Factsheet #1: Dissolved Iron

Phytoplankton who lives at the surface of the oceans is the responsible of half of the Earth oxygen production, through photosynthesis. In addition, it is fixing dissolved carbon (CO2) of atmospheric origin as solid particles which, when dying, are falling as detritus in the abyss and the sediment. This mechanism called the “Biological Carbon Pump” is an important sink for the anthropogenic CO2. Understanding the processes leading to the phytoplankton development is thus a major issue for the present-day climate modelling and the prediction of our future climate.

Iron (as other trace metals) is essential for the photosynthesis success of most of the phytoplanktonic species. However, its abundance in the marine waters is extremely low and its absence is limiting the phytoplankton development in roughly half of the world’s oceans. This led to the development of studies of artificial ocean iron fertilization, the hypothesis being that stimulating the photosynthesis will improve the capacity of the ocean to absorb CO2. However, thanks to studies on iron distribution and fate it is now proved that artificial ocean iron fertilization will never produce the expected result as photosynthesis continues to be limited due to the complexity of processes at play in surface waters. Such results prevent wasting money in useless operations.

Thus, to understand the carbon pump functioning or to test geoengineer’s hypothesis, studying the oceanic iron cycle is essential. This includes: understanding the iron sources to the ocean, its sinks, its distribution, etc. GEOTRACES is elucidating these questions, as well as, producing high quality data and representing it on an electronic Atlas that helps to easily convey the information.

Find below a summary of main GEOTRACES findings and products on iron research:

Atlas

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Atlantic Ocean:

Pacific Ocean:

3D scenes showing the distribution of dissolved iron in the Atlantic and the Pacific. In warm colours (red, orange, etc.) you can view high concentrations of dissolved iron. The diversity of hydrothermal iron inputs is identified along Mid Oceanic Ridges in the two basins. Important release of dissolved iron from the sediments are indicated along the African, South American, Asian and Peruvian coasts.

Data

Data is available to download after registration here: https://geotraces.webodv.awi.de/login

Discoveries include:

Below you can find a list of science highlights of main GEOTRACES discoveries on iron research:

Science Highlights

Volcanic emissions in the Southern Ocean: an efficient and unexpected source of iron for this remote area

This study suggests that volcanic emission can represent a significant source of bioavailable Fe to open ocean anaemic ecosystems.

Science Highlights

Surprising conservativity of trace metals along a costal embayment salinity gradient

Chen and co-workers analyzed an array of trace metals together with Rare Earth Elements in a salinity gradient in the Jinhae Bay, the largest semi-enclosed bay in South Korea…

Science Highlights

Pros and cons of nine bioactive trace elements as tracers of modern and paleo-productivity

Horner and co-authors assess whether nine bioactive trace metals and their isotopes can be used as paleo-productivity proxies.

Science Highlights

Retreat of large marine-terminating glaciers may increase iron supply to surface waters

The findings demonstrate that glacial retreat and loss of ice-shelves may potentially result in increases in dissolved iron supply to surface waters downstream of large marine terminating glaciers in future.

Science Highlights

Variable dissolution rates and fates of lithogenic tracers at the air-sea interface

Roy-Barman and co-authors established the dissolution rates from Saharan dust reaching Mediterranean seawater.

Science Highlights

Manganese: a surprising co-limiting factor of phytoplankton growth in the Southern Ocean

One of the main consequences of this work is that manganese should be included in ocean-climate models, more particularly to improve the accuracy of their predictions in this area.

List of publications

Scroll down to view the list of GEOTRACES publications on dissolved iron: (Not updated — IN CONSTRUCTION!!!)

Rechercher