Large regions of the world's oceans have low primary production despite having plenty of macronutrients such as phosphate, nitrate and silicate. This is due a shortage of the essential micro-nutrient iron, which is needed for the growth of phytoplankton.
These tiny, plant-like organisms sit at the base of the marine food chain and collectively draw vast amounts of the greenhouse gas carbon dioxide down from the atmosphere through the process of photosynthesis.
A proportion of the carbon is exported to the deep ocean, making the oceans a major carbon dioxide sink, without which global warming would rapidly accelerate. The natural supply of iron to such 'High Nutrient Low Chlorophyll (HNLC) regions is therefore, albeit indirectly, an important determinant of climate.
The importance of dissolved iron in seawater derived from bottom (benthic) sediments is increasingly recognised as being important. Around the continental margins, in particular, iron is released from the sediments during the decomposition of organic carbon by dissimilatory iron-reducing bacteria - micro-organisms that use elemental iron to obtain energy. This leads to the enrichment of iron in pore fluids and bottom waters. However the ubiquity of sedimentary iron inputs to seawater remains unknown.
Different biological and chemical processes can leave behind characteristic isotopic 'fingerprints'. Of specific interest here, iron isotopes in sediment pore fluids may be a unique tracer of sediment respiration by dissimilatory iron-reducing bacteria.
Dissimilatory iron reduction is thought to be one of the earliest metabolic pathways on Earth , thus sedimentary iron isotopes may also be useful in reconstructing past iron cycling in the ancient ocean.
Pore-fluid iron isotope measurements have so far been restricted to the continental shelves where the supply of carbon is typically high and dissimilatory iron reduction is extensive, precluding comparisons with low-carbon, deep-water environments. William Homoky, who is a research student at the University of Southampton's School of Ocean and Earth Sciences based at NOCS, and his colleagues have helped fill this gap be measuring iron isotopes in pore fluids from both the Eel River shelf on the northern California margin (120 m water depth), and deep-sea sediments from the Southern Ocean around the Crozet Island Plateau (3000� m water depth), about 1400 miles southeast of South Africa.
"We are excited by our findings not only because they represent the first measurements of their kind, but because they are telling us something important about iron cycling processes in the deep-sea, which can inform future iron isotope investigations in ancient rocks and the modern oceans," said William Homoky.
They find that the composition of iron isotopes in the pore fluids reflects the different extent of sedimentary iron recycling between the two sites. Specifically, the pore-fluid iron isotope compositions reflect the extent of iron recycling during early diagenesis, which is driven by organic carbon inputs from the overlying water column.
The researchers believe that iron isotope processing in carbon-limited environments, such as the deep-sea, is important and that it should help future interpretations of the rock record. "Additionally," they say, "the unique isotopic fingerprint of pore fluid iron in continental shelf settings is confirmed, highlighting the potential for iron isotopes to trace the inputs of continental shelf-derived iron in seawater."
Current thesis research aims to improve our understanding of iron cycling between sediments and seawater and compares the affects of contrasting sediment geochemistry on iron flux generating processes.
"In the future I would like to examine processes of sedimentary iron cycling in the high-latitudes, where sediments are subject to enhanced rates of environmental change due to changing climate in these regions," Said Homoky.
This work was supported by the UK Natural Environment Research Council (NERC) and the US National Science Foundation (NSF). Research cruises were undertaken on the RV Wecoma and the RRS Discovery.
For more information contact the NOCS Press Officer Rory Howlett on +44 (0)23 8059 8490 Email: firstname.lastname@example.org
Images are available from the NOCS Press Office (Tel. 02380596100).
William Homoky: Telephone +44 (0) 23 80596507; Email email@example.com
Homoky, W., S. Severmann, S., Mills, R., Statham, P. & Fones, G. Pore-fluid Fe isotopes reflect the extent of benthic Fe redox recycling: Evidence from continental shelf and deep-sea sediments. Geology XXX, xxxx-xxxx (2009).
The authors are William Homoky (NOCS), S. Severmann (Rutgers University), Rachel Mills (NOCS), Peter Statham (NOCS), and G. Fones (University of Portsmouth).
The National Oceanography Centre, Southampton is the UK's focus for ocean science. It is one of the world's leading institutions devoted to research, teaching and technology development in ocean and earth science. Over 500 research scientists, lecturing, support and seagoing staff are based at the centre's purpose-built waterside campus in Southampton along with over 700 undergraduate and postgraduate students.
The National Oceanography Centre, Southampton is a collaboration between the University of Southampton and the Natural Environment Research Council. The NERC royal research ships RRS James Cook and RRS Discovery are based at NOCS as is the National Marine Equipment Pool which includes Autosub and Isis, two of the world's deepest diving research vehicles.
Dr. Rory Howlett | EurekAlert!
NASA sees the end of ex-Tropical Cyclone 02W
21.04.2017 | NASA/Goddard Space Flight Center
New research unlocks forests' potential in climate change mitigation
21.04.2017 | Clemson University
The nearby, giant radio galaxy M87 hosts a supermassive black hole (BH) and is well-known for its bright jet dominating the spectrum over ten orders of magnitude in frequency. Due to its proximity, jet prominence, and the large black hole mass, M87 is the best laboratory for investigating the formation, acceleration, and collimation of relativistic jets. A research team led by Silke Britzen from the Max Planck Institute for Radio Astronomy in Bonn, Germany, has found strong indication for turbulent processes connecting the accretion disk and the jet of that galaxy providing insights into the longstanding problem of the origin of astrophysical jets.
Supermassive black holes form some of the most enigmatic phenomena in astrophysics. Their enormous energy output is supposed to be generated by the...
The probability to find a certain number of photons inside a laser pulse usually corresponds to a classical distribution of independent events, the so-called...
Microprocessors based on atomically thin materials hold the promise of the evolution of traditional processors as well as new applications in the field of flexible electronics. Now, a TU Wien research team led by Thomas Müller has made a breakthrough in this field as part of an ongoing research project.
Two-dimensional materials, or 2D materials for short, are extremely versatile, although – or often more precisely because – they are made up of just one or a...
Two researchers at Heidelberg University have developed a model system that enables a better understanding of the processes in a quantum-physical experiment...
Glaciers might seem rather inhospitable environments. However, they are home to a diverse and vibrant microbial community. It’s becoming increasingly clear that they play a bigger role in the carbon cycle than previously thought.
A new study, now published in the journal Nature Geoscience, shows how microbial communities in melting glaciers contribute to the Earth’s carbon cycle, a...
20.04.2017 | Event News
18.04.2017 | Event News
03.04.2017 | Event News
21.04.2017 | Physics and Astronomy
21.04.2017 | Health and Medicine
21.04.2017 | Physics and Astronomy