Clastic Fluxes of Iron (Oxyhydr)oxide.pdf

Clastic Fluxes of Iron (Oxyhydr)oxide Nanoparticles into the Oceans: Can Icebergs Deliver Bioavailable Fe ino the Oceans? Rob Raiswell (School of Earth and Environment, University of Leeds) With Liane Benning (University of Leeds) Simon Poulton (NordCEE, University of Newcastle) Martyn Tranter (University of Bristol Atmospheric dust is believed to be a source of bioavailable Fe to the ocean (Jickells et al., 2005)…………. .......but could other clastic sources also be important? SOURCE SINK river landslide glacier fjord beach fans deep sea slope delta canyon shelf floodplain weathering erosion SEDIMENTOLOGYTH SEDIMENT CYCLE Rivers 16000 to 20000 Tg/yr (~600-900 Tg/yr) Glaciers 800 to 5000 Tg/yr (34-210 Tg/yr) Atmosphere 250-1000 Tg/yr (Approx 16 Tg/yr) Coastal Erosion 200 to 900 Tg/yr (8-36 Tg/Yr) Sources to the Ocean Tg/yr Background *Dust fluxes undergo low pH cloud cycling to produce dissolved iron in seawater, which is a micronutrient limiting productivity in some areas of the ocean. *However the iron cycle is dominated by the non- dust clastic fluxes but the nature of these fluxes, and their potential reactivity/bioavailability, are poorly-known. * How reactive are these clastic fluxes? Here we examine the riverine and glacial contributions of iron (oxyhydr)oxides to the ocean. The Chemistry of Iron in Global Riverine Runoff Global Riverine Load: ‘Dissolved‘ ~ 1 Tg yr-1 (from Poulton and Raiswell, 2002) Total Fe ~800 Tg yr-1 Particulate Oxide Fe ~350 Tg yr-1 ? ‘Dissolved’ is operationally defined as the fraction passing a 0.45 _m filter ? Most of this fraction in river water is colloidal and truly dissolved species are a minor proportion. Dissolved, Colloidal and Particulate Fe in Seawater and Their Interactions DISSOLVED PARTICULATE (Total ~ 10-10M) Inorganic Fe(OH)2 + Fe Oxide Fe(OH)3 ? Colloids Fe3+