M4PE Seminar next Monday on Convergent Estimates of Marine Nitrogen Fixation to be delivered by visiting Professor Francois Primeau

Title: Convergent Estimates of Marine Nitrogen Fixation

Speaker: Francois Primeau (UC Irvine)

Date: Mon, 18/02/2019 – 4:00pm

Venue: RC-4082, The Red Centre (School of Mathematics and Statsitics), UNSW

Uncertainty in the global patterns of marine nitrogen fixation limits our understanding of the response of the ocean’s nitrogen and carbon cycles to environmental change. The geographical distribution and ecological controls on nitrogen fixation are difficult to constrain with limited in-situ measurements. Here Prof. Primeau will present an inverse model to constrain the residual mean circulation of the ocean and to estimate rates of marine nitrogen fixation.  The results demonstrate strong spatial variability in the nitrogen to phosphorus ratio of exported organic matter that greatly increases the global nitrogen-fixation rate. It is found that new nitrogen supports up to 50% of export in subtropical gyres, that nitrogen fixation and denitrification are spatially decoupled and that current-era nitrogen sources and sinks largely balance on multidecadal timescales. These findings suggest higher than expected ocean carbon export and weaker stabilizing nitrogen-cycle feedbacks than previously thought. 

Speaker Biography:

Francois Primeau is a Professor of Earth System Science at the University of California, Irvine. His research is at the interface between physical oceanography and biogeochemistry where he develops computational methods to make better inferences from data and models about the physical and biogeochemical state of the ocean.

All welcome!


Upcoming seminar by Sarah Perkins-Kirkpatrick on Stats and Heatwaves

Monday November 5th, 4pm
RC-4082, The Red Centre, UNSW 

Heatwaves are changing. What role does statistics have in understanding these changes?

Heatwaves are increasing in their frequency, intensity and duration. Loosely described as prolonged periods of excessive heat, statistical techniques underpin their measurement, understanding their changes, the physical mechanisms behind these changes, the role anthropogenic climate change plays, and estimates of uncertainty (or certainty)  surrounding these factors.  This talk will explore the vital role statistics has behind heatwaves, making our understanding of these high-impact events possible.

Dr Sarah Perkins-Kirkpatrick is an ARC Future Fellow at the Climate Change Research Centre, UNSW Sydney. Her background focuses on measuring heatwaves, what drives them, the role climate change plays and future projections in a warmer world. Sarah’s Future Fellowship is working towards improving the attribution methods of extreme events (such as heatwaves) to human influence, as well as determining whether the health impacts of heatwaves can be attributed to human influence on the climate. Since gaining her PhD in 2010, Sarah has published 60 peer reviewed scientific papers on climate extremes. She co-leads an expert team for the World Meteorological Organisation’s Commission for Climatology, and is a frequent voice in local and international media on all things climate change in heatwaves. Sarah has won numerous awards for her research, and was named one UNSW’s 20 rising stars who will change our world in 2016.

This seminar is part of the ‘Mathematics for Planet Earth’ initiative (mathsforearth.com) and is co-hosted by the Department of Statistic at the School of Mathematics and Statistics at UNSW, Sydney. Light refreshments will follow the seminar. 

Asymmetry of the ocean’s thermohaline circulation

The ocean is highly turbulent. Pathways of free-floating buoys are chaotic and circulation patterns are dominated by mesoscale eddies – the ocean’s equivalent to atmospheric storms. The ocean is at the same time organised.

Substances injected into the ocean follow broad and distinct routes near the sea surface from the Pacific to the Atlantic Ocean. As a result the North Pacific and North Atlantic Ocean’s are in marked contrast. The Pacific is cold and fresh and the Atlantic is warm and salty. Known as the thermohaline circulation, this helps maintain Europe’s relatively mild climate.

This project will explore the link between the asymmetry in northern hemisphere climates, the thermohaline circulation and the atmospheric forcing which sets the eventual temperature and salinity of sea-water. The project will pivot on the hypothesis that, by accident of geography and the position of southern hemisphere winds, warm saline water preferentially flows into the Atlantic. Moreover these effects will dictate the stability of the thermohaline circulation and European climate over coming centuries.

This project is supervised by Dr Jan Zika (UNSW Sydney). Please contact j.zika@unsw.edu.au for more information.

Submit your application by Oct 26 2018 for commencement in Term 1, 2019.

Linking the seasonal cycle of ocean water masses to transient climate change

In boreal winter the North Atlantic and Pacific Oceans become cold, dense and turbulent. Oxygen, carbon and other substances are drawn out of the atmosphere and ventilated into the deep ocean. In boreal summer, as the surface layers in the north warm, cooling and ventilation begins in the southern hemisphere in earnest.

The process of seasonal ventilation dictates the ocean’s role in climate – both present and future. Only in the last decade has a systematic understanding of seasonal ventilation become possible due to the presence of thousands of autonomous buoys (ARGO) and satellites measuring upper ocean temperature and salinity. Likewise never has the need to quantify it been more pressing.

This project will combine the latest observations to generate a quantitative picture of the formation, ventilation and destruction of cold dense water masses in both hemispheres. A key novelty of this project will be the use the water-mass transformation framework. Using this framework variability in water mass properties is attributed to surface heating and cooling, evaporation and precipitation, mixing and energetic drivers such as wind forcing.

This project is supervised by Dr Jan Zika (UNSW Sydney). Please contact j.zika@unsw.edu.au for more information.

Submit your application by Oct 26 2018 for commencement in Term 1, 2019.

Quantifying Global Water Cycle Change using Ocean Observations

Global rates of rainfall and evaporation are amplifying rapidly as a consequence of global warming. Recent studies have suggested that this ‘water cycle’ could be amplifying faster than global climate models had predicted. More accurate quantification of water cycle change and its causes is urgently needed. Changes in the water cycle leave an imprint on the ocean by changing ocean salinity. The candidate will quantify water cycle change based on new observations of ocean salinity and using novel methods developed by the supervisory team. These findings will help improve predictions of water cycle change that are relied upon by society.

This project is supervised by Dr Jan Zika (UNSW Sydney). Please contact j.zika@unsw.edu.au for more information.

Submit your application by Oct 26 2018 for commencement in Term 1, 2019.