# Presentation: 524099

## Assessment of River Margin Air-Sea CO2 Fluxes

- Steven E. Lohrenz, Wei-Jun Cai, Xiaogang Chen,
- Merritt Tuel, and Feizhou Chen

## Introduction

**A major objective of the U.S. Global Change Research Program Climate Change Science Program Strategic Plan and the North American Carbon Program is the application of  satellite ocean color to characterize the spatial variability of air-sea CO****2**** flux in the oceans adjacent to the North American continent**

**Notes:**
Yet margins are highly sensitive to change, both natural and anthropogenic.   Although a relatively small fraction of total ocean area, margins are characterized by high biogeochemical rates, and high fluxes of materials 

## Introduction

**Despite their relatively small surface area, ocean margins may have a significant impact on global biogeochemical cycles, and potentially, in the global air-sea fluxes of CO****2**

**Notes:**
Yet margins are highly sensitive to change, both natural and anthropogenic.   Although a relatively small fraction of total ocean area, margins are characterized by high biogeochemical rates, and high fluxes of materials 

## Introduction

**Margin ecosystems receive inputs of terrestrial organic and mineral matter and exhibit intense geochemical and biological processing of carbon and other elements **
**Nowhere is this more evident that in regions influenced by large rivers**

**Notes:**
Yet margins are highly sensitive to change, both natural and anthropogenic.   Although a relatively small fraction of total ocean area, margins are characterized by high biogeochemical rates, and high fluxes of materials 

## Introduction

**Recent studies (Lohrenz and Cai, 2006) in the northern Gulf of Mexico and elsewhere (Tsunogai et al., 1999; Ternon et al., 2000; Cai, 2003) demonstrate that enhanced biological production in large river plumes may lower surface *****p*****CO****2**** levels such that these regions may exhibit a net surface influx of atmospheric CO****2**
**But characterizations have not been conducted over representative seasonal and discharge conditions  **

**Notes:**
Yet margins are highly sensitive to change, both natural and anthropogenic.   Although a relatively small fraction of total ocean area, margins are characterized by high biogeochemical rates, and high fluxes of materials 

## Introduction

**Systems are likely to differ depending on the both biological, chemical, and meteorological properties**
**Quantification of the contributions of river-influenced margins to regional CO****2**** fluxes is difficult due to the high degree of spatial and temporal variability in these regions**

**Notes:**
Yet margins are highly sensitive to change, both natural and anthropogenic.   Although a relatively small fraction of total ocean area, margins are characterized by high biogeochemical rates, and high fluxes of materials 

## Introduction

**Satellite-based regional approaches (e.g., Lefevre et al., 2002; Ono et al., 2003; Olsen et al., 2004; Lohrenz and Cai, 2006) can be used to extend the spatial and temporal coverage for broad scale assessments of *****p*****CO****2**** distributions and air-sea fluxes of CO****2****  **
**The primary objective of our research is to apply these approaches to the characterization of *****p*****CO****2**** and air-sea fluxes of CO****2**** in the river-influenced margin of the northern Gulf of Mexico**

**Notes:**
Yet margins are highly sensitive to change, both natural and anthropogenic.   Although a relatively small fraction of total ocean area, margins are characterized by high biogeochemical rates, and high fluxes of materials 

## Outline

**Brief description of approach as applied to the Mississippi River outflow region**
**Summary of initial findings**
**June 2003**
**August 2004**
**October 2005**
**Challenges and future directions**

## Approach

## Approach

**In situ measurements of surface *****p*****CO****2**** and environmental variables (T, S, chlorophyll) conducted**

## Approach

**Algorithm based on empirical relationships of in situ measurements of surface *****p*****CO****2**** to environmental variables (T, S, chlorophyll)**
**June 2003**

## Approach

**Apply algorithm to products retrieved from MODIS-Aqua imagery **

## Approach

**Produce pCO2 map **

## Approach

**Additional cruises in August 2004 and October 2005**
**            ****August 2004****	****	****	****October 2005**

## Approach

**PCA algorithms**
**August 2004 (*****r*****2****=0.858)****	****            October 2005 (*****r*****2****=0.974)**

## Results

**Aug 2004**

**August 2004**

## Results

## Results

**Aug 2004**

**October 2005**

## Results

## Results

**Air-sea flux calculations:**
**CO****2**** fluxes across the air-sea interface were calculated by the one-dimensional thin-film model:**
**CO****2**** Flux = *****k*********[*****p*****CO****2****(*****w*****) – *****p*****CO****2****(*****a*****)]**
**where *****k***** is the gas transfer velocity and has the largest uncertainty in the flux calculation; ******** is the solubility of CO****2**** at given temperature and salinity **

## Results

**Air-sea flux calculations:**
**Various sets of the gas transfer velocity, *****k*****, vs. wind speed relationships were used to provide a range of values to bracket the gas flux including:**
**Liss and Merlivat, 1986; Wanninkhof and McGillis, 1999; Nightingale et al., 2000; McGillis et al., 2001**

## Results

**There was net uptake of CO****2**** in June, but a net release in August and October**
**October 2005 followed two major storm events accompanied by coastal flooding; strong winds**

| Cruise | Air-Sea Flux (mmol m-2 d-1) |
| --- | --- |
| June 2003 | -(2-4)  |
| August 2004 | 6-10 |
| October 2005 | 53-120 |

## Challenges and Future Directions

**Challenges**
**Variability in conditions in coastal waters limits the generality of algorithms across temporal and spatial ranges**
**Remedy is to provide ample in situ data, including ship-based surveys and moored time-series**
**Couple ship-based operations with radiometric measurements to provide complementary data set**

## Challenges and Future Directions

**Future Directions**
**Continued characterization of Mississippi River system to capture range of seasonal and discharge conditions**
**Comparison of other river systems and shelf environments**
**Relate patterns to biogeochemical rates (primary production, net ecosystem metabolism) **
**Couple observations with ecosystem models to provide more informed understanding of carbon cycle controlling mechanisms**

## Acknowledgements

**Funding for this work was provided by NASA (NNG05GD22G and NNS04AB84H) **