Project 4 - Sea Ice and Carbon Cycle Feedbacks
This project investigates drivers of variability in the cycles of sea ice growth and decay, and Southern Ocean CO2 uptake and release, in order to assess the resulting feedbacks on oceans, ice shelves, ecosystems, and carbon budgets
Why this research project, and what do we plan to do?
New understanding is needed to explain present-day trends and predict long-term change in sea ice and ocean CO2 exchange change in a +2°C (Paris Agreement) or warmer, world.
Research Questions
- What are the drivers of sea ice variability and changes in Southern Ocean CO2 uptake?
- Are they related?
- What are the consequences?
Research Activities
- explore spatio-temporal variability in sea ice characteristics (e.g. thickness, area, persistence)
- quantify processes that control break-up and advection of sea ice
- investigate the role of polynyas in sea ice dynamics
- assess the role of platelet sea ice as a key habitat and source of primary productivity for marine ecosystems
- consider how physical (e.g. wind stress, temperature, sea ice and deep-water formation) and biological (e.g. phytoplankton blooms) drivers contribute to Southern Ocean CO2 uptake
- explore linkages between sea ice, fast ice, the Ross Ice shelf, and implications for Antarctic ice sheet mass balance
The project focuses on the Ross Sea region, with particular attention to the Ross Sea and Terra Nova Bay polynyas. However, analysis of change and variability in sea ice and the carbon cycle on larger scales and connections to atmospheric circulation will involve climate processes across the whole of the Southern Ocean and much of the Southern Hemisphere. Past, present, and future change will be investigated using a combination of paleoclimate proxies, modern observations, remote sensing, and empirical and process modelling.
Objective 1: Seasonal to Interdecadal Variability of Sea Ice in the Ross Sea
Objective Leader: James Renwick
Goal: To understand large-scale influences on the seasonality and interdecadal variability of sea ice in the Ross Sea.
Hypotheses
- Sea ice concentration and extent over the Ross Sea is controlled on large scales by atmospheric variability (katabatic winds, the SAM, ENSO and Zonal Wave three) and ocean characteristics (freshening, stratification). This is being tested via analysis of reanalysis output and satellite estimates of sea ice concentration, combined with sea ice modelling experiments.
- Sea ice concentration over the Ross Sea is controlled on small scales by polynya-related energy fluxes and air-sea coupling. This is being tested via a combination of field observing campaigns and analysis of high-resolution (1km scale) satellite imagery.
Figure: Example extremes of the sea ice seasonal cycle, from 2008/2009. Source: National Snow and Ice Data Center, https://nsidc.org/
Objective 2: Interannual Variability of CO2 Uptake in the Southern Ocean
Objective Leader: Jocelyn Turnbull
Goal: To attribute recent changes in the Southern Ocean carbon sink to atmospheric, biological and oceanic processes, and add significantly to existing sparse and seasonally-biased data.
Hypotheses:
- The rate of upwelling of old, deep waters governs the overall rate of CO2 uptake. This is being tested through observations of 14CO2 and other trace gases over the Southern Ocean combined with dynamical process modelling.
- Increasing freshwater fluxes from glacial melt will enhance primary productivity and contribute to increased seasonal amplitude of CO2 uptake and release, and ultimately more carbon export to the deep ocean. This is being tested through plankton ecosystem modelling and comparison to paleoclimate evidence from past warm intervals.
Objective 3: Polynya Processes
Objective Leader: Wolfgang Rack
Goal: To quantify sea ice volume and its temporal and spatial variations, and improve understanding of the processes shaping the ice conditions in and around the polynyas (sea ice production areas).
Hypothesis:
- The interplay between the Ross Sea Polynya and the Terra Nova Bay Polynya manifests itself in the structure of the deformational ice zone in between. This is being tested by satellite data fusion and downscaling techniques combined with airborne measurements of ice thickness, ocean currents and wind conditions.
- Feedback loops between ocean-atmosphere heat fluxes and offshore winds are wind-regime dependent, influencing variability in the production of dense water masses. This is being tested by a snapshot of Electromagnetic (EM) Bird sea ice thickness and oceanographic data in combination with high-resolution satellite data.
Figure: Satellite image of Ross Sea, McMurdo Sound, and Terra Nova Bay Polynyas. The purple line indicated the ice shelf edge.
Objective 4: Platelet Ice as a Habitat
Objective Leader: Natalie Robinson
Goal: To quantify the spatial variability of key physical parameters influencing the distribution and structure of sub-ice platelet layers, and their role as a habitat.
Hypotheses:
- Platelet ice plays a critical role in supporting the ecosystem of McMurdo Sound and the wider Ross Sea, by providing a substrate for algae and a habitat for organisms. This is being tested through in-situ observing combined with biogeochemical modelling
- Spatial and temporal variability in the physical environment associated with sub-ice platelet layers is correlated with biomass variability over a range of scales in space and time. This is being tested through new in-situ observing combined with biogeochemical modelling.
