waters. Also, decay of settling organic material alters the
chemical properties of the subsurface ocean (e.g., oxygen
concentration). Finally, changes in both quantities and
systems of production could influence global climate
through regulation of atmospheric carbon dioxide content
(Loubere, 2012; Sigman and Hain, 2012).
What controls marine production?
Biological production depends on the availability of sunlight and required macronutrients (classically: carbon,
nitrogen, phosphorus) and micronutrients (with iron
receiving most attention, Sarmiento and Gruber, 2006;
Boyd et al., 2007). The intensity of sunlight useable by
phytoplankton (marine algae, the dominant marine primary producers) depends on latitude, water depth, water
clarity, and water column stability. Latitude controls the
day length and the angle of the sun on the sea surface.
Water depth is important because light intensity drops
exponentially with depth and penetration is generally negligible below 50–100 m. Because of this, any production
over most of the ocean will depend on populations of
floating algae. A stable water column will be resistant to
vertical mixing, which means that plankton can remain
close to the sunlit surface most of the time. Near shore,
an unstable water column and vertical mixing can lead to
increased turbidity from sediments, reducing light.
Essential nutrients are concentrated at depth in the
oceans, so resupply for upper ocean plankton consumption depends on processes which bring deep water to the
surface (Figure 1; upwelling, deep vertical mixing;
Sarmiento and Gruber, 2006). Some nutrients are also
delivered by rivers and prevailing winds (as dust). Supply
depends on continental geography and climatology.
New production: a key global environmental
variable
Algal primary production in the oceans is based on locally
recycled nutrients and on “new” nutrients supplied from
the deeper ocean reservoir (Sarmiento and Gruber,
2006). In most of the ocean, the majority of production
is maintained by local recycling of nutrients in the nearsurface water column. Since this recycling is not 100 %
efficient, however, there is transfer from the shallow to
the deep ocean. Consequently, replenishment of the surface, via upwelling and mixing, is necessary for biological
production to continue (Palter et al., 1991).
The supply of biological materials to the seafloor and
geological record depends on the production engendered
from the “new” nutrients reaching the upper ocean. This
is different from the “total” (recycled + new) production
which biologists routinely measure. In this way, analysis
of paleoproductivity provides insight to the rates of
exchange of waters (and their load of nutrients) between
ocean depths and the surface. This vertical cycling of
chemicals, since it includes carbon dioxide, is important
to the global climate (Sigman and Hain, 2012).
The efficiency of biological recycling in the upper
ocean’s productive zone is not constant. Efficiency drops
as production increases (Wassman, 1998; Antia et al.,
2001). Variation of recycling efficiency and associated
change in plankton communities can also affect the distribution of CO 2 in the oceans and global climate
(Matsumoto et al., 2002).
Making a record of past changes in productivity
In principle, reconstruction of paleoproductivity should be
simple, requiring only measurement of accumulation rates
of sedimentary biogenic material. Sadly, this is complicated by a number of factors.
The materials incorporated into the ocean floor are
those which were produced in the upper ocean, survived
recycling in the upper water column while sinking, and
then survived the passage to greater depth and the
recycling processes at the seabed. Observations with sediment traps in the ocean have demonstrated that attenuation of sinking biological particles is strong, especially in
Paleoproductivity, Figure 1 Distribution of marine algae in the surface ocean, revealed by chlorophyll concentrations (darker
green ¼ more chlorophyll) calculated from satellite observations (source: http://oceancolor.gsfc.nasa.gov/SeaWiFS/). Higher algal
concentrations are associated with upwelling of deeper, nutrient-rich waters or with enhanced vertical mixing of the water column.
PALEOPRODUCTIVITY
649
chemical properties of the subsurface ocean (e.g., oxygen
concentration). Finally, changes in both quantities and
systems of production could influence global climate
through regulation of atmospheric carbon dioxide content
(Loubere, 2012; Sigman and Hain, 2012).
What controls marine production?
Biological production depends on the availability of sunlight and required macronutrients (classically: carbon,
nitrogen, phosphorus) and micronutrients (with iron
receiving most attention, Sarmiento and Gruber, 2006;
Boyd et al., 2007). The intensity of sunlight useable by
phytoplankton (marine algae, the dominant marine primary producers) depends on latitude, water depth, water
clarity, and water column stability. Latitude controls the
day length and the angle of the sun on the sea surface.
Water depth is important because light intensity drops
exponentially with depth and penetration is generally negligible below 50–100 m. Because of this, any production
over most of the ocean will depend on populations of
floating algae. A stable water column will be resistant to
vertical mixing, which means that plankton can remain
close to the sunlit surface most of the time. Near shore,
an unstable water column and vertical mixing can lead to
increased turbidity from sediments, reducing light.
Essential nutrients are concentrated at depth in the
oceans, so resupply for upper ocean plankton consumption depends on processes which bring deep water to the
surface (Figure 1; upwelling, deep vertical mixing;
Sarmiento and Gruber, 2006). Some nutrients are also
delivered by rivers and prevailing winds (as dust). Supply
depends on continental geography and climatology.
New production: a key global environmental
variable
Algal primary production in the oceans is based on locally
recycled nutrients and on “new” nutrients supplied from
the deeper ocean reservoir (Sarmiento and Gruber,
2006). In most of the ocean, the majority of production
is maintained by local recycling of nutrients in the nearsurface water column. Since this recycling is not 100 %
efficient, however, there is transfer from the shallow to
the deep ocean. Consequently, replenishment of the surface, via upwelling and mixing, is necessary for biological
production to continue (Palter et al., 1991).
The supply of biological materials to the seafloor and
geological record depends on the production engendered
from the “new” nutrients reaching the upper ocean. This
is different from the “total” (recycled + new) production
which biologists routinely measure. In this way, analysis
of paleoproductivity provides insight to the rates of
exchange of waters (and their load of nutrients) between
ocean depths and the surface. This vertical cycling of
chemicals, since it includes carbon dioxide, is important
to the global climate (Sigman and Hain, 2012).
The efficiency of biological recycling in the upper
ocean’s productive zone is not constant. Efficiency drops
as production increases (Wassman, 1998; Antia et al.,
2001). Variation of recycling efficiency and associated
change in plankton communities can also affect the distribution of CO 2 in the oceans and global climate
(Matsumoto et al., 2002).
Making a record of past changes in productivity
In principle, reconstruction of paleoproductivity should be
simple, requiring only measurement of accumulation rates
of sedimentary biogenic material. Sadly, this is complicated by a number of factors.
The materials incorporated into the ocean floor are
those which were produced in the upper ocean, survived
recycling in the upper water column while sinking, and
then survived the passage to greater depth and the
recycling processes at the seabed. Observations with sediment traps in the ocean have demonstrated that attenuation of sinking biological particles is strong, especially in
Paleoproductivity, Figure 1 Distribution of marine algae in the surface ocean, revealed by chlorophyll concentrations (darker
green ¼ more chlorophyll) calculated from satellite observations (source: http://oceancolor.gsfc.nasa.gov/SeaWiFS/). Higher algal
concentrations are associated with upwelling of deeper, nutrient-rich waters or with enhanced vertical mixing of the water column.
PALEOPRODUCTIVITY
649