30th Session of the IOC Assembly

Abstract

The world’s oceans contain an amazing diversity of life that is a bountiful source of oxygen & food plus a sink for CO₂. Oceanic phytoplankton are the primary source of organic carbon in the ocean. They consume some 50 gigatonnes of CO₂ and produce ~ 40% of global oxygen every year. Over the last few billion years plants, primarily phytoplankton, have removed ~99% of the CO₂ from the atmosphere and replaced it with oxygen. The exponential rise of humans has put these natural processes under stress from increasing pollution and overexploitation.   

Our predictions of the future state of our oceans come mostly from models. For phytoplankton these models predict a decline due to oceans that will be warmer, more acidic, increasingly stratified and have less nutrients in the euphotic zone. There is an increasing amount of laboratory evidence regarding the magnitude of these risks for phytoplankton associated with changes in temperature, light, nutrients, pH and CO₂. A brief synopsis shows these factors have substantial potential to reduce phytoplankton abundance and biodiversity. While laboratory studies provide a strong basis for predicting the future of phytoplankton the complex interactions of many factors that vary in time and space makes reliable extrapolation challenging. A more reliable method of predicting the future may come from examining the past. Examples of regional and global changes in phytoplankton that can be associated with proximal factors will be presented. Some of these changes are complex and appear to be determined by factors not well represented in our global models.

At regional scale the increasing strength central oceanic gyre currents appears to be driving the translocation of phytoplankton populations. A strengthening East Australia Current has moved phytoplankton populations, and some aspects of their preferred environment, thousands of kilometres over several decades. Some of these translocated species have achieved complete dominance in their new locations.  In the Tasman Sea changes to stratification have also produced a new autumn phytoplankton bloom. Changing patterns of precipitation are driving changes in phytoplankton communities within estuaries and our coastal seas. Long term drying, or droughts, are reducing nutrients in the ocean thousands of kilometres away from their riverine inputs. The impacts of these changes on higher trophic levels are not known.

Satellites measuring ocean colour provide a magnificent picture of global phytoplankton biomass. They tell us that over the past 20 years 57% of the ocean has shown a decline in phytoplankton, primarily in the central gyres. At the same time, however, only 10% of the ocean is both warming and declining in phytoplankton while 22% is warming and increasing in phytoplankton. Therefore, temperature alone is not enough to predict phytoplankton ecology. The best global data for understanding mechanisms and impacts on taxa comes from the ~ 350 long-term time-series laboriously compiled as part of the UN IOC Working Group IGMETS.  They also show that climate impacts on phytoplankton are often different from our predictions. For example, the time-series indicate there have been significant long-term changes in the phytoplankton taxa with diatoms increasing and dinoflagellates decreasing.  These observations are in strong contrast to model predictions. 

The existing dichotomy between models and observations strongly suggests that both are needed to properly manage our marine resources in a changing world. The adage “you can't manage what you can't measure” is very applicable.

Biography

Peter Thompson graduated from the Department of Oceanography at the University of British Columbia (Canada) and has since conducted research for the Department of Fisheries and Oceans (Canada), the University of Tasmania, (Australia) and Commonwealth Scientific Industrial Research Organization (CSIRO, Australia). He has gladly participated in a number SCOR and IOC working groups and very much appreciates the global leadership provided by the UN-IOC.  

Peter has spent years studying how phytoplankton live and grow in the laboratory, in estuaries and oceans. He has completed many field campaigns including ~ 20 oceanic research voyages to the Pacific and Indian Oceans. He has served the Australian government as an expert on ocean dumping and provided advice on creation of national and state marine protected areas. Peter has published ~ 120 peer-reviewed papers. His current scientific passion is using time series data to understand the effects of environmental change on phytoplankton ecology and thereby better support the sustainable use of our oceans.