Marine Iron Biogeochemistry Under a Changing Climate: Impact on the Phytoplankton and the Diazotroph Communities

• Main Author: Li, Xuefeng
• Other Authors: Chou, Lei, Dehairs, Frank, Elskens, Marc M., Leermakers, Martine M., Bonneville, Steeve, Dubois, Philippe, Muylaert, Koenraad, Rees, Andy
• Format: Doctoral or Postdoctoral Thesis
• Language: English
• Published: Universite Libre de Bruxelles 2018
• Subjects: Océanographie physique et chimique; Océanographie biologique; Géochimie; Iron; Climate Change; Phytoplankton Growth; Nitrogen Fixation; Dust Deposition; Nutrient Dynamics; Ocean acidification
• Online Access: http://hdl.handle.net/2013/ULB-DIPOT:oai:dipot.ulb.ac.be:2013/266850; https://dipot.ulb.ac.be/dspace/bitstream/2013/266850/5/ContratDiLIXuefeng.pdf; https://dipot.ulb.ac.be/dspace/bitstream/2013/266850/4/Thesis.pdf; https://dipot.ulb.ac.be/dspace/bitstream/2013/266850/3/Table_of_content.pdf

Diatoms constitute a major group of phytoplankton, accounting for ~20% of the world’s primary production. Biological dinitrogen (N2) fixation by diazotrophic cyanobacteria has great biogeochemical implications in nitrogen (N) cycling, being the major source of new N input to the oceans and thereby contributing significantly to carbon (C) export production. It has been shown that iron (Fe) can be the limiting nutrient for phytoplankton growth, in particular, in the HNLC (High Nutrient Low Chlorophyll) regions. Iron plays thus an essential role in governing the marine primary productivity and the efficiency of biological carbon pump. Oceanic systems are undergoing continuous modifications at varying rates and magnitudes as a result of changing climate. The objective of our research is to evaluate the effects of global climate change processes (changing dust deposition, ocean acidification and sea-surface warming) on phytoplankton growth, biological N2 fixation, biogeochemical cycles, and the controlling role of Fe within these impacts. Laboratory culture experiments using a marine diatom Chaetoceros socialis were conducted at two temperatures (13 ℃ and 18 ℃) and two carbon dioxide partial pressures (pCO2, 400 µatm and 800 µatm). The present study clearly highlights the effect of ocean acidification on enhancing the release of Fe upon dust deposition. Our results also confirm that being a potential source of Fe, mineral dust provides in addition a readily utilizable source of macronutrients such as phosphorus (P) and silicon (Si). However, elevated atmospheric CO2 concentrations and ocean acidification may also have an adverse impact on diatom growth, causing a decrease in cell size and possible further changes in phytoplankton composition. Meanwhile, increasing temperature and ocean warming may lead to the reduction of diatom production as well as cell size, inducing poleward shifts in the biogeographic distribution of diatoms. Numerous factors can affect the extent of N2 fixation. A better understanding of the ...