Ocean Modelling (T. Frölicher)

Introduction

Extreme climate and weather events shape the structure of biological systems and affect the biogeochemical functions and services they provide for society in a fundamental manner. There is overwhelming evidence that the frequency, duration and intensity of extreme events on land are changing under global warming, increasing the risk of severe and pervasive impacts on natural and socio-economic systems. In contrast, we know very little how extreme events in the ocean, especially those associated with warming, acidification, deoxygenation and nutrient stress will unfold in time and space. Of particular concern are compound events, which correspond to events with multiple concurrent and/or consecutive drivers (e.g. marine heatwaves co-occuring with very low nutrient levels) resulting in extreme consequences for marine ecosystems. This knowledge gap is of particular concern as some recently observed physical-biogeochemical (compound) events revealed the high vulnerability of marine ecosystem and fisheries, but also human societies, to such events.

We investigate and attribute past and future changes in ocean (compound) extreme events and assess and map the risk of these events for marine organisms and ecosystems. In particular, we quantify changes in marine heatwaves and ocean acidification extreme events by synthesizing and analyzing satellite-based and in-situ physical and biogeochemical observations. We also run global Earth system model simulations to quantify and understand the drivers of past and future changes in ocean extreme events and to attribution specific ocean extreme events to human-caused climate change and natural variability. The integration of available and newly developed marine ecosystem exposure and vulnerability indices into the Earth system modeling framework allows us to quantify regional risk levels for marine organisms and ecosystems to key ocean extreme events. Overall, we aim at a major breakthrough in our understanding of the fundamental processes governing ocean extreme events and whether organisms and ecosystems might be pushed to the limits of their resilience and even beyond, potentially causing dramatic and irreversible changes.

Working at the interface between ocean dynamics, marine biogeochemistry and climate, another research activity in our group concentrates on understanding the ocean’s role in nutrient and carbon cycling, and ultimately climate. We are particular interested in understanding the processes that control ocean heat and carbon uptake, and ultimately transient climate change.

The most recent global distribution of marine heatwaves, where MHWs are defined to exceed local temperature thresholds. The thresholds are based on the local 99th percentiles of daily SST data from NOAA (reference period 1982-2011). Colors indicate the degree of threshold exceedance in degrees Celsius. Further information can be found here.

Methods

Our work combines observations and theoretical/statistical aspects with comprehensive climate models, such as the Earth system model of the Geophysical Fluid Dynamics Laboratory (GFDL ESM2M) and the Earth system model of the National Centre for Atmospheric Research (NCAR CSM1.4-carbon). We run the Earth system models at the Swiss National Supercomputing Centre and on a local Linux cluster.

 

Group members