Project

Discipline

GEOCHEMISTRY; ORGANIC BIOMARKERS; PALEOCLIMATE; NITROGEN ISOTOPES; CARBON CYLCE; SOUTHERN OCEAN; PALEOCEANOGRAPHY

Lead
Lay summary
The analysis of the air bubbles trapped in Antarctic ice has revealed that atmospheric carbon dioxide concentrations have varied in step with atmospheric temperatures and global ice volume over the glacial/interglacial (G/IG) cycles of the last 800,000 years. Model calculations suggest that these CO2 variations played a key role in the energy balance of the climate system that could represent up to half of the forcing governing G/IG climate change. Hence, the study of the relationship between atmospheric CO2 and climate across the G/IG transitions of the Pleistocene can provide important insights on the present-day and future response of the Earth system to anthropogenic forcing. However, after several decades of research the ultimate cause of G/IG variations in atmospheric carbon dioxide concentrations are not completely understood. In recent years, it has become increasingly apparent that a successful explanation of the full G/IG atmospheric CO2 change relies on a combination of physical and biogeochemical processes occurring in the Southern Ocean that are involved in the regulation of the deep ocean carbon reservoir, which include changes in atmospheric and ocean circulation, carbonate chemistry, air/sea gas exchange and marine biological productivity. The overall objective of this project is to investigate the main Southern Ocean processes driving changes in the marine carbon cycle though time, and assess their role in modulating atmospheric carbon dioxide concentrations. The project aims to provide new insights into these questions by applying a multidisciplinary approach that combine the generation of new biomarker and microfossil-bound N isotopes records covering the last G/IG cycle in previously unexplored regions of the SO.

Direct link to Lay Summary

Last update: 21.02.2013

Active participation

Communication	Title	Media	Place	Year

Number	Title	Start	Funding scheme

The response of the climate system to increasing atmospheric greenhouse gas concentrations is a subject of major concern in our society. Model simulations of future climate scenarios remain associated with significant uncertainty in both the magnitude and geographical distribution of this response (IPCC, 2007). The validation of these climate models relies on the comparison of its outputs to instrumental and paleoclimatic data as a way to assess the consistency of model predictions with the evidences from the past. Thus, the detailed reconstruction of the state of the Earth system in the past, and the evaluation of the magnitude, variability and causes of past climate changes has an obvious societal relevance, as this information is used as a base to guide long-term environmental policies, and to develop adaptation/mitigation strategies to the ongoing and future climate change (Jansen et al., 2007). The analysis of the air bubbles trapped in Antarctic ice has revealed that atmospheric carbon dioxide concentrations have varied in step with atmospheric temperatures and global ice volume over the glacial/interglacial (G/IG) cycles of the last 800,000 years (Luthi et al., 2008; Petit et al., 1999; Siegenthaler et al., 2005). Model calculations suggest that these CO2 variations played a key role in the energy balance of the climate system that could represent up to half of the forcing governing G/IG climate change (Sigman and Boyle, 2000; Sigman et al., 2010). Hence, the study of the relationship between atmospheric CO2 and climate across the G/IG transitions of the Pleistocene can provide key insights on the present-day and future response of the Earth system to anthropogenic forcing. However, after several decades of research the ultimate cause of G/IG variations in atmospheric carbon dioxide concentrations remains among the most important unresolved questions in Earth sciences. The modern Southern Ocean (SO) ventilates the largest fraction of the deep-ocean, and represents the biggest open ocean region where the extraction of nitrate and phosphate by marine phytoplankton is incomplete. This incomplete utilization of nutrients represents an important leak in the modern global biological pump because it allows the escape of deeply sequestered carbon back to the atmosphere, thereby contributing to keep atmospheric CO2 levels high during interglacial times. Hence, it has become increasingly apparent in recent years that a successful explanation of the full G/IG atmospheric CO2 change relies on a combination of physical and biogeochemical processes occurring in the Southern Ocean that are involved in the regulation of the deep ocean carbon reservoir, which include changes in atmospheric and ocean circulation, carbonate chemistry, air/sea gas exchange and marine biological productivity (Sigman and Boyle, 2000; Sigman et al., 2010). However, the relative contribution of the different process to the overall dynamics of the system is still not fully constrained, limiting our capability to predict the behaviour of the oceanic carbon cycle under current and future anthropogenic perturbation.The overall objective of this project is to investigate the main Southern Ocean processes driving changes in the marine carbon cycle though time, and assess their role in modulating atmospheric carbon dioxide concentrations. More specifically, the project aims to contribute to constrain the changes in dust/iron deposition, marine export production, nutrient utilization, and surface ocean hydrography during ice ages in previously unexplored regions of the Southern Ocean. In addition, the proposed project aims to provide new insights on the mechanisms of dust generation/transport, and the potentially associated changes in atmospheric circulation patterns in the SO. This objectives will be achieved applying an innovative multidisciplinary approach that combine the generation of new biomarker (including compound specific stable isotopes and radiocarbon) and microfossil-bound N isotopes records in previously unexplored regions of the SO, with the aim to better constrain the effect of different physical and biogeochemical processes on atmospheric CO2 concentrations under different climatic states of the past.Since 2005 I have been focusing my research on the study of the Southern Ocean, and its role in driving atmospheric CO2 changes through time. During this time, I have published various relevant articles on the field of this proposal, including several papers as first and corresponding author in leading scientific journals (e.g. Science and Nature), I have acquired experience on a wide range of techniques and methods applied in paleoceanographic studies, and I have participated in several research cruises to the polar oceans. This proposal will allow me to pursue my research on this topic and will offer me the opportunity to broaden my scientific horizons by adding new analytical skills for the study of the marine carbon cycle. My scientific background demonstrates that I have the necessary skills and experience to undertake this project. Indeed, the project proposed here represents in some ways the logical extension of my PhD and post-doctoral research, and will contribute to enhance my capabilities to consolidate an independent and successful research career.