University of Liverpool

Rhiannon Mather

Department of Earth & Ocean Sciences
Nicholson Building, Room 206
University of Liverpool
Tel: +44 151 7944091
Fax: +44 151 7945196
Email: Rhiannon.Mather@liverpool.ac.uk

My Background

I joined the Department of Earth and Ocean Sciences organic biogeochemistry group in October 2004 having taken a year out from education. During this year I worked as a research assistant for a wind farm company and also participated in the 24ºN Discovery cruise as part of the nutrients team, from April to May 2004. I graduated from the University of Southampton in June 2003 with a BSc in Marine Sciences (project title ‘Organic Nutrients in the North East Atlantic’).

Project Summary

Within the North Atlantic Subtropical Gyre (NASG) there is a reported loss of inorganic nutrients (RINTOUL and WUNSCH, 1991). It has long been recognised that these nutrients such as nitrate and phosphate are essential in maintaining primary production within the world’s oceans, and are required by phytoplankton to build biomolecules such as proteins. However the dissolved organic counterparts have been shown to be large and important fractions of the oceanic nutrient pools, especially in the euphotic zone (JACKSON and WILLIAMS, 1985) yet little is currently known of their reactivity or importance. Rintoul and Wunsch hypothesized that the ‘missing’ nutrients may be accounted for by a transfer of organic nutrients into the NASG.

Dissolved organic nutrients comprise of material ranging in size from monomeric molecules to macromolecules, with turnover times from minutes to decades or centuries. They are produced by a number of mechanisms, including passive exudation by phytoplankton, stress induced exudation by phytoplankton, zooplankton grazing on phytoplankton, and the solubilisation of particulate organic material (SANDERS and JICKELLS, 1999). A key question regarding the importance of organic nutrient pools within the oceans and their significance to the drawdown of carbon, relates to their availability to the phytoplankton community. For this to be assessed the size and biological reactivity of the organic nutrient pools must be determined.

This research aims to gain information on the composition and reactivity of the important organic nutrient pools along 36ºN and one Atlantic Meridonal Transect (AMT), along approximately 20°W in the Atlantic Ocean This will be achieved through quantification of dissolved organic nitrogen (DON), dissolved organic phosphorus (DOP) and dissolved organic carbon (DOC) using high temperature catalytic oxidation (HTCO) and standard colorimetric techniques of Kirkwood (1993). –D and –L enantiomers of the amino acid pool will be examined using high performance liquid chromatography (HPLC) to identify the cycling and source of DON and the d15N signal obtained from the isotopic characterization of PON will identify the sources of nitrate to the surface Atlantic Ocean. Following the method of Hoppe (1993) fluorogenic substrates are to be employed to assess the turnover rate of the organic nutrient pool following light and dark deck-board incubations. As part of a consortium, this information together with inverse model studies and 24ºN data will identify whether the transport of organic nutrients are important in closing the nutrient budget and sustaining export production over the subtropical North Atlantic.

This project is funded by NERC as part of the 36 ºN consortium, linking the expertise of the University of Liverpool, the National Oceanography Centre, Southampton, (NOC) and the University of Plymouth.

References

  • Hoppe H.-G. (1993) Use of Fluorogenic Model Substrates for Extracellular Enzyme Activity (EEA) Measurement of Bacteria. In Handbook of Methods in Aquatic Microbial Ecology (ed. P. Kemp, B. Sherr, E. Sherr, and J. J. Cole), pp. 423-431. Lewis Publishers.
  • Jackson G. A. and Williams P. M. (1985) Importance of dissolved organic nitrogen and phosphorus to biological nutrient cycling. Deep-Sea Research 32(2), 223-235.
  • Kirkwood D. S. (1993) Nutrients: Practical notes on their determination in sea water. HELCOM 1994, ICES/HELCOM Workshop on Quality Assurance of Chemical Analytical Procedures for the Baltic Monitoring Programme, 5-8 October 1993, Hamburg, Germany, Baltic Sea Environment Proceedings No. 58, 23-47.
  • Rintoul S. R. and Wunsch C. (1991) Mass, Heat, Oxygen And Nutrient Fluxes And Budgets In The North-Atlantic Ocean. Deep-Sea Research Part A-Oceanographic Research Papers 38, S355-S377.
  • Sanders R. and Jickells T. (1999) Total organic nutrients in Drake Passage. Deep-Sea Research I 47, 997-1014.