Project Funding: 2007 - 2010

NRA: 2006 NASA: Ocean Biology and Biogeochemistry   

Funded by NASA

Abstract:
This proposal seeks to address several aspects of biogeochemical cycling in the Southern Ocean (SO) through simulations with a state-of-the-art ocean biogeochemical elemental cycling (BEC) model (Moore et al., 2004). The model includes an ecosystem component with key phytoplankton functional groups (diatoms, picoplankton, coccolithophores, diazotrophs, and Phaeocystis) and explicit biogeochemistry of key elements (C, N, P, Fe, Si, and O). The proposed study region stretches from Antarctica to the boundary with the subtropical gyres. We will also examine the downstream impacts of SO biogeochemical processes at lower latitudes. Phase one involves further development and improvement of the BEC model, including: a more realistic sedimentary Fe source, improved grazing and aggregation parameterizations, addition of an Fe influence on phytoplankton photosynthetic efficiency, and optimization of key model parameters for the Southern Ocean. A database of available in situ observations of key biogeochemical pools and fluxes will be synthesized and made publicly available. Several satellite products, in conjunction with the in situ database, will be used to improve and constrain the model (chlorophyll a, total POC, phytoplankton POC and community composition, sea surface temperature, percent sea ice cover, and wind speed/direction). Phase two will utilize the improved, optimized BEC model to determine the relative influence of different controls (especially light, iron, and silicon) on phytoplankton community structure, primary and export production, and how these controls relate to climate forcings. We will also examine how these factors influence air-sea exchange of CO2 in different regions, and examine the BEC model output for correlations that could be used to estimate the air-sea CO2 flux from remote sensing data. The current-climate simulations will provide a range of physical and biogeochemical forcings, which include spatial and temporal gradients in seasonal sea ice cover, wind speed, iron input, and sea surface temperature. A model robust enough to simulate the observed biogeochemical patterns across these environmental gradients can then be applied to examine the Southern Ocean role in past and future climate states. Phase three will simulate Southern Ocean ecosystem and biogeochemical dynamics under a future warming scenario (~year 2100) and under last glacial maximum (LGM) conditions. It has been suggested that the Southern Ocean carbon cycle plays a key role in both these climate states. We will be able to quantitatively evaluate these hypotheses, placing Southern Ocean biogeochemical cycling into the context of the Earth System. This work addresses several key science questions relevant to NASA goals: What are the key controls on biological productivity in different regions of the Southern Ocean, and how do they change with variations in climate and biogeochemical forcings? How do iron inputs from mineral dust and sediments influence phytoplankton ecology and biogeochemical cycling in the Southern Ocean? What are the biogeochemical and ecosystem impacts of variability in dust deposition over different timescales (from daily to inter-annual to glacial-interglacial cycles)? How do phytoplankton ecology and production influence SO air-sea CO2 exchange? What is the role of Southern Ocean biology and biogeochemistry in the global carbon cycle under different climate states?

2008 NASA Carbon Cycle & Ecosystems Joint Science Workshop Posters

• Modeling the Southern Ocean Carbon Cycle   --   (Jefferson Keith Moore, Shanlin Wang, Aparna Krishnamurthy)   [abstract]   [poster]

More details may be found in the following project profile(s):

• NASA Ocean Biology & Biogeochemistry (OBB) Project Profile