Workshop on the Seasonal Cycle of the Carbon-Climate System in the Southern Ocean
Cape Town 23 – 25 August 2010
The seasonal cycle is not only one of the strongest modes of variability in different
components of the carbon cycle in the Southern Ocean but also the mode which couples
climate forcing to ecosystem responses such as productivity, diversity and ultimately carbon
export. We hypothesise that:
Evidence of adjustments in the climate forcing signal, through trends in the
interannual signal, will be reflected in changes in the magnitude, the phasing
and persistence of the seasonal cycle in the mixed layer physics and
particularly in the biogeochemistry through changes in the carbon cycle.
These signatures of climatic forcing could be used to better understand the influences of
altered physics, iron supply (atmospheric, deep and sea-bed), stratification, and changes in
trophic structures on the carbon fluxes of the Southern Ocean. However, important gaps
persist in our understanding of the sensitivity of biogeochemical processes to seasonal /
mesoscale forcing of surface ocean physics. These gaps are reflected in the capabilities of
observations and models to address both the seasonal and sub-seasonal as well as meso- and
sub-meso scales in understanding the coupling and feedbacks of the coupled carbon–climate
system in the Southern Ocean.
Coupled physics and biogeochemistry model capabilities have been improved significantly to
cope with the required resolution at the regional scale and maybe at the global scale.
Similarly, our observational capabilities, especially if planned at an integrated international
effort, make it possible to begin to address high resolution temporal and spatial domain at the
regional system scale.
This workshop will bring together an initial small interdisciplinary discussion group
comprised of physicists, biogeochemists, modellers and observationalists with the aim to:
1. Critically review our current understanding of the seasonal variability observed in the
Atlantic, Indian and Pacific sectors of the Southern Ocean, particularly:
a. Basin scale differences between the Pacific, Atlantic and Indian Oceans
physics – seasonal phenology – interannual variability in the carbon cycle
b. Role of changes in meridional advection
c. Scaling contributions to productivity of atmospheric and bottom derived iron
fluxes
d. Critical scales of mixed layer dynamics in coupling climate to carbon
2. Identify a series of 2 – 3 key questions on the drivers of the carbon – climate system
of the Southern Ocean that can be addressed collaboratively within 3 – 5 years in
order to constrain 21st century trends in this system
3. Discuss and identify modelling experiments to test the sensitivity of long term trends
of productivity and carbon fluxes to changes in the characteristics of the mixed layer
seasonal cycle.
4. Discuss the need, the feasibility and the format of a coordinated international (multiplatform) experiment(s) to understand the seasonal variability of the carbon cycle in
the Southern Ocean
The Workshop will be run over 3 days:
Day 1: Review our current understanding (plenary presentations followed by group
discussion)
Day 2: Workshop to formulate key questions and discuss modelling experiments
Day 3: Workshop to discuss the need for experiments and coordinated observations
Our aim in convening this workshop to is to explore ideas of scale sensitivities of the coupled
carbon–climate system as a basis to bring the physics and biogeochemistry communities
closer together but with a special focus on the biological pump – carbon export fluxes.
Co-conveners: Dr Pedro Monteiro, Dr Philip Boyd and Prof. Tom Trull
Workshop on the Seasonal Cycle of the Carbon-Climate System in the Southern Ocean
Cape Town 23 – 25 August 2010
Day 1:
The objective of Day 1 is to scope our understanding and recent learning around the theme of
the workshop. This will be done through a plenary day and a limited discussion. The main
discussion period will be in Days 2 & 3. Each presenter is asked to consider 2 – 3 questions
that they think will contribute to the objectives of Day 2 & 3. The presentation titles below
are indicative only and we ask that each of the participants come back by 15 August with a
final title that links their ideas to the workshop framework and objectives. Be provocative.
09:00 Welcome: TBD
09:15 Introduction and workshop goals: (Pedro Monteiro)
09:30 Synthesis of Southern Ocean Carbon Biogeochemistry in South Africa (Pedro
Monteiro et al)
09:50 Synthesis of Southern Ocean Carbon Biogeochemistry in Australia (Tom Trull et al)
10:10 Synthesis of Southern Ocean Carbon Biogeochemistry in New Zealand (Philip Boyd et
al)
10:30 Break
11:00 Interannual & Seasonal Production in the Southern Ocean: links between forcing,
production taxonomy and phenology (Kevin Arrigo)
11:30 Production in the Sub-Antarctic Zone: What do we know about seasonal control of
production? (Philip Boyd)
12:00 Comparative Basin scale seasonal cycle characteristics of Cholorophyll: Is there a
common link? (Sandy Thomalla / Nicolas Fauchereau)
12:30 Discussion
13:00 – 14:00 LUNCH
14:00 What might be the links between meso-scale – sub seasonal scale mixed layer
dynamics and the evolution of seasonal productivity in the Southern Ocean? (Marina Levy)
14:30 The basin scale contrasts of seasonal controls in the variability of NCP, GPP and
carbon export fluxes in the Southern Ocean? (Michael Bender / Nicolas Cassar)
15:00 Seasonal cycles in island ecosystem production are they different? (Crozex S Georgia
etc) (Mark Moore / Mike Lucas)
15:30 Break
16:00 What are the relative roles of ocean physics versus biogeochemistry in driving carbon
cycling in the contemporary Southern Ocean and how do these vary between basins and
zones? (Richard Matear)
16:30 What do models and observations tell us about the influence of sources and fluxes of
iron on the seasonal and interannual variability of productivity? (Alessandro Tagliabue)
17:00 Discussion
17:30 End – Transport to Dinner
Day 2 – Southern Ocean Biological Carbon Pump in 21st century climate
Objectives: Identify a series of 2 – 3 key questions on the drivers of the carbon – climate
system of the Southern Ocean that can be addressed collaboratively within 3 – 5 years in
order to constrain 21st century trends in this system. Identify what kind of modelling
experiments are required to address those questions and to optimise experimental and long
term observations
Eg: What kind of modelling experiments are needed to better understand
a. the climate – physics – biogeochemistry sensitivities
b. carbon – climate feedbacks
c. the highest priorities in observational experiments and long term observations
09:00 Synthesis of Workshop aims and key points arising from Day 1: 15 min
09:15: Short Plenary of Introductory Papers
09:15 What are the recent trends in the SAM and implications for seasonal mixed layer
dynamics and carbon biogeochemistry in the Southern Ocean? (Nicolas Fauchereau)
09:45 What do models tell us about the sensitivity of carbon fluxes (special focus on
biological pump) to the scales at which the Southern Ocean is forced? (Andrew Lenton /
Alessandro Tagliabue / Richard Matear)
10:15 Break
10:45 Workshop Discussion I: Chair Tom Trull
Possible Questions:
a) Is the seasonal cycle an important and useful mode to understand the linkages
between large scale Climate Modes and changes in the biological pump?
a. Ecosystem questions: phenology, taxonomy
b. Mixed layer dynamics – light vs nutrient supply
c. Influence of Fe sources: aerosol vs eddies, sediments, bottom pressure torque,
island wakes
b) How sensitive are these physics – biogeochemistry linkages to altered forcing due to
a changing climate?
c) What feedbacks could emerge as a result of a changing climate?
13:00 – 14:00 LUNCH
14:00 – 15:30 Workshop Discussion II
Discuss and identify modelling experiments to test the sensitivity of long term trends of
productivity and carbon fluxes to changes in the characteristics of the mixed layer seasonal
cycle.
16:00 – 17:30 Workshop Discussion III
Can modelling experiments help us to identify what type of observational requirements to
better understand the variability and long term trends in carbon fluxes in the Southern Ocean?
Day 3: Is there a strategic value of coordinating Cape Town, Hobart and Wellington as
centres of circumpolar Southern Ocean carbon – climate research and observation?
Questions:



What are the highest priorities in observational experiments and long term
observations in the Southern Ocean?
Is there the need and the feasibility of a coordinated international (multi-platform)
experiment(s) to understand the seasonal variability of the carbon cycle in the
Southern Ocean.
What form could it take?
This follows on from themes in Day 2 and in particular point - if the models are suggesting
where and what might be the most likely indicator of change - can we design an appropriately
scaled observational programme to confirm or refute this?
09:00 Review of Day 2
09:15 Scales of Variability of CO2 fluxes in the Southern Ocean. What does it tell us about
the scales at which models and observations should be made (Andrew Lenton)
09:45 Understanding the sensitivity of seasonal evolution of SAZ carbon fluxes to
interannual variability in forcing from time series experiments (Tom Trull/Scott Nodder)
10:15 Understanding the sensitivity of carbon fluxes to biogeochemical forcing from
observational experiments - from shipboard to large scale natural process studies eg: Crozex;
SAZ SENSE (Mark Moore / Mike Lucas / Tom Trull / Philip Boyd)
11: 15 – 13:00 Workshop Discussion I: Chair Phillip Boyd
13:00 – 14:00 LUNCH
14:00 – 15:30 Workshop Discussion II
15; 30 – 16:00 Coffee
16:00 – 17:30 Workshop Session III