Research

TROPICS cruise

with Laura Robinson (University of Bristol)
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GEOTRACES UK

with Gideon Henderson (Oxford University) and Alex Thomas (Edinburgh University)

NERC New Investigator Grant

Unravelling the carbon cycle using silicon isotopes in the oceans

With rising concerns surrounding the impacts of manmade climate change we need to look not only into the future but also into the past. By understanding how global temperatures and levels of carbon dioxide (CO2) in the atmosphere have naturally fluctuated throughout the earth's history, and the interaction with living organisms, we can take important steps towards predicting the changes that may lie ahead. It is undoubtedly a complex puzzle and there are many ways of trying to solve it.

My part of the story involves deep-sea sponges and silicon, the chemical element they use to build their glass-like opal skeletons. Sponge skeletons, or spicules, are helping me to piece together the links between the supply of vital nutrients in different parts of the ocean and the crucial role other marine organisms play in absorbing CO2 from the atmosphere and locking it away in deep sea sediments as organic carbon.

Marine sponges are one of the simplest groups of animals, living on the seafloor and feeding by filtering particles from seawater. They themselves don't play a central role in changing climates, but they do share a common need for silicon with another group of marine inhabitants that we think are vitally important to the global climate. Diatoms, a type of microscopic marine algae that live and photosynthesise at the sea surface, are responsible for sequestering nearly half the CO2 that is converted into organic carbon and sinks to the seafloor. By investigating sponges I can learn a lot about the changing availability of silicon that also makes life possible for diatoms. 

A scanning electron microscope image of sponge spicules - K.Hendry, 2013

Studies of ice-cores and ocean sediments tell us that over the past million years the earth's climate has cycled every 100 thousand years or so between cold ice ages, with low levels of atmospheric CO2, and warmer periods, with higher CO2 levels. My studies focus on the climate changes that took place since the end of the last ice age, around 15 thousand years ago. I can step back in time by combining analysis of living sponges brought up from the deep during research cruises at sea with fossil sponges taken from seafloor sediment samples.

I was amongst the first to show that the chemical fingerprints of sponges, in particular their silicon isotope composition, gives an accurate record of how much silicon was dissolved in the water they grew in. This opens up a unique archive stretching back millennia of the silicon levels in ocean waters down to as much as 4 km beneath the waves - the realm of sea sponges. In general, the more silicon there is supplied to the sea surface, the more diatoms can grow, and the more carbon dioxide they absorb and lock away in the seafloor sediments when they die. Building a picture of past levels of silicon in the oceans means I can test the crucial links between carbon dioxide uptake by diatoms and climate change.

Here, I plan to study key geographical areas, which have been sensitive to rapid climate change since the last ice age.

My work will provide essential insights into the dynamics of the carbon cycle and hence climate, and point to possible future scenarios and changes in ocean circulation patterns.

Leverhulme Research Project

Southern Ocean Sponges: The link between biogeography and geochemistry

The Southern Ocean is a key player in the regulation of global climate, through the upwelling and formation of deep-water masses, the exchange of heat, carbon and nutrients. Understanding the physical and chemical environment in the Southern Ocean is essential for our understanding of biogeographical distribution of marine organisms and the marine carbon cycle. Our goal is to carry out a multidisciplinary study of Southern Ocean sponges. We aim to provide taxomonic descriptions of over 500 sponge specimens collected in the Southern Ocean; assess biogeographical variation in assemblages, and the role of the environment in sponge distribution; and carry out geochemical analysis to assess further the silicon isotope variation between different individuals and taxonomic groupings, to improve our understanding of how sponges can be used as geochemical archives of past ocean chemistry. 

with Dr Claire Goodwin (National Museums Northern Ireland) and Dr Jade Berman (Ulster Wildlife Trust)

Marie Curie Career Integration Grant

BARIUM - Barium cycling in Antarctic waters: Understanding present and past ocean processes

 

Ice core records show that atmospheric carbon dioxide (pCO2), an important greenhouse gas that drives and amplifies climate change, varies naturally over a range of timescales.  Biological productivity in the oceans is a major contributor to carbon drawdown, and an important factor controlling atmospheric pCO2.  The Southern Ocean is linked with these climatic events, in part due to upwelling and subduction of deep waters during which carbon and heat are exchanged with the atmosphere, and partly because it exerts a primary control on the distribution of nutrients to a large portion of the modern ocean.  The aim here is to further the understanding of oceanic carbon storage over a range of timescales in the region of the West Antarctica Peninsula, the region experiencing the most rapid atmospheric and oceanic warming in recent decades.  I will use components of the biogeochemical cycle of barium (Ba) to understand and investigate different aspects of organic and inorganic carbon storage.  The analyses will provide data suitable for testing hypotheses linking Southern Ocean circulation to global climate over a range of timescales, and linking the response in biogeochemical cycles to future climatic change.

Sailing in the Southern Ocean - photo K.Hendry, 2011

with Stephanie Bates and Kimberley Pyle (PhD students, Cardiff University)
Click here to find out about Kim and Steph's research trips.