High particulate iron(II) content in glacially sourced dusts enhances productivity of a model diatom

ELIZABETH M. SHOENFELT; JING SUN,; GISELA WINCKLER,; MICHAEL R. KAPLAN; ALEJANDRA L. BORUNDA; KAYLA R. FARRELL; PATRICIO I. MORENO, ; DIEGO M. GAIERO; CRISTINA RECASENS,; RAYMOND N. SAMBROTTO; BENJAMIN C. BOSTICK

SCIENCE

AMER ASSOC ADVANCEMENT SCIENCE

Año: 2017 vol. 3 p. 1 - 10

0036-8075

Little is known about the bioavailability of iron (Fe) in natural dusts and the impact of dust mineralogy on Fe utilizationby photosynthetic organisms. Variation in the supply of bioavailable Fe to the ocean has the potential to influence theglobal carbon cycle by modulating primary production in the Southern Ocean. Much of the dust deposited across theSouthern Ocean is sourced from South America, particularly Patagonia, where the waxing and waning of past andpresent glaciers generate fresh glaciogenic material that contrasts with aged and chemically weathered nonglaciogenicsediments. We show that these two potential sources of modern-day dust are mineralogically distinct, whereglaciogenic dust sources contain mostly Fe(II)-rich primary silicate minerals, and nearby nonglaciogenic dust sourcescontain mostly Fe(III)-rich oxyhydroxide and Fe(III) silicate weathering products. In laboratory culture experiments,Phaeodactylum tricornutum, a well-studied coastal model diatom, grows more rapidly, and with higher photosyntheticefficiency, with input of glaciogenic particulates compared to that of nonglaciogenic particulates due to these differencesin Fe mineralogy. Monod nutrient accessibility models fit to our data suggest that particulate Fe(II) content,rather than abiotic solubility, controls the Fe bioavailability in our Fe fertilization experiments. Thus, it is possiblefor this diatom to access particulate Fe in dusts by another mechanism besides uptake of unchelated Fe (Fe′) dissolvedfrom particles into the bulk solution. If this capability is widespread in the Southern Ocean, then dusts deposited to theSouthern Ocean in cold glacial periods are likely more bioavailable than those deposited in warm interglacial periods.