Carbonates are the largest reservoirs of carbon on Earth. From mid‐Mesozoic time, the biologically catalyzed precipitation of calcium carbonates by pelagic phytoplankton has been primarily due to the production of calcite by coccolithophorids. In this paper we address the physical and chemical processes that select for coccolithophorid blooms detected in Sea‐viewing Wide Field‐of‐view Sensor (SeaWiFS) ocean color imagery. Our primary goal is to develop both diagnostic and prognostic models that represent the spatial and temporal dynamics of coccolithophorid blooms in order to improve our knowledge of the role of these organisms in mediating fluxes of carbon between the ocean, the atmosphere, and the lithosphere. On the basis of monthly composite images of classified coccolithophorid blooms and global climatological maps of physical variables and nutrient fields, we developed a probability density function that accounts for the physical chemical variables that predict the spatiotemporal distribution of coccolithophorids in the world oceans. Our analysis revealed that areas with sea surface temperatures (SST) between 3° and 15°C, a critical irradiance between 25 and 150 μmol quanta m −2 s −1 , and decreasing nitrate concentrations (ΔN/Δt < 0) are selective for upper ocean large‐scale coccolithophorid blooms. While these conditions favor both Northern and Southern Hemisphere blooms of the most abundant coccolithophorid in the modern oceans, Emiliania huxleyi , the Northern and Southern Hemisphere populations of this organism are genetically distinct. Applying amplified fragment length polymorphism as a marker of genetic diversity, we identified two major taxonomic clades of E. huxleyi ; one is associated with the Northern Hemisphere blooms, while the other is found in the Southern Hemisphere. We suggest a rule of “universal distribution and local selection”: that is, coccolithophorids can be considered cosmopolitan taxa, but their genetic plasticity provides physiological accommodation to local environmental selection pressure. Sea surface temperature, critical irradiance, and ΔN/Δt were predicted for the years 2060–2070 using the NCAR Community Climate System Model to generate future monthly probability distributions of coccolithophorids based upon the relationships observed between the environmental variables and coccolithophorid blooms in modern oceans. Our projected probability distribution analysis suggests that in the North Atlantic, the largest habitat for coccolithophorids on Earth, the areal extent of blooms will decrease by up to 50% by the middle of this century. We discuss how the magnitude of carbon fluxes may be affected by the evolutionary success of coccolithophorids in future climate scenarios.
The Sea-viewing Wide Field-of-view Sensor (SeaWiFS) provides global monthly measurements of both oceanic phytoplankton chlorophyll biomass and light harvesting by land plants. These measurements allowed the comparison of simultaneous ocean and land net primary production (NPP) responses to a major El Niño to La Niña transition. Between September 1997 and August 2000, biospheric NPP varied by 6 petagrams of carbon per year (from 111 to 117 petagrams of carbon per year). Increases in ocean NPP were pronounced in tropical regions where El Niño–Southern Oscillation (ENSO) impacts on upwelling and nutrient availability were greatest. Globally, land NPP did not exhibit a clear ENSO response, although regional changes were substantial.
Among the factors affecting the photosynthetic rate of marine phytoplankton, aeolian iron (Fe) fluxes appear to be critical in several large regions of the global ocean. Here we present an analysis of in situ aerosol iron data obtained from a wide variety of marine locations to quantify the seasonal Fe inputs to the global ocean. When extrapolated to the global ocean, our results indicate strong seasonal variations in aeolian Fe fluxes in different oceanic basins. The predominant fraction of the Fe inputs enters the oceans in the Northern Hemisphere, with the summer flux rates ca. twice those of winter. The high Fe fluxes in the Northern Hemisphere are concentrated in low and mid‐latitudes. With the promising new data from MODIS aboard the Terra satellite, the linkage between Fe fluxes and phytoplankton biomass and productivity may be soon further quantified.
In this report, we describe results from the first three years of global Sea-Viewing Wide Field-of-view Sensor (SeaWiFS) ocean chlorophyll and land plant measurements. This time period covered the end of one of the largest El Nino events in the past century and a strong La Nina. During this transition, terrestrial plant photosynthesis exhibited only a small change, whereas a significant increase in oceanic photosynthesis was observed. Latitudinal distributions of ocean production indicated that this increase in photosynthesis during the La Nina was distributed in the equatorial belt as well as in high production areas. The analysis also illustrated the large 'missing bloom' in ocean phytoplankton in the southern ocean. While land photosynthesis remained fairly steady during the third year of SeaWiFS measurements, ocean phytoplankton production continued to increase, albeit at a lower rate than from 1997 to 1999. Our results represent the first quantification of interannual variability in global scale ocean productivity. Significant Findings: An increase in ocean production during the first three years of the SeaWiFS mission; a strong hemispheric difference in the latitudinal distribution of ocean photosynthesis.
