Primary Productivity Measurements on NOAA's
Long Line Cruises
The partitioning of CO2 between ocean and atmosphere is affected by the pelagic food
web of the upper ocean. Photosynthesis, carried out primarily by small microscopic plants
(phytoplankton) in the shallow, well-lit layer of the ocean (the euphotic zone), converts
dissolved inorganic nutrients (primarily carbon dioxide) into particulate organic matter.
A major portion of this primary production is recycled within the food web above the
thermocline. The remaining fraction escapes from the upper ocean to the thermocline and
below, where most of it is recycled and only a minor fraction is deposited in the
sediments. It is the escaping fraction that regulates the concentration of carbon dioxide
in the upper ocean and since this layer is in contact with the atmosphere this process has
important consequences for the global carbon cycle and climate change. In the absence of
ocean primary production, surface total CO2 would be 20% higher, and at equilibrium with
such a surface ocean, the atmosphere would have a CO2 concentration close to double
present levels (Sarmiento et al., 1990). This simple exercise shows that ocean biological
processes have a profound impact on the global carbon cycle yet this impact is very poorly
understood and the subject of significant debate (Broecker 1991, Longhurst 1991, Banse
1991, Sarmiento 1991). Unraveling the role of biology in the ocean carbon cycle requires
simultaneous observations of biological and chemical properties over many temporal and
As we described the role of the ocean in the global ocean/atmosphere CO2 cycle is
intimately related to the biological production system. The primary producers influence
ocean/atmosphere exchange of biogenic gases (especially CO2) through the primary
production portion of the system. Eppley and Peterson (1979) recognized the need for a
relationship between primary production, new production and the export of primary
production to the deep ocean. New production is the process whereby new nutrients (e.g.,
nitrate), advected to the surface, are taken up and, with sunlight, used to synthesize new
plant material (Dugdale and Goering, 1967). At steady state this quantity is equivalent to
the nitrogen (and carbon) that are removed from the euphotic zone. We proposed to utilize
NOAA's commitment to make observations over a large portion of the global ocean and make
measurements of primary and new production in an attempt to quantify the effects of the
biological system on the carbon cycle.
Several studies have shown that the flux of carbon through the food web and to the deep
ocean is a function of total primary production (Betzer et al., 1984; Eppley and Peterson,
1979; Martin et al., 1987; Pace et al., 1987; Suess, 1980), however, it is clear that the
functions describing the coupling between the biological and chemical components are not
well resolved at present. Recent theoretical and experimental results point toward the
structure of the microbial food web as an important variable in regulating the fate of
primary production in the ocean (Michaels and Silver, 1988; Berger and Kier, 1984; Frost,
1984; Toggweiller et al., 1987, Sarmiento et al., 1989). Clearly the size distribution of
phytoplankton, linked to the supply of new nutrients, plays a role in the flow of
particulate matter through the upper ocean pelagic food web. For example, a diatom
dominated system, commonly dominated by large particles or aggregates and a short food
chain (Ryther, 1969), will have a different biogeochemical character than a picoplankton
dominated system, with small individual particles and a complex food web. Much of our
research has been geared at quantifying the relationship of major phytoplankton taxa to
primary production in Pacific and Equatorial equatorial and eastern Pacific boundary
upwelling regions (i.e. Chavez et al., 1990). The NOAA long line program is an opportunity
to determine if observations made in Pacific and Atlantic upwelling ecosystems hold for
the Indian Ocean.
As our understanding of the relationships between light, photosynthetic pigments, light
absorption and primary production has grown, bio-optical instrumentation has come to the
forefront of oceanographic research and become a serious candidate to at least partially
replace traditional discrete sampling and incubation experiments in measurements of
phytoplankton biomass, composition and production. What is presently required, however,
are more bio-optical measurements made concurrently with the traditional measurements.
These together with other carbon cycle measurements will allow for modeling biogeochemical
properties in terms of bio-optical properties. As noted by Platt and others (Platt and
Sathyendranath 1988, Mueller and Lange 1989) these models are likely to vary in each of
the oceans major biogeochemical provinces. The large-scale coverage
provided by NOAA's cruises is ideal for testing these models since several of these
biogeochemical provinces, including the equatorial divergence, the low latitude gyres and
the high latitude oceans will be sampled
1. Determine the horizontal and vertical variability in chlorophyll biomass and rates
of primary and new production and their relation to chemical ocean carbon properties.
2. Determine chlorophyll and primary productivity attributable to discrete size
3. Determine the growth rates of the total phytoplankton community and component size
fractions, from the estimates of biomass and production.
4. Determine the horizontal and vertical variability in biomass and composition of the
various components of the microbial food web including heterotrophic bacteria.
5. Determine the relationship between select bio-optical properties, more traditional
discrete measurements and develop models between bio-optical properties and ocean carbon
6. Investigate the relationship between food web structure and new and total primary
production using observations from different biogeochemical provinces.
7. Determine grazing rates of the small heterotrophs on picoplankton and bacteria.
Previous: NOAA Long Line Cruises
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Last Updated: 04 April, 2000