Project EARTH-17-HB1: Absorption of light by Arctic marine phytoplankton: its ecological and biogeochemical significance

Supervisors: Dr. Heather Bouman – Department of Earth Sciences, University of Oxford; Dr. David McKee – Department of Physics, University of Strathclyde

The structure of marine phytoplankton communities is linked intimately to the absorptive properties of the phytoplankton cells, which in turn vary with the size, type and physiological status (Sathyendranath et al. 1987, Bricaud et al. 1995, Bouman et al. 2003). Evidence is emerging that, over the annual cycle, Arctic phytoplankton assemblages undergo marked shifts in size and taxonomic structure. Blooms of diatoms and haptophytes (Phaeocystis and Emiliana huxleyii) are regularly observed in remote sensing imagery in Arctic and Subarctic Seas (e.g. Stuart et al. 2000, Smyth et al. 2004). In addition to bloom-forming species, microscopic, molecular, and pigment analyses reveal that phototrophic picoeukaryotes are omnipresent members of Arctic communities (Vidussi et al. 2004, Not et al. 2005, Lovejoy et al. 2007) and can dominate the algal assemblage prior to the spring bloom.  These green microalgae are believed to form the baseline community of polar ecosystems (Lovejoy et al. 2007).  One chlorophyte genus that appears to be particularly important is Micromonas (Prasinophyceae) which has been found to be highly adapted to low-temperature, low-light environments (Throndsen & Kristiansen 1991), dominates the subsurface chlorophyll maximum (Hollibaugh et al. 2007, Monier et al. 2015) and is able to persist throughout the polar night (Lovejoy et al. 2007). This dominance of Micromonas may be depend, in part, on the successful spectral coupling with the underwater light field (Sathyendranath and Platt 2007, Hickman et al. 2010).

Exploiting variation in the spectral signature of absorption by marine phytoplankton may also allow the large-scale monitoring of biogeochemically-significant phytoplankton groups (so-call Phytoplankton Functional Types or PFTs) from space.  Facilitating the use of earth observation to determine the large-scale distribution of PFTs will provide a cost-effective way of monitoring shifts in phytoplankton biogeography in regions that are remote, or, as in the case of the Arctic, inaccessible for most of the year. However, development of algorithms to derive phytoplankton community structure from satellite data requires ship-based observations of the physiological and optical characteristics of the microflora.  In the Arctic such data are currently lacking.

This studentship project will:

  1. Use in-situ data collected by the DPhil candidate and project collaborators during a series of oceanographic expeditions to the Barents Sea (HPLC pigment, cell counts by optical microscopy, and phytoplankton light absorption) to examine the relative importance of cell size, pigment complement and photoacclimation in determining the shape and magnitude of the specific-absorption coefficient of phytoplankton from optical theory.
  1. Using pigment data, cell counts, and phytoplankton absorption, and remote sensing reflectance data collected on the ship, test and refine satellite algorithms used to detect the presence of the major Arctic taxonomic groups: diatoms, Phaeocystis, coccolithophores, and small flagellates (including Micromonas).

The student will be jointly supervised by Dr. Heather Bouman (Oxford) and Dr. David McKee (Strathclyde).

Dr. Bouman has extensive expertise in phytoplankton ecology and marine bio-optics.  She is experienced in the collection, processing and interpretation of optical data for coastal and open ocean environments. Dr Bouman has used a variety of methods to assess the community structure of marine phytoplankton (flow cytometry, HPLC, microscopy, molecular probes). While at Oxford, the student will also have access to other Oxford researchers involved in Arctic research (Drs. Don Porcelli and Prof. Gideon Henderson – Geochemistry, Dr. Helen Johnson – Physical Oceanography).

Dr McKee provides expertise in marine optics and radiative transfer modelling. He has extensive experience in the collection of in situ inherent optical properties and hyperspectral radiometry. He has worked on the development of radiative transfer approaches to the interpretation of ocean colour imagery. The student will have access to a new DTC on Space Applications and will engage with the MASTS research pooling initiative.

hb1-project-17

The successful applicant, whose first degree might be in marine, environmental or earth sciences, will have a strong interest in multidisciplinary research, good quantitative and computing skills, and an aptitude for field-based experimental work.  The student will work closely with the national and international experts in the fields of Arctic oceanography, marine ecology and biogeochemistry.

Further Reading:

Bricaud A. et al. (1995) Journal of Geophysical Research 100:13,321-313,332

Bouman H. et al. (2003) Marine Ecology Progress Series, 258: 19-30

Hickman, A.E. et al. (2010) Marine Ecology Progress Series, 406: 1-17

Hollibaugh, J.T. et al. (2007) Oceanography 20:140-145

Lovejoy C. et al. (2007) Journal of Phycology 43:78-89

Monier A. et al. (2014) The ISME Journal 9: 990-1002

Not F. et al. (2005) Limnology and Oceanography 50:1677-1686

Sathyendranath S. et al. (1987) Limnology and Oceanography 32:403-415

Sathyendranath S & Platt T (2007) Oceanologia 49:5-39

Throndsen J & Kristiansen S (1991) Polar Research  10: 201-207

Vidussi F. et al. (2004) Canadian Journal of Fisheries and Aquatic Sciences 61:2038-2052