Green Ocean modelling

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A tool to understand the interactions between marine ecosystems and climate

Background

The Earth’s climate is changing. Indeed warmer temperatures, changes in precipitation, ice cover, river fluxes and atmospheric dust deposition have all been observed in recent decades. In addition, the ocean surface has become more acidic due to the absorption of increased atmospheric carbon dioxide (CO2). How do these changes impact marine ecosystems? To answer this we need better models capable of capturing the dynamics of marine ecosystems, and adequate and continued ocean observation programmes.

Why is ecosystem dynamics so important for interpreting climate change impacts?

Firstly, because of the nature of food webs in the ocean. Phytoplankton, the smallest marine organisms, transform energy from the sun into organic tissue. Phytoplankton are eaten by zooplankton, which are eaten by small fish, and these by bigger fish and so on. Changes in the abundance, type and distribution of phyto- and zoo-plankton result in complex impacts on the distribution and production of fish populations.

Secondly, because marine ecosystems have an influence on the composition of gases in the atmosphere. Indeed, the production and sinking of organic particles in the oceans helps regulate the concentration of the main greenhouse gas, CO2. Without the action of marine ecosystems atmospheric CO2 would be 1.5 times higher than it is today. Any changes in marine ecosystems could have an impact on atmospheric CO2. Marine ecosystems also emit other greenhouse gases and DMS (dimethyl sulfide), which has a cooling effect on climate.


What is Green Ocean Modelling?

Dynamic Green Ocean Models are mathematical representations of the ocean which include ocean currents, chemical processes and a representation of marine ecosystems that is based on the concept of Plankton Functional Types (PFTs). Plankton both responds to, and influences climate. In order to quantify and understand the interactions between marine ecosystems and climate, phytoplankton and zooplankton communities are simplified in the model into PFTs according to their size and functional role (Figure 1).


Bacteria
Phytoplankton
Zooplankton
0307.picohetero.PNG
0307.picoauto.PNG
0307.n2fixers.PNG
0307.coco.PNG
0307.DMS.PNG
0307.mixed.PNG
0307.silicifiers.PNG
0307.proto.PNG
0307.meso.PNG
0307.macro.PNG
pico-heterotrophs; remineralise dissolved and particulate organic matter
pico-autotrophs; contribute to primary production but not to export of carbon
N2-fixers; control total amount of reactive N
calcifiers; produce more than half the marine carbonate flux, sensitive to pH
DMS-producers; influence atmospheric sulphur cycle
mixed; the background biomass of phytoplankton
silicifiers; contribute to export of carbon to deep ocean
proto; graze on small phytoplankton, control blooms
meso; graze on all sizes of plankton, produce fast-sinking faecal pellets which export carbon
macro; graze on all sizes of phyto-plankton and produce fast-sinking faecal pellets
Figure 1. Ten PFTs were identified that need to be simulated explicitly in order to capture important biogeochemical processes in the ocean.
Bacteria
0307.picohetero.PNG
pico-heterotrophs; remineralise dissolved and particulate organic matter
0307.picoauto.PNG
pico-autotrophs; contribute to primary production but not to export of carbon
0307.n2fixers.PNG
N2-fixers; control total amount of reactive N
0307.coco.PNG
calcifiers; produce more than half the marine carbonate flux, sensitive to pH
Phytoplankton
0307.DMS.PNG
DMS-producers; influence atmospheric sulphur cycle
0307.mixed.PNG
mixed; the background biomass of phytoplankton
0307.silicifiers.PNG
silicifiers; contribute to export of carbon to deep ocean
0307.proto.PNG
proto; graze on small phytoplankton, control blooms
Zooplankton
0307.meso.PNG
meso; graze on all sizes of plankton, produce fast-sinking faecal pellets which export carbon
0307.macro.PNG
macro; graze on all sizes of phyto-plankton and produce fast-sinking faecal pellets
Figure 1. Ten PFTs were identified that need to be simulated explicitly in order to capture important biogeochemical processes in the ocean.