Emma Cavan

Emma Cavan
Imperial College London | Imperial · Department of Life Sciences

Doctor of Philosophy

About

32
Publications
10,245
Reads
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695
Citations
Additional affiliations
March 2019 - present
Imperial College London
Position
  • PostDoc Position
January 2017 - March 2019
University of Tasmania
Position
  • PostDoc Position
January 2013 - April 2015
University of Liverpool
Position
  • Honorary associate

Publications

Publications (32)
Article
Full-text available
The Southern Ocean (SO) is an important CO2 reservoir, some of which enters via the production, sinking and remineralization of organic matter. Recent work suggests the fraction of production that sinks is inversely related to production in the SO, a suggestion we confirm from 20 stations in the Scotia Sea. The efficiency with which exported materi...
Article
Full-text available
The efficiency of the ocean's biological carbon pump (BCPeff – here the product of particle export and transfer efficiencies) plays a key role in the air–sea partitioning of CO2. Despite its importance in the global carbon cycle, the biological processes that control BCPeff are poorly known. We investigate the potential role that zooplankton play i...
Article
Full-text available
Microbial respiration of particulate organic carbon (POC) is one of the key processes controlling the magnitude of POC export from the surface ocean and its storage on long timescales in the deep. Metabolic processes are a function of temperature, such that warming sea temperatures should increase microbial respiration, potentially reducing POC exp...
Article
Full-text available
Under future warming Earth System Models (ESMs) project a decrease in the magnitude of downward particulate organic carbon (POC) export, suggesting the potential for carbon storage in the deep ocean will be reduced. Projections of POC export can also be quantified using an alternative physiologically-based approach, the Metabolic Theory of Ecology...
Article
Full-text available
Antarctic krill (Euphausia superba) are swarming, oceanic crustaceans, up to two inches long, and best known as prey for whales and penguins – but they have another important role. With their large size, high biomass and daily vertical migrations they transport and transform essential nutrients, stimulate primary productivity and influence the carb...
Article
Full-text available
The transfer of organic carbon from the upper to the deep ocean by particulate export flux is the starting point for the long-term storage of photosynthetically fixed carbon. This ‘biological carbon pump’ is a critical component of the global carbon cycle, reducing atmospheric CO2 levels by ~200 ppm relative to a world without export flux. This car...
Article
Full-text available
Marine ecosystems and their associated biodiversity sustain life on Earth and hold intrinsic value. Critical marine ecosystem services include maintenance of global oxygen and carbon cycles, production of food and energy, and sustenance of human wellbeing. However marine ecosystems are swiftly being degraded due to the unsustainable use of marine e...
Article
Full-text available
Plankton drive a major sink of carbon across the global oceans. Dead plankton, their faeces and the faeces of plankton feeders, form a huge rain of carbon sinking to the seabed and deep ocean, reducing atmospheric CO2 levels and thus helping to regulate the climate. Any change in plankton communities, ecosystems or habitats will perturb this carbon...
Article
Full-text available
Zooplankton carcasses are an important, yet understudied, pathway of the biological gravitational pump. To understand their contribution to the downward carbon flux in the subantarctic, carcasses of the copepod Neocalanus tonsus were analyzed for carbon content, microbial remineralization rates, and sinking velocities. In addition, the sensitivity...
Article
Full-text available
Efforts to model marine food-webs are generally undertaken by small teams working separately on specific regions (<10⁶ km²) and making independent decisions about how to deal with data gaps and uncertainties. Differences in these largely arbitrary decisions (which we call ‘model personality’) can potentially obscure true differences between regiona...
Article
Full-text available
Sinking particles are critical to the ocean's “biological pump,” sequestering carbon from the atmosphere. Particles' sinking speeds are a primary factor determining fluxes and subsequent ecological and climatic impacts. While size is a key determinant of particles' sinking speeds, observations suggest a variable size‐sinking relationship, affected...
Article
Full-text available
• Detritivores need to upgrade their food to increase its nutritional value. One method is to fragment detritus promoting the colonization of nutrient‐rich microbes, which consumers then ingest along with the detritus; so‐called microbial gardening. Observations and numerical models of the detritus‐dominated ocean mesopelagic zone have suggested mi...
Preprint
Marine ecosystems and their associated biodiversity sustain life on Earth and hold intrinsic value. Critical marine ecosystem services include maintenance of global oxygen and carbon cycles, production of food and energy, and sustenance of human wellbeing. However marine ecosystems are rapidly declining due to the unsustainable use of marine enviro...
Article
Full-text available
Ocean life helps keep atmospheric levels of carbon dioxide lower by taking carbon out of the atmosphere and transporting it to the deep ocean, through sinking particles. Antarctic krill live in the Southern Ocean and gather in huge swarms. Importantly, they produce large, fast-sinking poo (called fecal strings), meaning that we get a rain of poo be...
Preprint
Full-text available
Primary production in the global oceans fuels multiple ecosystem services including fisheries, and the open-ocean biological carbon sink, which support food security and livelihoods ¹ , and the regulation of atmospheric CO 2 levels ² respectively. The spatial distributions of these two services are driven by primary production and it is likely that...
Article
Full-text available
Marine ecosystems regulate atmospheric carbon dioxide levels by transporting and storing photosynthetically fixed carbon in the ocean’s interior. In particular, the subantarctic and polar frontal zone of the Southern Ocean is a significant region for physically-driven carbon uptake due to mode water formation, although it is under-studied concernin...
Article
Full-text available
The Southern Ocean plays a critical role in regulating global climate as a major sink for atmospheric carbon dioxide (CO2), and in global ocean biogeochemistry by supplying nutrients to the global thermocline, thereby influencing global primary production and carbon export. Biogeochemical processes within the Southern Ocean regulate regional primar...
Article
Full-text available
Pressure in academia and science is rapidly increasing and early career researchers (ECRs) have a lot to gain from being involved in research initiatives such as large international projects. But just how inclusive are they? Here we discuss experiences of ECRs directly involved in the Marine Ecosystem Assessment for the Southern Ocean (MEASO), an A...
Article
Full-text available
Optical particle measurements are emerging as an important technique for understanding the ocean carbon cycle, including contributions to estimates of their downward flux, which sequesters carbon dioxide (CO2) in the deep sea. Optical instruments can be used from ships or installed on autonomous platforms, delivering much greater spatial and tempor...
Article
Full-text available
An amendment to this paper has been published and can be accessed via a link at the top of the paper.
Poster
Full-text available
The “Biological Carbon Pump” helps to decrease atmospheric carbon dioxide levels and consequently, counteracts anthropogenic climate change. However, the contribution of zooplankton to the carbon downward flux is still understudied in the subantarctic zone. This PhD project investigates the following questions: (1) How does zooplankton species comp...
Article
The oceans’ biological pump (BP) exports large amounts of particulate organic carbon (POC) to the mesopelagic zone (base of the euphotic zone – 1000 m depth). The efficiency at which POC is transferred through the mesopelagic zone determines the size of the deep ocean carbon store. Few observational BP studies focus on the mesopelagic, often leadin...
Article
Full-text available
A fraction of organic carbon produced in the oceans by phytoplankton sinks storing 5‐15 gigatonnes of carbon annually in the ocean interior. The accepted paradigm is that rapid aggregation of phytoplankton cells occurs forming large, fresh particles which sink quickly; this concept is incorporated into ecosystem models used to predict the future cl...
Article
The remineralization depth of particulate organic carbon (POC) fluxes exported from the surface ocean exert a major control over atmospheric CO₂ levels. According to a long held paradigm most of the POC exported to depth is associated with large particles. However, recent lines of evidence suggest that slow sinking POC (SSPOC) may be an important c...
Article
Full-text available
Biological oceanic processes, principally the surface production, sinking and interior remineralization of organic particles, keep atmospheric CO 2 lower than if the ocean was abiotic. The remineralization length scale (RLS, the vertical distance over which organic particle flux declines by 63%, affected by particle respiration, fragmentation and s...
Data
Supplementary Figures and Supplementary Tables
Thesis
Full-text available
Without small oceanic organisms atmospheric CO2 levels would be about 200 ppm higher than they are today; phytoplankton convert dissolved inorganic carbon (DIC) to particulate organic carbon (POC) during photosynthesis, influencing the air-sea exchange of CO2. Eventually some of this POC is exported out of the upper ocean, often as either phytodetr...
Article
Full-text available
The efficiency of the ocean’s biological carbon pump (BCPeff – here the product of particle export and transfer efficiencies) plays a key role in the air-sea partitioning of CO2. Despite its importance in the global carbon cycle, the biological processes that control BCPeff are poorly known. We investigate the potential role that zooplankton play i...
Article
The ocean contributes to regulating atmospheric CO2 levels, partly via variability in the fraction of primary production (PP) which is exported out of the surface layer (i.e., the e ratio). Southern Ocean studies have found that contrary to global-scale analyses, an inverse relationship exists between e ratio and PP. This relationship remains unexp...

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Projects

Projects (3)
Archived project
The ocean’s biological pump is one of the main pathways of biogenic carbon into the oceans interior. Zooplankton play a key role in the biological pump via particle transformations by grazing activities or building blocks for heterogeneous particles (e.g. faecal pellets, mucous nets or carcasses), and hence have a strong influence on the magnitude and efficiency of carbon export. This post-graduate research fellowship will explore how selected zooplankton taxa contribute to the passive and active carbon flux to determine the total export flux out of the epipelagic subantarctic Southern Ocean. Due to significant mode water formation, this region is naturally an important area for carbon sequestration in the ocean's interior. The project focuses on the following topics: 1. Linking the community composition of subantarctic zooplankton in sediment traps from a long-term time series from the Southern Ocean Time-Series (SOTS) site (47˚S) to environmental conditions and carbon flux. 2. Analyse the contribution of carcass production by different zooplankton taxa, i.e. copepods and pelagic tunicates, to the downward carbon flux of the subantarctic zone. 3. Explore new ways of measuring epi- and mesopelagic respiration of zooplankton.
Archived project
To further our understanding of the biological carbon pump in the upper mesopelagic zone. Observations were made in the Southern Ocean, Atlantic and Pacific and finally compared to an ecological model output
Project
https://tomcat-scor.org/ Sinking particles transport organic carbon to the deep sea, where they form the base of life. The magnitude of particle export and the rate at which particles are consumed determine carbon sequestration in the oceans, and directly influence atmospheric carbon dioxide concentrations and global climate. Traditionally, sinking particles have been collected using sediment traps. However, the limited spatial and temporal coverage of sediment traps have led to new technologies that focus on optical measurements to allow the collection of large data sets describing both frequencies and types of sinking particles. These can be used from ships or installed on remote platforms, promising greater spatial and temporal coverage. Yet, whilst technologies to image particles have advanced greatly during the last two decades, techniques to analyze the often immense data sets have not. One short-coming is the translation of optical particle properties (e.g. the image) into particle characteristics such as carbon content and sinking speed. Moreover, different devices often measure different optical properties, leading to difficulties in comparing results. This working group aims to bring together experts in observation, experimentation, theoretical modelling, and data analyses to systematically improve the process of converting in-situ particle measurements to global export estimates. Final outcomes will include publications detailing intermediate steps and a framework outlining the most efficient way of converting large volumes of particle measurements into export estimates. The output of this working group should have high impact on future ocean research by enabling efficient use of the rapidly developing field of optical sensors.