REVISITING THE NEODYMIUM PARADOX IN THE OCEAN

Global climate change is one of the big challenges society faces today. Warming of the climate system is unequivocal, and evident from observations of increasing global average temperatures. Warming is also observed in the oceans, and is accompanied by a change in salinity, with the high latitudes becoming 'fresher' (i.e., less saline) and the subtropics and tropics becoming more saline - a redistribution of properties that has the potential to affect ocean circulation. There are also clear effects of climate change on the chemistry of the oceans. Whilst increased uptake of more abundant atmospheric carbon dioxide leads to an acidification of the oceans that threatens marine ecosystems, only little is known about the effects of higher concentrations of certain trace metals, as a result of anthropogenic pollution and changing erosion patterns on land. Such changes are very important, however, as the ability of the ocean to take up carbon dioxide from the atmosphere is strongly coupled to the supply of so-called nutrients, elements that are essential for life in the ocean.

As part of this project, we will develop a better understanding of such 'biogeochemical cycles'. We picked out three trace metals, neodymium (Nd), cadmium (Cd), and lead (Pb), which together represent the behaviour of many different elements in the ocean. For example, both Cd and Pb are today supplied to the environment by human activity and this may alter their natural cycles. As Cd is an important micronutrient in the ocean, such changes could also affect the global carbon cycle. As part of our project, a PhD student will focus on understanding whether the natural flux of dust from desert areas to the ocean and the anthropogenic particles the dust scavenges in the atmosphere have an important impact on the marine Cd and Pb cycles. The student will furthermore study, how the cycling of these elements in the ocean is altered by changing oxygen concentrations. Oxygen is (next to the nutrients) another important player in biogeochemical cycles, and its solubility in seawater is temperature dependent. Climate models predict that extended zones with low oxygen concentrations will develop in the future oceans.

Another important aspect of the ocean system is that ocean currents are the key mechanism for distributing heat, and thus they have a significant impact on regional and local climate. Furthermore, water mass movements (both vertical and lateral) are very important for the carbon cycle, as the deep ocean contains 50-60 times more carbon than the atmosphere. Today we can monitor ocean circulation by measuring the physical properties of seawater. Observations over the past 50 years, however, do not give us any clear indication whether the pattern of ocean circulation is changing. From studies of the past we know, however, that ocean water masses had a different configuration during the ice ages and past periods of extreme warmth. Neodymium isotopes in seawater are often used for such reconstructions, and the results show stunning relationships between past temperatures, carbon dioxide levels, and ocean circulation.

A patchy understanding the modern Nd cycle however limits our confidence in such reconstructions, and thus our ability to transfer the inferred mechanisms to future models. In particular, it is generally assumed that away from ocean margins, Nd isotopes are an ideal ocean circulation tracer as they are only modified by mixing between water masses. However, there are many potential marine processes, which may not be in accord with this simplistic view. Such uncertainties will be addressed by the current project, based on a comprehensive suite of new observational data that will be collected for samples from strategic locations in the Atlantic Ocean. In conjunction with modelling efforts, our new data will shed light on the processes governing the marine Nd cycle and the suitability of Nd isotopes as circulation tracer.

This proposals aims to deliver substantial and lasting impact by providing an increased understanding of the role of diverse processes that control the chemical environment in the ocean. Ocean chemistry in turn is fundamentally coupled to global climate change and the stability of marine ecosystems. Global biogeochemical cycles are currently strongly altered by human activity, and future changes may have significant impacts on natural resources, economy and the environment of countries globally.

The outputs of this study will therefore be of direct and lasting benefit to a wide user community of policy forming bodies such as international and national Governmental Environment and Climate Change Departments (e.g. the European Union, the UK Met Office, UK Government departments, including DECC and DEFRA, and international equivalents), as well as international bodies and NGOs (IPCC, environmental and fisheries charities and pressure groups) interested in oceanography, climate modelling, and the way in which these systems can be managed, protected, and any undesirable changes predicted and mitigated against.

Societal impact is furthermore achieved by the fact that the isotope geochemical methods developed and deployed by the MAGIC group are used far beyond the fields of marine geochemistry and palaeoceanography, and even beyond fields such as the evolution of our solar system and planet Earth. We also apply stable isotope techniques to research in medical and life sciences and, most recently, the rapidly growing field of nanoparticle toxicology. In addition, we also have an excellent track record of publishing our method development work in the peer-reviewed literature, to ensure that novel procedures can be readily implemented by others.

For this project, we chose a range of methods for the dissemination of research results. We will engage the general public with 'Nature Live' outreach talks at the Natural History Museum (www.nhm.ac.uk/nature-live; see letter of support). Nature Live is a program delivered through the Attenborough studio and facilitated by Nature Live staff. It brings together scientists and visitors to explore, discover and discuss the natural world. The Natural History Museum in London is a world class visitor attraction welcoming 4 million public visitors each year. We furthermore plan to participate in science fairs hosted by Imperial College London and the Royal Society. We will also publicize our results through the Imperial College press centre, the MAGIC website (www.imperial.ac.uk/ese/research/magic), and the project web pages of UK GEOTRACES (www.ukgeotraces.com) and International GEOTRACES (www.geotraces.org) The project will also contribute to the education of the next generation of young scientists, by employing a PDRA who will be taught new methods and become an integral part of the wider chemical oceanography and ocean modelling community. The same is true for the PhD student, who will work on a stand-alone project that is well integrated with and complements the overall research goals. We also plan to involve undergraduate students in the research by offering small, well-defined MSci projects.

All junior researchers involved in the project will also participate in the workshop we will organize in year 3, entitled 'Seawater neodymium isotopes - modern constraints for a palaeo tracer'. For the workshop, we will invite the international community involved in marine Nd isotope research, additional researchers working on other marine geochemical cycles and ocean modellers, as well as stakeholders in public service. Finally, throughout the project, we will present research results at conferences (AGU, Goldschmidt, EGU), GEOTRACES workshops, and deliver seminars at academic institutions. In year 3 of the project we will also organize a special session that focuses on global marine biogeochemical cycles at one of these conferences.