Research Student 2012
Climate Change and Earth-Ocean-Atmosphere Systems
The role of Southern Ocean dynamics on the carbon cycle
The cause of the variability in atmospheric pCO2 over glacial-interglacial timescales has been a puzzle since its discovery in the early 1980s. It is widely believed to be related to changes in carbon storage in the deep ocean, but the exact mechanisms responsible for sequestering and releasing CO2 from the deep ocean reservoir, including the role of ocean density stratification remains an open question. My research attempts to reconstruct changes in the intermediate-deep ocean density gradient in the South Atlantic across the last deglaciation in order to assess the link between deep ocean stratification and atmospheric CO2. I use benthic foraminifera Mg/Ca and oxygen isotopic composition to derived seawater temperature and salinity estimates of sub-Antarctic South Atlantic water masses over the last deglaciation. We show that the major destratification event significantly lags the breakdown in the chemical divide, suggesting that the chemical and physical properties of the ocean are not as tightly coupled as generally assumed. See: Roberts et al. PNAS (2016). DOI: 10.1073/pnas.1511252113
The role of Southern Ocean biology on the carbon cycle
Patagonian dust deposited in the sub-Antarctic during glacial times has widely-cited as a potential mechanism for increasing the flux of carbon (and CO2) into the deep ocean, through increasing export productivity in the sub-Antarctic. Our current understanding has been informed by a few open ocean sites where significant changes in the export productivity have been observed. However, productivity in coastal environments is orders of magnitude greater, and thus much more significant in terms of the global carbon budget. I am interested in reconstructing glacial-interglacial changes in productivity from these sub-Antarctic coastal sites, to understand their effect on the global carbon cycle.
The Patagonian Ice Sheet
The glacial history of the southern Patagonian Ice Sheet has been interpreted through detailed mapping of terrestrial glacial landforms. Whilst these studies provide insight into the history of glacial advance and maximum ice sheet extent, however the scarcity of landforms specific to ice retreat makes interpreting the deglacial history more problematic. Marine sediment core can complement these studies by providing high-resolution continuous records of the deglacial history of the Patagonian Ice Sheet. I have used organic biomarkers from marine sediment cores off the coast of Patagonia to attempt to reconstruct the deglacial history of meltwater pulses being delivered to these coastal sites.
Cold water route of Antarctic Intermediate Water
The vast majority of Antarctic Intermediate Water that enters the Atlantic basin travels through the Drake Passage and overflows shallow sills immediately south of the Falkland Islands. This pathway is known as the cold water route of Antarctic Intermediate Water. Understanding the glacial-interglacial changes in the endmember composition of this branch of Antarctic Intermediate Water is fundamental for informing models based on end-member mixing. I have used sediment grain size proxies to reconstruct changes in the flow through the Drake Passage, and to better understand how changes in the position of the South Westerly Wind Belt might affect flow through this cold-water route.
I have been fortunate to be part of the scientific crew of the AWI cruise (Polarstern ANT-XXIX/4) and the NERC cruise (RRS James Cook JC089), from which I have first-hand experience of core recovery and seismic acquisition. As a direct consequence of work done during my PhD, we have submitted an IODP proposal to core a contourite deposit off the Falkland Islands to better understand ocean-air-ice interactions in the southwest Atlantic over the Quaternary Period.