Mary-Elena Carr

In collaboration with Andrew Thomas, University of Maine; P. Ted Strub, Oregon State University; Jose Luis Blanco, Old Dominion Universtity; and Edward Kearns, University of Miami.

Summary

The coastal upwelling regions associated with the Eastern Boundary Currents (EBC) are important because of their high productivity. Although their area is only 0.1% of the world ocean, they account for 5% of global primary production and 17% of global fish catch (Pauly and Christensen 1995). This high biological productivity is made possible by the presence of cold, nutrient-rich water in the illuminated surface layer as a result of equatorward wind-forced coastal upwelling. The shallow offshore flow maintains the recently-upwelled water in high light conditions for sufficient time to enable biological utilization. The Canary, Benguela, California, and Peru-Humboldt Currents have long been reknown for their productive fisheries, primarily of small pelagics such as sardine and anchovy. The anchoveta fishery of coastal Peru was the largest recorded fish stock before its collapse in 1972 due to the combined effect of El Niño and excessive fishing pressure. The yield of 12 million metric tons in 1971 accounted for one-sixth of global fish catch between 1963 and 1972 (Bakun 1996).

Approach

Satellite: We are carrying out studies of the seasonal pattern of upwelling as well as using satellites to study and monitor El Niño conditions.

Figure 1 below (Carr et al, submitted) shows the impact for the planktonic community of the evolution of oceanographic conditions associated with El Niño forcing. We changed changing the area over which we average chlorophyll concentrationsmeasured by SeaWiFS: nominal 18-, 36-, and 81-km bins. Although chlorophyll concentrations decreased in the 18-km bins (a) concurrent with the SSH peaks, the decrease was much more substantial for larger averaging areas (b and c). Averaging over a larger area incorporates increasing offshore extent, which directly informs of the width of the high nutrient upwelling zone. El Niño conditions are generally accompanied by reduced width of the coastal band of high chlorophyll and this is confirmed in this averaging scale exercise.

Carr, M.-E. and K. Broad. 2000. Satellites, society, and the Peruvian fisheries during the 1997-1998 El Niño. pp 171-190. Satellites, Oceanography and Society. Elsevier Press.

Thomas, A.C., Blanco, J. L., M.-E. Carr, P.T. Strub, and J. Osses. 2001. Variability of satellite-measured chlorophyll and temperature off off northern Chile during the 1996-1998 La Niña and El Niño. Journal of Geophysical Research 106, 899-915.

Blanco, J. L., A.C. Thomas, M.-E. Carr, and P.T. Strub. 2001. Seasonal climatology of hydrographic conditions in the upwelling region off northern Chile. Journal of Geophysical Research 106, 11,451--11,467.

Carr, M.-E. 2002. Estimation of potential productivity in Eastern Boundary Currents using remote sensing. Deep-Sea Res. Part II 49, 59-80.

Blanco, J. L., M.-E. Carr, A.C. Thomas, and P.T. Strub. 2002. Hydrographic conditions off off northern Chile during the 1996-1998 La Niña and El Niño. Journal of Geophysical Research, in press (vol 107).

Carr, M.-E., P. T. Strub, A. C. Thomas, J.-L. Blanco. Evolution of 1996-1999 La Niña and El Niño conditions off the western coast of South America: a remote sensing perspective. Submitted Journal of Geophysical Research.

Modeling:

We are using a size-based ecosystem model to study the effect of upwelling on the pathways of carbon in the planktonic ecosystem. This biological model has parameterized physical forcing and in future work will be coupled with numerical models of the mixed layer and of three-dimensional circulation.

Figure 2 below (Carr, submitted) shows the model output corresponding to six periods of 1996-1998: 'N' or normal conditions in 1996, 'EN1' the first El Niño maximum of sea level and SST in June 1997, 'REL', the relaxation period in August 1997, 'EN2' the second peak in December 1997, 'REC' the recovery conditions in May 1998, and 'LaN', La Niña conditions from June to December 1998. In the four parameters shown (phytoplankton biomass (a), photsythesis (b), carbon export due to sinking cells ad fecal pellets (c), and carbon available for higher trophic levels (D), and for a range of forcing conditions (El Niño and La Niña) the planktonic community is most impacted in the second El Nino maximum, reflecting the magnitude of the forcing variability and the duration of the anomalous conditions. The largest size class (net-phytoplankton) were most impacted in biomass, and carbon uptake, with implications for sinking cells and for higher trophic levels.

Carr, M.-E. 1998. A numerical study of the effect of periodic nutrient supply on pathways of carbon in a coastal upwelling regime. Journal of Plankton Research, 20 (3), 491-516.

Carr, M.-E. Simulation of carbon pathways in the planktonic ecosystem off Peru during the 1997-1998 El Ni\~no: the contribution of physical forcing and of phytoplankton size composition of the upwelling source water. Submitted to Journal of Geophysical Research.

Climatology:

This project is part of the JGOFS Synthesis and Modeling Project. We are working with Dr. Ed Kearns of the University of Miami to construct a historical climatology of the hydrography, nutrient concentrations and biology of the four EBC regions. These climatological fields will then be used to carry out carbon budget studies and as model input.

Kearns, E. and Carr, M-E. A hydrographic and nutrient climatology of four eastern boundary current regions. In preparation for the 2nd Deep-Sea Res. Special Issue on the Synthesis and Modeling Project.

Carr, M-E and Kearns, E. Production regimes in four eastern boundary current regions: a climatological and satellite comparison. In preparation for the 2nd Deep-Sea Res. Special Issue on the Synthesis and Modeling Project.