic Carbon Analyzer Based on Dual Isotope Dilution and Cavity Ring-Down Spectroscopy.

Journal Article Environmental science & technology · July 2015 We present a novel method for continuous and automated shipboard measurements of dissolved inorganic carbon concentration ([DIC]) in surface water. The method is based on dual isotope dilution and cavity ring-down spectroscopy (DID-CRDS). In this method, s ... Full text Link to item Cite

Marine diatom proteorhodopsins and their potential role in coping with low iron availability.

Journal Article The ISME journal · May 2015 Proteorhodopsins (PR) are retinal-binding membrane proteins that function as light-driven proton pumps to generate energy for metabolism and growth. Recently PR-like genes have been identified in some marine eukaryotic protists, including diatoms, dinoflag ... Full text Link to item Cite

Biological and physical O2/Ar, Ar, and pCO2 variability at the Western Antarctic Peninsula and Drake Passage

Journal Article Deep Sea Research Part II: Topical Studies in Oceanography · 2015 Cite

An isotope dilution method for high-frequency measurements of dissolved inorganic carbon concentration in the surface ocean

Journal Article Limnology and Oceanography: Methods · December 30, 2013 An autonomous system using isotope dilution as its core method has been developed to obtain high-frequency measurements of dissolved inorganic carbon (DIC) concentrations in the surface ocean. This system accurately mixes a seawater sample and a 13C-labele ... Full text Link to item Cite

Biological production in the Bellingshausen Sea from oxygen-to-argon ratios and oxygen triple isotopes

Journal Article Biogeosciences · April 5, 2013 We present estimates of mixed-layer net community oxygen production (N) and gross oxygen production (G) of the Bellingshausen Sea in March and April 2007. N was derived from oxygen-to-argon (O2/Ar) ratios; G was derived using the dual-delta method from tri ... Full text Link to item Cite

Estimation of phytoplankton size fractions based on spectral features of remote sensing ocean color data

Journal Article Journal of Geophysical Research: Oceans · 2013 Through its influence on the structure of pelagic ecosystems, phytoplankton size distribution (pico-, nano-, and micro-plankton) is believed to play a key role in "the biological pump." In this paper, an algorithm is proposed to estimate phytoplankton size ... Full text Link to item Cite

Short-term N2 fixation kinetics in a moss-associated cyanobacteria

Journal Article Environmental Science & Technology · August 2012 N-2 fixation by moss-associated cyanobacteria plays an important role in the nitrogen cycling of terrestrial ecosystems. Recent studies have mainly focused on boreal ecosystems; little is known about such association in other ecosystems. Moss-associated cy ... Full text Link to item Cite

The Southern Kalahari: a potential new dust source in the Southern Hemisphere?

Journal Article Environmental Research Letters · April 10, 2012 Most sources of atmospheric dust on Earth are located in the Northern Hemisphere. The lower dust emissions in the Southern Hemisphere in part limit the supply of micronutrients (primarily soluble iron) to the Southern Ocean, thereby constraining its produc ... Full text Link to item Cite

Dissolved O2/Ar and other methods reveal rapid changes in productivity during a Lagrangian experiment in the Southern Ocean

Journal Article Journal of Geophysical Research: Oceans · April 2012 We use continuous and discrete measurements of the dissolved O-2/Ar ratio in the mixed layer to investigate the dynamics of biological productivity during the Southern Ocean Gas Exchange Experiment in March and April 2008. Injections of SF6 defined two wat ... Full text Link to item Cite

Export production and its regulating factors in the West Antarctica Peninsula region of the Southern Ocean

Journal Article Global Biogeochemical Cycles · April 2012 In connection with the Palmer LTER program, mixed layer water samples were collected during the cruise of the L. M. Gould in Jan., 2008 at 49 stations on a 20 x 100 km grid in the West Antarctica Peninsula (WAP) region of the Southern Ocean. In this study, ... Full text Link to item Cite

Estimating net community production in the Southern Ocean based on atmospheric potential oxygen and satellite ocean color data

Journal Article Global Biogeochemical Cycles · March 2012 The seasonal cycle of atmospheric potential oxygen (APO similar to O-2 + 1.1 CO2) reflects three seasonally varying ocean processes: 1) thermal in- and outgassing, 2) mixed layer net community production (NCP) and 3) deep water ventilation. Previous studie ... Full text Link to item Cite

N2 fixation estimates in real-time by cavity ring-down laser absorption spectroscopy

Journal Article Oecologia · 2012 The most common currency for estimating N(2) fixation is acetylene reduction to ethylene. Real-time estimates of nitrogen fixation are needed to close the global nitrogen budget and these remain a critical gap in both laboratory and field experiments. We p ... Full text Link to item Cite

The influence of iron and light on net community production in the Subantarctic and Polar Frontal Zones

Journal Article Biogeosciences · February 9, 2011 The roles of iron and light in controlling biomass and primary productivity are clearly established in the Southern Ocean. However, their influence on net community production (NCP) and carbon export remains to be quantified. To improve our understanding o ... Full text Link to item Cite

Evaluating gas transfer velocity parameterizations using upper ocean radon distributions

Journal Article Journal of Geophysical Research: Oceans · February 9, 2011 Sea-air fluxes of gases are commonly calculated from the product of the gas transfer velocity (k) and the departure of the seawater concentration from atmospheric equilibrium. Gas transfer velocities, generally parameterized in terms of wind speed, continu ... Full text Link to item Cite

Net community production and gross primary production rates in the Western Equatorial Pacific

Journal Article Global Biogeochemical Cycles · October 12, 2010 Net community production (NCP) and gross primary production (GPP) are two key metrics for quantifying the biological carbon cycle. In this study, we present a detailed characterization of NCP and GPP in the western equatorial Pacific during August and Sept ... Full text Link to item Cite

Continuous high-frequency dissolved O2/Ar measurements by Equilibrator Inlet Mass Spectrometry (EIMS)

Journal Article Analytical Chemistry · February 4, 2009 The oxygen (O2) concentration in the surface ocean is influenced by biological and physical processes. With concurrent measurements of argon (Ar), which has similar solubility properties as oxygen, we can remove the physical contribution to O2 supersaturat ... Full text Link to item Cite

An improved comparison of atmospheric Ar/N2 time-series and paired ocean-atmosphere model predictions

Journal Article Journal of Geophysical Research: Atmospheres · November 16, 2008 Ar/N2 variations in the atmosphere reflect ocean heat fluxes, air-sea gas exchange, and atmospheric dynamics. Here atmospheric Ar/N2 time series are compared to paired ocean-atmosphere model predictions. Agreement between Ar/N2 observations and simulations ... Full text Link to item Cite

The Southern Ocean biological response to aeolian iron deposition

Journal Article Science · August 24, 2007 Biogeochemical rate processes in the Southern Ocean have an important impact on the global environment. Here, we summarize an extensive set of published and new data that establishes the pattern of gross primary production and net community production over ... Full text Link to item Cite

Potential contribution of beta-carboxylases to photosynthetic carbon isotope fractionation in a marine diatom

Journal Article Phycologia · May 2007 In vitro activities of phosphoenolpyruvate carboxylase (PEPC) and phosphoenolpyruvate carboxykinase (PEPCK) were measured in chemostat cultures of the marine diatom Phaeodactylum tricornutum grown under either phosphate-or nitrate-limited conditions and at ... Full text Link to item Cite

Carbon isotopic fractionation by the marine diatom Phaeodactylum tricornutum under nutrients and light-limited growth conditions

Journal Article Geochemica et Cosmochimica Acta · November 1, 2006 A theoretical model was developed to explain the characteristics of carbon isotopic fractionation (εP) by the marine diatom Phaeodactylum tricornutum under nutrient- and light-limited growth conditions. The model takes into consideration active transport a ... Full text Link to item Cite

Atmospheric O2/N2 changes, 1993-2002: Implications for the partitioning of fossil fuel CO2 sequestration

Journal Article Global Biogeochemical Cycles · December 7, 2005 Improvements made to an established mass spectrometric method for measuring changes in atmospheric O2/N2 are described. With the improvements in sample handling and analysis, sample throughput and analytical precision have both increased. Aliquots from dup ... Full text Link to item Cite

Bicarbonate uptake by Southern Ocean phytoplankton

Journal Article Global Biogeochemical Cycles · April 10, 2004 Marine phytoplankton have the potential to significantly buffer future increases in atmospheric carbon dioxide levels. However, in order for CO2 fertilization to have an effect on carbon sequestration to the deep ocean, the increase in dissolved CO2 must s ... Full text Link to item Cite

C-13 discrimination patterns in oceanic phytoplankton: likely influence of CO2 concentrating mechanisms, and implications for palaeoreconstructions

Journal Article Functional Plant Biology · March 20, 2002 The isotopic composition of organic carbon buried in marine sediments is an appealing proxy for palaeo CO2 concentrations due to the well-documented effect of CO2 concentrations on carbon fractionation by phytoplankton. However, a number of factors, in add ... Full text Link to item Cite

Sources of inorganic carbon for photosynthesis in a strain of Phaeodactylum tricornutum

Journal Article Limnology and Oceanography · 2002 Diatoms are an important functional group of marine phytoplankton because of their role in the fixation of atmospheric carbon dioxide (CO2) and transfer of organic carbon to deep waters. Carbon-concentrating-mechanisms, such as active CO2 and bicarbonate ( ... Link to item Cite

Isotope fractionation and atmospheric oxygen: Implications for Phanerozoic O2 Evolution

Journal Article Science · March 2000 Models describing the evolution of the partial pressure of atmospheric oxygen over Phanerozoic time are constrained by the mass balances required between the inputs and outputs of carbon and sulfur to the oceans. This constraint has limited the applicabili ... Full text Link to item Cite