labs_title

Caldeira Lab Research:Ocean acidification and ocean carbon cycle

Seasonal rhythms of net primary production and particulate organic carbon flux to depth describe the efficiency of biological pump in the global ocean

Michael J. Lutz, Ken Caldeira, Robert B. Dunbar, & Michael J. Behrenfeld

The marine biosphere is a major component of the global carbon cycle, responsible for roughly half of the annual photosynthetic absorption of CO2 from the atmosphere. However, there is little basis to predict how potential alterations in upper ocean ecosystems may influence the capacity of the ocean to store carbon.


Lutz, M. J., K. Caldeira, R. B. Dunbar, and M. J. Behrenfeld (2007), Seasonal rhythms of net primary production and particulate organic carbon flux to depth describe the efficiency of biological pump in the global ocean, J. Geophys. Res., 112, C10011, doi:10.1029/2006JC003706.

Figure 4: The geographic distribution of the seasonal variation index (annual standard deviation divided by average) of net primary production (NPP). This estimate is derived from NPP climatology modeled following Behrenfeld and Falkowski [1997a] and constructed from 7 years of satellite-based estimates of sea surface temperature and chlorophyll. Arrows indicate locations of the meridional transects of NPP time series shown in Figure 5. Missing data (dark grey) indicates landmasses and permanent ice cover.

Abstract

We investigate the functioning of the ocean’s biological pump by analyzing the vertical transfer efficiency of particulate organic carbon (POC). Data evaluated include globally distributed time series of sediment trap POC flux, and remotely sensed estimates of net primary production (NPP) and sea surface temperature (SST). Mathematical techniques are developed to compare these temporally discordant time series using NPP and POC flux climatologies. The seasonal variation of NPP is mapped and shows regional- and basin-scale biogeographic patterns reflecting solar, climatic, and oceanographic controls. Patterns of flux are similar, with more high-frequency variability and a subtropical-subpolar pattern of maximum flux delayed by about 5 days per degree latitude increase, coherent across multiple sediment trap time series. Seasonal production-to-flux analyses indicate during intervals of bloom production, the sinking fraction of NPP is typically half that of other seasons. This globally synchronous pattern may result from seasonally varying biodegradability or multiseasonal retention of POC. The relationship between NPP variability and flux variability reverses with latitude, and may reflect dominance by the large-amplitude seasonal NPP signal at higher latitudes. We construct algorithms describing labile and refractory flux components as a function of remotely sensed NPP rates, NPP variability, and SST, which predict POC flux with accuracies greater than equations typically employed by global climate models. Globally mapped predictions of POC export, flux to depth, and sedimentation are supplied. Results indicate improved ocean carbon cycle forecasts may be obtained by combining satellite-based observations and more mechanistic representations taking into account factors such as mineral ballasting and ecosystem structure.