GLOSSARY - Introduction to the Physical and Biological Oceanography of Shelf Seas - page 376

photosynthesis at a given light level,
normalized by some measure that
represents the light-gathering capacity of
the phytoplankton (e.g. chlorophyll
concentration). It is an important part of
the description of the light-growth curve of
a phytoplankton species or community,
and is a measure of the steepness of the
curve at low light.
Michaelis-Menten uptake kinetics A
description of phytoplankton nutrient
uptake rate as a function of the maximum
achievable uptake rate and the ambient
nutrient concentration in the water. The
uptake rate is initially low at low ambient
nutrient, and increases rapidly to reach a
plateau approaching the maximum uptake
rate at high ambient nutrient
concentrations.
microbial loop A vital pathway for
returning dissolved organic carbon (DOC)
to the marine food web. DOC is
unavailable to the micro- and
mesozooplankton, but is utilised by
heterotrophic bacteria which can then be
grazed by the zooplankton.
micronutrients Inorganic compounds
required by phytoplankton in small
quantities (compared to the
macronutrients). Iron, copper, nickel and
zinc are recognised as important
micronutrients. Iron, in particular, has
received much attention because it is now
known to limit primary production in the
High-Nutrient Low-Chlorophyll (HNLC)
regions of the open ocean, despite adequate
macronutrients being available.
mixotrophs (mixotrophic)

with a node located in the interface
between the layers.
Monod growth curve A curve describing a
functional response in which an organism's
growth rate is eventually limited by its
capacity to process resources. The
photosynthesis-PAR curve describing
phytoplankton growth as a function of
light is an example of this type of response,
with growth rate reaching a plateau at high
PAR as the photosystem becomes
saturated with light.
neap tides Smallest tides in the fortnightly
cycle usually occurring soon after the first
and third quarters of the Moon's orbital
cycle.
net community production The net primary

production achieved by all phytoplankton
within an autotrophic community.
net community respiration The total energy,
or carbon, requirements of a
phytoplankton community to support
cellular respiration. Respiration requires
dissolved oxygen. In practice, the use of
oxygen incubations to measure respiration
will also include respiration associated with
heterotrophic breakdown of organic
material.
net primary production The rate at which the
autotrophs fix inorganic carbon minus the
carbon fixation that is required for cellular
respiration. (See also gross primary
production.)
new production (new primary production)
The amount of carbon fixed by the
autotrophs in the photic zone that is
supported by a supply of 'new' nutrients
from below the photic zone or thermocline,
rather than the result of utilizing nutrients
recycled in the photic zone. If a steady state
is assumed, new production is the same as
export production. (See also f-ratio.)
nitracline A vertical region within the water
column where nitrate concentrations
change rapidly. Typically the nitracline
occurs coincident with, or within, the
thermocline.

Micro-organisms
that can use different sources of energy. In
the phytoplankton there are species in all
groups, which are able to mix autotrophy
and heterotrophy, allowing them to take
advantage of shifts in environmental
conditions.
mode 1 internal wave Lowest mode of
internal wave motion in which the surface
and bottom layers oscillate in antiphase