Figure 1.
Global carbon stocks and fluxes (arrows) estimated for the
preindustrial period (black arrows and numbers) and the industrial
period (red arrows and numbers). This figure is reproduced from
Sarmiento and Gruber 2002.
The strength of the biological pump, i.e. how much carbon is
sequestered, has been the focus of active oceanographic research for
over 4 decades. Two paradigms have evolved over time that have
driven much of the ocean research; these are the New Production and
Export Production paradigms. The New Production paradigm defines
primary production in nitrogen terms and states that a fraction of
primary production is supported by nitrogen that is introduced to the
ecosystem, and therefore could be removed from the system. This
paradigm was extended to relate new production to total production
(ie., primary production) represented by the f-ratio.
Moreover, new production was explicitly linked to export production
(ie., the amount of carbon that is exported). Eppley and Peterson
used the f-ratio as a metric to predict the strength of the biological
carbon pump across ocean regions. This paradigm has evolved over
time to include
additional data and take slightly different representations.
Although the generalities of the Export Production paradigm, coastal
regions have higher f-ratios than the open ocean, still hold values
for each system must be determined experimently and not 'estimated'
from the export production paradigm. A significant
finding from the NSF-funded ocean time-series in the Sargasso Sea is
that the f-ratio is variable in time. For example,
the export-ratio (equivalent to the f-ratio) can
range from 5-30% in the Sargasso Sea (Figure
2).
Investigations into the factors controlling this wide range of
variability are an active component of my research program.
Figure 2.
Time-series plots of the export ratio (upper panel) and primary
production and export flux (lower panel) in the Sargasso Sea.
Figure 3.
Time-series plots of (A) the anomaly in
haptophyte biomass (thick line) and 0-100m averaged temperature (thin
line), (B) the anomaly in haptophyte biomass and NAO index (thin line),
and (C) the model II linear regression between the haptophyte biomass
anomaly and the NAO index. Figure taken from Lomas and
Bates 2004.
However, all phytoplankton are not
created
equal. Some
phytoplankton require silicic acid to form a hard glass shell to
protect them from grazers, others may lack the
genes for assimilate various nitrogen
substrates, while others have inducible enzyme systems for organic
phosphorus assimilation.
This diversity in physiological capabilities
has a strong impact on nutrient
biogeochemical cycles in
the ocean, including our estimation of the f-ratio, and more
importantly our ability to understand and predict
them. Also, this physiological flexibility also allows phytoplankton to
respond
differently physical forcing in the open ocean. For example,
coccolithophorids (haptophyte phytoplankton that are covered in calcium
carbonate scales called coccoliths) are a dominant component of the
marine phytoplankton community in the Sargasso Sea, particularly during
the winter/spring bloom. Variability
in the abundance of coccolithophorids has been linked to variability in
the North Atlantic Oscillation (Figure
3). The NAO is the dominant multi-annual mode of climatic
variability in the Sargasso Sea and determines if winter storms moving
across the Atlantic Ocean take a more southerly track (negative
anomaly) or a more northerly track (positive anomaly). This
impacts the net heat loss in the Sargasso Sea and ultimately the extent
of convective mixing in the winter and ultimately nutrient
inputs.
Interrelationships between
phytoplankton diversity, biogeochemical macronutrient cycles and a
changing world.
The open ocean, those regions where the depth exceeds 500 meters, covers about 60% of the earth's surface area and accounts for greater than 99% of livable 'space' on planet earth. The open ocean is characterized by a thin layer, about 100 meters thick, at the surface where there is sufficient light for photosynthesis to occur. The single-cell plants, phytoplankton, that live in this sunlit realm account for only about 2% of the total biomass of photosynthetic organisms on earth yet they account for ~50% of the total global photosynthesis. This means that the average phytoplankton only lives for a week before being eaten or sinking into the ocean depths. This entire process is called the 'Biological Carbon Pump', and is responsible for absorbing a significant fraction of the carbon dioxide released by human activities (Figure 1).
The open ocean, those regions where the depth exceeds 500 meters, covers about 60% of the earth's surface area and accounts for greater than 99% of livable 'space' on planet earth. The open ocean is characterized by a thin layer, about 100 meters thick, at the surface where there is sufficient light for photosynthesis to occur. The single-cell plants, phytoplankton, that live in this sunlit realm account for only about 2% of the total biomass of photosynthetic organisms on earth yet they account for ~50% of the total global photosynthesis. This means that the average phytoplankton only lives for a week before being eaten or sinking into the ocean depths. This entire process is called the 'Biological Carbon Pump', and is responsible for absorbing a significant fraction of the carbon dioxide released by human activities (Figure 1).
Please visit the rest of my
lab group's web site to learn
more about the research that we are doing and how we are studying the
role of phytoplankton diversity on the functioning of the biological
carbon pump and how this might change in the future ocean.